[grilo/sam/meson-subproject-fix] build: Avoid using meson.source_root()

[Sam Thursfield <sthursfield src gnome org>]

commit b88735d143434bd6c7c4e25671b296e97ee5c30d
Author: Sam Thursfield <sam afuera me uk>
Date:   Sun Sep 29 16:51:23 2019 +0200

    build: Avoid using meson.source_root()
    
    The value of meson.source_root() can't be trusted because if we are
    embedded via subproject() into a larger project, the source root will
    be that of the parent project.
    
    Instead, use a variable to keep track of the toplevel source directory.

 doc/grilo/meson.build           | 14 +++++++-------
 meson.build                     |  2 ++
 tools/grilo-inspect/meson.build |  2 +-
 3 files changed, 10 insertions(+), 8 deletions(-)
---
diff --git a/doc/grilo/meson.build b/doc/grilo/meson.build
index b87d25d..ef5740f 100644
--- a/doc/grilo/meson.build
+++ b/doc/grilo/meson.build
@@ -23,8 +23,8 @@ private_headers = [
 gnome.gtkdoc('grilo',
     main_sgml: 'grilo-docs.sgml',
     src_dir: [
-        join_paths(meson.source_root(), 'src'),
-        join_paths(meson.source_root(), 'libs'),
+        join_paths(source_root, 'src'),
+        join_paths(source_root, 'libs'),
     ],
     dependencies: libgrl_dep,
     gobject_typesfile: types,
@@ -37,10 +37,10 @@ gnome.gtkdoc('grilo',
         'quick-start.xml',
         'writing-apps.xml',
         'overview.xml',
-        join_paths(meson.source_root(), 'examples', 'configuring-plugins.c'),
-        join_paths(meson.source_root(), 'examples', 'browsing.c'),
-        join_paths(meson.source_root(), 'examples', 'searching.c'),
-        join_paths(meson.source_root(), 'examples', 'multivalues.c'),
-        join_paths(meson.source_root(), 'examples', 'efficient-metadata-resolution.c'),
+        join_paths(source_root, 'examples', 'configuring-plugins.c'),
+        join_paths(source_root, 'examples', 'browsing.c'),
+        join_paths(source_root, 'examples', 'searching.c'),
+        join_paths(source_root, 'examples', 'multivalues.c'),
+        join_paths(source_root, 'examples', 'efficient-metadata-resolution.c'),
     ]
 )
diff --git a/meson.build b/meson.build
index 952651e..846041b 100644
--- a/meson.build
+++ b/meson.build
@@ -72,6 +72,8 @@ if enable_testui
     oauth_dep = dependency('oauth', required: false)
 endif
 
+source_root = meson.current_source_dir()
+
 prefix = get_option('prefix')
 includedir = join_paths(prefix, get_option('includedir'))
 libdir = join_paths(prefix, get_option('libdir'))
diff --git a/tools/grilo-inspect/meson.build b/tools/grilo-inspect/meson.build
index 048c232..3dd6c2f 100644
--- a/tools/grilo-inspect/meson.build
+++ b/tools/grilo-inspect/meson.build
@@ -14,7 +14,7 @@ if not python.found()
 endif
 run_command(python,
     '@0@/generate_core_keys.py'.format(meson.current_source_dir()),
-    '@0@/src/grl-metadata-key.h'.format(meson.source_root()),
+    '@0@/src/grl-metadata-key.h'.format(source_root),
     '@0@/grl-core-keys.h'.format(meson.current_build_dir()))
 
 configure_file(output: 'config.h',