[clang] [clang] Reject 'auto' storage class with type specifier in C++ (PR #166004)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++14 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++17 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++23 %s
+
+// Test that 'auto' cannot be combined with a type specifier in C++.
+void f() {
+  auto int x = 1;        // expected-error {{'auto' cannot be combined with a type specifier}}
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AaronBallman wrote:

What kind of test failures are you seeing, exactly? 

Btw, I think it should be `TryAnnotateTypeOrScopeToken(AllowImplicitTypename)` instead of `()`; that's an optional parameter, but one that is relevant to `ParseDeclarationSpecifiers()`.

Do we maybe also need to do `TryAnnotateTypeConstraint()` as well?

CC @erichkeane @mizvekov 

https://github.com/llvm/llvm-project/pull/166004