bug#29193: 26.0.90; Using (thing-at-point 'sexp) in flymake-diag-region might be suboptimal

[Dmitry Gutov]

Example:

Rubocop can report warning when 'end' is at wrong column. It just
reports the beginning column, of course.

In ruby-mode, (thing-at-point 'sexp) signals an error at this position.
I'm not sure exactly whether it's a problem in ruby-mode.

But Flycheck uses (thing-at-poing 'symbol) for the same purpose, and the
whole 'end' token gets highlighted (which is probably what we expect).

In contrast, Flymake only highlights its first character ('e').

++

In GNU Emacs 26.0.90 (build 5, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-11-07 built on zappa
Repository revision: ca2d94ba61dee678f85bfc7299d167e7219e6d8f
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
System Description:     Ubuntu 17.04