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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (c8ef)

<details>
<summary>Changes</summary>

Fixes #<!-- -->109538.

In this patch, we introduce diagnostic for required expression parameters in the same way as function parameters, fix the issue of handling void type parameters, and align the behavior with GCC and other compilers.

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


2 Files Affected:

- (modified) clang/lib/Sema/SemaExprCXX.cpp (+13) 
- (added) clang/test/SemaCXX/invalid-requirement-requires-parameter.cpp (+15) 


``````````diff
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index ac3fe6ab8f9bd0..d0914d990be6a7 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -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();
+      }
+    }
+
     if (Param->hasDefaultArg())
       // C++2a [expr.prim.req] p4
       //     [...] A local parameter of a requires-expression shall not have a
diff --git a/clang/test/SemaCXX/invalid-requirement-requires-parameter.cpp b/clang/test/SemaCXX/invalid-requirement-requires-parameter.cpp
new file mode 100644
index 00000000000000..01aa0ca4d229b5
--- /dev/null
+++ b/clang/test/SemaCXX/invalid-requirement-requires-parameter.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang -fsyntax-only -std=c++2a -Xclang -verify %s
+
+namespace GH109538 {
+static_assert(requires(void *t) { t; });
+static_assert(requires(void) { 42; });
+static_assert(requires(void t) { // expected-error {{argument may not have 'void' type}}
+  t;
+});
+static_assert(requires(void t, int a) {  // expected-error {{'void' must be the first and only parameter if specified}}
+  t;
+});
+static_assert(requires(const void) { // expected-error {{'void' as parameter must not have type qualifiers}}
+  42;
+});
+} // namespace GH109538

``````````

</details>


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