[libcamera-devel] [RFC PATCH] libcamera: Disable automatic vcs versioning

[Tomi Valkeinen]

On 22/08/2022 17:39, Laurent Pinchart via libcamera-devel wrote:
> On Mon, Aug 22, 2022 at 05:17:05PM +0300, Laurent Pinchart via libcamera-devel wrote:
>> On Sat, Aug 20, 2022 at 03:29:48PM +0200, Christian Rauch via libcamera-devel wrote:
>>> Hi Tomi,
>>>
>>> With the recent discussions on "versioning", I would actually argue that
>>> this should be removed entirely, and we should only rely on the semver
>>> versioning.
>>
>> I'd rather not. It has been proven very useful multiple times to have
>> the exact git commit ID in bug reports. If we were to drop it, it would
>> increase our support burden. I'm fine omitting the commit ID when the
>> libcamera version exactly matches a released version, but not otherwise.
>>
>>> Am 20.08.22 um 10:07 schrieb Tomi Valkeinen via libcamera-devel:
>>>> libcamera builds the git hash version into the libcamera library. This
>>>> makes ninja create the generated version.cpp on every build, and if the
>>>> git hash has changed, compilation of version.cpp and linking of
>>>> libcamera library.
>>>>
>>>> This patch adds a meson option to disable this behavior and instead use
>>>> the meson project-version as the version built into the library, which
>>>> is only generated at meson configuration time.
>>>>
>>>> With this change, ninja will nicely say "no work to do" if there's
>>>> nothing to compile, instead of starting the build and generating
>>>> version.cpp.
>>
>> I'd prefer a way to skip recompilation (and relinking) if the version
>> hasn't changed since the last build.
> 
> Which of course doesn't work for Tomi's use case.
> 
> /me needs to wake up
> 
> How can we get the best of both worlds ?

I think there are two different build types: for publishing and for your 
own use (development usually). With dev builds I'm fine with omitting 
versioning info, skipping any signing processes, and so forth. I think 
that can be a meson option. Which one should be the default, that's a 
more difficult question (maybe publishing).

>>>> But, more importantly, it often reduces build time. For example, this
>>>> takes a particular git range compilation (~20 py bindings patches) from
>>>> 43 seconds to 10 seconds. Obviously the improvement depends very much on
>>>> the patches in question. If every commit changes libcamera itself, there
>>>> is no difference.
>>>>
>>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
>>>> ---
>>>>   meson_options.txt         |  5 +++++
>>>>   src/libcamera/meson.build | 29 +++++++++++++++++++++--------
>>>>   2 files changed, 26 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/meson_options.txt b/meson_options.txt
>>>> index 7a9aecfc..6a0bd0be 100644
>>>> --- a/meson_options.txt
>>>> +++ b/meson_options.txt
>>>> @@ -63,3 +63,8 @@ option('pycamera',
>>>>           type : 'feature',
>>>>           value : 'disabled',
>>>>           description : 'Enable libcamera Python bindings (experimental)')
>>>> +
>>>> +option('disable-vcs-versioning',
>>>> +        type : 'boolean',
>>>> +        value : false,
>>>> +        description : 'Disable automatic libcamera library versioning with the git hash')
>>>> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
>>>> index ce1f0f2f..6fd6f084 100644
>>>> --- a/src/libcamera/meson.build
>>>> +++ b/src/libcamera/meson.build
>>>> @@ -121,14 +121,27 @@ endforeach
>>>>
>>>>   libcamera_sources += control_sources
>>>>
>>>> -gen_version = meson.project_source_root() / 'utils' / 'gen-version.sh'
>>>> -
>>>> -# Use vcs_tag() and not configure_file() or run_command(), to ensure that the
>>>> -# version gets updated with every ninja build and not just at meson setup time.
>>>> -version_cpp = vcs_tag(command : [gen_version, meson.project_build_root(), meson.project_source_root()],
>>>> -                      input : 'version.cpp.in',
>>>> -                      output : 'version.cpp',
>>>> -                      fallback : meson.project_version())
>>>> +if get_option('disable-vcs-versioning')
>>>> +    cdata = configuration_data()
>>>> +    cdata.set('VCS_TAG', meson.project_version())
>>>> +
>>>> +    # For some reason using 'version.cpp' as output file works fine for generation
>>>> +    # but causes meson to delete the file before build. Any other file name
>>>> +    # seems to work.
>>>> +    version_cpp = configure_file(input : 'version.cpp.in',
>>>> +                                 output : 'version_static.cpp',
>>>> +                                 configuration : cdata)
> 
> Do I understand correctly that this will cause a build failure if you
> don't first run meson setup with the disable-vcs-versioning option
> disabled ?

Isn't this piece of code always run when you change (enable) the option, 
even if you do it with "meson configure" after the initial setup?

  Tomi