[clang] [Clang] Implement CWG2496 (PR #142975)

[Aaron Ballman via cfe-commits]

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@@ -215,3 +215,32 @@ void (*q)() throw() = S();
 // since-cxx17-error at -1 {{no viable conversion from 'S' to 'void (*)() throw()'}}
 //   since-cxx17-note@#cwg2486-conv {{candidate function}}
 } // namespace cwg2486
+
+
+namespace cwg2496 { // cwg2496: 21
+#if __cplusplus >= 201102L
+struct S {
+    virtual void f(); // #cwg2496-f
+    virtual void g() &; // #cwg2496-g
+    virtual void h(); // #cwg2496-h
+    virtual void i();
+    virtual void j() &;
+    virtual void k() &&;
+};
+
+struct T : S {
+    virtual void f() &;
+    // expected-error at -1 {{cannot overload a member function with ref-qualifier '&' with a member function without a ref-qualifier}}
+    // expected-note@#cwg2496-f {{previous declaration is here}}
+    virtual void g();
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AaronBallman wrote:

I'd also like to see a case where it's declared as `&` in the base class and `&&` in the derived class.

https://github.com/llvm/llvm-project/pull/142975