From 868a6a1025781eeac3eb884040639119542b3f49 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 3 Apr 2017 17:35:21 +0200
Subject: Make extension method names semantic

---
 compiler/src/dotty/tools/dotc/core/NameKinds.scala | 33 ++++++++++++++++------
 .../dotty/tools/dotc/core/tasty/TastyFormat.scala  |  1 +
 .../tools/dotc/transform/ExtensionMethods.scala    |  5 ++--
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/NameKinds.scala b/compiler/src/dotty/tools/dotc/core/NameKinds.scala
index 8ea19bed2..cda6e0c83 100644
--- a/compiler/src/dotty/tools/dotc/core/NameKinds.scala
+++ b/compiler/src/dotty/tools/dotc/core/NameKinds.scala
@@ -132,6 +132,13 @@ object NameKinds {
       case DerivedTermName(underlying, info: this.NumberedInfo) => Some((underlying, info.num))
       case _ => None
     }
+    protected def skipSeparatorAndNum(name: SimpleTermName, separator: String): Int = {
+      var i = name.length
+      while (i > 0 && name(i - 1).isDigit) i -= 1
+      if (i > separator.length && i < name.length &&
+          name.slice(i - separator.length, i).toString == separator) i
+      else -1
+    }
   }
 
   case class UniqueNameKind(val separator: String)
@@ -205,6 +212,18 @@ object NameKinds {
   val SkolemName              = new UniqueNameKind("?")
   val LiftedTreeName          = new UniqueNameKind("liftedTree")
 
+  val UniqueExtMethName = new UniqueNameKind("$extension") {
+    override def unmangle(name: SimpleTermName): TermName = {
+      val i = skipSeparatorAndNum(name, separator)
+      if (i > 0) {
+        val index = name.drop(i).toString.toInt
+        var original = name.take(i - separator.length).asTermName
+        apply(original, index)
+      }
+      else name
+    }
+  }
+
   val PatMatStdBinderName     = new UniqueNameKind("x")
   val PatMatPiName            = new UniqueNameKind("pi") // FIXME: explain what this is
   val PatMatPName             = new UniqueNameKind("p")  // FIXME: explain what this is
@@ -218,15 +237,12 @@ object NameKinds {
       val prefix = if (underlying.isConstructorName) nme.DEFAULT_GETTER_INIT else underlying
       prefix.toString + str.DEFAULT_GETTER + (info.num + 1)
     }
-
-    private val dgLen = str.DEFAULT_GETTER.length
-
+    // TODO: Reduce code duplication with UniqueExtMethName
     override def unmangle(name: SimpleTermName): TermName = {
-      var i = name.length
-      while (i > 0 && name(i - 1).isDigit) i -= 1
-      if (i > dgLen && i < name.length && name.slice(i - dgLen, i) == nme.DEFAULT_GETTER) {
+      val i = skipSeparatorAndNum(name, str.DEFAULT_GETTER)
+      if (i > 0) {
         val index = name.drop(i).toString.toInt - 1
-        var original = name.take(i - dgLen).asTermName
+        var original = name.take(i - str.DEFAULT_GETTER.length).asTermName
         if (original == nme.DEFAULT_GETTER_INIT) original = Names.CONSTRUCTOR
         apply(original, index)
       }
@@ -260,6 +276,7 @@ object NameKinds {
   val AvoidClashName = new SuffixNameKind(AVOIDCLASH, "$_avoid_name_clash_$")
   val DirectName = new SuffixNameKind(DIRECT, "$direct")
   val FieldName = new SuffixNameKind(FIELD, "$$local")
+  val ExtMethName = new SuffixNameKind(EXTMETH, "$extension")
   val ModuleVarName = new SuffixNameKind(OBJECTVAR, "$module")
   val ModuleClassName = new SuffixNameKind(OBJECTCLASS, "$", optInfoString = "ModuleClass")
 
@@ -283,7 +300,7 @@ object NameKinds {
   }
 
   val Scala2MethodNameKinds: List[NameKind] =
-    List(DefaultGetterName, ProtectedAccessorName, ProtectedSetterName)
+    List(DefaultGetterName, ExtMethName, UniqueExtMethName, ProtectedAccessorName, ProtectedSetterName)
 
   def simpleNameKindOfTag      : collection.Map[Int, ClassifiedNameKind] = simpleNameKinds
   def qualifiedNameKindOfTag   : collection.Map[Int, QualifiedNameKind]  = qualifiedNameKinds
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
index 68c5bf10e..f03e279c6 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
@@ -240,6 +240,7 @@ object TastyFormat {
   final val DIRECT = 31
   final val FIELD = 32
   final val SETTER = 33
+  final val EXTMETH = 34
   final val OBJECTVAR = 39
   final val OBJECTCLASS = 40
 
diff --git a/compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala b/compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala
index 64474cecd..61f32edae 100644
--- a/compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala
@@ -16,6 +16,7 @@ import Types._, Contexts._, Constants._, Names._, NameOps._, Flags._, DenotTrans
 import SymDenotations._, Symbols._, StdNames._, Annotations._, Trees._, Scopes._, Denotations._
 import TypeErasure.{ valueErasure, ErasedValueType }
 import TypeUtils._
+import NameKinds.{ExtMethName, UniqueExtMethName}
 import util.Positions._
 import Decorators._
 import SymUtils._
@@ -206,11 +207,11 @@ object ExtensionMethods {
         val alts = decl.alternatives
         val index = alts indexOf imeth.denot
         assert(index >= 0, alts + " does not contain " + imeth)
-        def altName(index: Int) = (imeth.name + "$extension" + index).toTermName
+        def altName(index: Int) = UniqueExtMethName(imeth.name.asTermName, index)
         altName(index) #:: ((0 until alts.length).toStream filter (index != _) map altName)
       case decl =>
         assert(decl.exists, imeth.name + " not found in " + imeth.owner + "'s decls: " + imeth.owner.info.decls)
-        Stream((imeth.name + "$extension").toTermName)
+        Stream(ExtMethName(imeth.name.asTermName))
     }
   }
 
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