[clang] [Clang][Sema] Reject declaring an alias template with the same name as its template parameter. (PR #123533)

[Erich Keane via cfe-commits]

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@@ -13464,6 +13464,14 @@ Decl *Sema::ActOnAliasDeclaration(Scope *S, AccessSpecifier AS,
     }
     TemplateParameterList *TemplateParams = TemplateParamLists[0];
 
+    // Check shadowing of a template parameter name
+    for (NamedDecl *TP : TemplateParams->asArray()) {
+      if (NameInfo.getName() == TP->getDeclName()) {
+        DiagnoseTemplateParameterShadow(Name.StartLocation, TP);
+        return nullptr;
+      }
+    }
+
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erichkeane wrote:

That doesn't seem right... I would expect it to?  But someone probably needs to change it and see what happens, or dig through git history to see if there is justification for this.

https://github.com/llvm/llvm-project/pull/123533