Fix out of bounds on uncomment

babi/file.py

@@ -681,13 +681,18 @@ class File:
         rest_offset = ws_len + len(prefix)
         if line.startswith(prefix, ws_len):
             self.buf[lineno] = f'{ws_match[0]}{line[rest_offset:].lstrip()}'
+            if self.buf.y == lineno and self.buf.x > ws_len:
+                self.buf.x -= len(line) - len(self.buf[lineno])
 
     def _comment_add(self, lineno: int, prefix: str) -> None:
+        prefix = f'{prefix} '
         line = self.buf[lineno]
         ws_match = WS_RE.match(line)
         assert ws_match is not None
         ws_len = len(ws_match[0])
-        self.buf[lineno] = f'{ws_match[0]}{prefix} {line[ws_len:]}'
+        self.buf[lineno] = f'{ws_match[0]}{prefix}{line[ws_len:]}'
+        if lineno == self.buf.y:
+            self.buf.x += len(prefix)
 
     @edit_action('comment', final=True)
     def toggle_comment(self, prefix: str) -> None:

tests/features/comment_test.py

@@ -73,3 +73,27 @@ def test_comment_with_trailing_whitespace(run, ten_lines):
         h.press_and_enter(':comment //   ')
 
         h.await_text('// line_0\nline_1\n')
+
+
+def test_comment_cursor_at_end_of_line(run, ten_lines):
+    with run(str(ten_lines)) as h, and_exit(h):
+        h.press('# ')
+        h.press('End')
+        h.await_cursor_position(x=8, y=1)
+
+        trigger_command_mode(h)
+        h.press_and_enter(':comment')
+
+        h.await_cursor_position(x=6, y=1)
+
+
+def test_add_comment_moves_cursor(run, ten_lines):
+    with run(str(ten_lines)) as h, and_exit(h):
+        h.press('End')
+
+        h.await_cursor_position(x=6, y=1)
+
+        trigger_command_mode(h)
+        h.press_and_enter(':comment')
+
+        h.await_cursor_position(x=8, y=1)