Rollup merge of #118933 - nnethercote:cleanup-errors-even-more, r=compiler-errors

Cleanup errors handlers even more

A sequel to #118587.

r? `@compiler-errors`

compiler/rustc_borrowck/src/lib.rs

@@ -2502,8 +2502,8 @@ mod error {
             if !self.errors.buffered.is_empty() {
                 self.errors.buffered.sort_by_key(|diag| diag.sort_span);
 
-                for mut diag in self.errors.buffered.drain(..) {
-                    self.infcx.tcx.sess.diagnostic().emit_diagnostic(&mut diag);
+                for diag in self.errors.buffered.drain(..) {
+                    self.infcx.tcx.sess.diagnostic().emit_diagnostic(diag);
                 }
             }
 

compiler/rustc_builtin_macros/src/errors.rs

@@ -453,7 +453,7 @@ impl<'a> IntoDiagnostic<'a> for EnvNotDefinedWithUserMessage {
             rustc::untranslatable_diagnostic,
             reason = "cannot translate user-provided messages"
         )]
-        let mut diag = handler.struct_diagnostic(self.msg_from_user.to_string());
+        let mut diag = handler.struct_err(self.msg_from_user.to_string());
         diag.set_span(self.span);
         diag
     }
@@ -804,7 +804,7 @@ pub(crate) struct AsmClobberNoReg {
 impl<'a> IntoDiagnostic<'a> for AsmClobberNoReg {
     fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         let mut diag =
-            handler.struct_diagnostic(crate::fluent_generated::builtin_macros_asm_clobber_no_reg);
+            handler.struct_err(crate::fluent_generated::builtin_macros_asm_clobber_no_reg);
         diag.set_span(self.spans.clone());
         // eager translation as `span_labels` takes `AsRef<str>`
         let lbl1 = handler.eagerly_translate_to_string(

compiler/rustc_codegen_llvm/src/errors.rs

@@ -107,7 +107,8 @@ impl IntoDiagnostic<'_, FatalError> for ParseTargetMachineConfig<'_> {
         let (message, _) = diag.styled_message().first().expect("`LlvmError` with no message");
         let message = handler.eagerly_translate_to_string(message.clone(), diag.args());
 
-        let mut diag = handler.struct_diagnostic(fluent::codegen_llvm_parse_target_machine_config);
+        let mut diag =
+            handler.struct_almost_fatal(fluent::codegen_llvm_parse_target_machine_config);
         diag.set_arg("error", message);
         diag
     }

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -1848,7 +1848,7 @@ impl SharedEmitterMain {
                         d.code(code);
                     }
                     d.replace_args(diag.args);
-                    handler.emit_diagnostic(&mut d);
+                    handler.emit_diagnostic(d);
                 }
                 Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => {
                     let msg = msg.strip_prefix("error: ").unwrap_or(&msg).to_string();

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -277,8 +277,8 @@ 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 mut error in secondary_errors {
-                self.tcx.sess.diagnostic().emit_diagnostic(&mut error);
+            for error in secondary_errors {
+                self.tcx.sess.diagnostic().emit_diagnostic(error);
             }
         } else {
             assert!(self.tcx.sess.has_errors().is_some());

compiler/rustc_errors/src/diagnostic_builder.rs

@@ -132,7 +132,7 @@ impl EmissionGuarantee for ErrorGuaranteed {
             DiagnosticBuilderState::Emittable(handler) => {
                 db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
 
-                let guar = handler.emit_diagnostic(&mut db.inner.diagnostic);
+                let guar = handler.emit_diagnostic_without_consuming(&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`
@@ -181,7 +181,7 @@ impl EmissionGuarantee for () {
             DiagnosticBuilderState::Emittable(handler) => {
                 db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
 
-                handler.emit_diagnostic(&mut db.inner.diagnostic);
+                handler.emit_diagnostic_without_consuming(&mut db.inner.diagnostic);
             }
             // `.emit()` was previously called, disallowed from repeating it.
             DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
@@ -207,7 +207,7 @@ impl EmissionGuarantee for Noted {
             // First `.emit()` call, the `&Handler` is still available.
             DiagnosticBuilderState::Emittable(handler) => {
                 db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
-                handler.emit_diagnostic(&mut db.inner.diagnostic);
+                handler.emit_diagnostic_without_consuming(&mut db.inner.diagnostic);
             }
             // `.emit()` was previously called, disallowed from repeating it.
             DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
@@ -236,7 +236,7 @@ impl EmissionGuarantee for Bug {
             DiagnosticBuilderState::Emittable(handler) => {
                 db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
 
