Wp Php8 Migration

Union Types for Hook Returns

// BEFORE (PHP 7.4)
/** @param string|array $classes */
function filter_body_class( $classes ) { ... }

// AFTER (PHP 8.0)
function filter_body_class( string|array $classes ): string|array {
    if ( is_array( $classes ) ) {
        $classes[] = 'custom-class';
    }
    return $classes;
}

Nullsafe Operator for Chained WP Calls

// BEFORE (PHP 7.4)
$user = wp_get_current_user();
$name = null;
if ( $user !== null ) {
    $meta = get_user_meta( $user->ID, 'display_name', true );
    if ( $meta !== null ) {
        $name = $meta;
    }
}

// AFTER (PHP 8.0)
$name = wp_get_current_user()?->display_name;

Match Expressions Replacing Switch Statements

// BEFORE (PHP 7.4)
switch ( $post->post_status ) {
    case 'publish':
        $label = 'Published';
        break;
    case 'draft':
        $label = 'Draft';
        break;
    case 'pending':
        $label = 'Pending Review';
        break;
    default:
        $label = 'Unknown';
        break;
}

// AFTER (PHP 8.0)
$label = match ( $post->post_status ) {
    'publish' => 'Published',
    'draft'   => 'Draft',
    'pending' => 'Pending Review',
    default   => 'Unknown',
};

Constructor Promotion for Plugin Classes

// BEFORE (PHP 7.4)
class My_Plugin {
    private string $plugin_file;
    private string $version;
    private bool $debug;

    public function __construct( string $plugin_file, string $version, bool $debug = false ) {
        $this->plugin_file = $plugin_file;
        $this->version     = $version;
        $this->debug       = $debug;
    }
}

// AFTER (PHP 8.0)
class My_Plugin {
    public function __construct(
        private string $plugin_file,
        private string $version,
        private bool $debug = false,
    ) {}
}

str_contains / str_starts_with / str_ends_with

// BEFORE (PHP 7.4)
if ( strpos( $template, 'single-' ) === 0 ) { ... }
if ( strpos( $content, 'shortcode' ) !== false ) { ... }
if ( substr( $file, -4 ) === '.php' ) { ... }

// AFTER (PHP 8.0)
if ( str_starts_with( $template, 'single-' ) ) { ... }
if ( str_contains( $content, 'shortcode' ) ) { ... }
if ( str_ends_with( $file, '.php' ) ) { ... }

Note: WordPress 5.9+ includes polyfills for these functions. For older WP versions, use wp_polyfill or provide your own.

2. PHP 8.1 Features for WordPress

Enums for WordPress Constants

// BEFORE (PHP 7.4) — string constants scattered everywhere
define( 'POST_STATUS_PUBLISH', 'publish' );
define( 'POST_STATUS_DRAFT', 'draft' );

// AFTER (PHP 8.1)
enum PostStatus: string {
    case Publish = 'publish';
    case Draft   = 'draft';
    case Pending = 'pending';
    case Private = 'private';
    case Trash   = 'trash';

    public function label(): string {
        return match ( $this ) {
            self::Publish => __( 'Published', 'my-plugin' ),
            self::Draft   => __( 'Draft', 'my-plugin' ),
            self::Pending => __( 'Pending Review', 'my-plugin' ),
            self::Private => __( 'Private', 'my-plugin' ),
            self::Trash   => __( 'Trashed', 'my-plugin' ),
        };
    }
}

// Usage with WP_Query
$query = new WP_Query( [ 'post_status' => PostStatus::Publish->value ] );

Readonly Properties for Immutable Config

// BEFORE (PHP 7.4)
class Plugin_Config {
    private string $slug;
    public function __construct( string $slug ) {
        $this->slug = $slug;
    }
    public function get_slug(): string { return $this->slug; }
}

// AFTER (PHP 8.1)
class Plugin_Config {
    public function __construct(
        public readonly string $slug,
        public readonly string $version,
        public readonly string $file,
    ) {}
}
// $config->slug is publicly readable but cannot be modified after construction.

First-Class Callables for Hook Registration

// BEFORE (PHP 7.4)
add_action( 'init', [ $this, 'register_post_types' ] );
add_filter( 'the_content', [ $this, 'filter_content' ] );

// AFTER (PHP 8.1)
add_action( 'init', $this->register_post_types( ... ) );
add_filter( 'the_content', $this->filter_content( ... ) );

// WARNING: Closure::fromCallable() or the ( ... ) syntax creates a Closure.
// remove_action / remove_filter will NOT work because object identity differs.
// Use first-class callables only when you never need to unhook.

Intersection Types for WP Interfaces

// PHP 8.1 — require multiple interfaces
function process_entity( Countable&Iterator $items ): void {
    foreach ( $items as $item ) {
        // guaranteed to be both Countable and Iterator
    }
}

3. PHP 8.2 Features for WordPress

Readonly Classes for Value Objects

// PHP 8.2
readonly class Meta_Box_Args {
    public function __construct(
        public string $id,
        public string $title,
        public string $screen,
        public string $context = 'advanced',
        public string $priority = 'default',
    ) {}
}

Deprecated Dynamic Properties (Massive WP Impact)

This is the single largest PHP 8.2 issue for WordPress. See Section 9 for full remediation.

