From 6bf92166a4a11dadfdab2439503bfa4c226a2c85 Mon Sep 17 00:00:00 2001
From: ShiLiguo123 <2669380883@qq.com>
Date: Tue, 12 May 2026 20:54:51 +0800
Subject: [PATCH] Fix Segment._split_cells for non-unit-width characters

The old algorithm used a heuristic initial position estimate
int((cut / cell_length) * len(text)) and then adjusted in a
while loop. This fails for strings with mixed single/double
cell-width characters (emoji, CJK).

Replace with a simple character-by-character walk-through
that correctly tracks cumulative cell positions.

Fixes #3299
---
 rich/segment.py | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/rich/segment.py b/rich/segment.py
index dd1e8c2a4f..68a91a036b 100644
--- a/rich/segment.py
+++ b/rich/segment.py
@@ -126,32 +126,25 @@ def _split_cells(cls, segment: "Segment", cut: int) -> Tuple["Segment", "Segment
 
         cell_size = get_character_cell_size
 
-        pos = int((cut / cell_length) * len(text))
-
-        while True:
-            before = text[:pos]
-            cell_pos = cell_len(before)
-            out_by = cell_pos - cut
-            if not out_by:
-                return (
-                    _Segment(before, style, control),
-                    _Segment(text[pos:], style, control),
-                )
-            if out_by == -1 and cell_size(text[pos]) == 2:
+        # Walk through characters tracking cell position,
+        # avoids the heuristic + while-loop which fails on
+        # non-unit-width characters (emoji, CJK, etc.)
+        cell_pos = 0
+        for i, char in enumerate(text):
+            char_cells = cell_size(char)
+            if cell_pos + char_cells > cut:
+                if char_cells == 2:
+                    return (
+                        _Segment(text[:i] + " ", style, control),
+                        _Segment(" " + text[i + 1 :], style, control),
+                    )
                 return (
-                    _Segment(text[:pos] + " ", style, control),
-                    _Segment(" " + text[pos + 1 :], style, control),
+                    _Segment(text[:i], style, control),
+                    _Segment(text[i:], style, control),
                 )
-            if out_by == +1 and cell_size(text[pos - 1]) == 2:
-                return (
-                    _Segment(text[: pos - 1] + " ", style, control),
-                    _Segment(" " + text[pos:], style, control),
-                )
-            if cell_pos < cut:
-                pos += 1
-            else:
-                pos -= 1
+            cell_pos += char_cells
 
+        return segment, _Segment("", style, control)
     def split_cells(self, cut: int) -> Tuple["Segment", "Segment"]:
         """Split segment in to two segments at the specified column.