[PATCH] D39762: [ObjC] Boxed strings should use the nullability from stringWithUTF8String's return type

[Alex Lorenz via Phabricator via cfe-commits]

arphaman created this revision.

Objective-C NSString has a class method `stringWithUTF8String` that creates a new NSString from a C string. Objective-C box expression `@(...)` can be used to create an NSString instead of invoking the `stringWithUTF8String` method directly (The compiler lowers it down to the invocation though). This patch ensures that the type of `@(string-value)` gets the same nullability attributes as the return type of `stringWithUTF8String` to ensure that the diagnostics are consistent between the two.

rdar://33847186


Repository:
  rL LLVM

https://reviews.llvm.org/D39762

Files:
  lib/Sema/SemaExprObjC.cpp
  test/SemaObjC/transfer-boxed-string-nullability.m


Index: test/SemaObjC/transfer-boxed-string-nullability.m
===================================================================
--- /dev/null
+++ test/SemaObjC/transfer-boxed-string-nullability.m
@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -fblocks -fobjc-arc -Wnullable-to-nonnull-conversion -fsyntax-only -verify -Wno-objc-root-class %s
+// RUN: %clang_cc1 -fblocks -fobjc-arc -Wnullable-to-nonnull-conversion -fsyntax-only -verify -Wno-objc-root-class -DNOWARN %s
+
+ at interface NSString
+
++ (NSString*
+#ifndef NOWARN
+  _Nullable
+#else
+  _Nonnull
+#endif
+) stringWithUTF8String:(const char*)x;
+
+ at end
+
+void takesNonNull(NSString * _Nonnull ptr);
+
+void testBoxedString() {
+  const char *str = "hey";
+  takesNonNull([NSString stringWithUTF8String:str]);
+  takesNonNull(@(str));
+#ifndef NOWARN
+  // expected-warning at -3 {{implicit conversion from nullable pointer 'NSString * _Nullable' to non-nullable pointer type 'NSString * _Nonnull'}}
+  // expected-warning at -3 {{implicit conversion from nullable pointer 'NSString * _Nullable' to non-nullable pointer type 'NSString * _Nonnull'}}
+#else
+  // expected-no-diagnostics
+#endif
+}
Index: lib/Sema/SemaExprObjC.cpp
===================================================================
--- lib/Sema/SemaExprObjC.cpp
+++ lib/Sema/SemaExprObjC.cpp
@@ -564,6 +564,13 @@
       
       BoxingMethod = StringWithUTF8StringMethod;
       BoxedType = NSStringPointer;
+      // Transfer the nullability from method's return type.
+      Optional<NullabilityKind> Nullability =
+          BoxingMethod->getReturnType()->getNullability(Context);
+      if (Nullability)
+        BoxedType = Context.getAttributedType(
+            AttributedType::getNullabilityAttrKind(*Nullability), BoxedType,
+            BoxedType);
     }
   } else if (ValueType->isBuiltinType()) {
     // The other types we support are numeric, char and BOOL/bool. We could also


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