cmd/fix: change -diff to exit 1 if diffs exist

[Rican7]

Proposal Details

What?

Similar to #27005 and #46289, which were both accepted, go fix -diff should exit with a status code of 1 (rather than the current 0) if any diffs exist.

Why?

• For the same reasons as the other tools behaviors (go mod tidy -diff cmd/go: add mod tidy -diff #27005 and gofmt -d cmd/gofmt: change -d to exit 1 if diffs exist #46289), its useful for CI/CD, pre-commit hooks, and general code health checks.
• Consistency across tools is important.
• go fix now uses analysis to modernize code, so will be used much more commonly and consistently in code integration.
• The increasing usage of generative "AI" tooling fairs better when given "guardrails" to check generated code against.

[gabyhelp]

Related Issues

• cmd/gofmt: change -d to exit 1 if diffs exist #46289 (closed)
• proposal: cmd/gofmt: add a flag to make incorrect formatting return a non-zero exit code #74907 (closed)
• proposal: cmd/fmt: flag to set exit code when formatting occurs #24427 (closed)
• proposal: cmd/gofmt: add a flag to return an error exit status. #45953 (closed)
• proposal: cmd/gofmt: also exit 1 for `-l` (list paths) #76405
• x/tools/gopls: set non-zero exit code on `check` command when there are errors #67078
• proposal: cmd/go: add go mod tidy -diff #67242 (closed)
• Proposal: Allow go fmt to return non-zero if code violations are found #41189 (closed)
• Proposal: Allow gofmt to return non-zero if code violations are found #24230 (closed)
• "gofmt -d" should have non-zero exit if there is a diff #38551 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[Rican7]

For what it's worth, if anyone comes here looking for a workaround, I've got you.

POSIX sh (Bourne Shell)

errors=$(go fix -diff ./...); if [ "${errors}" != "" ]; then echo "${errors}"; exit 1; fi

POSIX Make

fix-check:
	errors=$$(go fix -diff ./...); if [ "$${errors}" != "" ]; then echo "$${errors}"; exit 1; fi

.PHONY: fix-check

[dmitshur]

@gopherbot Please create a backport issue for Go 1.26 (original request was in #77583 (comment)).

[gopherbot]

Backport issue(s) opened: #77801 (for 1.26).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.