PHP Version Upgrade

Upgrade one minor version at a time. Never skip versions -- each step surfaces deprecations that become errors in the next release. Every upgrade follows the same cycle: audit, automate, test, deploy.

Core Principles

Principle Meaning

Changelog first Before any upgrade, search the web for the official PHP migration guide (php.net/migration) or ask the user for the changelog -- never rely on static knowledge alone

One version at a time Upgrade 8.1 -> 8.2 -> 8.3 -> 8.4 sequentially -- skipping versions makes it impossible to isolate breakage

Fix deprecations before upgrading Deprecations in version N become errors in version N+1 -- treat them as mandatory fixes

Automate first, manual second Run Rector and PHPCompatibility before touching code by hand -- they catch 80%+ of required changes

Prove it with tests Never consider an upgrade complete without a passing test suite on the target version

Pin your platform Set config.platform.php in composer.json to match your lowest deployment target

Upgrade Process Overview

Phase 0: Read the Changelog

Before touching any code, obtain the actual changelog for the target PHP version:

• Search the web for PHP X.Y migration guide (e.g., PHP 8.4 migration guide php.net )

• Or ask the user to provide the changelog / release notes

• Read the official migration page at https://www.php.net/manual/en/migrationXY.php

This is non-negotiable. Each version has unique changes that static skill knowledge cannot fully capture.

Phase 1: Audit

Before changing any code, understand the scope of the upgrade.

• Run PHPCompatibility against the target version to identify incompatible code

• Run php-parallel-lint with the target PHP binary to catch syntax errors

• Run composer outdated to check if all dependencies support the target version

• Review the official migration guide at php.net for the target version

• Check PHP extensions for compatibility (ext-intl , ext-mbstring , etc.)

Phase 2: Automate

Use Rector to handle the bulk of code transformations automatically.

// rector.php use Rector\Config\RectorConfig;

return RectorConfig::configure() ->withPaths([DIR . '/src', DIR . '/tests']) ->withPhpSets(php84: true); // adjust to target version

Always dry-run first:

vendor/bin/rector process --dry-run

Review changes, then apply:

vendor/bin/rector process

Commit Rector changes separately from manual fixes for clean git history.

Phase 3: Update Dependencies

• Update composer.json with the new PHP version constraint: "php": ">=8.4"

• Update config.platform.php to match the target version

• Run composer update and resolve conflicts

• Update PHP extensions as needed

Phase 4: Test and Deploy

• Run the full test suite under the new PHP version

• Run static analysis (PHPStan/Psalm)

• Deploy to staging and verify

• Monitor production logs for deprecation notices after deployment

See Upgrade Process Reference for detailed tool configuration, CI pipeline setup, and Docker considerations.

Tools

Tool Purpose When to Use

Rector Automated AST-based code transformation First step after auditing -- handles most mechanical changes

PHPCompatibility PHP_CodeSniffer ruleset for cross-version compatibility Audit phase -- identifies all incompatible code before you start

php-parallel-lint Parallel syntax checking (~20x faster than serial) Audit phase -- catches syntax errors under the new version

PHPStan/Psalm Static analysis Verification phase -- catches type errors after transformation

symfony/phpunit-bridge Deprecation summary in test output Ongoing -- monitors deprecation count during upgrades

Breaking Changes by Version

Transition Key Breaking Changes

8.0 -> 8.1 Fibers introduced, enums added, readonly properties, intersection types, never return type

8.1 -> 8.2 Dynamic properties deprecated (use #[AllowDynamicProperties] temporarily), $GLOBALS access restrictions, readonly classes, disjunctive normal form types

8.2 -> 8.3 Typed class constants, json_validate() added, #[Override] attribute, Randomizer additions, date/time exception changes

8.3 -> 8.4 Implicit nullable types deprecated (function foo(string $bar = null) must become ?string $bar = null ), property hooks, asymmetric visibility, new without parentheses deprecated for no-arg constructors, DOM extension namespace changes

See Version Changes Reference for complete per-version details with code examples.

Common Pitfalls

Pitfall Why It Hurts Prevention

Skipping versions Cannot isolate which changes broke what Always upgrade one version at a time

Ignoring deprecation warnings Deprecations become fatal errors in the next version Fix all deprecations before upgrading

Not checking dependencies Third-party packages may not support the target version Run composer outdated and check support before starting

Using --ignore-platform-reqs

Bypasses safety checks, causes runtime errors Never use it -- fix the actual constraints instead

Not pinning config.platform.php

Local PHP differs from production, causing install mismatches Always set it to match production

Large unreviewed Rector runs Rector can make incorrect transformations in edge cases Always dry-run first, review changes, run on small batches

Forgetting PHP extensions Extensions change behavior or get deprecated between versions Audit all required extensions before upgrading

Quick Reference: Upgrade Checklist

• Review php.net migration guide for target version

• Run PHPCompatibility scan against target version

• Run php-parallel-lint with target PHP binary

• Verify all Composer dependencies support target version

• Configure and run Rector with target version set (dry-run first)

• Review and commit Rector changes

• Apply manual fixes for remaining issues

• Update composer.json PHP constraint and config.platform.php

• Run composer update

• Run full test suite on target PHP version

• Run static analysis (PHPStan/Psalm)

• Deploy to staging and verify

• Deploy to production and monitor logs

Reference Files

Reference Contents

Upgrade Process Detailed tool configuration, CI pipeline setup, Docker strategy, and step-by-step commands

Version Changes Per-version breaking changes, new features, and deprecations with code examples (PHP 8.0 through 8.4)

Integration with Other Skills

Situation Recommended Skill

Upgrading Symfony alongside PHP Use the symfony-upgrade skill in frameworks/symfony/

Updating Composer dependencies after PHP upgrade Use the composer-dependencies playbook skill

Modernizing PHP code patterns (DTOs, enums, strict types) Install php-modernization from dirnbauer/webconsulting-skills or netresearch/php-modernization-skill

Running static analysis after upgrade Install knowledge-virtuoso from krzysztofsurdy/code-virtuoso for testing strategies