Display an error for exceptions during GUI setup

Exceptions can occur between the start of GUI initialization and the Gtk
main loop, in particular if product images specify missing or bad
stylesheets. If an exception occurs in this code, the GUI must release
the GUI lock so that python-meh knows to start its own main loop.
Otherwise meh will enqueue itself in a main loop that will never be run,
and anaconda exits and reboots the system.

(cherry picked from commit 55a8cb7)

pyanaconda/ui/gui/__init__.py

@@ -654,55 +654,61 @@ def run(self):
             threads.threadMgr.wait_for_error_threads()
             sys.exit(1)
 
-        # Apply a widget-scale to hidpi monitors
-        self._widgetScale()
+        try:
+            # Apply a widget-scale to hidpi monitors
+            self._widgetScale()
 
-        while not self._currentAction:
-            self._currentAction = self._instantiateAction(self._actions[0])
-            if not self._currentAction:
-                self._actions.pop(0)
+            while not self._currentAction:
+                self._currentAction = self._instantiateAction(self._actions[0])
+                if not self._currentAction:
+                    self._actions.pop(0)
 
-            if not self._actions:
-                return
-
-        self._currentAction.initialize()
-        self._currentAction.entry_logger()
-        self._currentAction.refresh()
+                if not self._actions:
+                    return
 
-        self._currentAction.window.set_beta(not self._isFinal)
-        self._currentAction.window.set_property("distribution", self._distributionText().upper())
+            self._currentAction.initialize()
+            self._currentAction.entry_logger()
+            self._currentAction.refresh()
 
-        # Set some program-wide settings.
-        settings = Gtk.Settings.get_default()
-        settings.set_property("gtk-font-name", "Cantarell")
-        settings.set_property("gtk-icon-theme-name", "gnome")
+            self._currentAction.window.set_beta(not self._isFinal)
+            self._currentAction.window.set_property("distribution", self._distributionText().upper())
 
-        # Apply the application stylesheet
-        provider = Gtk.CssProvider()
-        provider.load_from_path("/usr/share/anaconda/anaconda-gtk.css")
-        Gtk.StyleContext.add_provider_for_screen(Gdk.Screen.get_default(), provider,
-                Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
+            # Set some program-wide settings.
+            settings = Gtk.Settings.get_default()
+            settings.set_property("gtk-font-name", "Cantarell")
+            settings.set_property("gtk-icon-theme-name", "gnome")
 
-        # Apply the installclass stylesheet
-        if self.instclass.stylesheet:
+            # Apply the application stylesheet
             provider = Gtk.CssProvider()
-            provider.load_from_path(self.instclass.stylesheet)
+            provider.load_from_path("/usr/share/anaconda/anaconda-gtk.css")
             Gtk.StyleContext.add_provider_for_screen(Gdk.Screen.get_default(), provider,
-                    STYLE_PROVIDER_PRIORITY_INSTALLCLASS)
+                    Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
 
-        # Look for updates to the stylesheet and apply them at a higher priority
-        for updates_dir in ("updates", "product"):
-            updates_css = "/run/install/%s/anaconda-gtk.css" % updates_dir
-            if os.path.exists(updates_css):
+            # Apply the installclass stylesheet
+            if self.instclass.stylesheet:
                 provider = Gtk.CssProvider()
-                provider.load_from_path(updates_css)
+                provider.load_from_path(self.instclass.stylesheet)
                 Gtk.StyleContext.add_provider_for_screen(Gdk.Screen.get_default(), provider,
-                        STYLE_PROVIDER_PRIORITY_UPDATES)
+                        STYLE_PROVIDER_PRIORITY_INSTALLCLASS)
 
-        self.mainWindow.setCurrentAction(self._currentAction)
+            # Look for updates to the stylesheet and apply them at a higher priority
+            for updates_dir in ("updates", "product"):
+                updates_css = "/run/install/%s/anaconda-gtk.css" % updates_dir
+                if os.path.exists(updates_css):
+                    provider = Gtk.CssProvider()
+                    provider.load_from_path(updates_css)
+                    Gtk.StyleContext.add_provider_for_screen(Gdk.Screen.get_default(), provider,
+                            STYLE_PROVIDER_PRIORITY_UPDATES)
 
-        # Do this at the last possible minute.
-        unbusyCursor()
+            self.mainWindow.setCurrentAction(self._currentAction)
+
+            # Do this at the last possible minute.
+            unbusyCursor()
+        # If anything went wrong before we start the Gtk main loop, release
+        # the gui lock and re-raise the exception so that meh can take over
+        except Exception:
+            self._gui_lock.release()
+            raise
 
         Gtk.main()