Filtering tab completion in input task implementation

Question

I'm currently implementing a SBT plugin for Gatling. One of its features will be to open the last generated report in a new browser tab from SBT. As each run can have a different "simulation ID" (basically a simple string), I'd like to offer tab completion on simulation ids.

An example :

Running the Gatling SBT plugin will produce several folders (named from simulationId + date of report generaation) in target/gatling, for example mysim-20140204234534, myothersim-20140203124534 and yetanothersim-20140204234534.

Let's call the task lastReport. If someone start typing lastReport my, I'd like to filter out tab-completion to only suggest mysim and myothersim.

Getting the simulation ID is a breeze, but how can help the parser and filter out suggestions so that it only suggest an existing simulation ID ?

To sum up, I'd like to do what testOnly do, in a way : I only want to suggest things that make sense in my context.

Thanks in advance for your answers,

Pierre

Edit : As I got a bit stuck after my latest tries, here is the code of my inputTask, in it's current state :

package io.gatling.sbt

import sbt._
import sbt.complete.{ DefaultParsers, Parser }

import io.gatling.sbt.Utils._

object GatlingTasks {

val lastReport = inputKey[Unit]("Open last report in browser")

val allSimulationIds = taskKey[Set[String]]("List of simulation ids found in reports folder")

val allReports = taskKey[List[Report]]("List of all reports by simulation id and timestamp")

def findAllReports(reportsFolder: File): List[Report] = {
    val allDirectories = (reportsFolder ** DirectoryFilter.&&(new PatternFilter(reportFolderRegex.pattern))).get
    allDirectories.map(file => (file, reportFolderRegex.findFirstMatchIn(file.getPath).get)).map {
        case (file, regexMatch) => Report(file, regexMatch.group(1), regexMatch.group(2))
    }.toList
}

def findAllSimulationIds(allReports: Seq[Report]): Set[String] = allReports.map(_.simulationId).distinct.toSet

def openLastReport(allReports: List[Report], allSimulationIds: Set[String]): Unit = {
    def simulationIdParser(allSimulationIds: Set[String]): Parser[Option[String]] =
        DefaultParsers.ID.examples(allSimulationIds, check = true).?

    def filterReportsIfSimulationIdSelected(allReports: List[Report], simulationId: Option[String]): List[Report] =
        simulationId match {
            case Some(id) => allReports.filter(_.simulationId == id)
            case None => allReports
        }

    Def.inputTaskDyn {
        val selectedSimulationId = simulationIdParser(allSimulationIds).parsed
        val filteredReports = filterReportsIfSimulationIdSelected(allReports, selectedSimulationId)
        val reportsSortedByDate = filteredReports.sorted.map(_.path)
        Def.task(reportsSortedByDate.headOption.foreach(file => openInBrowser((file / "index.html").toURI)))
    }
}

}

Of course, openReport is called using the results of allReports and allSimulationIds tasks. I think I'm close to a functioning input task but I'm still missing something...

Answer 1

1. Def.inputTaskDyn returns a value of type InputTask[T] and doesn't perform any side effects. The result needs to be bound to an InputKey, like lastReport. The return type of openLastReport is Unit, which means that openLastReport will construct a value that will be discarded, effectively doing nothing useful. Instead, have:

   def openLastReport(...): InputTask[...] = ...
   
   lastReport := openLastReport(...).evaluated
   

   (Or, the implementation of openLastReport can be inlined into the right hand side of :=)

2. You probably don't need inputTaskDyn, but just inputTask. You only need inputTaskDyn if you need to return a task. Otherwise, use inputTask and drop the Def.task.