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Some regexps use ? quantifiers for look-aheads #2842
Description
Probably purely a code style issue, but some regular expressions use constructs like (?=...)? which is valid in JavaScript but don't make sense and only complicate expressions. Here's a list of all the found ones:
{ input: '^http://www\\.heteml\\.jp/[^?]*(?=\\?)?',
error:
{ name: 'RegexSyntaxError',
type: 'NothingRepeat',
lastIndex: 36,
message: 'Nothing to repeat!Repeat after assertion doesn\'t make sense!' } }
{ input: '^http://store\\.mandriva\\.com/[^?]*(?=\\?.*)?',
error:
{ name: 'RegexSyntaxError',
type: 'NothingRepeat',
lastIndex: 43,
message: 'Nothing to repeat!Repeat after assertion doesn\'t make sense!' } }
{ input: '^http://soe\\.stanford\\.edu/+(?=\\?.*)?$',
error:
{ name: 'RegexSyntaxError',
type: 'NothingRepeat',
lastIndex: 37,
message: 'Nothing to repeat!Repeat after assertion doesn\'t make sense!' } }
{ input: '^http://(?:www\\.)?tescofinance\\.com/+(?=\\?.*)?$',
error:
{ name: 'RegexSyntaxError',
type: 'NothingRepeat',
lastIndex: 46,
message: 'Nothing to repeat!Repeat after assertion doesn\'t make sense!' } }
{ input: '^http://hilfe\\.udmedia\\.de/[^?]*(?=\\?.*)?',
error:
{ name: 'RegexSyntaxError',
type: 'NothingRepeat',
lastIndex: 41,
message: 'Nothing to repeat!Repeat after assertion doesn\'t make sense!' } }
{ input: '^http://livechat\\.udmedia\\.de/[^?]*(?=\\?.*)?',
error:
{ name: 'RegexSyntaxError',
type: 'NothingRepeat',
lastIndex: 44,
message: 'Nothing to repeat!Repeat after assertion doesn\'t make sense!' } }
Activity
fuglede commentedon Sep 12, 2015
Are you talking about that the
?after the look-ahead? If so, I'm not quite sure what it means that it doesn't make sense? While I agree that those expressions aren't the easiest to read, the question mark is not non-functional. For example, the string/is matched by/[^?](?=?.)?but not by/[^?](?=?.).forgreatsh commentedon Sep 12, 2015
Back references "don't make sense" if by "don't make sense" you mean describe something other than a formal language.
?!and?=make perfect sense in pcre (which I concede are irregular).There are at least two good reasons for using such lookaheads:
?!,?=, and\?[^?!:]makes so.?:Also serves this purpose, but it's even easier to see?!and?=.RReverser commentedon Sep 13, 2015
Original message was from regulex parser which is stricter than regular JS engines. My understanding is that it's correct, you just chose incorrect alternative. The thing is that either both me and regulex authors (cc @JexCheng) are missing something, or
/[^?]*(?=\?.*)?has just the same effect as/[^?]*since "optional lookahead" inside of the regular expression is just the same as if there would be no look-ahead at all. Thus it just hurts both readability and performance of such regexes without any real effect.RReverser commentedon Sep 13, 2015
@forgreatsh No, that's not what I mean by "doesn't make sense". I know what are look-aheads for in generic cases :) Please see explanation of this specific problem in previous comment.
CJex commentedon Sep 13, 2015
@RReverser Sorry it's my fault, I have noticed this kind bug these days, it was fixed now:
CJex/regulex#29
It should be a warning, not an error.
fuglede commentedon Sep 13, 2015
I think you're right though, that
/[^?](?=?.)?is equivalent to/[^?]*, so there must be a reason it was done the other way. The Mandriva ruleset has the following comment, which may or may not have something to do with it:RReverser commentedon Sep 13, 2015
I see, keeping it open then.
RReverser commentedon Sep 14, 2015
@fuglede If this is a reason, maybe it would make sense to fix rule validation. What do you think?
fuglede commentedon Sep 14, 2015
It validates just fine with
/[^?]*though. @2d1?fuglede commentedon Sep 29, 2015
Super. @RReverser, do you want to submit a PR fixing the redundant ones?
RReverser commentedon Sep 29, 2015
I can a bit later.
Remove redundant regex parts.
RReverser commentedon Sep 29, 2015
Done!
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