Move normalization and comparison logic to the E-Graph

Author: mbovel

compiler/src/dotty/tools/dotc/qualified_types/EGraph.scala

@@ -0,0 +1,106 @@
+package dotty.tools.dotc.qualified_types
+
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Hashable.Binders
+import dotty.tools.dotc.core.Names.Designator
+import dotty.tools.dotc.core.Names.Name
+import dotty.tools.dotc.core.StdNames.nme
+import dotty.tools.dotc.core.StdNames.tpnme
+import dotty.tools.dotc.core.Symbols.Symbol
+import dotty.tools.dotc.core.Types.{
+  CachedProxyType,
+  ConstantType,
+  MethodType,
+  NamedType,
+  NoPrefix,
+  SingletonType,
+  TermRef,
+  ThisType,
+  Type
+}
+
+// xs.forall(x == 2) <=> xs.forall(x == 2)
+
+enum ENode:
+  import ENode.*
+
+  case Atom(tp: SingletonType)
+  case New(clazz: ENode)
+  case Select(qual: ENode, member: Symbol)
+  case Apply(fn: ENode, args: List[ENode])
+  case OpApply(fn: ENode.Op, args: List[ENode])
+  case TypeApply(fn: ENode, args: List[Type])
+  case Lambda(paramTps: List[Type], retTp: Type, body: ENode)
+
+  override def toString(): String =
+    this match
+      case Atom(tp)             => typeToString(tp)
+      case New(clazz)           => s"new $clazz"
+      case Select(qual, member) => s"$qual.${designatorToString(member)}"
+      case Apply(fn, args)      => s"$fn(${args.mkString(", ")})"
+      case OpApply(op, args)    => s"(${args.mkString(op.operatorString())})"
+      case TypeApply(fn, args)  => s"$fn[${args.map(typeToString).mkString(", ")}]"
+      case Lambda(paramTps, retTp, body) =>
+        s"(${paramTps.map(typeToString).mkString(", ")}): ${{ typeToString(retTp) }} => $body"
+
+object ENode:
+  private def typeToString(tp: Type): String =
+    tp match
+      case tp: NamedType =>
+        val prefixString = if isEmptyPrefix(tp.prefix) then "" else typeToString(tp.prefix) + "."
+        prefixString + designatorToString(tp.designator)
+      case tp: ConstantType =>
+        tp.value.value.toString
+      case tp: ThisType =>
+        typeToString(tp.tref) + ".this"
+      case _ =>
+        tp.toString
+
+  private def isEmptyPrefix(tp: Type): Boolean =
+    tp match
+      case tp: NoPrefix.type =>
+        true
+      case tp: ThisType =>
+        tp.tref.designator match
+          case d: Symbol => d.lastKnownDenotation.name.toTermName == nme.EMPTY_PACKAGE
+          case _         => false
+      case _ => false
+
+  private def designatorToString(d: Designator): String =
+    d match
+      case d: Symbol => d.lastKnownDenotation.name.toString
+      case _         => d.toString
+
+  enum Op:
+    case IntSum
+    case IntProduct
+    case LongSum
+    case LongProduct
+    case Equal
+    case Not
+    case And
+    case Or
+    case LessThan
+
+    def operatorString(): String =
+      this match
+        case IntSum      => "+"
+        case IntProduct  => "*"
+        case LongSum     => "+"
+        case LongProduct => "*"
+        case Equal       => "=="
+        case Not         => "!"
+        case And         => "&&"
+        case Or          => "||"
+        case LessThan    => "<"
+
+  /** Reference to the argument of an [[ENode.Lambda]].
+   *
+   *  @param index 
+   *    Debruijn index of the argument, starting from 0
+   *  @param underyling
+   *    Underlying type of the argument
+   */
+  final case class ArgRefType(index: Int, underlying: Type) extends CachedProxyType, SingletonType:
+    override def underlying(using Context): Type = underlying
+    override def computeHash(bs: Binders): Int = doHash(bs, index, underlying)