Wrong Errors Is

Reports a call to errors.Is whose arguments are in the wrong order — errors.Is(ErrNotFound, err) instead of errors.Is(err, ErrNotFound).

errors.Is(err, target) takes the live error value first and the sentinel target second; it unwraps the value’s chain looking for the target. Swapping the arguments compares the bare sentinel — which wraps nothing — against the live error, so the check silently never matches and the error-handling branch becomes dead code. Because the mistake compiles cleanly and only misbehaves on the error path, it is easy to miss in testing.

To stay free of false positives the rule fires only on the unambiguous swap shape: the first argument is a bare sentinel identifier (Err/err followed by an upper-case letter) and the second argument is the bare identifier err.

Swap the arguments so the error value comes first and the sentinel target second: errors.Is(err, ErrNotFound).