[libhandy/wip/exalm/dark: 6/6] style-manager: Check if the current theme exists

[Alexander Mikhaylenko <alexm src gnome org>]

commit 2fa1b31af9bf58ca98af7eddf66fb0e41c2491e3
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Mon Sep 20 15:29:16 2021 +0500

    style-manager: Check if the current theme exists
    
    Avoid falling back to Adwaita with no way to set dark variant.
    
    The check is not perfect and will fail if libhandy and GTK prefixes differ.
    Nothing we can do about that though.
    
    Also it will stop picking up changes until restart if theme has been
    invalid even once. This is unfixable too, since we can't track changes
    on GdkScreen settings directly, and as soon as we set gtk-theme-name is set
    it can't be used to track changes anymore.
    
    Still better than nothing.

 src/hdy-style-manager.c | 217 ++++++++++++++++++++++++++++++++++++++++--------
 src/meson.build         |   1 +
 2 files changed, 183 insertions(+), 35 deletions(-)
---
diff --git a/src/hdy-style-manager.c b/src/hdy-style-manager.c
index a60cac9c..d52f2630 100644
--- a/src/hdy-style-manager.c
+++ b/src/hdy-style-manager.c
@@ -67,6 +67,145 @@ static GParamSpec *props[LAST_PROP];
 static GHashTable *display_style_managers = NULL;
 static HdyStyleManager *default_instance = NULL;
 
+static gchar *
+get_theme_dir (void)
+{
+  const gchar *var;
+
+  var = g_getenv ("GTK_DATA_PREFIX");
+  if (var == NULL)
+    var = PREFIX;
+
+  return g_build_filename (var, "share", "themes", NULL);
+}
+
+#if (GTK_MINOR_VERSION % 2)
+#define MINOR (GTK_MINOR_VERSION + 1)
+#else
+#define MINOR GTK_MINOR_VERSION
+#endif
+
+static gchar *
+find_theme_dir (const gchar *dir,
+                const gchar *subdir,
+                const gchar *name,
+                const gchar *variant)
+{
+  g_autofree gchar *file = NULL;
+  g_autofree gchar *base = NULL;
+  gchar *path;
+  gint i;
+
+  if (variant)
+    file = g_strconcat ("gtk-", variant, ".css", NULL);
+  else
+    file = g_strdup ("gtk.css");
+
+  if (subdir)
+    base = g_build_filename (dir, subdir, name, NULL);
+  else
+    base = g_build_filename (dir, name, NULL);
+
+  for (i = MINOR; i >= 0; i = i - 2) {
+    g_autofree gchar *subsubdir = NULL;
+
+    if (i < 14)
+      i = 0;
+
+    subsubdir = g_strdup_printf ("gtk-3.%d", i);
+    path = g_build_filename (base, subsubdir, file, NULL);
+
+    if (g_file_test (path, G_FILE_TEST_EXISTS))
+      break;
+
+    g_free (path);
+    path = NULL;
+  }
+
+  return path;
+}
+
+#undef MINOR
+
+static gchar *
+find_theme (const gchar *name,
+            const gchar *variant)
+{
+  g_autofree gchar *dir = NULL;
+  const gchar *const *dirs;
+  gchar *path;
+  gint i;
+
+  /* First look in the user's data directory */
+  path = find_theme_dir (g_get_user_data_dir (), "themes", name, variant);
+  if (path)
+    return path;
+
+  /* Next look in the user's home directory */
+  path = find_theme_dir (g_get_home_dir (), ".themes", name, variant);
+  if (path)
+    return path;
+
+  /* Look in system data directories */
+  dirs = g_get_system_data_dirs ();
+  for (i = 0; dirs[i]; i++) {
+    path = find_theme_dir (dirs[i], "themes", name, variant);
+    if (path)
+      return path;
+  }
+
+  /* Finally, try in the default theme directory */
+  dir = get_theme_dir ();
+  path = find_theme_dir (dir, NULL, name, variant);
+
+  return path;
+}
+
+static gboolean
+check_theme_exists (const gchar *name,
+                    const gchar *variant)
+{
+  g_autofree gchar *resource_path = NULL;
+  g_autofree gchar *path = NULL;
+
+  /* try loading the resource for the theme. This is mostly meant for built-in
+   * themes.
+   */
+  if (variant)
+    resource_path = g_strdup_printf ("/org/gtk/libgtk/theme/%s/gtk-%s.css", name, variant);
+  else
+    resource_path = g_strdup_printf ("/org/gtk/libgtk/theme/%s/gtk.css", name);
+
+  if (g_resources_get_info (resource_path, 0, NULL, NULL, NULL))
+    return TRUE;
+
+  /* Next try looking for files in the various theme directories. */
+  path = find_theme (name, variant);
+
+  return path != NULL;
+}
+
+static gchar *
+get_system_theme_name (void)
+{
+  GdkScreen *screen = gdk_screen_get_default ();
+  g_auto (GValue) value = G_VALUE_INIT;
+
+  g_value_init (&value, G_TYPE_STRING);
+  if (!gdk_screen_get_setting (screen, "gtk-theme-name", &value))
+    return g_strdup ("Adwaita");
+
+  return g_value_dup_string (&value);
+}
+
+static gboolean
+check_current_theme_exists (gboolean dark)
+{
+  g_autofree gchar *theme_name = get_system_theme_name ();
+
+  return check_theme_exists (theme_name, dark ? "dark" : NULL);
+}
+
 static void
 warn_prefer_dark_theme (HdyStyleManager *self)
 {
@@ -103,19 +242,6 @@ register_display (GdkDisplayManager *display_manager,
                     NULL);
 }
 
