[xml/sgml-pkgs] Bug#1073400: gtk-doc: FTBFS with libxml2 2.12.x: XInclude error : could not load ../../examples/gobject.c

[Simon McVittie]

Control: retitle -1 gtk-doc: FTBFS with libxml2 2.12.x: XInclude error : could not load ../../examples/gobject.c
Control: severity -1 important

On Sun, 08 Dec 2024 at 12:59:06 +0000, Rebecca N. Palmer wrote:
> gtk-doc also FTBFS in reproducible-builds from approximately 2024-05-30 to
> 2024-09-24 in unstable (but not in trixie, meaning the bug was in something
> other than gtk-doc) but now builds successfully:
> https://tests.reproducible-builds.org/debian/history/gtk-doc.html
> The logs aren't kept, so there's no proof that this was specifically this
> bug, but it seems likely.

Actually I'm going to downgrade this to non-RC but not close it, because
the combination of the error message and the timing strongly suggests
that this was triggered by the update of libxml2 from 2.9.x to 2.12.x on
2024-05-25, which was reverted on 2024-09-26.

To try to confirm or deny this, I'm now trying a gtk-doc build with
libxml2 2.13.x from experimental:

    sbuild -dexperimental --add-depends='libxml2-utils (>= 2.13)' --add-depends='libxml2 (>= 2.13)' gtk-doc

The output of the one failing test, test-gobject-mkhtml, is:
> warning: failed to load external entity "../../examples/gobject.c"
> ../xml/object.xml:139: element include: XInclude error : could not load ../../examples/gobject.c, and no fallback was found

I think this might be a behaviour change in libxml2, perhaps making it
more strict about the handling of missing resources with XInclude, or
perhaps changing the search path for those resources.

Because of the way gtk-doc is designed, this might trigger FTBFS in
packages that use gtk-doc for their documentation, not just a test
failure in gtk-doc itself. We'll need to take that into account (raising
the severity back to RC if not already fixed) when libxml2 gets upgraded
back to ≥ 2.12.x in future.

    smcv