[clang] [clang] Fix the local parameter of void type inside the `Requires` expression. (PR #109831)

[Younan Zhang via cfe-commits]

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@@ -9509,6 +9509,19 @@ Sema::ActOnStartRequiresExpr(SourceLocation RequiresKWLoc,
   PushDeclContext(BodyScope, Body);
 
   for (ParmVarDecl *Param : LocalParameters) {
+    if (Param->getType()->isVoidType()) {
+      if (LocalParameters.size() > 1) {
+        Diag(Param->getBeginLoc(), diag::err_void_only_param);
+        Body->setInvalidDecl();
+      } else if (Param->getIdentifier()) {
+        Diag(Param->getBeginLoc(), diag::err_param_with_void_type);
+        Body->setInvalidDecl();
+      } else if (Param->getType().hasQualifiers()) {
+        Diag(Param->getBeginLoc(), diag::err_void_param_qualified);
+        Body->setInvalidDecl();
+      }
+    }
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zyn0217 wrote:

I think the invalidity of the Decl should be used to indicate the "unsatisfied" flag such that the constant expression would result in a false value. That said, marking the parameters as invalid should also work.

Note that we don't seem ever to use the invalid flag. I think you need to examine that flag in `RequiresExpr`'s constructor.

https://github.com/llvm/llvm-project/pull/109831