Eliminate a hot closure in Reporter

Author: odersky

compiler/src/dotty/tools/dotc/reporting/Reporter.scala

@@ -31,8 +31,12 @@ object Reporter {
     def doReport(m: MessageContainer)(implicit ctx: Context): Unit = ()
     override def report(m: MessageContainer)(implicit ctx: Context): Unit = ()
   }
-}
 
+  type ErrorHandler = (MessageContainer, Context) => Unit
+
+  private val defaultIncompleteHandler: ErrorHandler =
+    (mc, ctx) => ctx.reporter.report(mc)(ctx)
+}
 
 trait Reporting { this: Context =>
 
@@ -138,6 +142,7 @@ trait Reporting { this: Context =>
  * error messages.
  */
 abstract class Reporter extends interfaces.ReporterResult {
+  import Reporter._
 
   /** Report a diagnostic */
   def doReport(m: MessageContainer)(implicit ctx: Context): Unit
@@ -155,8 +160,8 @@ abstract class Reporter extends interfaces.ReporterResult {
     finally _truncationOK = saved
   }
 
-  type ErrorHandler = MessageContainer => Context => Unit
-  private[this] var incompleteHandler: ErrorHandler = d => c => report(d)(c)
+  private[this] var incompleteHandler: ErrorHandler = defaultIncompleteHandler
+
   def withIncompleteHandler[T](handler: ErrorHandler)(op: => T): T = {
     val saved = incompleteHandler
     incompleteHandler = handler
@@ -204,7 +209,7 @@ abstract class Reporter extends interfaces.ReporterResult {
     }
 
   def incomplete(m: MessageContainer)(implicit ctx: Context): Unit =
-    incompleteHandler(m)(ctx)
+    incompleteHandler(m, ctx)
 
   /** Summary of warnings and errors */
   def summary: String = {

compiler/src/dotty/tools/repl/ParseResult.scala

@@ -157,7 +157,7 @@ object ParseResult {
       case _ => {
         val reporter = newStoreReporter
         var needsMore = false
-        reporter.withIncompleteHandler(_ => _ => needsMore = true) {
+        reporter.withIncompleteHandler((_, _) => needsMore = true) {
           parseStats(sourceCode)(ctx.fresh.setReporter(reporter))
           !reporter.hasErrors && needsMore
         }