Block Hooks: Don't erase post content if it isn't changed by client.

The `inject_ignored_hooked_blocks_metadata_attributes` filter that is attached to both the `rest_pre_insert_wp_template` and `rest_pre_insert_wp_template_part` hooks receives a `stdClass` object from the Templates REST API controller that contains all fields that the client would like to modify when making a `POST` request (plus the `id` to identify the relevant template or template part, respectively).

There are cases when the `post_content` field is not set, e.g. when the client would like to rename an existing template (in which case it would only set the `title` field).

Prior to this changeset, the filter would erroneously apply the Block Hooks algorithm to the non-existent `post_content` field regardless, which would result in it being set to the empty string `''`. As a consequence, renaming a template would have the unwanted side effect of wiping its contents.

This changeset fixes the issue by returning early from the filter if the `post_content` field is not set.

Props alshakero, bernhard-reiter.
Fixes #61550.

git-svn-id: https://develop.svn.wordpress.org/trunk@58785 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/block-template-utils.php

@@ -1602,6 +1602,10 @@ function inject_ignored_hooked_blocks_metadata_attributes( $changes, $deprecated
 		_deprecated_argument( __FUNCTION__, '6.5.3' );
 	}
 
+	if ( ! isset( $changes->post_content ) ) {
+		return $changes;
+	}
+
 	$hooked_blocks = get_hooked_blocks();
 	if ( empty( $hooked_blocks ) && ! has_filter( 'hooked_block_types' ) ) {
 		return $changes;

tests/phpunit/tests/block-templates/injectIgnoredHookedBlocksMetadataAttributes.php

@@ -621,4 +621,59 @@ public function test_inject_ignored_hooked_blocks_metadata_attributes_into_templ
 			'The template part\'s post content was modified.'
 		);
 	}
+
+	/**
+	 * @ticket 61550
+	 */
+	public function test_inject_ignored_hooked_blocks_metadata_attributes_into_template_with_no_changes_to_post_content() {
+		register_block_type(
+			'tests/hooked-block',
+			array(
+				'block_hooks' => array(
+					'core/heading' => 'after',
+				),
+			)
+		);
+
+		$id       = self::TEST_THEME . '//' . 'my_template';
+		$template = get_block_template( $id, 'wp_template' );
+
+		$changes     = new stdClass();
+		$changes->ID = $template->wp_id;
+
+		// Note that we're not setting `$changes->post_content`!
+
+		$post = inject_ignored_hooked_blocks_metadata_attributes( $changes );
+		$this->assertFalse(
+			isset( $post->post_content ),
+			"post_content shouldn't have been set."
+		);
+	}
+
+	/**
+	 * @ticket 61550
+	 */
+	public function test_inject_ignored_hooked_blocks_metadata_attributes_into_template_part_with_no_changes_to_post_content() {
+		register_block_type(
+			'tests/hooked-block',
+			array(
+				'block_hooks' => array(
+					'core/heading' => 'after',
+				),
+			)
+		);
+
+		$id       = self::TEST_THEME . '//' . 'my_template_part';
+		$template = get_block_template( $id, 'wp_template_part' );
+
+		$changes     = new stdClass();
+		$changes->ID = $template->wp_id;
+		// Note that we're not setting `$changes->post_content`!
+
+		$post = inject_ignored_hooked_blocks_metadata_attributes( $changes );
+		$this->assertFalse(
+			isset( $post->post_content ),
+			"post_content shouldn't have been set."
+		);
+	}
 }