Restrict Vim modeline parsing to a single line

[jatoben]

Description

Files which have a similar syntax to Vim modelines, such as YAML, can trigger regex matching behavior that makes filetype detection very slow. In this pull request, I've replaced \s in the Vim modeline regex (which considers newlines as whitespace) with the POSIX bracket expression [[:blank:]], which doesn't ([ \t] should also work, if that's preferred). This constrains the parsing of each modeline to a single line and avoids the pathological case.

This short YAML file can be used to reproduce the behavior:

# vim: ft=yaml:ts=2:sw=2:expandtab
defaults:
  milestone: q1
  priority:  2
branches:
  master:
    events:
      push:
        :state: integrate
        :resolution: change
      merge:
        :state: analyze
        :substate: review

Before the change, using Ruby 2.4.2 on Linux:

$ time bundle exec bin/linguist pathological.yml 
pathological.yml: 15 lines (13 sloc)
  type:      Text
  mime type: text/x-yaml
  language:  YAML

real	1m3.701s
user	1m3.144s
sys	0m0.156s

After:

$ time bundle exec bin/linguist pathological.yml 
pathological.yml: 15 lines (13 sloc)
  type:      Text
  mime type: text/x-yaml
  language:  YAML

real	0m0.850s
user	0m0.524s
sys	0m0.104s

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am adding a new language.

  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a syntax highlighting grammar.
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am changing the source of a syntax highlighting grammar

  • Old: https://github-lightshow.herokuapp.com/
  • New: https://github-lightshow.herokuapp.com/

• I am adding new or changing current functionality

  • I have added or updated the tests for the new or changed functionality.

I have not added any tests here, as I think the existing coverage in fixtures like test/fixtures/Data/Modelines/iamjs2.pl already covers the desired behavior. If I've missed anything, please let me know!

[Alhadis]

Nice work! 👍 Well done.

I've left some feedback.

[Alhadis]

I'd recommend the use of [ \t] instead, as it's arguably clearer than a POSIX character class.

[Alhadis]

You should indent this line so the comment matches the line above it.

[Alhadis]

Indent needed here too.

[jatoben]

Thanks for the review @Alhadis! I've made those updates in eda3e02 and 5fed5cd.

[Alhadis]

LGTM. 👍

[lildude]

Wow! Nice improvement @jatoben 🙇‍♂️

[sheerun]

better late than never :D