[clang] [clang][Sema] Fix particular operator overload crash (PR #105976)

[Matheus Izvekov via cfe-commits]

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@@ -7425,6 +7425,13 @@ void Sema::AddMethodCandidate(DeclAccessPair FoundDecl, QualType ObjectType,
                                /*ExplicitArgs*/ nullptr, ObjectType,
                                ObjectClassification, Args, CandidateSet,
                                SuppressUserConversions, false, PO);
+  } else if (UsingDecl *UD = dyn_cast<UsingDecl>(Decl)) {
+    for (auto *Shadow : UD->shadows()) {
+      AddMethodCandidate(cast<CXXMethodDecl>(Shadow->getTargetDecl()),
+                         FoundDecl, ActingContext, ObjectType,
+                         ObjectClassification, Args, CandidateSet,
+                         SuppressUserConversions, false, std::nullopt, PO);
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mizvekov wrote:

I think this needs better investigation why that commit introduced this change.

One concerns is that the target decl could be a FunctionTemplate as well.

https://github.com/llvm/llvm-project/pull/105976