diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index c784ee48675..97089dff31b 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -373,7 +373,7 @@ pub struct CodegenContext<B: WriteBackendMethods> {
 
 impl<B: WriteBackendMethods> CodegenContext<B> {
     pub fn create_dcx(&self) -> DiagCtxt {
-        DiagCtxt::with_emitter(Box::new(self.diag_emitter.clone()))
+        DiagCtxt::new(Box::new(self.diag_emitter.clone()))
     }
 
     pub fn config(&self, kind: ModuleKind) -> &ModuleConfig {
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 692c059beb0..410e7eba30a 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -21,6 +21,7 @@ use rustc_codegen_ssa::{traits::CodegenBackend, CodegenErrors, CodegenResults};
 use rustc_data_structures::profiling::{
     get_resident_set_size, print_time_passes_entry, TimePassesFormat,
 };
+use rustc_errors::emitter::stderr_destination;
 use rustc_errors::registry::Registry;
 use rustc_errors::{
     markdown, ColorConfig, DiagCtxt, ErrCode, ErrorGuaranteed, FatalError, PResult,
@@ -1384,11 +1385,11 @@ fn report_ice(
 ) {
     let fallback_bundle =
         rustc_errors::fallback_fluent_bundle(crate::DEFAULT_LOCALE_RESOURCES.to_vec(), false);
-    let emitter = Box::new(rustc_errors::emitter::HumanEmitter::stderr(
-        rustc_errors::ColorConfig::Auto,
+    let emitter = Box::new(rustc_errors::emitter::HumanEmitter::new(
+        stderr_destination(rustc_errors::ColorConfig::Auto),
         fallback_bundle,
     ));
-    let dcx = rustc_errors::DiagCtxt::with_emitter(emitter);
+    let dcx = rustc_errors::DiagCtxt::new(emitter);
 
     // a .span_bug or .bug call has already printed what
     // it wants to print.
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 0cf519d2029..1c820bfd01f 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -1308,11 +1308,9 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         drop(self);
     }
 
-    /// Stashes diagnostic for possible later improvement in a different,
-    /// later stage of the compiler. The diagnostic can be accessed with
-    /// the provided `span` and `key` through [`DiagCtxt::steal_diagnostic()`].
-    pub fn stash(mut self, span: Span, key: StashKey) {
-        self.dcx.stash_diagnostic(span, key, self.take_diag());
+    /// See `DiagCtxt::stash_diagnostic` for details.
+    pub fn stash(mut self, span: Span, key: StashKey) -> Option<ErrorGuaranteed> {
+        self.dcx.stash_diagnostic(span, key, self.take_diag())
     }
 
     /// Delay emission of this diagnostic as a bug.
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 304922018eb..5637c05d04c 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -21,12 +21,11 @@ use crate::{
     FluentBundle, LazyFallbackBundle, Level, MultiSpan, Subdiag, SubstitutionHighlight,
     SuggestionStyle, TerminalUrl,
 };
-use rustc_lint_defs::pluralize;
-
 use derive_setters::Setters;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
 use rustc_data_structures::sync::{DynSend, IntoDynSyncSend, Lrc};
 use rustc_error_messages::{FluentArgs, SpanLabel};
+use rustc_lint_defs::pluralize;
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use std::borrow::Cow;
 use std::cmp::{max, min, Reverse};
@@ -35,7 +34,7 @@ use std::io::prelude::*;
 use std::io::{self, IsTerminal};
 use std::iter;
 use std::path::Path;
-use termcolor::{Ansi, Buffer, BufferWriter, ColorChoice, ColorSpec, StandardStream};
+use termcolor::{Buffer, BufferWriter, ColorChoice, ColorSpec, StandardStream};
 use termcolor::{Color, WriteColor};
 
 /// Default column width, used in tests and when terminal dimensions cannot be determined.
@@ -58,18 +57,6 @@ impl HumanReadableErrorType {
             HumanReadableErrorType::AnnotateSnippet(cc) => (false, cc),
         }
     }
-    pub fn new_emitter(
-        self,
-        mut dst: Box<dyn WriteColor + Send>,
-        fallback_bundle: LazyFallbackBundle,
-    ) -> HumanEmitter {
-        let (short, color_config) = self.unzip();
-        let color = color_config.suggests_using_colors();
-        if !dst.supports_color() && color {
-            dst = Box::new(Ansi::new(dst));
-        }
-        HumanEmitter::new(dst, fallback_bundle).short_message(short)
-    }
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -130,8 +117,8 @@ impl Margin {
     fn was_cut_right(&self, line_len: usize) -> bool {
         let right =
             if self.computed_right == self.span_right || self.computed_right == self.label_right {
-                // Account for the "..." padding given above. Otherwise we end up with code lines that
-                // do fit but end in "..." as if they were trimmed.
+                // Account for the "..." padding given above. Otherwise we end up with code lines
+                // that do fit but end in "..." as if they were trimmed.
                 self.computed_right - 6
             } else {
                 self.computed_right
@@ -628,12 +615,6 @@ impl ColorConfig {
             ColorConfig::Auto => ColorChoice::Never,
         }
     }
-    fn suggests_using_colors(self) -> bool {
-        match self {
-            ColorConfig::Always | ColorConfig::Auto => true,
-            ColorConfig::Never => false,
-        }
-    }
 }
 
 /// Handles the writing of `HumanReadableErrorType::Default` and `HumanReadableErrorType::Short`
@@ -657,19 +638,14 @@ pub struct HumanEmitter {
 }
 
 #[derive(Debug)]
-pub struct FileWithAnnotatedLines {
-    pub file: Lrc<SourceFile>,
-    pub lines: Vec<Line>,
+pub(crate) struct FileWithAnnotatedLines {
+    pub(crate) file: Lrc<SourceFile>,
+    pub(crate) lines: Vec<Line>,
     multiline_depth: usize,
 }
 
 impl HumanEmitter {
-    pub fn stderr(color_config: ColorConfig, fallback_bundle: LazyFallbackBundle) -> HumanEmitter {
-        let dst = from_stderr(color_config);
-        Self::create(dst, fallback_bundle)
-    }
-
-    fn create(dst: Destination, fallback_bundle: LazyFallbackBundle) -> HumanEmitter {
+    pub fn new(dst: Destination, fallback_bundle: LazyFallbackBundle) -> HumanEmitter {
         HumanEmitter {
             dst: IntoDynSyncSend(dst),
             sm: None,
@@ -686,13 +662,6 @@ impl HumanEmitter {
         }
     }
 
-    pub fn new(
-        dst: Box<dyn WriteColor + Send>,
-        fallback_bundle: LazyFallbackBundle,
-    ) -> HumanEmitter {
-        Self::create(dst, fallback_bundle)
-    }
-
     fn maybe_anonymized(&self, line_num: usize) -> Cow<'static, str> {
         if self.ui_testing {
             Cow::Borrowed(ANONYMIZED_LINE_NUM)
@@ -724,8 +693,9 @@ impl HumanEmitter {
             .skip(left)
             .take_while(|ch| {
                 // Make sure that the trimming on the right will fall within the terminal width.
-                // FIXME: `unicode_width` sometimes disagrees with terminals on how wide a `char` is.
-                // For now, just accept that sometimes the code line will be longer than desired.
+                // FIXME: `unicode_width` sometimes disagrees with terminals on how wide a `char`
+                // is. For now, just accept that sometimes the code line will be longer than
+                // desired.
                 let next = unicode_width::UnicodeWidthChar::width(*ch).unwrap_or(1);
                 if taken + next > right - left {
                     return false;
@@ -2228,8 +2198,8 @@ impl HumanEmitter {
                 buffer.puts(*row_num - 1, max_line_num_len + 3, &line, Style::NoStyle);
                 *row_num += 1;
             }
-            // If the last line is exactly equal to the line we need to add, we can skip both of them.
-            // This allows us to avoid output like the following:
+            // If the last line is exactly equal to the line we need to add, we can skip both of
+            // them. This allows us to avoid output like the following:
             // 2 - &
             // 2 + if true { true } else { false }
             // 3 - if true { true } else { false }
@@ -2586,6 +2556,7 @@ fn num_overlap(
     let extra = if inclusive { 1 } else { 0 };
     (b_start..b_end + extra).contains(&a_start) || (a_start..a_end + extra).contains(&b_start)
 }
+
 fn overlaps(a1: &Annotation, a2: &Annotation, padding: usize) -> bool {
     num_overlap(
         a1.start_col.display,
@@ -2632,7 +2603,7 @@ fn emit_to_destination(
     Ok(())
 }
 
-pub type Destination = Box<(dyn WriteColor + Send)>;
+pub type Destination = Box<dyn WriteColor + Send>;
 
 struct Buffy {
     buffer_writer: BufferWriter,
@@ -2674,7 +2645,7 @@ impl WriteColor for Buffy {
     }
 }
 
-fn from_stderr(color: ColorConfig) -> Destination {
+pub fn stderr_destination(color: ColorConfig) -> Destination {
     let choice = color.to_color_choice();
     // On Windows we'll be performing global synchronization on the entire
     // system for emitting rustc errors, so there's no need to buffer
diff --git a/compiler/rustc_errors/src/error.rs b/compiler/rustc_errors/src/error.rs
index ec0a2fe8cd8..ca818a4d832 100644
--- a/compiler/rustc_errors/src/error.rs
+++ b/compiler/rustc_errors/src/error.rs
@@ -23,9 +23,11 @@ impl<'args> TranslateError<'args> {
     pub fn message(id: &'args Cow<'args, str>, args: &'args FluentArgs<'args>) -> Self {
         Self::One { id, args, kind: TranslateErrorKind::MessageMissing }
     }
+
     pub fn primary(id: &'args Cow<'args, str>, args: &'args FluentArgs<'args>) -> Self {
         Self::One { id, args, kind: TranslateErrorKind::PrimaryBundleMissing }
     }
+
     pub fn attribute(
         id: &'args Cow<'args, str>,
         args: &'args FluentArgs<'args>,
@@ -33,6 +35,7 @@ impl<'args> TranslateError<'args> {
     ) -> Self {
         Self::One { id, args, kind: TranslateErrorKind::AttributeMissing { attr } }
     }
+
     pub fn value(id: &'args Cow<'args, str>, args: &'args FluentArgs<'args>) -> Self {
         Self::One { id, args, kind: TranslateErrorKind::ValueMissing }
     }
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 88a83c8bf78..bc1822f83fc 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -9,42 +9,49 @@
 
 // FIXME: spec the JSON output properly.
 
-use rustc_span::source_map::{FilePathMapping, SourceMap};
-use termcolor::{ColorSpec, WriteColor};
-
-use crate::emitter::{should_show_source_code, Emitter, HumanReadableErrorType};
+use crate::emitter::{
+    should_show_source_code, ColorConfig, Destination, Emitter, HumanEmitter,
+    HumanReadableErrorType,
+};
 use crate::registry::Registry;
 use crate::translation::{to_fluent_args, Translate};
 use crate::{
     diagnostic::IsLint, CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel,
     Subdiag, TerminalUrl,
 };
-use rustc_lint_defs::Applicability;
-
+use derive_setters::Setters;
 use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
 use rustc_error_messages::FluentArgs;
+use rustc_lint_defs::Applicability;
 use rustc_span::hygiene::ExpnData;
+use rustc_span::source_map::SourceMap;
 use rustc_span::Span;
+use serde::Serialize;
 use std::error::Report;
 use std::io::{self, Write};
 use std::path::Path;
 use std::sync::{Arc, Mutex};
 use std::vec;
-
-use serde::Serialize;
+use termcolor::{ColorSpec, WriteColor};
 
 #[cfg(test)]
 mod tests;
 
+#[derive(Setters)]
 pub struct JsonEmitter {
+    #[setters(skip)]
     dst: IntoDynSyncSend<Box<dyn Write + Send>>,
     registry: Option<Registry>,
+    #[setters(skip)]
     sm: Lrc<SourceMap>,
     fluent_bundle: Option<Lrc<FluentBundle>>,
+    #[setters(skip)]
     fallback_bundle: LazyFallbackBundle,
+    #[setters(skip)]
     pretty: bool,
     ui_testing: bool,
     ignored_directories_in_source_blocks: Vec<String>,
+    #[setters(skip)]
     json_rendered: HumanReadableErrorType,
     diagnostic_width: Option<usize>,
     macro_backtrace: bool,
@@ -53,98 +60,30 @@ pub struct JsonEmitter {
 }
 
 impl JsonEmitter {
-    pub fn stderr(
-        registry: Option<Registry>,
-        source_map: Lrc<SourceMap>,
-        fluent_bundle: Option<Lrc<FluentBundle>>,
-        fallback_bundle: LazyFallbackBundle,
-        pretty: bool,
-        json_rendered: HumanReadableErrorType,
-        diagnostic_width: Option<usize>,
-        macro_backtrace: bool,
-        track_diagnostics: bool,
-        terminal_url: TerminalUrl,
-    ) -> JsonEmitter {
-        JsonEmitter {
-            dst: IntoDynSyncSend(Box::new(io::BufWriter::new(io::stderr()))),
-            registry,
-            sm: source_map,
-            fluent_bundle,
-            fallback_bundle,
-            pretty,
-            ui_testing: false,
-            ignored_directories_in_source_blocks: Vec::new(),
-            json_rendered,
-            diagnostic_width,
-            macro_backtrace,
-            track_diagnostics,
-            terminal_url,
-        }
-    }
-
-    pub fn basic(
-        pretty: bool,
-        json_rendered: HumanReadableErrorType,
-        fluent_bundle: Option<Lrc<FluentBundle>>,
-        fallback_bundle: LazyFallbackBundle,
-        diagnostic_width: Option<usize>,
-        macro_backtrace: bool,
-        track_diagnostics: bool,
-        terminal_url: TerminalUrl,
-    ) -> JsonEmitter {
-        let file_path_mapping = FilePathMapping::empty();
-        JsonEmitter::stderr(
-            None,
-            Lrc::new(SourceMap::new(file_path_mapping)),
-            fluent_bundle,
-            fallback_bundle,
-            pretty,
-            json_rendered,
-            diagnostic_width,
-            macro_backtrace,
-            track_diagnostics,
-            terminal_url,
-        )
-    }
-
     pub fn new(
         dst: Box<dyn Write + Send>,
-        registry: Option<Registry>,
-        source_map: Lrc<SourceMap>,
-        fluent_bundle: Option<Lrc<FluentBundle>>,
+        sm: Lrc<SourceMap>,
         fallback_bundle: LazyFallbackBundle,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
-        diagnostic_width: Option<usize>,
-        macro_backtrace: bool,
-        track_diagnostics: bool,
-        terminal_url: TerminalUrl,
     ) -> JsonEmitter {
         JsonEmitter {
             dst: IntoDynSyncSend(dst),
-            registry,
-            sm: source_map,
-            fluent_bundle,
+            registry: None,
+            sm,
+            fluent_bundle: None,
             fallback_bundle,
             pretty,
             ui_testing: false,
             ignored_directories_in_source_blocks: Vec::new(),
             json_rendered,
-            diagnostic_width,
-            macro_backtrace,
-            track_diagnostics,
-            terminal_url,
+            diagnostic_width: None,
+            macro_backtrace: false,
+            track_diagnostics: false,
+            terminal_url: TerminalUrl::No,
         }
     }
 
