Analyzes php-code for side-effects.

When code has no side-effects it can e.g. be used with eval($code) in the same process without interfering. Side-effects are classified into categories to filter them more easily depending on your use-case.

This library is used e.g. in PHPUnit to improve performance of PHPT test-cases.

Install

composer require staabm/side-effects-detector

Usage

Example:

use staabm\SideEffectsDetector\SideEffectsDetector;

$code = '<?php version_compare(PHP_VERSION, "8.0", ">=") or echo("skip because attributes are only available since PHP 8.0");';

$detector = new SideEffectsDetector();
// [SideEffect::STANDARD_OUTPUT]
var_dump($detector->getSideEffects($code));

In case functions are called which are not known to have side-effects - e.g. userland functions - null is returned.

use staabm\SideEffectsDetector\SideEffectsDetector;

$code = '<?php userlandFunction();';

$detector = new SideEffectsDetector();
// [SideEffect::MAYBE]
var_dump($detector->getSideEffects($code));

Code might have multiple side-effects:

use staabm\SideEffectsDetector\SideEffectsDetector;

$code = '<?php include "some-file.php"; echo "hello world"; exit(1);';

$detector = new SideEffectsDetector();
// [SideEffect::SCOPE_POLLUTION, SideEffect::STANDARD_OUTPUT, SideEffect::PROCESS_EXIT]
var_dump($detector->getSideEffects($code));

Compensate some side-effects

It might be useful to compensate some side-effects, so evaluation of code in the current process is still acceptable:

use staabm\SideEffectsDetector\SideEffectsDetector;

function runCodeInLocalSandbox(string $code): string
{
    $code = preg_replace('/^<\?(?:php)?|\?>\s*+$/', '', $code);
    $code = preg_replace('/declare\S?\([^)]+\)\S?;/', '', $code);

    // wrap in immediately invoked function to isolate local-side-effects
    // of $code from our own process
    $code = '(function() {' . $code . '})();';
    
    // wrap in output buffer to isolate stdout side-effects
    ob_start();
    @eval($code);

    return ob_get_clean();
}

function shouldRunInSubprocess(string $code): bool
{
    $detector    = new SideEffectsDetector;
    $sideEffects = $detector->getSideEffects($code);

    if ($sideEffects === []) {
        return false; // no side-effects
    }

    foreach ($sideEffects as $sideEffect) {
        // stdout is fine, we will catch it using output-buffering
        if ($sideEffect === SideEffect::STANDARD_OUTPUT) {
            continue;
        }

        return true;
    }

    return false;
}

function runCode(string $code) {
    if (!shouldRunInSubprocess($code)) {
        return runCodeInLocalSandbox($code);
    }
    
    // run $code in isolation, e.g. in a subprocess
    // ...
}

Disclaimer

Non goals are:

• find the best possible answer for all cases
• add runtime dependencies
• inspect additional metadata like attributes or phpdoc tags

If you are in need of a fully fledged side-effect analysis, use more advanced tools like PHPStan.

Look at the test-suite to get an idea of supported use-cases.