When I have a shell script that starts with:

!/usr/bin/env sh

the flycheck checker returns:
"Suspicious state from syntax checker sh-checkbashisms: Checker sh-checkbashisms returned non-zero exit code 2, but no errors from output: script (stdin) does not appear to be a /bin/sh script; skipping.

Checker definition probably flawed."

Before we can add this repo to our list of extensions I would like to see the relation between this syntax checker and the built-in shell script checkers clarified.

Currently I see a couple of issues:

• flycheck-checkbashisms-setup adds the new syntax checker to the front of flycheck-checkers, overriding all built-in syntax checkers.
• sh-checkbashisms does not have any :next-checkers at all. Combined with the above this essentially means that it disables all built-in checkers for shells other than bash.
• sh-checkbashisms runs for Zsh scripts, where it's probably not desired.

In my opinion that's a no-go, and it means that we cannot recommend this extension to our users with good conscience. Before we add this repo to our list of extensions, I'd like to see a couple of fixes applied. Specifically:

• sh-checkbashisms should only run for sh scripts.
• It should be added at the end of flycheck-checkers, to run after the built-in syntax checkers.
• It should register itself to run after the built-in sh syntax checkers with flycheck-add-next-checker.

In the end a sh buffer should be checked with sh-posix-dash or sh-bash-posix, then sh-shellcheck and ultimately sh-checkbashisms. sh-checkbashishms should not run for bash or zsh scripts, or any other non-sh shell script.