From 106e6f7b8e0966b52d12df56025d78d3a40b3880 Mon Sep 17 00:00:00 2001
From: Miguel Fonseca <miguelcsf@gmail.com>
Date: Tue, 4 May 2021 11:51:48 +0100
Subject: [PATCH 1/3] Post Content: Prevent infinite recursion

---
 .../block-library/src/post-content/edit.js    | 40 +++++++++++++++----
 .../block-library/src/post-content/index.php  | 33 ++++++++++++++-
 2 files changed, 63 insertions(+), 10 deletions(-)

diff --git a/packages/block-library/src/post-content/edit.js b/packages/block-library/src/post-content/edit.js
index fcdb14198d7b1..88ee3d2098b63 100644
--- a/packages/block-library/src/post-content/edit.js
+++ b/packages/block-library/src/post-content/edit.js
@@ -7,7 +7,9 @@ import {
 	useBlockProps,
 	__experimentalUseInnerBlocksProps as useInnerBlocksProps,
 	__experimentalUseEditorFeature as useEditorFeature,
+	__experimentalUseNoRecursiveRenders as useNoRecursiveRenders,
 	store as blockEditorStore,
+	Warning,
 } from '@wordpress/block-editor';
 import { useEntityBlockEditor } from '@wordpress/core-data';
 
@@ -55,19 +57,41 @@ function Placeholder() {
 	);
 }
 
+function RecursionError() {
+	const blockProps = useBlockProps();
+	return (
+		<div { ...blockProps }>
+			<Warning>
+				{ __( 'Block cannot be rendered inside itself.' ) }
+			</Warning>
+		</div>
+	);
+}
+
 export default function PostContentEdit( {
 	context: { postId: contextPostId, postType: contextPostType },
 	attributes,
 } ) {
 	const { layout = {} } = attributes;
+	const [ hasAlreadyRendered, RecursionProvider ] = useNoRecursiveRenders(
+		contextPostId
+	);
 
-	return contextPostId && contextPostType ? (
-		<Content
-			postType={ contextPostType }
-			postId={ contextPostId }
-			layout={ layout }
-		/>
-	) : (
-		<Placeholder />
+	if ( contextPostId && contextPostType && hasAlreadyRendered ) {
+		return <RecursionError />;
+	}
+
+	return (
+		<RecursionProvider>
+			{ contextPostId && contextPostType ? (
+				<Content
+					postType={ contextPostType }
+					postId={ contextPostId }
+					layout={ layout }
+				/>
+			) : (
+				<Placeholder />
+			) }
+		</RecursionProvider>
 	);
 }
diff --git a/packages/block-library/src/post-content/index.php b/packages/block-library/src/post-content/index.php
index d92bb8082e715..cc8a0a7b78221 100644
--- a/packages/block-library/src/post-content/index.php
+++ b/packages/block-library/src/post-content/index.php
@@ -14,25 +14,54 @@
  * @return string Returns the filtered post content of the current post.
  */
 function render_block_core_post_content( $attributes, $content, $block ) {
+	static $seen_ids = array();
+
 	if ( ! isset( $block->context['postId'] ) ) {
 		return '';
 	}
 
+	$post_id = $block->context['postId'];
+
+	if ( isset( $seen_ids[ $post_id ] ) ) {
+		if ( ! is_admin() ) {
+			trigger_error(
+				sprintf(
+					// translators: %s are the block attributes.
+					__( 'Could not render Post Content block with the attributes: <code>%s</code>. Block cannot be rendered inside itself.' ),
+					wp_json_encode( $attributes )
+				),
+				E_USER_WARNING
+			);
+		}
+
+		$is_debug = defined( 'WP_DEBUG' ) && WP_DEBUG &&
+			defined( 'WP_DEBUG_DISPLAY' ) && WP_DEBUG_DISPLAY;
+		return $is_debug ?
+			// translators: Visible only in the front end, this warning takes the place of a faulty block.
+			__( '[block rendering halted]' ) :
+			'';
+	}
+
+	$seen_ids[ $post_id ] = true;
+
 	if ( ! in_the_loop() ) {
 		the_post();
 	}
 
-	$content = get_the_content( null, false, $block->context['postId'] );
+	$content = get_the_content( null, false, $post_id );
 
 	if ( empty( $content ) ) {
+		unset( $seen_ids[ $post_id ] );
 		return '';
 	}
 
 	$wrapper_attributes = get_block_wrapper_attributes( array( 'class' => 'entry-content' ) );
+	$content            = apply_filters( 'the_content', str_replace( ']]>', ']]&gt;', $content ) );
+	unset( $seen_ids[ $post_id ] );
 
 	return (
 		'<div ' . $wrapper_attributes . '>' .
-			apply_filters( 'the_content', str_replace( ']]>', ']]&gt;', $content ) ) .
+			$content .
 		'</div>'
 	);
 }

From 45e9f6967a3b8cf5afdf9b9c1b1923948bee2d91 Mon Sep 17 00:00:00 2001
From: Miguel Fonseca <miguelcsf@gmail.com>
Date: Tue, 4 May 2021 12:03:37 +0100
Subject: [PATCH 2/3] Report post ID instead of attributes in error message

---
 packages/block-library/src/post-content/index.php | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/block-library/src/post-content/index.php b/packages/block-library/src/post-content/index.php
index cc8a0a7b78221..56e84992bf524 100644
--- a/packages/block-library/src/post-content/index.php
+++ b/packages/block-library/src/post-content/index.php
@@ -26,9 +26,9 @@ function render_block_core_post_content( $attributes, $content, $block ) {
 		if ( ! is_admin() ) {
 			trigger_error(
 				sprintf(
-					// translators: %s are the block attributes.
-					__( 'Could not render Post Content block with the attributes: <code>%s</code>. Block cannot be rendered inside itself.' ),
-					wp_json_encode( $attributes )
+					// translators: %s is a post ID (integer).
+					__( 'Could not render Post Content block with post ID: <code>%s</code>. Block cannot be rendered inside itself.' ),
+					$post_id
 				),
 				E_USER_WARNING
 			);

From bdd1f44c93a02ca61135ef79e5034770766704f6 Mon Sep 17 00:00:00 2001
From: Miguel Fonseca <miguelcsf@gmail.com>
Date: Tue, 4 May 2021 20:08:12 +0100
Subject: [PATCH 3/3] Reference documentation for filter 'the_content'

---
 packages/block-library/src/post-content/index.php | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/packages/block-library/src/post-content/index.php b/packages/block-library/src/post-content/index.php
index 56e84992bf524..253752d2acafc 100644
--- a/packages/block-library/src/post-content/index.php
+++ b/packages/block-library/src/post-content/index.php
@@ -56,7 +56,8 @@ function render_block_core_post_content( $attributes, $content, $block ) {
 	}
 
 	$wrapper_attributes = get_block_wrapper_attributes( array( 'class' => 'entry-content' ) );
-	$content            = apply_filters( 'the_content', str_replace( ']]>', ']]&gt;', $content ) );
+	/** This filter is documented in wp-includes/post-template.php */
+	$content = apply_filters( 'the_content', str_replace( ']]>', ']]&gt;', $content ) );
 	unset( $seen_ids[ $post_id ] );
 
 	return (