SI-9339 Support classpaths with no single compatible jline

As usual, the repl will use whatever jline 2 jar on the classpath,
if there is one. Failing that, there's a fallback and an override.

If instantiating the standard `jline.InteractiveReader` fails,
we fall back to an embedded, shaded, version of jline,
provided by `jline_embedded.InteractiveReader`.

(Assume `import scala.tools.nsc.interpreter._` for this message.)

The instantiation of `InteractiveReader` eagerly exercises jline,
so that a linkage error will result if jline is missing or if the
provided one is not binary compatible.

The property `scala.repl.reader` overrides this behavior, if set to
the FQN of a class that looks like `YourInteractiveReader` below.

```
class YourInteractiveReader(completer: () => Completion) extends InteractiveReader
```

The repl logs which classes it tried to instantiate under `-Ydebug`.

 # Changes to source & build

The core of the repl (`src/repl`) no longer depends on jline.
The jline interface is now in `src/repl-jline`.

The embedded jline + our interface to it are generated by the `quick.repl` target.
The build now also enforces that only `src/repl-jline` depends on jline.
The sources in `src/repl` are now sure to be independent of it,
though they do use reflection to instantiate a suitable subclass
of `InteractiveReader`, as explained above.

The `quick.repl` target builds the sources in `src/repl` and `src/repl-jline`,
producing a jar for the `repl-jline` classes, which is then transformed using
jarjar to obtain a shaded copy of the `scala.tools.nsc.interpreter.jline` package.

Jarjar is used to combine the `jline` jar and the `repl-jline` into a new jar,
rewriting package names as follows:
  - `org.fusesource` -> `scala.tools.fusesource_embedded`
  - `jline` -> `scala.tools.jline_embedded`
  - `scala.tools.nsc.interpreter.jline` -> `scala.tools.nsc.interpreter.jline_embedded`

Classes not reachable from `scala.tools.**` are pruned, as well as empty dirs.

The classes in the `repl-jline` jar as well as those in the rewritten one
are copied to the repl's output directory.

PS: The sbt build is not updated, sorry.
PPS: A more recent fork of jarjar: https://github.com/shevek/jarjar.

1 files changed, 30 insertions, 10 deletions

diff --git a/src/repl/scala/tools/nsc/interpreter/ILoop.scala b/src/repl/scala/tools/nsc/interpreter/ILoop.scala
index 3ce9668b97..a3047ccc8e 100644
--- a/src/repl/scala/tools/nsc/interpreter/ILoop.scala
+++ b/src/repl/scala/tools/nsc/interpreter/ILoop.scala
@@ -26,6 +26,8 @@ import scala.concurrent.{ ExecutionContext, Await, Future, future }
 import ExecutionContext.Implicits._
 import java.io.{ BufferedReader, FileReader }
 
+import scala.util.{Try, Success, Failure}
+
 /** The Scala interactive shell.  It provides a read-eval-print loop
  *  around the Interpreter class.
  *  After instantiation, clients should call the main() method.
@@ -860,18 +862,36 @@ class ILoop(in0: Option[BufferedReader], protected val out: JPrintWriter)
    *  with SimpleReader.
    */
   def chooseReader(settings: Settings): InteractiveReader = {
-    def mkJLineReader(completer: () => Completion): InteractiveReader =
-      try new jline.JLineReader(completer)
-      catch {
-        case ex@(_: Exception | _: NoClassDefFoundError) =>
-          Console.println(f"Failed to created JLineReader: ${ex}%nFalling back to SimpleReader.")
-          SimpleReader()
-      }
-
     if (settings.Xnojline || Properties.isEmacsShell) SimpleReader()
     else {
-      if (settings.noCompletion) mkJLineReader(() => NoCompletion)
-      else mkJLineReader(() => new JLineCompletion(intp))
+      type Completer = () => Completion
+      type ReaderMaker = Completer => InteractiveReader
+
+      def instantiate(className: String): ReaderMaker = completer => {
+        if (settings.debug) Console.println(s"Trying to instantiate a InteractiveReader from $className")
+        Class.forName(className).getConstructor(classOf[Completer]).
+          newInstance(completer).
+          asInstanceOf[InteractiveReader]
+      }
+
+      def mkReader(maker: ReaderMaker) =
+        if (settings.noCompletion) maker(() => NoCompletion)
+        else maker(() => new JLineCompletion(intp)) // JLineCompletion is a misnomer -- it's not tied to jline
+
+      def internalClass(kind: String) = s"scala.tools.nsc.interpreter.$kind.InteractiveReader"
+      val readerClasses = sys.props.get("scala.repl.reader").toStream ++ Stream(internalClass("jline"), internalClass("jline_embedded"))
+      val readers = readerClasses map (cls => Try { mkReader(instantiate(cls)) })
+
+      val reader = (readers collect { case Success(reader) => reader } headOption) getOrElse SimpleReader()
+
+      if (settings.debug) {
+        val readerDiags = (readerClasses, readers).zipped map {
+          case (cls, Failure(e)) => s"  - $cls --> " + e.getStackTrace.mkString(e.toString+"\n\t", "\n\t","\n")
+          case (cls, Success(_)) => s"  - $cls OK"
+        }
+        Console.println(s"All InteractiveReaders tried: ${readerDiags.mkString("\n","\n","\n")}")
+      }
+      reader
     }
   }