[clang] [Clang] disallow attributes on void parameters (PR #124920)

[Aaron Ballman via cfe-commits]

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@@ -453,3 +453,12 @@ namespace P2361 {
 }
 
 alignas(int) struct AlignAsAttribute {}; // expected-error {{misplaced attributes; expected attributes here}}
+
+namespace GH108819 {
+void a([[maybe_unused]] void) {}                 // expected-error {{an attribute list cannot appear here}} \
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AaronBallman wrote:

I think this is a confusing diagnostic -- an attribute list *can* appear here. The problem is that an attribute which appertains to a declaration cannot appertain to a void parameter. I think that should be handled in SemaDeclAttr.cpp when doing the usual appertainment checks.

https://github.com/llvm/llvm-project/pull/124920