Fix identityHash for BindingTypes

Author: odersky

compiler/src/dotty/tools/dotc/core/Hashable.scala

@@ -7,9 +7,8 @@ import annotation.tailrec
 
 object Hashable {
 
-  class Binders(tp: BindingType, next: Binders) {
-    val hash: Int = if (next == null) 31 else next.hash * 41 + 31
-  }
+  class Binders(val tp: BindingType, val next: Binders)
+
   class BinderPairs(tp1: BindingType, tp2: BindingType, next: BinderPairs) {
     @tailrec final def matches(t1: Type, t2: Type): Boolean =
       (t1 `eq` tp1) && (t2 `eq` tp2) || next != null && next.matches(t1, t2)
@@ -107,7 +106,7 @@ trait Hashable {
     if (elemHash == NotCached) NotCached
     else avoidSpecialHashes(elemHash + delta)
 
-  private def avoidSpecialHashes(h: Int) =
+  protected def avoidSpecialHashes(h: Int) =
     if (h == NotCached) NotCachedAlt
     else if (h == HashUnknown) HashUnknownAlt
     else h

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1528,8 +1528,15 @@ object Types {
    */
   trait BindingType extends Type {
 
-    override def identityHash(bs: Binders) =
-      if (bs == null) super.identityHash(bs) else bs.hash
+    override def identityHash(bs: Binders) = {
+       def recur(n: Int, tp: BindingType, rest: Binders): Int =
+        if (this `eq` tp) finishHash(hashing.mix(hashSeed, n), 1)
+        else if (rest == null) System.identityHashCode(this)
+        else recur(n + 1, rest.tp, rest.next)
+      avoidSpecialHashes(
+        if (bs == null) System.identityHashCode(this)
+        else recur(1, bs.tp, bs.next))
+    }
 
     def equalBinder(that: BindingType, bs: BinderPairs): Boolean =
       (this `eq` that) || bs != null && bs.matches(this, that)