gdbus-codegen: Don't assume bindir and datadir share prefix

This assumption breaks when, for instance:

* Called as /bin/gdbus-codegen
* Installed on Windows in a directory that is not `bin/`

For such cases, we cannot make any assumptions about the directory
structure, and must hard-code the datadir.

https://bugzilla.gnome.org/show_bug.cgi?id=786785

gio/gdbus-2.0/codegen/Makefile.am

@@ -21,7 +21,7 @@ CLEANFILES += gdbus-codegen
 EXTRA_DIST += gdbus-codegen.in
 
 gdbus-codegen: gdbus-codegen.in Makefile $(codegen_PYTHON)
-	$(AM_V_GEN) sed -e 's,@datadir\@,$(datadir),' -e 's,@PYTHON\@,$(PYTHON),' $< > $@.tmp && mv $@.tmp $@
+	$(AM_V_GEN) sed -e 's,@DATADIR\@,$(datadir),' -e 's,@PYTHON\@,$(PYTHON),' $< > $@.tmp && mv $@.tmp $@
 	@chmod a+x $@
 
 clean-local:

gio/gdbus-2.0/codegen/gdbus-codegen.in

@@ -37,6 +37,15 @@ else:
     # parent directory to the python path.
     path = os.path.join(filedir, '..')
 
+# If the above path detection failed, use the hard-coded datadir. This can
+# happen when, for instance, bindir and datadir are not in the same prefix or
+# on Windows where we cannot make any guarantees about the directory structure.
+#
+# In these cases our installation cannot be relocatable, but at least we should
+# be able to find the codegen module.
+if not os.path.isfile(os.path.join(path, 'codegen', 'codegen_main.py')):
+    path = os.path.join('@DATADIR@', 'glib-2.0')
+
 sys.path.insert(0, os.path.abspath(path))
 from codegen import codegen_main
 

gio/gdbus-2.0/codegen/meson.build

@@ -11,6 +11,7 @@ gdbus_codegen_files = [
 gdbus_codegen_conf = configuration_data()
 gdbus_codegen_conf.set('VERSION', glib_version)
 gdbus_codegen_conf.set('PYTHON', python.path())
+gdbus_codegen_conf.set('DATADIR', glib_datadir)
 
 # Install gdbus-codegen executable
 # FIXME: Set permissions