gofmt / go fmt — Find the Bug¶

Each scenario looks fine but misbehaves. Find the defect, explain it, fix it.

Bug 1 — File "formatted" but unchanged¶

$ gofmt messy.go
# nicely formatted output printed... but the file on disk is still messy

Bug: without -w, gofmt prints to stdout and does not modify the file. Fix: gofmt -w messy.go to write the changes back.

Bug 2 — CI rewrites files instead of failing¶

- run: go fmt ./...

Bug: go fmt writes changes (-w); in CI it silently mutates files and the step passes even though contributors committed unformatted code. Fix: check, don't write: test -z "$(gofmt -l .)" (fail if any file is unformatted).

Bug 3 — Formatted file fails CI¶

A developer on Go 1.23 formats and commits; CI on Go 1.19 reports the file as unformatted.

Bug: gofmt's output is tied to the toolchain version; the two gofmts disagree (e.g., doc-comment formatting). Fix: pin the toolchain so dev and CI use the same gofmt — go directive in go.mod plus GOTOOLCHAIN.

Bug 4 — Expecting unused imports to be removed¶

$ gofmt -w file.go    # unused import still there
./file.go:5:2: "strings" imported and not used

Bug: gofmt groups/sorts imports but never adds or removes them. Fix: use goimports -w file.go (or gopls organize-imports) to manage the import list.

Bug 5 — Generated code fails the fmt check¶

A code generator writes Go with inconsistent spacing; CI's gofmt -l flags the generated files.

Bug: the generator emits non-canonical source and nothing reformats it. Fix: pass output through go/format.Source in the generator, or run gofmt -w on generated files as a post-generation step.

Bug 6 — Reformat churn buried in a feature PR¶

A feature PR also runs gofmt -w ./... after a toolchain bump, mixing hundreds of formatting-only lines with logic changes.

Bug: the formatting churn pollutes the diff and git blame. Fix: do the reformat in a dedicated commit, add its SHA to .git-blame-ignore-revs, and keep logic changes separate.

Bug 7 — `gofmt` reports only one error¶

$ gofmt file.go    # stops reporting after the first parse error

Bug: by default gofmt limits reported errors; a file with many syntax errors looks like it has only one. Fix: gofmt -e file.go reports all errors. (Note gofmt needs the file to parse; fix syntax before formatting.)

Bug 8 — Editor inserts spaces, fighting gofmt¶

The editor is set to indent with spaces, so saving without format-on-save leaves space-indented Go that gofmt then rewrites to tabs on commit.

Bug: editor indentation config conflicts with gofmt's tabs. Fix: enable format-on-save (gopls) so gofmt normalizes indentation to tabs automatically; do not hand-indent Go.

Bug 9 — Inconsistent tools across the team¶

Editor uses gofumpt; CI checks plain gofmt. Files pass locally, fail CI (or vice versa).

Bug: different formatters produce different output, so the same file is "correct" in one place and "wrong" in another. Fix: standardize the exact same formatter (and version) in editor, pre-commit hook, and CI.

How to approach these¶

File unchanged? → missing -w.
CI not catching unformatted code? → use gofmt -l, not go fmt.
Spurious failures? → toolchain version skew; pin it.
Imports not fixed? → that's goimports, not gofmt.
Generated/edited files flagged? → run them through gofmt / go/format.