[clang] [clang] Exclude non-template classes when checking if constraint refers to containing template arguments (PR #74265)

[via cfe-commits]

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@@ -1714,6 +1714,8 @@ class ConstraintRefersToContainingTemplateChecker
   // Friend, likely because it was referred to without its template arguments.
   void CheckIfContainingRecord(const CXXRecordDecl *CheckingRD) {
     CheckingRD = CheckingRD->getMostRecentDecl();
+    if (!CheckingRD->isTemplated())
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antangelo wrote:

What do you think about this example, which exercises this issue in the above case? https://godbolt.org/z/Yz1WEqM7M

If I switch from `isTemplated()` to `getDescribedTemplate()` to only check `CheckingRD` itself, then clang will accept that code. Otherwise, as the patch is now, the example is rejected. What should be the correct behavior?

https://github.com/llvm/llvm-project/pull/74265