Created attachment 192129 [details]
a whole example package of this bug

When the user add --pkg gio-2.0, not all generated C files include this line:
#include <gio/gio.h>

As far as I understood, only files with the "DBus" attribute includes this line in C.
There is to ways to handle it:
1. Add all the generated C files this line.(simple)
2. Check for every file weather it depends on GIO-2.0.(complicated)
Approach 1 seams the best.

This cause this error to occur when compiling the C files:
Foo.vala.c:54:45: error: unknown type name ‘GDBusConnection’
error: cc exited with status 256

The following error is from the attached example.

Hope I made myself clear
Tal