Compare sourcefiles structurally

Avoid using `eq` for comparing sourcefiles. Optimize `equals`
with a fastpath for identical sourcefiles instead.

Author: odersky

compiler/src/dotty/tools/dotc/ast/Positioned.scala

@@ -75,7 +75,7 @@ abstract class Positioned(implicit @transientParam src: SourceFile) extends Prod
     case _ =>
       def include(span: Span, x: Any): Span = x match {
         case p: Positioned =>
-          if (p.source `ne` src) span
+          if (p.source != src) span
           else if (p.span.exists) span.union(p.span)
           else if (span.exists) {
             if (span.end != MaxOffset)

compiler/src/dotty/tools/dotc/core/tasty/PositionPickler.scala

@@ -72,7 +72,7 @@ class PositionPickler(pickler: TastyPickler, addrOfTree: untpd.Tree => Option[Ad
     def traverse(x: Any, current: SourceFile): Unit = x match {
       case x: untpd.Tree =>
         if (x.span.exists) {
-          val sourceChange = x.source `ne` current
+          val sourceChange = x.source != current
           val needsPos = x.span.toSynthetic != x.envelope(x.source) || alwaysNeedsPos(x)
           addrOfTree(x) match {
             case Some(addr)

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -228,7 +228,7 @@ class Typer extends Namer
        */
       def isDefinedInCurrentUnit(denot: Denotation)(implicit ctx: Context): Boolean = denot match {
         case MultiDenotation(d1, d2) => isDefinedInCurrentUnit(d1) || isDefinedInCurrentUnit(d2)
-        case denot: SingleDenotation => denot.symbol.source `eq` ctx.compilationUnit.source
+        case denot: SingleDenotation => denot.symbol.source == ctx.compilationUnit.source
       }
 
       /** Is `denot` the denotation of a self symbol? */

compiler/src/dotty/tools/dotc/util/SourceFile.scala

@@ -60,10 +60,14 @@ class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends
 
   def pathName: PathName = file.absolutePath.toTermName
 
-  override def equals(that : Any): Boolean = that match {
-    case that : SourceFile => file == that.file && start == that.start
-    case _ => false
-  }
+  override def equals(that: Any): Boolean =
+    (this `eq` that.asInstanceOf[AnyRef]) || {
+      that match {
+        case that : SourceFile => file == that.file && start == that.start
+        case _ => false
+      }
+    }
+
   override def hashCode: Int = file.hashCode * 41 + start.hashCode
 
   def apply(idx: Int): Char = content().apply(idx)