Add ReDoS check for nested quantifiers - #56
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Flag unbounded quantifiers (*, +, open-ended {n,}) applied to a group
whose whole body reduces to a single unbounded repetition, e.g. (a+)+,
(a+)*, ([ab]*)+, (a{1,})+ and (a+|b)*. These are the classic
catastrophic-backtracking shapes where the inner quantifier can split
the same input in exponentially many ways.
The check is deliberately conservative to stay false-positive-free on
real lexers: bodies with a mandatory fixed part (ab+, a+b), single-char
alternations (a|b), bounded outer quantifiers ((a+)?, (a+){2}) and the
common string-lexer idioms (\.|[^"])* / ([^"\\]|\\.)* are left alone.
This misses multi-atom overlaps like (\w+\s?)*.
Includes unit tests covering the positive, alternation-branch,
nested-group and safe/no-flag cases.
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Flag unbounded quantifiers (, +, open-ended {n,}) applied to a group whose whole body reduces to a single unbounded repetition, e.g. (a+)+, (a+), ([ab])+, (a{1,})+ and (a+|b). These are the classic catastrophic-backtracking shapes where the inner quantifier can split the same input in exponentially many ways.
The check is deliberately conservative to stay false-positive-free on real lexers: bodies with a mandatory fixed part (ab+, a+b), single-char alternations (a|b), bounded outer quantifiers ((a+)?, (a+){2}) and the common string-lexer idioms (.|[^"])* / ([^"\\]|\.)* are left alone. This misses multi-atom overlaps like (\w+\s?)*.
Includes unit tests covering the positive, alternation-branch, nested-group and safe/no-flag cases.