[pacman-dev] [PATCH 2/5] meson.build: Fix detection of symbols

[Allan McRae]

On 20/4/21 12:28 am, Mark Weiman wrote:
> On Tue, 2021-04-20 at 00:05 +1000, Allan McRae wrote:
>> On 19/4/21 9:34 pm, Emil Velikov wrote:
>>> On Mon, 19 Apr 2021 at 08:10, Allan McRae <allan at archlinux.org>
>>> wrote:
>>>>
>>>> On 17/4/21 1:45 pm, Mark Weiman wrote:
>>>>> This patch changes the behavior of meson to define
>>>>> configuration options
>>>>> *only* when the symbol checked is present. Currently, it
>>>>> defines all of
>>>>> them in config.h whether the symbol exists or not and the code
>>>>> that
>>>>> looks for it doesn't check the macro's value, but whether it's
>>>>> defined.
>>>>>
>>>>
>>>> Remember back when we used autotools and all this just worked! 
>>>> :D
>>>>
>>>> Patch looks good to me.
>>>>
>>> Food for thought:
>>>
>>> Usually the more robust approach is to always set the respective
>>> defines to 0/1 and evaluate them directly (aka #if HAVE_).
>>> In addition one could set -Werror=undef in the build to catch any
>>> issues.
>>>
>>> This will produce clear traces with potential issues, while #if
>>> defined will silently fallback to the "other" path.
>>> If people are OK with the above, I will follow-up with some
>>> patches.
>>>
>>> Note: above suggestion is not meant to dismiss the original patch.
>>>
>>
>>
>> I still live in the good old autotools days where there were lots of
>> #undef in config.h...
>>
>> It appears some of that still happens.  This is my build/config.h:
>>
>> #undef HAVE_STRUCT_STATFS_F_FLAGS
>> #define HAVE_STRUCT_STATVFS_F_FLAG
>>
>> But it is not consistent.
>>
> 
> This can be easily done by not using set10, but instead setting the
> values to true/false with set. That's why HAVE_STRUCT_STATFS_F_FLAGS is
> undef'd and those other ones that use set10 don't. I can modify this to
> mimick the old autotools behavior.
> 

I have pulled the patch as-is, because it improves the current state.
So any further changes can happen on top of that.  (currently sitting in
my patchqueue branch).

I have no strong opinion whether the changes should have #undef, or just
always defining as 0/1 and then using #if.   It is clear that one of
these needs to happen so we have consistency.

Allan