Auto merge of #95149 - cjgillot:once-diag, r=estebank

Remove `Session::one_time_diagnostic` This is untracked mutable state, which modified the behaviour of queries. It was used for 2 things: some full-blown errors, but mostly for lint declaration notes ("the lint level is defined here" notes). It is replaced by the diagnostic deduplication infra which already exists in the diagnostic emitter. A new diagnostic level `OnceNote` is introduced specifically for lint notes, to deduplicate subdiagnostics. As a drive-by, diagnostic emission takes a `&mut` to allow dropping the `SubDiagnostic`s.
2024-10-30 14:01:51 +00:00 · 2022-03-26 00:54:54 +00:00 · 2022-03-26 00:54:54 +00:00 · c74925438c
commit c74925438c
parent a2ebd5a1f1 f7d5b7afb7
46 changed files with 227 additions and 359 deletions
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@ -2361,8 +2361,8 @@ mod error {
            if !self.errors.buffered.is_empty() {
                self.errors.buffered.sort_by_key(|diag| diag.sort_span);

-                for diag in self.errors.buffered.drain(..) {
-                    self.infcx.tcx.sess.diagnostic().emit_diagnostic(&diag);
+                for mut diag in self.errors.buffered.drain(..) {
+                    self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
                }
            }

--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@ -1748,7 +1748,7 @@ impl SharedEmitterMain {
                    if let Some(code) = diag.code {
                        d.code(code);
                    }
-                    handler.emit_diagnostic(&d);
+                    handler.emit_diagnostic(&mut d);
                }
                Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => {
                    let msg = msg.strip_prefix("error: ").unwrap_or(&msg);
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@ -255,8 +255,8 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
        // "secondary" errors if they occurred.
        let secondary_errors = mem::take(&mut self.secondary_errors);
        if self.error_emitted.is_none() {
-            for error in secondary_errors {
-                self.tcx.sess.diagnostic().emit_diagnostic(&error);
+            for mut error in secondary_errors {
+                self.tcx.sess.diagnostic().emit_diagnostic(&mut error);
            }
        } else {
            assert!(self.tcx.sess.has_errors().is_some());
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@ -1181,8 +1181,8 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str) {
    // a .span_bug or .bug call has already printed what
    // it wants to print.
    if !info.payload().is::<rustc_errors::ExplicitBug>() {
-        let d = rustc_errors::Diagnostic::new(rustc_errors::Level::Bug, "unexpected panic");
-        handler.emit_diagnostic(&d);
+        let mut d = rustc_errors::Diagnostic::new(rustc_errors::Level::Bug, "unexpected panic");
+        handler.emit_diagnostic(&mut d);
    }

    let mut xs: Vec<Cow<'static, str>> = vec![
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@ -70,7 +70,7 @@ fn annotation_type_for_level(level: Level) -> AnnotationType {
            AnnotationType::Error
        }
        Level::Warning => AnnotationType::Warning,
-        Level::Note => AnnotationType::Note,
+        Level::Note | Level::OnceNote => AnnotationType::Note,
        Level::Help => AnnotationType::Help,
        // FIXME(#59346): Not sure how to map this level
        Level::FailureNote => AnnotationType::Error,
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@ -135,7 +135,12 @@ impl Diagnostic {
            | Level::Error { .. }
            | Level::FailureNote => true,

-            Level::Warning | Level::Note | Level::Help | Level::Allow | Level::Expect(_) => false,
+            Level::Warning
+            | Level::Note
+            | Level::OnceNote
+            | Level::Help
+            | Level::Allow
+            | Level::Expect(_) => false,
        }
    }

@ -333,6 +338,13 @@ impl Diagnostic {
        self
    }

+    /// Prints the span with a note above it.
+    /// This is like [`Diagnostic::note()`], but it gets its own span.
+    pub fn note_once(&mut self, msg: &str) -> &mut Self {
+        self.sub(Level::OnceNote, msg, MultiSpan::new(), None);
+        self
+    }
+
    /// Prints the span with a note above it.
    /// This is like [`Diagnostic::note()`], but it gets its own span.
    pub fn span_note<S: Into<MultiSpan>>(&mut self, sp: S, msg: &str) -> &mut Self {
@ -340,6 +352,13 @@ impl Diagnostic {
        self
    }

+    /// Prints the span with a note above it.
+    /// This is like [`Diagnostic::note()`], but it gets its own span.
+    pub fn span_note_once<S: Into<MultiSpan>>(&mut self, sp: S, msg: &str) -> &mut Self {
+        self.sub(Level::OnceNote, msg, sp.into(), None);
+        self
+    }
+
    /// Add a warning attached to this diagnostic.
    pub fn warn(&mut self, msg: &str) -> &mut Self {
        self.sub(Level::Warning, msg, MultiSpan::new(), None);
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@ -128,7 +128,7 @@ impl EmissionGuarantee for ErrorGuaranteed {
            DiagnosticBuilderState::Emittable(handler) => {
                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;

-                let guar = handler.emit_diagnostic(&db.inner.diagnostic);
+                let guar = handler.emit_diagnostic(&mut db.inner.diagnostic);

                // Only allow a guarantee if the `level` wasn't switched to a
                // non-error - the field isn't `pub`, but the whole `Diagnostic`
@ -190,7 +190,7 @@ impl EmissionGuarantee for () {
            DiagnosticBuilderState::Emittable(handler) => {
                db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;

-                handler.emit_diagnostic(&db.inner.diagnostic);
+                handler.emit_diagnostic(&mut db.inner.diagnostic);
            }
            // `.emit()` was previously called, disallowed from repeating it.
            DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
@ -396,11 +396,17 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
    ) -> &mut Self);

    forward!(pub fn note(&mut self, msg: &str) -> &mut Self);
+    forward!(pub fn note_once(&mut self, msg: &str) -> &mut Self);
    forward!(pub fn span_note(
        &mut self,
        sp: impl Into<MultiSpan>,
        msg: &str,
    ) -> &mut Self);
+    forward!(pub fn span_note_once(
+        &mut self,
+        sp: impl Into<MultiSpan>,
+        msg: &str,
+    ) -> &mut Self);
    forward!(pub fn warn(&mut self, msg: &str) -> &mut Self);
    forward!(pub fn span_warn(&mut self, sp: impl Into<MultiSpan>, msg: &str) -> &mut Self);
    forward!(pub fn help(&mut self, msg: &str) -> &mut Self);
@ -500,11 +506,11 @@ impl Drop for DiagnosticBuilderInner<'_> {
            // No `.emit()` or `.cancel()` calls.
            DiagnosticBuilderState::Emittable(handler) => {
                if !panicking() {
-                    handler.emit_diagnostic(&Diagnostic::new(
+                    handler.emit_diagnostic(&mut Diagnostic::new(
                        Level::Bug,
                        "the following error was constructed but not emitted",
                    ));
-                    handler.emit_diagnostic(&self.diagnostic);
+                    handler.emit_diagnostic(&mut self.diagnostic);
                    panic!();
                }
            }
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@ -542,7 +542,7 @@ impl Emitter for SilentEmitter {
            if let Some(ref note) = self.fatal_note {
                d.note(note);
            }
-            self.fatal_handler.emit_diagnostic(&d);
+            self.fatal_handler.emit_diagnostic(&mut d);
        }
    }
 }
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@ -4,6 +4,7 @@

