gh-156513: Match a backreference case-insensitively as a literal - #156514
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gh-156513: Match a backreference case-insensitively as a literal#156514serhiy-storchaka wants to merge 1 commit into
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sre_lower_unicode() now returns the lowercase of the simple case folding of the character, computed by the new _PyUnicode_ToFoldedLowercase(), with the four pairs which no case mapping unifies hardcoded. The key is the same for all characters matched case-insensitively, so a backreference matches what a literal matches: (?i)(.)\1 matches 'ςσ' as (?i)ς already matched 'σ'. _casefix._EXTRA_CASES is no longer needed and is removed, together with the alternatives which the compiler expanded a literal into. Its generator now emits no table, but keeps computing the groups of characters which have to be matched case-insensitively, and fails if sre_lower_unicode() does not fold such a group to a single code. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Implements the three steps proposed in the issue.
The four pairs which no case mapping unifies are hardcoded as special cases in
sre_lower_unicode()._PyUnicode_ToFoldedLowercase()combines the simple case folding and the lowercase in one function. It is added for performance: it reads the type record once, except for the few characters having a special single-character folding._casefix._EXTRA_CASESis removed, together with the alternatives which the compiler expanded a literal into. Its generator keeps computing the groups of characters which have to be matched case-insensitively, and now fails ifsre_lower_unicode()does not fold such a group to a single code.The set of characters matched case-insensitively does not change: the equivalence classes computed from
_sre.unicode_tolower()are the same as before for every code point.