Unreachable Code

ID

swift.unreachable_code

Severity

low

Remediation Complexity

auto_fix

Remediation Risk

low

Remediation Effort

low

Resource

Dead Code

Language

Swift

Tags

dead-code, reliability

Description

Reports a statement that can never execute because control flow always leaves the enclosing region before reaching it. The analysis walks the function’s control-flow graph: code becomes unreachable after an unconditional jump (return, throw, break, continue, fallthrough), after a never-returning call (fatalError, preconditionFailure, abort, exit), or inside an always-taken constant branch. Only the first statement of each dead region is flagged.

func compute() -> Int {
    return 0
    print("never")                  // FLAW
}

for x in xs {
    if x == 0 { continue }          // OK — conditional
    work(x)
}

Rationale

Code after an unconditional terminator is a classic typo or leftover from an incomplete refactor. Swift’s compiler warns about some of these, but not all — and even the warnings are easy to overlook in a busy build log.

Remediation

Either remove the dead statements, or move them above the terminator if the intent was to run them first. If you actually need a side effect after a fatalError, the function is doing something unusual and probably needs review anyway.

The rule only reports the first unreachable statement in each block — fixing that one usually reveals the rest.

References