 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(crate_visibility_modifier)]
+#![feature(drain_filter)]
 #![feature(backtrace)]
 #![feature(if_let_guard)]
 #![feature(let_else)]
@ -919,7 +920,7 @@ impl Handler {
        self.inner.borrow_mut().force_print_diagnostic(db)
    }

-    pub fn emit_diagnostic(&self, diagnostic: &Diagnostic) -> Option<ErrorGuaranteed> {
+    pub fn emit_diagnostic(&self, diagnostic: &mut Diagnostic) -> Option<ErrorGuaranteed> {
        self.inner.borrow_mut().emit_diagnostic(diagnostic)
    }

@ -993,25 +994,25 @@ impl HandlerInner {
        self.taught_diagnostics.insert(code.clone())
    }

-    fn force_print_diagnostic(&mut self, db: Diagnostic) {
-        self.emitter.emit_diagnostic(&db);
+    fn force_print_diagnostic(&mut self, mut db: Diagnostic) {
+        self.emitter.emit_diagnostic(&mut db);
    }

    /// Emit all stashed diagnostics.
    fn emit_stashed_diagnostics(&mut self) -> Option<ErrorGuaranteed> {
        let diags = self.stashed_diagnostics.drain(..).map(|x| x.1).collect::<Vec<_>>();
        let mut reported = None;
-        diags.iter().for_each(|diag| {
+        for mut diag in diags {
            if diag.is_error() {
                reported = Some(ErrorGuaranteed(()));
            }
-            self.emit_diagnostic(diag);
-        });
+            self.emit_diagnostic(&mut diag);
+        }
        reported
    }

    // FIXME(eddyb) this should ideally take `diagnostic` by value.
-    fn emit_diagnostic(&mut self, diagnostic: &Diagnostic) -> Option<ErrorGuaranteed> {
+    fn emit_diagnostic(&mut self, diagnostic: &mut Diagnostic) -> Option<ErrorGuaranteed> {
        if diagnostic.level == Level::DelayedBug {
            // FIXME(eddyb) this should check for `has_errors` and stop pushing
            // once *any* errors were emitted (and truncate `delayed_span_bugs`
@ -1070,7 +1071,23 @@ impl HandlerInner {
        // Only emit the diagnostic if we've been asked to deduplicate and
        // haven't already emitted an equivalent diagnostic.
        if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
-            self.emitter.emit_diagnostic(diagnostic);
+            debug!(?diagnostic);
+            debug!(?self.emitted_diagnostics);
+            let already_emitted_sub = |sub: &mut SubDiagnostic| {
+                debug!(?sub);
+                if sub.level != Level::OnceNote {
+                    return false;
+                }
+                let mut hasher = StableHasher::new();
+                sub.hash(&mut hasher);
+                let diagnostic_hash = hasher.finish();
+                debug!(?diagnostic_hash);
+                !self.emitted_diagnostics.insert(diagnostic_hash)
+            };
+
+            diagnostic.children.drain_filter(already_emitted_sub).for_each(|_| {});
+
+            self.emitter.emit_diagnostic(&diagnostic);
            if diagnostic.is_error() {
                self.deduplicated_err_count += 1;
            } else if diagnostic.level == Warning {
@ -1221,22 +1238,22 @@ impl HandlerInner {
        let mut diagnostic = Diagnostic::new(Level::DelayedBug, msg);
        diagnostic.set_span(sp.into());
        diagnostic.note(&format!("delayed at {}", std::panic::Location::caller()));
-        self.emit_diagnostic(&diagnostic).unwrap()
+        self.emit_diagnostic(&mut diagnostic).unwrap()
    }

    // FIXME(eddyb) note the comment inside `impl Drop for HandlerInner`, that's
    // where the explanation of what "good path" is (also, it should be renamed).
    fn delay_good_path_bug(&mut self, msg: &str) {
-        let diagnostic = Diagnostic::new(Level::DelayedBug, msg);
+        let mut diagnostic = Diagnostic::new(Level::DelayedBug, msg);
        if self.flags.report_delayed_bugs {
-            self.emit_diagnostic(&diagnostic);
+            self.emit_diagnostic(&mut diagnostic);
        }
        let backtrace = std::backtrace::Backtrace::force_capture();
        self.delayed_good_path_bugs.push(DelayedDiagnostic::with_backtrace(diagnostic, backtrace));
    }

    fn failure(&mut self, msg: &str) {
-        self.emit_diagnostic(&Diagnostic::new(FailureNote, msg));
+        self.emit_diagnostic(&mut Diagnostic::new(FailureNote, msg));
    }

    fn fatal(&mut self, msg: &str) -> FatalError {
@ -1253,11 +1270,11 @@ impl HandlerInner {
        if self.treat_err_as_bug() {
            self.bug(msg);
        }
-        self.emit_diagnostic(&Diagnostic::new(level, msg)).unwrap()
+        self.emit_diagnostic(&mut Diagnostic::new(level, msg)).unwrap()
    }

    fn bug(&mut self, msg: &str) -> ! {
-        self.emit_diagnostic(&Diagnostic::new(Bug, msg));
+        self.emit_diagnostic(&mut Diagnostic::new(Bug, msg));
        panic::panic_any(ExplicitBug);
    }

@ -1267,7 +1284,7 @@ impl HandlerInner {
            if no_bugs {
                // Put the overall explanation before the `DelayedBug`s, to
                // frame them better (e.g. separate warnings from them).
-                self.emit_diagnostic(&Diagnostic::new(Bug, explanation));
+                self.emit_diagnostic(&mut Diagnostic::new(Bug, explanation));
                no_bugs = false;
            }

@ -1283,7 +1300,7 @@ impl HandlerInner {
            }
            bug.level = Level::Bug;

-            self.emit_diagnostic(&bug);
+            self.emit_diagnostic(&mut bug);
        }

        // Panic with `ExplicitBug` to avoid "unexpected panic" messages.
@ -1350,6 +1367,8 @@ pub enum Level {
    },
    Warning,
    Note,
+    /// A note that is only emitted once.
+    OnceNote,
    Help,
    FailureNote,
    Allow,
@ -1372,7 +1391,7 @@ impl Level {
            Warning => {
                spec.set_fg(Some(Color::Yellow)).set_intense(cfg!(windows));
            }
-            Note => {
+            Note | OnceNote => {
                spec.set_fg(Some(Color::Green)).set_intense(true);
            }
            Help => {
@ -1389,7 +1408,7 @@ impl Level {
            Bug | DelayedBug => "error: internal compiler error",
            Fatal | Error { .. } => "error",
            Warning => "warning",
-            Note => "note",
+            Note | OnceNote => "note",
            Help => "help",
            FailureNote => "failure-note",
            Allow => panic!("Shouldn't call on allowed error"),
--- a/compiler/rustc_expand/src/proc_macro_server.rs
+++ b/compiler/rustc_expand/src/proc_macro_server.rs
@ -771,8 +771,8 @@ impl server::Diagnostic for Rustc<'_, '_> {
    ) {
        diag.sub(level.to_internal(), msg, MultiSpan::from_spans(spans), None);
    }
-    fn emit(&mut self, diag: Self::Diagnostic) {
-        self.sess().span_diagnostic.emit_diagnostic(&diag);
+    fn emit(&mut self, mut diag: Self::Diagnostic) {
+        self.sess().span_diagnostic.emit_diagnostic(&mut diag);
    }
 }

