[clang] [ASTImporter] Fix infinite recurse on return type declared inside body (#68775) (PR #89096)

[Ding Fei via cfe-commits]

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@@ -3647,15 +3647,28 @@ class IsTypeDeclaredInsideVisitor
 };
 } // namespace
 
-/// This function checks if the function has 'auto' return type that contains
+/// This function checks if the given function has a return type that contains
 /// a reference (in any way) to a declaration inside the same function.
-bool ASTNodeImporter::hasAutoReturnTypeDeclaredInside(FunctionDecl *D) {
+bool ASTNodeImporter::hasReturnTypeDeclaredInside(FunctionDecl *D) {
   QualType FromTy = D->getType();
   const auto *FromFPT = FromTy->getAs<FunctionProtoType>();
   assert(FromFPT && "Must be called on FunctionProtoType");
 
+  auto IsCXX11LambdaWithouTrailingReturn = [&]() {
+    if (!Importer.FromContext.getLangOpts().CPlusPlus11)
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danix800 wrote:

These `CPlusPlus` / `CPlusPlus11` / `CPlusPlus14` options are really misleading if no comments explaining how they works. Thanks for pointing this out!

https://github.com/llvm/llvm-project/pull/89096