Fix escaping issues in editor and rendered block

package.json

@@ -19,6 +19,7 @@
 		"preinstall": "npx npm-force-resolutions"
 	},
 	"dependencies": {
+		"@wordpress/escape-html": "1.9.0",
 		"cgb-scripts": "1.23.0",
 		"npm-force-resolutions": "0.0.3"
 	},

src/blocks.js

@@ -16,6 +16,11 @@ import {
 } from '@wordpress/components';
 import { PlainText, InspectorControls } from '@wordpress/editor';
 
+/**
+ * Internal dependencies
+ */
+import save from './save';
+
 registerBlockType( 'syntaxhighlighter/code', {
 	title: __( 'SyntaxHighlighter Code', 'syntaxhighlighter' ),
 
@@ -38,7 +43,7 @@ registerBlockType( 'syntaxhighlighter/code', {
 		content: {
 			type: 'string',
 				source: 'text',
-				selector: 'pre',
+				selector: 'code',
 		},
 
 		language: {
@@ -296,9 +301,5 @@ registerBlockType( 'syntaxhighlighter/code', {
 		return [ blockSettings, editView ];
 	},
 
-	save( { attributes } ) {
-		const { content } = attributes;
-
-		return( <pre>{ content }</pre> );
-	},
+	save,
 } );

src/save.js

@@ -0,0 +1,12 @@
+/**
+ * Internal dependencies
+ */
+import { escape } from './utils';
+
+export default function save( { attributes } ) {
+	return (
+		<pre>
+			<code>{ escape( attributes.content ) }</code>
+		</pre>
+	);
+}

src/utils.js

@@ -0,0 +1,61 @@
+/**
+ * External dependencies
+ */
+import { flow } from 'lodash';
+
+/**
+ * WordPress dependencies
+ */
+import { escapeEditableHTML } from '@wordpress/escape-html';
+
+/**
+ * Escapes ampersands, shortcodes, and links.
+ *
+ * @param {string} content The content of a code block.
+ * @return {string} The given content with some characters escaped.
+ */
+export function escape( content ) {
+	return flow(
+		escapeEditableHTML,
+		escapeOpeningSquareBrackets,
+		escapeProtocolInIsolatedUrls
+	)( content || '' );
+}
+
+/**
+ * Returns the given content with all opening shortcode characters converted
+ * into their HTML entity counterpart (i.e. [ => [). For instance, a
+ * shortcode like [embed] becomes [embed]
+ *
+ * This function replicates the escaping of HTML tags, where a tag like
+ * <strong> becomes &lt;strong>.
+ *
+ * @param {string}  content The content of a code block.
+ * @return {string} The given content with its opening shortcode characters
+ *                  converted into their HTML entity counterpart
+ *                  (i.e. [ => &#91;)
+ */
+function escapeOpeningSquareBrackets( content ) {
+	return content.replace( /\[/g, '&#91;' );
+}
+
+/**
+ * Converts the first two forward slashes of any isolated URL into their HTML
+ * counterparts (i.e. // => &#47;&#47;). For instance, https://youtube.com/watch?x
+ * becomes https:&#47;&#47;youtube.com/watch?x.
+ *
+ * An isolated URL is a URL that sits in its own line, surrounded only by spacing
+ * characters.
+ *
+ * See https://github.com/WordPress/wordpress-develop/blob/5.1.1/src/wp-includes/class-wp-embed.php#L403
+ *
+ * @param {string}  content The content of a code block.
+ * @return {string} The given content with its ampersands converted into
+ *                  their HTML entity counterpart (i.e. & => &amp;)
+ */
+function escapeProtocolInIsolatedUrls( content ) {
+	return content.replace(
+		/^(\s*https?:)\/\/([^\s<>"]+\s*)$/m,
+		'$1&#47;&#47;$2'
+	);
+}

syntaxhighlighter.php

@@ -524,10 +524,11 @@ public function render_block( $attributes, $content ) {
 			}
 		}
 
-		$code = preg_replace( '#<pre [^>]+>([^<]+)?</pre>#', '$1', $content );
+		$code = preg_replace( '#<pre [^>]+><code>([^<]+)?</code></pre>#', '$1', $content );
 
 		// Undo escaping done by WordPress
 		$code = str_replace( '&lt;', '<', $code );
+		$code = str_replace( '&amp;', '&', $code );
 
 		return $this->shortcode_callback( $attributes, $code, 'code' );
 	}