diff -r be944660c56a -r 3d72ae0968f4 wp/wp-includes/blocks/gallery.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/blocks/gallery.php	Tue Sep 27 16:37:53 2022 +0200
@@ -0,0 +1,106 @@
+<?php
+/**
+ * Server-side rendering of the `core/gallery` block.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Handles backwards compatibility for Gallery Blocks,
+ * whose images feature a `data-id` attribute.
+ *
+ * Now that the Gallery Block contains inner Image Blocks,
+ * we add a custom `data-id` attribute before rendering the gallery
+ * so that the Image Block can pick it up in its render_callback.
+ *
+ * @param array $parsed_block The block being rendered.
+ * @return array The migrated block object.
+ */
+function block_core_gallery_data_id_backcompatibility( $parsed_block ) {
+	if ( 'core/gallery' === $parsed_block['blockName'] ) {
+		foreach ( $parsed_block['innerBlocks'] as $key => $inner_block ) {
+			if ( 'core/image' === $inner_block['blockName'] ) {
+				if ( ! isset( $parsed_block['innerBlocks'][ $key ]['attrs']['data-id'] ) && isset( $inner_block['attrs']['id'] ) ) {
+					$parsed_block['innerBlocks'][ $key ]['attrs']['data-id'] = esc_attr( $inner_block['attrs']['id'] );
+				}
+			}
+		}
+	}
+
+	return $parsed_block;
+}
+
+add_filter( 'render_block_data', 'block_core_gallery_data_id_backcompatibility' );
+
+/**
+ * Adds a style tag for the --wp--style--unstable-gallery-gap var.
+ *
+ * The Gallery block needs to recalculate Image block width based on
+ * the current gap setting in order to maintain the number of flex columns
+ * so a css var is added to allow this.
+ *
+ * @param array  $attributes Attributes of the block being rendered.
+ * @param string $content Content of the block being rendered.
+ * @return string The content of the block being rendered.
+ */
+function block_core_gallery_render( $attributes, $content ) {
+	$gap = _wp_array_get( $attributes, array( 'style', 'spacing', 'blockGap' ) );
+	// Skip if gap value contains unsupported characters.
+	// Regex for CSS value borrowed from `safecss_filter_attr`, and used here
+	// because we only want to match against the value, not the CSS attribute.
+	if ( is_array( $gap ) ) {
+		foreach ( $gap as $key => $value ) {
+			$gap[ $key ] = $value && preg_match( '%[\\\(&=}]|/\*%', $value ) ? null : $value;
+		}
+	} else {
+		$gap = $gap && preg_match( '%[\\\(&=}]|/\*%', $gap ) ? null : $gap;
+	}
+
+	$class   = wp_unique_id( 'wp-block-gallery-' );
+	$content = preg_replace(
+		'/' . preg_quote( 'class="', '/' ) . '/',
+		'class="' . $class . ' ',
+		$content,
+		1
+	);
+
+	// --gallery-block--gutter-size is deprecated. --wp--style--gallery-gap-default should be used by themes that want to set a default
+	// gap on the gallery.
+	$fallback_gap = 'var( --wp--style--gallery-gap-default, var( --gallery-block--gutter-size, var( --wp--style--block-gap, 0.5em ) ) )';
+	$gap_value    = $gap ? $gap : $fallback_gap;
+	$gap_column   = $gap_value;
+
+	if ( is_array( $gap_value ) ) {
+		$gap_row    = isset( $gap_value['top'] ) ? $gap_value['top'] : $fallback_gap;
+		$gap_column = isset( $gap_value['left'] ) ? $gap_value['left'] : $fallback_gap;
+		$gap_value  = $gap_row === $gap_column ? $gap_row : $gap_row . ' ' . $gap_column;
+	}
+
+	// Set the CSS variable to the column value, and the `gap` property to the combined gap value.
+	$style = '.' . $class . '{ --wp--style--unstable-gallery-gap: ' . $gap_column . '; gap: ' . $gap_value . '}';
+
+	// Ideally styles should be loaded in the head, but blocks may be parsed
+	// after that, so loading in the footer for now.
+	// See https://core.trac.wordpress.org/ticket/53494.
+	add_action(
+		'wp_footer',
+		function () use ( $style ) {
+			echo '<style> ' . $style . '</style>';
+		},
+		11
+	);
+	return $content;
+}
+/**
+ * Registers the `core/gallery` block on server.
+ */
+function register_block_core_gallery() {
+	register_block_type_from_metadata(
+		__DIR__ . '/gallery',
+		array(
+			'render_callback' => 'block_core_gallery_render',
+		)
+	);
+}
+
+add_action( 'init', 'register_block_core_gallery' );