[geary/wip/web-extension-usr-local] Allow configuring the location of the web extension shared lib

[Michael Gratton <mjog src gnome org>]

commit 1877c81d00aadc0dc7f9c905729358b894081dfe
Author: Michael Gratton <mike vee net>
Date:   Thu Jan 17 11:08:26 2019 +1100

    Allow configuring the location of the web extension shared lib

 meson.build                                   |  2 ++
 src/client/application/geary-application.vala | 15 +++++++--------
 src/meson.build                               |  2 +-
 3 files changed, 10 insertions(+), 9 deletions(-)
---
diff --git a/meson.build b/meson.build
index ab69eb28..b3c34db0 100644
--- a/meson.build
+++ b/meson.build
@@ -27,6 +27,7 @@ locale_dir = join_paths(geary_prefix, get_option('localedir'))
 po_dir = join_paths(meson.source_root(), 'po')
 vapi_dir = join_paths(meson.source_root(), 'bindings', 'vapi')
 metadata_dir = join_paths(meson.source_root(), 'bindings', 'metadata')
+web_extensions_dir = join_paths(libdir, 'geary', 'web-extensions')
 
 # Make sure Meson can find our custom VAPI's
 add_project_arguments([
@@ -128,6 +129,7 @@ conf.set_quoted('_BUILD_ROOT_DIR', meson.build_root())
 conf.set_quoted('_SOURCE_ROOT_DIR', meson.source_root())
 conf.set_quoted('_GSETTINGS_DIR', join_paths(meson.build_root(), 'desktop'))
 conf.set_quoted('_INSTALL_PREFIX', geary_prefix)
+conf.set_quoted('_WEB_EXTENSIONS_DIR', web_extensions_dir)
 conf.set_quoted('LANGUAGE_SUPPORT_DIRECTORY', locale_dir)
 conf.set_quoted('ISO_CODE_639_XML', iso_639_xml)
 conf.set_quoted('ISO_CODE_3166_XML', iso_3166_xml)
diff --git a/src/client/application/geary-application.vala b/src/client/application/geary-application.vala
index e7ecc762..3d814cd2 100644
--- a/src/client/application/geary-application.vala
+++ b/src/client/application/geary-application.vala
@@ -7,6 +7,7 @@
 // Defined by CMake build script.
 extern const string _INSTALL_PREFIX;
 extern const string _GSETTINGS_DIR;
+extern const string _WEB_EXTENSIONS_DIR;
 extern const string _SOURCE_ROOT_DIR;
 extern const string _BUILD_ROOT_DIR;
 extern const string GETTEXT_PACKAGE;
@@ -295,16 +296,14 @@ public class GearyApplication : Gtk.Application {
     /**
      * Returns the directory containing the application's WebExtension libs.
      *
-     * If the application is installed, this will be
-     * `$INSTALL_PREFIX/lib/geary/web-extension`, else it will be
+     * When running from the installation prefix, this will be based
+     * on the Meson `libdir` option, and can be set by invoking `meson
+     * configure` as appropriate.
      */
     public File get_web_extensions_dir() {
-        File? dir = get_install_dir();
-        if (dir != null)
-            dir = dir.get_child("lib").get_child("geary").get_child("web-extensions");
-        else
-            dir = File.new_for_path(BUILD_ROOT_DIR).get_child("src");
-        return dir;
+        return (get_install_dir() != null)
+            ? File.new_for_path(_WEB_EXTENSIONS_DIR)
+            : File.new_for_path(BUILD_ROOT_DIR).get_child("src");
     }
 
     public File? get_desktop_file() {
diff --git a/src/meson.build b/src/meson.build
index c569a6a9..397d40cf 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -60,7 +60,7 @@ geary_web_process = library('geary-web-process',
     geary_engine_dep,
   ],
   install: true,
-  install_dir: join_paths(libdir, meson.project_name(), 'web-extensions'),
+  install_dir: web_extensions_dir
 )
 
 # Now finally, make the geary executable