Base multiversal equality on typeclass derivation

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

@@ -538,45 +538,6 @@ object desugar {
     if (isEnum)
       parents1 = parents1 :+ ref(defn.EnumType)
 
-    // The Eq instance for an Enum class. For an enum class
-    //
-    //    enum class C[T1, ..., Tn]
-    //
-    // we generate:
-    //
-    //    implicit def eqInstance[T1$1, ..., Tn$1, T1$2, ..., Tn$2](implicit
-    //      ev1: Eq[T1$1, T1$2], ..., evn: Eq[Tn$1, Tn$2]])
-    //      : Eq[C[T1$, ..., Tn$1], C[T1$2, ..., Tn$2]] = Eq
-    //
-    // Higher-kinded type arguments `Ti` are omitted as evidence parameters.
-    //
-    // FIXME: This is too simplistic. Instead of just generating evidence arguments
-    // for every first-kinded type parameter, we should look instead at the
-    // actual types occurring in cases and derive parameters from these. E.g. in
-    //
-    //    enum HK[F[_]] {
-    //      case C1(x: F[Int]) extends HK[F[Int]]
-    //      case C2(y: F[String]) extends HL[F[Int]]
-    //
-    // we would need evidence parameters for `F[Int]` and `F[String]`
-    // We should generate Eq instances with the techniques
-    // of typeclass derivation once that is available.
-    def eqInstance = {
-      val leftParams = constrTparams.map(derivedTypeParam(_, "$1"))
-      val rightParams = constrTparams.map(derivedTypeParam(_, "$2"))
-      val subInstances =
-        for ((param1, param2) <- leftParams `zip` rightParams if !isHK(param1))
-        yield appliedRef(ref(defn.EqType), List(param1, param2), widenHK = true)
-      DefDef(
-          name = nme.eqInstance,
-          tparams = leftParams ++ rightParams,
-          vparamss = if (subInstances.isEmpty) Nil else List(makeImplicitParameters(subInstances)),
-          tpt = appliedTypeTree(ref(defn.EqType),
-              appliedRef(classTycon, leftParams) :: appliedRef(classTycon, rightParams) :: Nil),
-          rhs = ref(defn.EqModule.termRef)).withFlags(Synthetic | Implicit)
-    }
-    def eqInstances = if (isEnum) eqInstance :: Nil else Nil
-
     // derived type classes of non-module classes go to their companions
     val (clsDerived, companionDerived) =
       if (mods.is(Module)) (impl.derived, Nil) else (Nil, impl.derived)
@@ -595,7 +556,7 @@ object desugar {
       mdefs
     }
 
-    val companionMembers = defaultGetters ::: eqInstances ::: enumCases
+    val companionMembers = defaultGetters ::: enumCases
 
     // The companion object definitions, if a companion is needed, Nil otherwise.
     // companion definitions include:
@@ -645,7 +606,7 @@ object desugar {
         }
         companionDefs(companionParent, applyMeths ::: unapplyMeth :: companionMembers)
       }
-      else if (companionMembers.nonEmpty || companionDerived.nonEmpty)
+      else if (companionMembers.nonEmpty || companionDerived.nonEmpty || isEnum)
         companionDefs(anyRef, companionMembers)
       else if (isValueClass) {
         impl.constr.vparamss match {

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

@@ -734,11 +734,11 @@ class Definitions {
   lazy val TastyReflectionModule: TermSymbol = ctx.requiredModule("scala.tasty.Reflection")
     lazy val TastyReflection_macroContext: TermSymbol = TastyReflectionModule.requiredMethod("macroContext")
 
-  lazy val EqType: TypeRef = ctx.requiredClassRef("scala.Eq")
-  def EqClass(implicit ctx: Context): ClassSymbol = EqType.symbol.asClass
-  def EqModule(implicit ctx: Context): Symbol = EqClass.companionModule
+  lazy val EqlType: TypeRef = ctx.requiredClassRef("scala.Eql")
+  def EqlClass(implicit ctx: Context): ClassSymbol = EqlType.symbol.asClass
+  def EqlModule(implicit ctx: Context): Symbol = EqlClass.companionModule
 
