Adds envVars propagation client -> server

Since Mill now executes in a long-lived JVM, the builds do not have a
chance to use environment variables as inputs. This propagates the
environment variables from the client all the way down to the context
available to the tasks as a `Map[String, String]` so that they can be
used as inputs should the user choose to do so.

https://github.com/lihaoyi/mill/issues/257

2 files changed, 10 insertions, 3 deletions

diff --git a/core/src/mill/eval/Evaluator.scala b/core/src/mill/eval/Evaluator.scala
index 33141c0a..7b3634ad 100644
--- a/core/src/mill/eval/Evaluator.scala
+++ b/core/src/mill/eval/Evaluator.scala
@@ -2,6 +2,8 @@ package mill.eval
 
 import java.net.URLClassLoader
 
+import scala.collection.JavaConverters._
+
 import mill.util.Router.EntryPoint
 import ammonite.ops._
 import ammonite.runtime.SpecialClassLoader
@@ -32,7 +34,8 @@ case class Evaluator[T](home: Path,
                         rootModule: mill.define.BaseModule,
                         log: Logger,
                         classLoaderSig: Seq[(Either[String, Path], Long)] = Evaluator.classLoaderSig,
-                        workerCache: mutable.Map[Segments, (Int, Any)] = mutable.Map.empty){
+                        workerCache: mutable.Map[Segments, (Int, Any)] = mutable.Map.empty,
+                        env : Map[String, String] = Evaluator.defaultEnv){
   val classLoaderSignHash = classLoaderSig.hashCode()
   def evaluate(goals: Agg[Task[_]]): Evaluator.Results = {
     mkdir(outPath)
@@ -271,7 +274,8 @@ case class Evaluator[T](home: Path,
                 }
             },
             multiLogger,
-            home
+            home,
+            env
           )
 
           val out = System.out
@@ -335,6 +339,8 @@ object Evaluator{
   // in directly) we are forced to pass it in via a ThreadLocal
   val currentEvaluator = new ThreadLocal[mill.eval.Evaluator[_]]
 
+  val defaultEnv: Map[String, String] = System.getenv().asScala.toMap
+
   case class Paths(out: Path,
                    dest: Path,
                    meta: Path,
diff --git a/core/src/mill/util/Ctx.scala b/core/src/mill/util/Ctx.scala
index 99818194..88a8baec 100644
--- a/core/src/mill/util/Ctx.scala
+++ b/core/src/mill/util/Ctx.scala
@@ -36,7 +36,8 @@ object Ctx{
 class Ctx(val args: IndexedSeq[_],
           dest0: () => Path,
           val log: Logger,
-          val home: Path)
+          val home: Path,
+          val env : Map[String, String])
   extends Ctx.Dest
   with Ctx.Log
   with Ctx.Args