--- a/compiler/rustc_middle/src/lint.rs
+++ b/compiler/rustc_middle/src/lint.rs
@ -12,7 +12,7 @@ use rustc_session::lint::{
    builtin::{self, FORBIDDEN_LINT_GROUPS},
    FutureIncompatibilityReason, Level, Lint, LintExpectationId, LintId,
 };
-use rustc_session::{DiagnosticMessageId, Session};
+use rustc_session::Session;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::{DesugaringKind, ExpnKind, MultiSpan};
 use rustc_span::{symbol, Span, Symbol, DUMMY_SP};
@ -245,7 +245,6 @@ impl<'a> LintDiagnosticBuilder<'a, ErrorGuaranteed> {
 }

 pub fn explain_lint_level_source(
-    sess: &Session,
    lint: &'static Lint,
    level: Level,
    src: LintLevelSource,
@ -254,11 +253,7 @@ pub fn explain_lint_level_source(
    let name = lint.name_lower();
    match src {
        LintLevelSource::Default => {
-            sess.diag_note_once(
-                err,
-                DiagnosticMessageId::from(lint),
-                &format!("`#[{}({})]` on by default", level.as_str(), name),
-            );
+            err.note_once(&format!("`#[{}({})]` on by default", level.as_str(), name));
        }
        LintLevelSource::CommandLine(lint_flag_val, orig_level) => {
            let flag = match orig_level {
@ -273,46 +268,29 @@ pub fn explain_lint_level_source(
            };
            let hyphen_case_lint_name = name.replace('_', "-");
            if lint_flag_val.as_str() == name {
-                sess.diag_note_once(
-                    err,
-                    DiagnosticMessageId::from(lint),
-                    &format!(
-                        "requested on the command line with `{} {}`",
-                        flag, hyphen_case_lint_name
-                    ),
-                );
+                err.note_once(&format!(
+                    "requested on the command line with `{} {}`",
+                    flag, hyphen_case_lint_name
+                ));
            } else {
                let hyphen_case_flag_val = lint_flag_val.as_str().replace('_', "-");
-                sess.diag_note_once(
-                    err,
-                    DiagnosticMessageId::from(lint),
-                    &format!(
-                        "`{} {}` implied by `{} {}`",
-                        flag, hyphen_case_lint_name, flag, hyphen_case_flag_val
-                    ),
-                );
+                err.note_once(&format!(
+                    "`{} {}` implied by `{} {}`",
+                    flag, hyphen_case_lint_name, flag, hyphen_case_flag_val
+                ));
            }
        }
        LintLevelSource::Node(lint_attr_name, src, reason) => {
            if let Some(rationale) = reason {
                err.note(rationale.as_str());
            }
-            sess.diag_span_note_once(
-                err,
-                DiagnosticMessageId::from(lint),
-                src,
-                "the lint level is defined here",
-            );
+            err.span_note_once(src, "the lint level is defined here");
            if lint_attr_name.as_str() != name {
                let level_str = level.as_str();
-                sess.diag_note_once(
-                    err,
-                    DiagnosticMessageId::from(lint),
-                    &format!(
-                        "`#[{}({})]` implied by `#[{}({})]`",
-                        level_str, name, level_str, lint_attr_name
-                    ),
-                );
+                err.note_once(&format!(
+                    "`#[{}({})]` implied by `#[{}({})]`",
+                    level_str, name, level_str, lint_attr_name
+                ));
            }
        }
    }
@ -412,7 +390,7 @@ pub fn struct_lint_level<'s, 'd>(
            return;
        }

-        explain_lint_level_source(sess, lint, level, src, &mut err);
+        explain_lint_level_source(lint, level, src, &mut err);

        let name = lint.name_lower();
        let is_force_warn = matches!(level, Level::ForceWarn);
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@ -17,9 +17,9 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_session::lint::builtin::{DEPRECATED, DEPRECATED_IN_FUTURE, SOFT_UNSTABLE};
 use rustc_session::lint::{BuiltinLintDiagnostics, Level, Lint, LintBuffer};
 use rustc_session::parse::feature_err_issue;
-use rustc_session::{DiagnosticMessageId, Session};
+use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
-use rustc_span::{MultiSpan, Span};
+use rustc_span::Span;
 use std::num::NonZeroU32;

 #[derive(PartialEq, Clone, Copy, Debug)]
@ -94,30 +94,15 @@ pub fn report_unstable(
        None => format!("use of unstable library feature '{}'", &feature),
    };

-    let msp: MultiSpan = span.into();
-    let sm = &sess.parse_sess.source_map();
-    let span_key = msp.primary_span().and_then(|sp: Span| {
-        if !sp.is_dummy() {
-            let file = sm.lookup_char_pos(sp.lo()).file;
-            if file.is_imported() { None } else { Some(span) }
-        } else {
-            None
-        }
-    });
-
-    let error_id = (DiagnosticMessageId::StabilityId(issue), span_key, msg.clone());
-    let fresh = sess.one_time_diagnostics.borrow_mut().insert(error_id);
-    if fresh {
-        if is_soft {
-            soft_handler(SOFT_UNSTABLE, span, &msg)
-        } else {
-            let mut err =
-                feature_err_issue(&sess.parse_sess, feature, span, GateIssue::Library(issue), &msg);
-            if let Some((inner_types, ref msg, sugg, applicability)) = suggestion {
-                err.span_suggestion(inner_types, msg, sugg, applicability);
-            }
-            err.emit();
+    if is_soft {
+        soft_handler(SOFT_UNSTABLE, span, &msg)
+    } else {
+        let mut err =
+            feature_err_issue(&sess.parse_sess, feature, span, GateIssue::Library(issue), &msg);
+        if let Some((inner_types, ref msg, sugg, applicability)) = suggestion {
+            err.span_suggestion(inner_types, msg, sugg, applicability);
        }
+        err.emit();
    }
 }

--- a/compiler/rustc_mir_transform/src/check_unsafety.rs
+++ b/compiler/rustc_mir_transform/src/check_unsafety.rs
@ -554,7 +554,6 @@ fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
                    tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, usage_lint_root);
                assert_eq!(level, Level::Allow);
                lint::explain_lint_level_source(
-                    tcx.sess,
                    UNSAFE_OP_IN_UNSAFE_FN,
                    Level::Allow,
                    source,
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@ -49,8 +49,8 @@ macro_rules! panictry_buffer {
        match $e {
            Ok(e) => e,
            Err(errs) => {
-                for e in errs {
-                    $handler.emit_diagnostic(&e);
+                for mut e in errs {
+                    $handler.emit_diagnostic(&mut e);
                }
                FatalError.raise()
            }
@ -167,8 +167,8 @@ fn try_file_to_source_file(
 fn file_to_source_file(sess: &ParseSess, path: &Path, spanopt: Option<Span>) -> Lrc<SourceFile> {
    match try_file_to_source_file(sess, path, spanopt) {
        Ok(source_file) => source_file,
-        Err(d) => {
-            sess.span_diagnostic.emit_diagnostic(&d);
+        Err(mut d) => {
+            sess.span_diagnostic.emit_diagnostic(&mut d);
            FatalError.raise();
        }
    }
--- a/compiler/rustc_query_system/src/dep_graph/graph.rs
+++ b/compiler/rustc_query_system/src/dep_graph/graph.rs
@ -784,8 +784,8 @@ impl<K: DepKind> DepGraph<K> {

            let handle = tcx.dep_context().sess().diagnostic();

