How can I conditionally add an sbt plugin, depending on the active sbt version?

Question

Use case: I like to be able to show the dependency tree for my sbt projects, so I have added addDependencyTreePlugin to my ~/.sbt/1.0/plugins.sbt, to make it globally available on my machine.

However, that plugin is only available since sbt 1.4.x (not sure about the exact version).

Problem: whenever I try to build a project that has an sbt.version=1.3.x or lower in the build.properties, it will fail.

Is there a way to conditionally do the addDependencyTreePlugin, based on the 'current' version of sbt that is being used by the build process?

This does not work:

addDependencyTreePlugin.filter(es => sbtVersion.value.startsWith("1.5")

sbt will complain about:

.../plugins.sbt:4: error: `value` can only be used within a task or setting macro, such as :=, +=, ++=, Def.task, or Def.setting.
addDependencyTreePlugin.filter(es => sbtVersion.value.startsWith("1.5"))
^

Why don't you just upgrade those projects? Sbt is compatible back to 1.0. — Matthias Berndt, Jan 10 '22 at 22:21
I'd love to, but corporate environments move slow, so not all projects can be updated all the time. Besides, when looking back at older branches I sometimes want to be able to reproduce builds with older versions. — JeanMarc, Jan 11 '22 at 08:43

score 1 · Answer 1 · answered Jan 10 '22 at 18:56

SBT addDependencyTreePlugin is defined as follow:

def addDependencyTreePlugin: Setting[Seq[ModuleID]] =
    libraryDependencies += sbtPluginExtra(
      ModuleID("org.scala-sbt", "sbt-dependency-tree", sbtVersion.value),
      sbtBinaryVersion.value,
      scalaBinaryVersion.value
    )

To apply the conditional logic, you'll have to use something like this:

def addDependencyTreePluginCustom: Setting[Seq[ModuleID]] =
    libraryDependencies ++= if (condition) Seq(sbtPluginExtra(
      ModuleID("org.scala-sbt", "sbt-dependency-tree", sbtVersion.value),
      sbtBinaryVersion.value,
      scalaBinaryVersion.value
    )) else Seq()

Note: there might exist a simpler way

I had to add parenthesis around the if statement (`(if (...)...else Seq())`), but then this works. Thanks. — JeanMarc, Jan 11 '22 at 09:05

JeanMarc · Accepted Answer · 2022-01-13T06:21:38.243

With the help of @Gaël, I have come up with:

libraryDependencies ++= (if (VersionNumber(sbtVersion.value).matchesSemVer(SemanticSelector(">=1.4"))) {
                           println(s"Adding dependency tree plugin, sbt version is ${sbtVersion.value}")
                           Seq(
                             sbtPluginExtra(
                               ModuleID("org.scala-sbt", "sbt-dependency-tree", sbtVersion.value),
                               sbtBinaryVersion.value,
                               scalaBinaryVersion.value
                             )
                           )
                         } else Seq[ModuleID]())
}

Which will work as long as the sbt version is 1.2 or later (since that is the version that introduced the VersionNumber and SemanticSelector accoding to https://stackoverflow.com/a/56587048/2037054

How can I conditionally add an sbt plugin, depending on the active sbt version?

2 Answers2