WordPress/wp-includes/blocks/post-comments.php

<?php
/**
 * Server-side rendering of the `core/post-comments` block.
 *
 * @package WordPress
 */

/**
 * Renders the `core/post-comments` block on the server.
 *
 * @param array    $attributes Block attributes.
 * @param string   $content    Block default content.
 * @param WP_Block $block      Block instance.
 * @return string Returns the filtered post comments for the current post wrapped inside "p" tags.
 */
function render_block_core_post_comments( $attributes, $content, $block ) {
	global $post;

	$post_id = $block->context['postId'];
	if ( ! isset( $post_id ) ) {
		return '';
	}

	$comment_args = array(
		'post_id' => $post_id,
		'count'   => true,
	);
	// Return early if there are no comments and comments are closed.
	if ( ! comments_open( $post_id ) && get_comments( $comment_args ) === 0 ) {
		return '';
	}

	$post_before = $post;
	$post        = get_post( $post_id );
	setup_postdata( $post );

	ob_start();
	// There's a deprecation warning generated by WP Core.
	// Ideally this deprecation is removed from Core.
	// In the meantime, this removes it from the output.
	add_filter( 'deprecated_file_trigger_error', '__return_false' );
	comments_template();
	remove_filter( 'deprecated_file_trigger_error', '__return_false' );
	$post = $post_before;

	$classes = '';
	if ( isset( $attributes['textAlign'] ) ) {
		$classes .= 'has-text-align-' . $attributes['textAlign'];
	}

	$wrapper_attributes = get_block_wrapper_attributes( array( 'class' => $classes ) );
	$output             = ob_get_clean();

	return sprintf( '<div %1$s>%2$s</div>', $wrapper_attributes, $output );
}

/**
 * Registers the `core/post-comments` block on the server.
 */
function register_block_core_post_comments() {
	register_block_type_from_metadata(
		__DIR__ . '/post-comments',
		array(
			'render_callback' => 'render_block_core_post_comments',
		)
	);
}
add_action( 'init', 'register_block_core_post_comments' );

/**
 * Use the button block classes for the form-submit button.
 *
 * @param array $fields The default comment form arguments.
 *
 * @return array Returns the modified fields.
 */
function post_comments_block_form_defaults( $fields ) {
	if ( wp_is_block_theme() ) {
		$fields['submit_button'] = '<input name="%1$s" type="submit" id="%2$s" class="%3$s wp-block-button__link" value="%4$s" />';
		$fields['submit_field']  = '<p class="form-submit wp-block-button">%1$s %2$s</p>';
	}

	return $fields;
}
add_filter( 'comment_form_defaults', 'post_comments_block_form_defaults' );