[clang] [Clang][Sema] Diagnose use of template keyword after declarative nested-name-specifiers (PR #78595)

[Krystian Stasiowski via cfe-commits]

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@@ -182,8 +182,8 @@ struct Bad2 { int a, b; };
 } // namespace dr2386
 namespace std {
 template <typename T> struct tuple_size;
-template <> struct std::tuple_size<dr2386::Bad1> {};
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sdkrystian wrote:

@Endilll if left unchanged this will result in a warning about redundant qualification, which I don't think is the point of the test... alternatively I can add `// expected-warning {{extra qualification on member}}`

https://github.com/llvm/llvm-project/pull/78595