Adds templateResolvers and new command

[eed3si9n]

This adds new command, which helps create a new build definition. The
new command is extensible via a mechanism called the template
resolver, which evaluates the arbitrary arguments passed to the command to find
and run a template.

See https://github.com/sbt/template-resolver/blob/master/src/main/java/sbt/template/TemplateResolver.java

As a reference implementation, Giter8 integration is provided, which works as follows:

$ sbt new eed3si9n/hello.g8

This will run eed3si9n/hello.g8 using Giter8.

templateResolvers is just a key in the Global scope, so you can write your own auto plugin to extend it:

object Giter8TemplatePlugin extends AutoPlugin {
  override def requires = CorePlugin
  override def trigger = allRequirements

  override lazy val globalSettings: Seq[Setting[_]] =
    Seq(
      templateResolvers += Giter8TemplateResolver
    )
}

The credit for the idea of extensible template support goes to @corruptmemory, but I take the blame for implementation details :)

update

If you want to make your own Giter8 template, see Making your own templates. All you need is a Git repo.

If you want to extend template resolving mechanism to something other than Giter8, just extend this Java class:

package sbt.template;

/** A way of specifying template resolver.
 */
public interface TemplateResolver {
  /** Returns true if this resolver can resolve the given argument.
   */
  public boolean isDefined(String[] arguments);
  /** Resolve the given argument and run the template.
   */
  public void run(String[] arguments);
}

and define an auto plugin that adds to templateResolvers. For example you might want to create Maven archetype-like template, or whatever mechanism that exists in-house.

[hseeberger]

Welcome back, g8 ;-)

[ktoso]

Excellent, looking forward to this!

[dwijnand]

LGTM

[huntc]

Love it!

[nafg]

You can use code like https://gist.github.com/nafg/05fafb7050ed38854184b4ca64612da7 to use Activator templates.

It seems the way IntelliJ (and I think also Activator itself) gets activator templates is through a very complex API that ultimately gives you a zip file containing a full-text search database (perhaps it was lucene?) which you can then use the client library for locally to search. Sounds like lightbend is really trying to be enterprise-ready...

What my code does instead, is simply scrape the Activator index page for template ids. You can then download the template bundle by appending the id to https://www.lightbend.com/activator/template/bundle/.

It shouldn't be a big deal to write a templateResolver that takes the same shortcut.