lint: check for bad white space habits

A little coding hygiene cannot hurt. Add a simple awk script to check
all source files for bad white space habits:

- trailing white space
- trailing new lines at the end of files
- missing new line at the end of files
- spaces followed by tabs

The script outputs color when the terminal supports it. It exits with
a non-zero code when there was at least one white space issue found.
Call the script in the lint step.

Example output of the awk script:

 config/default_styleset:1:# <-- trailing whitespace
 config/default_styleset:3:# <-- trailing whitespace
 doc/aerc.1.scd:78:        Executes an arbitrary command in the background. Aerc will set the <-- trailing whitespace
 doc/aerc.1.scd:234:        <-- trailing whitespace
 doc/aerc.1.scd:237:        <-- trailing whitespace
 worker/types/thread_test.go:74:        //         return ErrSkipThread<-- space(s) followed by tab(s)
 worker/lib/testdata/message/invalid/hexa: trailing new line(s)

Fix issues reported by the script.

NB: The ENDFILE match is a GNU extension. It will be ignored on BSD-awk
and trailing new lines will not be detected. The lint make target is
only invoked on alpine linux which has GNU awk anyway.

NB: Empty cells in scdoc tables require trailing white space... Avoid
this by setting content in these cells. I don't really see a use for
empty cells.

Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Moritz Poldrack <moritz@poldrack.dev>

1 files changed, 1 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 04ee08e4..7f1837a9 100644
--- a/Makefile
+++ b/Makefile
@@ -61,6 +61,7 @@ fmt:
 
 .PHONY: lint
 lint:
+	@contrib/check-whitespace `git ls-files` && echo white space ok.
 	@$(GO) run mvdan.cc/gofumpt -l . | grep ^ \
 		&& echo The above files need to be formatted, please run make fmt && exit 1 \
 		|| echo all files formatted.