Currently, people have to write their own build rules for generating Docbook files from D-Bus interface XML files using gdbus-codegen. They then have to tie that in to gtk-doc in the docs.xml file and gtk-doc.make.

It would be useful if there were a macro which made this easier. It could either come with GDBus, in which case the integration with gtk-doc would have to be very loose, or it could come with gtk-doc. I suggest the latter, but it could be argued either way.

Proposal:

 1. Add a DOC_DBUS_INTERFACE_XML input variable to gtk-doc.make. Add a DOC_DBUS_INTERFACE_PREFIX variable too.
 2. For each of the listed files, it runs
    gdbus-codegen --interface-prefix $(DOC_DBUS_INTERFACE_PREFIX) --xml-files=$(xml_file)
    and puts the output in $(builddir)/xml
 3. Build dependencies are updated so documentation is correctly regenerated if any of the interfaces change. The interface output files should be cleaned as appropriate.
 4. gtkdoc-check is updated to check that all DOC_DBUS_INTERFACE_XML files are <xi:include>d into $(DOC_MAIN_SGML_FILE).