gnome: Support configure_file() output in compile_resources

We can't support generated XML files with custom_target() because the
dependency scanning happens at configure time, but we *can* support
generating them with configure_file().

Closes https://github.com/mesonbuild/meson/issues/1380

mesonbuild/modules/gnome.py

@@ -105,7 +105,13 @@ can not be used with the current version of glib-compiled-resources, due to
 
         ifile = args[1]
         if isinstance(ifile, mesonlib.File):
-            ifile = os.path.join(ifile.subdir, ifile.fname)
+            # glib-compile-resources will be run inside the source dir,
+            # so we need either 'src_to_build' or the absolute path.
+            # Absolute path is the easiest choice.
+            if ifile.is_built:
+                ifile = os.path.join(state.environment.get_build_dir(), ifile.subdir, ifile.fname)
+            else:
+                ifile = os.path.join(ifile.subdir, ifile.fname)
         elif isinstance(ifile, str):
             ifile = os.path.join(state.subdir, ifile)
         elif isinstance(ifile, (interpreter.CustomTargetHolder,
@@ -206,9 +212,10 @@ can not be used with the current version of glib-compiled-resources, due to
             cmd += ['--sourcedir', os.path.join(state.subdir, source_dir)]
         cmd += ['--sourcedir', state.subdir] # Current dir
 
-        pc, stdout = Popen_safe(cmd, cwd=state.environment.get_source_dir())[0:2]
+        pc, stdout, stderr = Popen_safe(cmd, cwd=state.environment.get_source_dir())
         if pc.returncode != 0:
-            mlog.warning('glib-compile-resources has failed to get the dependencies for {}'.format(cmd[1]))
+            m = 'glib-compile-resources failed to get dependencies for {}:\n{}'
+            mlog.warning(m.format(cmd[1], stderr))
             raise subprocess.CalledProcessError(pc.returncode, cmd)
 
         dep_files = stdout.split('\n')[:-1]

test cases/frameworks/7 gnome/resources/copyfile.py

@@ -0,0 +1,6 @@
+#!/usr/bin/env python3
+
+import sys
+import shutil
+
+shutil.copy(sys.argv[1], sys.argv[2])

test cases/frameworks/7 gnome/resources/meson.build

@@ -1,8 +1,15 @@
 # There are two tests here, because the 2nd one depends on a version of
-# GLib (2.48.2) that is very recent at the time of writing.
+# GLib (2.51.1) that is very recent at the time of writing.
+
+copyfile = find_program('copyfile.py')
+
+simple_gresource = configure_file(
+  input : 'simple.gresource.xml',
+  output : 'simple-gen.gresource.xml',
+  command : [copyfile, '@INPUT@', '@OUTPUT@'])
 
 simple_resources = gnome.compile_resources('simple-resources',
-  'simple.gresource.xml',
+  simple_gresource,
   install_header : true,
   export : true,
   source_dir : '../resources-data',