First pass at splitting out worker-api from mill core. (#504)

This reduces the {scala,scalajs,scalanative}-worker dependency from the entirety of Mill to a much narrower `mill.api` module. This reduces the amount of classpath pollution within these workers, should mean they're much faster to download the first time, and reduces the amount of random junk they would pull in if they were to be used outside of the Mill project.

The interactions between the various *Modules and their *WorkerImpls has been narrowed down to the `*.api` modules, which only depend on other `*.api` modules.

A lot of things have been moved around; user code is unlikely to break, but it's possible some will if it references classes that have been moved around. Forwarders have been left for the few internal classes that Mill uses in it's own `build.sc`, to support bootstrapping. Third-party code which breaks should be a straightforward to fix just by updating imports

The `*.api` modules have minimal dependencies (mostly uPickle and os-lib) and minimal code. There is still a bunch of implementation code in there: some of it defining data-types that are commonly sent across the module/worker interface (`Agg`, `PathRef`, ...), and some of it just general helper functions that are needed both in modules and workers. The latter code isn't strictly API definitions, but for now is small enough it's not worth splitting into it's own module

3 files changed, 3 insertions, 3 deletions

diff --git a/scalalib/test/src/mill/scalalib/HelloJavaTests.scala b/scalalib/test/src/mill/scalalib/HelloJavaTests.scala
index ff0de5a6..5b7b93b2 100644
--- a/scalalib/test/src/mill/scalalib/HelloJavaTests.scala
+++ b/scalalib/test/src/mill/scalalib/HelloJavaTests.scala
@@ -2,7 +2,7 @@ package mill
 package scalalib
 
 
-import mill.eval.Result
+import mill.api.Result
 import mill.util.{TestEvaluator, TestUtil}
 import utest._
 import utest.framework.TestPath
diff --git a/scalalib/test/src/mill/scalalib/HelloWorldTests.scala b/scalalib/test/src/mill/scalalib/HelloWorldTests.scala
index 67c4b433..da08f056 100644
--- a/scalalib/test/src/mill/scalalib/HelloWorldTests.scala
+++ b/scalalib/test/src/mill/scalalib/HelloWorldTests.scala
@@ -5,7 +5,7 @@ import java.util.jar.JarFile
 
 import mill._
 import mill.define.Target
-import mill.eval.Result.Exception
+import mill.api.Result.Exception
 import mill.eval.{Evaluator, Result}
 import mill.modules.Assembly
 import mill.scalalib.publish._
diff --git a/scalalib/test/src/mill/scalalib/ResolveDepsTests.scala b/scalalib/test/src/mill/scalalib/ResolveDepsTests.scala
index 4240478c..78361625 100644
--- a/scalalib/test/src/mill/scalalib/ResolveDepsTests.scala
+++ b/scalalib/test/src/mill/scalalib/ResolveDepsTests.scala
@@ -2,7 +2,7 @@ package mill.scalalib
 
 import coursier.Cache
 import coursier.maven.MavenRepository
-import mill.eval.Result.{Failure, Success}
+import mill.api.Result.{Failure, Success}
 import mill.eval.{PathRef, Result}
 import mill.util.Loose.Agg
 import utest._