[clang] [Clang] [AST] Fix placeholder return type name mangling for MSVC 1920+ / VS2019+ (PR #102848)

[NAKAMURA Takumi via cfe-commits]

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@@ -2900,17 +2958,51 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
       // can differ by their calling convention and are typically deduced.  So
       // we make sure that this type gets mangled properly.
       mangleType(ResultType, Range, QMM_Result);
-    } else if (const auto *AT = dyn_cast_or_null<AutoType>(
-                   ResultType->getContainedAutoType())) {
-      Out << '?';
-      mangleQualifiers(ResultType.getLocalQualifiers(), /*IsMember=*/false);
-      Out << '?';
+    } else if (IsInLambda) {
+      if (const auto *AT = ResultType->getContainedAutoType()) {
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chapuni wrote:

AT is used only in +Asserts

https://github.com/llvm/llvm-project/pull/102848