Change case class desugaring and decouple Products and name-based-pattern-matching

.gitignore

@@ -55,3 +55,5 @@ testlogs/
 local/
 compiler/test/debug/Gen.jar
 
+compiler/before-pickling.txt
+compiler/after-pickling.txt

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

@@ -352,26 +352,45 @@ object desugar {
     lazy val creatorExpr = New(classTypeRef, constrVparamss nestedMap refOfDef)
 
     // Methods to add to a case class C[..](p1: T1, ..., pN: Tn)(moreParams)
-    //     def isDefined = true
-    //     def productArity = N
     //     def _1 = this.p1
     //     ...
     //     def _N = this.pN
     //     def copy(p1: T1 = p1: @uncheckedVariance, ...,
     //              pN: TN = pN: @uncheckedVariance)(moreParams) =
     //       new C[...](p1, ..., pN)(moreParams)
     //
+    // Above arity 22 we also synthesize:
+    //     def productArity = N
+    //     def productElement(i: Int): Any = i match { ... }
+    //
     // Note: copy default parameters need @uncheckedVariance; see
     // neg/t1843-variances.scala for a test case. The test would give
     // two errors without @uncheckedVariance, one of them spurious.
-    val caseClassMeths =
-      if (isCaseClass) {
-        def syntheticProperty(name: TermName, rhs: Tree) =
-          DefDef(name, Nil, Nil, TypeTree(), rhs).withMods(synthetic)
+    val caseClassMeths = {
+      def syntheticProperty(name: TermName, rhs: Tree) =
+        DefDef(name, Nil, Nil, TypeTree(), rhs).withMods(synthetic)
+      def productArity = syntheticProperty(nme.productArity, Literal(Constant(arity)))
+      def productElement = {
+        val param = makeSyntheticParameter(tpt = ref(defn.IntType))
+        // case N => _${N + 1}
+        val cases = 0.until(arity).map { i =>
+          CaseDef(Literal(Constant(i)), EmptyTree, Select(This(EmptyTypeIdent), nme.selectorName(i)))
+        }
+        val ioob  = ref(defn.IndexOutOfBoundsException.typeRef)
+        val error = Throw(New(ioob, List(List(Select(refOfDef(param), nme.toString_)))))
+        // case _ => throw new IndexOutOfBoundsException(i.toString)
+        val defaultCase = CaseDef(untpd.Ident(nme.WILDCARD), EmptyTree, error)
+        val body = Match(refOfDef(param), (cases :+ defaultCase).toList)
+        DefDef(nme.productElement, Nil, List(List(param)), TypeTree(defn.AnyType), body)
+          .withMods(synthetic)
+      }
+      def productElemMeths = {
         val caseParams = constrVparamss.head.toArray
-        val productElemMeths =
-          for (i <- 0 until arity if nme.selectorName(i) `ne` caseParams(i).name)
-          yield syntheticProperty(nme.selectorName(i), Select(This(EmptyTypeIdent), caseParams(i).name))
+        for (i <- 0 until arity if nme.selectorName(i) `ne` caseParams(i).name)
+        yield syntheticProperty(nme.selectorName(i), Select(This(EmptyTypeIdent), caseParams(i).name))
+      }
+      def enumTagMeths = if (isEnumCase) enumTagMeth(CaseKind.Class)._1 :: Nil else Nil
+      def copyMeths = {
         def isRepeated(tree: Tree): Boolean = tree match {
           case PostfixOp(_, Ident(nme.raw.STAR)) => true
           case ByNameTypeTree(tree1) => isRepeated(tree1)
@@ -381,38 +400,46 @@ object desugar {
           case ValDef(_, tpt, _) => isRepeated(tpt)
           case _ => false
         })
-
-        val copyMeths =
-          if (mods.is(Abstract) || hasRepeatedParam) Nil  // cannot have default arguments for repeated parameters, hence copy method is not issued
-          else {
-            def copyDefault(vparam: ValDef) =
-              makeAnnotated("scala.annotation.unchecked.uncheckedVariance", refOfDef(vparam))
-            val copyFirstParams = derivedVparamss.head.map(vparam =>
-              cpy.ValDef(vparam)(rhs = copyDefault(vparam)))
-            val copyRestParamss = derivedVparamss.tail.nestedMap(vparam =>
-              cpy.ValDef(vparam)(rhs = EmptyTree))
-            DefDef(nme.copy, derivedTparams, copyFirstParams :: copyRestParamss, TypeTree(), creatorExpr)
-              .withMods(synthetic) :: Nil
-          }
-
-        val enumTagMeths = if (isEnumCase) enumTagMeth(CaseKind.Class)._1 :: Nil else Nil
-        copyMeths ::: enumTagMeths ::: productElemMeths.toList
+        if (mods.is(Abstract) || hasRepeatedParam) Nil  // cannot have default arguments for repeated parameters, hence copy method is not issued
+        else {
+          def copyDefault(vparam: ValDef) =
+            makeAnnotated("scala.annotation.unchecked.uncheckedVariance", refOfDef(vparam))
+          val copyFirstParams = derivedVparamss.head.map(vparam =>
+            cpy.ValDef(vparam)(rhs = copyDefault(vparam)))
+          val copyRestParamss = derivedVparamss.tail.nestedMap(vparam =>
+            cpy.ValDef(vparam)(rhs = EmptyTree))
+          DefDef(nme.copy, derivedTparams, copyFirstParams :: copyRestParamss, TypeTree(), creatorExpr)
+            .withMods(synthetic) :: Nil
+        }
       }
+
+      // Above MaxTupleArity we extend Product instead of ProductN, in this
+      // case we need to synthesise productElement & productArity.
+      def largeProductMeths =
+        if (arity > Definitions.MaxTupleArity) productElement :: productArity :: Nil
+        else Nil
+
+      if (isCaseClass)
+        largeProductMeths ::: copyMeths ::: enumTagMeths ::: productElemMeths.toList
       else Nil
+    }
 
