Merge pull request #2101 from calamares/paolodongilli-calamares

Enable preferred-greeters with lightdm

src/modules/displaymanager/displaymanager.conf

@@ -64,6 +64,12 @@ sysconfigSetup: false
 #
 # greetd has configurable user and group; the user and group is created if it
 # does not exist, and the user is set as default-session user.
+#
+# lightdm has a list of greeters to look for, preferring them in order if
+# they are installed (if not, picks the alphabetically first greeter that is installed).
+#
 greetd:
   greeter_user: "tom_bombadil"
   greeter_group: "wheel"
+lightdm:
+  preferred_greeters: ["lightdm-greeter.desktop", "slick-greeter.desktop"]

src/modules/displaymanager/displaymanager.schema.yaml

@@ -26,4 +26,7 @@ properties:
             greeter_user: { type: string }
             greeter_group: { type: string }
         additionalProperties: false
-
+    lightdm:
+        type: object
+        properties:
+            preferred_greeters: { type: array, items: { type: string } }

src/modules/displaymanager/main.py

@@ -544,6 +544,11 @@ class DMlightdm(DisplayManager):
     name = "lightdm"
     executable = "lightdm"
 
+    # Can be overridden in the .conf file. With no value it won't match any
+    # desktop file in the xgreeters directory and instead we end up picking
+    # the alphabetically first file there.
+    preferred_greeters = []
+
     def set_autologin(self, username, do_autologin, default_desktop_environment):
         # Systems with LightDM as Desktop Manager
         # Ideally, we should use configparser for the ini conf file,
@@ -633,41 +638,56 @@ class DMlightdm(DisplayManager):
                 )
             )
 
+    def find_preferred_greeter(self, greeters_dir):
+        """
+        On Debian, lightdm-greeter.desktop is typically a symlink managed
+        by update-alternatives pointing to /etc/alternatives/lightdm-greeter
+        which is also a symlink to a real .desktop file back in /usr/share/xgreeters/
+
+        Returns a path *into the mounted target* of the preferred greeter -- usually
+        a .desktop file that specifies where the actual executable is. May return
+        None to indicate nothing-was-found.
+        """
+        greeters_dir = "usr/share/xgreeters"
+        greeters_target_path = os.path.join(self.root_mount_point, greeters_dir)
+        available_names = os.listdir(greeters_target_path)
+        available_names.sort()
+        desktop_names = [n for n in self.preferred_greeters if n in available_names] # Preferred ones
+        if desktop_names:
+            return desktop_names[0]
+        desktop_names = [n for n in available_names if n.endswith(".desktop")] # .. otherwise any .desktop
+        if desktop_names:
+            return desktop_names[0]
+        return None
+
+
     def greeter_setup(self):
-        lightdm_conf_path = os.path.join(
-            self.root_mount_point, "etc/lightdm/lightdm.conf"
-            )
+        lightdm_conf_path = os.path.join(self.root_mount_point, "etc/lightdm/lightdm.conf")
+        greeter_path = self.find_preferred_greeter()
 
-        # configure lightdm-greeter
-        greeter_path = os.path.join(
-            self.root_mount_point, "usr/share/xgreeters"
-            )
+        if greeter_path is not None and os.path.exists(greeter_path):
+            greeter = os.path.basename(os.path.realpath(greeter_path)) # Follow symlinks, hope they are not absolute
+            if greeter.endswith('.desktop'):
+                greeter = greeter[:-8] # Remove ".desktop" from end
 
-        if (os.path.exists(greeter_path)):
-            # configure first found lightdm-greeter
-            for entry in os.listdir(greeter_path):
-                if entry.endswith('.desktop'):
-                    greeter = entry.split('.')[0]
-                    libcalamares.utils.debug(
-                        "found greeter {!s}".format(greeter)
-                        )
-                    os.system(
-                        "sed -i -e \"s/^.*greeter-session=.*"
-                        "/greeter-session={!s}/\" {!s}".format(
-                            greeter,
-                            lightdm_conf_path
-                            )
-                        )
-                    libcalamares.utils.debug(
-                        "{!s} configured as greeter.".format(greeter)
-                        )
-                    break
+            libcalamares.utils.debug("found greeter {!s}".format(greeter))
+            os.system(
+                "sed -i -e \"s/^.*greeter-session=.*"
+                "/greeter-session={!s}/\" {!s}".format(
+                    greeter,
+                    lightdm_conf_path
+                )
+            )
+            libcalamares.utils.debug("{!s} configured as greeter.".format(greeter))
+        else:
+            if greeter_path is None:
+                libcalamares.utils.error("No greeter found at all, preferred {!s}".format(self.preferred_greeters))
             else:
-                return (
-                    _("Cannot configure LightDM"),
-                    _("No LightDM greeter installed.")
-                    )
-
+                libcalamares.utils.error("Greeter {!s} selected but file does not exist".format(greeter_path))
+            return (
+                _("Cannot configure LightDM"),
+                _("No LightDM greeter installed.")
+            )
 
 class DMslim(DisplayManager):
     name = "slim"