Don't emit -Wnullability-completeness warnings on weak Objective-…

…C properties.

Zeroing weak references are by definition `nullable`, and adding
`nonnull` or `_Nullable` yields a mutual-exclusivity error. When
`-Wnullability-completeness` is enabled, however, non-audited header
regions require adding the `nullable` property keyword to avoid a
warning. This should be unnecessary, since it restates known nullability
of the `weak` property.

Additionally, the fix-it hints are both non-idiomatic Objective-C
(adding `_Nullable` to the property's pointer type rather than in the
`@property` attributes) and suggest the option of adding `_Nonnull`,
which would be an error.

Differential Revision: https://reviews.llvm.org/D128031

clang/lib/Sema/SemaType.cpp

@@ -4748,8 +4748,13 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
       }
 
       // Weak properties are inferred to be nullable.
-      if (state.getDeclarator().isObjCWeakProperty() && inAssumeNonNullRegion) {
-        inferNullability = NullabilityKind::Nullable;
+      if (state.getDeclarator().isObjCWeakProperty()) {
+        // Weak properties cannot be nonnull, and should not complain about
+        // missing nullable attributes during completeness checks.
+        complainAboutMissingNullability = CAMN_No;
+        if (inAssumeNonNullRegion) {
+          inferNullability = NullabilityKind::Nullable;
+        }
         break;
       }
 

clang/test/SemaObjCXX/Inputs/nullability-consistency-2.h

@@ -19,13 +19,9 @@ void g3(const
 @property (retain,nullable) SomeClass *property2;
 - (nullable SomeClass *)method1;
 - (void)method2:(nonnull SomeClass *)param;
-@property (readonly, weak) SomeClass *property3; // expected-warning{{missing a nullability type specifier}}
-// expected-note@-1 {{insert '_Nullable' if the pointer may be null}}
-// expected-note@-2 {{insert '_Nonnull' if the pointer should never be null}}
+@property (readonly, weak) SomeClass *property3;
 @end
 
 @interface SomeClass ()
-@property (readonly, weak) SomeClass *property4; // expected-warning{{missing a nullability type specifier}}
-// expected-note@-1 {{insert '_Nullable' if the pointer may be null}}
-// expected-note@-2 {{insert '_Nonnull' if the pointer should never be null}}
+@property (readonly, weak) SomeClass *property4;
 @end