-    def Eq_eqAny(implicit ctx: Context): TermSymbol = EqModule.requiredMethod(nme.eqAny)
+    def Eql_eqlAny(implicit ctx: Context): TermSymbol = EqlModule.requiredMethod(nme.eqlAny)
 
   lazy val NotType: TypeRef = ctx.requiredClassRef("scala.implicits.Not")
   def NotClass(implicit ctx: Context): ClassSymbol = NotType.symbol.asClass

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

@@ -67,7 +67,7 @@ import collection.mutable.ListBuffer
  */
 object Denotations {
 
-  implicit def eqDenotation: Eq[Denotation, Denotation] = Eq
+  implicit def eqDenotation: Eql[Denotation, Denotation] = Eql.derived
 
   /** A PreDenotation represents a group of single denotations or a single multi-denotation
    *  It is used as an optimization to avoid forming MultiDenotations too eagerly.

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

@@ -52,6 +52,9 @@ object Mode {
   /** Allow GADTFlexType labelled types to have their bounds adjusted */
   val GADTflexible: Mode = newMode(8, "GADTflexible")
 
+  /** Assume -language:strictEquality */
+  val StrictEquality: Mode = newMode(9, "StrictEquality")
+
   /** We are currently printing something: avoid to produce more logs about
    *  the printing
    */

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

@@ -25,7 +25,7 @@ object Names {
     def toTermName: TermName
   }
 
-  implicit def eqName: Eq[Name, Name] = Eq
+  implicit def eqName: Eql[Name, Name] = Eql.derived
 
   /** A common superclass of Name and Symbol. After bootstrap, this should be
    *  just the type alias Name | Symbol

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

@@ -418,7 +418,7 @@ object StdNames {
     val equals_ : N             = "equals"
     val error: N                = "error"
     val eval: N                 = "eval"
-    val eqAny: N                = "eqAny"
+    val eqlAny: N               = "eqlAny"
     val ex: N                   = "ex"
     val experimental: N         = "experimental"
     val f: N                    = "f"

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

@@ -406,7 +406,7 @@ trait Symbols { this: Context =>
 
 object Symbols {
 
-  implicit def eqSymbol: Eq[Symbol, Symbol] = Eq
+  implicit def eqSymbol: Eql[Symbol, Symbol] = Eql.derived
 
   /** Tree attachment containing the identifiers in a tree as a sorted array */
   val Ids: Property.Key[Array[String]] = new Property.Key

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

@@ -40,7 +40,7 @@ object Types {
 
   @sharable private[this] var nextId = 0
 
-  implicit def eqType: Eq[Type, Type] = Eq
+  implicit def eqType: Eql[Type, Type] = Eql.derived
 
   /** Main class representing types.
    *

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

@@ -193,7 +193,7 @@ trait Deriving { this: Typer =>
           if (nparams == 0) Nil
           else if (nparams == 1) tparam :: Nil
           else typeClass.typeParams.map(tcparam =>
-            tparam.copy(name = s"${tparam.name}_${tcparam.name}".toTypeName)
+            tparam.copy(name = s"${tparam.name}_$$_${tcparam.name}".toTypeName)
               .asInstanceOf[TypeSymbol])
         }
         val firstKindedParamss = clsParamss.filter {

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

@@ -699,16 +699,65 @@ trait Implicits { self: Typer =>
       if (ctx.inInlineMethod || enclosingInlineds.nonEmpty) ref(defn.TastyReflection_macroContext)
       else EmptyTree
 
