Merge pull request #2552 from dotty-staging/add-enum-eq

Add Enum Eq

Author: felixmulder

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

@@ -72,9 +72,12 @@ object desugar {
             val defctx = ctx.outersIterator.dropWhile(_.scope eq ctx.scope).next
             var local = defctx.denotNamed(tp.name).suchThat(_ is ParamOrAccessor).symbol
             if (local.exists) (defctx.owner.thisType select local).dealias
-            else throw new java.lang.Error(
-              s"no matching symbol for ${tp.symbol.showLocated} in ${defctx.owner} / ${defctx.effectiveScope}"
-            )
+            else {
+              def msg =
+                s"no matching symbol for ${tp.symbol.showLocated} in ${defctx.owner} / ${defctx.effectiveScope}"
+              if (ctx.reporter.errorsReported) new ErrorType(msg)
+              else throw new java.lang.Error(msg)
+            }
           case _ =>
             mapOver(tp)
         }
@@ -124,7 +127,7 @@ object desugar {
     else vdef
   }
 
-  def makeImplicitParameters(tpts: List[Tree], forPrimaryConstructor: Boolean)(implicit ctx: Context) =
+  def makeImplicitParameters(tpts: List[Tree], forPrimaryConstructor: Boolean = false)(implicit ctx: Context) =
     for (tpt <- tpts) yield {
        val paramFlags: FlagSet = if (forPrimaryConstructor) PrivateLocalParamAccessor else Param
        val epname = EvidenceParamName.fresh()
@@ -265,7 +268,7 @@ object desugar {
     val mods = cdef.mods
     val companionMods = mods
         .withFlags((mods.flags & AccessFlags).toCommonFlags)
-        .withMods(mods.mods.filter(!_.isInstanceOf[Mod.EnumCase]))
+        .withMods(Nil)
 
     val (constr1, defaultGetters) = defDef(constr0, isPrimaryConstructor = true) match {
       case meth: DefDef => (meth, Nil)
@@ -291,7 +294,7 @@ object desugar {
 
     val isCaseClass  = mods.is(Case) && !mods.is(Module)
     val isCaseObject = mods.is(Case) && mods.is(Module)
-    val isEnum = mods.hasMod[Mod.Enum]
+    val isEnum = mods.hasMod[Mod.Enum] && !mods.is(Module)
     val isEnumCase = isLegalEnumCase(cdef)
     val isValueClass = parents.nonEmpty && isAnyVal(parents.head)
       // This is not watertight, but `extends AnyVal` will be replaced by `inline` later.
@@ -326,10 +329,12 @@ object desugar {
 
     val classTycon: Tree = new TypeRefTree // watching is set at end of method
 
-    def appliedRef(tycon: Tree) =
-      (if (constrTparams.isEmpty) tycon
-       else AppliedTypeTree(tycon, constrTparams map refOfDef))
-       .withPos(cdef.pos.startPos)
+    def appliedTypeTree(tycon: Tree, args: List[Tree]) =
+      (if (args.isEmpty) tycon else AppliedTypeTree(tycon, args))
+        .withPos(cdef.pos.startPos)
+
+    def appliedRef(tycon: Tree, tparams: List[TypeDef] = constrTparams) =
+      appliedTypeTree(tycon, tparams map refOfDef)
 
     // a reference to the class type bound by `cdef`, with type parameters coming from the constructor
     val classTypeRef = appliedRef(classTycon)
@@ -344,8 +349,7 @@ object desugar {
         else {
           ctx.error(i"explicit extends clause needed because type parameters of case and enum class differ"
               , cdef.pos.startPos)
-          AppliedTypeTree(enumClassRef, constrTparams map (_ => anyRef))
-            .withPos(cdef.pos.startPos)
+          appliedTypeTree(enumClassRef, constrTparams map (_ => anyRef))
         }
       case _ =>
         enumClassRef
@@ -411,6 +415,31 @@ 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$1, ..., Tn$1], C[T1$2, ..., Tn$2]] = Eq
+    def eqInstance = {
+      def append(tdef: TypeDef, str: String) = cpy.TypeDef(tdef)(name = tdef.name ++ str)
+      val leftParams = derivedTparams.map(append(_, "$1"))
+      val rightParams = derivedTparams.map(append(_, "$2"))
+      val subInstances = (leftParams, rightParams).zipped.map((param1, param2) =>
+        appliedRef(ref(defn.EqType), List(param1, param2)))
+      DefDef(
+          name = nme.eqInstance,
+          tparams = leftParams ++ rightParams,
+          vparamss = 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
+
     // The thicket which is the desugared version of the companion object
     //     synthetic object C extends parentTpt { defs }
     def companionDefs(parentTpt: Tree, defs: List[Tree]) =
@@ -420,6 +449,8 @@ object desugar {
             .withMods(companionMods | Synthetic))
       .withPos(cdef.pos).toList
 
