[clang] [CONCEPTS]Corrected comparison of constraints with out of line CTD (PR #69244)

[Mariya Podchishchaeva via cfe-commits]

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@@ -346,6 +351,11 @@ MultiLevelTemplateArgumentList Sema::getTemplateInstantiationArgs(
     CurDecl = Response::UseNextDecl(ND).NextDecl;
   }
 
+  if (!ND) {
+    assert(DC);
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Fznamznon wrote:

Does this assertion makes sense? If `ND` and `DC` both were null, the first assertion in this function would have failed already.

https://github.com/llvm/llvm-project/pull/69244