Thai combining marks cause width miscalculation in modern terminals (Kitty, Ghostty)

[noomzopendream]

Problem

Thai combining marks (vowels and tone marks) are marked as zero-width in CELL_WIDTHS, following Unicode's Mn (Nonspacing Mark) classification. However, modern terminal emulators (tested: Kitty, Ghostty) render Thai text with these characters taking visible width, causing table columns and other layouts to misalign.

Reproduction

from rich.console import Console
from rich.table import Table
from rich.cells import cell_len

console = Console()
table = Table(title='Thai Text Width Test')
table.add_column('Text', width=10)
table.add_column('cell_len')

for text in ['สวัสดี', 'น้ำ', 'กรุงเทพ']:
    table.add_row(text, str(cell_len(text)))

console.print(table)

Width Analysis

Text	Codepoints	Combining marks	Rich cell_len	Terminal width
สวัสดี	6	2	4	6
น้ำ	3	1	2	3
กรุงเทพ	7	1	6	7

The discrepancy equals the number of combining marks — terminals render each Thai codepoint as width 1.

Affected Ranges in CELL_WIDTHS

Range	Characters	Unicode Category
U+0E31	ั	Mn (sara am vowel)
U+0E34-U+0E3A	ิ ี ึ ื ุ ู ฺ	Mn (vowel signs)
U+0E47-U+0E4E	็ ่ ้ ๊ ๋ ์ ํ ๎	Mn (tone marks)

Environment

• Rich: 13.7.1
• Python: 3.14.2
• Terminals tested:
  • Kitty 0.45.0 — affected
  • Ghostty 1.2.3 — affected
• Platform: macOS

Proposed Fix

Change Thai combining mark ranges from width 0 to width 1 in _cell_widths.py. This matches actual terminal rendering behavior for Thai script.

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This is an automated reply, generated by FAQtory

[jquast]

Probably fixed by #3956