Add a `dotty-interfaces` package

We introduce a new entry point for the compiler in
`dotty.tools.dotc.Driver`:
```
def process(args: Array[String], simple: interfaces.SimpleReporter,
  callback: interfaces.CompilerCallback): interfaces.ReporterResult
```
Except for `args` which is just an array, the argument types and return
type of this method are Java interfaces defined in a new package called
`dotty-interfaces` which has a stable ABI. This means that you can
programmatically run a compiler with a custom reporter and callbacks
without having to recompile it against every version of dotty: you only
need to have `dotty-interfaces` present at compile-time and call the
`process` method using Java reflection.

See `test/test/InterfaceEntryPointTest.scala` for a concrete example.

This design is based on discussions with the IntelliJ IDEA Scala plugin
team. Thanks to Nikolay Tropin for the discussions and his PR
proposal (see #1011).

1 files changed, 12 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/reporting/Reporter.scala b/src/dotty/tools/dotc/reporting/Reporter.scala
index f4eb551a1..8236f93ef 100644
--- a/src/dotty/tools/dotc/reporting/Reporter.scala
+++ b/src/dotty/tools/dotc/reporting/Reporter.scala
@@ -11,7 +11,7 @@ import config.Settings.Setting
 import config.Printers
 import java.lang.System.currentTimeMillis
 import typer.Mode
-import Diagnostic.{ERROR, WARNING, INFO}
+import interfaces.Diagnostic.{ERROR, WARNING, INFO}
 
 object Reporter {
   class Error(msgFn: => String, pos: SourcePosition) extends Diagnostic(msgFn, pos, ERROR)
@@ -33,6 +33,16 @@ object Reporter {
   class MigrationWarning(msgFn: => String, pos: SourcePosition) extends ConditionalWarning(msgFn, pos) {
     def enablingOption(implicit ctx: Context) = ctx.settings.migration
   }
+
+  /** Convert a SimpleReporter into a real Reporter */
+  def fromSimpleReporter(simple: interfaces.SimpleReporter): Reporter =
+    new Reporter with UniqueMessagePositions with HideNonSensicalMessages {
+      override def doReport(d: Diagnostic)(implicit ctx: Context): Unit = d match {
+        case d: ConditionalWarning if !d.enablingOption.value =>
+        case _ =>
+          simple.report(d)
+      }
+    }
 }
 
 import Reporter._
@@ -157,7 +167,7 @@ trait Reporting { this: Context =>
  * This interface provides methods to issue information, warning and
  * error messages.
  */
-abstract class Reporter {
+abstract class Reporter extends interfaces.ReporterResult {
 
   /** Report a diagnostic */
   def doReport(d: Diagnostic)(implicit ctx: Context): Unit