-    pub fn ui_testing(self, ui_testing: bool) -> Self {
-        Self { ui_testing, ..self }
-    }
-
-    pub fn ignored_directories_in_source_blocks(self, value: Vec<String>) -> Self {
-        Self { ignored_directories_in_source_blocks: value, ..self }
-    }
-
     fn emit(&mut self, val: EmitTyped<'_>) -> io::Result<()> {
         if self.pretty {
             serde_json::to_writer_pretty(&mut *self.dst, &val)?
@@ -162,7 +101,7 @@ enum EmitTyped<'a> {
     Diagnostic(Diagnostic),
     Artifact(ArtifactNotification<'a>),
     FutureIncompat(FutureIncompatReport<'a>),
-    UnusedExtern(UnusedExterns<'a, 'a, 'a>),
+    UnusedExtern(UnusedExterns<'a>),
 }
 
 impl Translate for JsonEmitter {
@@ -332,14 +271,15 @@ struct FutureIncompatReport<'a> {
 // We could unify this struct the one in rustdoc but they have different
 // ownership semantics, so doing so would create wasteful allocations.
 #[derive(Serialize)]
-struct UnusedExterns<'a, 'b, 'c> {
+struct UnusedExterns<'a> {
     /// The severity level of the unused dependencies lint
     lint_level: &'a str,
     /// List of unused externs by their names.
-    unused_extern_names: &'b [&'c str],
+    unused_extern_names: &'a [&'a str],
 }
 
 impl Diagnostic {
+    /// Converts from `rustc_errors::DiagInner` to `Diagnostic`.
     fn from_errors_diagnostic(diag: crate::DiagInner, je: &JsonEmitter) -> Diagnostic {
         let args = to_fluent_args(diag.args.iter());
         let sugg = diag.suggestions.iter().flatten().map(|sugg| {
@@ -405,9 +345,14 @@ impl Diagnostic {
             .collect();
 
         let buf = BufWriter::default();
-        let output = buf.clone();
-        je.json_rendered
-            .new_emitter(Box::new(buf), je.fallback_bundle.clone())
+        let mut dst: Destination = Box::new(buf.clone());
+        let (short, color_config) = je.json_rendered.unzip();
+        match color_config {
+            ColorConfig::Always | ColorConfig::Auto => dst = Box::new(termcolor::Ansi::new(dst)),
+            ColorConfig::Never => {}
+        }
+        HumanEmitter::new(dst, je.fallback_bundle.clone())
+            .short_message(short)
             .sm(Some(je.sm.clone()))
             .fluent_bundle(je.fluent_bundle.clone())
             .diagnostic_width(je.diagnostic_width)
@@ -417,8 +362,8 @@ impl Diagnostic {
             .ui_testing(je.ui_testing)
             .ignored_directories_in_source_blocks(je.ignored_directories_in_source_blocks.clone())
             .emit_diagnostic(diag);
-        let output = Arc::try_unwrap(output.0).unwrap().into_inner().unwrap();
-        let output = String::from_utf8(output).unwrap();
+        let buf = Arc::try_unwrap(buf.0).unwrap().into_inner().unwrap();
+        let buf = String::from_utf8(buf).unwrap();
 
         Diagnostic {
             message: translated_message.to_string(),
@@ -426,7 +371,7 @@ impl Diagnostic {
             level,
             spans,
             children,
-            rendered: Some(output),
+            rendered: Some(buf),
         }
     }
 
diff --git a/compiler/rustc_errors/src/json/tests.rs b/compiler/rustc_errors/src/json/tests.rs
index 303de0a93f6..80b4d2bf75c 100644
--- a/compiler/rustc_errors/src/json/tests.rs
+++ b/compiler/rustc_errors/src/json/tests.rs
@@ -1,7 +1,7 @@
 use super::*;
 
-use crate::emitter::ColorConfig;
 use crate::DiagCtxt;
+use rustc_span::source_map::FilePathMapping;
 use rustc_span::BytePos;
 
 use std::str;
@@ -48,20 +48,14 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
         let output = Arc::new(Mutex::new(Vec::new()));
         let je = JsonEmitter::new(
             Box::new(Shared { data: output.clone() }),
-            None,
             sm,
-            None,
             fallback_bundle,
-            true,
+            true, // pretty
             HumanReadableErrorType::Short(ColorConfig::Never),
-            None,
-            false,
-            false,
-            TerminalUrl::No,
         );
 
         let span = Span::with_root_ctxt(BytePos(span.0), BytePos(span.1));
-        let dcx = DiagCtxt::with_emitter(Box::new(je));
+        let dcx = DiagCtxt::new(Box::new(je));
         dcx.span_err(span, "foo");
 
         let bytes = output.lock().unwrap();
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 2652feff62a..0a533833e64 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -59,11 +59,11 @@ pub use snippet::Style;
 // See https://github.com/rust-lang/rust/pull/115393.
 pub use termcolor::{Color, ColorSpec, WriteColor};
 
-use emitter::{is_case_difference, DynEmitter, Emitter, HumanEmitter};
+use emitter::{is_case_difference, DynEmitter, Emitter};
 use registry::Registry;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
-use rustc_data_structures::sync::{Lock, Lrc};
+use rustc_data_structures::sync::Lock;
 use rustc_data_structures::AtomicRef;
 use rustc_lint_defs::LintExpectationId;
 use rustc_span::source_map::SourceMap;
@@ -217,10 +217,10 @@ impl CodeSuggestion {
 
         use rustc_span::{CharPos, Pos};
 
-        /// Extracts a substring from the provided `line_opt` based on the specified low and high indices,
-        /// appends it to the given buffer `buf`, and returns the count of newline characters in the substring
-        /// for accurate highlighting.
-        /// If `line_opt` is `None`, a newline character is appended to the buffer, and 0 is returned.
+        /// Extracts a substring from the provided `line_opt` based on the specified low and high
+        /// indices, appends it to the given buffer `buf`, and returns the count of newline
+        /// characters in the substring for accurate highlighting. If `line_opt` is `None`, a
+        /// newline character is appended to the buffer, and 0 is returned.
         ///
         /// ## Returns
         ///
@@ -434,10 +434,6 @@ struct DiagCtxtInner {
     /// The delayed bugs and their error guarantees.
     delayed_bugs: Vec<(DelayedDiagInner, ErrorGuaranteed)>,
 
-    /// The number of stashed errors. Unlike the other counts, this can go up
-    /// and down, so it doesn't guarantee anything.
-    stashed_err_count: usize,
-
     /// The error count shown to the user at the end.
     deduplicated_err_count: usize,
     /// The warning count shown to the user at the end.
@@ -475,7 +471,7 @@ struct DiagCtxtInner {
     /// add more information). All stashed diagnostics must be emitted with
     /// `emit_stashed_diagnostics` by the time the `DiagCtxtInner` is dropped,
     /// otherwise an assertion failure will occur.
-    stashed_diagnostics: FxIndexMap<(Span, StashKey), DiagInner>,
+    stashed_diagnostics: FxIndexMap<(Span, StashKey), (DiagInner, Option<ErrorGuaranteed>)>,
 
     future_breakage_diagnostics: Vec<DiagInner>,
 
@@ -486,8 +482,8 @@ struct DiagCtxtInner {
     /// have been converted.
     check_unstable_expect_diagnostics: bool,
 
-    /// Expected [`DiagInner`][struct@diagnostic::DiagInner]s store a [`LintExpectationId`] as part of
-    /// the lint level. [`LintExpectationId`]s created early during the compilation
+    /// Expected [`DiagInner`][struct@diagnostic::DiagInner]s store a [`LintExpectationId`] as part
+    /// of the lint level. [`LintExpectationId`]s created early during the compilation
     /// (before `HirId`s have been defined) are not stable and can therefore not be
     /// stored on disk. This buffer stores these diagnostics until the ID has been
     /// replaced by a stable [`LintExpectationId`]. The [`DiagInner`][struct@diagnostic::DiagInner]s
@@ -559,10 +555,18 @@ pub struct DiagCtxtFlags {
 
 impl Drop for DiagCtxtInner {
     fn drop(&mut self) {
-        // Any stashed diagnostics should have been handled by
-        // `emit_stashed_diagnostics` by now.
-        assert!(self.stashed_diagnostics.is_empty());
+        // For tools using `interface::run_compiler` (e.g. rustc, rustdoc)
+        // stashed diagnostics will have already been emitted. But for others
+        // that don't use `interface::run_compiler` (e.g. rustfmt, some clippy
+        // lints) this fallback is necessary.
+        //
+        // Important: it is sound to produce an `ErrorGuaranteed` when stashing
+        // errors because they are guaranteed to be emitted here or earlier.
+        self.emit_stashed_diagnostics();
 
+        // Important: it is sound to produce an `ErrorGuaranteed` when emitting
+        // delayed bugs because they are guaranteed to be emitted here if
+        // necessary.
         if self.err_guars.is_empty() {
             self.flush_delayed()
         }
@@ -586,13 +590,6 @@ impl Drop for DiagCtxtInner {
 }
 
 impl DiagCtxt {
-    pub fn with_tty_emitter(
-        sm: Option<Lrc<SourceMap>>,
-        fallback_bundle: LazyFallbackBundle,
-    ) -> Self {
-        let emitter = Box::new(HumanEmitter::stderr(ColorConfig::Auto, fallback_bundle).sm(sm));
-        Self::with_emitter(emitter)
-    }
     pub fn disable_warnings(mut self) -> Self {
         self.inner.get_mut().flags.can_emit_warnings = false;
         self
@@ -608,14 +605,13 @@ impl DiagCtxt {
         self
     }
 
-    pub fn with_emitter(emitter: Box<DynEmitter>) -> Self {
+    pub fn new(emitter: Box<DynEmitter>) -> Self {
         Self {
             inner: Lock::new(DiagCtxtInner {
                 flags: DiagCtxtFlags { can_emit_warnings: true, ..Default::default() },
                 err_guars: Vec::new(),
                 lint_err_guars: Vec::new(),
                 delayed_bugs: Vec::new(),
-                stashed_err_count: 0,
                 deduplicated_err_count: 0,
                 deduplicated_warn_count: 0,
                 emitter,
@@ -676,7 +672,6 @@ impl DiagCtxt {
             err_guars,
             lint_err_guars,
             delayed_bugs,
-            stashed_err_count,
             deduplicated_err_count,
             deduplicated_warn_count,
             emitter: _,
@@ -699,7 +694,6 @@ impl DiagCtxt {
         *err_guars = Default::default();
         *lint_err_guars = Default::default();
         *delayed_bugs = Default::default();
-        *stashed_err_count = 0;
         *deduplicated_err_count = 0;
         *deduplicated_warn_count = 0;
         *must_produce_diag = false;
@@ -715,39 +709,111 @@ impl DiagCtxt {
         *fulfilled_expectations = Default::default();
     }
 
-    /// Stash a given diagnostic with the given `Span` and [`StashKey`] as the key.
-    /// Retrieve a stashed diagnostic with `steal_diagnostic`.
-    pub fn stash_diagnostic(&self, span: Span, key: StashKey, diag: DiagInner) {
-        let mut inner = self.inner.borrow_mut();
-
-        let key = (span.with_parent(None), key);
-
-        if diag.is_error() {
-            if diag.is_lint.is_none() {
-                inner.stashed_err_count += 1;
-            }
-        }
+    /// Stashes a diagnostic for possible later improvement in a different,
+    /// later stage of the compiler. Possible actions depend on the diagnostic
+    /// level:
+    /// - Level::Error: immediately counted as an error that has occurred, because it
+    ///   is guaranteed to be emitted eventually. Can be later accessed with the
+    ///   provided `span` and `key` through
+    ///   [`DiagCtxt::try_steal_modify_and_emit_err`] or
+    ///   [`DiagCtxt::try_steal_replace_and_emit_err`]. These do not allow
+    ///   cancellation or downgrading of the error. Returns
+    ///   `Some(ErrorGuaranteed)`.
+    /// - Level::Warning and lower (i.e. !is_error()): can be accessed with the
+    ///   provided `span` and `key` through [`DiagCtxt::steal_non_err()`]. This
+    ///   allows cancelling and downgrading of the diagnostic. Returns `None`.
+    /// - Others: not allowed, will trigger a panic.
+    pub fn stash_diagnostic(
+        &self,
+        span: Span,
+        key: StashKey,
+        diag: DiagInner,
+    ) -> Option<ErrorGuaranteed> {
+        let guar = if diag.level() == Level::Error {
+            // This `unchecked_error_guaranteed` is valid. It is where the
+            // `ErrorGuaranteed` for stashed errors originates. See
+            // `DiagCtxtInner::drop`.
+            #[allow(deprecated)]
+            Some(ErrorGuaranteed::unchecked_error_guaranteed())
+        } else if !diag.is_error() {
+            None
+        } else {
+            self.span_bug(span, format!("invalid level in `stash_diagnostic`: {}", diag.level));
+        };
 
         // FIXME(Centril, #69537): Consider reintroducing panic on overwriting a stashed diagnostic
         // if/when we have a more robust macro-friendly replacement for `(span, key)` as a key.
         // See the PR for a discussion.
-        inner.stashed_diagnostics.insert(key, diag);
+        let key = (span.with_parent(None), key);
+        self.inner.borrow_mut().stashed_diagnostics.insert(key, (diag, guar));
+
+        guar
     }
 
-    /// Steal a previously stashed diagnostic with the given `Span` and [`StashKey`] as the key.
-    pub fn steal_diagnostic(&self, span: Span, key: StashKey) -> Option<Diag<'_, ()>> {
-        let mut inner = self.inner.borrow_mut();
+    /// Steal a previously stashed non-error diagnostic with the given `Span`
+    /// and [`StashKey`] as the key. Panics if the found diagnostic is an
+    /// error.
+    pub fn steal_non_err(&self, span: Span, key: StashKey) -> Option<Diag<'_, ()>> {
         let key = (span.with_parent(None), key);
         // FIXME(#120456) - is `swap_remove` correct?
-        let diag = inner.stashed_diagnostics.swap_remove(&key)?;
-        if diag.is_error() {
-            if diag.is_lint.is_none() {
-                inner.stashed_err_count -= 1;
-            }
-        }
+        let (diag, guar) = self.inner.borrow_mut().stashed_diagnostics.swap_remove(&key)?;
+        assert!(!diag.is_error());
+        assert!(guar.is_none());
         Some(Diag::new_diagnostic(self, diag))
     }
 
+    /// Steals a previously stashed error with the given `Span` and
+    /// [`StashKey`] as the key, modifies it, and emits it. Returns `None` if
+    /// no matching diagnostic is found. Panics if the found diagnostic's level
+    /// isn't `Level::Error`.
+    pub fn try_steal_modify_and_emit_err<F>(
+        &self,
+        span: Span,
+        key: StashKey,
+        mut modify_err: F,
+    ) -> Option<ErrorGuaranteed>
+    where
+        F: FnMut(&mut Diag<'_>),
+    {
+        let key = (span.with_parent(None), key);
+        // FIXME(#120456) - is `swap_remove` correct?
+        let err = self.inner.borrow_mut().stashed_diagnostics.swap_remove(&key);
+        err.map(|(err, guar)| {
+            // The use of `::<ErrorGuaranteed>` is safe because level is `Level::Error`.
+            assert_eq!(err.level, Level::Error);
+            assert!(guar.is_some());
+            let mut err = Diag::<ErrorGuaranteed>::new_diagnostic(self, err);
+            modify_err(&mut err);
+            assert_eq!(err.level, Level::Error);
+            err.emit()
+        })
+    }
+
+    /// Steals a previously stashed error with the given `Span` and
+    /// [`StashKey`] as the key, cancels it if found, and emits `new_err`.
+    /// Panics if the found diagnostic's level isn't `Level::Error`.
+    pub fn try_steal_replace_and_emit_err(
+        &self,
+        span: Span,
+        key: StashKey,
+        new_err: Diag<'_>,
+    ) -> ErrorGuaranteed {
+        let key = (span.with_parent(None), key);
+        // FIXME(#120456) - is `swap_remove` correct?
+        let old_err = self.inner.borrow_mut().stashed_diagnostics.swap_remove(&key);
+        match old_err {
+            Some((old_err, guar)) => {
+                assert_eq!(old_err.level, Level::Error);
+                assert!(guar.is_some());
+                // Because `old_err` has already been counted, it can only be
+                // safely cancelled because the `new_err` supplants it.
+                Diag::<ErrorGuaranteed>::new_diagnostic(self, old_err).cancel();
+            }
+            None => {}
+        };
+        new_err.emit()
+    }
+
     pub fn has_stashed_diagnostic(&self, span: Span, key: StashKey) -> bool {
         self.inner.borrow().stashed_diagnostics.get(&(span.with_parent(None), key)).is_some()
     }
@@ -757,41 +823,40 @@ impl DiagCtxt {
         self.inner.borrow_mut().emit_stashed_diagnostics()
     }
 
