Generating code that includes reading and writing files

[davesmith00000]

Hi,

As discussed on Discord, I've moved here to a discussion topic.

Context, I'm trying to port the Indigo plugin to Mill 1.x and I'm having issues.

I've (...very quickly...) produced a minimised example that roughly follows the process I have - so on the positive, this works - what I want to know now, is whether or not this is a reasonably idiomatic way to do this ...or not.

Is this the right idea?

/read.txt

Yikes.

foo/src/example/Main.scala

package example

object Main:

  def main(args: Array[String]): Unit =
    val x = Stuff("Bob")
    println("Hello, world!")

build.mill

//| mill-version: 1.0.5

package build

import mill.*, scalalib.*
import mill.api.BuildCtx

object foo extends ScalaModule:

  def scalaVersion = "3.7.3"

  def generateTheCode(out: os.Path): Seq[os.FilePath] =
    val txtFile = BuildCtx.workspaceRoot / "read.txt"
    val comment = os.read.lines(txtFile).head
    val outFile = out / "Stuff.scala"

    val content =
      s"""
      |package example
      |
      |// $comment
      |
      |final case class Stuff(name: String)
      |""".stripMargin

    os.write(outFile, content)

    /* There must be a nicer way of doing this. Can't use os.SubPath because the
     * path gets manipulated (inserts the 'foo' directory incorrectly), and this
     * is a nasty way of making a 'FilePath'. What's wrong with os.Path and
     * os.RelPath anyway?
     */
    Seq(txtFile, outFile).map(p => os.FilePath(p.toString))

  private def customSources =
    // Would be nice if this accepted a Seq
    Task.Sources(generateTheCode(Task.dest)*)

  override def generatedSources: Task.Simple[Seq[PathRef]] =
    Task {
      val custom: Seq[PathRef] = 
        customSources()
          .map: p =>
            val from: os.Path  = p.path
            val to = Task.dest / from.last

            // This also copies the read.txt file.. not correct but not important.
            os.copy(from, to)
            PathRef(to)

      custom ++ super.generatedSources()
    }

[lihaoyi]

Writing to files in Task.Sources is something you shouldn't do. If you want to generate sources based on an input read.txt file, you should do something like

def readFile = Task.Source(BuildCtx.workspaceRoot / "read.txt")

def customSources = Task{
  generateTheCode(Task.dest, readFile())
  Seq(PathRef(Task.dest), readFile)
}

def generatedSources = Task{
  super.generatedSources() ++ customSources()
}

[davesmith00000]

Updated and simplified version following your suggestion, thanks, and I've moved the read.txt file into an assets folder, which is more inline with what the plugin does.

//| mill-version: 1.0.5

package build

import mill.*, scalalib.*
import mill.api.BuildCtx

object foo extends ScalaModule:

  def scalaVersion = "3.7.3"

  def readAssets =
    Task.Source(BuildCtx.workspaceRoot / "assets")

  def generateTheCode(out: os.Path, assetFolder: os.Path): Unit =
    val txtFile = assetFolder / "read.txt"
    val comment = os.read.lines(txtFile).head
    val outFile = out / "Stuff.scala"

    val content =
      s"""
      |package example
      |
      |// $comment
      |
      |final case class Stuff(name: String)
      |""".stripMargin

    os.write(outFile, content)

  private def customSources = Task {
    val assetFolder = readAssets()
    generateTheCode(Task.dest, assetFolder.path)
    Seq(PathRef(Task.dest))
  }

  override def generatedSources =
    Task {
      val custom: Seq[PathRef] = 
        customSources()
          .map: p =>
            val from: os.Path  = p.path
            val to = Task.dest / from.last

            os.copy(from, to)
            PathRef(to)

      custom ++ super.generatedSources()
    }

I think that'll work. I'll just need to update the options declaration a bit to somehow require people to use a Task.Source'd assets directory.

  val indigoOptions: IndigoOptions =
    IndigoOptions.defaults
      .withTitle("Triple")
      .withWindowSize(800, 600)
      .withBackgroundColor("black")
      .withAssetDirectory(os.RelPath.rel / "assets")
      .excludeAssets {
        case p if p.endsWith(os.RelPath.rel / ".gitkeep") => true
        case _                                            => false
      }

[davesmith00000]

Thanks for the assistance, I have it working now. Indigo can build games using Mill 1.x.