-                handler.emit_diagnostic(&mut db.inner.diagnostic);
+                handler.emit_diagnostic_without_consuming(&mut db.inner.diagnostic);
             }
             // `.emit()` was previously called, disallowed from repeating it.
             DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
@@ -260,7 +260,7 @@ impl EmissionGuarantee for ! {
             DiagnosticBuilderState::Emittable(handler) => {
                 db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
 
-                handler.emit_diagnostic(&mut db.inner.diagnostic);
+                handler.emit_diagnostic_without_consuming(&mut db.inner.diagnostic);
             }
             // `.emit()` was previously called, disallowed from repeating it.
             DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
@@ -284,7 +284,7 @@ impl EmissionGuarantee for rustc_span::fatal_error::FatalError {
             DiagnosticBuilderState::Emittable(handler) => {
                 db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
 
-                handler.emit_diagnostic(&mut db.inner.diagnostic);
+                handler.emit_diagnostic_without_consuming(&mut db.inner.diagnostic);
             }
             // `.emit()` was previously called, disallowed from repeating it.
             DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
@@ -365,7 +365,9 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         }
     }
 
-    /// Emit the diagnostic.
+    /// Emit the diagnostic. Does not consume `self`, which may be surprising,
+    /// but there are various places that rely on continuing to use `self`
+    /// after calling `emit`.
     #[track_caller]
     pub fn emit(&mut self) -> G {
         G::diagnostic_builder_emit_producing_guarantee(self)
@@ -640,13 +642,13 @@ impl Drop for DiagnosticBuilderInner<'_> {
             // No `.emit()` or `.cancel()` calls.
             DiagnosticBuilderState::Emittable(handler) => {
                 if !panicking() {
-                    handler.emit_diagnostic(&mut Diagnostic::new(
+                    handler.emit_diagnostic(Diagnostic::new(
                         Level::Bug,
                         DiagnosticMessage::from(
                             "the following error was constructed but not emitted",
                         ),
                     ));
-                    handler.emit_diagnostic(&mut self.diagnostic);
+                    handler.emit_diagnostic_without_consuming(&mut self.diagnostic);
                     panic!("error was constructed but not emitted");
                 }
             }

compiler/rustc_errors/src/emitter.rs

@@ -581,7 +581,7 @@ impl Emitter for SilentEmitter {
             if let Some(ref note) = self.fatal_note {
                 d.note(note.clone());
             }
-            self.fatal_handler.emit_diagnostic(&mut d);
+            self.fatal_handler.emit_diagnostic(d);
         }
     }
 }

compiler/rustc_errors/src/lib.rs

@@ -585,11 +585,6 @@ impl Handler {
         self
     }
 
-    pub fn treat_err_as_bug(mut self, treat_err_as_bug: NonZeroUsize) -> Self {
-        self.inner.get_mut().flags.treat_err_as_bug = Some(treat_err_as_bug);
-        self
-    }
-
     pub fn with_flags(mut self, flags: HandlerFlags) -> Self {
         self.inner.get_mut().flags = flags;
         self
@@ -727,7 +722,12 @@ impl Handler {
         self.inner.borrow_mut().emit_stashed_diagnostics()
     }
 
-    /// Construct a builder with the `msg` at the level appropriate for the specific `EmissionGuarantee`.
+    /// Construct a builder with the `msg` at the level appropriate for the
+    /// specific `EmissionGuarantee`.
+    ///
+    /// Note: this is necessary for `derive(Diagnostic)`, but shouldn't be used
+    /// outside of that. Instead use `struct_err`, `struct_warn`, etc., which
+    /// make the diagnostic kind clearer.
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn struct_diagnostic<G: EmissionGuarantee>(
@@ -942,13 +942,23 @@ impl Handler {
         result
     }
 
-    /// Construct a builder at the `Error` level with the `msg`.
+    /// Construct a builder at the `Fatal` level with the `msg`.
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn struct_fatal(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, !> {
         DiagnosticBuilder::new(self, Level::Fatal, msg)
     }
 
