Add EmitResult associated type to EmissionGuarantee.

This lets different error levels share the same return type from
`emit_*`.

- A lot of inconsistencies in the `DiagCtxt` API are removed.
- `Noted` is removed.
- `FatalAbort` is introduced for fatal errors (abort via `raise`),
  replacing the `EmissionGuarantee` impl for `!`.
- `Bug` is renamed `BugAbort` (to avoid clashing with `Level::Bug` and
  to mirror `FatalAbort`), and modified to work in the new way with bug
  errors (abort via panic).
- Various diagnostic creators and emitters updated to the new, better
  signatures. Note that `DiagCtxt::bug` no longer needs to call
  `panic_any`, because `emit` handles that.

Also shorten the obnoxiously long
`diagnostic_builder_emit_producing_guarantee` name.

compiler/rustc_errors/src/lib.rs

@@ -6,6 +6,7 @@
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 #![feature(array_windows)]
+#![feature(associated_type_defaults)]
 #![feature(extract_if)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
@@ -401,7 +402,7 @@ pub use diagnostic::{
     AddToDiagnostic, DecorateLint, Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId,
     DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
 };
-pub use diagnostic_builder::{DiagnosticBuilder, EmissionGuarantee, Noted};
+pub use diagnostic_builder::{BugAbort, DiagnosticBuilder, EmissionGuarantee, FatalAbort};
 pub use diagnostic_impls::{
     DiagnosticArgFromDisplay, DiagnosticSymbolList, ExpectedLifetimeParameter,
     IndicateAnonymousLifetime, InvalidFlushedDelayedDiagnosticLevel, LabelKind,
@@ -907,7 +908,7 @@ impl DiagCtxt {
         &self,
         span: impl Into<MultiSpan>,
         msg: impl Into<DiagnosticMessage>,
-    ) -> DiagnosticBuilder<'_, !> {
+    ) -> DiagnosticBuilder<'_, FatalAbort> {
         let mut result = self.struct_fatal(msg);
         result.set_span(span);
         result
@@ -921,7 +922,7 @@ impl DiagCtxt {
         span: impl Into<MultiSpan>,
         msg: impl Into<DiagnosticMessage>,
         code: DiagnosticId,
-    ) -> DiagnosticBuilder<'_, !> {
+    ) -> DiagnosticBuilder<'_, FatalAbort> {
         let mut result = self.struct_span_fatal(span, msg);
         result.code(code);
         result
@@ -930,7 +931,10 @@ impl DiagCtxt {
     /// 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<'_, !> {
+    pub fn struct_fatal(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, FatalAbort> {
         DiagnosticBuilder::new(self, Level::Fatal, msg)
     }
 
@@ -1101,8 +1105,7 @@ impl DiagCtxt {
     }
 
     pub fn bug(&self, msg: impl Into<DiagnosticMessage>) -> ! {
-        DiagnosticBuilder::<diagnostic_builder::Bug>::new(self, Bug, msg).emit();
-        panic::panic_any(ExplicitBug);
+        DiagnosticBuilder::<BugAbort>::new(self, Bug, msg).emit()
     }
 
     #[inline]
@@ -1294,37 +1297,34 @@ impl DiagCtxt {
 
     pub fn create_fatal<'a>(
         &'a self,
-        fatal: impl IntoDiagnostic<'a, !>,
-    ) -> DiagnosticBuilder<'a, !> {
+        fatal: impl IntoDiagnostic<'a, FatalAbort>,
+    ) -> DiagnosticBuilder<'a, FatalAbort> {
         fatal.into_diagnostic(self, Level::Fatal)
     }
 
-    pub fn emit_fatal<'a>(&'a self, fatal: impl IntoDiagnostic<'a, !>) -> ! {
+    pub fn emit_fatal<'a>(&'a self, fatal: impl IntoDiagnostic<'a, FatalAbort>) -> ! {
         self.create_fatal(fatal).emit()
     }
 
     pub fn create_bug<'a>(
         &'a self,
-        bug: impl IntoDiagnostic<'a, diagnostic_builder::Bug>,
-    ) -> DiagnosticBuilder<'a, diagnostic_builder::Bug> {
+        bug: impl IntoDiagnostic<'a, BugAbort>,
+    ) -> DiagnosticBuilder<'a, BugAbort> {
         bug.into_diagnostic(self, Level::Bug)
     }
 
-    pub fn emit_bug<'a>(
-        &'a self,
-        bug: impl IntoDiagnostic<'a, diagnostic_builder::Bug>,
-    ) -> diagnostic_builder::Bug {
+    pub fn emit_bug<'a>(&'a self, bug: impl IntoDiagnostic<'a, BugAbort>) -> ! {
         self.create_bug(bug).emit()
     }
 
-    pub fn emit_note<'a>(&'a self, note: impl IntoDiagnostic<'a, Noted>) -> Noted {
+    pub fn emit_note<'a>(&'a self, note: impl IntoDiagnostic<'a, ()>) {
         self.create_note(note).emit()
     }
 
     pub fn create_note<'a>(
         &'a self,
-        note: impl IntoDiagnostic<'a, Noted>,
-    ) -> DiagnosticBuilder<'a, Noted> {
+        note: impl IntoDiagnostic<'a, ()>,
+    ) -> DiagnosticBuilder<'a, ()> {
         note.into_diagnostic(self, Level::Note)
     }