// PHP 8.2 DEPRECATION — dynamic properties trigger E_DEPRECATED
$obj = new stdClass(); // stdClass is exempt
$obj->foo = 'bar';     // fine on stdClass

class My_Widget extends WP_Widget {
    // This triggers deprecation in PHP 8.2:
    // $this->custom_prop = 'value';
}

null, false, true as Standalone Types

// PHP 8.2
function wp_cache_get_or_set( string $key ): string|false {
    $cached = wp_cache_get( $key );
    if ( $cached === false ) {
        return false; // explicitly typed as false
    }
    return $cached;
}

4. PHP 8.3 Features for WordPress

Typed Class Constants

// BEFORE (PHP 8.2)
class My_REST_Controller extends WP_REST_Controller {
    const NAMESPACE = 'myplugin/v1'; // untyped
}

// AFTER (PHP 8.3)
class My_REST_Controller extends WP_REST_Controller {
    const string NAMESPACE = 'myplugin/v1';
    const int    VERSION   = 1;
}

json_validate()

// BEFORE (PHP 8.2)
function is_valid_json( string $data ): bool {
    json_decode( $data );
    return json_last_error() === JSON_ERROR_NONE;
}

// AFTER (PHP 8.3) — no decoding overhead
if ( json_validate( $raw_meta ) ) {
    $meta = json_decode( $raw_meta, true );
}

#[\Override] Attribute for Template Methods

// PHP 8.3
class Theme_Walker extends Walker_Nav_Menu {
    #[\Override]
    public function start_el( &$output, $item, $depth = 0, $args = null, $id = 0 ): void {
        // If parent signature changes, PHP will throw a compile-time error.
    }
}

5. Breaking Changes and Gotchas

Stricter Type Coercion (8.0)

// PHP 7.4: silently coerces — strlen( [] ) returns null with a warning
// PHP 8.0: throws TypeError for internal function type mismatches

// FIX: Always validate types before passing to internal functions
$length = is_string( $value ) ? strlen( $value ) : 0;

Internal Function Signature Enforcement (8.0)

// PHP 7.4: passing null to non-nullable internal parameter gives a warning
// PHP 8.0+: still a warning; PHP 8.1: deprecation notice; PHP 9.0: TypeError

// Common WP offender:
trim( null );           // Deprecated in 8.1
htmlspecialchars( null ); // Deprecated in 8.1

// FIX:
trim( $value ?? '' );
htmlspecialchars( $value ?? '' );

String Interpolation Changes (8.2)

// PHP 8.2 DEPRECATED: ${var} inside strings
$msg = "Hello ${name}";  // deprecated
$msg = "Hello {$name}";  // correct — use this form
$msg = "Hello $name";    // also fine for simple variables

Implicit Float-to-Int Conversions (8.1)

// PHP 8.1 DEPRECATED: implicit narrowing float-to-int
$index = 3.0;
$arr[$index]; // deprecated — use (int) $index explicitly

6. WordPress Core PHP Compatibility

Minimum PHP Version Roadmap

Always check the latest readme.html in WP core for the current minimum.

Setting Minimum PHP in Plugin Headers

/**
 * Plugin Name: My Plugin
 * Requires PHP: 8.0
 * Requires at least: 6.3
 */

WordPress will prevent activation on incompatible PHP versions when Requires PHP is set.

Site Health PHP Check

WordPress Site Health (Tools > Site Health) checks PHP version and reports recommendations. Programmatic check:

$compat = wp_check_php_version();
if ( $compat && isset( $compat['is_acceptable'] ) && ! $compat['is_acceptable'] ) {
    add_action( 'admin_notices', 'show_php_upgrade_notice' );
}

7. Migration Strategy

Step-by-Step Migration Path

Phase 1: Audit

# Install PHPCompatibility coding standard
composer require --dev phpcompatibility/phpcompatibility-wp:"*"

# Configure phpcs
cat > phpcs.xml <<'XML'
<?xml version="1.0"?>
<ruleset name="PHP8Migration">
    <rule ref="PHPCompatibilityWP"/>
    <config name="testVersion" value="8.0-"/>
    <file>./wp-content/themes/oshin_child/</file>
    <file>./wp-content/plugins/my-plugin/</file>
</ruleset>
XML

# Run the scan
vendor/bin/phpcs --standard=phpcs.xml --report=full

Phase 2: Fix Deprecations

Address issues in order of severity:

1. Fatal errors (TypeError from internal functions)
2. Deprecation notices (dynamic properties, string interpolation)
3. Behavioral changes (stricter comparisons, match vs switch)

Phase 3: CI Matrix Testing

# GitHub Actions example