gofmt / go fmt — Optimization¶

gofmt is already fast (no type checking), so "optimization" here means running it less wastefully and avoiding spurious CI cost. Numbers are illustrative.

Exercise 1: Check only changed files in PR CI¶

Before — gofmt -l ./... walks the entire monorepo on every PR.

After — restrict to changed Go files:

changed=$(git diff --name-only origin/main...HEAD | grep '\.go$' || true)
[ -z "$changed" ] && exit 0
unformatted=$(gofmt -s -l $changed)
test -z "$unformatted"

Run the full check on the main branch periodically as a safety net.

Exercise 2: Format-on-save instead of batch runs¶

Before — developers run go fmt ./... manually before each commit (and forget).

After — gopls formats the open file on save:

"editor.formatOnSave": true

Per-file formatting is effectively free and removes the "I forgot" failure mode.

Exercise 3: Pin the toolchain to kill spurious CI reruns¶

Before — gofmt version skew between dev and CI causes intermittent format failures, triggering reruns and reformat commits.

After — pin the toolchain so gofmt is deterministic:

go 1.23.0

export GOTOOLCHAIN=go1.23.0

Exercise 4: Make generators emit canonical code¶

Before — generated files are reformatted by a separate gofmt -w pass after every generation, doubling work and risking drift.

After — format inside the generator:

out, err := format.Source(buf.Bytes())
if err != nil { return err }
os.WriteFile(path, out, 0o644)

Exercise 5: Combine fmt check with the lint job¶

Before — a separate CI job spins up just to run gofmt, adding container start overhead.

After — fold the gofmt check into the existing lint job (golangci-lint can run the gofmt/gofumpt linters):

# .golangci.yml
linters:
  enable: [gofumpt]

One job, one toolchain, one cache — fewer moving parts and faster pipelines.

Measurement checklist¶

• Check only changed files in PR CI; full check on main periodically.
• Format-on-save so per-file cost is negligible and nothing is forgotten.
• Pin the toolchain to eliminate version-skew failures.
• Format inside generators (go/format) — single pass.
• Fold the fmt check into the existing lint job.