vala: add setup hook

Add datadir containing vapidir to XDG_DATA_DIRS and move vapipdir to dev output.

pkgs/development/compilers/vala/default.nix

···
 { stdenv, lib, fetchurl, fetchpatch, pkgconfig, flex, bison, libxslt, autoconf, automake, autoreconfHook
-, graphviz, glib, libiconv, libintl, libtool, expat
+, graphviz, glib, libiconv, libintl, libtool, expat, substituteAll
 }:
 
 let
···
   in stdenv.mkDerivation rec {
     name = "vala-${version}";
     version = "${major}.${minor}";
+
+    setupHook = substituteAll {
+      src = ./setup-hook.sh;
+      apiVersion = major;
+    };
 
     src = fetchurl {
       url = "mirror://gnome/sources/vala/${major}/${name}.tar.xz";

pkgs/development/compilers/vala/setup-hook.sh

···
+make_vala_find_vapi_files() {
+    # XDG_DATA_DIRS: required for finding .vapi files
+    if [ -d "$1/share/vala/vapi" -o -d "$1/share/vala-@apiVersion@/vapi" ]; then
+      addToSearchPath XDG_DATA_DIRS $1/share
+    fi
+}
+
+addEnvHooks "$hostOffset" make_vala_find_vapi_files
+
+_multioutMoveVapiDirs() {
+  moveToOutput share/vala/vapi "${!outputDev}"
+  moveToOutput share/vala-@apiVersion@/vapi "${!outputDev}"
+}
+
+preFixupHooks+=(_multioutMoveVapiDirs)