NeverFunctionFallsThrough

error native on by default PHP ≥ 8.1

Group: Probable bugs

Terminate every path in the never function.

Example

Finding:

<?php
function halt(bool $stop): never { if ($stop) { exit; } }

Reported:

• line 2: Terminate every path in the never function.

Detection

• For a function, method or closure with resolved builtin never return type, report its return type when a reachable path reaches the closing brace. Use bounded control-flow proof, recognizing throw, exit/die, unconditional infinite loops and calls with a resolved never return type. An explicit return is already illegal and is not this fall-through finding.
• Emit one finding per violating operation. Flow facts require a reachable path with no intervening mutation, escaped alias, unknown call involving the tracked value or analysis-budget exhaustion. Uncertain facts cannot prove a violation.

Exceptions (no report)

• Exclude unreachable closing braces, unknown control-flow summaries and budget exhaustion. A conditional throw proves termination only on its throwing branch.
• Exclude shadowed builtin symbols, unresolved required types, incomplete syntax and unsupported PHP versions.
• A while, do-while or for loop is not proven to end when its condition (the last one of a for) is a known truthy value such as 1, or is built only from literals, constants and operators, such as !false or 1 === 1, whose value the rule does not evaluate. The function is then not reported. A loop whose condition is known falsy, or reads a variable or the result of a call, can still end and does not prevent the report.

Fix

No automatic fix. Choosing a repair requires runtime information, error-handling policy or a semantic decision.

All edits use exact byte ranges, preserve comments and evaluation order, and require syntax supported by the target PHP version. A fix must never add an evaluation or silently change unrelated arguments.

PHP versions

Minimum PHP 8.1.

Configure

In custos.json:

{
  "rules": {
    "NeverFunctionFallsThrough": {
      "enabled": false
    }
  }
}

Suppress

Before the statement or declaration (or the first statement of the file):

// @custos-ignore NeverFunctionFallsThrough