Disable selection execution for run that occurs when enter is pressed during watch (#4149)

No tests for now, since our integration test suite doesn't easily
support feeding stdin to the mill subprocess

Author: lihaoyi

runner/src/mill/runner/MillMain.scala

@@ -233,7 +233,7 @@ object MillMain {
                       watch = config.watch.value,
                       streams = streams,
                       setIdle = setIdle,
-                      evaluate = (prevState: Option[RunnerState]) => {
+                      evaluate = (enterKeyPressed: Boolean, prevState: Option[RunnerState]) => {
                         adjustJvmProperties(userSpecifiedProperties, initialSystemProperties)
 
                         withOutLock(
@@ -256,6 +256,9 @@ object MillMain {
                             colored = colored,
                             colors = colors
                           )) { logger =>
+                            // Enter key pressed, removing mill-selective-execution.json to
+                            // ensure all tasks re-run even though no inputs may have changed
+                            if (enterKeyPressed) os.remove(out / OutFiles.millSelectiveExecution)
                             SystemStreams.withStreams(logger.systemStreams) {
                               tailManager.withOutErr(logger.outputStream, logger.errorStream) {
                                 new MillBuildBootstrap(

runner/src/mill/runner/Watching.scala

@@ -20,12 +20,13 @@ object Watching {
       watch: Boolean,
       streams: SystemStreams,
       setIdle: Boolean => Unit,
-      evaluate: Option[T] => Result[T],
+      evaluate: (Boolean, Option[T]) => Result[T],
       colors: Colors
   ): (Boolean, T) = {
     var prevState: Option[T] = None
+    var enterKeyPressed = false
     while (true) {
-      val Result(watchables, errorOpt, result) = evaluate(prevState)
+      val Result(watchables, errorOpt, result) = evaluate(enterKeyPressed, prevState)
       prevState = Some(result)
       errorOpt.foreach(streams.err.println)
       if (ringBell) {
@@ -42,8 +43,9 @@ object Watching {
       }
 
       val alreadyStale = watchables.exists(!_.validate())
+      enterKeyPressed = false
       if (!alreadyStale) {
-        Watching.watchAndWait(streams, setIdle, streams.in, watchables, colors)
+        enterKeyPressed = Watching.watchAndWait(streams, setIdle, streams.in, watchables, colors)
       }
     }
     ???
@@ -55,7 +57,7 @@ object Watching {
       stdin: InputStream,
       watched: Seq[Watchable],
       colors: Colors
-  ): Unit = {
+  ): Boolean = {
     setIdle(true)
     val watchedPaths = watched.collect { case p: Watchable.Path => p.p.path }
     val watchedValues = watched.size - watchedPaths.size
@@ -68,21 +70,25 @@ object Watching {
       ).toString
     )
 
-    statWatchWait(watched, stdin)
+    val enterKeyPressed = statWatchWait(watched, stdin)
     setIdle(false)
+    enterKeyPressed
   }
 
-  def statWatchWait(watched: Seq[Watchable], stdin: InputStream): Unit = {
+  // Returns `true` if enter key is pressed to re-run tasks explicitly
+  def statWatchWait(watched: Seq[Watchable], stdin: InputStream): Boolean = {
     val buffer = new Array[Byte](4 * 1024)
 
-    @tailrec def statWatchWait0(): Unit = {
+    @tailrec def statWatchWait0(): Boolean = {
       if (watched.forall(_.validate())) {
-        if (lookForEnterKey()) ()
-        else {
+        if (lookForEnterKey()) {
+          mill.main.client.DebugLog.println("ENTER KEY DETECTED")
+          true
+        } else {
           Thread.sleep(100)
           statWatchWait0()
         }
-      }
+      } else false
     }
 
     @tailrec def lookForEnterKey(): Boolean = {