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An ENSIME SideKick plugin for jEdit
Scala Shell
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An ENSIME SideKick plugin for jEdit. Note that this plugin operates very much like the equivalent Emacs mode: it starts the ENSIME server as a sub-process and initializes individual projects based on explicit user interaction. This was done very intentionally, since the Emacs mode of interaction is more flexible and certainly more amenable to one-off file editing.


  • Navigation
    • Jump to declaration
    • Public symbol search (think: ctags or 'Open Type' in Eclipse)
  • Editing
    • Error reporting (type checking on save)
    • Inspect type (determine what type is inferred for a particular symbol)
    • AST-based selection (e.g. select scope)
    • Import suggestions

Er...that's about it right now. :-) I have a proof-of-concept for popup completion (intellisense), but it's going to take a fair amount of effort to make it actually functional. I know what to do, but it's not trivial. And it's not particularly important to me, so I probably won't do it unless I'm bored. If anyone is interested, I'll lay out the roadmap for what needs to be done and let them handle the implementation.

Oh, if you want to contribute, feel free! I'm going to be fairly liberal with merging pull requests. I can commit to maintaining the parts of this project that I rely on for my day-to-day work. Everything else is caveat emptor.


The easiest way to install the plugin is to download the pre-built tar file and extract it into your jEdit/jars directory. Once you have done this, you should be able to load the plugin either by restarting jEdit or by manually scanning and loading in the Plugin Manager. Note that this plugin requires both Sidekick and ErrorList. It also packages scala-library.jar for Scala 2.9.1, so if you have any other plugins which use Scala, prepare to have their libraries stomped!

Before you start using this plugin, be sure to read this entire README. I haven't had a chance to organize this documentation in any sane way, and there are a lot of little tidbits and pitfalls to watch out for.

The plugin will not work on Windows. If you want to make this work, submit a pull request! It is unlikely that I will implement this feature myself.


Fortunately, building the plugin is really easy...provided your machine is set up identically to mine. The build is based on SBT, but it currently hard-codes the locations of the following three JAR files:

  • jedit.jar
  • SideKick.jar
  • ErrorList.jar

Factoring this out into something configurable is one of the big things that needs to be done to make this plugin not specific to my laptop. Once you have this overcome, you should be able to run sbt package to build the plugin JAR. After that, you can use the script to install the plugin. Unfortunately, this too is specific to my machine. Less so, but still using hard-coded paths. It should be very obvious how to make this process more generic though, or even to perform the installation yourself. All you need to do is copy the packaged JAR as well as scala-library.jar into the jEdit/jars/ directory. Once that is done, restart jEdit (or rescan the plugins directory using the Plugin Manager and load the ENSIME plugin manually).

Note that ENSIME has historically played a little sloppy with its sub-processes. There is currently a pull request open to fix this, but it won't rectify matters for older versions of ENSIME. Fortunately, it's a pretty easy issue to fix in your local ENSIME setup. Simply open the bin/server file in your ENSIME distribution and prefix the last line of the script with exec. This will cause ENSIME to load java in a single process, rather than spawning a parent shell process which loads java as a child. If you fail to perform this step, jEdit will be unable to automatically kill the ENSIME process at all and you will need to manually cleanup orphaned server processes. The easiest way to do this is to run ps aux | grep ensime and use kill on any results.


You must have a pre-existing .ensime file at the root of your project. If you don't, the server init will probably do something very strange. At the very least, it won't work. For debugging purposes, it is useful to run tail -f /tmp/ensime*log and watch the server's output in real time. This isn't necessary though.

To initialize your project, run the ensime command within jEdit. This is most easily done via the action bar (bound to C+ENTER by default) but can also be done via the Plugins > ENSIME > Initialize Project menu item. This action will recursively scan up the directory hierarchy from your currently focused open file and attempt to find a .ensime file. If it is successful, the dialog will be populated with the parent directory for that file. If not, then you will need to enter the path manually. It will not generate this file for you! (that may come later)

ENSIME messages are displayed in the status bar. Once the status bar displays "ENSIME: Indexer ready", you should be ready to go with development. Assuming your .ensime file is properly configured, you should now have type-check-on-save behavior in Scala files. Also, you should be able to inspect the type for the symbol under the cursor. This is done via the Plugins > ENSIME > Inspect Type action (I have this bound to A+s A+t). The type is displayed in the status bar. All types should be displayed in a reasonably friendly format, though I haven't yet implemented special formatting support for arrow types (functions). These types will display, but they'll be a little weird to read.

It's worth noting that ENSIME seems much happier with most functionality after it has done a typecheck on the project. jEdit won't trigger this automatically on startup, so if you're trying out the functionality immediately after initializing the ENSIME project, you may want to save a file (to trigger the typecheck) before running any of the actual ENSIME actions. This is only required once (in fact, ENSIME actions should work just fine even in a dirty buffer once the type checking has been run).

Oh, and Sidekick has some strange glitches with respect to typechecking files. The most reliable way I've found to keep it happy is to do two things. First, dock the "Sidekick" view in your sidebar and ensure that you have opened it at least once in your current editing session. You don't need to leave it open, just docked. Then, after you start ENSIME, switch buffers once and then come back to the buffer you actually wanted to edit. This will force Sidekick to trigger a type checking and everything should line up from that point. Type checking happens by default on buffer switch and on save (this is something you configure in Sidekick).

Popup completion is currently disabled, for which you should be very grateful. The implementation is in EnsimeParser.scala and EnsimeProtocolComponent.scala if you're interested in improving it. Please read ENSIME's SwankProtocol.scala before you jump in, since it will help you understand why this is such a thorny feature, particularly in jEdit.

Just in case the ENSIME server starts doing something weird, you can always restart it. This is done by first invoking the ensime.kill command and then re-running ensime.


One of the consequences of this effort is a generic ENSIME client implemented in Scala. It's not a full client yet, but I'm adding onto it bit by bit and trying to keep it as feature-agnostic as possible. Hopefully the source should prove at least a useful starting point for someone trying to work with the ENSIME server in Scala.

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