[Sema] fix false -Wcomma being emitted from void returning functions

Fixes https://github.com/llvm/llvm-project/issues/57151

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D131892

clang/docs/ReleaseNotes.rst

@@ -73,7 +73,8 @@ Bug Fixes
   number of arguments cause an assertion fault.
 - Fix multi-level pack expansion of undeclared function parameters.
   This fixes `Issue 56094 <https://github.com/llvm/llvm-project/issues/56094>`_.
-
+- Fix `#57151 <https://github.com/llvm/llvm-project/issues/57151>`_.
+  ``-Wcomma`` is emitted for void returning functions.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaExpr.cpp

@@ -13957,8 +13957,10 @@ QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
   return getLangOpts().CPlusPlus ? LHSType : LHSType.getAtomicUnqualifiedType();
 }
 
-// Only ignore explicit casts to void.
-static bool IgnoreCommaOperand(const Expr *E) {
+// Scenarios to ignore if expression E is:
+// 1. an explicit cast expression into void
+// 2. a function call expression that returns void
+static bool IgnoreCommaOperand(const Expr *E, const ASTContext &Context) {
   E = E->IgnoreParens();
 
   if (const CastExpr *CE = dyn_cast<CastExpr>(E)) {
@@ -13973,6 +13975,8 @@ static bool IgnoreCommaOperand(const Expr *E) {
     }
   }
 
+  if (const auto *CE = dyn_cast<CallExpr>(E))
+    return CE->getCallReturnType(Context)->isVoidType();
   return false;
 }
 
@@ -14014,7 +14018,7 @@ void Sema::DiagnoseCommaOperator(const Expr *LHS, SourceLocation Loc) {
   }
 
   // Only allow some expressions on LHS to not warn.
-  if (IgnoreCommaOperand(LHS))
+  if (IgnoreCommaOperand(LHS, Context))
     return;
 
   Diag(Loc, diag::warn_comma_operator);

clang/test/SemaCXX/warn-comma-operator.cpp

@@ -140,6 +140,27 @@ void test_nested_fixits(void) {
   // CHECK: fix-it:{{.*}}:{[[@LINE-8]]:46-[[@LINE-8]]:46}:")"
 }
 
+
+void void_func();
+int int_func() { return 0; }
+
+void void_function_comma(){
+  void_func(), int_func(); // expected no -Wcomma because of the returning type `void` 
+  // Reported by https://github.com/llvm/llvm-project/issues/57151
+  // Descriptions about -Wcomma: https://reviews.llvm.org/D3976
+}
+
+typedef void Void;
+Void typedef_func();
+
+void whatever() {
+  // We don't get confused about type aliases.
+  typedef_func(), int_func();
+  // Even function pointers don't confuse us.
+  void (*fp)() = void_func;
+  fp(), int_func();
+}
+
 #ifdef __cplusplus
 class S2 {
 public:
@@ -296,4 +317,23 @@ void test_dependent_cast() {
   (void)T{}, 0;
   static_cast<void>(T{}), 0;
 }
+
+namespace {
+
+// issue #57151
+
+struct S {
+  void mem() {}
+};
+
+void whatever() {
+  struct S s;
+  // Member function calls also work as expected.
+  s.mem(), int_func();
+  // As do lambda calls.
+  []() { return; }(), int_func();
+}
+
+} // namespace
+
 #endif  // ifdef __cplusplus