gh-155985: Do not fuse a set difference under IGNORECASE with LOCALE - #155993
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fedonman wants to merge 1 commit into
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gh-155985: Do not fuse a set difference under IGNORECASE with LOCALE#155993fedonman wants to merge 1 commit into
fedonman wants to merge 1 commit into
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…OCALE _fuse_difference() rewrites <flat charset A> (?<![B]) into the single charset [NEGATE] B [NEGATE] A. That is sound where the engine walks a set once, but SRE(charset_loc_ignore) walks it twice, once with the lowercased character and once with the uppercased one, and matches if either walk does. The second walk starts with the NEGATE polarity reset, so a character that matches B in one case and A in the other escapes the subtraction. The pass did not see the compile flags, so it could not tell the two apart. Thread the effective flags through optimize() and _walk(), combining them for a scoped group, and skip the fusion when IGNORECASE and LOCALE are both set, the condition _compiler.py already uses to emit IN_LOC_IGNORE.
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_fuse_difference()now sees the compile flags and skips the fusion whenIGNORECASEandLOCALEare both set, which is exactly when the fused set would compile toIN_LOC_IGNORE. The flags are threaded throughoptimize()and_walk()and recombined for a scoped group, so(?i:...)inside are.LOCALEpattern is covered too.No NEWS fragment: the fusion landed earlier in this cycle (GH-152214) and has never been in a release, so there is nothing a user could have hit.
re.IGNORECASE | re.LOCALE#155985