### Fixes with compatibility implications

- Deprecates the old sbt 0.12 DSL, 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]
- Improve `show` when key returns a `Seq` by showing the elements one per line. Disable with `-Dsbt.disable.show.seq=true`. [#2755][2755] by [@eed3si9n][@eed3si9n]
- Recycles classloaders to be anti-hostile to JIT. Disable with `-Dsbt.disable.interface.classloader.cache=true`. [#2754][2754] by [@retronym][@retronym]

### Improvements

- Adds `new` command and `templateResolverInfos`. 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]
- Adds `.jvmopts` support to the launcher script. [sbt/sbt-launcher-package#111][111] by [@fommil][@fommil]
- Adds `.java-version` support to the Windows launcher script. [sbt/sbt-launcher-package#111][111] by [@fommil][@fommil]
- The startup log level is dropped to `-error` in script mode using `scalas`. [#840][840]/[#2746][2746] by [@eed3si9n][@eed3si9n]
- Adds `CrossVersion.patch` which sits in between `CrossVersion.binary` and `CrossVersion.full` in that it strips off any
  trailing `-bin-...` suffix which is used to distinguish variant but binary compatible Scala toolchain builds. Most things
  which are currently `CrossVersion.full` (eg. Scala compiler plugins, esp. macro-paradise) would be more appropriately
  depended on as `CrossVersion.patch` from this release on.

### 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 a regression in sbt 0.13.12 that was misfiring Scala version enforcement when an alternative `scalaOrganization` is set. [#2703][2703] by [@milessabin][@milessabin]
- Fixes `Tags.ForkedTestGroup`. [#2677][2677]/[#2681][2681] by [@pauldraper][@pauldraper]
- Fixes forked tests being reported as successful when the test harness fails. [#2442][2442]/[#2722][2722]/[#2730][2730] by [@eed3si9n][@eed3si9n]/[@dwijnand][@dwijnand]
- Fixes incorrect installation path on Windows. [sbt/sbt-launcher-package#110][110] by [@dwijnand][@dwijnand]

### new command and templateResolverInfos

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.
A template resolver pattern matches on the passed in arguments after `new`,
and if it's a match it will apply the template.

As a reference implementation, template resolver for [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 sbt 0.12 DSL

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

Generally,

    task3 <<= (task1, task2) map { (t1, t2) => println(t1 + t2); t1 + t2 }

should migrate to

    task3 := {
      println(task1.value + task2.value)
      task1.value + task2.value
    }

Except for source generators, which requires task values:

    sourceGenerators in Compile <+= buildInfo

This becomes:

    sourceGenerators in Compile += buildInfo.taskValue

Another exception is input task:

    run <<= docsRunSetting

This becomes:

    run := docsRunSetting.evaluated

See [Migrating from sbt 0.12.x](https://www.scala-sbt.org/0.13/docs/Migrating-from-sbt-012x.html) for more details.

[#2716][2716]/[#2763][2763]/[#2764][2764] by [@eed3si9n][@eed3si9n] and [@dwijnand][@dwijnand]

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

  [840]: https://github.com/sbt/sbt/issues/840
  [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
  [2677]: https://github.com/sbt/sbt/issues/2677
  [2681]: https://github.com/sbt/sbt/pull/2681
  [2705]: https://github.com/sbt/sbt/pull/2705
  [2682]: https://github.com/sbt/sbt/pull/2682
  [2703]: https://github.com/sbt/sbt/pull/2703
  [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
  [2746]: https://github.com/sbt/sbt/pull/2746
  [2754]: https://github.com/sbt/sbt/pull/2754
  [2755]: https://github.com/sbt/sbt/pull/2755
  [2763]: https://github.com/sbt/sbt/issues/2763
  [2764]: https://github.com/sbt/sbt/pull/2764
  [110]: https://github.com/sbt/sbt-launcher-package/pull/110
  [111]: https://github.com/sbt/sbt-launcher-package/pull/111
  [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
  [@fommil]: https://github.com/fommil
  [@milessabin]: https://github.com/milessabin
  [@pauldraper]: https://github.com/pauldraper
  [@retronym]: https://github.com/retronym