     def anyRef = ref(defn.AnyRefAlias.typeRef)
     def productConstr(n: Int) = {
       val tycon = scalaDot((tpnme.Product.toString + n).toTypeName)
       val targs = constrVparamss.head map (_.tpt)
       if (targs.isEmpty) tycon else AppliedTypeTree(tycon, targs)
     }
+    def product =
+      if (arity > Definitions.MaxTupleArity) scalaDot(nme.Product.toTypeName)
+      else productConstr(arity)
 
-    // Case classes and case objects get a ProductN parent
+    // Case classes and case objects get Product/ProductN parents
     var parents1 = parents
     if (isEnumCase && parents.isEmpty)
       parents1 = enumClassTypeRef :: Nil
-    if (mods.is(Case) && arity <= Definitions.MaxTupleArity)
-      parents1 = parents1 :+ productConstr(arity) // TODO: This also adds Product0 to caes objects. Do we want that?
+    if (mods.is(Case))
+      parents1 = parents1 :+ product // TODO: This also adds Product0 to case objects. Do we want that?
     if (isEnum)
       parents1 = parents1 :+ ref(defn.EnumType)
 

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

@@ -10,6 +10,7 @@ import scala.collection.{ mutable, immutable }
 import PartialFunction._
 import collection.mutable
 import util.common.alwaysZero
+import typer.Applications
 
 object Definitions {
 
@@ -477,6 +478,7 @@ class Definitions {
 
   lazy val JavaCloneableClass        = ctx.requiredClass("java.lang.Cloneable")
   lazy val NullPointerExceptionClass = ctx.requiredClass("java.lang.NullPointerException")
+  lazy val IndexOutOfBoundsException = ctx.requiredClass("java.lang.IndexOutOfBoundsException")
   lazy val ClassClass                = ctx.requiredClass("java.lang.Class")
   lazy val BoxedNumberClass          = ctx.requiredClass("java.lang.Number")
   lazy val ThrowableClass            = ctx.requiredClass("java.lang.Throwable")
@@ -846,17 +848,9 @@ class Definitions {
   }
 
   def isProductSubType(tp: Type)(implicit ctx: Context) =
-    (tp derivesFrom ProductType.symbol) && tp.baseClasses.exists(isProductClass)
+    Applications.extractorMemberType(tp, nme._1).exists
 
-  def productArity(tp: Type)(implicit ctx: Context) =
-    if (tp derivesFrom ProductType.symbol)
-      tp.baseClasses.find(isProductClass) match {
-        case Some(prod) => prod.typeParams.length
-        case None => -1
-      }
-    else -1
-
-  /** Is `tp` (an alias) of either a scala.FunctionN or a scala.ImplicitFunctionN ? */
+  /** Is `tp` (an alias) of either a scala.FunctionN or a scala.ImplicitFunctionN? */
   def isFunctionType(tp: Type)(implicit ctx: Context) = {
     val arity = functionArity(tp)
     val sym = tp.dealias.typeSymbol

compiler/src/dotty/tools/dotc/repl/ammonite/Protocol.scala

@@ -5,7 +5,7 @@ package ammonite.terminal
 
 case class TermInfo(ts: TermState, width: Int)
 
-sealed trait TermAction
+trait TermAction
 case class Printing(ts: TermState, stdout: String) extends TermAction
 case class TermState(
   inputs: LazyList[Int],

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -233,7 +233,7 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {
         // next: MatchMonad[U]
         // returns MatchMonad[U]
         def flatMap(prev: Tree, b: Symbol, next: Tree): Tree = {
-          val resultArity = defn.productArity(b.info)
+          val resultArity = productArity(b.info)
           if (isProductMatch(prev.tpe, resultArity)) {
             val nullCheck: Tree = prev.select(defn.Object_ne).appliedTo(Literal(Constant(null)))
             ifThenElseZero(

