Disallows the alternatives of lookarounds that end with a non-constant quantifier.
configuration in plugin:clean-regex/recommended: "warn"
Non-constant quantifiers are quantifiers that describe a range (e.g. ?, *,
+, {0,1}, {5,9}, {3,}). They have to match some number of times (the
minimum) after which further matches are optional until a certain maximum (may
be infinite) is reached.
It's obvious that /ba{2}/ and /ba{2,6}/ will match differently because of
the different quantifiers of a but that not the case if for lookarounds. Both
/b(?=a{2})/ and /b(?=a{2,6})/ will match strings the same way. I.e. for the
input string "baaa", both will create the same match arrays. The two regular
expression are actually equivalent, meaning that (?=a{2}) is equivalent to
(?=a{2,6}).
More generally, if a non-constant quantifier is an end of the expression tree of a lookahead, that quantifier can be replaced with a constant quantifier that matched the element minimum-if-the-non-constant-quantifier many times. For lookbehinds, the non-constant quantifier has to be at the start of the expression tree as lookbehinds are matched from right to left.
Examples of valid code for this rule:
// lookaheads
/\w+(?=\s*:)/
// lookbehinds
/(?<=ab+)/Examples of invalid code for this rule:
// lookaheads
/(?=ab+)/ == /(?=ab)/
/(?=ab*)/ == /(?=a)/
/(?!ab?)/ == /(?!a)/
/(?!ab{6,})/ == /(?!ab{6})/
// lookbehinds
/(?<=a+b)/ == /(?<=ab)/
/(?<!\w*\s*,)/ == /(?<!,)/