fix: avoid PHP 8.5 null array offset deprecation in memoizers

src/memoizers/meta-tags-context-memoizer.php

@@ -132,7 +132,10 @@ public function for_current_page() {
 	 * @return Meta_Tags_Context The meta tags context.
 	 */
 	public function get( Indexable $indexable, $page_type ) {
-		if ( ! isset( $this->cache[ $indexable->id ] ) ) {
+		// An unsaved indexable has a null id; normalise it to a stable integer cache key.
+		$cache_key = (int) $indexable->id;
+
+		if ( ! isset( $this->cache[ $cache_key ] ) ) {
 			$blocks = [];
 			$post   = null;
 			if ( $indexable->object_type === 'post' ) {
@@ -151,10 +154,10 @@ public function get( Indexable $indexable, $page_type ) {
 
 			$context->presentation = $this->presentation_memoizer->get( $indexable, $context, $page_type );
 
-			$this->cache[ $indexable->id ] = $context;
+			$this->cache[ $cache_key ] = $context;
 		}
 
-		return $this->cache[ $indexable->id ];
+		return $this->cache[ $cache_key ];
 	}
 
 	/**

src/memoizers/presentation-memoizer.php

@@ -46,7 +46,10 @@ public function __construct( ContainerInterface $service_container ) {
 	 * @return Indexable_Presentation The indexable presentation.
 	 */
 	public function get( Indexable $indexable, Meta_Tags_Context $context, $page_type ) {
-		if ( ! isset( $this->cache[ $indexable->id ] ) ) {
+		// An unsaved indexable has a null id; normalise it to a stable integer cache key.
+		$cache_key = (int) $indexable->id;
+
+		if ( ! isset( $this->cache[ $cache_key ] ) ) {
 			$presentation = $this->container->get( "Yoast\WP\SEO\Presentations\Indexable_{$page_type}_Presentation", ContainerInterface::NULL_ON_INVALID_REFERENCE );
 
 			if ( ! $presentation ) {
@@ -60,10 +63,10 @@ public function get( Indexable $indexable, Meta_Tags_Context $context, $page_typ
 				],
 			);
 
-			$this->cache[ $indexable->id ] = $context->presentation;
+			$this->cache[ $cache_key ] = $context->presentation;
 		}
 
-		return $this->cache[ $indexable->id ];
+		return $this->cache[ $cache_key ];
 	}
 
 	/**

tests/Unit/Doubles/Memoizers/Presentation_Memoizer_Double.php

@@ -20,4 +20,13 @@ final class Presentation_Memoizer_Double extends Presentation_Memoizer {
 	public function set_cache( $key, $value ) {
 		$this->cache[ $key ] = $value;
 	}
+
+	/**
+	 * Used to retrieve the internal cache for testing purposes.
+	 *
+	 * @return array<int|string, mixed> The cache.
+	 */
+	public function get_cache() {
+		return $this->cache;
+	}
 }

tests/Unit/Memoizers/Meta_Tags_Context_Memoizer_Test.php

@@ -260,6 +260,36 @@ public function test_get_without_cache_for_post() {
 		$this->assertEquals( $this->meta_tags_context_mock, $this->instance->get( $this->indexable, 'the_page_type' ) );
 	}
 
+	/**
+	 * Tests getting the meta tags context for an indexable whose id is null, ensuring it is
+	 * cached under a stable integer key instead of a null array offset.
+	 *
+	 * @covers ::get
+	 *
+	 * @return void
+	 */
+	public function test_get_caches_when_indexable_id_is_null() {
+		$this->indexable->id = null;
+
+		$this->meta_tags_context
+			->expects( 'of' )
+			->once()
+			->andReturn( $this->meta_tags_context_mock );
+
+		$this->presentation_memoizer
+			->expects( 'get' )
+			->once()
+			->with( $this->indexable, $this->meta_tags_context_mock, 'the_page_type' )
+			->andReturn( $this->meta_tags_context_mock->presentation );
+
+		$first  = $this->instance->get( $this->indexable, 'the_page_type' );
+		$second = $this->instance->get( $this->indexable, 'the_page_type' );
+
+		$this->assertEquals( $this->meta_tags_context_mock, $first );
+		$this->assertSame( $first, $second );
+		$this->assertArrayHasKey( 0, $this->instance->get_cache() );
+	}
+
 	/**
 	 * Tests clearing the memoization of a specific indexable.
 	 *

tests/Unit/Memoizers/Presentation_Memoizer_Test.php

@@ -152,6 +152,35 @@ public function test_get_without_cache_and_without_presentation() {
 		$this->assertEquals( $this->meta_tags_context_mock->presentation, $this->instance->get( $this->indexable, $this->meta_tags_context_mock, 'the_page_type' ) );
 	}
 
+	/**
+	 * Tests getting the presentation of an indexable whose id is null, ensuring it is
+	 * cached under a stable integer key instead of a null array offset.
+	 *
+	 * @covers ::get
+	 *
+	 * @return void
+	 */
+	public function test_get_caches_when_indexable_id_is_null() {
+		$this->indexable->id = null;
+
+		$this->container
+			->expects( 'get' )
+			->once()
+			->andReturn( $this->indexable_presentation );
+
+		$this->indexable_presentation
+			->expects( 'of' )
+			->once()
+			->andReturn( $this->meta_tags_context_mock->presentation );
+
+		$first  = $this->instance->get( $this->indexable, $this->meta_tags_context_mock, 'the_page_type' );
+		$second = $this->instance->get( $this->indexable, $this->meta_tags_context_mock, 'the_page_type' );
+
+		$this->assertSame( $this->meta_tags_context_mock->presentation, $first );
+		$this->assertSame( $first, $second );
+		$this->assertArrayHasKey( 0, $this->instance->get_cache() );
+	}
+
 	/**
 	 * Tests clearing the memoization of an indexable when the indexable is given.
 	 *