Interpolates $MILL_VERSION in ivy imports (#649)

* Interpolates $MILL_VERSION in ivy imports

This overrides the default $ivy magic import by replacing the
`$MILL_VERSION` string with mill's version, in order to facilitate
the loading/update of contrib modules.

Ammonite had to be bumped to 1.6.9

* Removed bloop import

* AmmoniteExit import fix

* Removed repl dep check

* Removed problematic check

* Made ammonite version override-able

2 files changed, 19 insertions, 1 deletions

diff --git a/main/src/main/MainRunner.scala b/main/src/main/MainRunner.scala
index 6705a4b3..354b6173 100644
--- a/main/src/main/MainRunner.scala
+++ b/main/src/main/MainRunner.scala
@@ -9,6 +9,7 @@ import mill.eval.{Evaluator, PathRef}
 import mill.util.PrintLogger
 
 import scala.annotation.tailrec
+import ammonite.runtime.ImportHook
 
 
 /**
@@ -120,11 +121,13 @@ class MainRunner(val config: ammonite.main.Cli.Config,
   }
 
   override def initMain(isRepl: Boolean) = {
+    val hooks = ImportHook.defaults + (Seq("ivy") -> MillIvyHook)
     super.initMain(isRepl).copy(
       scriptCodeWrapper = CustomCodeWrapper,
       // Ammonite does not properly forward the wd from CliConfig to Main, so
       // force forward it outselves
-      wd = config.wd
+      wd = config.wd,
+      importHooks = hooks
     )
   }
 
diff --git a/main/src/main/MillIvyHook.scala b/main/src/main/MillIvyHook.scala
new file mode 100644
index 00000000..2b4eb6a7
--- /dev/null
+++ b/main/src/main/MillIvyHook.scala
@@ -0,0 +1,15 @@
+package mill.main
+import ammonite.runtime.ImportHook.BaseIvy
+import ammonite.runtime.ImportHook
+import java.io.File
+
+/**
+ * Overrides the ivy hook to interpret $MILL_VERSION as the version of mill
+ * the user runs.
+ *
+ * Can be used to ensure loaded contrib modules keep up to date.
+ */
+object MillIvyHook extends BaseIvy(plugin = false){
+  override def resolve(interp: ImportHook.InterpreterInterface, signatures: Seq[String]): Either[String,Set[File]] =
+    super.resolve(interp, signatures.map(_.replace("$MILL_VERSION", mill.BuildInfo.millVersion)))
+}