-    /// This excludes lint errors, delayed bugs and stashed errors.
+    /// This excludes lint errors, and delayed bugs.
     #[inline]
     pub fn err_count_excluding_lint_errs(&self) -> usize {
-        self.inner.borrow().err_guars.len()
+        let inner = self.inner.borrow();
+        inner.err_guars.len()
+            + inner
+                .stashed_diagnostics
+                .values()
+                .filter(|(diag, guar)| guar.is_some() && diag.is_lint.is_none())
+                .count()
     }
 
-    /// This excludes delayed bugs and stashed errors.
+    /// This excludes delayed bugs.
     #[inline]
     pub fn err_count(&self) -> usize {
         let inner = self.inner.borrow();
-        inner.err_guars.len() + inner.lint_err_guars.len()
+        inner.err_guars.len()
+            + inner.lint_err_guars.len()
+            + inner.stashed_diagnostics.values().filter(|(_diag, guar)| guar.is_some()).count()
     }
 
-    /// This excludes normal errors, lint errors, and delayed bugs. Unless
-    /// absolutely necessary, avoid using this. It's dubious because stashed
-    /// errors can later be cancelled, so the presence of a stashed error at
-    /// some point of time doesn't guarantee anything -- there are no
-    /// `ErrorGuaranteed`s here.
-    pub fn stashed_err_count(&self) -> usize {
-        self.inner.borrow().stashed_err_count
-    }
-
-    /// This excludes lint errors, delayed bugs, and stashed errors. Unless
-    /// absolutely necessary, prefer `has_errors` to this method.
+    /// This excludes lint errors and delayed bugs. Unless absolutely
+    /// necessary, prefer `has_errors` to this method.
     pub fn has_errors_excluding_lint_errors(&self) -> Option<ErrorGuaranteed> {
         self.inner.borrow().has_errors_excluding_lint_errors()
     }
 
-    /// This excludes delayed bugs and stashed errors.
+    /// This excludes delayed bugs.
     pub fn has_errors(&self) -> Option<ErrorGuaranteed> {
         self.inner.borrow().has_errors()
     }
 
-    /// This excludes stashed errors. Unless absolutely necessary, prefer
-    /// `has_errors` to this method.
+    /// This excludes nothing. Unless absolutely necessary, prefer `has_errors`
+    /// to this method.
     pub fn has_errors_or_delayed_bugs(&self) -> Option<ErrorGuaranteed> {
         self.inner.borrow().has_errors_or_delayed_bugs()
     }
@@ -876,10 +941,10 @@ impl DiagCtxt {
         }
     }
 
-    /// This excludes delayed bugs and stashed errors. Used for early aborts
-    /// after errors occurred -- e.g. because continuing in the face of errors is
-    /// likely to lead to bad results, such as spurious/uninteresting
-    /// additional errors -- when returning an error `Result` is difficult.
+    /// This excludes delayed bugs. Used for early aborts after errors occurred
+    /// -- e.g. because continuing in the face of errors is likely to lead to
+    /// bad results, such as spurious/uninteresting additional errors -- when
+    /// returning an error `Result` is difficult.
     pub fn abort_if_errors(&self) {
         if self.has_errors().is_some() {
             FatalError.raise();
@@ -963,7 +1028,7 @@ impl DiagCtxt {
         inner
             .stashed_diagnostics
             .values_mut()
-            .for_each(|diag| diag.update_unstable_expectation_id(unstable_to_stable));
+            .for_each(|(diag, _guar)| diag.update_unstable_expectation_id(unstable_to_stable));
         inner
             .future_breakage_diagnostics
             .iter_mut()
@@ -1270,12 +1335,8 @@ impl DiagCtxtInner {
     fn emit_stashed_diagnostics(&mut self) -> Option<ErrorGuaranteed> {
         let mut guar = None;
         let has_errors = !self.err_guars.is_empty();
-        for (_, diag) in std::mem::take(&mut self.stashed_diagnostics).into_iter() {
-            if diag.is_error() {
-                if diag.is_lint.is_none() {
-                    self.stashed_err_count -= 1;
-                }
-            } else {
+        for (_, (diag, _guar)) in std::mem::take(&mut self.stashed_diagnostics).into_iter() {
+            if !diag.is_error() {
                 // Unless they're forced, don't flush stashed warnings when
                 // there are errors, to avoid causing warning overload. The
                 // stash would've been stolen already if it were important.
@@ -1334,7 +1395,8 @@ impl DiagCtxtInner {
                 } else {
                     let backtrace = std::backtrace::Backtrace::capture();
                     // This `unchecked_error_guaranteed` is valid. It is where the
-                    // `ErrorGuaranteed` for delayed bugs originates.
+                    // `ErrorGuaranteed` for delayed bugs originates. See
+                    // `DiagCtxtInner::drop`.
                     #[allow(deprecated)]
                     let guar = ErrorGuaranteed::unchecked_error_guaranteed();
                     self.delayed_bugs
@@ -1446,11 +1508,31 @@ impl DiagCtxtInner {
     }
 
     fn has_errors_excluding_lint_errors(&self) -> Option<ErrorGuaranteed> {
-        self.err_guars.get(0).copied()
+        self.err_guars.get(0).copied().or_else(|| {
+            if let Some((_diag, guar)) = self
+                .stashed_diagnostics
+                .values()
+                .find(|(diag, guar)| guar.is_some() && diag.is_lint.is_none())
+            {
+                *guar
+            } else {
+                None
+            }
+        })
     }
 
     fn has_errors(&self) -> Option<ErrorGuaranteed> {
-        self.has_errors_excluding_lint_errors().or_else(|| self.lint_err_guars.get(0).copied())
+        self.err_guars.get(0).copied().or_else(|| self.lint_err_guars.get(0).copied()).or_else(
+            || {
+                if let Some((_diag, guar)) =
+                    self.stashed_diagnostics.values().find(|(_diag, guar)| guar.is_some())
+                {
+                    *guar
+                } else {
+                    None
+                }
+            },
+        )
     }
 
     fn has_errors_or_delayed_bugs(&self) -> Option<ErrorGuaranteed> {
diff --git a/compiler/rustc_expand/src/tests.rs b/compiler/rustc_expand/src/tests.rs
index 3c14ad5e7b8..b242ce795fd 100644
--- a/compiler/rustc_expand/src/tests.rs
+++ b/compiler/rustc_expand/src/tests.rs
@@ -33,7 +33,7 @@ fn create_test_handler() -> (DiagCtxt, Lrc<SourceMap>, Arc<Mutex<Vec<u8>>>) {
     let emitter = HumanEmitter::new(Box::new(Shared { data: output.clone() }), fallback_bundle)
         .sm(Some(source_map.clone()))
         .diagnostic_width(Some(140));
-    let dcx = DiagCtxt::with_emitter(Box::new(emitter));
+    let dcx = DiagCtxt::new(Box::new(emitter));
     (dcx, source_map, output)
 }
 
diff --git a/compiler/rustc_hir_analysis/src/astconv/lint.rs b/compiler/rustc_hir_analysis/src/astconv/lint.rs
index fb5f3426cea..227254b4cc8 100644
--- a/compiler/rustc_hir_analysis/src/astconv/lint.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/lint.rs
@@ -1,5 +1,5 @@
 use rustc_ast::TraitObjectSyntax;
-use rustc_errors::{codes::*, Diag, EmissionGuarantee, StashKey};
+use rustc_errors::{codes::*, Diag, EmissionGuarantee, Level, StashKey};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_lint_defs::{builtin::BARE_TRAIT_OBJECTS, Applicability};
@@ -237,7 +237,15 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }
                 // check if the impl trait that we are considering is a impl of a local trait
                 self.maybe_lint_blanket_trait_impl(self_ty, &mut diag);
-                diag.stash(self_ty.span, StashKey::TraitMissingMethod);
+                match diag.level() {
+                    Level::Error => {
+                        diag.stash(self_ty.span, StashKey::TraitMissingMethod);
+                    }
+                    Level::DelayedBug => {
+                        diag.emit();
+                    }
+                    _ => unreachable!(),
+                }
             } else {
                 let msg = "trait objects without an explicit `dyn` are deprecated";
                 tcx.node_span_lint(BARE_TRAIT_OBJECTS, self_ty.hir_id, self_ty.span, msg, |lint| {
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 81e84860b82..96bebda5828 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -1350,8 +1350,7 @@ fn check_type_alias_type_params_are_used<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalD
     let ty = tcx.type_of(def_id).instantiate_identity();
     if ty.references_error() {
         // If there is already another error, do not emit an error for not using a type parameter.
-        // Without the `stashed_err_count` part this can fail (#120856).
-        assert!(tcx.dcx().has_errors().is_some() || tcx.dcx().stashed_err_count() > 0);
+        assert!(tcx.dcx().has_errors().is_some());
         return;
     }
 
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index c0128afe2bf..417f0fceaa8 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -596,10 +596,11 @@ fn infer_placeholder_type<'a>(
     // then the user may have written e.g. `const A = 42;`.
     // In this case, the parser has stashed a diagnostic for
     // us to improve in typeck so we do that now.
-    match tcx.dcx().steal_diagnostic(span, StashKey::ItemNoType) {
-        Some(mut err) => {
+    let guar = tcx
+        .dcx()
+        .try_steal_modify_and_emit_err(span, StashKey::ItemNoType, |err| {
             if !ty.references_error() {
-                // Only suggest adding `:` if it was missing (and suggested by parsing diagnostic)
+                // Only suggest adding `:` if it was missing (and suggested by parsing diagnostic).
                 let colon = if span == item_ident.span.shrink_to_hi() { ":" } else { "" };
 
                 // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
@@ -622,12 +623,8 @@ fn infer_placeholder_type<'a>(
                     ));
                 }
             }
-
-            err.emit();
-            // diagnostic stashing loses the information of whether something is a hard error.
-            Ty::new_error_with_message(tcx, span, "ItemNoType is a hard error")
-        }
-        None => {
+        })
+        .unwrap_or_else(|| {
             let mut diag = bad_placeholder(tcx, vec![span], kind);
 
             if !ty.references_error() {
@@ -645,10 +642,9 @@ fn infer_placeholder_type<'a>(
                     ));
                 }
             }
-
-            Ty::new_error(tcx, diag.emit())
-        }
-    }
+            diag.emit()
+        });
+    Ty::new_error(tcx, guar)
 }
 
 fn check_feature_inherent_assoc_ty(tcx: TyCtxt<'_>, span: Span) {
diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index bb6d1ecae02..b87d71e3533 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -484,12 +484,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                 if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = &callee_expr.kind
                     && let [segment] = path.segments
-                    && let Some(mut diag) =
-                        self.dcx().steal_diagnostic(segment.ident.span, StashKey::CallIntoMethod)
                 {
-                    // Try suggesting `foo(a)` -> `a.foo()` if possible.
-                    self.suggest_call_as_method(&mut diag, segment, arg_exprs, call_expr, expected);
-                    diag.emit();
+                    self.dcx().try_steal_modify_and_emit_err(
+                        segment.ident.span,
+                        StashKey::CallIntoMethod,
+                        |err| {
+                            // Try suggesting `foo(a)` -> `a.foo()` if possible.
+                            self.suggest_call_as_method(
+                                err, segment, arg_exprs, call_expr, expected,
+                            );
+                        },
+                    );
                 }
 
                 let err = self.report_invalid_callee(call_expr, callee_expr, callee_ty, arg_exprs);
@@ -601,7 +606,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// and suggesting the fix if the method probe is successful.
     fn suggest_call_as_method(
         &self,
-        diag: &mut Diag<'_, ()>,
+        diag: &mut Diag<'_>,
         segment: &'tcx hir::PathSegment<'tcx>,
         arg_exprs: &'tcx [hir::Expr<'tcx>],
         call_expr: &'tcx hir::Expr<'tcx>,
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 2b7bce3f485..054be89a7c4 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -1460,18 +1460,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             && let hir::ArrayLen::Body(hir::AnonConst { hir_id, .. }) = length
         {
             let span = self.tcx.hir().span(hir_id);
-            match self.dcx().steal_diagnostic(span, StashKey::UnderscoreForArrayLengths) {
-                Some(mut err) => {
+            self.dcx().try_steal_modify_and_emit_err(
+                span,
+                StashKey::UnderscoreForArrayLengths,
+                |err| {
                     err.span_suggestion(
                         span,
                         "consider specifying the array length",
                         array_len,
                         Applicability::MaybeIncorrect,
                     );
-                    err.emit();
-                }
-                None => (),
-            }
+                },
+            );
         }
     }
 
@@ -1751,11 +1751,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let (_, diag) =
                 self.demand_coerce_diag(field.expr, ty, field_type, None, AllowTwoPhase::No);
 
-            if let Some(mut diag) = diag {
+            if let Some(diag) = diag {
                 if idx == ast_fields.len() - 1 {
                     if remaining_fields.is_empty() {
-                        self.suggest_fru_from_range(field, variant, args, &mut diag);
-                        diag.emit();
+                        self.suggest_fru_from_range_and_emit(field, variant, args, diag);
                     } else {
                         diag.stash(field.span, StashKey::MaybeFruTypo);
                     }
@@ -1986,20 +1985,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         err.span_label(span, format!("missing {remaining_fields_names}{truncated_fields_error}"));
 
         if let Some(last) = ast_fields.last() {
-            self.suggest_fru_from_range(last, variant, args, &mut err);
+            self.suggest_fru_from_range_and_emit(last, variant, args, err);
+        } else {
+            err.emit();
         }
-
-        err.emit();
     }
 
     /// If the last field is a range literal, but it isn't supposed to be, then they probably
     /// meant to use functional update syntax.
-    fn suggest_fru_from_range(
+    fn suggest_fru_from_range_and_emit(
         &self,
         last_expr_field: &hir::ExprField<'tcx>,
         variant: &ty::VariantDef,
         args: GenericArgsRef<'tcx>,
-        err: &mut Diag<'_>,
+        mut err: Diag<'_>,
     ) {
         // I don't use 'is_range_literal' because only double-sided, half-open ranges count.
         if let ExprKind::Struct(QPath::LangItem(LangItem::Range, ..), [range_start, range_end], _) =
@@ -2012,16 +2011,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .map(|adt| adt.did())
                 != range_def_id
         {
-            // Suppress any range expr type mismatches
-            if let Some(diag) =
-                self.dcx().steal_diagnostic(last_expr_field.span, StashKey::MaybeFruTypo)
-            {
-                diag.delay_as_bug();
-            }
-
             // Use a (somewhat arbitrary) filtering heuristic to avoid printing
             // expressions that are either too long, or have control character
-            //such as newlines in them.
+            // such as newlines in them.
             let expr = self
                 .tcx
                 .sess
@@ -2043,6 +2035,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.dcx(),
                 TypeMismatchFruTypo { expr_span: range_start.span, fru_span, expr },
             );
+
+            // Suppress any range expr type mismatches
+            self.dcx().try_steal_replace_and_emit_err(
+                last_expr_field.span,
+                StashKey::MaybeFruTypo,
+                err,
+            );
+        } else {
+            err.emit();
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index a5892dea1a5..dd44fdd8893 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -848,11 +848,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .resolve_fully_qualified_call(span, item_name, ty.normalized, qself.span, hir_id)
             .map(|r| {
                 // lint bare trait if the method is found in the trait
-                if span.edition().at_least_rust_2021()
-                    && let Some(diag) =
-                        self.dcx().steal_diagnostic(qself.span, StashKey::TraitMissingMethod)
-                {
-                    diag.emit();
+                if span.edition().at_least_rust_2021() {
+                    self.dcx().try_steal_modify_and_emit_err(
+                        qself.span,
+                        StashKey::TraitMissingMethod,
+                        |_err| {},
+                    );
                 }
                 r
             })
@@ -879,17 +880,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     );
                 }
 
