Change pretyping of argument closure

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

@@ -281,12 +281,21 @@ trait UntypedTreeInfo extends TreeInfo[Untyped] { self: Trees.Instance[Untyped]
     case _ => false
   }
 
-  def isFunctionWithUnknownParamType(tree: Tree) = tree match {
+  /** Is this a function literal (either a lambda or a case-block) with an
+   *  unknown parameter type?
+   *
+   *  @param idx  If a non-negative value is given, only the specific parameter
+   *              at that index is tested, otherwise all parameters are tested.
+   */
+  def isFunctionWithUnknownParamType(tree: Tree, idx: Int = -1): Boolean = tree match {
     case Function(args, _) =>
-      args.exists {
+      val hasUnknownParamType: Tree => Boolean = {
         case ValDef(_, tpt, _) => tpt.isEmpty
         case _ => false
       }
+      if (idx >= 0) hasUnknownParamType(args(idx)) else args.exists(hasUnknownParamType)
+    case Match(EmptyTree, _) =>
+      true
     case _ => false
   }
 

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

@@ -1227,6 +1227,8 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
     def typeShape(tree: untpd.Tree): Type = tree match {
       case untpd.Function(args, body) =>
         defn.FunctionOf(args map Function.const(defn.AnyType), typeShape(body))
+      case Match(EmptyTree, _) =>
+        defn.PartialFunctionType.appliedTo(defn.AnyType :: defn.NothingType :: Nil)
       case _ =>
         defn.NothingType
     }
@@ -1271,7 +1273,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
           alts filter (alt => sizeFits(alt, alt.widen))
 
         def narrowByShapes(alts: List[TermRef]): List[TermRef] = {
-          if (normArgs exists (_.isInstanceOf[untpd.Function]))
+          if (normArgs exists (untpd.isFunctionWithUnknownParamType(_)))
             if (hasNamedArg(args)) narrowByTrees(alts, args map treeShape, resultType)
             else narrowByTypes(alts, normArgs map typeShape, resultType)
           else
@@ -1351,33 +1353,34 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
           case ValDef(_, tpt, _) => tpt.isEmpty
           case _ => false
         }
-        arg match {
-          case arg: untpd.Function if arg.args.exists(isUnknownParamType) =>
-            def isUniform[T](xs: List[T])(p: (T, T) => Boolean) = xs.forall(p(_, xs.head))
-            val formalsForArg: List[Type] = altFormals.map(_.head)
-            // For alternatives alt_1, ..., alt_n, test whether formal types for current argument are of the form
-            //   (p_1_1, ..., p_m_1) => r_1
-            //   ...
-            //   (p_1_n, ..., p_m_n) => r_n
-            val decomposedFormalsForArg: List[Option[(List[Type], Type, Boolean)]] =
-              formalsForArg.map(defn.FunctionOf.unapply)
-            if (decomposedFormalsForArg.forall(_.isDefined)) {
-              val formalParamTypessForArg: List[List[Type]] =
-                decomposedFormalsForArg.map(_.get._1)
-              if (isUniform(formalParamTypessForArg)((x, y) => x.length == y.length)) {
-                val commonParamTypes = formalParamTypessForArg.transpose.map(ps =>
-                  // Given definitions above, for i = 1,...,m,
-                  //   ps(i) = List(p_i_1, ..., p_i_n)  -- i.e. a column
-                  // If all p_i_k's are the same, assume the type as formal parameter
-                  // type of the i'th parameter of the closure.
-                  if (isUniform(ps)(ctx.typeComparer.isSameTypeWhenFrozen(_, _))) ps.head
-                  else WildcardType)
-                val commonFormal = defn.FunctionOf(commonParamTypes, WildcardType)
-                overload.println(i"pretype arg $arg with expected type $commonFormal")
-                pt.typedArg(arg, commonFormal)
-              }
+        if (untpd.isFunctionWithUnknownParamType(arg)) {
+          def isUniform[T](xs: List[T])(p: (T, T) => Boolean) = xs.forall(p(_, xs.head))
+          val formalsForArg: List[Type] = altFormals.map(_.head)
+          // For alternatives alt_1, ..., alt_n, test whether formal types for current argument are of the form
+          //   (p_1_1, ..., p_m_1) => r_1
+          //   ...
+          //   (p_1_n, ..., p_m_n) => r_n
+          val decomposedFormalsForArg: List[Option[(List[Type], Type, Boolean)]] =
+            formalsForArg.map(defn.FunctionOf.unapply)
+          if (decomposedFormalsForArg.forall(_.isDefined)) {
+            val formalParamTypessForArg: List[List[Type]] =
+              decomposedFormalsForArg.map(_.get._1)
+            if (isUniform(formalParamTypessForArg)((x, y) => x.length == y.length)) {
+              val commonParamTypes = formalParamTypessForArg
+                .transpose
+                .zipWithIndex
+                .map {
+                  case (ps, idx) =>
+                    if (untpd.isFunctionWithUnknownParamType(arg, idx))
+                      ps.reduceLeft(_ | _)
+                    else
+                      WildcardType
+                }
+              val commonFormal = defn.FunctionOf(commonParamTypes, WildcardType)
+              overload.println(i"pretype arg $arg with expected type $commonFormal")
+              pt.typedArg(arg, commonFormal)
             }
-          case _ =>
+          }
         }
         recur(altFormals.map(_.tail), args1)
       case _ =>

tests/pos/inferOverloaded.scala

@@ -0,0 +1,41 @@
+class MySeq[T] {
+  def map1[U](f: T => U): MySeq[U] = new MySeq[U]
+  def map2[U](f: T => U): MySeq[U] = new MySeq[U]
+}
+
+class MyMap[A, B] extends MySeq[(A, B)] {
+  def map1[C](f: (A, B) => C): MySeq[C] = new MySeq[C]
+  def map1[C, D](f: (A, B) => (C, D)): MyMap[C, D] = new MyMap[C, D]
+  def map1[C, D](f: ((A, B)) => (C, D)): MyMap[C, D] = new MyMap[C, D]
+
+  def foo(f: Function2[Int, Int, Int]): Unit = ()
+  def foo[R](pf: PartialFunction[(A, B), R]): MySeq[R] = new MySeq[R]
+}
+
+object Test {
+  val m = new MyMap[Int, String]
+
+  // This one already worked because it is not overloaded:
+  m.map2 { case (k, v) => k - 1 }
+
+  // These already worked because preSelectOverloaded eliminated the non-applicable overload:
+  m.map1(t => t._1)
+  m.map1((kInFunction, vInFunction) => kInFunction - 1)
+  val r1 = m.map1(t => (t._1, 42.0))
+  val r1t: MyMap[Int, Double] = r1
+
+  // These worked because the argument types are known for overload resolution:
+  m.map1({ case (k, v) => k - 1 }: PartialFunction[(Int, String), Int])
+  m.map2({ case (k, v) => k - 1 }: PartialFunction[(Int, String), Int])
+
+  // These ones did not work before:
+  m.map1 { case (k, v) => k }
+  val r = m.map1 { case (k, v) => (k, k*10) }
+  val rt: MyMap[Int, Int] = r
+  m.foo { case (k, v) => k - 1 }
+
+  // Used to be ambiguous but overload resolution now favors PartialFunction
+  def h[R](pf: Function2[Int, String, R]): Unit = ()
+  def h[R](pf: PartialFunction[(Double, Double), R]): Unit = ()
+  h { case (a: Double, b: Double) => 42: Int }
+}