Rollup of 9 pull requests

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -362,6 +362,19 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         }
     }
 
+    fn visit_generic_args(&mut self, args: &'a ast::GenericArgs) {
+        // This check needs to happen here because the never type can be returned from a function,
+        // but cannot be used in any other context. If this check was in `visit_fn_ret_ty`, it
+        // include both functions and generics like `impl Fn() -> !`.
+        if let ast::GenericArgs::Parenthesized(generic_args) = args
+            && let ast::FnRetTy::Ty(ref ty) = generic_args.output
+            && matches!(ty.kind, ast::TyKind::Never)
+        {
+            gate!(&self, never_type, ty.span, "the `!` type is experimental");
+        }
+        visit::walk_generic_args(self, args);
+    }
+
     fn visit_expr(&mut self, e: &'a ast::Expr) {
         match e.kind {
             ast::ExprKind::TryBlock(_) => {

compiler/rustc_error_codes/src/error_codes/E0091.md

@@ -1,11 +1,11 @@
-An unnecessary type or const parameter was given in a type alias.
+An unnecessary type parameter was given in a type alias.
 
 Erroneous code example:
 
 ```compile_fail,E0091
-type Foo<T> = u32; // error: type parameter `T` is unused
+type Foo<T> = u32; // error: type parameter `T` is never used
 // or:
-type Foo<A,B> = Box<A>; // error: type parameter `B` is unused
+type Foo<A, B> = Box<A>; // error: type parameter `B` is never used
 ```
 
 Please check you didn't write too many parameters. Example:

compiler/rustc_error_messages/src/lib.rs

@@ -378,7 +378,7 @@ impl From<Cow<'static, str>> for DiagnosticMessage {
     }
 }
 
-/// A workaround for "good path" ICEs when formatting types in disabled lints.
+/// A workaround for good_path_delayed_bug ICEs when formatting types in disabled lints.
 ///
 /// Delays formatting until `.into(): DiagnosticMessage` is used.
 pub struct DelayDm<F>(pub F);

compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs

@@ -85,7 +85,11 @@ fn source_string(file: Lrc<SourceFile>, line: &Line) -> String {
 /// Maps `Diagnostic::Level` to `snippet::AnnotationType`
 fn annotation_type_for_level(level: Level) -> AnnotationType {
     match level {
-        Level::Bug | Level::DelayedBug(_) | Level::Fatal | Level::Error => AnnotationType::Error,
+        Level::Bug
+        | Level::Fatal
+        | Level::Error
+        | Level::DelayedBug
+        | Level::GoodPathDelayedBug => AnnotationType::Error,
         Level::ForceWarning(_) | Level::Warning => AnnotationType::Warning,
         Level::Note | Level::OnceNote => AnnotationType::Note,
         Level::Help | Level::OnceHelp => AnnotationType::Help,

compiler/rustc_errors/src/diagnostic.rs

@@ -1,8 +1,7 @@
 use crate::snippet::Style;
 use crate::{
-    CodeSuggestion, DelayedBugKind, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee,
-    ErrCode, Level, MultiSpan, SubdiagnosticMessage, Substitution, SubstitutionPart,
-    SuggestionStyle,
+    CodeSuggestion, DiagnosticBuilder, DiagnosticMessage, EmissionGuarantee, ErrCode, Level,
+    MultiSpan, SubdiagnosticMessage, Substitution, SubstitutionPart, SuggestionStyle,
 };
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_error_messages::fluent_value_from_str_list_sep_by_and;
@@ -233,19 +232,16 @@ impl Diagnostic {
 
     pub fn is_error(&self) -> bool {
         match self.level {
-            Level::Bug
-            | Level::DelayedBug(DelayedBugKind::Normal)
-            | Level::Fatal
-            | Level::Error
-            | Level::FailureNote => true,
+            Level::Bug | Level::Fatal | Level::Error | Level::DelayedBug => true,
 
-            Level::ForceWarning(_)
+            Level::GoodPathDelayedBug
+            | Level::ForceWarning(_)
             | Level::Warning
-            | Level::DelayedBug(DelayedBugKind::GoodPath)
             | Level::Note
             | Level::OnceNote
             | Level::Help
             | Level::OnceHelp
+            | Level::FailureNote
             | Level::Allow
             | Level::Expect(_) => false,
         }
@@ -304,11 +300,11 @@ impl Diagnostic {
     #[track_caller]
     pub fn downgrade_to_delayed_bug(&mut self) {
         assert!(
-            self.is_error(),
+            matches!(self.level, Level::Error | Level::DelayedBug),
             "downgrade_to_delayed_bug: cannot downgrade {:?} to DelayedBug: not an error",
             self.level
         );
-        self.level = Level::DelayedBug(DelayedBugKind::Normal);
+        self.level = Level::DelayedBug;
     }
 
     /// Appends a labeled span to the diagnostic.

compiler/rustc_errors/src/emitter.rs

@@ -2118,6 +2118,7 @@ impl HumanEmitter {
                 }
                 if !self.short_message {
                     for child in children {
+                        assert!(child.level.can_be_top_or_sub().1);
                         let span = &child.span;
                         if let Err(err) = self.emit_messages_default_inner(
                             span,