Add a label to point to the lacking macro name definition

Author: linyihai

compiler/rustc_resolve/src/diagnostics.rs

@@ -1439,7 +1439,11 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         );
 
         if macro_kind == MacroKind::Bang && ident.name == sym::macro_rules {
-            err.subdiagnostic(MaybeMissingMacroRulesName { span: ident.span });
+            let primary_span = ident.span;
+            let label_span = primary_span.with_hi(primary_span.hi() + BytePos(1)).shrink_to_hi();
+            let mut spans = MultiSpan::from_span(label_span);
+            spans.push_span_label(label_span, "put a macro name here");
+            err.subdiagnostic(MaybeMissingMacroRulesName { spans: spans });
             return;
         }
 

compiler/rustc_resolve/src/errors.rs

@@ -667,7 +667,7 @@ pub(crate) struct MacroSuggMovePosition {
 #[note(resolve_missing_macro_rules_name)]
 pub(crate) struct MaybeMissingMacroRulesName {
     #[primary_span]
-    pub(crate) span: Span,
+    pub(crate) spans: MultiSpan,
 }
 
 #[derive(Subdiagnostic)]

tests/ui/macros/issue-118786.rs

@@ -7,6 +7,7 @@ macro_rules! make_macro {
         macro_rules! $macro_name {
         //~^ ERROR macro expansion ignores token `{` and any following
         //~| ERROR cannot find macro `macro_rules` in this scope
+        //~| put a macro name here
             () => {}
         }
     }

tests/ui/macros/issue-118786.stderr

@@ -1,5 +1,5 @@
 error: macros that expand to items must be delimited with braces or followed by a semicolon
-  --> $DIR/issue-118786.rs:15:13
+  --> $DIR/issue-118786.rs:16:13
    |
 LL | make_macro!((meow));
    |             ^^^^^^
@@ -34,10 +34,10 @@ LL | make_macro!((meow));
    | ------------------- in this macro invocation
    |
 note: maybe you have forgotten to define a name for this `macro_rules!`
-  --> $DIR/issue-118786.rs:7:9
+  --> $DIR/issue-118786.rs:7:21
    |
 LL |         macro_rules! $macro_name {
-   |         ^^^^^^^^^^^
+   |                     ^ put a macro name here
 ...
 LL | make_macro!((meow));
    | ------------------- in this macro invocation

tests/ui/resolve/issue-118295.rs

@@ -1,5 +1,6 @@
 macro_rules! {}
 //~^ ERROR cannot find macro `macro_rules` in this scope
 //~| NOTE maybe you have forgotten to define a name for this `macro_rules!`
+//~| put a macro name here
 
 fn main() {}

tests/ui/resolve/issue-118295.stderr

@@ -5,10 +5,10 @@ LL | macro_rules! {}
    | ^^^^^^^^^^^
    |
 note: maybe you have forgotten to define a name for this `macro_rules!`
-  --> $DIR/issue-118295.rs:1:1
+  --> $DIR/issue-118295.rs:1:13
    |
 LL | macro_rules! {}
-   | ^^^^^^^^^^^
+   |             ^ put a macro name here
 
 error: aborting due to 1 previous error