The GNU coding standards rules can be found in:
https://gcc.gnu.org/wiki/FormattingCodeForGCC
I added a few rules, like if the file has existing tabs, we want to show
them as 8 columns. Yet typing tabs automatically expands to 2 spaces.
I also added a rule to highlight (in red) trailing whitespaces, but also
tabs (everywhere, not only trailing) making them easy to spot.
This file can be easily sourced from vimrc for the whole GIMP tree, but
I advise against setting VIM to automatic discover a locale .vimrc,
which is possible but a high security risk since a third-party vimrc
could contain random shell commands.
Jehan