[gobject-introspection/bochecha/pkgconfig-prefix] m4: Take prefix the into account for the gir and typelib dirs

[Mathieu Bridon <mbridon src gnome org>]

commit 0dbf209f72bd8c700668971cd6f31760c72d9181
Author: Mathieu Bridon <bochecha daitauha fr>
Date:   Fri Jan 11 17:54:18 2019 +0100

    m4: Take prefix the into account for the gir and typelib dirs
    
    When building a Flatpak application, all the modules bundled with the
    app are built/installed with prefix=/app.
    
    Those modules which use gobject-introspection's introspection.m4 will
    use pkgconfig to query the installation directory for their own gir and
    typelib files.
    
    As it is, that will always return something under /usr, which causes
    build failures in flatpak-builder.
    
    With the original pkg-config implementation, app authors would work
    around this in their manifests by defining a couple of environment
    variables:
    
        PKG_CONFIG_GOBJECT_INTROSPECTION_1_0_GIRDIR=/app/share/gir-1.0
        PKG_CONFIG_GOBJECT_INTROSPECTION_1_0_TYPELIBDIR=/app/lib/girepository-1.0
    
    With the pkgconf implementation though, as used in the Freedesktop Sdk
    18.08 and the GNOME Sdk >= 3.30, this does not work any more. One
    workaround is now to pass those directories to `make install`
    explicitly:
    
        make install girdir=/app/share/gir-1.0 typelibdir=/app/lib/girepository-1.0
    
    Both methods are workarounds though, which amount to completely
    short-circuiting the introspection.m4 code, and require knowing the
    exact directory to install those files. As such they are fragile, and
    could break if the install directories ever change.
    
    This commit changes the m4 code, so that it takes the prefix into
    account, removing the need for those workarounds entirely.
    
    More details:
    
    *   pkgconf doesn't support use env vars like pkg-config does:
    
        https://git.dereferenced.org/pkgconf/pkgconf/issues/2
    
    *   an example of the old and new workarounds:
    
        https://gitlab.gnome.org/GNOME/gnome-contacts/merge_requests/26/diffs

 m4/introspection.m4 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/m4/introspection.m4 b/m4/introspection.m4
index d89c3d90..6afe0304 100644
--- a/m4/introspection.m4
+++ b/m4/introspection.m4
@@ -59,8 +59,8 @@ m4_define([_GOBJECT_INTROSPECTION_CHECK_INTERNAL],
        INTROSPECTION_SCANNER=`$PKG_CONFIG --variable=g_ir_scanner gobject-introspection-1.0`
        INTROSPECTION_COMPILER=`$PKG_CONFIG --variable=g_ir_compiler gobject-introspection-1.0`
        INTROSPECTION_GENERATE=`$PKG_CONFIG --variable=g_ir_generate gobject-introspection-1.0`
-       INTROSPECTION_GIRDIR=`$PKG_CONFIG --variable=girdir gobject-introspection-1.0`
-       INTROSPECTION_TYPELIBDIR="$($PKG_CONFIG --variable=typelibdir gobject-introspection-1.0)"
+       INTROSPECTION_GIRDIR=`$PKG_CONFIG --define-variable=prefix=${prefix} --variable=girdir 
gobject-introspection-1.0`
+       INTROSPECTION_TYPELIBDIR="$($PKG_CONFIG --define-variable=prefix=${prefix} --variable=typelibdir 
gobject-introspection-1.0)"
        INTROSPECTION_CFLAGS=`$PKG_CONFIG --cflags gobject-introspection-1.0`
        INTROSPECTION_LIBS=`$PKG_CONFIG --libs gobject-introspection-1.0`
        INTROSPECTION_MAKEFILE=`$PKG_CONFIG --variable=datadir 
gobject-introspection-1.0`/gobject-introspection-1.0/Makefile.introspection