+    /// Construct a builder at the `Fatal` level with the `msg`, that doesn't abort.
+    #[rustc_lint_diagnostics]
+    #[track_caller]
+    pub fn struct_almost_fatal(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, FatalError> {
+        DiagnosticBuilder::new(self, Level::Fatal, msg)
+    }
+
     /// Construct a builder at the `Help` level with the `msg`.
     #[rustc_lint_diagnostics]
     pub fn struct_help(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
@@ -965,8 +975,7 @@ impl Handler {
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn span_fatal(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) -> ! {
-        self.emit_diag_at_span(Diagnostic::new(Fatal, msg), span);
-        FatalError.raise()
+        self.struct_span_fatal(span, msg).emit()
     }
 
     #[rustc_lint_diagnostics]
@@ -977,8 +986,7 @@ impl Handler {
         msg: impl Into<DiagnosticMessage>,
         code: DiagnosticId,
     ) -> ! {
-        self.emit_diag_at_span(Diagnostic::new_with_code(Fatal, Some(code), msg), span);
-        FatalError.raise()
+        self.struct_span_fatal_with_code(span, msg, code).emit()
     }
 
     #[rustc_lint_diagnostics]
@@ -988,7 +996,7 @@ impl Handler {
         span: impl Into<MultiSpan>,
         msg: impl Into<DiagnosticMessage>,
     ) -> ErrorGuaranteed {
-        self.emit_diag_at_span(Diagnostic::new(Error { lint: false }, msg), span).unwrap()
+        self.struct_span_err(span, msg).emit()
     }
 
     #[rustc_lint_diagnostics]
@@ -999,17 +1007,13 @@ impl Handler {
         msg: impl Into<DiagnosticMessage>,
         code: DiagnosticId,
     ) -> ErrorGuaranteed {
-        self.emit_diag_at_span(
-            Diagnostic::new_with_code(Error { lint: false }, Some(code), msg),
-            span,
-        )
-        .unwrap()
+        self.struct_span_err_with_code(span, msg, code).emit()
     }
 
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn span_warn(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) {
-        self.emit_diag_at_span(Diagnostic::new(Warning(None), msg), span);
+        self.struct_span_warn(span, msg).emit()
     }
 
     #[rustc_lint_diagnostics]
@@ -1020,10 +1024,10 @@ impl Handler {
         msg: impl Into<DiagnosticMessage>,
         code: DiagnosticId,
     ) {
-        self.emit_diag_at_span(Diagnostic::new_with_code(Warning(None), Some(code), msg), span);
+        self.struct_span_warn_with_code(span, msg, code).emit()
     }
 
-    pub fn span_bug(&self, span: impl Into<MultiSpan>, msg: impl Into<String>) -> ! {
+    pub fn span_bug(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) -> ! {
         self.inner.borrow_mut().span_bug(span, msg)
     }
 
@@ -1035,7 +1039,7 @@ impl Handler {
     pub fn span_delayed_bug(
         &self,
         sp: impl Into<MultiSpan>,
-        msg: impl Into<String>,
+        msg: impl Into<DiagnosticMessage>,
     ) -> ErrorGuaranteed {
         let mut inner = self.inner.borrow_mut();
 
@@ -1046,11 +1050,11 @@ impl Handler {
             inner.err_count + inner.lint_err_count + inner.delayed_bug_count() + 1 >= c.get()
         }) {
             // FIXME: don't abort here if report_delayed_bugs is off
-            inner.span_bug(sp, msg.into());
+            inner.span_bug(sp, msg);
         }
-        let mut diagnostic = Diagnostic::new(Level::DelayedBug, msg.into());
-        diagnostic.set_span(sp.into());
-        inner.emit_diagnostic(&mut diagnostic).unwrap()
+        let mut diagnostic = Diagnostic::new(Level::DelayedBug, msg);
+        diagnostic.set_span(sp);
+        inner.emit_diagnostic(diagnostic).unwrap()
     }
 
     // FIXME(eddyb) note the comment inside `impl Drop for HandlerInner`, that's
@@ -1060,7 +1064,7 @@ impl Handler {
 
         let mut diagnostic = Diagnostic::new(Level::DelayedBug, msg);
         if inner.flags.report_delayed_bugs {
-            inner.emit_diagnostic(&mut diagnostic);
+            inner.emit_diagnostic_without_consuming(&mut diagnostic);
         }
         let backtrace = std::backtrace::Backtrace::capture();
         inner.good_path_delayed_bugs.push(DelayedDiagnostic::with_backtrace(diagnostic, backtrace));
@@ -1068,20 +1072,22 @@ impl Handler {
 
