gh-141336: Fix Unicode escape assertion failure in error handler#141344
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mohsinm-dev wants to merge 2 commits into
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gh-141336: Fix Unicode escape assertion failure in error handler#141344mohsinm-dev wants to merge 2 commits into
mohsinm-dev wants to merge 2 commits into
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When unicode_decode_call_errorhandler_writer() processes a replacement string of length 1 and the error handler rewinds the input position (increasing remaining input), the original code failed to account for the replacement length in writer.min_length calculations. This resulted in assertion failures when writer capacity was insufficient after writing the replacement: assert(end - s <= writer.size - writer.pos). The fix ensures the full replacement length is always included in writer.min_length, regardless of replacement size, maintaining the buffer capacity invariant for all decoders using this error helper.
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Fixes assertion failure in Unicode escape decoding when using custom error handlers that return single-character replacements and rewind input position.
Root Cause
The issue occurs in unicode_decode_call_errorhandler_writer() when:
This led to assertion failures in debug builds.
Fix
Testing
Fixes #141336
_PyUnicode_DecodeUnicodeEscapeInternal2: Assertion 'end - s <= writer.size - writer.pos' failed#141336