LibGRss or libgrss is a 'library for easy management of RSS/Atom/Pie feeds.' (from wiki.gnome.org).
I wanted to use this glib library in Vala but there is/was no VAPI file and no reference in Valadoc.
From the Vala documentation, on generating VAPI files, we will need the GObject Introspection file (gir).
Install libgrss-0.7 runtime and devel packages. The GIR (GObject Introspection) will also be installed .
Then, from the console, issue the command:
vapigen --pkg glib-2.0 --pkg libsoup-2.4 --library Grss /usr/share/gir-1.0/Grss-0.7.gir
The resulting VAPI file will be located in the same folder where the shell command was issued, with the name defined on the --library switch, in this case Grss.vapi.
For some reason i did not dig in detail, the VAPI file references libxml2 xmlDocPtr instead of Xml.Doc. Another needed change is replacing 'Grss-0.7.h' to 'libgrss/libgrss.h'. This last issue probably can be avoided by better naming of the Grss.vapi library switch... whatever...
The VAPI file should be copied into valac VAPI folder and use the -X switch to indicate the library. C code works ok with pkg-config and valac can generate C code that will compile but to compile directly from valac, we must use '-X -lgrss' (this can be solved, probably, but needs more time)