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

@@ -48,12 +48,12 @@ object Applications {
   }
 
   /** Does `tp` fit the "product match" conditions as an unapply result type
-   *  for a pattern with `numArgs` subpatterns>
-   *  This is the case of `tp` is a subtype of the Product<numArgs> class.
+   *  for a pattern with `numArgs` subpatterns?
+   *  This is the case of `tp` has members `_1` to `_N` where `N == numArgs`.
    */
   def isProductMatch(tp: Type, numArgs: Int)(implicit ctx: Context) =
-    0 <= numArgs && numArgs <= Definitions.MaxTupleArity &&
-    tp.derivesFrom(defn.ProductNType(numArgs).typeSymbol)
+    numArgs > 0 && defn.isProductSubType(tp) &&
+    productSelectorTypes(tp).size == numArgs
 
   /** Does `tp` fit the "get match" conditions as an unapply result type?
    *  This is the case of `tp` has a `get` member as well as a
@@ -68,6 +68,9 @@ object Applications {
     sels.takeWhile(_.exists).toList
   }
 
+  def productArity(tp: Type)(implicit ctx: Context) =
+    if (defn.isProductSubType(tp)) productSelectorTypes(tp).size else -1
+
   def productSelectors(tp: Type)(implicit ctx: Context): List[Symbol] = {
     val sels = for (n <- Iterator.from(0)) yield tp.member(nme.selectorName(n)).symbol
     sels.takeWhile(_.exists).toList

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

@@ -761,10 +761,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
 
       /** Is `formal` a product type which is elementwise compatible with `params`? */
       def ptIsCorrectProduct(formal: Type) = {
-        val pclass = defn.ProductNType(params.length).symbol
         isFullyDefined(formal, ForceDegree.noBottom) &&
-        formal.derivesFrom(pclass) &&
-        formal.baseArgTypes(pclass).corresponds(params) {
+        defn.isProductSubType(formal) &&
+        Applications.productSelectorTypes(formal).corresponds(params) {
           (argType, param) =>
             param.tpt.isEmpty || argType <:< typedAheadType(param.tpt).tpe
         }

tests/run/1938.scala

@@ -0,0 +1,45 @@
+case class Large(
+  e1: Int,
+  e2: Int,
+  e3: Int,
+  e4: Int,
+  e5: Int,
+  e6: Int,
+  e7: Int,
+  e8: Int,
+  e9: Int,
+  e10: Int,
+  e11: Int,
+  e12: Int,
+  e13: Int,
+  e14: Int,
+  e15: Int,
+  e16: Int,
+  e17: Int,
+  e18: Int,
+  e19: Int,
+  e20: Int,
+  e21: Int,
+  e22: Int,
+  e23: Int
+)
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val l = Large(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
+
+    assert(l.productArity == 23)
+
+    assert(l.productElement(0) == 1)
+    assert(l.productElement(1) == 2)
+    assert(l.productElement(21) == 22)
+    assert(l.productElement(22) == 23)
+
+    try {
+      l.productElement(23)
+      ???
+    } catch {
+      case e: IndexOutOfBoundsException => assert(e.getMessage == "23")
+    }
+  }
+}

tests/run/double-pattern-type.scala

@@ -0,0 +1,40 @@
+case class C1(i: String, s: Int) { def isEmpty = false; def get = ("EMPTY", -1) }
+case class C2(i: String, s: String) { def isEmpty = false; def get = (-1, -2, -3) }
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    // When both Product and name based patterns with same arity are available,
+    // we follow scalac and silently use the Product one:
+
+    val c1 = C1("s", 0)
+    c1 match {
+      case C1(a, b) =>
+        assert(a == "s")
+        assert(b == 0)
+    }
+
+    // When the size differ, both are patterns become usable:
+
+    val c2 = C2("a", "b")
+    c2 match {
+      case C2(a, b) =>
+        assert(a == "a")
+        assert(b == "b")
+    }
+
+    c2 match {
+      case C2(a, b, c) =>
+        assert(a == -1)
+        assert(b == -2)
+        assert(c == -3)
+    }
+
+    // Interestingly things also compile with a single pattern, in which case
+    // the tuple returned by get is binded to `a`:
+
+    c2 match {
+      case C2(a) =>
+        assert(a == (-1, -2, -3))
+    }
+  }
+}

tests/run/zero-arity-case-class.scala

@@ -0,0 +1,26 @@
+case class Foo()
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert(Foo.unapply(Foo()) == true)
+
+    // unapply generate by scalac are `_ != null`,
+    // dotty returns true in all cases
+    assert(Foo.unapply(null) == true)
+
+    Foo() match {
+      case Foo() => ()
+      case _     => ???
+    }
+
+    Foo() match {
+      case _: Foo => ()
+      case _      => ???
+    }
+
+    (Foo(): Any) match {
+      case Foo() => ()
+      case _     => ???
+    }
+  }
+}