Maintainability Rules

This document details the rules available in the Maintainability category.

Available Rules

Rule	Code
Cyclomatic Complexity	cyclomatic-complexity
Excessive Nesting	excessive-nesting
Excessive Parameter List	excessive-parameter-list
Halstead	halstead
Kan Defect	kan-defect
No Boolean Flag Parameter	no-boolean-flag-parameter
No Else Clause	no-else-clause
No Goto	no-goto
Too Many Enum Cases	too-many-enum-cases
Too Many Methods	too-many-methods
Too Many Properties	too-many-properties

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cyclomatic-complexity

Checks the cyclomatic complexity of classes, traits, enums, interfaces, functions, and closures.

Cyclomatic complexity is a measure of the number of linearly independent paths through a program's source code.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"error"
threshold	integer	20

---

excessive-nesting

Checks if the nesting level in any block exceeds a configurable threshold.

Deeply nested code is harder to read, understand, and maintain. Consider refactoring to use early returns, helper methods, or clearer control flow.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"warning"
threshold	integer	7

Examples

Correct Code

<?php

if ($condition) {
    while ($otherCondition) {
        echo "Hello"; // nesting depth = 2
    }
}

Incorrect Code

<?php

if ($a) {
    if ($b) {
        if ($c) {
            if ($d) {
                if ($e) {
                    if ($f) {
                        if ($g) {
                            if ($h) {
                                echo "Too deeply nested!";
                            }
                        }
                    }
                }
            }
        }
    }
}

---

excessive-parameter-list

Detects functions, closures, and methods with too many parameters.

If the number of parameters exceeds a configurable threshold, an issue is reported.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"error"
threshold	integer	5

---

halstead

Computes Halstead metrics (volume, difficulty, effort) and reports if they exceed configured thresholds.

Halstead metrics are calculated by counting operators and operands in the analyzed code. For more info: https://en.wikipedia.org/wiki/Halstead_complexity_measures

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"warning"
volume-threshold	double	1000
difficulty-threshold	double	12
effort-threshold	double	7000

---

kan-defect

Detects classes, traits, interfaces, functions, and closures with high kan defect.

The "Kan Defect" metric is a heuristic for estimating defect proneness in a class or similar structure. It counts control-flow statements (while, do, foreach, if, and switch) and sums them using a formula loosely based on the work of Stephen H. Kan.

References:

• https://github.com/phpmetrics/PhpMetrics/blob/c43217cd7783bbd54d0b8c1dd43f697bc36ef79d/src/Hal/Metric/Class_/Complexity/KanDefectVisitor.php
• https://phpmetrics.org/

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"error"
threshold	double	1.9

---

no-boolean-flag-parameter

Flags function-like parameters that use a boolean type.

Boolean flag parameters can indicate a violation of the Single Responsibility Principle (SRP). Refactor by extracting the flag logic into its own class or method.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"help"

Examples

Correct Code

<?php

function get_difference(string $a, string $b): string {
    // ...
}

function get_difference_case_insensitive(string $a, string $b): string {
    // ...
}

Incorrect Code

<?php

function get_difference(string $a, string $b, bool $ignore_case): string {
    // ...
}

---

no-else-clause

Flags if statements that include an else or elseif branch.

Using else or elseif can lead to deeply nested code and complex control flow. This can often be simplified by using early returns (guard clauses), which makes the code easier to read and maintain by reducing its cyclomatic complexity.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"help"

Examples

Correct Code

<?php

function process($user) {
    if (!$user->isVerified()) {
        return; // Early return
    }

    // "Happy path" continues here
    $user->login();
}

Incorrect Code

<?php

function process($user) {
    if ($user->isVerified()) {
        // "Happy path" is nested
        $user->login();
    } else {
        // Logic is split across branches
        return;
    }
}

---

no-goto

Detects the use of goto statements and labels. The goto statement can make code harder to read, understand, and maintain. It can lead to "spaghetti code" and make it difficult to follow the flow of execution.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"note"

Examples

Correct Code

<?php

$i = 0;
while ($i < 10) {
    if ($i === 5) {
        break; // Structured control flow.
    }
    $i++;
}

Incorrect Code

<?php

$i = 0;
loop:
if ($i >= 10) {
    goto end;
}

$i++;
goto loop;
end:

---

too-many-enum-cases

Detects enums with too many cases.

This rule checks the number of cases in enums. If the number of cases exceeds a configurable threshold, an issue is reported.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"error"
threshold	integer	30

Examples

Correct Code

enum SimpleEnum {
    case A;
    case B;
    case C;
}

Incorrect Code

enum LargeEnum {
    case A;
    case B;
    case C;
    case D;
    case E;
    case F;
    case G;
    case H;
    case I;
    case J;
    case K;
    case L;
    case M;
    case N;
    case O;
    case P;
    case Q;
    case R;
    case S;
    case T;
    case U;
}

---

too-many-methods

Detects class-like structures with too many methods.

This rule checks the number of methods in classes, traits, enums, and interfaces. If the number of methods exceeds a configurable threshold, an issue is reported.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"error"
threshold	integer	10
count-hooks	boolean	false
count-setters-and-getters	boolean	false

Examples

Correct Code

class SimpleClass {
    public function a() {}

    public function b() {}
}

Incorrect Code

class ComplexClass {
    public function a() {}
    public function b() {}
    public function c() {}
    public function d() {}
    public function e() {}
    public function f() {}
    public function g() {}
    public function h() {}
    public function i() {}
    public function j() {}
    public function k() {}
    public function l() {}
    public function m() {}
    public function n() {}
    public function o() {}
    public function p() {}
    public function q() {}
    public function r() {}
    public function s() {}
    public function t() {}
    public function u() {}
}

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too-many-properties

Detects class-like structures with too many properties.

This rule checks the number of properties in classes, traits, and interfaces. If the number of properties exceeds a configurable threshold, an issue is reported.

Configuration

Option	Type	Default
enabled	boolean	true
level	string	"error"
threshold	integer	10

Examples

Correct Code

class SimpleClass {
    public $a;
    public $b;
}

Incorrect Code

class ComplexClass {
    public $a; public $b; public $c; public $d; public $e;
    public $f; public $g; public $h; public $i; public $j; public $k;
}

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