improve handling of windows multiline prompt (#4053)

This generally tries to avoid clearing and re-rendering parts of the UI
unnecessarily, which which reduce flicker in slower terminals like
Windows

build.mill

@@ -576,6 +576,9 @@ trait MillStableScalaModule extends MillPublishScalaModule with Mima {
     ),
     ProblemFilter.exclude[Problem](
       "mill.scalalib.RunModule#RunnerImpl.*"
+    ),
+    ProblemFilter.exclude[Problem](
+      "mill.util.PromptLogger#*"
     )
   )
   def mimaPreviousVersions: T[Seq[String]] = Settings.mimaBaseVersions
@@ -691,7 +694,6 @@ implicit object DepSegment extends Cross.ToSegments[Dep]({ dep =>
  */
 object dummy extends Cross[DependencyFetchDummy](dummyDeps)
 trait DependencyFetchDummy extends ScalaModule with Cross.Module[Dep] {
-
   def scalaVersion = Deps.scalaVersion
   def compileIvyDeps = Agg(crossValue)
 }

dist/package.mill

@@ -224,8 +224,9 @@ object `package` extends RootModule with build.MillPublishJavaModule {
     )
   }
 
+  val batExt = if (scala.util.Properties.isWin) ".bat" else ""
   val DefaultLocalMillReleasePath =
-    s"target/mill-release${if (scala.util.Properties.isWin) ".bat" else ""}"
+    s"target/mill-release$batExt"
 
   /**
    * Build and install Mill locally.
@@ -240,7 +241,7 @@ object `package` extends RootModule with build.MillPublishJavaModule {
 
   def installLocalCache() = Task.Command {
     val path = installLocalTask(
-      Task.Anon((os.home / ".cache" / "mill" / "download" / build.millVersion()).toString())
+      Task.Anon((os.home / ".cache" / "mill" / "download" / (build.millVersion() + batExt)).toString())
     )()
     Task.log.outputStream.println(path.toString())
     PathRef(path)

main/client/src/mill/main/client/ProxyStream.java

@@ -120,7 +120,9 @@ public Pumper(InputStream src, OutputStream destOut, OutputStream destErr) {
 
     public void preRead(InputStream src) {}
 
-    public void preWrite(byte[] buffer, int length) {}
+    public void write(OutputStream dest, byte[] buffer, int length) throws IOException {
+      dest.write(buffer, 0, length);
+    }
 
     public void run() {
 
@@ -152,13 +154,12 @@ public void run() {
 
             if (delta != -1) {
               synchronized (synchronizer) {
-                this.preWrite(buffer, offset);
                 switch (stream) {
                   case ProxyStream.OUT:
-                    destOut.write(buffer, 0, offset);
+                    this.write(destOut, buffer, offset);
                     break;
                   case ProxyStream.ERR:
-                    destErr.write(buffer, 0, offset);
+                    this.write(destErr, buffer, offset);
                     break;
                 }
               }

main/util/src/mill/util/PromptLogger.scala

@@ -2,13 +2,7 @@ package mill.util
 
 import mill.api.SystemStreams
 import mill.main.client.ProxyStream
-import mill.util.PromptLoggerUtil.{
-  Status,
-  clearScreenToEndBytes,
-  defaultTermHeight,
-  defaultTermWidth,
-  renderPrompt
-}
+import mill.util.PromptLoggerUtil.{Status, defaultTermHeight, defaultTermWidth, renderPrompt}
 import pprint.Util.literalize
 
 import java.io._
@@ -90,8 +84,8 @@ private[mill] class PromptLogger(
   )
 
   def refreshPrompt(ending: Boolean = false): Unit = synchronized {
-    promptLineState.updatePrompt(ending)
-    streamManager.refreshPrompt()
+    val updated = promptLineState.updatePrompt(ending)
+    if (updated) streamManager.refreshPrompt()
   }
 
   if (enableTicker && autoUpdate) promptUpdaterThread.start()
@@ -289,16 +283,21 @@ private[mill] object PromptLogger {
         }
       }
 
-      override def preWrite(buf: Array[Byte], end: Int): Unit = {
-        // Before any write, make sure we clear the terminal of any prompt that was
-        // written earlier and not yet cleared, so the following output can be written
-        // to a clean section of the terminal
-
+      override def write(dest: OutputStream, buf: Array[Byte], end: Int): Unit = {
         lastCharWritten = buf(end - 1).toChar
         if (interactive() && !paused() && promptShown) {
-          systemStreams0.err.write(clearScreenToEndBytes)
           promptShown = false
         }
+
+        // Clear each line as they are drawn, rather than relying on clearing
+        // the entire screen before each batch of writes, to try and reduce the
+        // amount of terminal flickering in slow terminals (e.g. windows)
+        // https://stackoverflow.com/questions/71452837/how-to-reduce-flicker-in-terminal-re-drawing
+        dest.write(
+          new String(buf, 0, end)
+            .replaceAll("(\r\n|\n)", AnsiNav.clearLine(0) + "$1")
+            .getBytes
+        )
       }
     }
 
@@ -338,7 +337,7 @@ private[mill] object PromptLogger {
 
     def getCurrentPrompt() = currentPromptBytes
 
-    def updatePrompt(ending: Boolean = false): Unit = {
+    def updatePrompt(ending: Boolean = false): Boolean = {
       val now = currentTimeMillis()
       for (k <- statuses.keySet) {
         val removedTime = statuses(k).beginTransitionTime
@@ -367,8 +366,9 @@ private[mill] object PromptLogger {
         ending = ending
       )
 
+      val oldPromptBytes = currentPromptBytes
       currentPromptBytes = renderPromptWrapped(currentPromptLines, interactive, ending).getBytes
-
+      !java.util.Arrays.equals(oldPromptBytes, currentPromptBytes)
     }
 
     def clearStatuses(): Unit = { statuses.clear() }

main/util/src/mill/util/PromptLoggerUtil.scala

@@ -171,7 +171,9 @@ private object PromptLoggerUtil {
         if (ending) "\n"
         else AnsiNav.left(9999) + AnsiNav.up(currentPromptLines.length - 1)
 
-      AnsiNav.clearScreen(0) + currentPromptLines.mkString("\n") + backUp
+      currentPromptLines.map(_ + AnsiNav.clearLine(0)).mkString("\n") +
+        AnsiNav.clearScreen(0) +
+        backUp
     }
   }