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, 1 insertions, 0 deletions

diff --git a/build.sbt b/build.sbt
index 553c217d4a..76d66481d0 100644
--- a/build.sbt
+++ b/build.sbt
@@ -191,6 +191,7 @@ lazy val interactive = configureAsSubproject(project)
   .settings(disableDocsAndPublishingTasks: _*)
   .dependsOn(compiler)
 
+// TODO: SI-9339 embed shaded copy of jline & its interface (see #4563)
 lazy val repl = configureAsSubproject(project)
   .settings(libraryDependencies += jlineDep)
   .settings(disableDocsAndPublishingTasks: _*)