I tried to use accountsservice from vala, but got an error "error: Package `accountsservice' not found in specified Vala API directories or GObject-Introspection GIR directories"
After checking, found the commit  removing the VAPI file as it's not needed.
Asking around on #vala I got some help on how to generate a VAPI file for accountsservice, as 'vapigen --library accountsservice AccountsService-1.0.gir' didn't work because of the following error:
Virtual method `G.Resolver.lookup_service_async' conflicts with method of the same name
Gio-2.0.gir:58270.7-58270.31: warning: Signal `G.Settings.change_event' conflicts with method of the same name
Gio-2.0.gir:77083.7-77087.24: error: `UnixSocketAddress' already contains a definition for `abstract'
Gio-2.0.gir:76929.7-76931.21: note: previous definition of `abstract' was here
Generation failed: 1 error(s), 2 warning(s)
The person helping me in the vala channel, suggested adding --pkg gio-2.0 to vapigen, and that did help to generate the VAPI. He also mentioned that this probably shouldn't be required, and the gir file seems broken, as it should contain a <package name="gio-2.0" /> element.
Closing assuming this is out of date, please re-open if you're still using it like that.