[Clang] disallow attributes on void parameters

clang/docs/ReleaseNotes.rst

@@ -107,6 +107,8 @@ Removed Compiler Flags
 Attribute Changes in Clang
 --------------------------
 
+- Clang now disallows the use of attributes on void parameters. (#GH108819)
+
 Improvements to Clang's diagnostics
 -----------------------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3830,6 +3830,8 @@ def warn_type_attribute_wrong_type : Warning<
   "'%0' only applies to %select{function|pointer|"
   "Objective-C object or block pointer}1 types; type here is %2">,
   InGroup<IgnoredAttributes>;
+def warn_attribute_on_void_param: Warning<
+  "attribute %0 cannot be applied to a 'void' parameter">, InGroup<IgnoredAttributes>;
 def err_type_attribute_wrong_type : Error<
   warn_type_attribute_wrong_type.Summary>;
 def warn_incomplete_encoded_type : Warning<

clang/lib/Sema/SemaDecl.cpp

@@ -10326,6 +10326,15 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
       }
     }
 
+    if (FTIHasSingleVoidParameter(FTI)) {
+      ParmVarDecl *Param = cast<ParmVarDecl>(FTI.Params[0].Param);
+      if (Param->hasAttrs()) {
+        for (const auto *A : Param->attrs())
+          Diag(A->getLoc(), diag::warn_attribute_on_void_param)
+              << A << A->getRange();
+      }
+    }
+
     if (!getLangOpts().CPlusPlus) {
       // In C, find all the tag declarations from the prototype and move them
       // into the function DeclContext. Remove them from the surrounding tag

clang/test/Misc/pragma-attribute-strict-subjects.c

@@ -50,8 +50,8 @@ struct testRecoverStrictnessStruct { };
 
 #pragma clang attribute pop
 
-#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(function, record(unless(is_union)), variable, enum))
-// expected-error@-1 {{attribute 'abi_tag' cannot be applied to 'enum'}}
+#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(function, record(unless(is_union)), variable, enum)) // expected-warning {{attribute 'abi_tag' cannot be applied to a 'void' parameter}}
+                                                                                                                                 // expected-error@-1 {{attribute 'abi_tag' cannot be applied to 'enum'}}
 
 int testRecoverExtraVar = 0;
 // CHECK-LABEL: VarDecl{{.*}} testRecoverExtraVar
@@ -90,7 +90,7 @@ struct testSubset1Struct { };
 
 #pragma clang attribute pop
 
-#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = variable)
+#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = variable) // expected-warning {{attribute 'abi_tag' cannot be applied to a 'void' parameter}}
 
 int testSubset2Var;
 // CHECK-LABEL: VarDecl{{.*}} testSubset2Var
@@ -122,7 +122,7 @@ struct testSubset3Struct { };
 
 #pragma clang attribute pop
 
-#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(function, variable))
+#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(function, variable)) // expected-warning {{attribute 'abi_tag' cannot be applied to a 'void' parameter}}
 
 int testSubset4Var;
 // CHECK-LABEL: VarDecl{{.*}} testSubset4Var
@@ -138,7 +138,7 @@ struct testSubset4Struct { };
 
 #pragma clang attribute pop
 
-#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(variable, record(unless(is_union))))
+#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(variable, record(unless(is_union)))) // expected-warning {{attribute 'abi_tag' cannot be applied to a 'void' parameter}}
 
 int testSubset5Var;
 // CHECK-LABEL: VarDecl{{.*}} testSubset5Var
@@ -170,7 +170,7 @@ struct testSubset6Struct { };
 
 #pragma clang attribute pop
 
-#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(record(unless(is_union)), function, variable))
+#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(record(unless(is_union)), function, variable)) // expected-warning {{attribute 'abi_tag' cannot be applied to a 'void' parameter}}
 
 int testSubset7Var;
 // CHECK-LABEL: VarDecl{{.*}} testSubset7Var
@@ -187,8 +187,8 @@ struct testSubset7Struct { };
 #pragma clang attribute pop
 
 
-#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(record(unless(is_union)), function, variable, enum, enum_constant))
-// expected-error@-1 {{attribute 'abi_tag' cannot be applied to 'enum_constant', and 'enum'}}
+#pragma clang attribute push (__attribute__((abi_tag("a"))), apply_to = any(record(unless(is_union)), function, variable, enum, enum_constant)) // expected-warning {{attribute 'abi_tag' cannot be applied to a 'void' parameter}}
+                                                                                                                                                // expected-error@-1 {{attribute 'abi_tag' cannot be applied to 'enum_constant', and 'enum'}}
 
 int testSubsetRecoverVar;
 // CHECK-LABEL: VarDecl{{.*}} testSubsetRecoverVar

clang/test/SemaCXX/attr-cxx0x.cpp

@@ -53,3 +53,14 @@ alignas(4) auto PR19252 = 0;
 
 // Check the diagnostic message
 class alignas(void) AlignasVoid {}; // expected-error {{invalid application of 'alignas' to an incomplete type 'void'}}
+
+namespace GH108819 {
+void a([[maybe_unused]] void) {}                 // expected-warning {{attribute 'maybe_unused' cannot be applied to a 'void' parameter}}\
+                                                 // expected-warning {{use of the 'maybe_unused' attribute is a C++17 extension}}
+void b([[deprecated, maybe_unused]] void) {}     // expected-warning {{attribute 'deprecated' cannot be applied to a 'void' parameter}} \
+                                                 // expected-warning {{attribute 'maybe_unused' cannot be applied to a 'void' parameter}} \
+                                                 // expected-warning {{use of the 'deprecated' attribute is a C++14 extension}} \
+                                                 // expected-warning {{use of the 'maybe_unused' attribute is a C++17 extension}}
+void c([[clang::lifetimebound]] void) {}         // expected-warning {{attribute 'lifetimebound' cannot be applied to a 'void' parameter}}
+void d([[clang::annotate("a", "b", 1)]] void) {} // expected-warning {{attribute 'annotate' cannot be applied to a 'void' parameter}}
+}