-            for diagnostic in side_effects.diagnostics {
-                handle.emit_diagnostic(&diagnostic);
+            for mut diagnostic in side_effects.diagnostics {
+                handle.emit_diagnostic(&mut diagnostic);
            }
        }
    }
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@ -19,7 +19,7 @@ use rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitterWriter;
 use rustc_errors::emitter::{Emitter, EmitterWriter, HumanReadableErrorType};
 use rustc_errors::json::JsonEmitter;
 use rustc_errors::registry::Registry;
-use rustc_errors::{Diagnostic, DiagnosticBuilder, DiagnosticId, ErrorGuaranteed};
+use rustc_errors::{DiagnosticBuilder, DiagnosticId, ErrorGuaranteed};
 use rustc_macros::HashStable_Generic;
 pub use rustc_span::def_id::StableCrateId;
 use rustc_span::edition::Edition;
@ -35,7 +35,6 @@ use std::cell::{self, RefCell};
 use std::env;
 use std::fmt;
 use std::io::Write;
-use std::num::NonZeroU32;
 use std::ops::{Div, Mul};
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
@ -136,10 +135,6 @@ pub struct Session {
    /// `None` means that there is no source file.
    pub local_crate_source_file: Option<PathBuf>,

-    /// Set of `(DiagnosticId, Option<Span>, message)` tuples tracking
-    /// (sub)diagnostics that have been set once, but should not be set again,
-    /// in order to avoid redundantly verbose output (Issue #24690, #44953).
-    pub one_time_diagnostics: Lock<FxHashSet<(DiagnosticMessageId, Option<Span>, String)>>,
    crate_types: OnceCell<Vec<CrateType>>,
    /// The `stable_crate_id` is constructed out of the crate name and all the
    /// `-C metadata` arguments passed to the compiler. Its value forms a unique
@ -209,13 +204,6 @@ pub struct PerfStats {
    pub normalize_projection_ty: AtomicUsize,
 }

-/// Enum to support dispatch of one-time diagnostics (in `Session.diag_once`).
-enum DiagnosticBuilderMethod {
-    Note,
-    SpanNote,
-    // Add more variants as needed to support one-time diagnostics.
-}
-
 /// Trait implemented by error types. This should not be implemented manually. Instead, use
 /// `#[derive(SessionDiagnostic)]` -- see [rustc_macros::SessionDiagnostic].
 pub trait SessionDiagnostic<'a> {
@ -224,21 +212,6 @@ pub trait SessionDiagnostic<'a> {
    fn into_diagnostic(self, sess: &'a Session) -> DiagnosticBuilder<'a, ErrorGuaranteed>;
 }

-/// Diagnostic message ID, used by `Session.one_time_diagnostics` to avoid
-/// emitting the same message more than once.
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
-pub enum DiagnosticMessageId {
-    ErrorId(u16), // EXXXX error code as integer
-    LintId(lint::LintId),
-    StabilityId(Option<NonZeroU32>), // issue number
-}
-
-impl From<&'static lint::Lint> for DiagnosticMessageId {
-    fn from(lint: &'static lint::Lint) -> Self {
-        DiagnosticMessageId::LintId(lint::LintId::of(lint))
-    }
-}
-
 impl Session {
    pub fn miri_unleashed_feature(&self, span: Span, feature_gate: Option<Symbol>) {
        self.miri_unleashed_features.lock().push((span, feature_gate));
@ -497,50 +470,6 @@ impl Session {
        &self.parse_sess.span_diagnostic
    }

-    /// Analogous to calling methods on the given `DiagnosticBuilder`, but
-    /// deduplicates on lint ID, span (if any), and message for this `Session`
-    fn diag_once(
-        &self,
-        diag: &mut Diagnostic,
-        method: DiagnosticBuilderMethod,
-        msg_id: DiagnosticMessageId,
-        message: &str,
-        span_maybe: Option<Span>,
-    ) {
-        let id_span_message = (msg_id, span_maybe, message.to_owned());
-        let fresh = self.one_time_diagnostics.borrow_mut().insert(id_span_message);
-        if fresh {
-            match method {
-                DiagnosticBuilderMethod::Note => {
-                    diag.note(message);
-                }
-                DiagnosticBuilderMethod::SpanNote => {
-                    let span = span_maybe.expect("`span_note` needs a span");
-                    diag.span_note(span, message);
-                }
-            }
-        }
-    }
-
-    pub fn diag_span_note_once(
-        &self,
-        diag: &mut Diagnostic,
-        msg_id: DiagnosticMessageId,
-        span: Span,
-        message: &str,
-    ) {
-        self.diag_once(diag, DiagnosticBuilderMethod::SpanNote, msg_id, message, Some(span));
-    }
-
-    pub fn diag_note_once(
-        &self,
-        diag: &mut Diagnostic,
-        msg_id: DiagnosticMessageId,
-        message: &str,
-    ) {
-        self.diag_once(diag, DiagnosticBuilderMethod::Note, msg_id, message, None);
-    }
-
    #[inline]
    pub fn source_map(&self) -> &SourceMap {
        self.parse_sess.source_map()
@ -1306,7 +1235,6 @@ pub fn build_session(
        parse_sess,
        sysroot,
        local_crate_source_file,
-        one_time_diagnostics: Default::default(),
        crate_types: OnceCell::new(),
        stable_crate_id: OnceCell::new(),
        features: OnceCell::new(),
--- a/compiler/rustc_trait_selection/src/autoderef.rs
+++ b/compiler/rustc_trait_selection/src/autoderef.rs
@ -5,7 +5,7 @@ use rustc_hir as hir;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt};
 use rustc_middle::ty::{ToPredicate, TypeFoldable};
-use rustc_session::{DiagnosticMessageId, Limit};
+use rustc_session::Limit;
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::Span;

@ -222,24 +222,19 @@ pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Spa
        Limit(0) => Limit(2),
        limit => limit * 2,
    };
-    let msg = format!("reached the recursion limit while auto-dereferencing `{:?}`", ty);
-    let error_id = (DiagnosticMessageId::ErrorId(55), Some(span), msg);
-    let fresh = tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
-    if fresh {
-        struct_span_err!(
-            tcx.sess,
-            span,
-            E0055,
-            "reached the recursion limit while auto-dereferencing `{:?}`",
-            ty
-        )
-        .span_label(span, "deref recursion limit reached")
-        .help(&format!(
-            "consider increasing the recursion limit by adding a \
+    struct_span_err!(
+        tcx.sess,
+        span,
+        E0055,
+        "reached the recursion limit while auto-dereferencing `{:?}`",
+        ty
+    )
+    .span_label(span, "deref recursion limit reached")
+    .help(&format!(
+        "consider increasing the recursion limit by adding a \
             `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
-            suggested_limit,
-            tcx.crate_name(LOCAL_CRATE),
-        ))
-        .emit();
-    }
+        suggested_limit,
+        tcx.crate_name(LOCAL_CRATE),
+    ))
+    .emit();
 }
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@ -28,7 +28,6 @@ use rustc_middle::ty::fold::TypeFolder;
 use rustc_middle::ty::{
    self, SubtypePredicate, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable,
 };
-use rustc_session::DiagnosticMessageId;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::{ExpnKind, MultiSpan, Span, DUMMY_SP};
 use std::fmt;
@ -1406,60 +1405,49 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                }
            }

