Fix crash w/ GUI if Proton install is incomplete

Fix Protontricks GUI crashing if the Proton installation used by the
game is incomplete. We already show a human-readable error message in
the CLI use case, so do the same for the GUI.

Refs #274

CHANGELOG.md

@@ -7,6 +7,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## [Unreleased]
 ### Fixed
  - Fix Protontricks crash when custom Proton has an empty `compatibilitytool.vdf` manifest
+ - Fix Protontricks GUI crash when Proton installation is incomplete
 
 ## [1.11.0] - 2023-12-30
 ### Added

src/protontricks/cli/main.py

@@ -280,6 +280,13 @@ def exit_(error):
         if not proton_app:
             exit_("Proton installation could not be found!")
 
+        if not proton_app.is_proton_ready:
+            exit_(
+                "Proton installation is incomplete. Have you launched a Steam "
+                "app using this Proton version at least once to finish the "
+                "installation?"
+            )
+
         run_command(
             winetricks_path=winetricks_path,
             proton_app=proton_app,

tests/cli/test_main.py

@@ -760,6 +760,25 @@ def test_run_gui_no_games(self, cli, default_proton):
 
         assert "Found no games" in result
 
+    def test_run_gui_proton_incomplete(
+            self, cli, steam_app_factory, default_proton, gui_provider):
+        """
+        Try running Protontricks GUI using a Proton installation that
+        is incomplete because it hasn't been launched yet.
+        """
+        # Remove the 'dist' directory to make the Proton installation
+        # incomplete
+        shutil.rmtree(str(default_proton.install_path / "dist"))
+
+        steam_app_factory(name="Fake game", appid=10)
+
+        # Fake the user selecting the game
+        gui_provider.mock_stdout = "Fake game 1: 10"
+
+        result = cli(["--gui"], expect_returncode=1)
+
+        assert "Proton installation is incomplete" in result
+
 
 class TestCLICommand:
     def test_run_command(