-                // emit or cancel the diagnostic for bare traits
-                if span.edition().at_least_rust_2021()
-                    && let Some(diag) =
-                        self.dcx().steal_diagnostic(qself.span, StashKey::TraitMissingMethod)
-                {
-                    if trait_missing_method {
-                        // cancel the diag for bare traits when meeting `MyTrait::missing_method`
-                        diag.cancel();
-                    } else {
-                        diag.emit();
-                    }
+                // Emit the diagnostic for bare traits. (We used to cancel for slightly better
+                // error messages, but cancelling stashed diagnostics is no longer allowed because
+                // it causes problems when tracking whether errors have actually occurred.)
+                if span.edition().at_least_rust_2021() {
+                    self.dcx().try_steal_modify_and_emit_err(
+                        qself.span,
+                        StashKey::TraitMissingMethod,
+                        |_err| {},
+                    );
                 }
 
                 if item_name.name != kw::Empty {
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 61c52422d19..1311cc8968a 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -1941,53 +1941,49 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         errors_causecode: Vec<(Span, ObligationCauseCode<'tcx>)>,
     ) {
         for (span, code) in errors_causecode {
-            let Some(mut diag) = self.dcx().steal_diagnostic(span, StashKey::MaybeForgetReturn)
-            else {
-                continue;
-            };
-
-            if let Some(fn_sig) = self.body_fn_sig()
-                && let ExprBindingObligation(_, _, hir_id, ..) = code
-                && !fn_sig.output().is_unit()
-            {
-                let mut block_num = 0;
-                let mut found_semi = false;
-                for (_, node) in self.tcx.hir().parent_iter(hir_id) {
-                    match node {
-                        hir::Node::Stmt(stmt) => {
-                            if let hir::StmtKind::Semi(expr) = stmt.kind {
-                                let expr_ty = self.typeck_results.borrow().expr_ty(expr);
-                                let return_ty = fn_sig.output();
-                                if !matches!(expr.kind, hir::ExprKind::Ret(..))
-                                    && self.can_coerce(expr_ty, return_ty)
-                                {
-                                    found_semi = true;
+            self.dcx().try_steal_modify_and_emit_err(span, StashKey::MaybeForgetReturn, |err| {
+                if let Some(fn_sig) = self.body_fn_sig()
+                    && let ExprBindingObligation(_, _, hir_id, ..) = code
+                    && !fn_sig.output().is_unit()
+                {
+                    let mut block_num = 0;
+                    let mut found_semi = false;
+                    for (_, node) in self.tcx.hir().parent_iter(hir_id) {
+                        match node {
+                            hir::Node::Stmt(stmt) => {
+                                if let hir::StmtKind::Semi(expr) = stmt.kind {
+                                    let expr_ty = self.typeck_results.borrow().expr_ty(expr);
+                                    let return_ty = fn_sig.output();
+                                    if !matches!(expr.kind, hir::ExprKind::Ret(..))
+                                        && self.can_coerce(expr_ty, return_ty)
+                                    {
+                                        found_semi = true;
+                                    }
                                 }
                             }
-                        }
-                        hir::Node::Block(_block) => {
-                            if found_semi {
-                                block_num += 1;
+                            hir::Node::Block(_block) => {
+                                if found_semi {
+                                    block_num += 1;
+                                }
                             }
-                        }
-                        hir::Node::Item(item) => {
-                            if let hir::ItemKind::Fn(..) = item.kind {
-                                break;
+                            hir::Node::Item(item) => {
+                                if let hir::ItemKind::Fn(..) = item.kind {
+                                    break;
+                                }
                             }
+                            _ => {}
                         }
-                        _ => {}
+                    }
+                    if block_num > 1 && found_semi {
+                        err.span_suggestion_verbose(
+                            span.shrink_to_lo(),
+                            "you might have meant to return this to infer its type parameters",
+                            "return ",
+                            Applicability::MaybeIncorrect,
+                        );
                     }
                 }
-                if block_num > 1 && found_semi {
-                    diag.span_suggestion_verbose(
-                        span.shrink_to_lo(),
-                        "you might have meant to return this to infer its type parameters",
-                        "return ",
-                        Applicability::MaybeIncorrect,
-                    );
-                }
-            }
-            diag.emit();
+            });
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 28771ae40f5..e5b0d0ae0da 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -2194,59 +2194,59 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let [seg1, seg2] = segs else {
             return;
         };
-        let Some(mut diag) =
-            self.dcx().steal_diagnostic(seg1.ident.span, StashKey::CallAssocMethod)
-        else {
-            return;
-        };
-
-        let map = self.infcx.tcx.hir();
-        let body_id = self.tcx.hir().body_owned_by(self.body_id);
-        let body = map.body(body_id);
-        struct LetVisitor<'a> {
-            result: Option<&'a hir::Expr<'a>>,
-            ident_name: Symbol,
-        }
-
-        // FIXME: This really should be taking scoping, etc into account.
-        impl<'v> Visitor<'v> for LetVisitor<'v> {
-            fn visit_stmt(&mut self, ex: &'v hir::Stmt<'v>) {
-                if let hir::StmtKind::Local(hir::Local { pat, init, .. }) = &ex.kind
-                    && let Binding(_, _, ident, ..) = pat.kind
-                    && ident.name == self.ident_name
-                {
-                    self.result = *init;
-                } else {
-                    hir::intravisit::walk_stmt(self, ex);
+        self.dcx().try_steal_modify_and_emit_err(
+            seg1.ident.span,
+            StashKey::CallAssocMethod,
+            |err| {
+                let map = self.infcx.tcx.hir();
+                let body_id = self.tcx.hir().body_owned_by(self.body_id);
+                let body = map.body(body_id);
+                struct LetVisitor<'a> {
+                    result: Option<&'a hir::Expr<'a>>,
+                    ident_name: Symbol,
                 }
-            }
-        }
 
-        let mut visitor = LetVisitor { result: None, ident_name: seg1.ident.name };
-        visitor.visit_body(body);
+                // FIXME: This really should be taking scoping, etc into account.
+                impl<'v> Visitor<'v> for LetVisitor<'v> {
+                    fn visit_stmt(&mut self, ex: &'v hir::Stmt<'v>) {
+                        if let hir::StmtKind::Local(hir::Local { pat, init, .. }) = &ex.kind
+                            && let Binding(_, _, ident, ..) = pat.kind
+                            && ident.name == self.ident_name
+                        {
+                            self.result = *init;
+                        } else {
+                            hir::intravisit::walk_stmt(self, ex);
+                        }
+                    }
+                }
 
-        if let Node::Expr(call_expr) = self.tcx.parent_hir_node(seg1.hir_id)
-            && let Some(expr) = visitor.result
-            && let Some(self_ty) = self.node_ty_opt(expr.hir_id)
-        {
-            let probe = self.lookup_probe_for_diagnostic(
-                seg2.ident,
-                self_ty,
-                call_expr,
-                ProbeScope::TraitsInScope,
-                None,
-            );
-            if probe.is_ok() {
-                let sm = self.infcx.tcx.sess.source_map();
-                diag.span_suggestion_verbose(
-                    sm.span_extend_while(seg1.ident.span.shrink_to_hi(), |c| c == ':').unwrap(),
-                    "you may have meant to call an instance method",
-                    ".",
-                    Applicability::MaybeIncorrect,
-                );
-            }
-        }
-        diag.emit();
+                let mut visitor = LetVisitor { result: None, ident_name: seg1.ident.name };
+                visitor.visit_body(body);
+
+                if let Node::Expr(call_expr) = self.tcx.parent_hir_node(seg1.hir_id)
+                    && let Some(expr) = visitor.result
+                    && let Some(self_ty) = self.node_ty_opt(expr.hir_id)
+                {
+                    let probe = self.lookup_probe_for_diagnostic(
+                        seg2.ident,
+                        self_ty,
+                        call_expr,
+                        ProbeScope::TraitsInScope,
+                        None,
+                    );
+                    if probe.is_ok() {
+                        let sm = self.infcx.tcx.sess.source_map();
+                        err.span_suggestion_verbose(
+                            sm.span_extend_while(seg1.ident.span.shrink_to_hi(), |c| c == ':')
+                                .unwrap(),
+                            "you may have meant to call an instance method",
+                            ".",
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                }
+            },
+        );
     }
 
     /// Suggest calling a method on a field i.e. `a.field.bar()` instead of `a.bar()`
diff --git a/compiler/rustc_hir_typeck/src/writeback.rs b/compiler/rustc_hir_typeck/src/writeback.rs
index ed102a7fac0..0740a3fd3e9 100644
--- a/compiler/rustc_hir_typeck/src/writeback.rs
+++ b/compiler/rustc_hir_typeck/src/writeback.rs
@@ -772,10 +772,6 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
     fn report_error(&self, p: impl Into<ty::GenericArg<'tcx>>) -> ErrorGuaranteed {
         if let Some(guar) = self.fcx.dcx().has_errors() {
             guar
-        } else if self.fcx.dcx().stashed_err_count() > 0 {
-            // Without this case we sometimes get uninteresting and extraneous
-            // "type annotations needed" errors.
-            self.fcx.dcx().delayed_bug("error in Resolver")
         } else {
             self.fcx
                 .err_ctxt()
diff --git a/compiler/rustc_infer/src/infer/at.rs b/compiler/rustc_infer/src/infer/at.rs
index cc09a094688..a086d89b933 100644
--- a/compiler/rustc_infer/src/infer/at.rs
+++ b/compiler/rustc_infer/src/infer/at.rs
@@ -87,7 +87,6 @@ impl<'tcx> InferCtxt<'tcx> {
             reported_signature_mismatch: self.reported_signature_mismatch.clone(),
             tainted_by_errors: self.tainted_by_errors.clone(),
             err_count_on_creation: self.err_count_on_creation,
-            stashed_err_count_on_creation: self.stashed_err_count_on_creation,
             universe: self.universe.clone(),
             intercrate,
             next_trait_solver: self.next_trait_solver,
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index d7e16488508..6f52ded3551 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -306,12 +306,6 @@ pub struct InferCtxt<'tcx> {
     // FIXME(matthewjasper) Merge into `tainted_by_errors`
     err_count_on_creation: usize,
 
-    /// Track how many errors were stashed when this infcx is created.
-    /// Used for the same purpose as `err_count_on_creation`, even
-    /// though it's weaker because the count can go up and down.
-    // FIXME(matthewjasper) Merge into `tainted_by_errors`
-    stashed_err_count_on_creation: usize,
-
     /// What is the innermost universe we have created? Starts out as
     /// `UniverseIndex::root()` but grows from there as we enter
     /// universal quantifiers.
@@ -717,7 +711,6 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             reported_signature_mismatch: Default::default(),
             tainted_by_errors: Cell::new(None),
             err_count_on_creation: tcx.dcx().err_count_excluding_lint_errs(),
-            stashed_err_count_on_creation: tcx.dcx().stashed_err_count(),
             universe: Cell::new(ty::UniverseIndex::ROOT),
             intercrate,
             next_trait_solver,
@@ -1274,14 +1267,6 @@ impl<'tcx> InferCtxt<'tcx> {
             let guar = self.dcx().has_errors().unwrap();
             self.set_tainted_by_errors(guar);
             Some(guar)
-        } else if self.dcx().stashed_err_count() > self.stashed_err_count_on_creation {
-            // Errors stashed since this infcx was made. Not entirely reliable
-            // because the count of stashed errors can go down. But without
-            // this case we get a moderate number of uninteresting and
-            // extraneous "type annotations needed" errors.
-            let guar = self.dcx().delayed_bug("tainted_by_errors: stashed bug awaiting emission");
-            self.set_tainted_by_errors(guar);
-            Some(guar)
         } else {
             None
         }
diff --git a/compiler/rustc_lint/src/array_into_iter.rs b/compiler/rustc_lint/src/array_into_iter.rs
index 993b1d739a1..3a5c585366a 100644
--- a/compiler/rustc_lint/src/array_into_iter.rs
+++ b/compiler/rustc_lint/src/array_into_iter.rs
@@ -70,15 +70,11 @@ impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
 
             // Check if the method call actually calls the libcore
             // `IntoIterator::into_iter`.
-            let trait_id = cx
-                .typeck_results()
-                .type_dependent_def_id(expr.hir_id)
-                .and_then(|did| cx.tcx.trait_of_item(did));
-            if trait_id.is_none()
-                || !cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id.unwrap())
-            {
-                return;
-            }
+            let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
+            match cx.tcx.trait_of_item(def_id) {
+                Some(trait_id) if cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_id) => {}
+                _ => return,
+            };
 
             // As this is a method call expression, we have at least one argument.
             let receiver_ty = cx.typeck_results().expr_ty(receiver_arg);
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 2ad592174f1..65875ff3f9a 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -815,7 +815,9 @@ pub enum PatKind<'tcx> {
 /// The boundaries must be of the same type and that type must be numeric.
 #[derive(Clone, Debug, PartialEq, HashStable, TypeVisitable)]
 pub struct PatRange<'tcx> {
+    /// Must not be `PosInfinity`.
     pub lo: PatRangeBoundary<'tcx>,
+    /// Must not be `NegInfinity`.
     pub hi: PatRangeBoundary<'tcx>,
     #[type_visitable(ignore)]
     pub end: RangeEnd,
@@ -958,22 +960,6 @@ impl<'tcx> PatRangeBoundary<'tcx> {
             Self::NegInfinity | Self::PosInfinity => None,
         }
     }
-    #[inline]
-    pub fn to_const(self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> mir::Const<'tcx> {
-        match self {
-            Self::Finite(value) => value,
-            Self::NegInfinity => {
-                // Unwrap is ok because the type is known to be numeric.
-                let c = ty.numeric_min_val(tcx).unwrap();
-                mir::Const::from_ty_const(c, tcx)
-            }
-            Self::PosInfinity => {
-                // Unwrap is ok because the type is known to be numeric.
-                let c = ty.numeric_max_val(tcx).unwrap();
-                mir::Const::from_ty_const(c, tcx)
-            }
-        }
-    }
     pub fn eval_bits(self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> u128 {
         match self {
             Self::Finite(value) => value.eval_bits(tcx, param_env),
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index d97f0e4c321..6fdb03c0bab 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -847,13 +847,15 @@ impl<'tcx> OpaqueHiddenType<'tcx> {
         opaque_def_id: LocalDefId,
         tcx: TyCtxt<'tcx>,
     ) -> Result<Diag<'tcx>, ErrorGuaranteed> {
-        if let Some(diag) = tcx
-            .sess
-            .dcx()
-            .steal_diagnostic(tcx.def_span(opaque_def_id), StashKey::OpaqueHiddenTypeMismatch)
-        {
-            diag.cancel();
-        }
+        // We used to cancel here for slightly better error messages, but
+        // cancelling stashed diagnostics is no longer allowed because it
+        // causes problems when tracking whether errors have actually
+        // occurred.
+        tcx.sess.dcx().try_steal_modify_and_emit_err(
+            tcx.def_span(opaque_def_id),
+            StashKey::OpaqueHiddenTypeMismatch,
+            |_err| {},
+        );
         (self.ty, other.ty).error_reported()?;
         // Found different concrete types for the opaque type.
         let sub_diag = if self.span == other.span {
diff --git a/compiler/rustc_middle/src/ty/region.rs b/compiler/rustc_middle/src/ty/region.rs
index b206727f051..51a4a9f411c 100644
--- a/compiler/rustc_middle/src/ty/region.rs
+++ b/compiler/rustc_middle/src/ty/region.rs
@@ -91,8 +91,8 @@ impl<'tcx> Region<'tcx> {
 
     /// Constructs a `RegionKind::ReError` region.
     #[track_caller]
-    pub fn new_error(tcx: TyCtxt<'tcx>, reported: ErrorGuaranteed) -> Region<'tcx> {
-        tcx.intern_region(ty::ReError(reported))
+    pub fn new_error(tcx: TyCtxt<'tcx>, guar: ErrorGuaranteed) -> Region<'tcx> {
+        tcx.intern_region(ty::ReError(guar))
     }
 
     /// Constructs a `RegionKind::ReError` region and registers a delayed bug to ensure it gets
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 27c78d18d19..06be8191dc4 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1528,8 +1528,8 @@ impl<'tcx> Ty<'tcx> {
     }
 
     /// Constructs a `TyKind::Error` type with current `ErrorGuaranteed`
-    pub fn new_error(tcx: TyCtxt<'tcx>, reported: ErrorGuaranteed) -> Ty<'tcx> {
-        Ty::new(tcx, Error(reported))
+    pub fn new_error(tcx: TyCtxt<'tcx>, guar: ErrorGuaranteed) -> Ty<'tcx> {
+        Ty::new(tcx, Error(guar))
     }
 
