Fix diagnostic for qualifier in extern block

Closes: rust-lang#123306

compiler/rustc_ast/src/ast.rs

@@ -2483,6 +2483,14 @@ pub enum CoroutineKind {
 }
 
 impl CoroutineKind {
+    pub fn span(self) -> Span {
+        match self {
+            CoroutineKind::Async { span, .. } => span,
+            CoroutineKind::Gen { span, .. } => span,
+            CoroutineKind::AsyncGen { span, .. } => span,
+        }
+    }
+
     pub fn is_async(self) -> bool {
         matches!(self, CoroutineKind::Async { .. })
     }

compiler/rustc_ast_passes/messages.ftl

@@ -68,7 +68,7 @@ ast_passes_extern_block_suggestion = if you meant to declare an externally defin
 
 ast_passes_extern_fn_qualifiers = functions in `extern` blocks cannot have qualifiers
     .label = in this `extern` block
-    .suggestion = remove the qualifiers
+    .suggestion = remove this qualifier
 
 ast_passes_extern_item_ascii = items in `extern` blocks cannot use non-ascii identifiers
     .label = in this `extern` block

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -514,13 +514,49 @@ impl<'a> AstValidator<'a> {
     }
 
     /// An `fn` in `extern { ... }` cannot have qualifiers, e.g. `async fn`.
-    fn check_foreign_fn_headerless(&self, ident: Ident, span: Span, header: FnHeader) {
-        if header.has_qualifiers() {
-            self.dcx().emit_err(errors::FnQualifierInExtern {
-                span: ident.span,
-                block: self.current_extern_span(),
-                sugg_span: span.until(ident.span.shrink_to_lo()),
-            });
+    fn check_foreign_fn_headerless(&self, header: FnHeader) {
+        let FnHeader { unsafety, coroutine_kind, constness, ext } = header;
+        match unsafety {
+            Unsafe::Yes(span) => {
+                self.dcx().emit_err(errors::FnQualifierInExtern {
+                    span: span,
+                    block: self.current_extern_span(),
+                });
+            }
+            Unsafe::No => (),
+        }
+        match coroutine_kind {
+            Some(knd) => {
+                self.dcx().emit_err(errors::FnQualifierInExtern {
+                    span: knd.span(),
+                    block: self.current_extern_span(),
+                });
+            }
+            None => (),
+        }
+        match constness {
+            Const::Yes(span) => {
+                self.dcx().emit_err(errors::FnQualifierInExtern {
+                    span,
+                    block: self.current_extern_span(),
+                });
+            }
+            Const::No => (),
+        }
+        match ext {
+            Extern::None => (),
+            Extern::Implicit(span) => {
+                self.dcx().emit_err(errors::FnQualifierInExtern {
+                    span,
+                    block: self.current_extern_span(),
+                });
+            }
+            Extern::Explicit(_, span) => {
+                self.dcx().emit_err(errors::FnQualifierInExtern {
+                    span,
+                    block: self.current_extern_span(),
+                });
+            }
         }
     }
 
@@ -1145,7 +1181,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             ForeignItemKind::Fn(box Fn { defaultness, sig, body, .. }) => {
                 self.check_defaultness(fi.span, *defaultness);
                 self.check_foreign_fn_bodyless(fi.ident, body.as_deref());
-                self.check_foreign_fn_headerless(fi.ident, fi.span, sig.header);
+                self.check_foreign_fn_headerless(sig.header);
                 self.check_foreign_item_ascii_only(fi.ident);
             }
             ForeignItemKind::TyAlias(box TyAlias {

compiler/rustc_ast_passes/src/errors.rs

@@ -266,15 +266,14 @@ pub struct FnBodyInExtern {
     pub block: Span,
 }
 
-#[derive(Diagnostic)]
+#[derive(Diagnostic, Debug)]
 #[diag(ast_passes_extern_fn_qualifiers)]
 pub struct FnQualifierInExtern {
     #[primary_span]
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
     pub span: Span,
     #[label]
     pub block: Span,
-    #[suggestion(code = "fn ", applicability = "maybe-incorrect", style = "verbose")]
-    pub sugg_span: Span,
 }
 