-    /** If `formal` is of the form Eq[T, U], where no `Eq` instance exists for
-     *  either `T` or `U`, synthesize `Eq.eqAny[T, U]` as solution.
+    /** If `formal` is of the form Eql[T, U], try to synthesize an
+     *  `Eql.eqlAny[T, U]` as solution.
      */
     def synthesizedEq(formal: Type)(implicit ctx: Context): Tree = {
-      //println(i"synth eq $formal / ${formal.argTypes}%, %")
+
+      /** Is there an `Eql[T, T]` instance, assuming -strictEquality? */
+      def hasEq(tp: Type)(implicit ctx: Context): Boolean = {
+        val inst = inferImplicitArg(defn.EqlType.appliedTo(tp, tp), span)
+        !inst.isEmpty && !inst.tpe.isError
+      }
+
+      /** Can we assume the eqlAny instance for `tp1`, `tp2`?
+       *  This is the case if assumedCanEqual(tp1, tp2), or
+       *  one of `tp1`, `tp2` has a reflexive `Eql` instance.
+       */
+      def validEqAnyArgs(tp1: Type, tp2: Type)(implicit ctx: Context) =
+        assumedCanEqual(tp1, tp2) || {
+          val nestedCtx = ctx.fresh.addMode(Mode.StrictEquality)
+          !hasEq(tp1)(nestedCtx) && !hasEq(tp2)(nestedCtx)
+        }
+
+      /** Is an `Eql[cls1, cls2]` instance assumed for predefined classes `cls1`, cls2`? */
+      def canComparePredefinedClasses(cls1: ClassSymbol, cls2: ClassSymbol): Boolean = {
+        def cmpWithBoxed(cls1: ClassSymbol, cls2: ClassSymbol) =
+          cls2 == defn.boxedType(cls1.typeRef).symbol ||
+          cls1.isNumericValueClass && cls2.derivesFrom(defn.BoxedNumberClass)
+
+        if (cls1.isPrimitiveValueClass)
+          if (cls2.isPrimitiveValueClass)
+            cls1 == cls2 || cls1.isNumericValueClass && cls2.isNumericValueClass
+          else
+            cmpWithBoxed(cls1, cls2)
+        else if (cls2.isPrimitiveValueClass)
+          cmpWithBoxed(cls2, cls1)
+        else if (cls1 == defn.NullClass)
+          cls1 == cls2 || cls2.derivesFrom(defn.ObjectClass)
+        else if (cls2 == defn.NullClass)
+          cls1.derivesFrom(defn.ObjectClass)
+        else
+          false
+      }
+
+      /** Some simulated `Eql` instances for predefined types. It's more efficient
+       *  to do this directly instead of setting up a lot of `Eql` instances to
+       *  interpret.
+       */
+      def canComparePredefined(tp1: Type, tp2: Type) =
+        tp1.classSymbols.exists(cls1 =>
+          tp2.classSymbols.exists(cls2 => canComparePredefinedClasses(cls1, cls2)))
+
       formal.argTypes match {
-        case args @ (arg1 :: arg2 :: Nil)
-        if !ctx.featureEnabled(defn.LanguageModuleClass, nme.strictEquality) &&
-           ctx.test(implicit ctx => validEqAnyArgs(arg1, arg2)) =>
-          ref(defn.Eq_eqAny).appliedToTypes(args).withSpan(span)
+        case args @ (arg1 :: arg2 :: Nil) =>
+          List(arg1, arg2).foreach(fullyDefinedType(_, "eq argument", span))
+          if (canComparePredefined(arg1, arg2)
+              ||
+              !strictEquality &&
+              ctx.test(implicit ctx => validEqAnyArgs(arg1, arg2)))
+            ref(defn.Eql_eqlAny).appliedToTypes(args).withSpan(span)
+          else EmptyTree
         case _ =>
           EmptyTree
       }
@@ -737,14 +786,6 @@ trait Implicits { self: Typer =>
       }
     }
 
-    def hasEq(tp: Type): Boolean =
-      inferImplicit(defn.EqType.appliedTo(tp, tp), EmptyTree, span).isSuccess
-
-    def validEqAnyArgs(tp1: Type, tp2: Type)(implicit ctx: Context) = {
-      List(tp1, tp2).foreach(fullyDefinedType(_, "eqAny argument", span))
-      assumedCanEqual(tp1, tp2) || !hasEq(tp1) && !hasEq(tp2)
-    }
-
     /** If `formal` is of the form `scala.reflect.Generic[T]` for some class type `T`,
      *  synthesize an instance for it.
      */
@@ -776,7 +817,7 @@ trait Implicits { self: Typer =>
             trySpecialCase(defn.QuotedTypeClass, synthesizedTypeTag,
               trySpecialCase(defn.GenericClass, synthesizedGeneric,
                 trySpecialCase(defn.TastyReflectionClass, synthesizedTastyContext,
-                  trySpecialCase(defn.EqClass, synthesizedEq,
+                  trySpecialCase(defn.EqlClass, synthesizedEq,
                     trySpecialCase(defn.ValueOfClass, synthesizedValueOf, failed))))))
     }
   }
@@ -885,16 +926,16 @@ trait Implicits { self: Typer =>
         em"parameter ${paramName} of $methodStr"
     }
 
