Better CMAKE_PREFIX_PATH error (#102)

Author: chris-smith

src/ros_msg_utils/lib/message_cache.js

@@ -21,6 +21,9 @@ const fs = require('fs');
 const path = require('path');
 
 const CMAKE_PREFIX_PATH = process.env.CMAKE_PREFIX_PATH;
+if (!CMAKE_PREFIX_PATH) {
+  throw new Error('Unable to find CMAKE_PREFIX_PATH environment variable. Did you source setup.bash?')
+}
 const cmakePaths = CMAKE_PREFIX_PATH.split(path.delimiter);
 const jsMsgPath = path.join('share', 'gennodejs', 'ros');