[clang] [Clang] Implement C++26 Attributes for Structured Bindings (P0609R3) (PR #89906)

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@@ -102,11 +102,21 @@ namespace PR33839 {
     for (auto [x] : a) { // expected-warning {{unused variable '[x]'}}
     }
   }
-  void use() { 
+  void use() {
     f<int>(); // expected-note {{instantiation of}}
     g<true>();
     g<false>();
     h<int>(); // expected-note {{instantiation of}}
   }
 }
+
+namespace maybe_unused_binding {
+
+void test() {
+  struct X { int a, b; } x;
+  auto [a [[maybe_unused]], b] = x; // expected-warning {{an attribute specifier sequence attached to a structured binding declaration is a C++2c extension}}
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yronglin wrote:

Should we add a test to check the `[[maybe_unused]]` takes effect. 
e.g. checks whether there has `warning: unused variable '[a, b]' [-Wunused-variable]`.

I've a question about this test case. We only add `[[maybe_unused]]` to `a` , IIUC, should we also emit a warning that `unused variable 'b'`?

https://github.com/llvm/llvm-project/pull/89906