Fix incremental compilation when a Scala project depends on a Java project (#414)

* Upgrade ammonite to 1.1.2-30-53edc31

This is mainly to get https://github.com/lihaoyi/Ammonite/pull/851 which
should reduce the amount of unnecessary work done by incremental
compilation in the Mill build. This requires some code changes since
this means we now depend on a more recent version of coursier, as a
side-effect this means that we do not depend on scalaz anymore.

Also use the same ammonite version in the Mill build and in
ScalaModule#ammoniteReplClasspath.

Also remove an incorrect dependency in the caffeine integration test.
This was always wrong but did not start failing until this commit,
probably due to dependencies appearing in a different order on the
classpath.

* Rename ScalaWorker to ZincWorker

Starting with the next commit, it will be used in Java-only projects
too, so the name is misleading.

* Upgrade to Zinc 1.2.1

* Fix incremental compilation when a Scala project depends on a Java project

Before this commit, JavaModule#compile simply called javac
unconditionally, thus generating new classfiles every time. But if a
Scala project depends on a Java project, this will throw off the
incremental compilation algorithm which will unnecessarily recompile
files. To avoid this we now use Zinc to compile Java projects too (as a
bonus this means that Java compilation becomes incremental). This
required some refactoring in ZincWorkerImpl to be able to compile stuff
without having to pass Scala-specific options.

The issue solved by this commit could be reproduced by running in the
Mill repository:

$ mill main.compile
$ mill -i
@ main.compile()

and observing that before this commit, the `main.compile()` call ended
up recompiling code.

