hir-analysis: make where-clause-on-main diagnostic translatable

compiler/rustc_hir_analysis/locales/en-US.ftl

@@ -127,5 +127,8 @@ hir_analysis_auto_deref_reached_recursion_limit = reached the recursion limit wh
     .label = deref recursion limit reached
     .help = consider increasing the recursion limit by adding a `#![recursion_limit = "{$suggested_limit}"]` attribute to your crate (`{$crate_name}`)
 
+hir_analysis_where_clause_on_main = `main` function is not allowed to have a `where` clause
+    .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]`

compiler/rustc_hir_analysis/src/errors.rs

@@ -316,6 +316,15 @@ pub struct AutoDerefReachedRecursionLimit<'a> {
     pub crate_name: Symbol,
 }
 
+#[derive(Diagnostic)]
+#[diag(hir_analysis_where_clause_on_main, code = "E0646")]
+pub(crate) struct WhereClauseOnMain {
+    #[primary_span]
+    pub span: Span,
+    #[label]
+    pub generics_span: Option<Span>,
+}
+
 #[derive(Diagnostic)]
 #[diag(hir_analysis_track_caller_on_main)]
 pub(crate) struct TrackCallerOnMain {

compiler/rustc_hir_analysis/src/lib.rs

@@ -271,16 +271,10 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
     } else if !main_fn_predicates.predicates.is_empty() {
         // generics may bring in implicit predicates, so we skip this check if generics is present.
         let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
-        let mut diag = struct_span_err!(
-            tcx.sess,
-            generics_where_clauses_span.unwrap_or(main_span),
-            E0646,
-            "`main` function is not allowed to have a `where` clause"
-        );
-        if let Some(generics_where_clauses_span) = generics_where_clauses_span {
-            diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
-        }
-        diag.emit();
+        tcx.sess.emit_err(errors::WhereClauseOnMain {
+            span: generics_where_clauses_span.unwrap_or(main_span),
+            generics_span: generics_where_clauses_span,
+        });
         error = true;
     }