-            let msg = format!("type mismatch resolving `{}`", predicate);
-            let error_id = (DiagnosticMessageId::ErrorId(271), Some(obligation.cause.span), msg);
-            let fresh = self.tcx.sess.one_time_diagnostics.borrow_mut().insert(error_id);
-            if fresh {
-                let mut diag = struct_span_err!(
-                    self.tcx.sess,
-                    obligation.cause.span,
-                    E0271,
-                    "type mismatch resolving `{}`",
-                    predicate
-                );
-                let secondary_span = match predicate.kind().skip_binder() {
-                    ty::PredicateKind::Projection(proj) => self
-                        .tcx
-                        .opt_associated_item(proj.projection_ty.item_def_id)
-                        .and_then(|trait_assoc_item| {
+            let mut diag = struct_span_err!(
+                self.tcx.sess,
+                obligation.cause.span,
+                E0271,
+                "type mismatch resolving `{}`",
+                predicate
+            );
+            let secondary_span = match predicate.kind().skip_binder() {
+                ty::PredicateKind::Projection(proj) => self
+                    .tcx
+                    .opt_associated_item(proj.projection_ty.item_def_id)
+                    .and_then(|trait_assoc_item| {
+                        self.tcx
+                            .trait_of_item(proj.projection_ty.item_def_id)
+                            .map(|id| (trait_assoc_item, id))
+                    })
+                    .and_then(|(trait_assoc_item, id)| {
+                        let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
+                        self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
                            self.tcx
-                                .trait_of_item(proj.projection_ty.item_def_id)
-                                .map(|id| (trait_assoc_item, id))
+                                .associated_items(did)
+                                .in_definition_order()
+                                .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
                        })
-                        .and_then(|(trait_assoc_item, id)| {
-                            let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
-                            self.tcx.find_map_relevant_impl(
-                                id,
-                                proj.projection_ty.self_ty(),
-                                |did| {
-                                    self.tcx
-                                        .associated_items(did)
-                                        .in_definition_order()
-                                        .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
-                                },
-                            )
-                        })
-                        .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
-                            Some(
-                                hir::Node::TraitItem(hir::TraitItem {
-                                    kind: hir::TraitItemKind::Type(_, Some(ty)),
-                                    ..
-                                })
-                                | hir::Node::ImplItem(hir::ImplItem {
-                                    kind: hir::ImplItemKind::TyAlias(ty),
-                                    ..
-                                }),
-                            ) => {
-                                Some((ty.span, format!("type mismatch resolving `{}`", predicate)))
-                            }
-                            _ => None,
-                        }),
-                    _ => None,
-                };
-                self.note_type_err(&mut diag, &obligation.cause, secondary_span, values, err, true);
-                self.note_obligation_cause(&mut diag, obligation);
-                diag.emit();
-            }
+                    })
+                    .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
+                        Some(
+                            hir::Node::TraitItem(hir::TraitItem {
+                                kind: hir::TraitItemKind::Type(_, Some(ty)),
+                                ..
+                            })
+                            | hir::Node::ImplItem(hir::ImplItem {
+                                kind: hir::ImplItemKind::TyAlias(ty),
+                                ..
+                            }),
+                        ) => Some((ty.span, format!("type mismatch resolving `{}`", predicate))),
+                        _ => None,
+                    }),
+                _ => None,
+            };
+            self.note_type_err(&mut diag, &obligation.cause, secondary_span, values, err, true);
+            self.note_obligation_cause(&mut diag, obligation);
+            diag.emit();
        });
    }

--- a/compiler/rustc_typeck/src/check/writeback.rs
+++ b/compiler/rustc_typeck/src/check/writeback.rs
@ -467,8 +467,8 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {

        if !errors_buffer.is_empty() {
            errors_buffer.sort_by_key(|diag| diag.span.primary_span());
-            for diag in errors_buffer.drain(..) {
-                self.tcx().sess.diagnostic().emit_diagnostic(&diag);
+            for mut diag in errors_buffer.drain(..) {
+                self.tcx().sess.diagnostic().emit_diagnostic(&mut diag);
            }
        }
    }
--- a/src/test/rustdoc-ui/check-fail.stderr
+++ b/src/test/rustdoc-ui/check-fail.stderr
@ -32,11 +32,6 @@ LL | | //! let x = 12;
 LL | | //! ```
   | |_______^
   |
-note: the lint level is defined here
-  --> $DIR/check-fail.rs:4:9
-   |
-LL | #![deny(rustdoc::all)]
-   |         ^^^^^^^^^^^^
   = note: `#[deny(rustdoc::invalid_codeblock_attributes)]` implied by `#[deny(rustdoc::all)]`
   = help: the code block will either not be tested if not marked as a rust one or the code will be wrapped inside a main function

--- a/src/test/rustdoc-ui/check.stderr
+++ b/src/test/rustdoc-ui/check.stderr
@ -43,11 +43,6 @@ LL | |
 LL | | pub fn foo() {}
   | |_______________^
   |
-note: the lint level is defined here
-  --> $DIR/check.rs:8:9
-   |
-LL | #![warn(rustdoc::all)]
-   |         ^^^^^^^^^^^^
   = note: `#[warn(rustdoc::missing_doc_code_examples)]` implied by `#[warn(rustdoc::all)]`

 warning: missing code example in this documentation
--- a/src/test/rustdoc-ui/display-output.stdout
+++ b/src/test/rustdoc-ui/display-output.stdout
@ -30,11 +30,6 @@ warning: function is never used: `foo`
 LL | fn foo(x: &dyn std::fmt::Display) {}
   |    ^^^
   |
-note: the lint level is defined here
-  --> $DIR/display-output.rs:9:9
-   |
-LL | #![warn(unused)]
-   |         ^^^^^^
   = note: `#[warn(dead_code)]` implied by `#[warn(unused)]`

 warning: 3 warnings emitted
--- a/src/test/rustdoc-ui/lint-group.stderr
+++ b/src/test/rustdoc-ui/lint-group.stderr
@ -21,11 +21,6 @@ LL | | /// println!("sup");
 LL | | /// ```
   | |_______^
   |
-note: the lint level is defined here
-  --> $DIR/lint-group.rs:7:9
-   |
-LL | #![deny(rustdoc::all)]
-   |         ^^^^^^^^^^^^
   = note: `#[deny(rustdoc::private_doc_tests)]` implied by `#[deny(rustdoc::all)]`

 error: missing code example in this documentation
@ -40,11 +35,6 @@ error: unresolved link to `error`
 LL | /// what up, let's make an [error]
   |                             ^^^^^ no item named `error` in scope
   |
-note: the lint level is defined here
-  --> $DIR/lint-group.rs:7:9
-   |
-LL | #![deny(rustdoc::all)]
-   |         ^^^^^^^^^^^^
   = note: `#[deny(rustdoc::broken_intra_doc_links)]` implied by `#[deny(rustdoc::all)]`
   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`

