File size column in the media library

<?php

add_filter(
	'manage_media_columns',
	static function ( $columns ) {
		$columns['snipfire_size'] = __( 'File size' );
		return $columns;
	}
);
add_action(
	'manage_media_custom_column',
	static function ( $column, $post_id ) {
		if ( 'snipfire_size' !== $column ) {
			return;
		}
		$meta = wp_get_attachment_metadata( $post_id );
		$size = is_array( $meta ) && ! empty( $meta['filesize'] ) ? (int) $meta['filesize'] : 0;
		if ( ! $size ) {
			$file = get_attached_file( $post_id );
			$size = $file && file_exists( $file ) ? (int) filesize( $file ) : 0;
		}
		echo $size ? esc_html( size_format( $size, 1 ) ) : '—';
	},
	10,
	2
);