Unreachable Code

Also Known As

TL;DR

Explanation

Unreachable code appears after unconditional return/throw/exit/break/continue, inside dead conditions, or in catch blocks that can never be triggered. It is always a defect: either the code was meant to execute (logic error) or it is leftover debris from refactoring. PHPStan and Psalm report unreachable statements. The never return type in PHP 8.1 lets static analysers know that certain functions never return, improving detection.

Common Misconception

Why It Matters

Common Mistakes

• Placing cleanup code after return instead of before it.
• Adding code after a throw in an exception handler — the throw terminates the current path.
• A catch block for an exception the try block cannot throw — wastes maintenance effort.
• Early return refactoring that leaves else blocks unreachable but visually present.

Code Examples

// Code after return — never executes:
function processOrder(Order $order): string {
    return 'processed';
    $this->audit->log($order); // Never runs — silently skipped!
    $order->markComplete();    // Never runs
}

// Unreachable catch:
try {
    $result = purePHPCalculation($x); // Cannot throw
} catch (DatabaseException $e) { // Unreachable
    handleError($e);
}

// Correct order — execution before return:
function processOrder(Order $order): string {
    $this->audit->log($order); // Runs first
    $order->markComplete();    // Runs second
    return 'processed';        // Returns last
}

// Remove unreachable catch:
$result = purePHPCalculation($x); // No try needed

References

• ↗ https://phpstan.org/

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