config: Handle config.py errors while updating mutables

Fixes #3580

3 files changed, 25 insertions, 1 deletions

diff --git a/qutebrowser/config/configfiles.py b/qutebrowser/config/configfiles.py
index db9eda2f3..556cae4e5 100644
--- a/qutebrowser/config/configfiles.py
+++ b/qutebrowser/config/configfiles.py
@@ -680,7 +680,9 @@ class ConfigAPI:
                  " (to load settings configured via the GUI) or "
                  "`config.load_autoconfig(False)` (to not do so)"))
             self.errors.append(desc)
-        self._config.update_mutables()
+
+        with self._handle_error("updating mutated values"):
+            self._config.update_mutables()
 
     def load_autoconfig(self, load_config: bool = True) -> None:
         """Load the autoconfig.yml file which is used for :set/:bind/etc."""
diff --git a/tests/unit/config/test_configcommands.py b/tests/unit/config/test_configcommands.py
index d7031de94..22de04070 100644
--- a/tests/unit/config/test_configcommands.py
+++ b/tests/unit/config/test_configcommands.py
@@ -587,6 +587,19 @@ class TestSource:
                     " division by zero")
         assert str(excinfo.value) == expected
 
+    def test_invalid_mutable(self, commands, config_tmpdir):
+        pyfile = config_tmpdir / 'config.py'
+        src = 'c.url.searchengines["maps"] = "https://www.google.com/maps?q=%s"'
+        pyfile.write_text(src, encoding="utf-8")
+
+        with pytest.raises(cmdutils.CommandError) as excinfo:
+            commands.config_source()
+
+        err = "Invalid value 'https://www.google.com/maps?q=%s' - must contain \"{}\""
+        expected = ("Errors occurred while reading config.py:\n"
+                    f"  While updating mutated values: {err}")
+        assert str(excinfo.value) == expected
+
 
 class TestEdit:
 
diff --git a/tests/unit/config/test_configfiles.py b/tests/unit/config/test_configfiles.py
index 760992e15..00bc8a806 100644
--- a/tests/unit/config/test_configfiles.py
+++ b/tests/unit/config/test_configfiles.py
@@ -1060,6 +1060,15 @@ class TestConfigPy:
         assert config.instance.get_obj('aliases')['foo'] == 'message-info foo'
         assert config.instance.get_obj('aliases')['bar'] == 'message-info bar'
 
+    def test_mutating_invalid_value(self, confpy):
+        confpy.write('c.url.searchengines["maps"] = "https://www.google.com/maps?q=%s"')
+        error = confpy.read(error=True)
+
+        assert error.text == "While updating mutated values"
+        assert isinstance(error.exception, configexc.ValidationError)
+
+        assert 'maps' not in config.instance.get_obj("url.searchengines")
+
     @pytest.mark.parametrize('option, value', [
         ('content.user_stylesheets', 'style.css'),
         ('url.start_pages', 'https://www.python.org/'),