3 files changed, 19 insertions, 19 deletions

diff --git a/docs/VisualizePlan.svg b/docs/VisualizePlan.svg
index f6e50b39..9f13384f 100644
--- a/docs/VisualizePlan.svg
+++ b/docs/VisualizePlan.svg
@@ -3,33 +3,33 @@
 <g id="graph0" class="graph" transform="scale(1 1) rotate(0) translate(4 328)">
 <title>example1</title>
 <polygon fill="#ffffff" stroke="transparent" points="-4,4 -4,-328 3469.1473,-328 3469.1473,4 -4,4"/>
-<!-- mill.scalalib.ScalaWorkerModule.classpath -->
+<!-- mill.scalalib.ZincWorkerModule.classpath -->
 <g id="node1" class="node">
-<title>mill.scalalib.ScalaWorkerModule.classpath</title>
+<title>mill.scalalib.ZincWorkerModule.classpath</title>
 <ellipse fill="none" stroke="#000000" stroke-dasharray="1,5" cx="179.1736" cy="-162" rx="179.3473" ry="18"/>
-<text text-anchor="middle" x="179.1736" y="-157.8" font-family="Times,serif" font-size="14.00" fill="#000000">mill.scalalib.ScalaWorkerModule.classpath</text>
+<text text-anchor="middle" x="179.1736" y="-157.8" font-family="Times,serif" font-size="14.00" fill="#000000">mill.scalalib.ZincWorkerModule.classpath</text>
 </g>
-<!-- mill.scalalib.ScalaWorkerModule.compilerInterfaceClasspath -->
+<!-- mill.scalalib.ZincWorkerModule.compilerInterfaceClasspath -->
 <g id="node2" class="node">
-<title>mill.scalalib.ScalaWorkerModule.compilerInterfaceClasspath</title>
+<title>mill.scalalib.ZincWorkerModule.compilerInterfaceClasspath</title>
 <ellipse fill="none" stroke="#000000" stroke-dasharray="1,5" cx="626.1736" cy="-162" rx="249.9102" ry="18"/>
-<text text-anchor="middle" x="626.1736" y="-157.8" font-family="Times,serif" font-size="14.00" fill="#000000">mill.scalalib.ScalaWorkerModule.compilerInterfaceClasspath</text>
+<text text-anchor="middle" x="626.1736" y="-157.8" font-family="Times,serif" font-size="14.00" fill="#000000">mill.scalalib.ZincWorkerModule.compilerInterfaceClasspath</text>
 </g>
-<!-- mill.scalalib.ScalaWorkerModule.worker -->
+<!-- mill.scalalib.ZincWorkerModule.worker -->
 <g id="node3" class="node">
-<title>mill.scalalib.ScalaWorkerModule.worker</title>
+<title>mill.scalalib.ZincWorkerModule.worker</title>
 <ellipse fill="none" stroke="#000000" stroke-dasharray="1,5" cx="626.1736" cy="-234" rx="171.2452" ry="18"/>
-<text text-anchor="middle" x="626.1736" y="-229.8" font-family="Times,serif" font-size="14.00" fill="#000000">mill.scalalib.ScalaWorkerModule.worker</text>
+<text text-anchor="middle" x="626.1736" y="-229.8" font-family="Times,serif" font-size="14.00" fill="#000000">mill.scalalib.ZincWorkerModule.worker</text>
 </g>
-<!-- mill.scalalib.ScalaWorkerModule.worker&#45;&gt;mill.scalalib.ScalaWorkerModule.classpath -->
+<!-- mill.scalalib.ZincWorkerModule.worker&#45;&gt;mill.scalalib.ZincWorkerModule.classpath -->
 <g id="edge1" class="edge">
-<title>mill.scalalib.ScalaWorkerModule.worker&#45;&gt;mill.scalalib.ScalaWorkerModule.classpath</title>
+<title>mill.scalalib.ZincWorkerModule.worker&#45;&gt;mill.scalalib.ZincWorkerModule.classpath</title>
 <path fill="none" stroke="#000000" d="M532.4677,-218.9064C459.9462,-207.2251 359.5232,-191.0496 284.2741,-178.9289"/>
 <polygon fill="#000000" stroke="#000000" points="284.7249,-175.4565 274.2956,-177.3217 283.6117,-182.3675 284.7249,-175.4565"/>
 </g>
-<!-- mill.scalalib.ScalaWorkerModule.worker&#45;&gt;mill.scalalib.ScalaWorkerModule.compilerInterfaceClasspath -->
+<!-- mill.scalalib.ZincWorkerModule.worker&#45;&gt;mill.scalalib.ZincWorkerModule.compilerInterfaceClasspath -->
 <g id="edge2" class="edge">
-<title>mill.scalalib.ScalaWorkerModule.worker&#45;&gt;mill.scalalib.ScalaWorkerModule.compilerInterfaceClasspath</title>
+<title>mill.scalalib.ZincWorkerModule.worker&#45;&gt;mill.scalalib.ZincWorkerModule.compilerInterfaceClasspath</title>
 <path fill="none" stroke="#000000" d="M626.1736,-215.8314C626.1736,-208.131 626.1736,-198.9743 626.1736,-190.4166"/>
 <polygon fill="#000000" stroke="#000000" points="629.6737,-190.4132 626.1736,-180.4133 622.6737,-190.4133 629.6737,-190.4132"/>
 </g>
@@ -297,9 +297,9 @@
 <ellipse fill="none" stroke="#000000" cx="1913.1736" cy="-306" rx="89.7283" ry="18"/>
 <text text-anchor="middle" x="1913.1736" y="-301.8" font-family="Times,serif" font-size="14.00" fill="#000000">moduledefs.compile</text>
 </g>
-<!-- moduledefs.compile&#45;&gt;mill.scalalib.ScalaWorkerModule.worker -->
+<!-- moduledefs.compile&#45;&gt;mill.scalalib.ZincWorkerModule.worker -->
 <g id="edge24" class="edge">
-<title>moduledefs.compile&#45;&gt;mill.scalalib.ScalaWorkerModule.worker</title>
+<title>moduledefs.compile&#45;&gt;mill.scalalib.ZincWorkerModule.worker</title>
 <path fill="none" stroke="#000000" d="M1824.9751,-302.6013C1641.2815,-295.2954 1204.2998,-276.7314 838.1736,-252 814.9556,-250.4316 790.326,-248.5451 766.3857,-246.592"/>
 <polygon fill="#000000" stroke="#000000" points="766.4274,-243.0836 756.174,-245.7515 765.8532,-250.06 766.4274,-243.0836"/>
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diff --git a/docs/pages/2 - Configuring Mill.md b/docs/pages/2 - Configuring Mill.md
index 7db19833..989272dd 100644
--- a/docs/pages/2 - Configuring Mill.md
+++ b/docs/pages/2 - Configuring Mill.md
@@ -72,20 +72,20 @@ def repositories = super.repositories ++ Seq(
 ```
 
 To add custom resolvers to the initial bootstrap of the build, you can create a 
-custom `ScalaWorkerModule`, and override the `scalaWorker` method in your 
+custom `ZincWorkerModule`, and override the `zincWorker` method in your 
 `ScalaModule` by pointing it to that custom object:
 
 ```scala
 import coursier.maven.MavenRepository
 
-object CustomScalaWorkerModule extends ScalaWorkerModule {
+object CustomZincWorkerModule extends ZincWorkerModule {
   def repositories() = super.repositories ++ Seq(
     MavenRepository("https://oss.sonatype.org/content/repositories/releases")
   )  
 }
 
 object YourBuild extends ScalaModule {
-  def scalaWorker = CustomScalaWorkerModule
+  def zincWorker = CustomZincWorkerModule
   // ... rest of your build definitions
 }
 ```
diff --git a/docs/pages/5 - Modules.md b/docs/pages/5 - Modules.md
index 2c13a3e9..fa6260f3 100644
--- a/docs/pages/5 - Modules.md
+++ b/docs/pages/5 - Modules.md
@@ -152,7 +152,7 @@ mill foo.Bar/qux
 
 `ExternalModule`s are useful for someone providing a library for use with Mill
 that is shared by the entire build: for example,
-`mill.scalalib.ScalaWorkerApi/scalaWorker` provides a shared Scala compilation
+`mill.scalalib.ZincWorkerApi/zincWorker` provides a shared Scala compilation
 service & cache that is shared between all `ScalaModule`s, and
 `mill.scalalib.GenIdea/idea` lets you generate IntelliJ projects without
 needing to define your own `T.command` in your `build.sc` file