Add :bind --default

Closes #3059

doc/help/commands.asciidoc

@@ -122,7 +122,7 @@ How many pages to go back.
 
 [[bind]]
 === bind
-Syntax: +:bind [*--mode* 'mode'] 'key' ['command']+
+Syntax: +:bind [*--mode* 'mode'] [*--default*] 'key' ['command']+
 
 Bind a key to a command.
 
@@ -135,6 +135,7 @@ Bind a key to a command.
 * +*-m*+, +*--mode*+: A comma-separated list of modes to bind the key in (default: `normal`). See `:help bindings.commands` for the
  available modes.
 
+* +*-d*+, +*--default*+: If given, restore a default binding.
 
 ==== note
 * This command does not split arguments after the last argument and handles quotes literally.

qutebrowser/config/config.py

@@ -180,6 +180,18 @@ class KeyConfig:
         bindings[mode][key] = command
         self._config.update_mutables(save_yaml=save_yaml)
 
+    def bind_default(self, key, *, mode='normal', save_yaml=False):
+        """Restore a default keybinding"""
+        key = self._prepare(key, mode)
+
+        bindings_commands = self._config.get_obj('bindings.commands')
+        try:
+            del bindings_commands[mode][key]
+        except KeyError:
+            raise configexc.KeybindingError(
+                "Can't find binding '{}' in {} mode".format(key, mode))
+        self._config.update_mutables(save_yaml=save_yaml)
+
     def unbind(self, key, *, mode='normal', save_yaml=False):
         """Unbind the given key in the given mode."""
         key = self._prepare(key, mode)

qutebrowser/config/configcommands.py

@@ -92,7 +92,7 @@ class ConfigCommands:
     @cmdutils.register(instance='config-commands', maxsplit=1,
                        no_cmd_split=True, no_replace_variables=True)
     @cmdutils.argument('command', completion=configmodel.bind)
-    def bind(self, key, command=None, *, mode='normal'):
+    def bind(self, key, command=None, *, mode='normal', default=False):
         """Bind a key to a command.
 
         Args:
@@ -102,8 +102,17 @@ class ConfigCommands:
             mode: A comma-separated list of modes to bind the key in
                   (default: `normal`). See `:help bindings.commands` for the
                   available modes.
+            default: If given, restore a default binding.
         """
         if command is None:
+            if default:
+                # :bind --default: Restore default
+                with self._handle_config_error():
+                    self._keyconfig.bind_default(key, mode=mode,
+                                                 save_yaml=True)
+                return
+
+            # No --default -> print binding
             if utils.is_special_key(key):
                 # self._keyconfig.get_command does this, but we also need it
                 # normalized for the output below

tests/unit/config/test_config.py

@@ -205,6 +205,27 @@ class TestKeyConfig:
         key_config_stub.bind('a', 'set-cmd-text :nop ;; rl-beginning-of-line',
                              mode='normal')
 
+    def test_bind_default(self, key_config_stub, config_stub):
+        """Bind a key to its default."""
+        default_cmd = 'message-info default'
+        bound_cmd = 'message-info bound'
+        config_stub.val.bindings.default = {'normal': {'a': default_cmd}}
+        config_stub.val.bindings.commands = {'normal': {'a': bound_cmd}}
+        assert key_config_stub.get_command('a', mode='normal') == bound_cmd
+
+        key_config_stub.bind_default('a', mode='normal')
+
+        assert key_config_stub.get_command('a', mode='normal') == default_cmd
+
+    def test_bind_default_unbound(self, key_config_stub, config_stub,
+                                  no_bindings):
+        """Try binding a key to default which is not bound."""
+        config_stub.val.bindings.default = no_bindings
+        config_stub.val.bindings.commands = no_bindings
+        with pytest.raises(configexc.KeybindingError,
+                           match="Can't find binding 'foobar' in normal mode"):
+            key_config_stub.bind_default('foobar', mode='normal')
+
     @pytest.mark.parametrize('key, normalized', [
         ('a', 'a'),  # default bindings
         ('b', 'b'),  # custom bindings

tests/unit/config/test_configcommands.py

@@ -494,6 +494,30 @@ class TestBind:
         config_stub.val.bindings.commands = None
         commands.bind(',x', 'nop')
 
+    def test_bind_default(self, commands, key_config_stub, config_stub):
+        """Bind a key to its default."""
+        default_cmd = 'message-info default'
+        bound_cmd = 'message-info bound'
+        config_stub.val.bindings.default = {'normal': {'a': default_cmd}}
+        config_stub.val.bindings.commands = {'normal': {'a': bound_cmd}}
+        assert key_config_stub.get_command('a', mode='normal') == bound_cmd
+
+        commands.bind('a', mode='normal', default=True)
+
+        assert key_config_stub.get_command('a', mode='normal') == default_cmd
+
+    @pytest.mark.parametrize('key, mode, expected', [
+        ('foobar', 'normal', "Can't find binding 'foobar' in normal mode"),
+        ('x', 'wrongmode', "Invalid mode wrongmode!"),
+    ])
+    def test_bind_default_invalid(self, commands, key, mode, expected):
+        """Run ':bind --default foobar' / ':bind --default x wrongmode'.
+
+        Should show an error.
+        """
+        with pytest.raises(cmdexc.CommandError, match=expected):
+            commands.bind(key, mode=mode, default=True)
+
     def test_unbind_none(self, commands, config_stub):
         config_stub.val.bindings.commands = None
         commands.unbind('H')