[Sema][ObjC] Do not propagate the nullability specifier on the receiver

to the result type of a message send if the result type cannot have a
nullability specifier.

Previously, clang would print the following message when the code in
nullability.m was compiled:

"incompatible integer to pointer conversion initializing 'int *' with
an expression of type 'int _Nullable'"

This is wrong as 'int' isn't supposed to have any nullability
specifiers.

rdar://problem/40830514

llvm-svn: 338048

clang/lib/Sema/SemaExprObjC.cpp

@@ -1357,6 +1357,11 @@ QualType Sema::getMessageSendResultType(QualType ReceiverType,
   if (isClassMessage)
     return resultType;
 
+  // There is nothing left to do if the result type cannot have a nullability
+  // specifier.
+  if (!resultType->canHaveNullability())
+    return resultType;
+
   // Map the nullability of the result into a table index.
   unsigned receiverNullabilityIdx = 0;
   if (auto nullability = ReceiverType->getNullability(Context))

clang/test/SemaObjC/nullability.m

@@ -279,3 +279,14 @@ void test(ArraysInMethods *obj) {
   [obj simpleSugar:0]; // expected-warning {{null passed to a callee that requires a non-null argument}}
   [obj sugarWithTypedef:0]; // expected-warning {{null passed to a callee that requires a non-null argument}}
 }
+
+// Check that we don't propagate the nullability specifier on the receiver to
+// the result type of a message send if the result type cannot have a
+// nullability specifier.
+@interface C0
+-(int) count;
+@end
+
+void testMessageSendResultType(C0 * _Nullable c0) {
+  int *p = [c0 count]; // expected-warning {{incompatible integer to pointer conversion initializing 'int *' with an expression of type 'int'}}
+}