[manav4u]

At width 1, leading whitespace combined with SGR sequences can leave a visually empty first line or drop the opening style:

from wcwidth import wrap

wrap('\x1b[31m a\x1b[0m', 1)
# before: ['a\x1b[0m']
# after:  ['\x1b[31ma\x1b[0m']

wrap('\x1b[31m a-b\x1b[0m', 1)
# before: a sequence-only first line, then a, -, b
# after: three individually red lines, a, -, b

This extends the whitespace-only-line behavior from #292 to styled text. Transfer sequences from a discarded whitespace chunk to the next chunk when there is no current line to receive them. Check visible whitespace before appending a line, retaining sequences for the next chunk instead of emitting a whitespace-only line.

Only perform the additional visible-content scan for lines containing escape sequences, leaving plain-text whitespace on the existing path.

Apply the corresponding change to libwcwidth. Its wrapper intentionally does not propagate SGR per line, so the C tests check its existing raw-sequence behavior rather than Python's default per-line resets.

Tests cover both SGR propagation settings, preserving whitespace when requested, and initial indentation. Six Python regressions fail before the fix; the C regression fails for all three inputs before the fix.

Validation on Linux/Python 3.12.15:

• Python suite with compiled extension: 1,790 passed, 12 skipped.
• Pure-Python suite: 1,754 passed, 48 skipped.
• Native C suite with AddressSanitizer and UndefinedBehaviorSanitizer: 12 executables, 91 tests, zero failures.
• Strict source MyPy, changed-file Flake8 and isort, pydocstyle, Pylint 10/10 for textwrap.py, and diff whitespace checks pass.

Other Python versions, documentation builds and upstream CI have not been run. No performance improvement is claimed.

Prepared with AI assistance.

[jquast]

This is only a problem for width 1, no other width?

[manav4u]

No, it also affects wider widths when the leading whitespace fills the available line. I used width 1 to keep the original examples small.

For example, at width 2:

wrap('\x1b[31m  abc\x1b[0m', 2)
# before: ['\x1b[31m\x1b[0m', '\x1b[31mab\x1b[0m', '\x1b[31mc\x1b[0m']
# after:  ['\x1b[31mab\x1b[0m', '\x1b[31mc\x1b[0m']

And at width 5:

wrap('\x1b[31m     hello world\x1b[0m', 5)
# before: ['hello', 'world\x1b[0m']
# after:  ['\x1b[31mhello\x1b[0m', '\x1b[31mworld\x1b[0m']

The first emits a sequence-only line; the second loses the opening color. I also checked widths 3, 10 and 20. The current patch fixes these without a source change. The regression tests in the PR should cover wider widths too.