fix some errors

Author: noti0na1

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

@@ -12,7 +12,9 @@ import scala.annotation.tailrec
 
 class Uniques extends WeakHashSet[Type](Config.initialUniquesCapacity):
   override def hash(x: Type): Int = x.hash
-  override def isEqual(x: Type, y: Type) = x.eql(y)
+  override def isEqual(x: Type | Null, y: Type | Null) =
+    if x == null then y == null
+    else y != null && x.eql(y)
 
 /** Defines operation `unique` for hash-consing types.
  *  Also defines specialized hash sets for hash consing uniques of a specific type.

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

@@ -9,6 +9,8 @@ import java.lang.ref.{ReferenceQueue, WeakReference}
 import scala.annotation.{ constructorOnly, tailrec }
 import scala.collection.mutable
 
+import dotty.tools.uncheckedNN
+
 /**
  * A HashSet where the elements are stored weakly. Elements in this set are eligible for GC if no other
  * hard references are associated with them. Its primary use case is as a canonical reference
@@ -61,7 +63,7 @@ abstract class WeakHashSet[A <: AnyRef](initialCapacity: Int = 8, loadFactor: Do
 
   private def computeThreshold: Int = (table.size * loadFactor).ceil.toInt
 
-  protected def hash(key: A | Null): Int
+  protected def hash(key: A): Int
   protected def isEqual(x: A | Null, y: A | Null): Boolean =
     if x == null then y == null else x.equals(y)
 
@@ -149,7 +151,7 @@ abstract class WeakHashSet[A <: AnyRef](initialCapacity: Int = 8, loadFactor: Do
       case null                    => null
       case _                       =>
         val entryElem = entry.get
-        if (isEqual(elem, entryElem.asInstanceOf[A])) entryElem
+        if (isEqual(elem, entryElem)) entryElem
         else linkedListLoop(entry.tail)
     }
 
@@ -165,8 +167,6 @@ abstract class WeakHashSet[A <: AnyRef](initialCapacity: Int = 8, loadFactor: Do
   }
 
   def put(elem: A): A = {
-    // case null => throw new NullPointerException("WeakHashSet cannot hold nulls")
-    // case _    =>
     Stats.record(statsItem("put"))
     removeStaleEntries()
     val h = hash(elem)
@@ -177,8 +177,8 @@ abstract class WeakHashSet[A <: AnyRef](initialCapacity: Int = 8, loadFactor: Do
     def linkedListLoop(entry: Entry[A] | Null): A = entry match {
       case null                    => addEntryAt(bucket, elem, h, oldHead)
       case _                       =>
-        val entryElem = entry.get.asInstanceOf[A]
-        if (isEqual(elem, entryElem)) entryElem
+        val entryElem = entry.get
+        if (isEqual(elem, entryElem)) entryElem.uncheckedNN
         else linkedListLoop(entry.tail)
     }
 
@@ -294,7 +294,7 @@ abstract class WeakHashSet[A <: AnyRef](initialCapacity: Int = 8, loadFactor: Do
           assert(entry.get != null, s"$entry had a null value indicated that gc activity was happening during diagnostic validation or that a null value was inserted")
           computedCount += 1
           val cachedHash = entry.hash
-          val realHash = hash(entry.get)
+          val realHash = hash(entry.get.uncheckedNN)
           assert(cachedHash == realHash, s"for $entry cached hash was $cachedHash but should have been $realHash")
           val computedBucket = index(realHash)
           assert(computedBucket == bucket, s"for $entry the computed bucket was $computedBucket but should have been $bucket")