+    val companionMeths = defaultGetters ::: eqInstances
+
     // The companion object definitions, if a companion is needed, Nil otherwise.
     // companion definitions include:
     // 1. If class is a case class case class C[Ts](p1: T1, ..., pN: TN)(moreParams):
@@ -465,10 +496,10 @@ object desugar {
           DefDef(nme.unapply, derivedTparams, (unapplyParam :: Nil) :: Nil, TypeTree(), unapplyRHS)
             .withMods(synthetic)
         }
-        companionDefs(parent, applyMeths ::: unapplyMeth :: defaultGetters)
+        companionDefs(parent, applyMeths ::: unapplyMeth :: companionMeths)
       }
-      else if (defaultGetters.nonEmpty)
-        companionDefs(anyRef, defaultGetters)
+      else if (companionMeths.nonEmpty)
+        companionDefs(anyRef, companionMeths)
       else if (isValueClass) {
         constr0.vparamss match {
           case List(_ :: Nil) => companionDefs(anyRef, Nil)
@@ -739,7 +770,7 @@ object desugar {
   }
 
   def makeImplicitFunction(formals: List[Type], body: Tree)(implicit ctx: Context): Tree = {
-    val params = makeImplicitParameters(formals.map(TypeTree), forPrimaryConstructor = false)
+    val params = makeImplicitParameters(formals.map(TypeTree))
     new ImplicitFunction(params, body)
   }
 

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

@@ -547,6 +547,7 @@ class Definitions {
 
   lazy val EqType = ctx.requiredClassRef("scala.Eq")
   def EqClass(implicit ctx: Context) = EqType.symbol.asClass
+  def EqModule(implicit ctx: Context) = EqClass.companionModule
 
   lazy val XMLTopScopeModuleRef = ctx.requiredModuleRef("scala.xml.TopScope")
 

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

@@ -400,6 +400,7 @@ object StdNames {
     val ensureAccessible : N    = "ensureAccessible"
     val enumTag: N              = "enumTag"
     val eq: N                   = "eq"
+    val eqInstance: N           = "eqInstance"
     val equalsNumChar : N       = "equalsNumChar"
     val equalsNumNum : N        = "equalsNumNum"
     val equalsNumObject : N     = "equalsNumObject"

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

@@ -656,7 +656,7 @@ trait Implicits { self: Typer =>
     if (!ctx.isAfterTyper && !assumedCanEqual(ltp, rtp)) {
       val res = inferImplicitArg(
         defn.EqType.appliedTo(ltp, rtp), msgFun => ctx.error(msgFun(""), pos), pos)
-      implicits.println(i"Eq witness found: $res: ${res.tpe}")
+      implicits.println(i"Eq witness found for $ltp / $rtp: $res: ${res.tpe}")
     }
 
