File is not `gofmt`-ed with `-s`: why is this happening and how to resolve it?

Question

We use a linter (for Golang) that run through a Github Actions workflow every time we open or update a Pull Request on our repository.

It recently started to return the following error:

File is not `gofmt`-ed with `-s` (gofmt)

After what happened in this other PR to the file pkg/api/api/go.
(EDIT: link added to evaluate and eventually reproduce the error)

Evidences:

I would like to understand what was the source of this error, as well as how to resolve it?

Answer 1

Source of the error

It seems this error can be returned when the file is not properly formatted according to Go rules.

For example: If you accidentally used tab indentation rather than spaces.

EDIT: blackgreen's answer gives more accurate details about the source of the error

---

How to resolve it

You can use the following Go command:

gofmt -s -w <path_to_file>.go

... then commit the code.

Note that in my case: gofmt -w pkg/api/api.go was enough to resolve the problem (without the -s flag, which I found strange as the error specifically asked for the -s).

Source 1 + Source 2

Answer 2

The -s flag in gofmt has nothing to do with formatting. It's about simplifying the code:

Try to simplify code (after applying the rewrite rule, if any).

The warning you see comes from the linter golangci-lint. Since you claim to have fixed the error by running gofmt -w, the presence of the hint "with -s" may be due to this bug: https://github.com/golangci/golangci-lint/issues/513.

The linked issue was fixed in 2019 and released with v1.17.0. You might want to check if your pipeline is using an older version.

Assuming that your file pkg/api/api.go triggered the warning just because it was not formatted, gofmt -w solves the issue because -w overwrites the file:

If a file's formatting is different from gofmt's, overwrite it with gofmt's version.