Avoid forcing lambda parameter types in overloading resolution

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -195,21 +195,16 @@ object messages {
         else
           ""
 
+      val inferred =
+        if (pt == WildcardType) ""
+        else i"\nWhat I could infer was: $pt"
+
       i"""Missing parameter type
          |
-         |The argument types of an anonymous function must be fully known. (SLS 8.5)
-         |Expected type: $pt
-         |Missing type for parameter ${param.name}$ofFun"""
+         |I could not infer the type of the parameter ${param.name}$ofFun.$inferred"""
     }
 
-    val explanation: String =
-      hl"""|Anonymous functions must define a type. For example, if you define a function like this one:
-           |
-           |${"val f = { case x: Int => x + 1 }"}
-           |
-           |Make sure you give it a type of what you expect to match and help the type inference system:
-           |
-           |${"val f: Any => Int = { case x: Int => x + 1 }"} """
+    val explanation: String = ""
   }
 
   case class WildcardOnTypeArgumentNotAllowedOnNew()(implicit ctx: Context)

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

@@ -832,7 +832,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
           case funRef: TermRef =>
             val app =
               if (proto.allArgTypesAreCurrent())
-                new ApplyToTyped(tree, fun1, funRef, proto.typedArgs, pt)
+                new ApplyToTyped(tree, fun1, funRef, proto.unforcedTypedArgs, pt)
               else
                 new ApplyToUntyped(tree, fun1, funRef, proto, pt)(argCtx(tree))
             convertNewGenericArray(app.result)
@@ -857,7 +857,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
           }
 
       fun1.tpe match {
-        case err: ErrorType => cpy.Apply(tree)(fun1, proto.typedArgs).withType(err)
+        case err: ErrorType => cpy.Apply(tree)(fun1, proto.unforcedTypedArgs).withType(err)
         case TryDynamicCallType => typedDynamicApply(tree, pt)
         case _ =>
           if (originalProto.isDropped) fun1
@@ -1604,7 +1604,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
           if (isDetermined(alts2)) alts2
           else {
             pretypeArgs(alts2, pt)
-            narrowByTrees(alts2, pt.typedArgs, resultType)
+            narrowByTrees(alts2, pt.unforcedTypedArgs, resultType)
           }
         }
 
