hir-analysis: make a helpful note

Author: tshepang

compiler/rustc_hir_analysis/locales/en-US.ftl

@@ -131,7 +131,7 @@ hir_analysis_where_clause_on_main = `main` function is not allowed to have a `wh
     .label = `main` cannot have a `where` clause
 
 hir_analysis_track_caller_on_main = `main` function is not allowed to be `#[track_caller]`
-    .label = `main` function is not allowed to be `#[track_caller]`
+    .suggestion = remove this annotation
 
 hir_analysis_start_not_track_caller = `start` is not allowed to be `#[track_caller]`
     .label = `start` is not allowed to be `#[track_caller]`

compiler/rustc_hir_analysis/src/errors.rs

@@ -329,8 +329,9 @@ pub(crate) struct WhereClauseOnMain {
 #[diag(hir_analysis_track_caller_on_main)]
 pub(crate) struct TrackCallerOnMain {
     #[primary_span]
+    #[suggestion(applicability = "maybe-incorrect", code = "")]
     pub span: Span,
-    #[label]
+    #[label(hir_analysis_track_caller_on_main)]
     pub annotated: Span,
 }
 

tests/ui/rfc-2091-track-caller/error-with-main.stderr

@@ -2,7 +2,7 @@ error: `main` function is not allowed to be `#[track_caller]`
   --> $DIR/error-with-main.rs:1:1
    |
 LL | #[track_caller]
-   | ^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^ help: remove this annotation
 LL | fn main() {
    | --------- `main` function is not allowed to be `#[track_caller]`