The most convenient way to check in a script the result of a command or another shell script is to check its exit code. However checking in a script (eg. in a CI job) that the formatting of source files is correct requires a bit of scripting with gofmt. In particular, a one-liner is not very readable as demonstrated below.

As an example, here's what I do on my CI job:

test "`gofmt $src_files -l | wc -l`" -eq 0 || exit 1

(granted that my CI job fails if the command returns an error code != 0, and fails otherwise)

To simplify such a use case, I propose to add a flag to the gofmt: -x which exits the program with an error code != 0 iff there were any files that were modified (or any file that must be modified in case the program is dry-run with -l).

I proposed an implementation on https://go-review.googlesource.com/c/go/+/316930 that was -2 because its an API change, hence this proposal.

On the implementation itself, there are two things that could be discussed IMO:

• the program returns an error code 2; returning anything else would complicate the implementation as an error during the formatting (eg. permissions insufficient) also returns 2. However I think it's safe to assume nobody want to differentiate between errors and wrongly formatted source code.
• the -x flag name is maybe not the best choice, I chose it because of e[x]it and both [e]xit and [r]eturn code are taken.