Some questions about next versions of SIP

[Dmitry Shachnev]

Hi Phil, and thanks for your reply,

On Mon, Sep 14, 2020 at 10:23:39PM +0100, Phil Thompson wrote:
> There will be no more SIP v4 or v5 releases after v6 is released. SIP v4 has
> been deprecated for more than a year. *Nobody* should still be using it.

Unfortunately, in Debian there are still around 20 packages using it.

I was going to migrate them to SIP v5 and using sip5 tool (because I don't
have enough time to port them all to the new build system myself), but now
that SIP v6 won't have that legacy tool and SIP v5 won't be installable
together with SIP v6, probably I will have to change my plan and let them
remain on v4 until someone ports them to the new build system.

So it would be really nice if tools built with SIP v4 are still compatible
with PyQt5 built with SIP v5/v6.

> > - Is it possible to mix different SIP versions in the same project?
> >   For example, some upstreams (like Calibre) can be built only with SIP
> >   v4, but is it fine to use these projects together with PyQt5 that is
> >   built with newer sip?
>
> Yes, assuming the exact version of SIP v4 is relatively recent. SIP v4 only
> supports one (major/minor) version of the ABI. SIP v5 supports all versions
> of the ABI with the project specifying which version it wants to use.

The exact version is the latest one, 4.19.24. However the ABI version is
still different from what PyQt5 is built with (12.7 vs. 12.8). I guess it's
fine?

And what if PyQt5 ABI changes to 13.0 — will it be still fine?

> > - Is there any migration guide how to switch to sipbuild for projects that
> >   are calling sip or sip5 executable from their custom build system? For
> >   example, Krita and QGIS are such projects, they are calling sip/sip5
> >   from their CMake-based build system.
> >
> >   Ideally it would be nice to have a guide that would also cover other
> >   aspects of updating to a newer SIP, such as API changes.
>
> The main difference between SIP v4 and v5 is the *addition* of a build
> system, so it's not possible to write a guide to converting from something I
> know nothing about.

I was thinking about something like that: “If you were calling sip with these
command line options, add this to your pyproject.toml / whatever file.”

I don't personally need this, but having such documentation may help to
convince some upstreams to port to new build system.

> > - Will SIP v5 and SIP v6 be co-installable? Or both will use the same
> >   Python module name (sipbuild) and the same set of binaries (sip-build &
> >   friends)? I am asking this because I will have to continue shipping
> >   older versions of SIP for packages that are using sip5 legacy tool.
>
> No, but one approach a project might take is to implement something similar
> to the sip5 legacy tool that uses the documented sipbuild API. I'd be happy
> to refine that API to make that easier - but I'm not providing a sip6 legacy
> tool.

If a copy of sipbuild/legacy/sip5.py will work with SIP v6 without many
changes, that would be nice indeed.

--
Dmitry Shachnev
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