     #[track_caller]
     pub fn span_bug_no_panic(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) {
-        self.emit_diag_at_span(Diagnostic::new(Bug, msg), span);
+        let mut diag = Diagnostic::new(Bug, msg);
+        diag.set_span(span);
+        self.emit_diagnostic(diag);
     }
 
     #[track_caller]
     #[rustc_lint_diagnostics]
     pub fn span_note(&self, span: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) {
-        self.emit_diag_at_span(Diagnostic::new(Note, msg), span);
+        self.struct_span_note(span, msg).emit()
     }
 
     #[track_caller]
     #[rustc_lint_diagnostics]
     pub fn struct_span_note(
         &self,
-        span: Span,
+        span: impl Into<MultiSpan>,
         msg: impl Into<DiagnosticMessage>,
     ) -> DiagnosticBuilder<'_, ()> {
         let mut db = DiagnosticBuilder::new(self, Note, msg);
@@ -1091,22 +1097,22 @@ impl Handler {
 
     #[rustc_lint_diagnostics]
     pub fn fatal(&self, msg: impl Into<DiagnosticMessage>) -> ! {
-        DiagnosticBuilder::<FatalError>::new(self, Fatal, msg).emit().raise()
+        self.struct_fatal(msg).emit()
     }
 
     #[rustc_lint_diagnostics]
     pub fn err(&self, msg: impl Into<DiagnosticMessage>) -> ErrorGuaranteed {
-        DiagnosticBuilder::<ErrorGuaranteed>::new(self, Error { lint: false }, msg).emit()
+        self.struct_err(msg).emit()
     }
 
     #[rustc_lint_diagnostics]
     pub fn warn(&self, msg: impl Into<DiagnosticMessage>) {
-        DiagnosticBuilder::<()>::new(self, Warning(None), msg).emit();
+        self.struct_warn(msg).emit()
     }
 
     #[rustc_lint_diagnostics]
     pub fn note(&self, msg: impl Into<DiagnosticMessage>) {
-        DiagnosticBuilder::<()>::new(self, Note, msg).emit();
+        self.struct_note(msg).emit()
     }
 
     pub fn bug(&self, msg: impl Into<DiagnosticMessage>) -> ! {
@@ -1181,10 +1187,10 @@ impl Handler {
                 DiagnosticMessage::Str(warnings),
             )),
             (_, 0) => {
-                inner.emit_diagnostic(&mut Diagnostic::new(Fatal, errors));
+                inner.emit_diagnostic(Diagnostic::new(Fatal, errors));
             }
             (_, _) => {
-                inner.emit_diagnostic(&mut Diagnostic::new(Fatal, format!("{errors}; {warnings}")));
+                inner.emit_diagnostic(Diagnostic::new(Fatal, format!("{errors}; {warnings}")));
             }
         }
 
@@ -1251,8 +1257,17 @@ impl Handler {
         self.inner.borrow_mut().emitter.emit_diagnostic(&db);
     }
 
-    pub fn emit_diagnostic(&self, diagnostic: &mut Diagnostic) -> Option<ErrorGuaranteed> {
-        self.inner.borrow_mut().emit_diagnostic(diagnostic)
+    pub fn emit_diagnostic(&self, mut diagnostic: Diagnostic) -> Option<ErrorGuaranteed> {
+        self.emit_diagnostic_without_consuming(&mut diagnostic)
+    }
+
+    // It's unfortunate this exists. `emit_diagnostic` is preferred, because it
+    // consumes the diagnostic, thus ensuring it is emitted just once.
+    pub(crate) fn emit_diagnostic_without_consuming(
+        &self,
+        diagnostic: &mut Diagnostic,
+    ) -> Option<ErrorGuaranteed> {
+        self.inner.borrow_mut().emit_diagnostic_without_consuming(diagnostic)
     }
 
     pub fn emit_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> ErrorGuaranteed {
@@ -1327,14 +1342,6 @@ impl Handler {
         note.into_diagnostic(self)
     }
 