 #[derive(Diagnostic)]

tests/ui/extern/extern-headerless.rs

@@ -0,0 +1,20 @@
+//@ edition:2018
+
+extern "C" {
+    const fn a();
+    //~^ ERROR functions in `extern` blocks cannot have qualifiers
+
+    unsafe fn b();
+    //~^ ERROR functions in `extern` blocks cannot have qualifiers
+
+    async fn c();
+    //~^ ERROR functions in `extern` blocks cannot have qualifiers
+
+    extern fn d();
+    //~^ ERROR functions in `extern` blocks cannot have qualifiers
+
+    extern "C" fn e();
+    //~^ ERROR functions in `extern` blocks cannot have qualifiers
+}
+
+pub fn main() {}

tests/ui/extern/extern-headerless.stderr

@@ -0,0 +1,46 @@
+error: functions in `extern` blocks cannot have qualifiers
+  --> $DIR/extern-headerless.rs:4:5
+   |
+LL | extern "C" {
+   | ---------- in this `extern` block
+LL |     const fn a();
+   |     ^^^^^ help: remove this qualifier
+
+error: functions in `extern` blocks cannot have qualifiers
+  --> $DIR/extern-headerless.rs:7:5
+   |
+LL | extern "C" {
+   | ---------- in this `extern` block
+...
+LL |     unsafe fn b();
+   |     ^^^^^^ help: remove this qualifier
+
+error: functions in `extern` blocks cannot have qualifiers
+  --> $DIR/extern-headerless.rs:10:5
+   |
+LL | extern "C" {
+   | ---------- in this `extern` block
+...
+LL |     async fn c();
+   |     ^^^^^ help: remove this qualifier
+
+error: functions in `extern` blocks cannot have qualifiers
+  --> $DIR/extern-headerless.rs:13:5
+   |
+LL | extern "C" {
+   | ---------- in this `extern` block
+...
+LL |     extern fn d();
+   |     ^^^^^^ help: remove this qualifier
+
+error: functions in `extern` blocks cannot have qualifiers
+  --> $DIR/extern-headerless.rs:16:5
+   |
+LL | extern "C" {
+   | ---------- in this `extern` block
+...
+LL |     extern "C" fn e();
+   |     ^^^^^^^^^^ help: remove this qualifier
+
+error: aborting due to 5 previous errors
+

tests/ui/extern/issue-95829.stderr

@@ -16,17 +16,12 @@ LL | |     }
    = note: for more information, visit https://doc.rust-lang.org/std/keyword.extern.html
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/issue-95829.rs:4:14
+  --> $DIR/issue-95829.rs:4:5
    |
 LL | extern {
    | ------ in this `extern` block
 LL |     async fn L() {
-   |              ^
-   |
-help: remove the qualifiers
-   |
-LL |     fn L() {
-   |     ~~
+   |     ^^^^^ help: remove this qualifier
 
 error: aborting due to 2 previous errors
 

tests/ui/parser/no-const-fn-in-extern-block.stderr

@@ -1,29 +1,28 @@
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/no-const-fn-in-extern-block.rs:2:14
+  --> $DIR/no-const-fn-in-extern-block.rs:2:5
    |
 LL | extern "C" {
    | ---------- in this `extern` block
 LL |     const fn foo();
-   |              ^^^
-   |
-help: remove the qualifiers
-   |
-LL |     fn foo();
-   |     ~~
+   |     ^^^^^ help: remove this qualifier
 
 error: functions in `extern` blocks cannot have qualifiers
-  --> $DIR/no-const-fn-in-extern-block.rs:4:21
+  --> $DIR/no-const-fn-in-extern-block.rs:4:11
    |
 LL | extern "C" {
    | ---------- in this `extern` block
 ...
 LL |     const unsafe fn bar();
-   |                     ^^^
-   |
-help: remove the qualifiers
+   |           ^^^^^^ help: remove this qualifier
+
+error: functions in `extern` blocks cannot have qualifiers
+  --> $DIR/no-const-fn-in-extern-block.rs:4:5
    |
-LL |     fn bar();
-   |     ~~
+LL | extern "C" {
+   | ---------- in this `extern` block
+...
+LL |     const unsafe fn bar();
+   |     ^^^^^ help: remove this qualifier
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors