r293199 - Turn on -Wblock-capture-autoreleasing by default.

[Nico Weber via cfe-commits]

Hi Akira,

this fires in internal chrome/ios code like so:

somefile.m: error: block captures an autoreleasing out-parameter, which may
result in use-after-free bugs [-Werror,-Wblock-capture-autoreleasing]
          if (error) {
              ^
somefile.m: note: declare the parameter __autoreleasing explicitly to
suppress this warning
- (NSDictionary *)fooWithError:(NSError **)error {
                                                  ^
                                                  __autoreleasing
somefile.m: note: declare the parameter __strong or capture a __block
__strong variable to keep values alive across autorelease pools


A colleague points out that
http://clang.llvm.org/docs/AutomaticReferenceCounting.html#indirect-parameters
suggests NSError ** should "be implicitly qualified with __autoreleasing."
Is that a bug in the implementation of the warning,
is AutomaticReferenceCounting.html incorrect, or are we just
misunderstanding that document?

Thanks,
Nico

On Thu, Jan 26, 2017 at 1:51 PM, Akira Hatanaka via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: ahatanak
> Date: Thu Jan 26 12:51:10 2017
> New Revision: 293199
>
> URL: http://llvm.org/viewvc/llvm-project?rev=293199&view=rev
> Log:
> Turn on -Wblock-capture-autoreleasing by default.
>
> Turning on the warning by default helps the users as it's a common
> mistake to capture out-parameters in a block without ensuring the object
> assigned doesn't get released.
>
> rdar://problem/30200058
>
> Modified:
>     cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>     cfe/trunk/test/SemaObjC/arc.m
>
> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/
> DiagnosticSemaKinds.td?rev=293199&r1=293198&r2=293199&view=diff
> ============================================================
> ==================
> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Thu Jan 26
> 12:51:10 2017
> @@ -5185,7 +5185,7 @@ def err_arc_inconsistent_property_owners
>  def warn_block_capture_autoreleasing : Warning<
>    "block captures an autoreleasing out-parameter, which may result in "
>    "use-after-free bugs">,
> -  InGroup<BlockCaptureAutoReleasing>, DefaultIgnore;
> +  InGroup<BlockCaptureAutoReleasing>;
>  def note_declare_parameter_autoreleasing : Note<
>    "declare the parameter __autoreleasing explicitly to suppress this
> warning">;
>  def note_declare_parameter_strong : Note<
>
> Modified: cfe/trunk/test/SemaObjC/arc.m
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/
> SemaObjC/arc.m?rev=293199&r1=293198&r2=293199&view=diff
> ============================================================
> ==================
> --- cfe/trunk/test/SemaObjC/arc.m (original)
> +++ cfe/trunk/test/SemaObjC/arc.m Thu Jan 26 12:51:10 2017
> @@ -1,4 +1,4 @@
> -// RUN: %clang_cc1 -triple x86_64-apple-darwin11 -fobjc-runtime-has-weak
> -fsyntax-only -fobjc-arc -fblocks -verify -Wno-objc-root-class
> -Wblock-capture-autoreleasing %s
> +// RUN: %clang_cc1 -triple x86_64-apple-darwin11 -fobjc-runtime-has-weak
> -fsyntax-only -fobjc-arc -fblocks -verify -Wno-objc-root-class %s
>
>  typedef unsigned long NSUInteger;
>  typedef const void * CFTypeRef;
>
>
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