Fix query loop bugs by correctly relying on the main query and removi…

…ng problematic workaround (#49904)

* Use global main query directly so that global query loop works as expected.

* Remove hack to enforce query loop as it causes problems, and the loop needs to be handled in block templates instead.

* Maintain fix from #43198.

* Clarify logic with comment.

* Add test coverage.

packages/block-library/src/post-content/index.php

@@ -35,12 +35,6 @@ function render_block_core_post_content( $attributes, $content, $block ) {
 
 	$seen_ids[ $post_id ] = true;
 
-	// Check is needed for backward compatibility with third-party plugins
-	// that might rely on the `in_the_loop` check; calling `the_post` sets it to true.
-	if ( ! in_the_loop() && have_posts() ) {
-		the_post();
-	}
-
 	// When inside the main loop, we want to use queried object
 	// so that `the_preview` for the current post can apply.
 	// We force this behavior by omitting the third argument (post ID) from the `get_the_content`.

packages/block-library/src/post-featured-image/index.php

@@ -19,12 +19,6 @@ function render_block_core_post_featured_image( $attributes, $content, $block )
 	}
 	$post_ID = $block->context['postId'];
 
-	// Check is needed for backward compatibility with third-party plugins
-	// that might rely on the `in_the_loop` check; calling `the_post` sets it to true.
-	if ( ! in_the_loop() && have_posts() ) {
-		the_post();
-	}
-
 	$is_link        = isset( $attributes['isLink'] ) && $attributes['isLink'];
 	$size_slug      = isset( $attributes['sizeSlug'] ) ? $attributes['sizeSlug'] : 'post-thumbnail';
 	$attr           = get_block_core_post_featured_image_border_attributes( $attributes );

packages/block-library/src/post-template/index.php

@@ -50,7 +50,18 @@ function render_block_core_post_template( $attributes, $content, $block ) {
 	$use_global_query = ( isset( $block->context['query']['inherit'] ) && $block->context['query']['inherit'] );
 	if ( $use_global_query ) {
 		global $wp_query;
-		$query = clone $wp_query;
+
+		/*
+		 * If already in the main query loop, duplicate the query instance to not tamper with the main instance.
+		 * Since this is a nested query, it should start at the beginning, therefore rewind posts.
+		 * Otherwise, the main query loop has not started yet and this block is responsible for doing so.
+		 */
+		if ( in_the_loop() ) {
+			$query = clone $wp_query;
+			$query->rewind_posts();
+		} else {
+			$query = $wp_query;
+		}
 	} else {
 		$query_args = build_query_vars_from_query_block( $block, $page );
 		$query      = new WP_Query( $query_args );

phpunit/blocks/render-post-template-test.php

@@ -70,4 +70,90 @@ public function test_rendering_post_template() {
 			str_replace( array( "\n", "\t" ), '', $markup )
 		);
 	}
+
+	/**
+	 * Tests that the `core/post-template` block triggers the main query loop when rendering within a corresponding
+	 * `core/query` block.
+	 */
+	public function test_rendering_post_template_with_main_query_loop() {
+		global $wp_query, $wp_the_query;
+
+		// Query block with post template block.
+		$content  = '<!-- wp:query {"query":{"inherit":true}} -->';
+		$content .= '<!-- wp:post-template {"align":"wide"} -->';
+		$content .= '<!-- wp:post-title /--><!-- wp:test/in-the-loop-logger /-->';
+		$content .= '<!-- /wp:post-template -->';
+		$content .= '<!-- /wp:query -->';
+
+		$expected  = '<ul class="alignwide wp-block-post-template is-layout-flow wp-block-post-template-is-layout-flow wp-block-query-is-layout-flow">';
+		$expected .= '<li class="wp-block-post post-' . self::$post->ID . ' post type-post status-publish format-standard hentry category-uncategorized">';
+		$expected .= '<h2 class="wp-block-post-title">' . self::$post->post_title . '</h2>';
+		$expected .= '</li>';
+		$expected .= '</ul>';
+
+		// Set main query to single post.
+		$wp_query     = new WP_Query( array( 'p' => self::$post->ID ) );
+		$wp_the_query = $wp_query;
+
+		// Register test block to log `in_the_loop()` results.
+		$in_the_loop_logs = array();
+		register_block_type(
+			'test/in-the-loop-logger',
+			array(
+				'render_callback' => static function() use ( &$in_the_loop_logs ) {
+					$in_the_loop_logs[] = in_the_loop();
+					return '';
+				},
+			)
+		);
+
+		$output = do_blocks( $content );
+		$this->assertSame( $expected, $output, 'Unexpected parsed blocks content' );
+		$this->assertSame( array( true ), $in_the_loop_logs, 'Unexpected in_the_loop() result' );
+	}
+
+	/**
+	 * Tests that the `core/post-template` block does not tamper with the main query loop when rendering within a post
+	 * as the main query loop has already been started. In this case, the main query object needs to be cloned to
+	 * prevent an infinite loop.
+	 */
+	public function test_rendering_post_template_with_main_query_loop_already_started() {
+		global $wp_query, $wp_the_query;
+
+		// Query block with post template block.
+		$content  = '<!-- wp:query {"query":{"inherit":true}} -->';
+		$content .= '<!-- wp:post-template {"align":"wide"} -->';
+		$content .= '<!-- wp:post-title /-->';
+		$content .= '<!-- /wp:post-template -->';
+		$content .= '<!-- /wp:query -->';
+
+		$expected  = '<ul class="alignwide wp-block-post-template is-layout-flow wp-block-post-template-is-layout-flow wp-block-query-is-layout-flow">';
+		$expected .= '<li class="wp-block-post post-' . self::$post->ID . ' post type-post status-publish format-standard hentry category-uncategorized">';
+		$expected .= '<h2 class="wp-block-post-title">' . self::$post->post_title . '</h2>';
+		$expected .= '</li>';
+		$expected .= '</ul>';
+
+		// Update the post's content to have a query block for the same query as the main query.
+		wp_update_post(
+			array(
+				'ID'                    => self::$post->ID,
+				'post_content'          => $content,
+				'post_content_filtered' => $content,
+			)
+		);
+
+		// Set main query to single post.
+		$wp_query     = new WP_Query( array( 'p' => self::$post->ID ) );
+		$wp_the_query = $wp_query;
+
+		// Get post content within main query loop.
+		$output = '';
+		while ( $wp_query->have_posts() ) {
+			$wp_query->the_post();
+
+			$output = get_echo( 'the_content' );
+		}
+
+		$this->assertSame( $expected, $output, 'Unexpected parsed post content' );
+	}
 }