-  private def assumedCanEqual(ltp: Type, rtp: Type)(implicit ctx: Context) = {
-    def eqNullable: Boolean = {
-      val other =
-        if (ltp.isRef(defn.NullClass)) rtp
-        else if (rtp.isRef(defn.NullClass)) ltp
-        else NoType
-
-      (other ne NoType) && !other.derivesFrom(defn.AnyValClass)
-    }
+  private def strictEquality(implicit ctx: Context): Boolean =
+    ctx.mode.is(Mode.StrictEquality) ||
+    ctx.featureEnabled(defn.LanguageModuleClass, nme.strictEquality)
 
+  /** An Eql[T, U] instance is assumed
+   *   - if one of T, U is an error type, or
+   *   - if one of T, U is a subtype of the lifted version of the other,
+   *     unless strict equality is set.
+   */
+  private def assumedCanEqual(ltp: Type, rtp: Type)(implicit ctx: Context) = {
     // Map all non-opaque abstract types to their upper bound.
     // This is done to check whether such types might plausibly be comparable to each other.
     val lift = new TypeMap {
@@ -910,14 +951,20 @@ trait Implicits { self: Typer =>
           if (variance > 0) mapOver(t) else t
       }
     }
-    ltp.isError || rtp.isError || ltp <:< lift(rtp) || rtp <:< lift(ltp) || eqNullable
+
+    ltp.isError ||
+    rtp.isError ||
+    !strictEquality && {
+      ltp <:< lift(rtp) ||
+      rtp <:< lift(ltp)
+    }
   }
 
   /** Check that equality tests between types `ltp` and `rtp` make sense */
   def checkCanEqual(ltp: Type, rtp: Type, span: Span)(implicit ctx: Context): Unit =
     if (!ctx.isAfterTyper && !assumedCanEqual(ltp, rtp)) {
-      val res = implicitArgTree(defn.EqType.appliedTo(ltp, rtp), span)
-      implicits.println(i"Eq witness found for $ltp / $rtp: $res: ${res.tpe}")
+      val res = implicitArgTree(defn.EqlType.appliedTo(ltp, rtp), span)
+      implicits.println(i"Eql witness found for $ltp / $rtp: $res: ${res.tpe}")
     }
 
   /** Find an implicit parameter or conversion.
@@ -985,7 +1032,7 @@ trait Implicits { self: Typer =>
       if (argument.isEmpty) f(resultType) else ViewProto(f(argument.tpe.widen), f(resultType))
         // Not clear whether we need to drop the `.widen` here. All tests pass with it in place, though.
 
-    private def isCoherent = pt.isRef(defn.EqClass)
+    private def isCoherent = pt.isRef(defn.EqlClass)
 
     private val cmpContext = nestedContext()
     private val cmpCandidates = (c1: Candidate, c2: Candidate) => compare(c1.ref, c2.ref, c1.level, c2.level)(cmpContext)

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

@@ -1029,7 +1029,7 @@ class Namer { typer: Typer =>
 
       if (impl.derived.nonEmpty) {
         val (derivingClass, derivePos) = original.removeAttachment(desugar.DerivingCompanion) match {
-          case Some(pos) => (cls.companionClass.asClass, pos)
+          case Some(pos) => (cls.companionClass.orElse(cls).asClass, pos)
           case None => (cls, impl.sourcePos.startPos)
         }
         val deriver = new Deriver(derivingClass, derivePos)(localCtx)

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

@@ -190,7 +190,7 @@ class SourceFile(val file: AbstractFile, computeContent: => Array[Char]) extends
   }
 }
 object SourceFile {
-  implicit def eqSource: Eq[SourceFile, SourceFile] = Eq
+  implicit def eqSource: Eql[SourceFile, SourceFile] = Eql.derived
 
   implicit def fromContext(implicit ctx: Context): SourceFile = ctx.source
 

compiler/test-resources/repl/i4184

@@ -2,8 +2,8 @@ scala> object foo { class Foo }
 // defined object foo
 scala> object bar { class Foo }
 // defined object bar
-scala> implicit def eqFoo: Eq[foo.Foo, foo.Foo] = Eq
-def eqFoo: Eq[foo.Foo, foo.Foo]
+scala> implicit def eqFoo: Eql[foo.Foo, foo.Foo] = Eql.derived
+def eqFoo: Eql[foo.Foo, foo.Foo]
 scala> object Bar { new foo.Foo == new bar.Foo }
 1 | object Bar { new foo.Foo == new bar.Foo }
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^