Bug#1030223: gobject-introspection mini-policy: separate GIR XML from -dev package to make cross-compilation possible?

[Simon McVittie]

Package: gobject-introspection
Version: 1.74.0-3
Severity: wishlist
File: /usr/share/doc/gobject-introspection/policy.txt.gz
Tags: trixie sid

At the moment, a typical introspected library (I'm using libflatpak as my
example) has this layout, where the files marked [*] are generated by
GObject-Introspection:

    libflatpak-dev
        /usr/include/flatpak
        /usr/lib/*/libflatpak.so
        /usr/lib/*/pkgconfig/flatpak.pc
        /usr/share/gir-1.0/Flatpak-1.0.gir                        [*]

    libflatpak0
        /usr/lib/*/libflatpak.so.0.*
        /usr/lib/*/libflatpak.so.0

    gir1.2-flatpak-1.0
        /usr/lib/*/girepository-1.0/Flatpak-1.0.typelib           [*]

GObject-Introspection gets some of its information by parsing the source
code, and that's fine. However, it gets other information by introspecting
the just-built libflatpak.so.0 (hence its name): linking a small executable
to libflatpak.so.0, and running it. When doing "true" cross-compiling
(without the ability to run host executables via qemu-user or similar),
this is not possible.

Ideally, when cross-compiling Flatpak, we'd prefer to build it with
a build profile like cross or nogir that has the effect of building it with
./configure --disable-introspection, which disables the generation of the
files marked [*]. However, that would make this build profile cause a
functional change to the contents of libflatpak-dev, which is strongly
discouraged.

If we separated the GIR XML into a new binary package, perhaps named
gir1.2-flatpak-1.0-dev or something like that, then we would be able to
turn off both gir1.2-flatpak-1.0 and gir1.2-flatpak-1.0-dev under the
nogir build profile (similar to how the noudeb, nocil and noinsttest
profiles work), making cross-compilation possible (as long as you don't
care about GObject-Introspection-based language bindings).

I think this would require changes to dependent packages if they make
use of the GIR XML (because build-depending on libflatpak-dev would
no longer be enough, and it would also be necessary to build-depend on
gir1.2-flatpak-1.0-dev <!nogir> or similar). If so, this would have to
be done on a package-by-package basis, with dependent packages changed
before their dependency. A migration path would be to add
Provides: gir1.2-flatpak-1.0-dev (= ${binary:Version}) on libflatpak-dev.

A side benefit of this would be that we could separate out the GIR XML
that is provided by src:gobject-introspection (#859013) into one or more
similar gir1.2-*-dev packages.

    smcv