Make serial command execution at the evaluation end optional (#3429)

Introduced a new `serialCommandExec` parameter in `Evaluator.evaluate`
and added required binary compatibility shims.

Fix #3359

Pull request: #3429

main/eval/src/mill/eval/Evaluator.scala

@@ -6,6 +6,7 @@ import mill.define.{BaseModule, BaseModuleTree, Segments, Task}
 import mill.eval.Evaluator.{Results, formatFailing}
 import mill.util.{ColorLogger, MultiBiMap}
 
+import scala.annotation.nowarn
 import scala.jdk.CollectionConverters._
 import scala.reflect.ClassTag
 import scala.util.DynamicVariable
@@ -24,12 +25,30 @@ trait Evaluator {
   def pathsResolver: EvaluatorPathsResolver
   def workerCache: collection.Map[Segments, (Int, Val)]
   def disableCallgraphInvalidation: Boolean = false
+
+  @deprecated(
+    "Binary compatibility shim. Use overload with parameter serialCommandExec=false instead",
+    "Mill 0.12.0-RC1"
+  )
+  def evaluate(
+      goals: Agg[Task[_]],
+      reporter: Int => Option[CompileProblemReporter],
+      testReporter: TestReporter,
+      logger: ColorLogger
+  ): Evaluator.Results = evaluate(goals, reporter, testReporter, logger, serialCommandExec = false)
+
   def evaluate(
       goals: Agg[Task[_]],
       reporter: Int => Option[CompileProblemReporter] = _ => Option.empty[CompileProblemReporter],
       testReporter: TestReporter = DummyTestReporter,
-      logger: ColorLogger = baseLogger
-  ): Evaluator.Results
+      logger: ColorLogger = baseLogger,
+      serialCommandExec: Boolean = false
+  ): Evaluator.Results = {
+    // TODO: cleanup once we break bin-compat in Mill 0.13
+    // this method should be abstract, but to preserve bin-compat, we default-implement
+    // by delegating to an binary pre-existing overload, by ignoring the new parameters
+    evaluate(goals, reporter, testReporter, logger): @nowarn("cat=deprecation")
+  }
 
   def withBaseLogger(newBaseLogger: ColorLogger): Evaluator
   def withFailFast(newFailFast: Boolean): Evaluator

main/eval/src/mill/eval/EvaluatorCore.scala

@@ -29,7 +29,8 @@ private[mill] trait EvaluatorCore extends GroupEvaluator {
       goals: Agg[Task[_]],
       reporter: Int => Option[CompileProblemReporter] = _ => Option.empty[CompileProblemReporter],
       testReporter: TestReporter = DummyTestReporter,
-      logger: ColorLogger = baseLogger
+      logger: ColorLogger = baseLogger,
+      serialCommandExec: Boolean = false
   ): Evaluator.Results = {
     os.makeDir.all(outPath)
 
@@ -42,7 +43,7 @@ private[mill] trait EvaluatorCore extends GroupEvaluator {
         if (effectiveThreadCount == 1) ""
         else s"[#${if (effectiveThreadCount > 9) f"$threadId%02d" else threadId}] "
 
-      try evaluate0(goals, logger, reporter, testReporter, ec, contextLoggerMsg)
+      try evaluate0(goals, logger, reporter, testReporter, ec, contextLoggerMsg, serialCommandExec)
       finally ec.close()
     }
   }
@@ -68,7 +69,8 @@ private[mill] trait EvaluatorCore extends GroupEvaluator {
       reporter: Int => Option[CompileProblemReporter] = _ => Option.empty[CompileProblemReporter],
       testReporter: TestReporter = DummyTestReporter,
       ec: ExecutionContext with AutoCloseable,
-      contextLoggerMsg0: Int => String
+      contextLoggerMsg0: Int => String,
+      serialCommandExec: Boolean
   ): Evaluator.Results = {
     os.makeDir.all(outPath)
     val chromeProfileLogger = new ChromeProfileLogger(outPath / millChromeProfile)
@@ -170,7 +172,7 @@ private[mill] trait EvaluatorCore extends GroupEvaluator {
     val tasksTransitive = tasksTransitive0.toSet
     val (tasks, leafCommands) = terminals0.partition {
       case Terminal.Labelled(t, _) if tasksTransitive.contains(t) => true
-      case _ => false
+      case _ => !serialCommandExec
     }
 
     // Run all non-command tasks according to the threads

main/eval/src/mill/eval/EvaluatorImpl.scala

@@ -1,9 +1,10 @@
 package mill.eval
 
-import mill.api.Val
+import mill.api.{CompileProblemReporter, Strict, TestReporter, Val}
 import mill.api.Strict.Agg
 import mill.define._
 import mill.util._
+
 import scala.collection.mutable
 import scala.reflect.ClassTag
 
@@ -43,6 +44,18 @@ private[mill] case class EvaluatorImpl(
     Plan.plan(goals)
   }
 
+  override def evaluate(
+      goals: Strict.Agg[Task[_]],
+      reporter: Int => Option[CompileProblemReporter],
+      testReporter: TestReporter,
+      logger: ColorLogger,
+      serialCommandExec: Boolean
+  ): Evaluator.Results = {
+    // TODO: cleanup once we break bin-compat in Mill 0.13
+    // disambiguate override hierarchy
+    super.evaluate(goals, reporter, testReporter, logger, serialCommandExec)
+  }
+
   override def evalOrThrow(exceptionFactory: Evaluator.Results => Throwable)
       : Evaluator.EvalOrThrow =
     new EvalOrThrow(this, exceptionFactory)

main/src/mill/main/RunScript.scala

@@ -35,7 +35,7 @@ object RunScript {
       evaluator: Evaluator,
       targets: Agg[Task[Any]]
   ): (Seq[Watchable], Either[String, Seq[(Any, Option[(TaskName, ujson.Value)])]]) = {
-    val evaluated: Results = evaluator.evaluate(targets)
+    val evaluated: Results = evaluator.evaluate(targets, serialCommandExec = true)
 
     val watched = evaluated.results
       .iterator