[PATCH] D44539: [Sema][Objective-C] Add check to warn when property of objc type has assign attribute

[Alfred Zien via Phabricator via cfe-commits]

QF5690 created this revision.
QF5690 added a reviewer: rsmith.
QF5690 added a project: clang.
Herald added a subscriber: cfe-commits.

There is a problem, that `assign` attribute very often getting out of attention. For example, consider this code:

  @property(nonatomic, strong, readonly, nullable) SomeObjcClassType1* foo;
  @property(nonatomic, strong, readwrite) SomeObjcClassType2* bar;
  @property(nonatomic, assign, readonly) SomeObjcClassType* property;
  @property(nonatomic, assign, readonly) SomeCStructType state;

It is very easy to miss that `assign` keyword, and it leads to hard to find and reproduce bugs. Most of the time, we found such bugs in crash reports from already in production code.

Now, consider this code:

  @property(nonatomic, strong, readonly, nullable) SomeObjcClassType1* foo;
  @property(nonatomic, strong, readwrite) SomeObjcClassType2* bar;
  @property(nonatomic, unsafe_unretained, readonly) SomeObjcClassType* property;
  @property(nonatomic, assign, readonly) SomeCStructType state;

It is now much harder to even make that mistake and it will be much obvious during code review.

As there is no difference in behaviour between `assign` and `unsafe_unretained` attribute, but second is much more verbose, saying "think twice when doing this", I suggest to have, at least, optional warning, that will catch such constructs.

This is my first revision in llvm, so any help would be very much appreciated.


Repository:
  rC Clang

https://reviews.llvm.org/D44539

Files:
  include/clang/Basic/DiagnosticGroups.td
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaObjCProperty.cpp
  test/SemaObjC/property-assign-on-object-type.m
  test/SemaObjC/property-in-class-extension-1.m


Index: test/SemaObjC/property-in-class-extension-1.m
===================================================================
--- test/SemaObjC/property-in-class-extension-1.m
+++ test/SemaObjC/property-in-class-extension-1.m
@@ -15,12 +15,12 @@
 @property (readonly) NSString* none;
 @property (readonly) NSString* none1;
 
- at property (assign, readonly) NSString* changeMemoryModel; // expected-note {{property declared here}}
+ at property (unsafe_unretained, readonly) NSString* changeMemoryModel; // expected-note {{property declared here}}
 
 @property (readonly) __weak id weak_prop;
 @property (readonly) __weak id weak_prop1;
 
- at property (assign, readonly) NSString* assignProperty;
+ at property (unsafe_unretained, readonly) NSString* unsafeUnretainedProperty;
 
 @property (readonly) NSString* readonlyProp;
 
@@ -43,8 +43,8 @@
 @property () __weak id weak_prop;
 @property (readwrite) __weak id weak_prop1;
 
- at property (assign, readwrite) NSString* assignProperty;
- at property (assign) NSString* readonlyProp;
+ at property (unsafe_unretained, readwrite) NSString* unsafeUnretainedProperty;
+ at property (unsafe_unretained) NSString* readonlyProp;
 @end
 
 // rdar://12214070
Index: test/SemaObjC/property-assign-on-object-type.m
===================================================================
--- /dev/null
+++ test/SemaObjC/property-assign-on-object-type.m
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wobjc-property-assign-on-object-type
+
+ at interface Foo @end
+
+ at interface Bar
+ at property(assign, readonly) Foo* o1; // expected-warning {{'assign' attribute must not be of object type, use 'unsafe_unretained' instead}}
+ at property(unsafe_unretained, readonly) Foo* o2;
+
+ at property(assign) int s1;
+ at property(assign) int* s2;
+ at end
+
+ at interface Bar ()
+ at property(readwrite) Foo* o1;
+ at property(readwrite) Foo* o2;
+ at end
Index: lib/Sema/SemaObjCProperty.cpp
===================================================================
--- lib/Sema/SemaObjCProperty.cpp
+++ lib/Sema/SemaObjCProperty.cpp
@@ -2547,6 +2547,13 @@
     PropertyDecl->setInvalidDecl();
   }
 
+  // Check for assign on object types.
+  if ((Attributes & ObjCDeclSpec::DQ_PR_assign) &&
+      !(Attributes & ObjCDeclSpec::DQ_PR_unsafe_unretained) &&
+      PropertyTy->isObjCRetainableType()) {
+    Diag(Loc, diag::warn_objc_property_assign_on_object);
+  }
+
   // Check for more than one of { assign, copy, retain }.
   if (Attributes & ObjCDeclSpec::DQ_PR_assign) {
     if (Attributes & ObjCDeclSpec::DQ_PR_copy) {
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -1014,6 +1014,9 @@
   "property attributes '%0' and '%1' are mutually exclusive">;
 def err_objc_property_requires_object : Error<
   "property with '%0' attribute must be of object type">;
+def warn_objc_property_assign_on_object : Warning<
+  "'assign' attribute must not be of object type, use 'unsafe_unretained' instead">,
+  InGroup<ObjCPropertyAssignOnObjectType>, DefaultIgnore;
 def warn_objc_property_no_assignment_attribute : Warning<
   "no 'assign', 'retain', or 'copy' attribute is specified - "
   "'assign' is assumed">,
Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -367,6 +367,7 @@
 def BadFunctionCast : DiagGroup<"bad-function-cast">;
 def ObjCPropertyImpl : DiagGroup<"objc-property-implementation">;
 def ObjCPropertyNoAttribute : DiagGroup<"objc-property-no-attribute">;
+def ObjCPropertyAssignOnObjectType : DiagGroup<"objc-property-assign-on-object-type">;
 def ObjCProtocolQualifiers : DiagGroup<"objc-protocol-qualifiers">;
 def ObjCMissingSuperCalls : DiagGroup<"objc-missing-super-calls">;
 def ObjCDesignatedInit : DiagGroup<"objc-designated-initializers">;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D44539.138616.patch
Type: text/x-patch
Size: 3969 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20180315/11359188/attachment.bin>