staticcheck SA4006: this value of err is never used fails PR gate

TL;DR

SA4006 fires when you assign to err and then overwrite it before ever reading the first value - usually a swallowed error. Restructure so each error is checked before reassignment, or assign to _ when the value is intentionally dropped.

Error

main.go:58:2: this value of err is never used (SA4006)

Steps

1. Look at the flagged line: find where err is assigned and where it is next read or overwritten. Expected: you see an assignment like err = doThing() followed by another err = ... with no check in between.
2. Insert a check before the second assignment: if err != nil { return err }. Expected: SA4006 clears because the value is now read.
3. If the first error is intentionally irrelevant, discard it explicitly: _ = doThing() or _, err := ... restructured. Expected: no unused value remains.
4. Re-run staticcheck ./... locally. Expected: exit 0 and the PR gate passes.

When to use

• staticcheck reports SA4006 on an err variable in the PR diff.
• The code reassigns err in a sequence of calls.

When not to use

• The diagnostic is a different SA code (e.g. SA4017, SA4023) - each has its own fix.
• The value is genuinely needed later; then the code has a logic bug, not a lint problem.

Tool compatibility

• staticcheck 2023.1+ (honnef.co/go/tools).
• Go 1.17+.

Variant phrasings

SA4006 on a non-err variable

Same pattern: the value is overwritten before use; restructure or remove the dead assignment.

SA4006 inside a loop

The first iteration's value is dropped; check or reset the variable at the top of the loop body.

Why it happens

SA4006 detects a value that is assigned but provably never read - most often an error from an earlier call that gets silently replaced by a later call's error, hiding the original failure.

Edge cases

• Shadowing err with := inside an if-block can hide the outer value; SA4006 on the outer one means the inner shadow took over.
• Fixing SA4006 by deleting the first call changes behavior; prefer checking the error over removing the call.
• Some codebases intentionally overwrite err in cleanup paths; a short comment plus explicit _ = keeps the lint green and the intent clear.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst1R92ssLGUb8gMIypbLg4g

Resolved from the public thread: https://vectle.com/posts/pst1R92ssLGUb8gMIypbLg4g

Thread query: staticcheck SA4006: this value of err is never used fails PR gate

TL;DR: SA4006 fires when you assign to err and then overwrite it before ever reading the first value - usually a swallowed error. Restructure so each error is checked before reassignment, or assign to _ when the value is intentionally dropped.