@ -54,11 +44,6 @@ error: unclosed HTML tag `unknown`
 LL | /// <unknown>
   |     ^^^^^^^^^
   |
-note: the lint level is defined here
-  --> $DIR/lint-group.rs:7:9
-   |
-LL | #![deny(rustdoc::all)]
-   |         ^^^^^^^^^^^^
   = note: `#[deny(rustdoc::invalid_html_tags)]` implied by `#[deny(rustdoc::all)]`

 error: aborting due to 5 previous errors
--- a/src/test/ui-fulldeps/hash-stable-is-unstable.rs
+++ b/src/test/ui-fulldeps/hash-stable-is-unstable.rs
@ -1,5 +1,5 @@
 // ignore-stage1
-
+// compile-flags: -Zdeduplicate-diagnostics=yes
 extern crate rustc_data_structures;
 //~^ use of unstable library feature 'rustc_private'
 extern crate rustc_macros;
--- a/src/test/ui-fulldeps/lint-tool-test.stderr
+++ b/src/test/ui-fulldeps/lint-tool-test.stderr
@ -83,11 +83,6 @@ error: item is named 'lintmetoo'
 LL |     fn lintmetoo() { }
   |     ^^^^^^^^^^^^^^^^^^
   |
-note: the lint level is defined here
-  --> $DIR/lint-tool-test.rs:14:9
-   |
-LL | #![deny(clippy_group)]
-   |         ^^^^^^^^^^^^
   = note: `#[deny(clippy::test_group)]` implied by `#[deny(clippy::group)]`

 warning: lint name `test_group` is deprecated and may not have an effect in the future.
--- a/src/test/ui/autoref-autoderef/issue-38940.rs
+++ b/src/test/ui/autoref-autoderef/issue-38940.rs
@ -2,8 +2,10 @@
 // Test that the recursion limit can be changed. In this case, we have
 // deeply nested types that will fail the `Send` check by overflow
 // when the recursion limit is set very low.
+// compile-flags: -Zdeduplicate-diagnostics=yes
+
 #![allow(dead_code)]
-#![recursion_limit="10"]
+#![recursion_limit = "10"]
 macro_rules! link {
    ($outer:ident, $inner:ident) => {
        struct $outer($inner);
@ -18,14 +20,17 @@ macro_rules! link {
                &self.0
            }
        }
-    }
+    };
 }
+
 struct Bottom;
+
 impl Bottom {
    fn new() -> Bottom {
        Bottom
    }
 }
+
 link!(Top, A);
 link!(A, B);
 link!(B, C);
@ -38,6 +43,7 @@ link!(H, I);
 link!(I, J);
 link!(J, K);
 link!(K, Bottom);
+
 fn main() {
    let t = Top::new();
    let x: &Bottom = &t;
--- a/src/test/ui/autoref-autoderef/issue-38940.stderr
+++ b/src/test/ui/autoref-autoderef/issue-38940.stderr
@ -1,5 +1,5 @@
 error[E0055]: reached the recursion limit while auto-dereferencing `J`
-  --> $DIR/issue-38940.rs:43:22
+  --> $DIR/issue-38940.rs:49:22
   |
 LL |     let x: &Bottom = &t;
   |                      ^^ deref recursion limit reached
@ -7,7 +7,7 @@ LL |     let x: &Bottom = &t;
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`issue_38940`)

 error[E0308]: mismatched types
-  --> $DIR/issue-38940.rs:43:22
+  --> $DIR/issue-38940.rs:49:22
   |
 LL |     let x: &Bottom = &t;
   |            -------   ^^ expected struct `Bottom`, found struct `Top`
--- a/src/test/ui/closures/2229_closure_analysis/diagnostics/liveness.stderr
+++ b/src/test/ui/closures/2229_closure_analysis/diagnostics/liveness.stderr
@ -18,11 +18,6 @@ warning: unused variable: `a`
 LL |         a += 1;
   |         ^
   |
-note: the lint level is defined here
-  --> $DIR/liveness.rs:5:9
-   |
-LL | #![warn(unused)]
-   |         ^^^^^^
   = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
   = help: did you mean to capture by reference instead?

--- a/src/test/ui/closures/2229_closure_analysis/diagnostics/liveness_unintentional_copy.stderr
+++ b/src/test/ui/closures/2229_closure_analysis/diagnostics/liveness_unintentional_copy.stderr
@ -18,11 +18,6 @@ warning: unused variable: `a`
 LL |         a = s;
   |         ^
   |
-note: the lint level is defined here
-  --> $DIR/liveness_unintentional_copy.rs:4:9
-   |
-LL | #![warn(unused)]
-   |         ^^^^^^
   = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
   = help: did you mean to capture by reference instead?

--- a/src/test/ui/did_you_mean/recursion_limit_deref.rs
+++ b/src/test/ui/did_you_mean/recursion_limit_deref.rs
@ -1,6 +1,7 @@
 // Test that the recursion limit can be changed and that the compiler
 // suggests a fix. In this case, we have a long chain of Deref impls
 // which will cause an overflow during the autoderef loop.
+// compile-flags: -Zdeduplicate-diagnostics=yes

 #![allow(dead_code)]
 #![recursion_limit="10"]
--- a/src/test/ui/did_you_mean/recursion_limit_deref.stderr
+++ b/src/test/ui/did_you_mean/recursion_limit_deref.stderr
@ -1,5 +1,5 @@
 error[E0055]: reached the recursion limit while auto-dereferencing `J`
-  --> $DIR/recursion_limit_deref.rs:50:22
+  --> $DIR/recursion_limit_deref.rs:51:22
   |
 LL |     let x: &Bottom = &t;
   |                      ^^ deref recursion limit reached
@ -7,7 +7,7 @@ LL |     let x: &Bottom = &t;
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`recursion_limit_deref`)

 error[E0308]: mismatched types
-  --> $DIR/recursion_limit_deref.rs:50:22
+  --> $DIR/recursion_limit_deref.rs:51:22
   |
 LL |     let x: &Bottom = &t;
   |            -------   ^^ expected struct `Bottom`, found struct `Top`
--- a/src/test/ui/infinite/infinite-autoderef.rs
+++ b/src/test/ui/infinite/infinite-autoderef.rs
@ -1,6 +1,5 @@
 // error-pattern: reached the recursion limit while auto-dereferencing
-
-
+// compile-flags: -Zdeduplicate-diagnostics=yes

 use std::ops::Deref;

