sbt: Support nested version specifiers

[rafikk]

Tell us more.

First of all, thanks for the excellent project!

We'd like to group our sbt-package updates based on shared variables. Right now, the following works:

val specs2Version = "4.23.0"

...

    libraryDependencies ++= Seq(
      "org.specs2" %% "specs2-core" % specs2Version % "test,it",
      "org.specs2" %% "specs2-mock" % specs2Version % "test"
    )

However, we have several projects that use one of the following patterns instead:

val versions = new {
  val specs2 = "4.23.0"
}


...

    libraryDependencies ++= Seq(
      "org.specs2" %% "specs2-core" % versions.specs2 % "test,it",
      "org.specs2" %% "specs2-mock" % versions.specs2 % "test"
    )

or:

val versions = Map(
  "specs2" -> "4.23.0"
)

...

    libraryDependencies ++= Seq(
      "org.specs2" %% "specs2-core" % versions("specs2") % "test,it",
      "org.specs2" %% "specs2-mock" % versions("specs2") % "test"
    )

Both of these patterns produce errors with a skipReason of invalid-value.

Would it be possible to support these as well? One upside of this pattern is that PR names are better-formatted. I.e. instead of "update specs2version to v4.23.0" we get "update specs2 to v4.23.0".

[rafikk]

#40699 is now open which fulfills this feature request.