[gimp] app: identifier of MyPaint brush GimpData using ${mypaint_brushes_dir}.

[Jehan Pagès <jehanp src gnome org>]

commit f6b586237cb8c912c1503f8e6086edd17f07d4df
Author: Jehan <jehan girinstud io>
Date:   Sun Apr 29 00:32:21 2018 +0200

    app: identifier of MyPaint brush GimpData using ${mypaint_brushes_dir}.
    
    Absolute paths not to be used in $XDG_CONFIG/GIMP/{version}/tags.xml.
    These are actually only an identifier, and not used as a path at all
    anyway. Moreover MyPaint brushes even generate checksum (which allows
    to remap the GimpData appropriately even if the paths are changing).
    But anyway it's better not to have absolute paths when we can prevent
    so.

 app/core/Makefile.am |    1 +
 app/core/gimpdata.c  |    8 ++++++++
 2 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/app/core/Makefile.am b/app/core/Makefile.am
index 1d4855f..792bb02 100644
--- a/app/core/Makefile.am
+++ b/app/core/Makefile.am
@@ -19,6 +19,7 @@ AM_CPPFLAGS = \
        $(GEGL_CFLAGS)                                  \
        $(GDK_PIXBUF_CFLAGS)                            \
        $(LIBMYPAINT_CFLAGS)                            \
+       $(MYPAINT_BRUSHES_CFLAGS)                       \
        $(GEXIV2_CFLAGS)                                \
        -I$(includedir)
 
diff --git a/app/core/gimpdata.c b/app/core/gimpdata.c
index 5dcc26e..f909ed8 100644
--- a/app/core/gimpdata.c
+++ b/app/core/gimpdata.c
@@ -498,6 +498,14 @@ gimp_data_get_identifier (GimpTagged *tagged)
           identifier = g_filename_to_utf8 (tmp, -1, NULL, NULL, NULL);
           g_free (tmp);
         }
+      else if (g_str_has_prefix (path, MYPAINT_BRUSHES_DIR))
+        {
+          tmp = g_strconcat ("${mypaint_brushes_dir}",
+                             path + strlen (MYPAINT_BRUSHES_DIR),
+                             NULL);
+          identifier = g_filename_to_utf8 (tmp, -1, NULL, NULL, NULL);
+          g_free (tmp);
+        }
       else
         {
           identifier = g_filename_to_utf8 (path, -1,