@@ -1665,7 +1665,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
     else pt match {
       case pt @ FunProto(_, resType: FunProto) =>
         // try to narrow further with snd argument list
-        val advanced = advanceCandidates(pt.typedArgs.tpes)
+        val advanced = advanceCandidates(pt.unforcedTypedArgs.tpes)
         resolveOverloaded(advanced.map(_._1), resType, Nil) // resolve with candidates where first params are stripped
           .map(advanced.toMap) // map surviving result(s) back to original candidates
       case _ =>
@@ -1697,40 +1697,38 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
   private def pretypeArgs(alts: List[TermRef], pt: FunProto)(implicit ctx: Context): Unit = {
     def recur(altFormals: List[List[Type]], args: List[untpd.Tree]): Unit = args match {
       case arg :: args1 if !altFormals.exists(_.isEmpty) =>
-        def isUnknownParamType(t: untpd.Tree) = t match {
-          case ValDef(_, tpt, _) => tpt.isEmpty
-          case _ => false
-        }
-        val fn = untpd.functionWithUnknownParamType(arg)
-        if (fn.isDefined) {
-          def isUniform[T](xs: List[T])(p: (T, T) => Boolean) = xs.forall(p(_, xs.head))
-          val formalsForArg: List[Type] = altFormals.map(_.head)
-          def argTypesOfFormal(formal: Type): List[Type] =
-            formal match {
-              case defn.FunctionOf(args, result, isImplicit, isErased) => args
-              case defn.PartialFunctionOf(arg, result) => arg :: Nil
-              case _ => Nil
+        untpd.functionWithUnknownParamType(arg) match {
+          case Some(fn) =>
+            def isUniform[T](xs: List[T])(p: (T, T) => Boolean) = xs.forall(p(_, xs.head))
+            val formalsForArg: List[Type] = altFormals.map(_.head)
+            def argTypesOfFormal(formal: Type): List[Type] =
+              formal match {
+                case defn.FunctionOf(args, result, isImplicit, isErased) => args
+                case defn.PartialFunctionOf(arg, result) => arg :: Nil
+                case _ => Nil
+              }
+            val formalParamTypessForArg: List[List[Type]] =
+              formalsForArg.map(argTypesOfFormal)
+            if (formalParamTypessForArg.forall(_.nonEmpty) &&
+                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)(_ frozen_=:= _)) ps.head
+                else WildcardType)
+              def isPartial = // we should generate a partial function for the arg
+                fn.isInstanceOf[untpd.Match] &&
+                formalsForArg.exists(_.isRef(defn.PartialFunctionClass))
+              val commonFormal =
+                if (isPartial) defn.PartialFunctionOf(commonParamTypes.head, WildcardType)
+                else defn.FunctionOf(commonParamTypes, WildcardType)
+              overload.println(i"pretype arg $arg with expected type $commonFormal")
+              if (commonParamTypes.forall(isFullyDefined(_, ForceDegree.noBottom)))
+                pt.typedArg(arg, commonFormal)(ctx.addMode(Mode.ImplicitsEnabled))
             }
-          val formalParamTypessForArg: List[List[Type]] =
-            formalsForArg.map(argTypesOfFormal)
-          if (formalParamTypessForArg.forall(_.nonEmpty) &&
-              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)(_ frozen_=:= _)) ps.head
-              else WildcardType)
-            def isPartial = // we should generate a partial function for the arg
-              fn.get.isInstanceOf[untpd.Match] &&
-              formalsForArg.exists(_.isRef(defn.PartialFunctionClass))
-            val commonFormal =
-              if (isPartial) defn.PartialFunctionOf(commonParamTypes.head, WildcardType)
-              else defn.FunctionOf(commonParamTypes, WildcardType)
-            overload.println(i"pretype arg $arg with expected type $commonFormal")
-            pt.typedArg(arg, commonFormal)(ctx.addMode(Mode.ImplicitsEnabled))
-          }
+          case None =>
         }
         recur(altFormals.map(_.tail), args1)
       case _ =>

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

@@ -47,7 +47,7 @@ object ErrorReporting {
           case _: WildcardType | _: IgnoredProto => ""
           case tp => em" and expected result type $tp"
         }
-        em"arguments (${tp.typedArgs.tpes}%, %)$result"
+        em"arguments (${tp.unforcedTypedArgs.tpes}%, %)$result"
       case _ =>
         em"expected type $tp"
     }

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

@@ -1078,7 +1078,7 @@ class Namer { typer: Typer =>
   }
 
   /** Typecheck `tree` during completion using `typed`, and remember result in TypedAhead map */
-  def typedAheadImpl(tree: Tree, typed: untpd.Tree => tpd.Tree)(implicit ctx: Context): tpd.Tree = {
+  def typedAhead(tree: Tree, typed: untpd.Tree => tpd.Tree)(implicit ctx: Context): tpd.Tree = {
     val xtree = expanded(tree)
     xtree.getAttachment(TypedAhead) match {
       case Some(ttree) => ttree
@@ -1090,10 +1090,10 @@ class Namer { typer: Typer =>
   }
 
   def typedAheadType(tree: Tree, pt: Type = WildcardType)(implicit ctx: Context): tpd.Tree =
-    typedAheadImpl(tree, typer.typed(_, pt)(ctx retractMode Mode.PatternOrTypeBits addMode Mode.Type))
+    typedAhead(tree, typer.typed(_, pt)(ctx retractMode Mode.PatternOrTypeBits addMode Mode.Type))
 
   def typedAheadExpr(tree: Tree, pt: Type = WildcardType)(implicit ctx: Context): tpd.Tree =
-    typedAheadImpl(tree, typer.typed(_, pt)(ctx retractMode Mode.PatternOrTypeBits))
+    typedAhead(tree, typer.typed(_, pt)(ctx retractMode Mode.PatternOrTypeBits))
 
   def typedAheadAnnotation(tree: Tree)(implicit ctx: Context): tpd.Tree =
     typedAheadExpr(tree, defn.AnnotationType)

