Re: [PATCH v2 03/15] python: add VERSION file

[Andrea Bolognani <abologna@redhat.com>]

On Wed, 2020-10-14 at 10:29 -0400, John Snow wrote:
> Python infrastructure as it exists today is not capable reliably of
> single-sourcing a package version from a parent directory. The authors
> of pip are working to correct this, but as of today this is not possible
> to my knowledge.
> 
> The problem is that when using pip to build and install a python
> package, it copies files over to a temporary directory and performs its
> build there. This loses access to any information in the parent
> directory, including git itself.
> 
> Further, Python versions have a standard (PEP 440) that may or may not
> follow QEMU's versioning. In general, it does; but naturally QEMU does
> not follow PEP 440. To avoid any automatically-generated conflict, a
> manual version file is preferred.
> 
> 
> I am proposing:
> 
> - Python core tooling synchronizes with the QEMU version directly
>   (5.2.0, 5.1.1, 5.3.0, etc.)
> 
> - In the event that a Python package needs to be updated independently
>   of the QEMU version, a pre-release alpha version should be preferred,
>   but *only* after inclusion to the qemu development or stable branches.
> 
>   e.g. 5.2.0a1, 5.2.0a2, and so on should be preferred prior to 5.2.0's
>   release.
> 
> - The Python core tooling makes absolutely no version compatibility
>   checks or constraints. It *may* work with releases of QEMU from the
>   past or future, but it is not required to.
> 
>   i.e., "qemu.core" will always remain in lock-step with QEMU.
> 
> - We reserve the right to split out e.g. qemu.core.qmp to qemu.qmp
>   and begin indepedently versioning such a package separately from the
>   QEMU version it accompanies.

I think this need to be considered very carefully.

I'm not overly familiar with the Python ecosystem but it would appear
that, despite PEP 440 not mandating this, many (most?) of the
packages uploaded to PyPi are using semantic versioning.

With that in mind, I think it would be unwise for qemu.* not to do
the same; in particular, using a version number that's not <1.0.0 for
a package that is very much in flux will almost certainly break
people's expectations, and is also not something that you can easily
take back at a later time.

-- 
Andrea Bolognani / Red Hat / Virtualization