     /// Constructs a `TyKind::Error` type and registers a `span_delayed_bug` to ensure it gets used.
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 1c97de58863..1b6994966d1 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -291,33 +291,41 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
 
             TestKind::Range(ref range) => {
-                let lower_bound_success = self.cfg.start_new_block();
-
-                // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
-                // FIXME: skip useless comparison when the range is half-open.
-                let lo = range.lo.to_const(range.ty, self.tcx);
-                let hi = range.hi.to_const(range.ty, self.tcx);
-                let lo = self.literal_operand(test.span, lo);
-                let hi = self.literal_operand(test.span, hi);
-                let val = Operand::Copy(place);
-
                 let [success, fail] = *target_blocks else {
                     bug!("`TestKind::Range` should have two target blocks");
                 };
-                self.compare(
-                    block,
-                    lower_bound_success,
-                    fail,
-                    source_info,
-                    BinOp::Le,
-                    lo,
-                    val.clone(),
-                );
-                let op = match range.end {
-                    RangeEnd::Included => BinOp::Le,
-                    RangeEnd::Excluded => BinOp::Lt,
+                // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
+                let val = Operand::Copy(place);
+
+                let intermediate_block = if !range.lo.is_finite() {
+                    block
+                } else if !range.hi.is_finite() {
+                    success
+                } else {
+                    self.cfg.start_new_block()
                 };
-                self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
+
+                if let Some(lo) = range.lo.as_finite() {
+                    let lo = self.literal_operand(test.span, lo);
+                    self.compare(
+                        block,
+                        intermediate_block,
+                        fail,
+                        source_info,
+                        BinOp::Le,
+                        lo,
+                        val.clone(),
+                    );
+                };
+
+                if let Some(hi) = range.hi.as_finite() {
+                    let hi = self.literal_operand(test.span, hi);
+                    let op = match range.end {
+                        RangeEnd::Included => BinOp::Le,
+                        RangeEnd::Excluded => BinOp::Lt,
+                    };
+                    self.compare(intermediate_block, success, fail, source_info, op, val, hi);
+                }
             }
 
             TestKind::Len { len, op } => {
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index f5a7bfd42ff..316a9c4f8df 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1762,24 +1762,25 @@ impl<'a> Parser<'a> {
         err: impl FnOnce(&Self) -> Diag<'a>,
     ) -> L {
         assert!(could_be_unclosed_char_literal(ident));
-        if let Some(diag) = self.dcx().steal_diagnostic(ident.span, StashKey::LifetimeIsChar) {
-            diag.with_span_suggestion_verbose(
-                ident.span.shrink_to_hi(),
-                "add `'` to close the char literal",
-                "'",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
-        } else {
-            err(self)
-                .with_span_suggestion_verbose(
+        self.dcx()
+            .try_steal_modify_and_emit_err(ident.span, StashKey::LifetimeIsChar, |err| {
+                err.span_suggestion_verbose(
                     ident.span.shrink_to_hi(),
                     "add `'` to close the char literal",
                     "'",
                     Applicability::MaybeIncorrect,
-                )
-                .emit();
-        }
+                );
+            })
+            .unwrap_or_else(|| {
+                err(self)
+                    .with_span_suggestion_verbose(
+                        ident.span.shrink_to_hi(),
+                        "add `'` to close the char literal",
+                        "'",
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit()
+            });
         let name = ident.without_first_quote().name;
         mk_lit_char(name, ident.span)
     }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index c12d35ec73c..04c0cf7436e 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -2520,14 +2520,6 @@ fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
         if attr.style == AttrStyle::Inner {
             for attr_to_check in ATTRS_TO_CHECK {
                 if attr.has_name(*attr_to_check) {
-                    if let AttrKind::Normal(ref p) = attr.kind
-                        && let Some(diag) = tcx.dcx().steal_diagnostic(
-                            p.item.path.span,
-                            StashKey::UndeterminedMacroResolution,
-                        )
-                    {
-                        diag.cancel();
-                    }
                     let item = tcx
                         .hir()
                         .items()
@@ -2537,7 +2529,7 @@ fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
                             span: item.ident.span,
                             kind: item.kind.descr(),
                         });
-                    tcx.dcx().emit_err(errors::InvalidAttrAtCrateLevel {
+                    let err = tcx.dcx().create_err(errors::InvalidAttrAtCrateLevel {
                         span: attr.span,
                         sugg_span: tcx
                             .sess
@@ -2553,6 +2545,16 @@ fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
                         name: *attr_to_check,
                         item,
                     });
+
+                    if let AttrKind::Normal(ref p) = attr.kind {
+                        tcx.dcx().try_steal_replace_and_emit_err(
+                            p.item.path.span,
+                            StashKey::UndeterminedMacroResolution,
+                            err,
+                        );
+                    } else {
+                        err.emit();
+                    }
                 }
             }
         }
diff --git a/compiler/rustc_pattern_analysis/src/constructor.rs b/compiler/rustc_pattern_analysis/src/constructor.rs
index b1f910b947a..767227619b0 100644
--- a/compiler/rustc_pattern_analysis/src/constructor.rs
+++ b/compiler/rustc_pattern_analysis/src/constructor.rs
@@ -688,6 +688,9 @@ pub enum Constructor<Cx: TypeCx> {
     /// Fake extra constructor for constructors that are not seen in the matrix, as explained at the
     /// top of the file.
     Missing,
+    /// Fake extra constructor that indicates and empty field that is private. When we encounter one
+    /// we skip the column entirely so we don't observe its emptiness. Only used for specialization.
+    PrivateUninhabited,
 }
 
 impl<Cx: TypeCx> Clone for Constructor<Cx> {
@@ -709,6 +712,7 @@ impl<Cx: TypeCx> Clone for Constructor<Cx> {
             Constructor::NonExhaustive => Constructor::NonExhaustive,
             Constructor::Hidden => Constructor::Hidden,
             Constructor::Missing => Constructor::Missing,
+            Constructor::PrivateUninhabited => Constructor::PrivateUninhabited,
         }
     }
 }
@@ -763,6 +767,8 @@ impl<Cx: TypeCx> Constructor<Cx> {
             }
             // Wildcards cover anything
             (_, Wildcard) => true,
+            // `PrivateUninhabited` skips everything.
+            (PrivateUninhabited, _) => true,
             // Only a wildcard pattern can match these special constructors.
             (Missing { .. } | NonExhaustive | Hidden, _) => false,
 
diff --git a/compiler/rustc_pattern_analysis/src/lib.rs b/compiler/rustc_pattern_analysis/src/lib.rs
index 164dc36b679..d4b38d260e7 100644
--- a/compiler/rustc_pattern_analysis/src/lib.rs
+++ b/compiler/rustc_pattern_analysis/src/lib.rs
@@ -82,6 +82,11 @@ use crate::usefulness::{compute_match_usefulness, ValidityConstraint};
 pub trait Captures<'a> {}
 impl<'a, T: ?Sized> Captures<'a> for T {}
 
+/// `bool` newtype that indicates whether this is a privately uninhabited field that we should skip
+/// during analysis.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct PrivateUninhabitedField(pub bool);
+
 /// Context that provides type information about constructors.
 ///
 /// Most of the crate is parameterized on a type that implements this trait.
@@ -105,13 +110,12 @@ pub trait TypeCx: Sized + fmt::Debug {
     /// The number of fields for this constructor.
     fn ctor_arity(&self, ctor: &Constructor<Self>, ty: &Self::Ty) -> usize;
 
-    /// The types of the fields for this constructor. The result must have a length of
-    /// `ctor_arity()`.
+    /// The types of the fields for this constructor. The result must contain `ctor_arity()` fields.
     fn ctor_sub_tys<'a>(
         &'a self,
         ctor: &'a Constructor<Self>,
         ty: &'a Self::Ty,
-    ) -> impl Iterator<Item = Self::Ty> + ExactSizeIterator + Captures<'a>;
+    ) -> impl Iterator<Item = (Self::Ty, PrivateUninhabitedField)> + ExactSizeIterator + Captures<'a>;
 
     /// The set of all the constructors for `ty`.
     ///
diff --git a/compiler/rustc_pattern_analysis/src/pat.rs b/compiler/rustc_pattern_analysis/src/pat.rs
index d9b2b31643d..decbfa5c0cf 100644
--- a/compiler/rustc_pattern_analysis/src/pat.rs
+++ b/compiler/rustc_pattern_analysis/src/pat.rs
@@ -5,7 +5,7 @@ use std::fmt;
 use smallvec::{smallvec, SmallVec};
 
 use crate::constructor::{Constructor, Slice, SliceKind};
-use crate::TypeCx;
+use crate::{PrivateUninhabitedField, TypeCx};
 
 use self::Constructor::*;
 
@@ -23,11 +23,6 @@ impl PatId {
 /// Values and patterns can be represented as a constructor applied to some fields. This represents
 /// a pattern in this form. A `DeconstructedPat` will almost always come from user input; the only
 /// exception are some `Wildcard`s introduced during pattern lowering.
-///
-/// Note that the number of fields may not match the fields declared in the original struct/variant.
-/// This happens if a private or `non_exhaustive` field is uninhabited, because the code mustn't
-/// observe that it is uninhabited. In that case that field is not included in `fields`. Care must
-/// be taken when converting to/from `thir::Pat`.
 pub struct DeconstructedPat<Cx: TypeCx> {
     ctor: Constructor<Cx>,
     fields: Vec<DeconstructedPat<Cx>>,
@@ -84,6 +79,8 @@ impl<Cx: TypeCx> DeconstructedPat<Cx> {
         match (&self.ctor, other_ctor) {
             // Return a wildcard for each field of `other_ctor`.
             (Wildcard, _) => wildcard_sub_tys(),
+            // Skip this column.
+            (_, PrivateUninhabited) => smallvec![],
             // The only non-trivial case: two slices of different arity. `other_slice` is
             // guaranteed to have a larger arity, so we fill the middle part with enough
             // wildcards to reach the length of the new, larger slice.
@@ -192,7 +189,9 @@ impl<Cx: TypeCx> fmt::Debug for DeconstructedPat<Cx> {
                 }
                 Ok(())
             }
-            Wildcard | Missing { .. } | NonExhaustive | Hidden => write!(f, "_ : {:?}", pat.ty()),
+            Wildcard | Missing | NonExhaustive | Hidden | PrivateUninhabited => {
+                write!(f, "_ : {:?}", pat.ty())
+            }
         }
     }
 }
@@ -300,7 +299,11 @@ impl<Cx: TypeCx> WitnessPat<Cx> {
     /// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
     /// `Some(_)`.
     pub(crate) fn wild_from_ctor(cx: &Cx, ctor: Constructor<Cx>, ty: Cx::Ty) -> Self {
-        let fields = cx.ctor_sub_tys(&ctor, &ty).map(|ty| Self::wildcard(ty)).collect();
+        let fields = cx
+            .ctor_sub_tys(&ctor, &ty)
+            .filter(|(_, PrivateUninhabitedField(skip))| !skip)
+            .map(|(ty, _)| Self::wildcard(ty))
+            .collect();
         Self::new(ctor, fields, ty)
     }
 
diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index 5b62731e202..7a0562e12f1 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -10,7 +10,7 @@ use rustc_middle::mir::interpret::Scalar;
 use rustc_middle::mir::{self, Const};
 use rustc_middle::thir::{FieldPat, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
-use rustc_middle::ty::{self, OpaqueTypeKey, Ty, TyCtxt, TypeVisitableExt, VariantDef};
+use rustc_middle::ty::{self, FieldDef, OpaqueTypeKey, Ty, TyCtxt, TypeVisitableExt, VariantDef};
 use rustc_session::lint;
 use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
 use rustc_target::abi::{FieldIdx, Integer, VariantIdx, FIRST_VARIANT};
@@ -18,7 +18,7 @@ use rustc_target::abi::{FieldIdx, Integer, VariantIdx, FIRST_VARIANT};
 use crate::constructor::{
     IntRange, MaybeInfiniteInt, OpaqueId, RangeEnd, Slice, SliceKind, VariantVisibility,
 };
-use crate::{errors, Captures, TypeCx};
+use crate::{errors, Captures, PrivateUninhabitedField, TypeCx};
 
 use crate::constructor::Constructor::*;
 
@@ -158,34 +158,19 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
         }
     }
 
-    // In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide
-    // uninhabited fields in order not to reveal the uninhabitedness of the whole variant.
-    // This lists the fields we keep along with their types.
-    pub(crate) fn list_variant_nonhidden_fields(
+    pub(crate) fn variant_sub_tys(
         &self,
         ty: RevealedTy<'tcx>,
         variant: &'tcx VariantDef,
-    ) -> impl Iterator<Item = (FieldIdx, RevealedTy<'tcx>)> + Captures<'p> + Captures<'_> {
-        let cx = self;
-        let ty::Adt(adt, args) = ty.kind() else { bug!() };
-        // Whether we must not match the fields of this variant exhaustively.
-        let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
-
-        variant.fields.iter().enumerate().filter_map(move |(i, field)| {
-            let ty = field.ty(cx.tcx, args);
+    ) -> impl Iterator<Item = (&'tcx FieldDef, RevealedTy<'tcx>)> + Captures<'p> + Captures<'_>
+    {
+        let ty::Adt(_, args) = ty.kind() else { bug!() };
+        variant.fields.iter().map(move |field| {
+            let ty = field.ty(self.tcx, args);
             // `field.ty()` doesn't normalize after instantiating.
-            let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
-            let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
-            let is_uninhabited = (cx.tcx.features().exhaustive_patterns
-                || cx.tcx.features().min_exhaustive_patterns)
-                && cx.is_uninhabited(ty);
-
-            if is_uninhabited && (!is_visible || is_non_exhaustive) {
-                None
-            } else {
-                let ty = cx.reveal_opaque_ty(ty);
-                Some((FieldIdx::new(i), ty))
-            }
+            let ty = self.tcx.normalize_erasing_regions(self.param_env, ty);
+            let ty = self.reveal_opaque_ty(ty);
+            (field, ty)
         })
     }
 
