README

Overview

This PHP CLI tool analyzes the usage of local variables in PHP source code, focusing on their scope and update frequency. It helps developers identify potential issues in handling local variables, improving code quality and maintainability.

What is "Local Variable Hard Usage"?

"Local Variable Hard Usage" is a concept that evaluates how intensely local variables are used in a function or method. This metric helps identify variables that might negatively impact code readability and maintainability due to excessive scope width and frequent updates.

The idea behind this metric is that when a local variable is referenced over a wide range of lines or is frequently modified, it becomes harder to understand and refactor. By quantifying this, we can gain insights into potential problem areas in the code.

This concept is introduced and explained in detail in the following blog post: Understanding Local Variable Hard Usage

This tool analyzes PHP code using PHP-Parser to measure the "Local Variable Hard Usage" for each function and method. It calculates the average reference line span of each variable and sums the deviations from this average, providing a score that represents how heavily a variable is used within its scope.

Features

Analyzes local variable scope and update frequency.
Provides insights into variable usage patterns.
Helps identify potential issues related to variable handling.

Installation

To install the PHP CLI tool, follow these steps:

Clone the repository:

git clone https://github.com/smeghead/php-variable-hard-usage.git
cd php-variable-hard-usage

Install dependencies using Composer:
```
composer install
```

Alternatively, you can install the tool via Composer as a development dependency:

composer require --dev smeghead/php-variable-hard-usage

Usage

The tool provides two operation modes: single mode for analyzing individual files and scopes mode for analyzing multiple files or directories.

Single File Analysis

Use the single command to analyze a single PHP file:

$ vendor/bin/php-variable-hard-usage single path/to/your-file.php
{
    "filename": "path/to/your-file.php",
    "maxVariableHardUsage": 65,
    "avarageVariableHardUsage": 26.833333333333332,
    "scopes": [
        {
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "VariableParser::__construct",
            "variableHardUsage": 1
        },
        {
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "VariableParser::resolveNames",
            "variableHardUsage": 9
        },
        {
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "VariableParser::parse",
            "variableHardUsage": 39
        }
    ]
}

For backward compatibility, you can also run without specifying the single command:

$ vendor/bin/php-variable-hard-usage path/to/your-file.php

Multiple Files Analysis

Use the scopes command to analyze multiple files or entire directories:

# Analyze all PHP files in a directory
$ vendor/bin/php-variable-hard-usage scopes src/

# Analyze multiple directories
$ vendor/bin/php-variable-hard-usage scopes src/ tests/

# Analyze specific files and directories
$ vendor/bin/php-variable-hard-usage scopes src/Command.php config/ tests/

The output for scopes mode is a combined report with results sorted by variable hard usage:

{
    "scopes": [
        {
            "file": "src/Parse/VariableParser.php",
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "VariableParser::collectParseResultPerFunctionLike",
            "variableHardUsage": 65
        },
        {
            "file": "src/Parse/VariableParser.php",
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "Expr_Closure@65",
            "variableHardUsage": 47
        },
        {
            "file": "src/Parse/VariableParser.php",
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "VariableParser::parse",
            "variableHardUsage": 39
        }
    ]
}

CI Integration with Check Mode

Use the check command with an optional threshold to analyze files and enforce variable usage standards in CI/CD pipelines:

# Check files with default threshold (200)
$ vendor/bin/php-variable-hard-usage check src/

# Check with custom threshold
$ vendor/bin/php-variable-hard-usage check --threshold=500 src/ tests/

# Check specific files and directories
$ vendor/bin/php-variable-hard-usage check --threshold=300 src/Command.php config/

The check mode returns different exit codes based on the result:

Exit code 0: Success - No analysis errors and no scopes exceeding the threshold
Exit code 1: Analysis failure - Errors occurred during file parsing or analysis
Exit code 2: Threshold exceeded - One or more scopes exceeded the specified variable hard usage threshold

The output includes the threshold used, result status, and a list of scopes that exceeded the threshold:

{
    "threshold": 500,
    "result": "failure",
    "scopes": [
        {
            "file": "src/Parse/VariableParser.php",
            "namespace": "Smeghead\\PhpVariableHardUsage\\Parse",
            "name": "VariableParser::collectParseResultPerFunctionLike",
            "variableHardUsage": 655
        },
        {
            "file": "src/Command/SingleCommand.php",
            "namespace": "Smeghead\\PhpVariableHardUsage\\Command",
            "name": "SingleCommand::execute",
            "variableHardUsage": 530
        }
    ]
}

This mode is particularly useful for integrating the tool into your CI/CD pipeline to fail builds when variable usage exceeds acceptable thresholds.

Help and Version Information

To display help information:

$ vendor/bin/php-variable-hard-usage --help

$ vendor/bin/php-variable-hard-usage --version

How to calculate VariableHardUsage

VariableHardUsage is an index used to evaluate the frequency of use and scope of local variables within a function. This measure is calculated based on the variance of the line number of references to the same variable and the frequency with which the variable is assigned.

Calculation Procedure

This tool calculates the Variable Hard Usage score for each scope (i.e., a function or method) based on how local variables are used. The calculation consists of the following steps:

1. Extract local variables in a scope

For each scope $S$, extract all local variables:

$V = {v_1, v_2, ..., v_m}$

2. For each variable $v_j$, identify lines where it is referenced

Let the variable $v_j$ be referenced at line numbers:

$L^{(j)} = {l^{(j)}_1, l^{(j)}_2, ..., l^{(j)}_{n_j}} \quad$

3. Assign weights to each reference

Each reference line $l^{(j)}_i$ is assigned a weight $w^{(j)}_i$ depending on whether it is a simple read or an assignment:

If the reference is an assignment (update):
$w^{(j)}_i = \alpha \quad (\text{default: } \alpha = 2)$
If the reference is a read-only access:
$w^{(j)}_i = 1$

4. Calculate Variable Hard Usage for each variable

Let $l^{(j)}_\text{base} = l^{(j)}_1$, the first line where $v_j$ appears.

Then, the hard usage score for $v_j$ is calculated as:

$H(v_j) = \sum_{i=1}^{n_j} w^{(j)}_i \cdot |l^{(j)}_i - l^{(j)}_\text{base}|$

This measures how widely and intensely the variable is used, with updates having a stronger impact.

5. Sum all variable scores to get the score for the scope

The total Variable Hard Usage for the scope $S$ is:

$H(S) = \sum_{j=1}^{m} H(v_j) = \sum_{j=1}^{m} \sum_{i=1}^{n_j} w^{(j)}_i \cdot |l^{(j)}_i - l^{(j)}_\text{base}|$

A larger value of $H(S)$ indicates that variables in the scope are heavily and broadly used, which may reduce code readability and maintainability.

Example

Suppose, for example, that there are three reference points in a function, each with line numbers 10, 20, and 30, and that some assignments are made and some are not made. In this case, the line number of the first occurrence is 10.

Reference A: line 10, with assignment
Reference B: line 20, no assignment
Reference C: line 30, with assignment

In this case, VariableHardUsage is calculated as follows

Reference A: (10 - 10) * 2 = 0
Reference B: (20 - 10) * 1 = 10
Reference C: (30 - 10) * 2 = 40

Summing these, VariableHardUsage is 0 + 10 + 40 = 50.

VariableHardUsage is thus calculated as a measure of the frequency of use and scope of a variable. This metric can be used to quantitatively evaluate the usage of local variables within a function and help improve code readability and maintainability.

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