Fix bug with 'Segment._split_cells'.

We replace the linear search with a binary search like the one in cells.py::set_sell_size.
This doesn't seem to produce a significant impact in the performance of the method but it does fix bug #3299.

rich/segment.py

@@ -1,6 +1,7 @@
+import bisect
 from enum import IntEnum
 from functools import lru_cache
-from itertools import filterfalse
+from itertools import accumulate, filterfalse
 from logging import getLogger
 from operator import attrgetter
 from typing import (
@@ -115,35 +116,24 @@ def _split_cells(cls, segment: "Segment", cut: int) -> Tuple["Segment", "Segment
  cell_length = segment.cell_length
  if cut >= cell_length:
  return segment, _Segment("", style, control)
+ elif cut <= 0:
+ return _Segment("", style, control), segment
 
- cell_size = get_character_cell_size
+ _cell_size = get_character_cell_size
+ widths = [_cell_size(char) for char in text]
+ lengths = list(accumulate(widths))
 
- pos = int((cut / cell_length) * (len(text) - 1))
-
- before = text[:pos]
- cell_pos = cell_len(before)
- if cell_pos == cut:
+ idx = bisect.bisect_left(lengths, cut)
+ if lengths[idx] == cut:
  return (
- _Segment(before, style, control),
- _Segment(text[pos:], style, control),
+ _Segment(text[:idx + 1], style, control),
+ _Segment(text[idx + 1:], style, control)
+ )
+ else: # Character at position idx + 1 has width 2.
+ return (
+ _Segment(text[:idx] + " ", style, control),
+ _Segment(" " + text[idx + 1:], style, control),
  )
- while pos < len(text):
- char = text[pos]
- pos += 1
- cell_pos += cell_size(char)
- before = text[:pos]
- if cell_pos == cut:
- return (
- _Segment(before, style, control),
- _Segment(text[pos:], style, control),
- )
- if cell_pos > cut:
- return (
- _Segment(before[: pos - 1] + " ", style, control),
- _Segment(" " + text[pos:], style, control),
- )
-
- raise AssertionError("Will never reach here")
 
  def split_cells(self, cut: int) -> Tuple["Segment", "Segment"]:
  """Split segment in to two segments at the specified column.