@@ -210,12 +195,17 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
         &'a self,
         ctor: &'a Constructor<'p, 'tcx>,
         ty: RevealedTy<'tcx>,
-    ) -> impl Iterator<Item = RevealedTy<'tcx>> + ExactSizeIterator + Captures<'a> {
+    ) -> impl Iterator<Item = (RevealedTy<'tcx>, PrivateUninhabitedField)>
+    + ExactSizeIterator
+    + Captures<'a> {
         fn reveal_and_alloc<'a, 'tcx>(
             cx: &'a RustcMatchCheckCtxt<'_, 'tcx>,
             iter: impl Iterator<Item = Ty<'tcx>>,
-        ) -> &'a [RevealedTy<'tcx>] {
-            cx.dropless_arena.alloc_from_iter(iter.map(|ty| cx.reveal_opaque_ty(ty)))
+        ) -> &'a [(RevealedTy<'tcx>, PrivateUninhabitedField)] {
+            cx.dropless_arena.alloc_from_iter(
+                iter.map(|ty| cx.reveal_opaque_ty(ty))
+                    .map(|ty| (ty, PrivateUninhabitedField(false))),
+            )
         }
         let cx = self;
         let slice = match ctor {
@@ -229,7 +219,21 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                     } else {
                         let variant =
                             &adt.variant(RustcMatchCheckCtxt::variant_index_for_adt(&ctor, *adt));
-                        let tys = cx.list_variant_nonhidden_fields(ty, variant).map(|(_, ty)| ty);
+
+                        // In the cases of either a `#[non_exhaustive]` field list or a non-public
+                        // field, we skip uninhabited fields in order not to reveal the
+                        // uninhabitedness of the whole variant.
+                        let is_non_exhaustive =
+                            variant.is_field_list_non_exhaustive() && !adt.did().is_local();
+                        let tys = cx.variant_sub_tys(ty, variant).map(|(field, ty)| {
+                            let is_visible =
+                                adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
+                            let is_uninhabited = (cx.tcx.features().exhaustive_patterns
+                                || cx.tcx.features().min_exhaustive_patterns)
+                                && cx.is_uninhabited(*ty);
+                            let skip = is_uninhabited && (!is_visible || is_non_exhaustive);
+                            (ty, PrivateUninhabitedField(skip))
+                        });
                         cx.dropless_arena.alloc_from_iter(tys)
                     }
                 }
@@ -246,16 +250,8 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                 }
                 _ => bug!("bad slice pattern {:?} {:?}", ctor, ty),
             },
-            Bool(..)
-            | IntRange(..)
-            | F32Range(..)
-            | F64Range(..)
-            | Str(..)
-            | Opaque(..)
-            | NonExhaustive
-            | Hidden
-            | Missing { .. }
-            | Wildcard => &[],
+            Bool(..) | IntRange(..) | F32Range(..) | F64Range(..) | Str(..) | Opaque(..)
+            | NonExhaustive | Hidden | Missing | PrivateUninhabited | Wildcard => &[],
             Or => {
                 bug!("called `Fields::wildcards` on an `Or` ctor")
             }
@@ -274,25 +270,16 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                         // patterns. If we're here we can assume this is a box pattern.
                         1
                     } else {
-                        let variant =
-                            &adt.variant(RustcMatchCheckCtxt::variant_index_for_adt(&ctor, *adt));
-                        self.list_variant_nonhidden_fields(ty, variant).count()
+                        let variant_idx = RustcMatchCheckCtxt::variant_index_for_adt(&ctor, *adt);
+                        adt.variant(variant_idx).fields.len()
                     }
                 }
                 _ => bug!("Unexpected type for constructor `{ctor:?}`: {ty:?}"),
             },
             Ref => 1,
             Slice(slice) => slice.arity(),
-            Bool(..)
-            | IntRange(..)
-            | F32Range(..)
-            | F64Range(..)
-            | Str(..)
-            | Opaque(..)
-            | NonExhaustive
-            | Hidden
-            | Missing { .. }
-            | Wildcard => 0,
+            Bool(..) | IntRange(..) | F32Range(..) | F64Range(..) | Str(..) | Opaque(..)
+            | NonExhaustive | Hidden | Missing | PrivateUninhabited | Wildcard => 0,
             Or => bug!("The `Or` constructor doesn't have a fixed arity"),
         }
     }
@@ -520,20 +507,12 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                         };
                         let variant =
                             &adt.variant(RustcMatchCheckCtxt::variant_index_for_adt(&ctor, *adt));
-                        // For each field in the variant, we store the relevant index into `self.fields` if any.
-                        let mut field_id_to_id: Vec<Option<usize>> =
-                            (0..variant.fields.len()).map(|_| None).collect();
-                        let tys = cx.list_variant_nonhidden_fields(ty, variant).enumerate().map(
-                            |(i, (field, ty))| {
-                                field_id_to_id[field.index()] = Some(i);
-                                ty
-                            },
-                        );
-                        fields = tys.map(|ty| DeconstructedPat::wildcard(ty)).collect();
+                        fields = cx
+                            .variant_sub_tys(ty, variant)
+                            .map(|(_, ty)| DeconstructedPat::wildcard(ty))
+                            .collect();
                         for pat in subpatterns {
-                            if let Some(i) = field_id_to_id[pat.field.index()] {
-                                fields[i] = self.lower_pat(&pat.pattern);
-                            }
+                            fields[pat.field.index()] = self.lower_pat(&pat.pattern);
                         }
                     }
                     _ => bug!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, ty),
@@ -775,11 +754,9 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                 ty::Adt(adt_def, args) => {
                     let variant_index =
                         RustcMatchCheckCtxt::variant_index_for_adt(&pat.ctor(), *adt_def);
-                    let variant = &adt_def.variant(variant_index);
-                    let subpatterns = cx
-                        .list_variant_nonhidden_fields(*pat.ty(), variant)
-                        .zip(subpatterns)
-                        .map(|((field, _ty), pattern)| FieldPat { field, pattern })
+                    let subpatterns = subpatterns
+                        .enumerate()
+                        .map(|(i, pattern)| FieldPat { field: FieldIdx::new(i), pattern })
                         .collect();
 
                     if adt_def.is_enum() {
@@ -830,7 +807,7 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                 }
             }
             &Str(value) => PatKind::Constant { value },
-            Wildcard | NonExhaustive | Hidden => PatKind::Wild,
+            Wildcard | NonExhaustive | Hidden | PrivateUninhabited => PatKind::Wild,
             Missing { .. } => bug!(
                 "trying to convert a `Missing` constructor into a `Pat`; this is probably a bug,
                 `Missing` should have been processed in `apply_constructors`"
@@ -866,7 +843,8 @@ impl<'p, 'tcx: 'p> TypeCx for RustcMatchCheckCtxt<'p, 'tcx> {
         &'a self,
         ctor: &'a crate::constructor::Constructor<Self>,
         ty: &'a Self::Ty,
-    ) -> impl Iterator<Item = Self::Ty> + ExactSizeIterator + Captures<'a> {
+    ) -> impl Iterator<Item = (Self::Ty, PrivateUninhabitedField)> + ExactSizeIterator + Captures<'a>
+    {
         self.ctor_sub_tys(ctor, *ty)
     }
     fn ctors_for_ty(
diff --git a/compiler/rustc_pattern_analysis/src/usefulness.rs b/compiler/rustc_pattern_analysis/src/usefulness.rs
index f672051be5a..bbe02f94c0a 100644
--- a/compiler/rustc_pattern_analysis/src/usefulness.rs
+++ b/compiler/rustc_pattern_analysis/src/usefulness.rs
@@ -716,7 +716,7 @@ use std::fmt;
 
 use crate::constructor::{Constructor, ConstructorSet, IntRange};
 use crate::pat::{DeconstructedPat, PatId, PatOrWild, WitnessPat};
-use crate::{Captures, MatchArm, TypeCx};
+use crate::{Captures, MatchArm, PrivateUninhabitedField, TypeCx};
 
 use self::ValidityConstraint::*;
 
@@ -817,6 +817,9 @@ impl fmt::Display for ValidityConstraint {
 struct PlaceInfo<Cx: TypeCx> {
     /// The type of the place.
     ty: Cx::Ty,
+    /// Whether the place is a private uninhabited field. If so we skip this field during analysis
+    /// so that we don't observe its emptiness.
+    private_uninhabited: bool,
     /// Whether the place is known to contain valid data.
     validity: ValidityConstraint,
     /// Whether the place is the scrutinee itself or a subplace of it.
@@ -833,8 +836,9 @@ impl<Cx: TypeCx> PlaceInfo<Cx> {
     ) -> impl Iterator<Item = Self> + ExactSizeIterator + Captures<'a> {
         let ctor_sub_tys = cx.ctor_sub_tys(ctor, &self.ty);
         let ctor_sub_validity = self.validity.specialize(ctor);
-        ctor_sub_tys.map(move |ty| PlaceInfo {
+        ctor_sub_tys.map(move |(ty, PrivateUninhabitedField(private_uninhabited))| PlaceInfo {
             ty,
+            private_uninhabited,
             validity: ctor_sub_validity,
             is_scrutinee: false,
         })
@@ -856,6 +860,11 @@ impl<Cx: TypeCx> PlaceInfo<Cx> {
     where
         Cx: 'a,
     {
+        if self.private_uninhabited {
+            // Skip the whole column
+            return Ok((smallvec![Constructor::PrivateUninhabited], vec![]));
+        }
+
         let ctors_for_ty = cx.ctors_for_ty(&self.ty)?;
 
         // We treat match scrutinees of type `!` or `EmptyEnum` differently.
@@ -914,7 +923,12 @@ impl<Cx: TypeCx> PlaceInfo<Cx> {
 
 impl<Cx: TypeCx> Clone for PlaceInfo<Cx> {
     fn clone(&self) -> Self {
-        Self { ty: self.ty.clone(), validity: self.validity, is_scrutinee: self.is_scrutinee }
+        Self {
+            ty: self.ty.clone(),
+            private_uninhabited: self.private_uninhabited,
+            validity: self.validity,
+            is_scrutinee: self.is_scrutinee,
+        }
     }
 }
 
@@ -1121,7 +1135,12 @@ impl<'p, Cx: TypeCx> Matrix<'p, Cx> {
         scrut_ty: Cx::Ty,
         scrut_validity: ValidityConstraint,
     ) -> Self {
-        let place_info = PlaceInfo { ty: scrut_ty, validity: scrut_validity, is_scrutinee: true };
+        let place_info = PlaceInfo {
+            ty: scrut_ty,
+            private_uninhabited: false,
+            validity: scrut_validity,
+            is_scrutinee: true,
+        };
         let mut matrix = Matrix {
             rows: Vec::with_capacity(arms.len()),
             place_info: smallvec![place_info],
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 1c6bd887128..9d8a9f5fce3 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -988,10 +988,7 @@ impl<'tcx> Visitor<'tcx> for NamePrivacyVisitor<'tcx> {
     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
         if let hir::ExprKind::Struct(qpath, fields, ref base) = expr.kind {
             let res = self.typeck_results().qpath_res(qpath, expr.hir_id);
-            let Some(adt) = self.typeck_results().expr_ty(expr).ty_adt_def() else {
-                self.tcx.dcx().span_delayed_bug(expr.span, "no adt_def for expression");
-                return;
-            };
+            let adt = self.typeck_results().expr_ty(expr).ty_adt_def().unwrap();
             let variant = adt.variant_of_res(res);
             if let Some(base) = *base {
                 // If the expression uses FRU we need to make sure all the unmentioned fields
diff --git a/compiler/rustc_query_system/src/query/plumbing.rs b/compiler/rustc_query_system/src/query/plumbing.rs
index e4c596b10b8..40517407ee6 100644
--- a/compiler/rustc_query_system/src/query/plumbing.rs
+++ b/compiler/rustc_query_system/src/query/plumbing.rs
@@ -149,8 +149,7 @@ where
             let guar = if let Some(root) = cycle_error.cycle.first()
                 && let Some(span) = root.query.span
             {
-                error.stash(span, StashKey::Cycle);
-                qcx.dep_context().sess().dcx().span_delayed_bug(span, "delayed cycle error")
+                error.stash(span, StashKey::Cycle).unwrap()
             } else {
                 error.emit()
             };
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index 752bb05f3d7..9170b265748 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -13,9 +13,10 @@ use crate::Session;
 use rustc_ast::node_id::NodeId;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
 use rustc_data_structures::sync::{AppendOnlyVec, Lock, Lrc};
-use rustc_errors::{emitter::SilentEmitter, DiagCtxt};
+use rustc_errors::emitter::{stderr_destination, HumanEmitter, SilentEmitter};
 use rustc_errors::{
-    fallback_fluent_bundle, Diag, DiagnosticMessage, EmissionGuarantee, MultiSpan, StashKey,
+    fallback_fluent_bundle, ColorConfig, Diag, DiagCtxt, DiagnosticMessage, EmissionGuarantee,
+    MultiSpan, StashKey,
 };
 use rustc_feature::{find_feature_issue, GateIssue, UnstableFeatures};
 use rustc_span::edition::Edition;
@@ -105,8 +106,7 @@ pub fn feature_err_issue(
 
     // Cancel an earlier warning for this same error, if it exists.
     if let Some(span) = span.primary_span() {
-        if let Some(err) = sess.parse_sess.dcx.steal_diagnostic(span, StashKey::EarlySyntaxWarning)
-        {
+        if let Some(err) = sess.parse_sess.dcx.steal_non_err(span, StashKey::EarlySyntaxWarning) {
             err.cancel()
         }
     }
@@ -236,7 +236,11 @@ impl ParseSess {
     pub fn new(locale_resources: Vec<&'static str>, file_path_mapping: FilePathMapping) -> Self {
         let fallback_bundle = fallback_fluent_bundle(locale_resources, false);
         let sm = Lrc::new(SourceMap::new(file_path_mapping));
-        let dcx = DiagCtxt::with_tty_emitter(Some(sm.clone()), fallback_bundle);
+        let emitter = Box::new(
+            HumanEmitter::new(stderr_destination(ColorConfig::Auto), fallback_bundle)
+                .sm(Some(sm.clone())),
+        );
+        let dcx = DiagCtxt::new(emitter);
         ParseSess::with_dcx(dcx, sm)
     }
 
@@ -265,9 +269,11 @@ impl ParseSess {
     pub fn with_silent_emitter(fatal_note: String) -> Self {
         let fallback_bundle = fallback_fluent_bundle(Vec::new(), false);
         let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-        let fatal_dcx = DiagCtxt::with_tty_emitter(None, fallback_bundle).disable_warnings();
-        let dcx = DiagCtxt::with_emitter(Box::new(SilentEmitter { fatal_dcx, fatal_note }))
-            .disable_warnings();
+        let emitter =
+            Box::new(HumanEmitter::new(stderr_destination(ColorConfig::Auto), fallback_bundle));
+        let fatal_dcx = DiagCtxt::new(emitter);
+        let dcx =
+            DiagCtxt::new(Box::new(SilentEmitter { fatal_dcx, fatal_note })).disable_warnings();
         ParseSess::with_dcx(dcx, sm)
     }
 
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index e9db96dc356..09fb6aa5d8f 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -18,7 +18,7 @@ use rustc_data_structures::sync::{
     AtomicU64, DynSend, DynSync, Lock, Lrc, MappedReadGuard, ReadGuard, RwLock,
 };
 use rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitter;
-use rustc_errors::emitter::{DynEmitter, HumanEmitter, HumanReadableErrorType};
+use rustc_errors::emitter::{stderr_destination, DynEmitter, HumanEmitter, HumanReadableErrorType};
 use rustc_errors::json::JsonEmitter;
 use rustc_errors::registry::Registry;
 use rustc_errors::{
@@ -28,7 +28,7 @@ use rustc_errors::{
 use rustc_macros::HashStable_Generic;
 pub use rustc_span::def_id::StableCrateId;
 use rustc_span::edition::Edition;
-use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMap};
+use rustc_span::source_map::{FileLoader, FilePathMapping, RealFileLoader, SourceMap};
 use rustc_span::{SourceFileHashAlgorithm, Span, Symbol};
 use rustc_target::asm::InlineAsmArch;
 use rustc_target::spec::{CodeModel, PanicStrategy, RelocModel, RelroLevel};
@@ -39,6 +39,7 @@ use rustc_target::spec::{
 use std::any::Any;
 use std::env;
 use std::fmt;
+use std::io;
 use std::ops::{Div, Mul};
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
@@ -982,7 +983,7 @@ fn default_emitter(
                 );
                 Box::new(emitter.ui_testing(sopts.unstable_opts.ui_testing))
             } else {
-                let emitter = HumanEmitter::stderr(color_config, fallback_bundle)
+                let emitter = HumanEmitter::new(stderr_destination(color_config), fallback_bundle)
                     .fluent_bundle(bundle)
                     .sm(Some(source_map))
                     .short_message(short)
@@ -998,22 +999,23 @@ fn default_emitter(
             }
         }
         config::ErrorOutputType::Json { pretty, json_rendered } => Box::new(
-            JsonEmitter::stderr(
-                Some(registry),
+            JsonEmitter::new(
+                Box::new(io::BufWriter::new(io::stderr())),
                 source_map,
-                bundle,
                 fallback_bundle,
                 pretty,
                 json_rendered,
-                sopts.diagnostic_width,
-                macro_backtrace,
-                track_diagnostics,
-                terminal_url,
             )
+            .registry(Some(registry))
+            .fluent_bundle(bundle)
             .ui_testing(sopts.unstable_opts.ui_testing)
             .ignored_directories_in_source_blocks(
                 sopts.unstable_opts.ignore_directory_in_diagnostics_source_blocks.clone(),
-            ),
+            )
+            .diagnostic_width(sopts.diagnostic_width)
+            .macro_backtrace(macro_backtrace)
+            .track_diagnostics(track_diagnostics)
+            .terminal_url(terminal_url),
         ),
     }
 }
@@ -1080,8 +1082,8 @@ pub fn build_session(
     );
     let emitter = default_emitter(&sopts, registry, source_map.clone(), bundle, fallback_bundle);
 
