Unreachable Code

ID

kotlin.unreachable_code

Severity

low

Remediation Complexity

auto_fix

Remediation Risk

low

Remediation Effort

low

Resource

Dead Code

Language

Kotlin

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), after a never-returning call (exitProcess(…​), error(…​), TODO(…​)), or inside an always-taken constant branch. Only the first statement of each dead region is flagged.

Rationale

Code that follows an unconditional jump is dead code. It misleads readers who may believe the code does something meaningful, and it typically indicates a logic error (the jump was meant to be conditional) or leftover code from a refactoring.

// Bad — unreachable code after throw
fun divide(a: Int, b: Int): Int {
    if (b == 0) {
        throw ArithmeticException("divide by zero")
        return -1   // FLAW — never reached
    }
    return a / b
}

// Bad — unreachable code after return
fun first(items: List<Int>): Int {
    return items[0]
    println("returned")   // FLAW — never reached
}

// Good
fun first(items: List<Int>): Int = items[0]

Remediation

Remove the unreachable statement. If it was meant to execute, move the terminating statement after it, or make the terminating statement conditional.

References