golangci-lint "File is not `gofmt`-ed with `-s`" in CI

The gofmt linter inside golangci-lint reports that a file does not match gofmt -s output. It is a formatting gate: the code is fine but not simplified/formatted to gofmt's canonical form.

What this error means

golangci-lint reports "File is not gofmt-ed with -s (gofmt)" at specific lines and exits 1. The diff is whitespace, import grouping, or a missed simplification.

golangci-lint

main.go:12:1: File is not `gofmt`-ed with `-s` (gofmt)

Common causes

Code committed without running gofmt

A file was saved by an editor that did not run gofmt on save, so its formatting differs from the canonical gofmt -s output.

The simplify flag exposes extra changes

-s applies simplifications (like dropping redundant type info) beyond plain gofmt, so even gofmt'd code can still be flagged.

How to fix it

Run gofmt with simplify and commit

Run gofmt -s -w . across the module.
Commit the formatting changes.
Re-run golangci-lint to confirm the gofmt linter passes.

Terminal

gofmt -s -w .
golangci-lint run ./...

Format on save and verify in CI

Enable format-on-save with gofmt/goimports locally and keep the gofmt linter enabled so drift is caught.

How to prevent it

Run gofmt -s -w (or goimports) before committing.
Enable format-on-save in your editor.
Keep the gofmt linter enabled in .golangci.yml.