-    let mut dcx = DiagCtxt::with_emitter(emitter)
-        .with_flags(sopts.unstable_opts.dcx_flags(can_emit_warnings));
+    let mut dcx =
+        DiagCtxt::new(emitter).with_flags(sopts.unstable_opts.dcx_flags(can_emit_warnings));
     if let Some(ice_file) = ice_file {
         dcx = dcx.with_ice_file(ice_file);
     }
@@ -1402,7 +1404,7 @@ pub struct EarlyDiagCtxt {
 impl EarlyDiagCtxt {
     pub fn new(output: ErrorOutputType) -> Self {
         let emitter = mk_emitter(output);
-        Self { dcx: DiagCtxt::with_emitter(emitter) }
+        Self { dcx: DiagCtxt::new(emitter) }
     }
 
     /// Swap out the underlying dcx once we acquire the user's preference on error emission
@@ -1412,7 +1414,7 @@ impl EarlyDiagCtxt {
         self.dcx.abort_if_errors();
 
         let emitter = mk_emitter(output);
-        self.dcx = DiagCtxt::with_emitter(emitter);
+        self.dcx = DiagCtxt::new(emitter);
     }
 
     #[allow(rustc::untranslatable_diagnostic)]
@@ -1473,17 +1475,17 @@ fn mk_emitter(output: ErrorOutputType) -> Box<DynEmitter> {
     let emitter: Box<DynEmitter> = match output {
         config::ErrorOutputType::HumanReadable(kind) => {
             let (short, color_config) = kind.unzip();
-            Box::new(HumanEmitter::stderr(color_config, fallback_bundle).short_message(short))
+            Box::new(
+                HumanEmitter::new(stderr_destination(color_config), fallback_bundle)
+                    .short_message(short),
+            )
         }
-        config::ErrorOutputType::Json { pretty, json_rendered } => Box::new(JsonEmitter::basic(
+        config::ErrorOutputType::Json { pretty, json_rendered } => Box::new(JsonEmitter::new(
+            Box::new(io::BufWriter::new(io::stderr())),
+            Lrc::new(SourceMap::new(FilePathMapping::empty())),
+            fallback_bundle,
             pretty,
             json_rendered,
-            None,
-            fallback_bundle,
-            None,
-            false,
-            false,
-            TerminalUrl::No,
         )),
     };
     emitter
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnu.rs b/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnu.rs
index 9e964d248bf..d6b44e7cfd4 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnu.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnu.rs
@@ -3,6 +3,7 @@ use crate::spec::{base, Cc, LinkerFlavor, Lld, Target};
 pub fn target() -> Target {
     let mut base = base::windows_gnu::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3,+sahf".into();
     base.plt_by_default = false;
     // Use high-entropy 64 bit address space for ASLR
     base.add_pre_link_args(
@@ -10,7 +11,7 @@ pub fn target() -> Target {
         &["-m", "i386pep", "--high-entropy-va"],
     );
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64", "-Wl,--high-entropy-va"]);
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
     base.linker = Some("x86_64-w64-mingw32-gcc".into());
 
     Target {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnullvm.rs b/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnullvm.rs
index 1facf9450cd..b84a9a5a8a1 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnullvm.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_gnullvm.rs
@@ -3,9 +3,10 @@ use crate::spec::{base, Cc, LinkerFlavor, Lld, Target};
 pub fn target() -> Target {
     let mut base = base::windows_gnullvm::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3,+sahf".into();
     base.plt_by_default = false;
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]);
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
     base.linker = Some("x86_64-w64-mingw32-clang".into());
 
     Target {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_msvc.rs b/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_msvc.rs
index 357261073a8..51807bdba5d 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_msvc.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_pc_windows_msvc.rs
@@ -3,8 +3,9 @@ use crate::spec::{base, SanitizerSet, Target};
 pub fn target() -> Target {
     let mut base = base::windows_msvc::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3,+sahf".into();
     base.plt_by_default = false;
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
     base.supported_sanitizers = SanitizerSet::ADDRESS;
 
     Target {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_gnu.rs b/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_gnu.rs
index c2981ddbad6..b37d33601e6 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_gnu.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_gnu.rs
@@ -3,6 +3,7 @@ use crate::spec::{base, Cc, LinkerFlavor, Lld, Target};
 pub fn target() -> Target {
     let mut base = base::windows_uwp_gnu::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3,+sahf".into();
     base.plt_by_default = false;
     // Use high-entropy 64 bit address space for ASLR
     base.add_pre_link_args(
@@ -10,7 +11,7 @@ pub fn target() -> Target {
         &["-m", "i386pep", "--high-entropy-va"],
     );
     base.add_pre_link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64", "-Wl,--high-entropy-va"]);
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
 
     Target {
         llvm_target: "x86_64-pc-windows-gnu".into(),
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_msvc.rs b/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_msvc.rs
index 3f0702c7ad6..fe2b4c8e92d 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_msvc.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_uwp_windows_msvc.rs
@@ -3,8 +3,9 @@ use crate::spec::{base, Target};
 pub fn target() -> Target {
     let mut base = base::windows_uwp_msvc::opts();
     base.cpu = "x86-64".into();
+    base.features = "+cx16,+sse3,+sahf".into();
     base.plt_by_default = false;
-    base.max_atomic_width = Some(64);
+    base.max_atomic_width = Some(128);
 
     Target {
         llvm_target: "x86_64-pc-windows-msvc".into(),
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
index dcbb63f00f7..d9e49f1eb0a 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
@@ -889,7 +889,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 }
             }
 
-            SelectionError::OpaqueTypeAutoTraitLeakageUnknown(def_id) => self.report_opaque_type_auto_trait_leakage(
+            SelectionError::OpaqueTypeAutoTraitLeakageUnknown(def_id) => return self.report_opaque_type_auto_trait_leakage(
                 &obligation,
                 def_id,
             ),
@@ -2252,8 +2252,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                 ErrorCode::E0282,
                                 false,
                             );
-                            err.stash(span, StashKey::MaybeForgetReturn);
-                            return self.dcx().delayed_bug("stashed error never reported");
+                            return err.stash(span, StashKey::MaybeForgetReturn).unwrap();
                         }
                         Some(e) => return e,
                     }
@@ -2766,7 +2765,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             self.suggest_unsized_bound_if_applicable(err, obligation);
             if let Some(span) = err.span.primary_span()
                 && let Some(mut diag) =
-                    self.tcx.dcx().steal_diagnostic(span, StashKey::AssociatedTypeSuggestion)
+                    self.tcx.dcx().steal_non_err(span, StashKey::AssociatedTypeSuggestion)
                 && let Ok(ref mut s1) = err.suggestions
                 && let Ok(ref mut s2) = diag.suggestions
             {
@@ -3291,7 +3290,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         &self,
         obligation: &PredicateObligation<'tcx>,
         def_id: DefId,
-    ) -> Diag<'tcx> {
+    ) -> ErrorGuaranteed {
         let name = match self.tcx.opaque_type_origin(def_id.expect_local()) {
             hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_) => {
                 "opaque type".to_string()
@@ -3318,12 +3317,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             }
         };
 
-        if let Some(diag) = self.dcx().steal_diagnostic(self.tcx.def_span(def_id), StashKey::Cycle)
-        {
-            diag.cancel();
-        }
-
-        err
+        self.note_obligation_cause(&mut err, &obligation);
+        self.point_at_returns_when_relevant(&mut err, &obligation);
+        self.dcx().try_steal_replace_and_emit_err(self.tcx.def_span(def_id), StashKey::Cycle, err)
     }
 
     fn report_signature_mismatch_error(
diff --git a/library/std/src/sys/pal/windows/thread_local_key.rs b/library/std/src/sys/pal/windows/thread_local_key.rs
index 5eee4a9667b..1d9cb316a45 100644
--- a/library/std/src/sys/pal/windows/thread_local_key.rs
+++ b/library/std/src/sys/pal/windows/thread_local_key.rs
@@ -1,7 +1,7 @@
 use crate::cell::UnsafeCell;
 use crate::ptr;
 use crate::sync::atomic::{
-    AtomicBool, AtomicPtr, AtomicU32,
+    AtomicPtr, AtomicU32,
     Ordering::{AcqRel, Acquire, Relaxed, Release},
 };
 use crate::sys::c;
@@ -9,10 +9,6 @@ use crate::sys::c;
 #[cfg(test)]
 mod tests;
 
-/// An optimization hint. The compiler is often smart enough to know if an atomic
-/// is never set and can remove dead code based on that fact.
-static HAS_DTORS: AtomicBool = AtomicBool::new(false);
-
 // Using a per-thread list avoids the problems in synchronizing global state.
 #[thread_local]
 #[cfg(target_thread_local)]
@@ -24,12 +20,11 @@ static DESTRUCTORS: crate::cell::RefCell<Vec<(*mut u8, unsafe extern "C" fn(*mut
 #[inline(never)]
 #[cfg(target_thread_local)]
 pub unsafe fn register_keyless_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
+    dtors_used();
     match DESTRUCTORS.try_borrow_mut() {
         Ok(mut dtors) => dtors.push((t, dtor)),
         Err(_) => rtabort!("global allocator may not use TLS"),
     }
-
-    HAS_DTORS.store(true, Relaxed);
 }
 
 #[inline(never)] // See comment above
@@ -130,6 +125,7 @@ impl StaticKey {
     #[cold]
     unsafe fn init(&'static self) -> Key {
         if self.dtor.is_some() {
+            dtors_used();
             let mut pending = c::FALSE;
             let r = c::InitOnceBeginInitialize(self.once.get(), 0, &mut pending, ptr::null_mut());
             assert_eq!(r, c::TRUE);
@@ -215,7 +211,6 @@ unsafe fn register_dtor(key: &'static StaticKey) {
             Err(new) => head = new,
         }
     }
-    HAS_DTORS.store(true, Release);
 }
 
 // -------------------------------------------------------------------------
@@ -281,17 +276,16 @@ unsafe fn register_dtor(key: &'static StaticKey) {
 // the address of the symbol to ensure it sticks around.
 
 #[link_section = ".CRT$XLB"]
-#[allow(dead_code, unused_variables)]
-#[used] // we don't want LLVM eliminating this symbol for any reason, and
-// when the symbol makes it to the linker the linker will take over
 pub static p_thread_callback: unsafe extern "system" fn(c::LPVOID, c::DWORD, c::LPVOID) =
     on_tls_callback;
 
-#[allow(dead_code, unused_variables)]
-unsafe extern "system" fn on_tls_callback(h: c::LPVOID, dwReason: c::DWORD, pv: c::LPVOID) {
-    if !HAS_DTORS.load(Acquire) {
-        return;
-    }
+fn dtors_used() {
+    // we don't want LLVM eliminating p_thread_callback when destructors are used.
+    // when the symbol makes it to the linker the linker will take over
+    unsafe { crate::intrinsics::volatile_load(&p_thread_callback) };
+}
+
+unsafe extern "system" fn on_tls_callback(_h: c::LPVOID, dwReason: c::DWORD, _pv: c::LPVOID) {
     if dwReason == c::DLL_THREAD_DETACH || dwReason == c::DLL_PROCESS_DETACH {
         #[cfg(not(target_thread_local))]
         run_dtors();
@@ -301,19 +295,16 @@ unsafe extern "system" fn on_tls_callback(h: c::LPVOID, dwReason: c::DWORD, pv:
 
     // See comments above for what this is doing. Note that we don't need this
     // trickery on GNU windows, just on MSVC.
-    reference_tls_used();
-    #[cfg(target_env = "msvc")]
-    unsafe fn reference_tls_used() {
+    #[cfg(all(target_env = "msvc", not(target_thread_local)))]
+    {
         extern "C" {
             static _tls_used: u8;
         }
         crate::intrinsics::volatile_load(&_tls_used);
     }
-    #[cfg(not(target_env = "msvc"))]
-    unsafe fn reference_tls_used() {}
 }
 
-#[allow(dead_code)] // actually called below
+#[cfg(not(target_thread_local))]
 unsafe fn run_dtors() {
     for _ in 0..5 {
         let mut any_run = false;
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index c662f054d05..9ba79cf5d29 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -1,7 +1,7 @@
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::unord::UnordSet;
-use rustc_errors::emitter::{DynEmitter, HumanEmitter};
+use rustc_errors::emitter::{stderr_destination, DynEmitter, HumanEmitter};
 use rustc_errors::json::JsonEmitter;
 use rustc_errors::{codes::*, ErrorGuaranteed, TerminalUrl};
 use rustc_feature::UnstableFeatures;
@@ -20,6 +20,7 @@ use rustc_span::symbol::sym;
 use rustc_span::{source_map, Span};
 
 use std::cell::RefCell;
+use std::io;
 use std::mem;
 use std::rc::Rc;
 use std::sync::LazyLock;
@@ -141,7 +142,7 @@ pub(crate) fn new_dcx(
         ErrorOutputType::HumanReadable(kind) => {
             let (short, color_config) = kind.unzip();
             Box::new(
-                HumanEmitter::stderr(color_config, fallback_bundle)
+                HumanEmitter::new(stderr_destination(color_config), fallback_bundle)
                     .sm(source_map.map(|sm| sm as _))
                     .short_message(short)
                     .teach(unstable_opts.teach)
@@ -155,24 +156,22 @@ pub(crate) fn new_dcx(
                 Lrc::new(source_map::SourceMap::new(source_map::FilePathMapping::empty()))
             });
             Box::new(
-                JsonEmitter::stderr(
-                    None,
+                JsonEmitter::new(
+                    Box::new(io::BufWriter::new(io::stderr())),
                     source_map,
-                    None,
                     fallback_bundle,
                     pretty,
                     json_rendered,
-                    diagnostic_width,
-                    false,
-                    unstable_opts.track_diagnostics,
-                    TerminalUrl::No,
                 )
-                .ui_testing(unstable_opts.ui_testing),
+                .ui_testing(unstable_opts.ui_testing)
+                .diagnostic_width(diagnostic_width)
+                .track_diagnostics(unstable_opts.track_diagnostics)
+                .terminal_url(TerminalUrl::No),
             )
         }
     };
 
-    rustc_errors::DiagCtxt::with_emitter(emitter).with_flags(unstable_opts.dcx_flags(true))
+    rustc_errors::DiagCtxt::new(emitter).with_flags(unstable_opts.dcx_flags(true))
 }
 
 /// Parse, resolve, and typecheck the given crate.
diff --git a/src/librustdoc/doctest.rs b/src/librustdoc/doctest.rs
index e2b4ec5908b..3d92444364f 100644
--- a/src/librustdoc/doctest.rs
+++ b/src/librustdoc/doctest.rs
@@ -1,6 +1,7 @@
 use rustc_ast as ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::Lrc;
+use rustc_errors::emitter::stderr_destination;
 use rustc_errors::{ColorConfig, ErrorGuaranteed, FatalError};
 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::{self as hir, intravisit, CRATE_HIR_ID};
@@ -576,14 +577,14 @@ pub(crate) fn make_test(
                 rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
                 false,
             );
-            supports_color = HumanEmitter::stderr(ColorConfig::Auto, fallback_bundle.clone())
-                .diagnostic_width(Some(80))
-                .supports_color();
+            supports_color =
+                HumanEmitter::new(stderr_destination(ColorConfig::Auto), fallback_bundle.clone())
+                    .supports_color();
 
             let emitter = HumanEmitter::new(Box::new(io::sink()), fallback_bundle);
 
             // FIXME(misdreavus): pass `-Z treat-err-as-bug` to the doctest parser
-            let dcx = DiagCtxt::with_emitter(Box::new(emitter)).disable_warnings();
+            let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
             let sess = ParseSess::with_dcx(dcx, sm);
 
             let mut found_main = false;
@@ -768,7 +769,7 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
 
             let emitter = HumanEmitter::new(Box::new(io::sink()), fallback_bundle);
 
