On 30-Jul-2014 12:53 +0200, Bram Moolenaar wrote:
> Tim Brosnan wrote:
>
>> I initially send a version of this message through the google groups
>> interface, but it seems to have disappeared. Apologies if there is
>> duplication.
>>
>> When going through some regex examples from
>> VimRegexTutor(https://github.com/dahu/VimRegexTutor) I found that one of
>> the examples did not match the provided text when run in 7.4.383. Here
>> is the regex and the sample text:
>>
>> *30* : Find Text between HTML tags >
>>
>> /\%(<\1>\)\@<=.*\%(<\/\(\w\+\)>\)\@=
>>
>> OR
>>
>> /\v%(\<\1\>)@<=.*%(\<\/(\w+)\>)@=
>> <
>> <level>Can I play, daddy?</level>
>>
>> Neither of the provided regexs would watch the sample text (it should
>> match the text between html tags). However, when I tried 7.1.42 (only
>> other version at hand) I found that the text between tags was matched
>> correctly. Both versions were fun as -u NONE and "set nocompatible" to
>> try to rule out option or plugin clashes.
>>
>> Is this is a bug or has regex behaviour changed between 7.1.42 and 7.4.383?
>
> I don't think the pattern is supposed to work. The backreference is
> before the capturing group.
Well, it does work in the old engine.
> It's a suprise it works at all. Probably because in the old regex
> engine the "\@<=" part is used only after finding a match for the
> rest.
>
> It's a very inefficient pattern too, better use:
>
> /<\(\w\+\).\{-}>\zs.*\ze<\/\1>
You cannot always use \zs in place of \@<= (for example, with :syntax
match, or when already using a \zs elsewhere in the pattern).
Just changing the example in the help isn't going to solve the problem
of backwards compatibility. I think the new engine either has to support
it, or detect that special situation and then dynamically switch to the
old engine (like \%#=1 does).
-- regards, ingo
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