add query string cache buster to stylesheets minified by W3 Total Cache

w3tc-minify-cache-buster.php

<?php

// add query string cache buster to W3TC minified stylesheet links
add_action( 'init', function() {

	// is css minify enabled?
	if ( isset( $GLOBALS[ '_w3tc_ob_callbacks' ][ 'minify' ] ) && $GLOBALS[ '_w3tc_ob_callbacks' ][ 'minify' ][0]->_config->get_cache_option( 'minify.css.enable' ) ) {

		// store original minify callback
		$GLOBALS[ '_w3tc_ob_callbacks' ][ 'minify-org' ] = $GLOBALS[ '_w3tc_ob_callbacks' ][ 'minify' ];

		// replace minify callback
		$GLOBALS[ '_w3tc_ob_callbacks' ][ 'minify' ] = function( &$buffer )  {

			// run original minify callback
			$buffer = call_user_func( $GLOBALS[ '_w3tc_ob_callbacks' ][ 'minify-org' ], $buffer );

			// add `?ver=<your-cache-buster>` cache buster to stylesheet link
			$buffer = preg_replace( '~<link(.+)href="(.+\/cache\/minify\/.+)"(.+)\/>~U', '<link$1href="$2?ver=<your-cache-buster>"$3/>', $buffer );

			return $buffer;

		};

	}

});