-    fn emit_diag_at_span(
-        &self,
-        mut diag: Diagnostic,
-        sp: impl Into<MultiSpan>,
-    ) -> Option<ErrorGuaranteed> {
-        self.emit_diagnostic(diag.set_span(sp))
-    }
-
     pub fn emit_artifact_notification(&self, path: &Path, artifact_type: &str) {
         self.inner.borrow_mut().emitter.emit_artifact_notification(path, artifact_type);
     }
@@ -1374,7 +1381,7 @@ impl Handler {
                 // Here the diagnostic is given back to `emit_diagnostic` where it was first
                 // intercepted. Now it should be processed as usual, since the unstable expectation
                 // id is now stable.
-                inner.emit_diagnostic(&mut diag);
+                inner.emit_diagnostic(diag);
             }
         }
 
@@ -1416,7 +1423,7 @@ impl HandlerInner {
         let has_errors = self.has_errors();
         let diags = self.stashed_diagnostics.drain(..).map(|x| x.1).collect::<Vec<_>>();
         let mut reported = None;
-        for mut diag in diags {
+        for diag in diags {
             // Decrement the count tracking the stash; emitting will increment it.
             if diag.is_error() {
                 if matches!(diag.level, Level::Error { lint: true }) {
@@ -1436,14 +1443,20 @@ impl HandlerInner {
                     }
                 }
             }
-            let reported_this = self.emit_diagnostic(&mut diag);
+            let reported_this = self.emit_diagnostic(diag);
             reported = reported.or(reported_this);
         }
         reported
     }
 
-    // FIXME(eddyb) this should ideally take `diagnostic` by value.
-    fn emit_diagnostic(&mut self, diagnostic: &mut Diagnostic) -> Option<ErrorGuaranteed> {
+    fn emit_diagnostic(&mut self, mut diagnostic: Diagnostic) -> Option<ErrorGuaranteed> {
+        self.emit_diagnostic_without_consuming(&mut diagnostic)
+    }
+
+    fn emit_diagnostic_without_consuming(
+        &mut self,
+        diagnostic: &mut Diagnostic,
+    ) -> Option<ErrorGuaranteed> {
         if matches!(diagnostic.level, Level::Error { .. } | Level::Fatal) && self.treat_err_as_bug()
         {
             diagnostic.level = Level::Bug;
@@ -1579,17 +1592,15 @@ impl HandlerInner {
     }
 
     #[track_caller]
-    fn span_bug(&mut self, sp: impl Into<MultiSpan>, msg: impl Into<String>) -> ! {
-        self.emit_diag_at_span(Diagnostic::new(Bug, msg.into()), sp);
+    fn span_bug(&mut self, sp: impl Into<MultiSpan>, msg: impl Into<DiagnosticMessage>) -> ! {
+        let mut diag = Diagnostic::new(Bug, msg);
+        diag.set_span(sp);
+        self.emit_diagnostic(diag);
         panic::panic_any(ExplicitBug);
     }
 
-    fn emit_diag_at_span(&mut self, mut diag: Diagnostic, sp: impl Into<MultiSpan>) {
-        self.emit_diagnostic(diag.set_span(sp));
-    }
-
     fn failure_note(&mut self, msg: impl Into<DiagnosticMessage>) {
-        self.emit_diagnostic(&mut Diagnostic::new(FailureNote, msg));
+        self.emit_diagnostic(Diagnostic::new(FailureNote, msg));
     }
 
     fn flush_delayed(
@@ -1621,7 +1632,7 @@ 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(&mut Diagnostic::new(Bug, explanation));
+                self.emit_diagnostic(Diagnostic::new(Bug, explanation));
                 no_bugs = false;
             }
 
@@ -1636,7 +1647,7 @@ impl HandlerInner {
             }
             bug.level = Level::Bug;
 
-            self.emit_diagnostic(&mut bug);
+            self.emit_diagnostic(bug);
         }
 
         // Panic with `DelayedBugPanic` to avoid "unexpected panic" messages.

