Re: [PATCH 4/4] Add -Wmisleading-indentation to -Wall

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Fri, Oct 30, 2015 at 5:03 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Thu, Oct 29, 2015 at 6:38 PM, Jeff Law <law@redhat.com> wrote:
>> On 10/29/2015 10:49 AM, David Malcolm wrote:
>>>
>>> Our documentation describes -Wall as enabling "all the warnings about
>>> constructions that some users consider questionable, and that are easy to
>>> avoid
>>> (or modify to prevent the warning), even in conjunction with macros."
>>>
>>> I believe that -Wmisleading-indentation meets these criteria, and is
>>> likely to be of benefit to users who may not read release notes; it
>>> warns for indentation that's misleading, but not for indentation
>>> that's merely bad: the former are places where a user will likely
>>> want to fix the code.
>>>
>>> The fix is usually easy and obvious: fix the misleadingly-indented
>>> code.  If that isn't an option for some reason, pragmas can be used to
>>> turn off the warning for a particular fragment of code:
>>>
>>>    #pragma GCC diagnostic push
>>>    #pragma GCC diagnostic ignored "-Wmisleading-indentation"
>>>      if (flag)
>>>        x = 3;
>>>        y = 2;
>>>    #pragma GCC diagnostic pop
>>>
>>> -Wmisleading-indentation has been tested with a variety of indentation
>>> styles (see gcc/testsuite/c-c++-common/Wmisleading-indentation.c)
>>> and on a variety of real-world projects.  For example, in:
>>>    https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg119790.html
>>> Patrick reports:
>>> "Tested by building the linux, git, vim, sqlite and gdb-binutils sources
>>>   with -Wmisleading-indentation."
>>>
>>> With the tweak earlier in this kit I believe we now have a good
>>> enough signal:noise ratio for this warning to be widely used; hence this
>>> patch adds the warning to -Wall.
>>>
>>> Bootstrapped&regrtested with x86_64-pc-linux-gnu.
>>>
>>> OK for trunk?
>>>
>>> gcc/c-family/ChangeLog:
>>>         * c.opt (Wmisleading-indentation): Add to -Wall for C and C++.
>>>
>>> gcc/ChangeLog:
>>>         * doc/invoke.texi (-Wall): Add -Wmisleading-indentation to the
>>>         list.
>>>         (-Wmisleading-indentation): Update documentation to reflect
>>>         being enabled by -Wall in C/C++.
>>
>> I'm sure we'll get some grief for this :-)
>>
>> Approved once we're clean in GCC.  I'm going to explicitly say that we'll
>> have to watch for fallout, particularly as we start getting feedback from
>> Debian & Fedora mass-rebuilds as we approach release time.  If the fallout
>> is too bad, we'll have to reconsider.
>>
>> I'll pre-approve patches which fix anything caught by this option in GCC as
>> long as the fix just adjusts whitespace :-)
>
> Please at least check also binutils and gdb and other packages that use -Werror
> (well, just rebuild Fedora world).

FYI binutils, gdb and glibc, from git, all fail to build due to
-Wmisleading-indentation warnings/errors. (None of the warnings are
bogus (IMO), though I don't think any of the warnings expose a real
bug either.)