Stop telling every desktop that it is KDE

Only GNOME was recognised, and everything else was handed to KWin. On i3,
XFCE, Cinnamon, MATE, sway and the rest, Dikte wrote an entry into
kglobalshortcutsrc that nothing reads, called the session KDE, and
promised that the keys would work after the next login. They never did.

There is no backend to write for any of them. The /dev/input listener is
already desktop-agnostic, so those sessions are the case macOS has always
been: no registry, nothing to install, nothing to remove, and the
combination held by the running process. One backend() function decides
which of the four this session has, and the name shown, the status read
back, what Install writes, what Settings explains and what the installer
promises are all taken from it, so they cannot disagree.

A desktop now only counts when the program that writes its registry is
there too. A GNOME session without gsettings and a Plasma one without
kwriteconfig6 fall to the listener rather than to a file, which is also
how Plasma 5 stops erroring on a kwriteconfig6 it never had.

What Settings shows on those desktops is the truth: no Install button, no
KWin, no listener checkbox (it is the mechanism, not a choice), what
reading /dev/input costs, that the focused application sees the keys too,
and the command to bind if you would rather your desktop owned them. The
evdev listener records what it is listening for the way the Carbon one
does, so the status line has something to say there at all.

Closes #28

tests/test_ui.py

@@ -6,6 +6,7 @@ save, so a setting added to one half and not the other is silently reset the
 next time anybody presses Save. That is the failure this catches.
 """
 
+import os
 import sys
 import unittest
 from typing import ClassVar
@@ -107,13 +108,21 @@ class Settings(DikteTest):
     # one. Everything else about the window is the same on both.
     changed = CHANGED
     platform = "linux"
+    # A session with no shortcut registry, which is what most Linux desktops
+    # are. The subclasses below stand on the other two. Pinned rather than
+    # inherited from whatever the machine running the suite is logged into,
+    # since half the shortcut tab is built from the answer.
+    desktop = "i3"
+    tools: ClassVar[tuple] = ()
 
     def setUp(self):
         super().setUp()
         # No pactl, no model lists over the network, and no modal dialogue
         # waiting for somebody to press OK.
         self.enterContext(mock.patch.object(sys, "platform", self.platform))
-        self.enterContext(only_these_tools())
+        self.enterContext(only_these_tools(*self.tools))
+        self.enterContext(mock.patch.dict(
+            os.environ, {"XDG_CURRENT_DESKTOP": self.desktop}))
         self.enterContext(mock.patch.object(QMessageBox, "information"))
         self.enterContext(mock.patch.object(settings_ui.SettingsWindow,
                                             "_load_models"))
@@ -254,6 +263,31 @@ class Settings(DikteTest):
         window = self.window(cfg.Config())
         self.assertEqual(set(window._shortcut_rows), set(hotkey.SHORTCUTS))
 
+    def shortcut_tab_text(self, window):
+        """Everything the shortcut tab says, as one string."""
+        return "\n".join(
+            widget.text() for widget in
+            window.findChildren(settings_ui.QLabel)
+            + window.findChildren(settings_ui.QLineEdit)
+            + window.findChildren(settings_ui.QPushButton)
+        )
+
+    def test_the_shortcut_tab_talks_about_this_session_and_no_other(self):
+        """A desktop with no registry is told the truth: nothing is installed
+        anywhere, Dikte is listening, and here is the command to bind if the
+        desktop should own the keys instead. It used to be promised a KWin that
+        was not running."""
+        window = self.window(cfg.Config())
+        text = self.shortcut_tab_text(window)
+        self.assertIn("i3 keeps no shortcut registry", text)
+        self.assertNotIn("KWin", text)
+        self.assertIn("dikte.py toggle", text)
+        # Not a choice to offer where it is the only mechanism there is.
+        self.assertTrue(window.evdev_enabled.isHidden())
+        self.assertFalse([button for button in
+                          window.findChildren(settings_ui.QPushButton)
+                          if "install" in button.text().lower()])
+
     def test_emptying_a_shortcut_turns_it_off_but_not_the_toggle(self):
         """The application is unusable without the toggle, so that one box
         falls back. The rest stay empty, which is how they are switched off.
@@ -415,7 +449,16 @@ class MacSettings(Settings):
     def test_the_listener_is_not_offered_as_a_choice(self):
         """It is the whole mechanism there; turning it off would leave nothing."""
         window = self.window(cfg.Config())
-        self.assertFalse(window.evdev_enabled.isVisible())
+        self.assertTrue(window.evdev_enabled.isHidden())
+
+    def test_the_shortcut_tab_talks_about_this_session_and_no_other(self):
+        """Carbon holds the keys here, so there is no command to bind and no
+        /dev/input to be let into."""
+        window = self.window(cfg.Config())
+        text = self.shortcut_tab_text(window)
+        self.assertIn("Dikte asks macOS for these combinations", text)
+        self.assertNotIn("KWin", text)
+        self.assertNotIn("dikte.py toggle", text)
 
     def test_the_paste_keys_on_offer_are_the_ones_a_mac_uses(self):
         window = self.window(cfg.Config())
@@ -424,6 +467,27 @@ class MacSettings(Settings):
         self.assertEqual(offered, paste.MACOS.shortcuts)
 
 
+class KdeSettings(Settings):
+    """The same window on the one desktop that keeps a registry and makes you
+    wait for it. Nothing here is about KDE: it is the rest of the window,
+    checked on the platform where Install, Remove and the listener's own
+    checkbox are all on screen."""
+
+    desktop = "KDE"
+    tools: ClassVar[tuple] = ("kwriteconfig6",)
+
+    def test_the_shortcut_tab_talks_about_this_session_and_no_other(self):
+        window = self.window(cfg.Config())
+        text = self.shortcut_tab_text(window)
+        self.assertIn("KWin only reads shortcut settings at startup", text)
+        self.assertIn("Install as a KDE shortcut", text)
+        self.assertNotIn("keeps no shortcut registry", text)
+        self.assertNotIn("dikte.py toggle", text)
+        # Here it is a choice: the wait for the next login, or the key press
+        # reaching the focused application as well.
+        self.assertFalse(window.evdev_enabled.isHidden())
+
+
 class Overlay(DikteTest):
     def overlay(self, **kwargs):
         widget = overlay_module.Overlay(**kwargs)