Task graph / .. task that depends on other settings - broken example

[kelemensanyi]

In the Getting Started Guide this example is not working as described with sbt 1.0.2:
http://www.scala-sbt.org/1.x/docs/Task-Graph.html#Defining+a+task+that+depends+on+other+settings

$ cat build.sbt 
lazy val root = (project in file("."))
  .settings(
    name := "Hello",
    organization := "com.example",
    scalaVersion := "2.12.3",
    version := "0.1.0-SNAPSHOT",
    scalacOptions := List("-encoding", "utf8", "-Xfatal-warnings", "-deprecation", "-unchecked"),
    scalacOptions := {
      val old = scalacOptions.value
      scalaBinaryVersion.value match {
        case "2.12" => old
        case _      => old filterNot (Set("-Xfatal-warnings", "-deprecation").apply)
      }
    }
  )

$ sbt about
[info] Updated file /home/kelemen/temp/sbt-started/project/build.properties: set sbt.version to 1.0.2
[info] Loading project definition from /home/kelemen/temp/sbt-started/project
[info] Updating {file:/home/kelemen/temp/sbt-started/project/}sbt-started-build...
[info] Done updating.
[info] Loading settings from build.sbt ...
[info] Set current project to Hello (in build file:/home/kelemen/temp/sbt-started/)
[info] This is sbt 1.0.2
[info] The current project is {file:/home/kelemen/temp/sbt-started/}root 0.1.0-SNAPSHOT
[info] The current project is built against Scala 2.12.3
[info] Available Plugins: sbt.plugins.IvyPlugin, sbt.plugins.JvmPlugin, sbt.plugins.CorePlugin, sbt.plugins.JUnitXmlReportPlugin, sbt.plugins.Giter8TemplatePlugin
[info] sbt, sbt plugins, and build definitions are using Scala 2.12.3

$ sbt
[info] Loading project definition from /home/kelemen/temp/sbt-started/project
[info] Loading settings from build.sbt ...
[info] Set current project to Hello (in build file:/home/kelemen/temp/sbt-started/)
[info] sbt server started at 127.0.0.1:5797
sbt:Hello> show scalacOptions
[info] * -encoding
[info] * utf8
[info] * -Xfatal-warnings
[info] * -deprecation
[info] * -unchecked
[success] Total time: 0 s, completed Sep 28, 2017 5:53:13 PM
sbt:Hello> ++2.11.8
[info] Setting Scala version to 2.11.8 on 0 projects.
[info] Excluded 1 projects, run ++ 2.11.8 -v for more details.
[info] Reapplying settings...
[info] Set current project to Hello (in build file:/home/kelemen/temp/sbt-started/)
sbt:Hello> show scalacOptions
[info] * -encoding
[info] * utf8
[info] * -Xfatal-warnings
[info] * -deprecation
[info] * -unchecked
[success] Total time: 0 s, completed Sep 28, 2017 5:53:30 PM

The problem is with the second execution of show scalacOptions, because according to the example it should only display -encoding, utf8, -unchecked and NOT -Xfatal-warnings and -deprecation.

[kelemensanyi]

Adding crossScalaVersions := Seq(scalaVersion.value, "2.11.8"), seems to solve it:

$ cat build.sbt 
lazy val root = (project in file("."))
  .settings(
    name := "Hello",
    organization := "com.example",
    scalaVersion := "2.12.3",
    crossScalaVersions := Seq(scalaVersion.value, "2.11.8"),
    version := "0.1.0-SNAPSHOT",
    scalacOptions := List("-encoding", "utf8", "-Xfatal-warnings", "-deprecation", "-unchecked"),
    scalacOptions := {
      val old = scalacOptions.value
      scalaBinaryVersion.value match {
        case "2.12" => old
        case _      => old filterNot (Set("-Xfatal-warnings", "-deprecation").apply)
      }
    }
  )

$ sbt
[info] Updated file /home/kelemen/temp/sbt-started/project/build.properties: set sbt.version to 1.0.2
[info] Loading project definition from /home/kelemen/temp/sbt-started/project
[info] Updating {file:/home/kelemen/temp/sbt-started/project/}sbt-started-build...
[info] Done updating.
[info] Loading settings from build.sbt ...
[info] Set current project to Hello (in build file:/home/kelemen/temp/sbt-started/)
[info] sbt server started at 127.0.0.1:5797
sbt:Hello> show scalacOptions
[info] * -encoding
[info] * utf8
[info] * -Xfatal-warnings
[info] * -deprecation
[info] * -unchecked
[success] Total time: 0 s, completed Sep 28, 2017 6:03:10 PM
sbt:Hello> ++2.11.8
[info] Setting Scala version to 2.11.8 on 1 projects.
[info] Reapplying settings...
[info] Set current project to Hello (in build file:/home/kelemen/temp/sbt-started/)
sbt:Hello> show scalacOptions
[info] * -encoding
[info] * utf8
[info] * -unchecked
[success] Total time: 0 s, completed Sep 28, 2017 6:03:23 PM

[kelemensanyi]

Might be related to sbt/sbt#2613

[dwijnand]

Thank you for bringing this to our attention, @kelemensanyi!