title: Eclipse keeps losing source location of library
body: <p>I am doing plugin development in Eclipse. I have a bunch of projects that use a plugin in their dependencies that I use frequently and need to look into its source. This plugin is referenced as a jar in the Plug-In Dependencies.</p>
  
  <p>I have the source code on my local machine, and I attached it to the jar by doing right click > Properties > External Location > External folder, where put in the path to the location. </p>
  
  <p>After I do this, I can access the source code in Eclipse. However, if I close eclipse and open it again, the source attachment is gone and I get the ugly 'Source not found' window again.</p>
  
  <p>Can somebody tell me how to fix this?</p>