Handle null pointer constants properly

Author: AaronBallman

clang/lib/Sema/SemaExpr.cpp

@@ -9818,15 +9818,36 @@ Sema::CheckSingleAssignmentConstraints(QualType LHSType, ExprResult &CallerRHS,
       ((getLangOpts().C23 && RHS.get()->getType()->isNullPtrType()) ||
        RHS.get()->isNullPointerConstant(Context,
                                         Expr::NPC_ValueDependentIsNull))) {
+    AssignConvertType Ret = Compatible;
     if (Diagnose || ConvertRHS) {
       CastKind Kind;
       CXXCastPath Path;
       CheckPointerConversion(RHS.get(), LHSType, Kind, Path,
                              /*IgnoreBaseAccess=*/false, Diagnose);
+
+      // If there is a conversion of some kind, check to see what kind of
+      // pointer conversion happened so we can diagnose a C++ compatibility
+      // diagnostic if the conversion is invalid. This only matters if the RHS
+      // is some kind of void pointer.
+      if (Kind != CK_NoOp && !getLangOpts().CPlusPlus) {
+        QualType CanRHS =
+            RHS.get()->getType().getCanonicalType().getUnqualifiedType();
+        QualType CanLHS = LHSType.getCanonicalType().getUnqualifiedType();
+        if (CanRHS->isVoidPointerType() && CanLHS->isPointerType()) {
+          Ret = checkPointerTypesForAssignment(*this, CanLHS, CanRHS,
+                                               RHS.get()->getExprLoc());
+          // Anything that's not considered perfectly compatible would be
+          // incompatible in C++.
+          if (Ret != Compatible)
+            Ret = CompatibleVoidPtrToNonVoidPtr;
+        }
+      }
+
+
       if (ConvertRHS)
         RHS = ImpCastExprToType(RHS.get(), LHSType, Kind, VK_PRValue, &Path);
     }
-    return Compatible;
+    return Ret;
   }
   // C23 6.5.16.1p1: the left operand has type atomic, qualified, or
   // unqualified bool, and the right operand is a pointer or its type is
@@ -13946,10 +13967,8 @@ QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
           LHSType->isObjCObjectPointerType())))
       ConvTy = Compatible;
 
-    if (ConvTy == Compatible &&
-        LHSType->isObjCObjectType())
-        Diag(Loc, diag::err_objc_object_assignment)
-          << LHSType;
+    if (IsAssignConvertCompatible(ConvTy) && LHSType->isObjCObjectType())
+      Diag(Loc, diag::err_objc_object_assignment) << LHSType;
 
     // If the RHS is a unary plus or minus, check to see if they = and + are
     // right next to each other.  If so, the user may have typo'd "x =+ 4"
@@ -13971,7 +13990,7 @@ QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
       }
     }
 
-    if (ConvTy == Compatible) {
+    if (IsAssignConvertCompatible(ConvTy)) {
       if (LHSType.getObjCLifetime() == Qualifiers::OCL_Strong) {
         // Warn about retain cycles where a block captures the LHS, but
         // not if the LHS is a simple variable into which the block is