compiler/rustc_expand/src/base.rs

@@ -1145,7 +1145,7 @@ impl<'a> ExtCtxt<'a> {
     pub fn span_err<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) {
         self.sess.diagnostic().span_err(sp, msg);
     }
-    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<String>) -> ! {
+    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) -> ! {
         self.sess.diagnostic().span_bug(sp, msg);
     }
     pub fn trace_macros_diag(&mut self) {

compiler/rustc_expand/src/proc_macro_server.rs

@@ -502,7 +502,7 @@ impl server::FreeFunctions for Rustc<'_, '_> {
                 None,
             );
         }
-        self.sess().span_diagnostic.emit_diagnostic(&mut diag);
+        self.sess().span_diagnostic.emit_diagnostic(diag);
     }
 }
 

compiler/rustc_hir_typeck/src/writeback.rs

@@ -504,8 +504,8 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
 
             if !errors_buffer.is_empty() {
                 errors_buffer.sort_by_key(|diag| diag.span.primary_span());
-                for mut diag in errors_buffer {
-                    self.tcx().sess.diagnostic().emit_diagnostic(&mut diag);
+                for diag in errors_buffer {
+                    self.tcx().sess.diagnostic().emit_diagnostic(diag);
                 }
             }
         }

compiler/rustc_middle/src/ty/sty.rs

@@ -15,7 +15,9 @@ use hir::def::DefKind;
 use polonius_engine::Atom;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::intern::Interned;
-use rustc_errors::{DiagnosticArgValue, ErrorGuaranteed, IntoDiagnosticArg, MultiSpan};
+use rustc_errors::{
+    DiagnosticArgValue, DiagnosticMessage, ErrorGuaranteed, IntoDiagnosticArg, MultiSpan,
+};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::LangItem;
@@ -2005,7 +2007,7 @@ impl<'tcx> Ty<'tcx> {
     pub fn new_error_with_message<S: Into<MultiSpan>>(
         tcx: TyCtxt<'tcx>,
         span: S,
-        msg: impl Into<String>,
+        msg: impl Into<DiagnosticMessage>,
     ) -> Ty<'tcx> {
         let reported = tcx.sess.span_delayed_bug(span, msg);
         Ty::new(tcx, Error(reported))

compiler/rustc_mir_transform/src/errors.rs

@@ -65,7 +65,7 @@ pub(crate) struct RequiresUnsafe {
 impl<'sess> IntoDiagnostic<'sess> for RequiresUnsafe {
     #[track_caller]
     fn into_diagnostic(self, handler: &'sess Handler) -> DiagnosticBuilder<'sess, ErrorGuaranteed> {
-        let mut diag = handler.struct_diagnostic(fluent::mir_transform_requires_unsafe);
+        let mut diag = handler.struct_err(fluent::mir_transform_requires_unsafe);
         diag.code(rustc_errors::DiagnosticId::Error("E0133".to_string()));
         diag.set_span(self.span);
         diag.span_label(self.span, self.details.label());

compiler/rustc_parse/src/errors.rs

@@ -1046,7 +1046,7 @@ impl<'a> IntoDiagnostic<'a> for ExpectedIdentifier {
     ) -> rustc_errors::DiagnosticBuilder<'a, ErrorGuaranteed> {
         let token_descr = TokenDescription::from_token(&self.token);
 
-        let mut diag = handler.struct_diagnostic(match token_descr {
+        let mut diag = handler.struct_err(match token_descr {
             Some(TokenDescription::ReservedIdentifier) => {
                 fluent::parse_expected_identifier_found_reserved_identifier_str
             }
@@ -1103,7 +1103,7 @@ impl<'a> IntoDiagnostic<'a> for ExpectedSemi {
     ) -> rustc_errors::DiagnosticBuilder<'a, ErrorGuaranteed> {
         let token_descr = TokenDescription::from_token(&self.token);
 
-        let mut diag = handler.struct_diagnostic(match token_descr {
+        let mut diag = handler.struct_err(match token_descr {
             Some(TokenDescription::ReservedIdentifier) => {
                 fluent::parse_expected_semi_found_reserved_identifier_str
             }

compiler/rustc_parse/src/lexer/unicode_chars.rs

@@ -350,8 +350,7 @@ pub(super) fn check_for_substitution(
 
     let Some((_, ascii_name, token)) = ASCII_ARRAY.iter().find(|&&(s, _, _)| s == ascii_str) else {
         let msg = format!("substitution character not found for '{ch}'");
-        reader.sess.span_diagnostic.span_bug_no_panic(span, msg);
-        return (None, None);
+        reader.sess.span_diagnostic.span_bug(span, msg);
     };
 
