[cfe-commits] Clang change to detect and warn about unused private members

[Chandler Carruth]

Can you re-send the patch? that way patchwork can track it.

On Thu, Jan 26, 2012 at 6:24 PM, Daniel Jasper <djasper at google.com> wrote:

> Hi,
>
> has anyone had a chance to look at this?
>
> Kind regards,
> Daniel
>
>
> On Wed, Jan 18, 2012 at 10:28 PM, Daniel Jasper <djasper at google.com>wrote:
>
>> Hi,
>>
>> here is a new version of the proposed change. Changes:
>>
>> 1) The warning is more conservative. Members of a class-type can now only
>> count as unused if a trivial default constructor and a trivial destructor
>> are used (as these don't have side-effects). A smarter analysis for
>> side-effect-free constructors and destructors can follow. This prevents
>> false positives on RAII-style classes.
>> 2) The warning gives up if a class has a template friend (specializations
>> of this friend could use any unused member).
>> 3) Only instantiations of template classes are analyzed, not the template
>> classes themselves (this was a major source of false positives).
>> 4) Testcase is include in the patch this time.
>>
>> Please let me know, what you think!
>>
>> Cheers,
>> Daniel
>>
>>
>> On Thu, Jan 12, 2012 at 7:26 PM, Daniel Jasper <djasper at google.com>wrote:
>>
>>> Hi Nico,
>>>
>>> comments inline.
>>>
>>> On Wed, Jan 11, 2012 at 10:49 PM, Nico Weber <thakis at chromium.org>wrote:
>>>
>>>> Hi Daniel,
>>>>
>>>> On Wed, Jan 11, 2012 at 1:11 AM, Daniel Jasper <djasper at google.com>
>>>> wrote:
>>>> > Hi,
>>>> >
>>>> > the attached change is designed to detect and warn about private
>>>> unused
>>>> > members of C++ classes. It checks whether a class is fully defined in
>>>> the
>>>> > current translation unit, i.e. all methods are either defined or pure
>>>> > virtual and all friends are defined. Otherwise, the private member
>>>> could be
>>>> > used by a function defined in another translation unit.
>>>>
>>>> that's a cool warning! Here are a few cases where it flags false
>>>> positives (it finds tons of true positives too, but those are boring
>>>> :-) ).
>>>>
>>>> It flags |stackArray| in ICU's cmemory.h. This is declared for storage
>>>> and accessed through pointer aliasing, probably not much that can be
>>>> done about this:
>>>>
>>>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/third_party/icu/source/common/cmemory.h&exact_package=chromium&q=file:cmemory.h&l=285
>>>
>>>
>>> As you said in the other email, it is the wrong code line and I think,
>>> it is correct to warn about the other |stackArray|.
>>>
>>>
>>>>
>>>> In flags StaticResource::instance_ in v8's utils.h:
>>>>
>>>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/v8/src/utils.h&exact_package=chromium&q=file:v8/src/utils.h&l=300
>>>> This is supposed to be accessed through the class below, Access, which
>>>> is a friend of utils.h. Do you check if any friends use private
>>>> variables?
>>>>
>>>
>>> Yes, I check friends. This is a bug, I know why it happens (it is
>>> because of the dependent templates) and I will fix it.
>>>
>>>
>>>> In chromium itself, it flags ShadowingAtExitManager member variables.
>>>> This is basically a RAII class which only exists to call a protected
>>>> superclass constructor, and which only exists if UNIT_TESTS is
>>>> defined:
>>>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/base/at_exit.h&l=71
>>>> So maybe the "constructor without arguments" heuristic could be
>>>> tweaked to exclude constructors that call superclass constructors with
>>>> arguments?
>>>> (Here's another RAII class whose constructor takes 0 arguments:
>>>>
>>>> http://codesearch.google.com/codesearch#OAMlx_jo-ck/src/base/logging_unittest.cc&exact_package=chromium&q=logstatesaver&l=26
>>>> )
>>>>
>>>
>>> I have changed it to be more conservative (I will send a new patch once
>>> I have fixed the bug mentioned above). It now only accepts members without
>>> initializer or with an argument-less initializer, if the field's type has a
>>> trivial default constructor and a trivial destructor. Unfortunately, we now
>>> also miss a lot of true positives, but I guess the false positives are
>>> worse, especially because there is no easy way to explicitly suppress the
>>> warning for these cases within the standard syntax.
>>>
>>> Cheers,
>>> Daniel
>>>
>>>
>>>>
>>>> (This is not an exhaustive list, just the things I found after a quick
>>>> look.)
>>>>
>>>> Nico
>>>>
>>>
>>>
>>
>
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