Implement readline's backward-kill-word.

This restores the previous behavior of `unix-word-rubout` as
`backward-kill-word`, which is closer to the naming used in readline.
It is bound to <Alt-Backspace> by default, though <Ctrl-Backspace> will
also work due to a builtin binding.

Resolves #1698.

doc/help/commands.asciidoc

@@ -946,6 +946,7 @@ How many steps to zoom out.
 |<<repeat-command,repeat-command>>|Repeat the last executed command.
 |<<rl-backward-char,rl-backward-char>>|Move back a character.
 |<<rl-backward-delete-char,rl-backward-delete-char>>|Delete the character before the cursor.
+|<<rl-backward-kill-word,rl-backward-kill-word>>|Remove chars from the cursor to the beginning of the word.
 |<<rl-backward-word,rl-backward-word>>|Move back to the start of the current or previous word.
 |<<rl-beginning-of-line,rl-beginning-of-line>>|Move to the start of the line.
 |<<rl-delete-char,rl-delete-char>>|Delete the character after the cursor.
@@ -1193,6 +1194,12 @@ Delete the character before the cursor.
 
 This acts like readline's backward-delete-char.
 
+[[rl-backward-kill-word]]
+=== rl-backward-kill-word
+Remove chars from the cursor to the beginning of the word.
+
+This acts like readline's backward-kill-word. Any non-alphanumeric character is considered a word delimiter.
+
 [[rl-backward-word]]
 === rl-backward-word
 Move back to the start of the current or previous word.
@@ -1251,7 +1258,7 @@ This acts like readline's unix-line-discard.
 === rl-unix-word-rubout
 Remove chars from the cursor to the beginning of the word.
 
-This acts like readline's unix-word-rubout.
+This acts like readline's unix-word-rubout. Whitespace is used as a word delimiter.
 
 [[rl-yank]]
 === rl-yank

qutebrowser/config/configdata.py

@@ -1587,7 +1587,8 @@ KEY_DATA = collections.OrderedDict([
         ('rl-unix-line-discard', ['<Ctrl-U>']),
         ('rl-kill-line', ['<Ctrl-K>']),
         ('rl-kill-word', ['<Alt-D>']),
-        ('rl-unix-word-rubout', ['<Ctrl-W>', '<Alt-Backspace>']),
+        ('rl-unix-word-rubout', ['<Ctrl-W>']),
+        ('rl-backward-kill-word', ['<Alt-Backspace>']),
         ('rl-yank', ['<Ctrl-Y>']),
         ('rl-delete-char', ['<Ctrl-?>']),
         ('rl-backward-delete-char', ['<Ctrl-H>']),

qutebrowser/misc/readline.py

@@ -153,7 +153,8 @@ class ReadlineBridge:
     def rl_unix_word_rubout(self):
         """Remove chars from the cursor to the beginning of the word.
 
-        This acts like readline's unix-word-rubout.
+        This acts like readline's unix-word-rubout. Whitespace is used as a
+        word delimiter.
         """
         widget = self._widget()
         if widget is None:
@@ -178,6 +179,21 @@ class ReadlineBridge:
         self._deleted[widget] = widget.selectedText()
         widget.del_()
 
+    @cmdutils.register(instance='readline-bridge', hide=True,
+                       modes=[typ.KeyMode.command, typ.KeyMode.prompt])
+    def rl_backward_kill_word(self):
+        """Remove chars from the cursor to the beginning of the word.
+
+        This acts like readline's backward-kill-word. Any non-alphanumeric
+        character is considered a word delimiter.
+        """
+        widget = self._widget()
+        if widget is None:
+            return
+        widget.cursorWordBackward(True)
+        self._deleted[widget] = widget.selectedText()
+        widget.del_()
+
     @cmdutils.register(instance='readline-bridge', hide=True,
                        modes=[typ.KeyMode.command, typ.KeyMode.prompt])
     def rl_kill_word(self):

tests/unit/misc/test_readline.py

@@ -269,6 +269,25 @@ def test_rl_kill_word(lineedit, bridge, text, deleted, rest):
     assert lineedit.aug_text() == deleted + '|'
 
 
+@pytest.mark.parametrize('text, deleted, rest', [
+    ('test delete|foobar', 'delete', 'test |foobar'),
+    ('test delete |foobar', 'delete ', 'test |foobar'),
+    ('open -t github.com/foo/bar  |', 'bar  ', 'open -t github.com/foo/|'),
+    ('open -t |github.com/foo/bar', 't ', 'open -|github.com/foo/bar'),
+    fixme(('test del<ete>foobar', 'delete', 'test |foobar')),
+    ('test del<ete >foobar', 'del', 'test |ete foobar'),  # wrong
+])
+def test_rl_backward_kill_word(lineedit, bridge, text, deleted, rest):
+    """Delete to word beginning and see if it comes back with yank."""
+    lineedit.set_aug_text(text)
+    bridge.rl_backward_kill_word()
+    assert bridge._deleted[lineedit] == deleted
+    assert lineedit.aug_text() == rest
+    lineedit.clear()
+    bridge.rl_yank()
+    assert lineedit.aug_text() == deleted + '|'
+
+
 def test_rl_yank_no_text(lineedit, bridge):
     """Test yank without having deleted anything."""
     lineedit.clear()