sbt/notes/0.13.13.markdown

### Fixes with compatibility implications

- Deprecates the old symbolic operators, to be removed in sbt 1.0. See below for more details.
- The `.value` method is deprecated for input tasks. Calling `.value` on an input key returns an `InputTask[A]`,
  which is completely unintuitive and often results in a bug. In most cases `.evaluated` should be called,
  which returns `A` by evaluating the task.
  Just in case `InputTask[A]` is needed, `.inputTaskValue` method is now provided. [#2709][2709] by [@eed3si9n][@eed3si9n]
- sbt 0.13.13 renames the early command `--<command>` that was added in 0.13.1 to `early(<command>)`. This fixes the regression [#1041][1041]. For backward compatibility `--error`, `--warn`, `--info`, and `--debug` will continue to function during the 0.13 series, but it is strongly encouraged to migrate to the single hyphen options: `-error`, `-warn`, `-info`, and `-debug`. [#2742][2742] by [@eed3si9n][@eed3si9n]

### Improvements

- Adds `new` command and `templateResolvers`. See below for more details.
- Auto plugins can add synthetic subprojects. See below for more details.
- Supports wildcard exclusions in POMs [#1431][1431]/[sbt/ivy#22][sbt-ivy-22]/[#2731][2731] by [@jtgrabowski][@jtgrabowski]
- Adds the ability to call `aggregateProjects(..)` for the current project inside a build sbt file. [#2682][2682] by [@xuwei-k][@xuwei-k]

### Bug fixes

- Fixes a regression in sbt 0.13.12 that wrongly reports build-level keys to be ambiguous. [#2707][2707]/[#2708][2708] by [@Duhemm][@Duhemm]
- Fixes forked tests being reported as successful when the test harness fails. [#2442][2442]/[#2722][2722]/[#2730][2730] by [@eed3si9n][@eed3si9n]/[@dwijnand][@dwijnand]

### new command and templateResolvers

sbt 0.13.13 adds a `new` command, which helps create new build definitions.
The `new` command is extensible via a mechanism called the template resolver,
which evaluates the arguments passed to the command to find and run a template.
As a reference implementation [Giter8][g8] is provided. For instance:

    sbt new eed3si9n/hello.g8

will run [eed3si9n/hello.g8][] using Giter8.

[#2705][2705] by [@eed3si9n][@eed3si9n]

### Synthetic subprojects

sbt 0.13.13 adds support for `AutoPlugin`s to define subprojects programmatically,
by overriding the `extraProjects` method:

    import sbt._, Keys._

    object ExtraProjectsPlugin extends AutoPlugin {
      override def extraProjects: Seq[Project] =
        List("foo", "bar", "baz") map generateProject

      def generateProject(id: String): Project =
        Project(id, file(id)).
          settings(
            name := id
          )
    }

In addition, subprojects may be derived from an existing subproject
by overriding `derivedProjects`:

    import sbt._, Keys._

    object DerivedProjectsPlugin extends AutoPlugin {
      // Enable this plugin by default
      override def requires: Plugins = sbt.plugins.CorePlugin
      override def trigger = allRequirements

      override def derivedProjects(proj: ProjectDefinition[_]): Seq[Project] =
        // Make sure to exclude project extras to avoid recursive generation
        if (proj.projectOrigin != ProjectOrigin.DerivedProject) {
          val id = proj.id + "1"
          Seq(
            Project(id, file(id)).
              enablePlugins(DatabasePlugin)
          )
        }
        else Nil
    }

[#2532][2532]/[#2717][2717]/[#2738][2738] by [@eed3si9n][@eed3si9n]

### Deprecate old operators

The no-longer-documented operators `<<=`, `<+=`, and `<++=` are deprecated,
and will be removed in sbt 1.0.

For `<<=`, the suggested migration would be to use either `:=` or `~=` operators.
The RHS of `<<=` takes an `Initialize[_]` expression, which can be converted to `:=` style
by wrapping the expression in parenthesis, and calling `.value` at the end.
For example:

    key := (key.dependsOn(compile in Test)).value

For `<+=` and `<++=`, use `+= { x.value }` and `++= { x.value }`.

[#2716][2716] by [@eed3si9n][@eed3si9n]

  [g8]: http://www.foundweekends.org/giter8/
  [eed3si9n/hello.g8]: https://github.com/eed3si9n/hello.g8

  [1041]: https://github.com/sbt/sbt/issues/1041
  [1431]: https://github.com/sbt/sbt/issues/1431
  [2442]: https://github.com/sbt/sbt/issues/2442
  [2532]: https://github.com/sbt/sbt/issues/2532
  [2705]: https://github.com/sbt/sbt/pull/2705
  [2682]: https://github.com/sbt/sbt/pull/2682
  [2707]: https://github.com/sbt/sbt/issues/2707
  [2708]: https://github.com/sbt/sbt/issues/2708
  [2709]: https://github.com/sbt/sbt/pull/2709
  [2716]: https://github.com/sbt/sbt/pull/2716
  [2717]: https://github.com/sbt/sbt/pull/2717
  [2722]: https://github.com/sbt/sbt/issues/2722
  [2730]: https://github.com/sbt/sbt/pull/2730
  [2731]: https://github.com/sbt/sbt/pull/2731
  [2738]: https://github.com/sbt/sbt/issues/2738
  [2742]: https://github.com/sbt/sbt/pull/2742
  [sbt-ivy-22]: https://github.com/sbt/ivy/pull/22

  [@eed3si9n]: https://github.com/eed3si9n
  [@dwijnand]: https://github.com/dwijnand
  [@Duhemm]: https://github.com/Duhemm
  [@xuwei-k]: https://github.com/xuwei-k
  [@jtgrabowski]: https://github.com/jtgrabowski