   /** Find an implicit parameter or conversion.
@@ -676,7 +676,7 @@ trait Implicits { self: Typer =>
       val isearch =
         if (ctx.settings.explainImplicits.value) new ExplainedImplicitSearch(pt, argument, pos)
         else new ImplicitSearch(pt, argument, pos)
-      val result = isearch.bestImplicit
+      val result = isearch.bestImplicit(contextual = true)
       result match {
         case result: SearchSuccess =>
           result.tstate.commit()
@@ -743,7 +743,7 @@ trait Implicits { self: Typer =>
       def typedImplicit(cand: Candidate)(implicit ctx: Context): SearchResult = track("typedImplicit") { ctx.traceIndented(i"typed implicit ${cand.ref}, pt = $pt, implicitsEnabled == ${ctx.mode is ImplicitsEnabled}", implicits, show = true) {
         assert(constr eq ctx.typerState.constraint)
         val ref = cand.ref
-        var generated: Tree = tpd.ref(ref).withPos(pos.startPos)
+        var generated: Tree = tpd.ref(ref).withPos(pos)
         if (!argument.isEmpty)
           generated = typedUnadapted(
             untpd.Apply(untpd.TypedSplice(generated), untpd.TypedSplice(argument) :: Nil),
@@ -759,13 +759,20 @@ trait Implicits { self: Typer =>
               case _ => false
             }
           }
-        // Does there exist an implicit value of type `Eq[tp, tp]`?
-        def hasEq(tp: Type): Boolean =
-          new ImplicitSearch(defn.EqType.appliedTo(tp, tp), EmptyTree, pos).bestImplicit match {
-            case result: SearchSuccess => result.ref.symbol != defn.Predef_eqAny
-            case result: AmbiguousImplicits => true
-            case _ => false
-          }
+        // Does there exist an implicit value of type `Eq[tp, tp]`
+        // which is different from `eqAny`?
+        def hasEq(tp: Type): Boolean = {
+          def search(contextual: Boolean): Boolean =
+            new ImplicitSearch(defn.EqType.appliedTo(tp, tp), EmptyTree, pos)
+              .bestImplicit(contextual) match {
+              case result: SearchSuccess =>
+                result.ref.symbol != defn.Predef_eqAny ||
+                contextual && search(contextual = false)
+              case result: AmbiguousImplicits => true
+              case _ => false
+            }
+          search(contextual = true)
+        }
 
         def validEqAnyArgs(tp1: Type, tp2: Type) = {
           List(tp1, tp2).foreach(fullyDefinedType(_, "eqAny argument", pos))
@@ -872,12 +879,15 @@ trait Implicits { self: Typer =>
     }
 
     /** Find a unique best implicit reference */
-    def bestImplicit: SearchResult = {
-      searchImplicits(ctx.implicits.eligible(wildProto), contextual = true) match {
+    def bestImplicit(contextual: Boolean): SearchResult = {
+      val eligible =
+        if (contextual) ctx.implicits.eligible(wildProto)
+        else implicitScope(wildProto).eligible
+      searchImplicits(eligible, contextual) match {
         case result: SearchSuccess => result
         case result: AmbiguousImplicits => result
         case result: SearchFailure =>
-          searchImplicits(implicitScope(wildProto).eligible, contextual = false)
+          if (contextual) bestImplicit(contextual = false) else result
       }
     }
 

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

@@ -1996,7 +1996,8 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
             case _: RefTree | _: Literal
             if !isVarPattern(tree) &&
                !(tree.tpe <:< pt)(ctx.addMode(Mode.GADTflexible)) =>
-              checkCanEqual(pt, wtp, tree.pos)(ctx.retractMode(Mode.Pattern))
+              val tp1 :: tp2 :: Nil = harmonizeTypes(pt :: wtp :: Nil)
+              checkCanEqual(tp1, tp2, tree.pos)(ctx.retractMode(Mode.Pattern))
             case _ =>
           }
           tree

docs/docs/reference/auto-parameter-tupling.md

@@ -0,0 +1,33 @@
+---
+layout: doc-page
+title: "Automatic Tupling of Function Parameters"
+---
+
+Say you have a list of pairs
+
+     val xs: List[(Int, Int)]
+
+and you want to map `xs` to a list of `Int`s so that eich pair of numbers is mapped to
+their sum. Previously, the best way to do this was with a pattern-matching decomposition:
+
+    xs map {
+      case (x, y) => x + y
+    }
+
+While correct, this is also inconvenient. Dotty now also allows:
+
+    xs.map {
+      (x, y) => x + y
+    }
+
+or, equivalently:
+
+    xs.map(_ + _)
+
+Generally, a function value with `n > 1` parameters is converted to a
+pattern-matching closure using `case` if the expected type is a unary
+function type of the form `((T_1, ..., T_n)) => U`.
+
+
+
+

docs/docs/reference/desugarEnums.md

@@ -89,7 +89,7 @@ comma separated simple cases into a sequence of cases.
 
        case C <params> ...
 
