We were setting it to a file list that would always be wrong, and
always out of date since it would never exist.
However, the output list is not predictable. It usually has a 1-1
relationship with the input XML files, but it may not.
This must be fixed later with API for users to provide the output
names.
See: https://github.com/mesonbuild/meson/pull/3539
If we pass a source files() object, we will look for it in the build
directory, which is wrong. If we pass a build files() object (from
configure_file()), we will find it in the build directory, and then
try to copy it on top of itself in gtkdochelper.py getting a
SameFileError.
Add a test for it, and also properly iterate custom target outputs
when adding to content files.
The GtkDoc test has been extended to also test the inclusion of
generated files.
To test this, a new python script has been included which generates
a new docbook file which is included as content file.
Nirbheek Chauhan
Iñigo Martínez
Elliott Sales de Andrade
Jussi Pakkanen