Cyclomatic Complexity

ID

php.cyclomatic_complexity

Severity

info

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Complexity

Language

Php

Tags

complexity

Description

Reports functions, methods and closures whose cyclomatic complexity exceeds a configurable threshold (default 30). Cyclomatic complexity counts the number of linearly-independent paths through a routine; it grows with every branch — if/elseif, loops, switch cases, catch clauses and the like. The value is computed from the routine’s control-flow graph.

Rationale

A high cyclomatic complexity means many independent execution paths, which makes a routine hard to read, hard to reason about and hard to cover with tests: the number of test cases needed to exercise every path grows with the metric. Routines that accumulate branch after branch tend to mix several responsibilities and become a magnet for defects when changed.

<?php
class Classifier
{
    public function classify(int $n): string   // FLAW — far too many branches
    {
        if ($n < 0) { return 'negative'; }
        if ($n === 0) { return 'zero'; }
        if ($n === 1) { return 'one'; }
        if ($n === 2) { return 'two'; }
        for ($i = 1; $i < $n; $i++) {
            if ($i % 2 === 0) { continue; }
            if ($i % 3 === 0) { continue; }
        }
        if ($n > 1000) { return 'big'; }
        if ($n < -1000) { return 'small'; }
        return 'normal';
    }

    public function trivial(int $a, int $b): int
    {
        return $a + $b;                          // OK — straight-line, complexity 1
    }
}

Remediation

Break the routine into smaller, single-responsibility helpers. Replace long if/elseif ladders or switch blocks with a lookup table or polymorphism, use guard clauses to flatten nesting, and extract loop bodies into their own functions. Tune the maxCcn property to match your team’s standard.

References