[clang] [clang][Diagnostic] Clarify error message for auto (PR #149781)

[Emily Dror via cfe-commits]

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@@ -8237,12 +8237,24 @@ Sema::CheckTemplateDeclScope(Scope *S, TemplateParameterList *TemplateParams) {
     if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Ctx)) {
       // C++ [temp.mem]p2:
       //   A local class shall not have member templates.
-      if (RD->isLocalClass())
-        return Diag(TemplateParams->getTemplateLoc(),
-                    diag::err_template_inside_local_class)
-          << TemplateParams->getSourceRange();
-      else
-        return false;
+      if (RD->isLocalClass()) {
+        SourceLocation DiagLoc = TemplateParams->getTemplateLoc();
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emily-dror wrote:

Good catch, thanks for the review. Would you direct me to the documentation for writing test cases? 
> Also: we need a test for this. A simple reproducer that uses //expected-error lines that point to a line instead of 'in general' i think will work.

https://github.com/llvm/llvm-project/pull/149781