Filtering tab completion in input task implementation - sbt

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

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 :=)
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.