--- a/src/test/ui/infinite/infinite-autoderef.stderr
+++ b/src/test/ui/infinite/infinite-autoderef.stderr
@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/infinite-autoderef.rs:20:13
+  --> $DIR/infinite-autoderef.rs:19:13
   |
 LL |         x = Box::new(x);
   |             ^^^^^^^^^^^ cyclic type of infinite size
@ -10,7 +10,7 @@ LL |         x = *Box::new(x);
   |             +

 error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
-  --> $DIR/infinite-autoderef.rs:25:5
+  --> $DIR/infinite-autoderef.rs:24:5
   |
 LL |     Foo.foo;
   |     ^^^^^^^ deref recursion limit reached
@ -18,7 +18,7 @@ LL |     Foo.foo;
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_autoderef`)

 error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
-  --> $DIR/infinite-autoderef.rs:25:9
+  --> $DIR/infinite-autoderef.rs:24:9
   |
 LL |     Foo.foo;
   |         ^^^ deref recursion limit reached
@ -26,13 +26,13 @@ LL |     Foo.foo;
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_autoderef`)

 error[E0609]: no field `foo` on type `Foo`
-  --> $DIR/infinite-autoderef.rs:25:9
+  --> $DIR/infinite-autoderef.rs:24:9
   |
 LL |     Foo.foo;
   |         ^^^ unknown field

 error[E0055]: reached the recursion limit while auto-dereferencing `Foo`
-  --> $DIR/infinite-autoderef.rs:26:9
+  --> $DIR/infinite-autoderef.rs:25:9
   |
 LL |     Foo.bar();
   |         ^^^ deref recursion limit reached
@ -40,7 +40,7 @@ LL |     Foo.bar();
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`infinite_autoderef`)

 error[E0599]: no method named `bar` found for struct `Foo` in the current scope
-  --> $DIR/infinite-autoderef.rs:26:9
+  --> $DIR/infinite-autoderef.rs:25:9
   |
 LL | struct Foo;
   | ----------- method `bar` not found for this
--- a/src/test/ui/issues/issue-33941.rs
+++ b/src/test/ui/issues/issue-33941.rs
@ -1,6 +1,9 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
+
 use std::collections::HashMap;

 fn main() {
    for _ in HashMap::new().iter().cloned() {} //~ ERROR type mismatch
    //~^ ERROR type mismatch
+    //~| ERROR type mismatch
 }
--- a/src/test/ui/issues/issue-33941.stderr
+++ b/src/test/ui/issues/issue-33941.stderr
@ -1,5 +1,5 @@
 error[E0271]: type mismatch resolving `<std::collections::hash_map::Iter<'_, _, _> as Iterator>::Item == &_`
-  --> $DIR/issue-33941.rs:4:36
+  --> $DIR/issue-33941.rs:6:36
   |
 LL |     for _ in HashMap::new().iter().cloned() {}
   |                                    ^^^^^^ expected reference, found tuple
@ -13,7 +13,7 @@ LL |         Self: Sized + Iterator<Item = &'a T>,
   |                                ^^^^^^^^^^^^ required by this bound in `cloned`

 error[E0271]: type mismatch resolving `<std::collections::hash_map::Iter<'_, _, _> as Iterator>::Item == &_`
-  --> $DIR/issue-33941.rs:4:14
+  --> $DIR/issue-33941.rs:6:14
   |
 LL |     for _ in HashMap::new().iter().cloned() {}
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected tuple, found reference
@ -23,6 +23,16 @@ LL |     for _ in HashMap::new().iter().cloned() {}
   = note: required because of the requirements on the impl of `Iterator` for `Cloned<std::collections::hash_map::Iter<'_, _, _>>`
   = note: required because of the requirements on the impl of `IntoIterator` for `Cloned<std::collections::hash_map::Iter<'_, _, _>>`

-error: aborting due to 2 previous errors
+error[E0271]: type mismatch resolving `<std::collections::hash_map::Iter<'_, _, _> as Iterator>::Item == &_`
+  --> $DIR/issue-33941.rs:6:14
+   |
+LL |     for _ in HashMap::new().iter().cloned() {}
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected tuple, found reference
+   |
+   = note:  expected tuple `(&_, &_)`
+           found reference `&_`
+   = note: required because of the requirements on the impl of `Iterator` for `Cloned<std::collections::hash_map::Iter<'_, _, _>>`
+
+error: aborting due to 3 previous errors

 For more information about this error, try `rustc --explain E0271`.
--- a/src/test/ui/lint/issue-17718-const-naming.stderr
+++ b/src/test/ui/lint/issue-17718-const-naming.stderr
@ -17,11 +17,6 @@ error: constant `foo` should have an upper case name
 LL | const foo: isize = 3;
   |       ^^^ help: convert the identifier to upper case (notice the capitalization): `FOO`
   |
-note: the lint level is defined here
-  --> $DIR/issue-17718-const-naming.rs:2:9
-   |
-LL | #![deny(warnings)]
-   |         ^^^^^^^^
   = note: `#[deny(non_upper_case_globals)]` implied by `#[deny(warnings)]`

 error: aborting due to 2 previous errors
--- a/src/test/ui/lint/lint-group-nonstandard-style.stderr
+++ b/src/test/ui/lint/lint-group-nonstandard-style.stderr
@ -43,11 +43,6 @@ error: static variable `bad` should have an upper case name
 LL |         static bad: isize = 1;
   |                ^^^ help: convert the identifier to upper case: `BAD`
   |
-note: the lint level is defined here
-  --> $DIR/lint-group-nonstandard-style.rs:10:14
-   |
-LL |     #[forbid(nonstandard_style)]
-   |              ^^^^^^^^^^^^^^^^^
   = note: `#[forbid(non_upper_case_globals)]` implied by `#[forbid(nonstandard_style)]`

 warning: function `CamelCase` should have a snake case name
@ -56,11 +51,6 @@ warning: function `CamelCase` should have a snake case name
 LL |         fn CamelCase() {}
   |            ^^^^^^^^^ help: convert the identifier to snake case: `camel_case`
   |
-note: the lint level is defined here
-  --> $DIR/lint-group-nonstandard-style.rs:18:17
-   |
-LL |         #![warn(nonstandard_style)]
-   |                 ^^^^^^^^^^^^^^^^^
   = note: `#[warn(non_snake_case)]` implied by `#[warn(nonstandard_style)]`

 error: aborting due to 3 previous errors; 2 warnings emitted
--- a/src/test/ui/lint/unused/issue-47390-unused-variable-in-struct-pattern.stderr
+++ b/src/test/ui/lint/unused/issue-47390-unused-variable-in-struct-pattern.stderr
@ -49,11 +49,6 @@ warning: value assigned to `hours_are_suns` is never read
 LL |         hours_are_suns = false;
   |         ^^^^^^^^^^^^^^
   |
-note: the lint level is defined here
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:5:9
-   |
-LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
-   |         ^^^^^^
   = note: `#[warn(unused_assignments)]` implied by `#[warn(unused)]`
   = help: maybe it is overwritten before being read?

@ -107,11 +102,6 @@ LL |     let mut mut_unused_var = 1;
   |         |
   |         help: remove this `mut`
   |
-note: the lint level is defined here
-  --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:5:9
-   |
-LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
-   |         ^^^^^^
   = note: `#[warn(unused_mut)]` implied by `#[warn(unused)]`

 warning: variable does not need to be mutable
--- a/src/test/ui/liveness/liveness-consts.stderr
+++ b/src/test/ui/liveness/liveness-consts.stderr
@ -18,11 +18,6 @@ warning: value assigned to `b` is never read
 LL |     b += 1;
   |     ^
   |
-note: the lint level is defined here
-  --> $DIR/liveness-consts.rs:2:9
-   |
-LL | #![warn(unused)]
-   |         ^^^^^^
   = note: `#[warn(unused_assignments)]` implied by `#[warn(unused)]`
   = help: maybe it is overwritten before being read?