-   expands analogous to a case class:
+   expands analogous to a final case class:
 
        final case class C <params> ...
 
@@ -138,6 +138,15 @@ comma separated simple cases into a sequence of cases.
    Any modifiers or annotations on the original case extend to all expanded
    cases.
 
+## Equality
+
+An `enum` type contains a `scala.Eq` instance that restricts values of the `enum` type to
+be compared only to other values of the same enum type. Furtermore, generic
+`enum` types are comparable only if their type arguments are. For instance the
+`Option` enum type will get the following definition in its companion object:
+
+    implicit def eqOption[T, U](implicit ev1: Eq[T, U]): Eq[Option[T], Option[U]] = Eq
+
 ## Translation of Enumerations
 
 Non-generic enum classes `E` that define one or more singleton cases

docs/docs/reference/implicit-function-types.md

@@ -0,0 +1,99 @@
+---
+layout: doc-page
+title: "Implicit Function Types"
+---
+
+An implicit funciton type describes functions with implicit parameters. Example:
+
+    type Contextual[T] = implicit Context => T
+
+A value of implicit function type is applied to implicit arguments, in
+the same way a method with implicit parameters is applied. For instance:
+
+    implicit ctx: Context = ...
+
+    def f(x: Int): Contextual[Int] = ...
+
+    f(2)    // is expanded to f(2)(ctx)
+
+Conversely, if the expected type of an expression `E` is an implicit
+function type `implicit (T_1, ..., T_n) => U` and `E` is not already an
+implicit function value, `E` is converted to an implicit function value
+by rewriting to
+
+    implicit (x_1: T1, ..., x_n: Tn) => E
+
+where the names `x_1`, ..., `x_n` are arbitrary. For example, continuing
+with the previous definitions,
+
+    def g(arg: Contextual[Int]) = ...
+
+    g(22)      // is expanded to g { implicit ctx => 22 }
+
+    g(f(2))    // is expanded to g { implicit ctx => f(2)(ctx) }
+
+    g(implicit ctx => f(22)(ctx)) // is left as it is
+
+Implicit function types have considerable expressive power. For
+instance, here is how they can support the "builder pattern", where
+the aim is to construct tables like this:
+
+    table {
+      row {
+        cell("top left")
+        cell("top right")
+      }
+      row {
+        cell("botttom left")
+        cell("bottom right")
+      }
+    }
+
+The idea is to define classes for `Table` and `Row` that allow
+addition of elements via `add`:
+
+    class Table {
+      val rows = new ArrayBuffer[Row]
+      def add(r: Row): Unit = rows += r
+      override def toString = rows.mkString("Table(", ", ", ")")
+    }
+
+    class Row {
+      val cells = new ArrayBuffer[Cell]
+      def add(c: Cell): Unit = cells += c
+      override def toString = cells.mkString("Row(", ", ", ")")
+    }
+
+    case class Cell(elem: String)
+
+Then, the `table`, `row` and `cell` constructor methods can be defined
+in terms of implicit function types to avoid the plumbing boilerplate
+that would otherwise be necessary.
+
+    def table(init: implicit Table => Unit) = {
+      implicit val t = new Table
+      init
+      t
+    }
+
+    def row(init: implicit Row => Unit)(implicit t: Table) = {
+      implicit val r = new Row
+      init
+      t.add(r)
+    }
+
+    def cell(str: String)(implicit r: Row) =
+      r.add(new Cell(str))
+
+With that setup, the table construction code above compiles and expands to:
+
+    table { implicit $t: Table =>
+      row { implicit $r: Row =>
+        cell("top left")($r)
+        cell("top right")($r)
+      }($t)
+      row { implicit $r: Row =>
+        cell("botttom left")($r)
+        cell("bottom right")($r)
+      }($t)
+    }