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

@@ -232,9 +232,6 @@ object ProtoTypes {
     /** A map in which typed arguments can be stored to be later integrated in `typedArgs`. */
     var typedArg: SimpleIdentityMap[untpd.Tree, Tree] = SimpleIdentityMap.Empty
 
-    /** A map recording the typer states and constraints in which arguments stored in myTypedArg were typed */
-    var evalState: SimpleIdentityMap[untpd.Tree, (TyperState, Constraint)] = SimpleIdentityMap.Empty
-
     /** The tupled version of this prototype, if it has been computed */
     var tupled: Type = NoType
 
@@ -265,66 +262,51 @@ object ProtoTypes {
 
     override def notApplied: Type = WildcardType
 
-    /** Forget the types of any arguments that have been typed producing a constraint
-     *    - that is in a typer state that is not yet committed into the one of the current context `ctx`,
-     *    - or that has been retracted from its typestate because oif a failed operation.
-     *  This is necessary to avoid "orphan" TypeParamRefs that are referred to from
-     *  type variables in the typed arguments, but that are not registered in the
-     *  current constraint. Test cases are pos/t1756.scala and pos/i3538.scala.
-     *  @return True if all arguments have types (in particular, no types were forgotten).
+    /** @return True if all arguments have types.
      */
-    def allArgTypesAreCurrent()(implicit ctx: Context): Boolean = {
-      state.evalState foreachBinding { (arg, tstateConstr) =>
-        if ((tstateConstr._1.uncommittedAncestor.constraint `ne` ctx.typerState.constraint) ||
-            tstateConstr._2.isRetracted) {
-          typr.println(i"need to invalidate $arg / ${state.typedArg(arg)}, ${tstateConstr._2}, current = ${ctx.typerState.constraint}")
-          state.typedArg = state.typedArg.remove(arg)
-          state.evalState = state.evalState.remove(arg)
-        }
-      }
+    def allArgTypesAreCurrent()(implicit ctx: Context): Boolean =
       state.typedArg.size == args.length
+
+    private def isUndefined(tp: Type): Boolean = tp match {
+      case _: WildcardType => true
+      case defn.FunctionOf(args, result, _, _) => args.exists(isUndefined) || isUndefined(result)
+      case _ => false
     }
 
     private def cacheTypedArg(arg: untpd.Tree, typerFn: untpd.Tree => Tree, force: Boolean)(implicit ctx: Context): Tree = {
       var targ = state.typedArg(arg)
       if (targ == null) {
-        if (!force && untpd.functionWithUnknownParamType(arg).isDefined)
-          // If force = false, assume ? rather than reporting an error.
-          // That way we don't cause a "missing parameter" error in `typerFn(arg)`
-          targ = arg.withType(WildcardType)
-        else {
-          targ = typerFn(arg)
-          if (!ctx.reporter.hasUnreportedErrors) {
-            // FIXME: This can swallow warnings by updating the typerstate from a nested
-            // context that gets discarded later. But we do have to update the
-            // typerstate if there are no errors. If we also omitted the next two lines
-            // when warning were emitted, `pos/t1756.scala` would fail when run with -feature.
-            // It would produce an orphan type parameter for CI when pickling.
-            state.typedArg = state.typedArg.updated(arg, targ)
-            state.evalState = state.evalState.updated(arg, (ctx.typerState, ctx.typerState.constraint))
-          }
+        untpd.functionWithUnknownParamType(arg) match {
+          case Some(untpd.Function(args, _)) if !force =>
+            // If force = false, assume what we know about the parameter types rather than reporting an error.
+            // That way we don't cause a "missing parameter" error in `typerFn(arg)`
+            val paramTypes = args map {
+              case ValDef(_, tpt, _) if !tpt.isEmpty => typer.typedType(tpt).typeOpt
+              case _ => WildcardType
+            }
+            targ = arg.withType(defn.FunctionOf(paramTypes, WildcardType))
+          case Some(_) if !force =>
+            targ = arg.withType(WildcardType)
+          case _ =>
+            targ = typerFn(arg)
+            if (!ctx.reporter.hasUnreportedErrors)
+              state.typedArg = state.typedArg.updated(arg, targ)
         }
       }
       targ
     }
 
