Source

File: wp-includes/media.php

function wp_get_attachment_image( $attachment_id, $size = 'thumbnail', $icon = false, $attr = '' ) {
	$html  = '';
	$image = wp_get_attachment_image_src( $attachment_id, $size, $icon );

	if ( $image ) {
		list( $src, $width, $height ) = $image;

		$attachment = get_post( $attachment_id );
		$hwstring   = image_hwstring( $width, $height );
		$size_class = $size;

		if ( is_array( $size_class ) ) {
			$size_class = join( 'x', $size_class );
		}

		$default_attr = array(
			'src'   => $src,
			'class' => "attachment-$size_class size-$size_class",
			'alt'   => trim( strip_tags( get_post_meta( $attachment_id, '_wp_attachment_image_alt', true ) ) ),
		);

		// Add `loading` attribute.
		if ( wp_lazy_loading_enabled( 'img', 'wp_get_attachment_image' ) ) {
			$default_attr['loading'] = 'lazy';
		}

		$attr = wp_parse_args( $attr, $default_attr );

		// If the default value of `lazy` for the `loading` attribute is overridden
		// to omit the attribute for this image, ensure it is not included.
		if ( array_key_exists( 'loading', $attr ) && ! $attr['loading'] ) {
			unset( $attr['loading'] );
		}

		// Generate 'srcset' and 'sizes' if not already present.
		if ( empty( $attr['srcset'] ) ) {
			$image_meta = wp_get_attachment_metadata( $attachment_id );

			if ( is_array( $image_meta ) ) {
				$size_array = array( absint( $width ), absint( $height ) );
				$srcset     = wp_calculate_image_srcset( $size_array, $src, $image_meta, $attachment_id );
				$sizes      = wp_calculate_image_sizes( $size_array, $src, $image_meta, $attachment_id );

				if ( $srcset && ( $sizes || ! empty( $attr['sizes'] ) ) ) {
					$attr['srcset'] = $srcset;

					if ( empty( $attr['sizes'] ) ) {
						$attr['sizes'] = $sizes;
					}
				}
			}
		}

		/**
		 * Filters the list of attachment image attributes.
		 *
		 * @since 2.8.0
		 *
		 * @param array        $attr       Array of attribute values for the image markup, keyed by attribute name.
		 *                                 See wp_get_attachment_image().
		 * @param WP_Post      $attachment Image attachment post.
		 * @param string|array $size       Requested size. Image size or array of width and height values
		 *                                 (in that order). Default 'thumbnail'.
		 */
		$attr = apply_filters( 'wp_get_attachment_image_attributes', $attr, $attachment, $size );

		$attr = array_map( 'esc_attr', $attr );
		$html = rtrim( "<img $hwstring" );

		foreach ( $attr as $name => $value ) {
			$html .= " $name=" . '"' . $value . '"';
		}

		$html .= ' />';
	}

	return $html;
}