Beginner's guide to SBT 0.10 and IDEA

Question

I'm new to SBT and am unsure how to get a project started. Can someone point me to a beginner's guide to creating a Hello World type project, or give me some clues?

My preferred IDE is IDEA. I have run sbt-idea according to the instruction on the IDEA Plugins page. At the moment I'm a bit confused because

• there are no source folders created - where / how am I supposed to create them and how will SBT know where to look?
• why is it trying to use Scala 2.8.1, when I have already put scalaVersion := "2.9.0" in the build.sbt file? This means IDEA doesn't recognize object HelloWorld extends App {}.
• the instructions on the plugins page above suggest changing the Before Launch options of "a Run Configuration (including the Default Run Configuration)". There are 13 different default configurations for different things listed - which one to change? Should I be creating a new one? Are these default configurations just for this project or will it adversely affect all my other projects that don't use SBT?

Thanks.

Mocha

Answer 1

This worked for me:

First get sbt and the gen-idea plugin going...

1. Download the sbt-launch.jar and create the script for launching it as described on the SBT Github wiki.
2. Create a directory for your new project, such as (on linux) ~/myCode/myNewProject and change to that directory
3. Run sbt command. This should download the scala libraries and create a 'project' and 'target' directories.
4. Change to the 'project' directory.

5. Create a new file 'build.sbt' in this directory with the following lines, as described on the sbt-idea plugin Github wiki:

   resolvers += "sbt-idea-repo" at "http://mpeltonen.github.com/maven/"
   
   addSbtPlugin("com.github.mpeltonen" % "sbt-idea" % "1.0.0")
   

6. Change back to your main project directory such as ~/myCode/myNewProject. Run sbt. It should download the gen-idea plugin.

7. From the sbt console (which should be running now), run the gen-idea command. It should create the IDEA project directories. For me, it also emits copious warnings.

Now get the IDEA SBT console plugin going...

1. Open IDEA and install the "SBT" plugin from the plugin manager and restart IDEA. (Note this is the IDEA plugin, not the sbt plugin described above.) Configure the SBT plugin as described on its wiki (run configurations, location of sbt-launch.jar etc).
2. Open the freshly generated IDEA project in IDEA.
3. Put your code and other things in the expected default directories as described on the sbt wiki under 'Directory Layout'. You need to create these directories yourself - sbt doesn't create them automatically. The 'src' and 'test' directories should be at the same level as the 'project' and 'target' directories that sbt created.

4. Make up a new 'build.sbt' file and put it in ~/myCode/myProject (or whatever you called it). Since I am just figuring out sbt, mine is simple so far - just nominates scalatest as a dependency and uses Scala 2.9:

   name := "myProject"
   
   version := "0.1"
   
   organization := "me"
   
   libraryDependencies += "org.scalatest" % "scalatest_2.9.0" % "1.6.1"
   
   scalaVersion := "2.9.0"
   

5. Enter the reload command in the SBT console at the bottom of the IDEA screen. It should download scalatest and Scala 2.9 for you. Maybe you need to run 'update' too.

County

Thanks for the detailed guide and useful links. It may be better to put the build.sbt file in step 5 into ~/.sbt/plugins/ as the wiki suggests since then you don't have to do it for every project... on Windows you have to create this directory yourself in `Users\yourname\`, using the command line. Anyway, now I have set up the folders as per the Directory Layout in the sbt wiki, it works fine! – Mocha

Answer 2

I wrote a very quick guide about it. It is not intended to be an SBT guide -- there's no way to beat the SBT Wiki for that. It would be pointless too, since one can just contribute to the wiki itself.

But, I think my very quick guide will get you up and running as you wish.

As for directory creation, the answer I got was that SBT expects the IDE to handle that -- I don't really like that attitude, but a plugin can do the job. You'll see I install the sbt eclipse plugin just so it will do it for me, even though I use IDEA myself (when I use an IDE).

Also, note that, ideally, you use both the IDEA plugin for SBT that you mentioned, and the SBT plugin for IDEA. See here for the list of plugins.

Unless the IDEA plugin has evolved a lot, you really need to generate an IDEA configuration from SBT iself -- IDEA won't "read" your configuration. That's what the SBT plugin for IDEA does. Install it, and sbt gen-idea. I expect that will solve the problem you mentioned.

Note, however, that the version of Scala you use to compile your project and the version of Scala that SBT uses for itself are different indeed. This is not a problem, it is as expected. I'm not sure from your question if the 2.8.1 version you mentioned is the one used by SBT, or one used by IDEA -- or even one used to compile your project, indicating that something is not working.

Where did you put the example you mentioned anyway? You should follow maven-style directory hierarchy, which means putting it on src/main/scala/, and possibly a subdirectory of that related to the package, if you follow Java convention as well.

And try to compile with sbt, to make sure that is working, before proceeding to IDEA.

Harangue

Thanks. I did see your guide, which was helpful, but I didn't know you were just running the Eclipse plugin to make the directories! I haven't used Maven before so I'm not really familiar with the structure there. I did put my source files in the project directory and it didn't work, but it does when I move them to the right place! – Mocha

@Luigi In that case, take a look at the "Scala application structure" question. – Harangue

Answer 3

I normally put the src into a folder "src/test/scala" and "src/main/scala". sbt-idea will add this folders ase source/test folder in idea.

sbt itself needs Scala 2.8.1 but this version has nothing to do with the version of your code. If you try to compile some source sbt will download Scala 2.9.0.

Uuge

sbt-idea didn't add any source folders when I ran it. It's put both versions of Scala in the external libraries but it still doesn't recognize the App class. – Mocha