-static char *
-get_system_theme_name (void)
-{
-  GdkScreen *screen = gdk_screen_get_default ();
-  g_auto (GValue) value = G_VALUE_INIT;
-
-  g_value_init (&value, G_TYPE_STRING);
-  if (!gdk_screen_get_setting (screen, "gtk-theme-name", &value))
-    return g_strdup ("Adwaita");
-
-  return g_value_dup_string (&value);
-}
-
 static gboolean
 enable_animations_cb (HdyStyleManager *self)
 {
@@ -130,13 +256,29 @@ enable_animations_cb (HdyStyleManager *self)
   return G_SOURCE_REMOVE;
 }
 
+static void update_stylesheet (HdyStyleManager *self);
+
+static gboolean
+unblock_theme_name_changed_cb (HdyStyleManager *self)
+{
+  GdkScreen *screen;
+  GtkSettings *gtk_settings;
+
+  screen = gdk_display_get_default_screen (self->display);
+  gtk_settings = gtk_settings_get_for_screen (screen);
+
+  g_signal_handlers_unblock_by_func (gtk_settings,
+                                     G_CALLBACK (update_stylesheet),
+                                     self);
+
+  return G_SOURCE_REMOVE;
+}
+
 static void
 update_stylesheet (HdyStyleManager *self)
 {
   GdkScreen *screen;
   GtkSettings *gtk_settings;
-  const char *theme_name;
-  gboolean enable_animations;
 
   if (!self->display)
     return;
@@ -144,40 +286,40 @@ update_stylesheet (HdyStyleManager *self)
   screen = gdk_display_get_default_screen (self->display);
   gtk_settings = gtk_settings_get_for_screen (screen);
 
-  if (hdy_settings_get_high_contrast (self->settings))
-    theme_name = g_strdup (self->dark ? "HighContrastInverse" : "HighContrast");
-  else
-    theme_name = get_system_theme_name ();
-
-  if (self->animation_timeout_id) {
-    g_clear_handle_id (&self->animation_timeout_id, g_source_remove);
-    enable_animations = TRUE;
-  } else {
-    g_object_get (gtk_settings,
-                  "gtk-enable-animations", &enable_animations,
-                  NULL);
-  }
+  g_clear_handle_id (&self->animation_timeout_id, g_source_remove);
 
   g_signal_handlers_block_by_func (gtk_settings,
                                    G_CALLBACK (warn_prefer_dark_theme),
                                    self);
+  g_signal_handlers_block_by_func (gtk_settings,
+                                   G_CALLBACK (update_stylesheet),
+                                   self);
 
   g_object_set (gtk_settings,
                 "gtk-enable-animations", FALSE,
-                "gtk-theme-name", theme_name,
                 "gtk-application-prefer-dark-theme", self->dark,
                 NULL);
 
+  if (hdy_settings_get_high_contrast (self->settings))
+    g_object_set (gtk_settings,
+                  "gtk-theme-name",
+                  self->dark ? "HighContrastInverse" : "HighContrast",
+                  NULL);
+  else if (check_current_theme_exists (self->dark))
+    gtk_settings_reset_property (gtk_settings, "gtk-theme-name");
+  else
+    g_object_set (gtk_settings, "gtk-theme-name", "Adwaita", NULL);;
+
   g_signal_handlers_unblock_by_func (gtk_settings,
                                      G_CALLBACK (warn_prefer_dark_theme),
                                      self);
 
-  if (enable_animations) {
-    self->animation_timeout_id =
-      g_timeout_add (SWITCH_DURATION,
-                     G_SOURCE_FUNC (enable_animations_cb),
-                     self);
-  }
+  self->animation_timeout_id =
+    g_timeout_add (SWITCH_DURATION,
+                   G_SOURCE_FUNC (enable_animations_cb),
+                   self);
+
+  g_idle_add (G_SOURCE_FUNC (unblock_theme_name_changed_cb), self);
 }
 
 static inline gboolean
@@ -251,6 +393,11 @@ hdy_style_manager_constructed (GObject *object)
                              G_CALLBACK (warn_prefer_dark_theme),
                              self,
                              G_CONNECT_SWAPPED);
+    g_signal_connect_object (settings,
+                             "notify::gtk-theme-name",
+                             G_CALLBACK (update_stylesheet),
+                             self,
+                             G_CONNECT_SWAPPED);
   }
 
   self->settings = hdy_settings_get_default ();
diff --git a/src/meson.build b/src/meson.build
index a4be923b..d0873237 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -220,6 +220,7 @@ libhandy_c_args = [
 config_h = configuration_data()
 config_h.set_quoted('GETTEXT_PACKAGE', 'libhandy')
 config_h.set_quoted('LOCALEDIR', get_option('prefix') / get_option('localedir'))
+config_h.set_quoted('PREFIX', get_option('prefix'))
 
 # Symbol visibility
 if target_system == 'windows'