[easy] add a check for trailing newlines in files

[pylint-bot]

Originally reported by: Mike Frysinger (BitBucket: vapier, GitHub: @vapier?)

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it's not uncommon for people to add trailing blank lines to files by accident. it'd be nice if pylint could warn about it. it already has a missing-final-newline check.

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• Bitbucket: https://bitbucket.org/logilab/pylint/issue/682

[pylint-bot]

Original comment by Claudiu Popa (BitBucket: PCManticore, GitHub: @PCManticore):

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Sounds good. I presume the fix is easy, although I didn't check the exact implementation.

[pylint-bot]

Original comment by Mike Frysinger (BitBucket: vapier, GitHub: @vapier?):

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i glanced at pylint/checkers/format.py and it seemed pretty easy. update check_lines to do something like:

#!python
 lines = lines.splitlines(True)
 for line in lines:
   ...
 if len(lines) > 1 and not lines[-1].strip('\r\n'):
   self.add_message('trailing-newlines', line=i)

it gets a little tricky if you want to warn for each trailing newline (when there are more than one), but i don't think it needs to.

[pylint-bot]

Original comment by Claudiu Popa (BitBucket: PCManticore, GitHub: @PCManticore):

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Just for the record, I add the [easy] tag for issues which are friendly for new contributors. ;-)

[pylint-bot]

Original comment by Mike Frysinger (BitBucket: vapier, GitHub: @vapier?):

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sure. i'll try writing a diff, but i generally gave up on trying to use mercurial.

[pylint-bot]

Original comment by Mike Frysinger (BitBucket: vapier, GitHub: @vapier?):

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the good news is the new lint test caught a lot of trailing newlines in existing tests ;)