-            let dcx = DiagCtxt::with_emitter(Box::new(emitter)).disable_warnings();
+            let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
             let sess = ParseSess::with_dcx(dcx, sm);
             let mut parser =
                 match maybe_new_parser_from_source_str(&sess, filename, source.to_owned()) {
diff --git a/src/librustdoc/passes/lint/check_code_block_syntax.rs b/src/librustdoc/passes/lint/check_code_block_syntax.rs
index c6571e72fc5..5145d8babef 100644
--- a/src/librustdoc/passes/lint/check_code_block_syntax.rs
+++ b/src/librustdoc/passes/lint/check_code_block_syntax.rs
@@ -42,7 +42,7 @@ fn check_rust_syntax(
     let emitter = BufferEmitter { buffer: Lrc::clone(&buffer), fallback_bundle };
 
     let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-    let dcx = DiagCtxt::with_emitter(Box::new(emitter)).disable_warnings();
+    let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
     let source = dox[code_block.code].to_owned();
     let sess = ParseSess::with_dcx(dcx, sm);
 
diff --git a/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs b/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
index 58656140352..fdb9ceb7179 100644
--- a/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
+++ b/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
@@ -45,7 +45,7 @@ pub fn check(
                 let fallback_bundle =
                     rustc_errors::fallback_fluent_bundle(rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(), false);
                 let emitter = HumanEmitter::new(Box::new(io::sink()), fallback_bundle);
-                let dcx = DiagCtxt::with_emitter(Box::new(emitter)).disable_warnings();
+                let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
                 #[expect(clippy::arc_with_non_send_sync)] // `Lrc` is expected by with_dcx
                 let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
                 let sess = ParseSess::with_dcx(dcx, sm);
diff --git a/src/tools/clippy/tests/ui/crashes/unreachable-array-or-slice.rs b/src/tools/clippy/tests/ui/crashes/unreachable-array-or-slice.rs
new file mode 100644
index 00000000000..b56abccbd41
--- /dev/null
+++ b/src/tools/clippy/tests/ui/crashes/unreachable-array-or-slice.rs
@@ -0,0 +1,8 @@
+struct Foo(isize, isize, isize, isize);
+
+pub fn main() {
+    let Self::anything_here_kills_it(a, b, ..) = Foo(5, 5, 5, 5);
+    match [5, 5, 5, 5] {
+        [..] => { }
+    }
+}
diff --git a/src/tools/clippy/tests/ui/crashes/unreachable-array-or-slice.stderr b/src/tools/clippy/tests/ui/crashes/unreachable-array-or-slice.stderr
new file mode 100644
index 00000000000..9e0d3b934b8
--- /dev/null
+++ b/src/tools/clippy/tests/ui/crashes/unreachable-array-or-slice.stderr
@@ -0,0 +1,9 @@
+error[E0433]: failed to resolve: `Self` is only available in impls, traits, and type definitions
+  --> tests/ui/crashes/unreachable-array-or-slice.rs:4:9
+   |
+LL |     let Self::anything_here_kills_it(a, b, ..) = Foo(5, 5, 5, 5);
+   |         ^^^^ `Self` is only available in impls, traits, and type definitions
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0433`.
diff --git a/src/tools/miri/src/bin/miri.rs b/src/tools/miri/src/bin/miri.rs
index 8a7133fea43..281a32b77c5 100644
--- a/src/tools/miri/src/bin/miri.rs
+++ b/src/tools/miri/src/bin/miri.rs
@@ -68,7 +68,7 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
         queries: &'tcx rustc_interface::Queries<'tcx>,
     ) -> Compilation {
         queries.global_ctxt().unwrap().enter(|tcx| {
-            if tcx.sess.dcx().has_errors().is_some() {
+            if tcx.sess.dcx().has_errors_or_delayed_bugs().is_some() {
                 tcx.dcx().fatal("miri cannot be run on programs that fail compilation");
             }
 
diff --git a/src/tools/rustfmt/src/formatting.rs b/src/tools/rustfmt/src/formatting.rs
index 323ae83fe6e..1c64921b1a6 100644
--- a/src/tools/rustfmt/src/formatting.rs
+++ b/src/tools/rustfmt/src/formatting.rs
@@ -109,7 +109,7 @@ fn format_project<T: FormatHandler>(
     let main_file = input.file_name();
     let input_is_stdin = main_file == FileName::Stdin;
 
-    let mut parse_session = ParseSess::new(config)?;
+    let parse_session = ParseSess::new(config)?;
     if config.skip_children() && parse_session.ignore_file(&main_file) {
         return Ok(FormatReport::new());
     }
@@ -118,20 +118,11 @@ fn format_project<T: FormatHandler>(
     let mut report = FormatReport::new();
     let directory_ownership = input.to_directory_ownership();
 
-    // rustfmt doesn't use `run_compiler` like other tools, so it must emit any
-    // stashed diagnostics itself, otherwise the `DiagCtxt` will assert when
-    // dropped. The final result here combines the parsing result and the
-    // `emit_stashed_diagnostics` result.
-    let parse_res = Parser::parse_crate(input, &parse_session);
-    let stashed_res = parse_session.emit_stashed_diagnostics();
-    let krate = match (parse_res, stashed_res) {
-        (Ok(krate), None) => krate,
-        (parse_res, _) => {
-            // Surface parse error via Session (errors are merged there from report).
-            let forbid_verbose = match parse_res {
-                Err(e) if e != ParserError::ParsePanicError => true,
-                _ => input_is_stdin,
-            };
+    let krate = match Parser::parse_crate(input, &parse_session) {
+        Ok(krate) => krate,
+        // Surface parse error via Session (errors are merged there from report)
+        Err(e) => {
+            let forbid_verbose = input_is_stdin || e != ParserError::ParsePanicError;
             should_emit_verbose(forbid_verbose, config, || {
                 eprintln!("The Rust parser panicked");
             });
diff --git a/src/tools/rustfmt/src/parse/session.rs b/src/tools/rustfmt/src/parse/session.rs
index e33f1ca755c..d6386a9504d 100644
--- a/src/tools/rustfmt/src/parse/session.rs
+++ b/src/tools/rustfmt/src/parse/session.rs
@@ -3,11 +3,9 @@ use std::path::Path;
 use std::sync::atomic::{AtomicBool, Ordering};
 
 use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
-use rustc_errors::emitter::{DynEmitter, Emitter, HumanEmitter};
+use rustc_errors::emitter::{stderr_destination, DynEmitter, Emitter, HumanEmitter};
 use rustc_errors::translation::Translate;
-use rustc_errors::{
-    ColorConfig, Diag, DiagCtxt, DiagInner, ErrorGuaranteed, Level as DiagnosticLevel,
-};
+use rustc_errors::{ColorConfig, Diag, DiagCtxt, DiagInner, Level as DiagnosticLevel};
 use rustc_session::parse::ParseSess as RawParseSess;
 use rustc_span::{
     source_map::{FilePathMapping, SourceMap},
@@ -152,9 +150,12 @@ fn default_dcx(
             rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
             false,
         );
-        Box::new(HumanEmitter::stderr(emit_color, fallback_bundle).sm(Some(source_map.clone())))
+        Box::new(
+            HumanEmitter::new(stderr_destination(emit_color), fallback_bundle)
+                .sm(Some(source_map.clone())),
+        )
     };
-    DiagCtxt::with_emitter(Box::new(SilentOnIgnoredFilesEmitter {
+    DiagCtxt::new(Box::new(SilentOnIgnoredFilesEmitter {
         has_non_ignorable_parser_errors: false,
         source_map,
         emitter,
@@ -230,12 +231,8 @@ impl ParseSess {
         self.ignore_path_set.as_ref().is_match(path)
     }
 
-    pub(crate) fn emit_stashed_diagnostics(&mut self) -> Option<ErrorGuaranteed> {
-        self.parse_sess.dcx.emit_stashed_diagnostics()
-    }
-
     pub(crate) fn set_silent_emitter(&mut self) {
-        self.parse_sess.dcx = DiagCtxt::with_emitter(silent_emitter());
+        self.parse_sess.dcx = DiagCtxt::new(silent_emitter());
     }
 
     pub(crate) fn span_to_filename(&self, span: Span) -> FileName {
diff --git a/tests/codegen/sse42-implies-crc32.rs b/tests/codegen/sse42-implies-crc32.rs
index c627be5c30e..94fcd77bc88 100644
--- a/tests/codegen/sse42-implies-crc32.rs
+++ b/tests/codegen/sse42-implies-crc32.rs
@@ -12,4 +12,4 @@ pub unsafe fn crc32sse(v: u8) -> u32 {
     _mm_crc32_u8(out, v)
 }
 
-// CHECK: attributes #0 {{.*"target-features"="\+sse4.2,\+crc32"}}
+// CHECK: attributes #0 {{.*"target-features"=".*\+sse4.2,\+crc32"}}
diff --git a/tests/ui/foreign/stashed-issue-121451.rs b/tests/ui/foreign/stashed-issue-121451.rs
new file mode 100644
index 00000000000..97a4af37475
--- /dev/null
+++ b/tests/ui/foreign/stashed-issue-121451.rs
@@ -0,0 +1,4 @@
+extern "C" fn _f() -> libc::uintptr_t {}
+//~^ ERROR failed to resolve: use of undeclared crate or module `libc`
+
+fn main() {}
diff --git a/tests/ui/foreign/stashed-issue-121451.stderr b/tests/ui/foreign/stashed-issue-121451.stderr
new file mode 100644
index 00000000000..440d98d6f46
--- /dev/null
+++ b/tests/ui/foreign/stashed-issue-121451.stderr
@@ -0,0 +1,9 @@
+error[E0433]: failed to resolve: use of undeclared crate or module `libc`
+  --> $DIR/stashed-issue-121451.rs:1:23
+   |
+LL | extern "C" fn _f() -> libc::uintptr_t {}
+   |                       ^^^^ use of undeclared crate or module `libc`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0433`.
diff --git a/tests/ui/impl-trait/stashed-diag-issue-121504.rs b/tests/ui/impl-trait/stashed-diag-issue-121504.rs
new file mode 100644
index 00000000000..4ac8ffe8931
--- /dev/null
+++ b/tests/ui/impl-trait/stashed-diag-issue-121504.rs
@@ -0,0 +1,13 @@
+//@ edition: 2021
+
+trait MyTrait {
+    async fn foo(self) -> (Self, i32);
+}
+
+impl MyTrait for xyz::T { //~ ERROR failed to resolve: use of undeclared crate or module `xyz`
+    async fn foo(self, key: i32) -> (u32, i32) {
+        (self, key)
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/stashed-diag-issue-121504.stderr b/tests/ui/impl-trait/stashed-diag-issue-121504.stderr
new file mode 100644
index 00000000000..6a881dc7f9f
--- /dev/null
+++ b/tests/ui/impl-trait/stashed-diag-issue-121504.stderr
@@ -0,0 +1,9 @@
+error[E0433]: failed to resolve: use of undeclared crate or module `xyz`
+  --> $DIR/stashed-diag-issue-121504.rs:7:18
+   |
+LL | impl MyTrait for xyz::T {
+   |                  ^^^ use of undeclared crate or module `xyz`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0433`.
diff --git a/tests/ui/lowering/issue-121108.rs b/tests/ui/lowering/issue-121108.rs
index 6b2dd24e4a8..6dfb7e00821 100644
--- a/tests/ui/lowering/issue-121108.rs
+++ b/tests/ui/lowering/issue-121108.rs
@@ -3,7 +3,7 @@
 use std::ptr::addr_of;
 
 const UNINHABITED_VARIANT: () = unsafe {
-    let v = *addr_of!(data).cast(); //~ ERROR cannot determine resolution for the macro `addr_of`
+    let v = *addr_of!(data).cast();
 };
 
 fn main() {}
diff --git a/tests/ui/lowering/issue-121108.stderr b/tests/ui/lowering/issue-121108.stderr
index c2c5746d6f1..e4942e8cb07 100644
--- a/tests/ui/lowering/issue-121108.stderr
+++ b/tests/ui/lowering/issue-121108.stderr
@@ -13,13 +13,5 @@ LL - #![derive(Clone, Copy)]
 LL + #[derive(Clone, Copy)]
    |
 
-error: cannot determine resolution for the macro `addr_of`
-  --> $DIR/issue-121108.rs:6:14
-   |
-LL |     let v = *addr_of!(data).cast();
-   |              ^^^^^^^
-   |
-   = note: import resolution is stuck, try simplifying macro imports
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
diff --git a/tests/ui/resolve/issue-111312.rs b/tests/ui/resolve/issue-111312.rs
index 68fc8573dde..79c6f67dadd 100644
--- a/tests/ui/resolve/issue-111312.rs
+++ b/tests/ui/resolve/issue-111312.rs
@@ -7,5 +7,7 @@ trait Has {
 trait HasNot {}
 
 fn main() {
-    HasNot::has(); //~ ERROR
+    HasNot::has();
+    //~^ ERROR trait objects must include the `dyn` keyword
+    //~| ERROR no function or associated item named `has` found for trait `HasNot`
 }
diff --git a/tests/ui/resolve/issue-111312.stderr b/tests/ui/resolve/issue-111312.stderr
index 7e7ef22ae61..431802ead30 100644
--- a/tests/ui/resolve/issue-111312.stderr
+++ b/tests/ui/resolve/issue-111312.stderr
@@ -1,3 +1,14 @@
+error[E0782]: trait objects must include the `dyn` keyword
+  --> $DIR/issue-111312.rs:10:5
+   |
+LL |     HasNot::has();
+   |     ^^^^^^
+   |
+help: add `dyn` keyword before this trait
+   |
+LL |     <dyn HasNot>::has();
+   |     ++++       +
+
 error[E0599]: no function or associated item named `has` found for trait `HasNot`
   --> $DIR/issue-111312.rs:10:13
    |
@@ -10,6 +21,7 @@ note: `Has` defines an item `has`
 LL | trait Has {
    | ^^^^^^^^^
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0599`.
+Some errors have detailed explanations: E0599, E0782.
+For more information about an error, try `rustc --explain E0599`.
diff --git a/tests/ui/resolve/issue-111727.rs b/tests/ui/resolve/issue-111727.rs
index 740037fe434..fcab924b809 100644
--- a/tests/ui/resolve/issue-111727.rs
+++ b/tests/ui/resolve/issue-111727.rs
@@ -1,5 +1,7 @@
 //@ edition: 2021
 
 fn main() {
-    std::any::Any::create(); //~ ERROR
+    std::any::Any::create();
+    //~^ ERROR trait objects must include the `dyn` keyword
+    //~| ERROR no function or associated item named `create` found for trait `Any`
 }
diff --git a/tests/ui/resolve/issue-111727.stderr b/tests/ui/resolve/issue-111727.stderr
index b58168d0e75..1ef5a1a1d5e 100644
--- a/tests/ui/resolve/issue-111727.stderr
+++ b/tests/ui/resolve/issue-111727.stderr
@@ -1,9 +1,21 @@
+error[E0782]: trait objects must include the `dyn` keyword
+  --> $DIR/issue-111727.rs:4:5
+   |
+LL |     std::any::Any::create();
+   |     ^^^^^^^^^^^^^
+   |
+help: add `dyn` keyword before this trait
+   |
+LL |     <dyn std::any::Any>::create();
+   |     ++++              +
+
 error[E0599]: no function or associated item named `create` found for trait `Any`
   --> $DIR/issue-111727.rs:4:20
    |
 LL |     std::any::Any::create();
    |                    ^^^^^^ function or associated item not found in `Any`
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0599`.
+Some errors have detailed explanations: E0599, E0782.
+For more information about an error, try `rustc --explain E0599`.
diff --git a/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.rs b/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.rs
index b2842df150a..4b5f455e381 100644
--- a/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.rs
+++ b/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.rs
@@ -11,6 +11,7 @@ fn foo<'a, 'b>() -> Tait<'a> {
     }
     let x: Tait<'a> = ();
     x
+    //~^ ERROR concrete type differs from previous defining opaque type use
 }
 
 fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.stderr b/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.stderr
index e5cee49cf29..6f5be5467f7 100644
--- a/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.stderr
+++ b/tests/ui/type-alias-impl-trait/different_defining_uses_never_type-2.stderr
@@ -1,3 +1,15 @@
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/different_defining_uses_never_type-2.rs:13:5
+   |
+LL |     x
+   |     ^ expected `i32`, got `()`
+   |
+note: previous use here
+  --> $DIR/different_defining_uses_never_type-2.rs:8:31
+   |
+LL |             let y: Tait<'b> = 1i32;
+   |                               ^^^^
+
 error: concrete type differs from previous defining opaque type use
   --> $DIR/different_defining_uses_never_type-2.rs:8:31
    |
@@ -10,5 +22,5 @@ note: previous use here
 LL |         if { return } {
    |              ^^^^^^
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors