[clang] [Clang] Fix crash on template-specialization (PR #142338)

[Mark de Wever via cfe-commits]

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@@ -5120,6 +5121,10 @@ bool Sema::addInstantiatedParametersToScope(
       // Simple case: not a parameter pack.
       assert(FParamIdx < Function->getNumParams());
       ParmVarDecl *FunctionParam = Function->getParamDecl(FParamIdx);
+      DeclarationName name = FunctionParam->getDeclName();
+      auto _ = llvm::make_scope_exit([&]() {
+        FunctionParam->setDeclName(name);
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mark-de-wever-sonarsource wrote:

This approach is based on what Richard suggested in https://github.com/llvm/llvm-project/issues/54279#issuecomment-2623325977 " for example, we need to set the name back when we're done with it.".

The crash is caused due to another scope-exit. In that scope a `FETokenInfo` "attached" to the name of the function argument. This function is unaware of that scope so the "rename" is unknown to that scope and at that scope's scope-exit the information "attached" to the current name (_not_ the original name) is removed. This is where an assertion triggers.

So this change basically restores the original name so the other scope-exit will "detach" the `FETokenInfo` using the original name and the crash is resolved.

https://github.com/llvm/llvm-project/pull/142338