bug#34808: 27.0.50; compilation buffer does not catch on lines

[Eli Zaretskii <eliz@gnu.org>]

> From: Alex Koval <alex@koval.kharkov.ua>
> Date: Sun, 10 Mar 2019 20:05:00 +0200
> 
> 
> 1) Have pycodestyle installed
> 2) Create some simple python file with error, for example:
> 
> ~~~
> from datetime import datetime
> 
> 
> 
> print(datetime.strptime("2015-03-11", "%Y-%m-%d"))
> ~~~
> 
> 3) Run M-x compile
> 4) pycodestyle a.py
> 5) See error list:
> 
> a.py:5:1: E303 too many blank lines (3)
> 
> Process compilation exited abnormally with code 1
> 
> 6) In previous emacs versions, including previous version of emacs 27 it
> worked well.
> 7) Now the line is not highlited and when I press on it I see this
> message:
> user-error: No error here

If you create a new buffer, insert this line there:

 a.py:5:1: E303 too many blank lines (3)

and turn on compilation-minor-mode in that buffer, don't you see
highlighting you expect?