From d1f22bd4d43fdb78d86e0d03616c8f69ab771ee3 Mon Sep 17 00:00:00 2001
From: Grzegorz Ziolkowski <grzegorz@gziolo.pl>
Date: Mon, 25 Jan 2021 10:43:06 +0100
Subject: [PATCH] Template Part: Prevent infinite recursion Based on #28405
 from @mcsf. Tries to apply the same technique used for Reusable block to
 prevent infinite recursion when the same block is inserted into itself at any
 level of nesting.

---
 .../src/template-part/edit/index.js           | 23 +++++++++++++---
 .../block-library/src/template-part/index.php | 27 +++++++++++++++++++
 2 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/packages/block-library/src/template-part/edit/index.js b/packages/block-library/src/template-part/edit/index.js
index da36745fd4b3ce..35819cc3752060 100644
--- a/packages/block-library/src/template-part/edit/index.js
+++ b/packages/block-library/src/template-part/edit/index.js
@@ -6,6 +6,7 @@ import {
 	BlockControls,
 	InspectorAdvancedControls,
 	useBlockProps,
+	__experimentalUseNoRecursiveRenders as useNoRecursiveRenders,
 	Warning,
 } from '@wordpress/block-editor';
 import {
@@ -33,6 +34,10 @@ export default function TemplatePartEdit( {
 } ) {
 	const templatePartId = theme && slug ? theme + '//' + slug : null;
 
+	const [ hasAlreadyRendered, RecursionProvider ] = useNoRecursiveRenders(
+		templatePartId
+	);
+
 	// Set the postId block attribute if it did not exist,
 	// but wait until the inner blocks have loaded to allow
 	// new edits to trigger this.
@@ -63,9 +68,18 @@ export default function TemplatePartEdit( {
 	);
 
 	const blockProps = useBlockProps();
-	const isPlaceholder = ! slug;
-	const isEntityAvailable = ! isPlaceholder && ! isMissing;
 
+	if ( hasAlreadyRendered ) {
+		return (
+			<TagName { ...blockProps }>
+				<Warning>
+					{ __( 'Block cannot be rendered inside itself.' ) }
+				</Warning>
+			</TagName>
+		);
+	}
+
+	const isPlaceholder = ! slug;
 	if ( ! isPlaceholder && isMissing ) {
 		return (
 			<TagName { ...blockProps }>
@@ -78,6 +92,7 @@ export default function TemplatePartEdit( {
 		);
 	}
 
+	const isEntityAvailable = ! isPlaceholder && ! isMissing;
 	const inspectorAdvancedControls = (
 		<InspectorAdvancedControls>
 			<SelectControl
@@ -98,7 +113,7 @@ export default function TemplatePartEdit( {
 	);
 
 	return (
-		<>
+		<RecursionProvider>
 			{ inspectorAdvancedControls }
 			<TagName { ...blockProps }>
 				{ isPlaceholder && (
@@ -146,6 +161,6 @@ export default function TemplatePartEdit( {
 				) }
 				{ ! isPlaceholder && ! isResolved && <Spinner /> }
 			</TagName>
-		</>
+		</RecursionProvider>
 	);
 }
diff --git a/packages/block-library/src/template-part/index.php b/packages/block-library/src/template-part/index.php
index a960aa969bc906..c999b931e21b42 100644
--- a/packages/block-library/src/template-part/index.php
+++ b/packages/block-library/src/template-part/index.php
@@ -13,6 +13,8 @@
  * @return string The render.
  */
 function render_block_core_template_part( $attributes ) {
+	static $seen_content = array();
+
 	$content = null;
 
 	if ( ! empty( $attributes['postId'] ) && get_post_status( $attributes['postId'] ) ) {
@@ -55,6 +57,31 @@ function render_block_core_template_part( $attributes ) {
 		return 'Template Part Not Found';
 	}
 
+	if ( in_array( $content, $seen_content, true ) ) {
+		if ( ! is_admin() ) {
+			trigger_error(
+				sprintf(
+					// translators: %s is the user-provided title of the reusable block.
+					__( 'Could not render Template Part with the slug <strong>%s</strong>: blocks cannot be rendered inside themselves.' ),
+					$attributes['slug']
+				),
+				E_USER_WARNING
+			);
+		}
+
+		// WP_DEBUG_DISPLAY must only be honored when WP_DEBUG. This precedent
+		// is set in `wp_debug_mode()`.
+		$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_content[] = $content;
+
 	// Run through the actions that are typically taken on the_content.
 	$content = do_blocks( $content );
 	$content = wptexturize( $content );