Detecting project class type in plugin to fix Play 2 bug

[benmccann]

Hi,

There is a bug in Play 2's sbtgoodies plugin.  The plugin adds a "dist-unzip" task to all projects.  However, since it depends on Play's "dist" task, it fails if you have any non-Play projects in your build file since it tries to apply it to those projects and cannot.  I believe SbtGoodiesPlugin.scala is where this is happening:

object SbtGoodiesPlugin extends Plugin with SbtGoodiesTasks {
  override def settings: Seq[Setting[_]] = super.settings ++ Seq(
     distUnzip <<= distUnzipTask,
     distUnzip <<= distUnzip.dependsOn(PlayProject.dist)
  )
}

I'd like to fix this, but I'm totally stumped.  Are there any tips you can give me to get me pointed in the right direction?  Can I detect whether the current project is a PlayProject somehow before extending the settings?

Thanks,

Ben

[Josh Suereth]

You can actually detect whether or not the current project *has* a PlayProject.dist setting defined.   That's a bit spiffier.

So, you'll have to deconstruct the distUnzipTask.

(PlayProject.dist.?? zip (foo, bar, baz)) apply { 

  case (None, _) => // Not a play project, return an empty task.

  case (Some(dist), (foo, bar, baz)) =>  

     // Here's where it gets funky, maybe mark can help here?  I'm writing this off the cuff, and I can dig in to give you exact syntax if needed.

     Task(myImplementation(foo,bar,baz)) dependOn dist

}

Note: I highly recommend, when defining tasks, to have a pure function which implements them in addition to/rather than a single member which initializes them.   This way, you have more flexibility in how you wire things together, as do your users.

- Josh

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[Ben McCann]

Thanks for the tip Josh.  I found in the SBT Plugins Best Practices doc that "Overriding val settings should only be done by plugins intending to provide commands. Regular plugins defining tasks and settings should provide a sequence named after the plugin.", so I've gone ahead and made a pull request that makes that change, which solves the problem just fine for me.

Your solution seems pretty interesting, but I'm afraid given my lack of SBT knowledge it's a bit tough for me to comprehend.  Which file would that code go in?  Is there some variable that is assigned the value of that construct or is it a stand-alone construct?

Thanks,

Ben