     // special help suggestion for "directed" double quotes

compiler/rustc_parse/src/lib.rs

@@ -51,8 +51,8 @@ macro_rules! panictry_buffer {
         match $e {
             Ok(e) => e,
             Err(errs) => {
-                for mut e in errs {
-                    $handler.emit_diagnostic(&mut e);
+                for e in errs {
+                    $handler.emit_diagnostic(e);
                 }
                 FatalError.raise()
             }
@@ -165,8 +165,8 @@ 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(mut d) => {
-            sess.span_diagnostic.emit_diagnostic(&mut d);
+        Err(d) => {
+            sess.span_diagnostic.emit_diagnostic(d);
             FatalError.raise();
         }
     }

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -249,8 +249,8 @@ impl<'a> Parser<'a> {
         self.diagnostic().struct_span_err(sp, m)
     }
 
-    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: impl Into<String>) -> ! {
-        self.diagnostic().span_bug(sp, m)
+    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) -> ! {
+        self.diagnostic().span_bug(sp, msg)
     }
 
     pub(super) fn diagnostic(&self) -> &'a Handler {

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -926,8 +926,8 @@ impl<D: Deps> DepGraphData<D> {
 
             let handle = qcx.dep_context().sess().diagnostic();
 
-            for mut diagnostic in side_effects.diagnostics {
-                handle.emit_diagnostic(&mut diagnostic);
+            for diagnostic in side_effects.diagnostics {
+                handle.emit_diagnostic(diagnostic);
             }
         }
     }

compiler/rustc_session/src/errors.rs

@@ -19,7 +19,7 @@ impl<'a> IntoDiagnostic<'a> for FeatureGateError {
         self,
         handler: &'a rustc_errors::Handler,
     ) -> rustc_errors::DiagnosticBuilder<'a, ErrorGuaranteed> {
-        let mut diag = handler.struct_diagnostic(self.explain);
+        let mut diag = handler.struct_err(self.explain);
         diag.set_span(self.span);
         diag.code(error_code!(E0658));
         diag

compiler/rustc_session/src/parse.rs

@@ -14,7 +14,7 @@ use rustc_data_structures::sync::{AppendOnlyVec, Lock, Lrc};
 use rustc_errors::{emitter::SilentEmitter, Handler};
 use rustc_errors::{
     fallback_fluent_bundle, Diagnostic, DiagnosticBuilder, DiagnosticId, DiagnosticMessage,
-    EmissionGuarantee, ErrorGuaranteed, IntoDiagnostic, MultiSpan, Noted, StashKey,
+    ErrorGuaranteed, IntoDiagnostic, MultiSpan, Noted, StashKey,
 };
 use rustc_feature::{find_feature_issue, GateIssue, UnstableFeatures};
 use rustc_span::edition::Edition;
@@ -390,13 +390,4 @@ impl ParseSess {
     pub fn struct_fatal(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, !> {
         self.span_diagnostic.struct_fatal(msg)
     }
-
-    #[rustc_lint_diagnostics]
-    #[track_caller]
-    pub fn struct_diagnostic<G: EmissionGuarantee>(
-        &self,
-        msg: impl Into<DiagnosticMessage>,
-    ) -> DiagnosticBuilder<'_, G> {
-        self.span_diagnostic.struct_diagnostic(msg)
-    }
 }

compiler/rustc_session/src/session.rs

@@ -632,7 +632,7 @@ impl Session {
     pub fn span_delayed_bug<S: Into<MultiSpan>>(
         &self,
         sp: S,
-        msg: impl Into<String>,
+        msg: impl Into<DiagnosticMessage>,
     ) -> ErrorGuaranteed {
         self.diagnostic().span_delayed_bug(sp, msg)
     }

src/tools/miri/src/diagnostics.rs

@@ -512,7 +512,7 @@ pub fn report_msg<'tcx>(
         }
     }
 
-    handler.emit_diagnostic(&mut err);
+    handler.emit_diagnostic(err);
 }
 
 impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {

src/tools/rustfmt/src/parse/session.rs

@@ -284,10 +284,8 @@ impl ParseSess {
 // Methods that should be restricted within the parse module.
 impl ParseSess {
     pub(super) fn emit_diagnostics(&self, diagnostics: Vec<Diagnostic>) {
-        for mut diagnostic in diagnostics {
-            self.parse_sess
-                .span_diagnostic
-                .emit_diagnostic(&mut diagnostic);
+        for diagnostic in diagnostics {
+            self.parse_sess.span_diagnostic.emit_diagnostic(diagnostic);
         }
     }