Show nicer errors when trying to set deleted/renamed options

qutebrowser/config/config.py

@@ -272,7 +272,11 @@ class Config(QObject):
         try:
             return configdata.DATA[name]
         except KeyError:
-            raise configexc.NoOptionError(name) from None
+            deleted = name in configdata.MIGRATIONS.deleted
+            renamed = configdata.MIGRATIONS.renamed.get(name)
+            exception = configexc.NoOptionError(
+                name, deleted=deleted, renamed=renamed)
+            raise exception from None
 
     def get(self, name):
         """Get the given setting converted for Python code."""

qutebrowser/config/configexc.py

@@ -63,8 +63,16 @@ class NoOptionError(Error):
 
     """Raised when an option was not found."""
 
-    def __init__(self, option):
-        super().__init__("No option {!r}".format(option))
+    def __init__(self, option, *, deleted=False, renamed=None):
+        if deleted:
+            assert renamed is None
+            suffix = ' (this option was removed from qutebrowser)'
+        elif renamed is not None:
+            suffix = ' (this option was renamed to {!r})'.format(renamed)
+        else:
+            suffix = ''
+
+        super().__init__("No option {!r}{}".format(option, suffix))
         self.option = option
 
 

tests/unit/config/test_configexc.py

@@ -32,10 +32,20 @@ def test_validation_error():
     assert str(e) == "Invalid value 'val' - msg"
 
 
-def test_no_option_error():
-    e = configexc.NoOptionError('opt')
+@pytest.mark.parametrize('deleted, renamed, expected', [
+    (False, None, "No option 'opt'"),
+    (True, None, "No option 'opt' (this option was removed from qutebrowser)"),
+    (False, 'new', "No option 'opt' (this option was renamed to 'new')"),
+])
+def test_no_option_error(deleted, renamed, expected):
+    e = configexc.NoOptionError('opt', deleted=deleted, renamed=renamed)
     assert e.option == 'opt'
-    assert str(e) == "No option 'opt'"
+    assert str(e) == expected
+
+
+def test_no_option_error_clash():
+    with pytest.raises(AssertionError):
+        e = configexc.NoOptionError('opt', deleted=True, renamed='foo')
 
 
 def test_backend_error():

tests/unit/config/test_configfiles.py

@@ -534,6 +534,18 @@ class TestConfigPy:
         assert str(error.exception) == "No option 'foo'"
         assert error.traceback is None
 
+    def test_renamed_option_error(self, confpy, monkeypatch):
+        """Setting an option which has been renamed should show a hint."""
+        monkeypatch.setattr(configdata.MIGRATIONS, 'renamed',
+                            {'qt_args': 'qt.args'})
+        confpy.write('c.qt_args = ["foo"]')
+
+        error = confpy.read(error=True)
+        assert isinstance(error.exception, configexc.NoOptionError)
+        expected = ("No option 'qt_args' (this option was renamed to "
+                    "'qt.args')")
+        assert str(error.exception) == expected
+
     def test_multiple_errors(self, confpy):
         confpy.write("c.foo = 42", "config.set('foo', 42)", "1/0")