     /** The typed arguments. This takes any arguments already typed using
      *  `typedArg` into account.
-     *  @param  force   if true try to typecheck arguments even if they are functions
-     *                  with unknown parameter types - this will then cause a
-     *                  "missing parameter type" error
      */
-    private def typedArgs(force: Boolean): List[Tree] =
+    def unforcedTypedArgs: List[Tree] =
       if (state.typedArgs.size == args.length) state.typedArgs
       else {
-        val args1 = args.mapconserve(cacheTypedArg(_, typer.typed(_), force))
-        if (force || !args1.contains(WildcardType)) state.typedArgs = args1
+        val args1 = args.mapconserve(cacheTypedArg(_, typer.typed(_), force = false))
+        if (!args1.exists(arg => isUndefined(arg.tpe))) state.typedArgs = args1
         args1
       }
 
-    def typedArgs: List[Tree] = typedArgs(force = true)
-    def unforcedTypedArgs: List[Tree] = typedArgs(force = false)
-
     /** Type single argument and remember the unadapted result in `myTypedArg`.
      *  used to avoid repeated typings of trees when backtracking.
      */
@@ -376,7 +358,7 @@ object ProtoTypes {
       derivedFunProto(args, tm(resultType), typer)
 
     def fold[T](x: T, ta: TypeAccumulator[T])(implicit ctx: Context): T =
-      ta(ta.foldOver(x, typedArgs.tpes), resultType)
+      ta(ta.foldOver(x, unforcedTypedArgs.tpes), resultType)
 
     override def deepenProto(implicit ctx: Context): FunProto = derivedFunProto(args, resultType.deepenProto, typer)
 
@@ -390,7 +372,7 @@ object ProtoTypes {
    *  [](args): resultType, where args are known to be typed
    */
   class FunProtoTyped(args: List[tpd.Tree], resultType: Type)(typer: Typer, isContextual: Boolean)(implicit ctx: Context) extends FunProto(args, resultType)(typer, isContextual)(ctx) {
-    override def typedArgs: List[tpd.Tree] = args
+    override def unforcedTypedArgs: List[tpd.Tree] = args
     override def withContext(ctx: Context): FunProtoTyped = this
   }
 

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

@@ -525,7 +525,7 @@ class Typer extends Namer
           templ1 = cpy.Template(templ)(parents = untpd.TypeTree(pt) :: Nil)
         templ1.parents foreach {
           case parent: RefTree =>
-            typedAheadImpl(parent, tree => inferTypeParams(typedType(tree), pt))
+            typedAhead(parent, tree => inferTypeParams(typedType(tree), pt))
           case _ =>
         }
         val x = tpnme.ANON_CLASS
@@ -940,7 +940,7 @@ class Typer extends Namer
           }
         case _ =>
       }
-      errorType(AnonymousFunctionMissingParamType(param, params, tree, pt), param.sourcePos)
+      errorType(AnonymousFunctionMissingParamType(param, params, tree, formal), param.sourcePos)
     }
 
     def protoFormal(i: Int): Type =

compiler/test-resources/repl/errorThenValid

@@ -1,10 +1,8 @@
 scala> val xs = scala.collection.mutable.ListBuffer[Int]
 1 | val xs = scala.collection.mutable.ListBuffer[Int]
   |          ^
-  |Missing parameter type
+  |          Missing parameter type
   |
-  |The argument types of an anonymous function must be fully known. (SLS 8.5)
-  |Expected type: ?
-  |Missing type for parameter elems
+  |          I could not infer the type of the parameter elems.
 scala> val xs = scala.collection.mutable.ListBuffer[Int]()
 val xs: scala.collection.mutable.ListBuffer[Int] = ListBuffer()