Added new target TestModule.testCached which caches the last test result (#712)

* Added new target TestModule.testCached which caches the last test result

Implements https://github.com/lihaoyi/mill/issues/711

* Fixed task-in-task evaluation issue

1 files changed, 26 insertions, 8 deletions

diff --git a/scalalib/src/JavaModule.scala b/scalalib/src/JavaModule.scala
index b9987ca1..dc412f3b 100644
--- a/scalalib/src/JavaModule.scala
+++ b/scalalib/src/JavaModule.scala
@@ -5,8 +5,7 @@ import java.io.ByteArrayInputStream
 import java.io.ByteArrayOutputStream
 
 import coursier.Repository
-import mill.define.Task
-import mill.define.TaskModule
+import mill.define.{Command, Task, TaskModule}
 import mill.eval.{PathRef, Result}
 import mill.modules.{Assembly, Jvm}
 import mill.modules.Jvm.{createAssembly, createJar}
@@ -565,9 +564,29 @@ trait TestModule extends JavaModule with TaskModule {
   def testFrameworks: T[Seq[String]]
   /**
     * Discovers and runs the module's tests in a subprocess, reporting the
-    * results to the console
+    * results to the console.
+    * @see [[testCached]]
     */
-  def test(args: String*) = T.command{
+  def test(args: String*): Command[(String, Seq[TestRunner.Result])] = T.command {
+    testTask(T.task{args})()
+  }
+
+  /**
+    * Args to be used by [[testCached]].
+    */
+  def testCachedArgs: T[Seq[String]] = T{ Seq[String]() }
+
+  /**
+    * Discovers and runs the module's tests in a subprocess, reporting the
+    * results to the console.
+    * If no input has changed since the last run, no test were executed.
+    * @see [[test()]]
+    */
+  def testCached: T[(String, Seq[TestRunner.Result])] = T {
+    testTask(testCachedArgs)()
+  }
+
+  protected def testTask(args: Task[Seq[String]]): Task[(String, Seq[TestRunner.Result])] = T.task {
     val outputPath = T.ctx().dest/"out.json"
 
     Jvm.runSubprocess(
@@ -580,8 +599,8 @@ trait TestModule extends JavaModule with TaskModule {
         testFrameworks() ++
         Seq(runClasspath().length.toString) ++
         runClasspath().map(_.path.toString) ++
-        Seq(args.length.toString) ++
-        args ++
+        Seq(args().length.toString) ++
+        args() ++
         Seq(outputPath.toString, T.ctx().log.colored.toString, compile().classes.path.toString, T.ctx().home.toString),
       workingDir = forkWorkingDir()
     )
@@ -593,14 +612,13 @@ trait TestModule extends JavaModule with TaskModule {
     }catch{case e: Throwable =>
       Result.Failure("Test reporting failed: " + e)
     }
-
   }
 
   /**
     * Discovers and runs the module's tests in-process in an isolated classloader,
     * reporting the results to the console
     */
-  def testLocal(args: String*) = T.command{
+  def testLocal(args: String*) = T.command {
     val outputPath = T.ctx().dest/"out.json"
 
     val (doneMsg, results) = TestRunner.runTests(