--- a/src/test/ui/liveness/liveness-upvars.stderr
+++ b/src/test/ui/liveness/liveness-upvars.stderr
@ -18,11 +18,6 @@ warning: unused variable: `last`
 LL |         last = Some(s);
   |         ^^^^
   |
-note: the lint level is defined here
-  --> $DIR/liveness-upvars.rs:4:9
-   |
-LL | #![warn(unused)]
-   |         ^^^^^^
   = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
   = help: did you mean to capture by reference instead?

--- a/src/test/ui/never_type/never-assign-dead-code.stderr
+++ b/src/test/ui/never_type/never-assign-dead-code.stderr
@ -27,11 +27,6 @@ warning: unused variable: `x`
 LL |     let x: ! = panic!("aah");
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`
   |
-note: the lint level is defined here
-  --> $DIR/never-assign-dead-code.rs:6:9
-   |
-LL | #![warn(unused)]
-   |         ^^^^^^
   = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`

 warning: 3 warnings emitted
--- a/src/test/ui/proc-macro/generate-mod.stderr
+++ b/src/test/ui/proc-macro/generate-mod.stderr
@ -101,6 +101,7 @@ error: cannot find type `OuterDerive` in this scope
 LL | #[derive(generate_mod::CheckDerive)]
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^ names from parent modules are not accessible without an explicit import
   |
+   = note: `#[deny(proc_macro_derive_resolution_fallback)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83583 <https://github.com/rust-lang/rust/issues/83583>
   = note: this error originates in the derive macro `generate_mod::CheckDerive` (in Nightly builds, run with -Z macro-backtrace for more info)
@ -112,6 +113,7 @@ error: cannot find type `FromOutside` in this scope
 LL |     #[derive(generate_mod::CheckDerive)]
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^ names from parent modules are not accessible without an explicit import
   |
+   = note: `#[deny(proc_macro_derive_resolution_fallback)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83583 <https://github.com/rust-lang/rust/issues/83583>
   = note: this error originates in the derive macro `generate_mod::CheckDerive` (in Nightly builds, run with -Z macro-backtrace for more info)
@ -123,6 +125,7 @@ error: cannot find type `OuterDerive` in this scope
 LL |     #[derive(generate_mod::CheckDerive)]
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^ names from parent modules are not accessible without an explicit import
   |
+   = note: `#[deny(proc_macro_derive_resolution_fallback)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83583 <https://github.com/rust-lang/rust/issues/83583>
   = note: this error originates in the derive macro `generate_mod::CheckDerive` (in Nightly builds, run with -Z macro-backtrace for more info)
@ -150,6 +153,11 @@ warning: cannot find type `OuterDeriveLint` in this scope
 LL | #[derive(generate_mod::CheckDeriveLint)] // OK, lint is suppressed
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ names from parent modules are not accessible without an explicit import
   |
+note: the lint level is defined here
+  --> $DIR/generate-mod.rs:30:10
+   |
+LL | #[derive(generate_mod::CheckDeriveLint)] // OK, lint is suppressed
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83583 <https://github.com/rust-lang/rust/issues/83583>
   = note: this warning originates in the derive macro `generate_mod::CheckDeriveLint` (in Nightly builds, run with -Z macro-backtrace for more info)
--- a/src/test/ui/proc-macro/group-compat-hack/group-compat-hack.stderr
+++ b/src/test/ui/proc-macro/group-compat-hack/group-compat-hack.stderr
@ -111,6 +111,7 @@ LL |         #[my_macro] struct One($name);
 LL |     impl_macros!(Foo);
   |     ----------------- in this macro invocation
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: the `time-macros-impl` crate will stop compiling in futures version of Rust. Please update to the latest version of the `time` crate to avoid breakage
@ -128,6 +129,7 @@ LL |         #[my_macro] struct Two($name);
 LL |     arrays!(Foo);
   |     ------------ in this macro invocation
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: older versions of the `js-sys` crate will stop compiling in future versions of Rust; please update to `js-sys` v0.3.40 or above
@ -145,6 +147,7 @@ LL |         #[my_macro] struct Three($T);
 LL |     tuple_from_req!(Foo);
   |     -------------------- in this macro invocation
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: the version of `actix-web` you are using might stop compiling in future versions of Rust; please update to the latest version of the `actix-web` crate to avoid breakage
@ -162,6 +165,7 @@ LL |         #[my_macro] struct Three($T);
 LL |     tuple_from_req!(Foo);
   |     -------------------- in this macro invocation
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: the version of `actix-web` you are using might stop compiling in future versions of Rust; please update to the latest version of the `actix-web` crate to avoid breakage
--- a/src/test/ui/proc-macro/issue-73933-procedural-masquerade.stderr
+++ b/src/test/ui/proc-macro/issue-73933-procedural-masquerade.stderr
@ -60,6 +60,7 @@ error: using `procedural-masquerade` crate
 LL | enum ProceduralMasqueradeDummyType {
   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: The `procedural-masquerade` crate has been unnecessary since Rust 1.30.0. Versions of this crate below 0.1.7 will eventually stop compiling.
@ -71,6 +72,7 @@ error: using `procedural-masquerade` crate
 LL | enum ProceduralMasqueradeDummyType {
   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: The `procedural-masquerade` crate has been unnecessary since Rust 1.30.0. Versions of this crate below 0.1.7 will eventually stop compiling.
@ -82,6 +84,7 @@ error: using `procedural-masquerade` crate
 LL | enum ProceduralMasqueradeDummyType {
   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
+   = note: `#[deny(proc_macro_back_compat)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
   = note: The `procedural-masquerade` crate has been unnecessary since Rust 1.30.0. Versions of this crate below 0.1.7 will eventually stop compiling.
--- a/src/tools/clippy/src/driver.rs
+++ b/src/tools/clippy/src/driver.rs
@ -178,8 +178,8 @@ fn report_clippy_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str) {
    // a .span_bug or .bug call has already printed what
    // it wants to print.
    if !info.payload().is::<rustc_errors::ExplicitBug>() {
-        let d = rustc_errors::Diagnostic::new(rustc_errors::Level::Bug, "unexpected panic");
-        handler.emit_diagnostic(&d);
+        let mut d = rustc_errors::Diagnostic::new(rustc_errors::Level::Bug, "unexpected panic");
+        handler.emit_diagnostic(&mut d);
    }

    let version_info = rustc_tools_util::get_version_info!();
--- a/src/tools/rustfmt/src/parse/session.rs
+++ b/src/tools/rustfmt/src/parse/session.rs
@ -225,8 +225,10 @@ impl ParseSess {
 // Methods that should be restricted within the parse module.
 impl ParseSess {
    pub(super) fn emit_diagnostics(&self, diagnostics: Vec<Diagnostic>) {
-        for diagnostic in diagnostics {
-            self.parse_sess.span_diagnostic.emit_diagnostic(&diagnostic);
+        for mut diagnostic in diagnostics {
+            self.parse_sess
+                .span_diagnostic
+                .emit_diagnostic(&mut diagnostic);
        }
    }