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gh-130273: Fix incorrectly colored error locations when wide unicode characters exists #130277

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gh-130273: Fix incorrectly colored error locations when wide unicode characters exists #130277

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46 changes: 35 additions & 11 deletions 46 Lib/traceback.py
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Original file line number Diff line number Diff line change
Expand Up @@ -656,18 +656,29 @@ def output_line(lineno):
line = result[-1]
colorized_line_parts = []
colorized_carets_parts = []

for color, group in itertools.groupby(itertools.zip_longest(line, carets, fillvalue=""), key=lambda x: x[1]):
caret_group = list(group)
if color == "^":
colorized_line_parts.append(ANSIColors.BOLD_RED + "".join(char for char, _ in caret_group) + ANSIColors.RESET)
colorized_carets_parts.append(ANSIColors.BOLD_RED + "".join(caret for _, caret in caret_group) + ANSIColors.RESET)
elif color == "~":
colorized_line_parts.append(ANSIColors.RED + "".join(char for char, _ in caret_group) + ANSIColors.RESET)
colorized_carets_parts.append(ANSIColors.RED + "".join(caret for _, caret in caret_group) + ANSIColors.RESET)
line_part_col = 0
for char, group in itertools.groupby(carets):
carets_part = "".join(group)
width = len(carets_part)
if char == "^":
color = ANSIColors.BOLD_RED
elif char == "~":
color = ANSIColors.RED
else:
colorized_line_parts.append("".join(char for char, _ in caret_group))
colorized_carets_parts.append("".join(caret for _, caret in caret_group))
colorized_carets_parts.append(carets_part)
line_part_col, line_part = _offset_at_width(line, width, start=line_part_col)
colorized_line_parts.append(line_part)
continue

colorized_carets_parts.append(color)
colorized_carets_parts.append(carets_part)
colorized_carets_parts.append(ANSIColors.RESET)

colorized_line_parts.append(color)
line_part_col, line_part = _offset_at_width(line, width, start=line_part_col)
colorized_line_parts.append(line_part)
colorized_line_parts.append(ANSIColors.RESET)
colorized_line_parts.append(line[line_part_col:])

colorized_line = "".join(colorized_line_parts)
colorized_carets = "".join(colorized_carets_parts)
Expand Down Expand Up @@ -965,6 +976,19 @@ def _display_width(line, offset=None):
for char in line[:offset]
)

def _offset_at_width(line, width, start=0):
col = start + width
part = line[start:col]
if part.isascii():
return col, part

from unicodedata import east_asian_width

for i in range(start, len(line)):
if width <= 0:
return i, line[start:i]
width -= 2 if east_asian_width(line[i]) in _WIDE_CHAR_SPECIFIERS else 1
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does this correctly handle zero-width characters? e.g. the '\u0301' from 'cafe\u0301'

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No.
However, _display_width() does not correctly handle zero-width characters for carets positions either.

>>> café = 1/0
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    café = 1/0
            ~^~
ZeroDivisionError: division by zero
>>>

They can be fixed in the same way. I wonder how I can find all the zero-width characters.

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It looks like there are many zero-width characters: https://wcwidth.readthedocs.io/en/latest/specs.html#width-of-0

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This is how wcwidth implements wcswidth() and wcwidth(): https://wcwidth.readthedocs.io/en/latest/_modules/wcwidth/wcwidth.html#wcswidth
Maybe it is too complicated for our traceback? Could we have a simple way that can handle most of the cases?

return len(line), line[start:]


class _ExceptionPrintContext:
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