[libcamera-devel] versioning

[Christian Rauch]

Hi Kieran,

Am 14.08.22 um 16:12 schrieb Kieran Bingham:
> Hi Christian,
>
> Quoting Christian Rauch via libcamera-devel (2022-08-13 22:14:44)
>> Hi all,
>>
>> I am aware that the libcamera API is unstable and because of this, there
>> is no versioning. I am using libcamera in another project, and it would
>> be helpful if I could check some version constraints in order to prevent
>> compiling with an incompatible API.
>
> I've been long advocating that we should have a version number, even
> with an unstable API. The last time I tried to push on this topic we
> added 0.0.0 at the very first commit which gives us some degree of
> patchlevel versioning for every commit.  It has taken a long time to
> identify clear reasons /why/ we should have more specific versions, when
> we have a clear unstable API, and we refer to the latest.
>
> However as you have reported here, with more API breakages recently -
> having other pacakges compiling against libcamera, they likely want to
> check what is installed. It's not always under the control and can
> depend upon the installation of the distro.
>
>
>> Would you be willing to start versioning the minor or patch-level of
>> libcamera? I imagine that the major version will stay at "0" until the
>
> I believe the answer is 'yes' now. But we still need to implement the
> 'how'.
>
> Personally - I would like to use something like abi-compliance-checker
> to automatically detect any ABI/API change, and automatically increment
> the minor patch level. libabigail looks interesting and relevant too:
> https://developers.redhat.com/blog/2020/04/02/how-to-write-an-abi-compliance-checker-using-libabigail#
>
> That would give us a version scheme of:
>
>  0.a[bp]i.patch
>
> Where other packages and applications could then use the second value to
> determine if they are compatible, (or to make conditional changes to be
> compilation compatible).
>
> The patch level of course would just be the number of patches since that
> change, and the leading version 0, would not be incremented until we
> were at a point that we could be comfortable stating we are 'ABI stable'.
>
>
>> API is stable, but that either the minor or patch-level could be
>> incremented (0.1, 0.2, ...) every time the API changes, or simply on a
>> monthly or quarterly basis.
>
> Every time I've suggested we should start making release versions, I
> always face push back of "What decrees a release, when should it be
> made?".
>
> To me time based milestones are acceptable, but don't make it
> easy/straightforwards to perform the version specific compilation
> changes required.
>
> I think they help users understand how new or old the library is though,
> and at least that is more helpful than our current versioning scheme
> where comparing 074fa98ac4e against 18d61deb3c0 is just not human
> readable, and doesn't convey any useful information. We have tagged our
> first commit as 0.0.0 which does now at least provide version strings
> generated by utils/gen-version.sh:
>
>  - 0.0.0+2819-18d61deb
>  - 0.0.0+3459-074fa98a
>
> So we could already say we could (manually) identify API/ABI changes
> between the patch level numbers after the + (2819, to 3459) - but that's
> quite labour intensive otherwise and prone to error, which is why I'd
> really like to see API/ABI breakages identifiable through something like
>
>
>  - 0.25.245-18d61deb
>  - 0 29.15-074fa98a
>
> Which we can then parse and extract more useful information from.
>
> I would envisage the automatic abi checker to be able to provide the
> 0.<abi> tags automatically on every change if run on every commit (and
> could be back dated right to the beginning of the tree history) ...
> however the point I have difficulty with is how we get those tags to
> then convey the correct information about the release in external
> systems.
>
> Is a 'tag' sufficient? or do we have to (for every 'release') manually
> edit the meson.build version string, or make other manual explicit
> changes.
>
> If we can do something around simply adding a tag on every abi/api
> version change, - I think that would provide the cleanest/simplest way
> forwards for now.
>
> Any ideas or extended comments?

I have seen CMake projects generating the version information from git.
This somehow works that a git command is executed as part of the build
process and then the stdout is parsed. Of course, this only works when
the source is checked out as a git repo. But I think something similar
could be done in meson. Then, you only need to create a new git tag and
the next time libcamera is compiled, it would generate the version.

>
>
>> This way, projects could check for a specific version before compiling
>> or search for a specific "API version". It wouldn't guarantee that the
>> API is compatible between versions, it's just useful to know which
>> version you have to use to compile a project.
>
> Agreed!
>
> It's also clear from other recent discussions that we should bump the
> SONAME for every ABI breakage, so again - if this can be handled through
> automatically detecting those breakages - I think that would help too.
> Having the SONAME as 0.<abi-version> as above would be a great benefit
> already I think.
>
> --
> Kieran
>
>
>> Best,
>> Christian
>>