Question: New to Eclipse and Solr, I imported apache-solr-3.6.0.war into Eclipse and run Solr with tomcat plugin. Now i want to debug some existing code, however how do i import the Solr source code?

Answer: 
Without knowing how you imported it exactly: sounds like you are looking for [Source attachment](https://stackoverflow.com/questions/122160/is-there-an-easy-way-to-attach-source-in-eclipse).

It might be better if you use the [Solr source code](http://apache.mirror.clusters.cc/lucene/solr/3.6.0/) directly. Check the README file included in the release, there is an ant task to init eclipse:

> 
> To setup your ide run [...] 'ant eclipse'.
> 
> 
> 

Then all dependencies are loaded using [ivy](http://ant.apache.org/ivy/) and you can run it from within the IDE.
You can also check out the whole Lucene/Solr source:

1. install Subclipse add-in
2. choose `New...` > `Project...`
3. `SVN` > `Checkout projects from SVN...`
4. add [this link](http://svn.apache.org/repos/asf/lucene/dev) as new repository
5. select branch `/branches/lucene_solr_3_6` (if you want last stable version. Use trunk if you want to use cutting edge source)
6. choose `Check out as a project in a workspace` and leave everything else default

Then, after the checkout completes, to complete setup, you don't have to fiddle with JARs manually, simply:

1. right click on main `build.xml`, the one in your project's root
2. choose `Run As...` > `Ant build...` select (in this order)
3. `ivy-bootstrap` and `resolve` tasks (which will download all JAR dependencies)
4. then run in this order: `validate, clean-idea, eclipse, compile, get-maven-poms, generate-maven-artifacts` (the last two only if you plan to use Maven).

And that's it, you should now see no redness in your workspace and have Lucene and Solr JARs built.