Make mill show skip -j prefixes to ensure machine readability (#2884

)

This requires us add another method `Logger#rawOutputStream`, which the
various implementations forward without decorating with prefixes or
other things.

We cannot just use `SystemStreams.original` because when running Mill in
client/server mode we still need to use the `OutputStream` that gets
forwarded from server to client, as the `SystemStreams.original.out`
just ends up forwarded to `out/mill-worker-hash-1/stdout` files that
aren't surfaced to users

Tested manually with `./mill -i dev.run tmp -i -j 2 show foo` on an
example build in the `tmp/` folder. Previously it would show the output
of `show` with a prefix e.g. `[#0] "bar"`, after this PR it shows the
output without any prefixes `"bar"`

`Logger#rawOutputStream` has to be a non-abstract method for binary
compatibility. This makes it a bit error prone since you can easily
forget to override it where necessary. So I first made it abstract, made
sure everyone overrides it, and then added the default case.

Pull request: #2884

bsp/src/mill/bsp/BspContext.scala

@@ -56,7 +56,10 @@ private[mill] class BspContext(
       override def error(s: String): Unit = streams.err.println(s)
       override def ticker(s: String): Unit = streams.err.println(s)
       override def debug(s: String): Unit = streams.err.println(s)
+
       override def debugEnabled: Boolean = true
+
+      override def rawOutputStream: PrintStream = systemStreams.out
     }
 
     BspWorker(os.pwd, home, log).flatMap { worker =>

main/api/src/mill/api/Logger.scala

@@ -31,6 +31,14 @@ trait Logger {
 
   def errorStream: PrintStream = systemStreams.err
   def outputStream: PrintStream = systemStreams.out
+
+  /**
+   * [[rawOutputStream]] is intended to be a version of [[outputStream]]
+   * without decoration: colors, prefixes, timestamps, etc. It is intended
+   * for the use of tasks like `show` which output data in a way that is
+   * easily readable by downstream programs.
+   */
+  def rawOutputStream: PrintStream = systemStreams.out
   def inStream: InputStream = systemStreams.in
 
   def info(s: String): Unit

main/eval/src/mill/eval/GroupEvaluator.scala

@@ -7,6 +7,7 @@ import mill.define._
 import mill.eval.Evaluator.TaskResult
 import mill.util._
 
+import java.io.PrintStream
 import scala.collection.mutable
 import scala.reflect.NameTransformer.{encode, decode}
 import scala.util.DynamicVariable
@@ -274,6 +275,8 @@ private[mill] trait GroupEvaluator {
           if (enableTicker) super.ticker(tickerPrefix.getOrElse("") + s)
           else () // do nothing
         }
+
+        override def rawOutputStream: PrintStream = logger.rawOutputStream
       }
       // This is used to track the usage of `T.dest` in more than one Task
       // But it's not really clear what issue we try to prevent here

main/src/mill/main/MainModule.scala

@@ -50,7 +50,7 @@ object MainModule {
       case Right((watched, Right(res))) =>
         val output = f(res)
         watched.foreach(watch0)
-        log.outputStream.println(output.render(indent = 2))
+        log.rawOutputStream.println(output.render(indent = 2))
         Result.Success(output)
     }
   }

main/util/src/mill/util/DummyLogger.scala

@@ -12,6 +12,7 @@ object DummyLogger extends Logger {
     new PrintStream(_ => ()),
     new ByteArrayInputStream(Array())
   )
+  override def rawOutputStream = systemStreams.out
 
   def info(s: String) = ()
   def error(s: String) = ()

main/util/src/mill/util/FileLogger.scala

@@ -52,4 +52,6 @@ class FileLogger(
     if (outputStreamUsed)
       outputStream.close()
   }
+
+  override def rawOutputStream: PrintStream = outputStream
 }

main/util/src/mill/util/MultiLogger.scala

@@ -40,6 +40,8 @@ class MultiLogger(
     logger1.close()
     logger2.close()
   }
+
+  override def rawOutputStream: PrintStream = systemStreams.out
 }
 
 class MultiStream(stream1: OutputStream, stream2: OutputStream)

main/util/src/mill/util/PrefixLogger.scala

@@ -36,6 +36,8 @@ class PrefixLogger(
     logger0.systemStreams.in
   )
 
+  override def rawOutputStream = logger0.rawOutputStream
+
   override def info(s: String): Unit = logger0.info(context + s)
   override def error(s: String): Unit = logger0.error(context + s)
   override def ticker(s: String): Unit = logger0.ticker(context + tickerContext + s)

main/util/src/mill/util/PrintLogger.scala

@@ -76,6 +76,8 @@ class PrintLogger(
       systemStreams.err.println(context + s)
     }
   }
+
+  override def rawOutputStream: PrintStream = systemStreams.out
 }
 
 object PrintLogger {

main/util/src/mill/util/ProxyLogger.scala

@@ -2,6 +2,8 @@ package mill.util
 
 import mill.api.Logger
 
+import java.io.PrintStream
+
 /**
  * A Logger that forwards all logging to another Logger.  Intended to be
  * used as a base class for wrappers that modify logging behavior.
@@ -19,4 +21,6 @@ class ProxyLogger(logger: Logger) extends Logger {
   override def debugEnabled: Boolean = logger.debugEnabled
 
   override def close() = logger.close()
+
+  override def rawOutputStream: PrintStream = logger.rawOutputStream
 }