golangci-lint errcheck error: error return value not checked blocks PR

TL;DR

errcheck fails the PR because a function return value (usually err) is discarded without a check. Wrap the call in an explicit error check, or add a //nolint:errcheck comment with a reason when the error is intentionally ignored.

Error

main.go:42:13: Error return value of `w.Write` is not checked (errcheck)

Steps

1. Find every errcheck hit: run golangci-lint run ./... locally and note each file and line. Expected: the same Error return value ... is not checked lines CI reports.
2. If the error matters, handle it explicitly: if _, err := w.Write(b); err != nil { return err }. Expected: errcheck passes and the failure path is no longer silent.
3. If the error is intentionally ignored (e.g. best-effort logging), annotate with a reason: //nolint:errcheck // best-effort log write. Expected: errcheck skips the line; the reason documents intent.
4. For project-wide exclusions of noisy calls, add them to the errcheck exclude-functions list in .golangci.yml. Expected: golangci-lint run ./... is clean with no new nolint comments.

When to use

• CI reports Error return value of ... is not checked (errcheck) and blocks the PR.
• The flagged call is in Go code and you control the repository.

When not to use

• The failure comes from a different linter (staticcheck, govet) - those have different fixes.
• You cannot add nolint comments because the project forbids them; handle the error instead.

Tool compatibility

• golangci-lint 1.5x with the errcheck linter enabled.
• Any Go version errcheck supports.

Variant phrasings

error return value of fmt.Sprintf is not checked

Same fix: assign the value or drop the call if the result is unused.

errcheck: defer f.Close() return not checked

Wrap in a closure that checks the error, or nolint with a reason when the close error is irrelevant.

Why it happens

errcheck exists because silently discarded errors hide failures. Go has no exceptions, so an unchecked return is the only signal a failure happened - the linter treats discarding it as a likely bug.

Edge cases

• Blanket //nolint:errcheck on whole files hides real bugs; keep annotations line-scoped.
• Excluding fmt.Print* style functions in config is fine for CLIs, but keep errcheck on for I/O and network calls.
• errcheck does not flag assignments to _; _ = f() is an explicit (if lazy) acknowledgement.

Provenance

Resolved from the public thread: https://vectle.com/posts/psttRsXQELwXtMovilzBxJ0A