Fix scala#6190: eta-expand companion object if functions are expected

Author: liufengyun

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

@@ -676,28 +676,6 @@ object desugar {
           mods.is(Private) || (!mods.is(Protected) && mods.hasPrivateWithin)
         }
 
-        /** Does one of the parameter's types (in the first param clause)
-         *  mention a preceding parameter?
-         */
-        def isParamDependent = constrVparamss match
-          case vparams :: _ =>
-            val paramNames = vparams.map(_.name).toSet
-            vparams.exists(_.tpt.existsSubTree {
-              case Ident(name: TermName) => paramNames.contains(name)
-              case _ => false
-            })
-          case _ => false
-
-        val companionParent =
-          if constrTparams.nonEmpty
-             || constrVparamss.length > 1
-             || mods.is(Abstract)
-             || restrictedAccess
-             || isParamDependent
-             || isEnumCase
-          then anyRef
-          else
-            constrVparamss.foldRight(classTypeRef)((vparams, restpe) => Function(vparams map (_.tpt), restpe))
         val applyMeths =
           if (mods.is(Abstract)) Nil
           else {
@@ -727,7 +705,7 @@ object desugar {
         val toStringMeth =
           DefDef(nme.toString_, Nil, Nil, TypeTree(), Literal(Constant(className.toString))).withMods(Modifiers(Override | Synthetic))
 
-        companionDefs(companionParent, applyMeths ::: unapplyMeth :: toStringMeth :: companionMembers)
+        companionDefs(anyRef, applyMeths ::: unapplyMeth :: toStringMeth :: companionMembers)
       }
       else if (companionMembers.nonEmpty || companionDerived.nonEmpty || isEnum)
         companionDefs(anyRef, companionMembers)

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

@@ -3222,9 +3222,6 @@ class Typer extends Namer
       *  Examples for these cases are found in run/implicitFuns.scala and neg/i2006.scala.
       */
     def adaptNoArgsUnappliedMethod(wtp: MethodType, functionExpected: Boolean, arity: Int): Tree = {
-      def isExpandableApply =
-        defn.isContextFunctionClass(tree.symbol.maybeOwner) && functionExpected
-
       /** Is reference to this symbol `f` automatically expanded to `f()`? */
       def isAutoApplied(sym: Symbol): Boolean =
         sym.isConstructor
@@ -3241,7 +3238,7 @@ class Typer extends Namer
           !tree.symbol.isConstructor &&
           !tree.symbol.isAllOf(InlineMethod) &&
           !ctx.mode.is(Mode.Pattern) &&
-          !(isSyntheticApply(tree) && !isExpandableApply)) {
+          !(isSyntheticApply(tree) && !functionExpected)) {
         if (!defn.isFunctionType(pt))
           pt match {
             case SAMType(_) if !pt.classSymbol.hasAnnotation(defn.FunctionalInterfaceAnnot) =>
@@ -3266,9 +3263,18 @@ class Typer extends Namer
         defn.isContextFunctionClass(underlying.classSymbol)
     }
 
-    def adaptNoArgsOther(wtp: Type): Tree = {
-      if (isContextFunctionRef(wtp) &&
-          !untpd.isContextualClosure(tree) &&
+    def adaptNoArgsOther(wtp: Type, functionExpected: Boolean): Tree = {
+      val implicitFun = isContextFunctionRef(wtp) && !untpd.isContextualClosure(tree)
+      def caseCompanion =
+          functionExpected &&
+          tree.symbol.is(Module) &&
+          tree.symbol.companionClass.is(Case) &&
+          !tree.tpe.widen.classSymbol.asClass.classParents.exists(defn.isFunctionType(_)) && {
+            report.warning("The method `apply` is inserted. The auto insertion will be deprecated, please write `" + tree.show + ".apply` explicitly.", tree.sourcePos)
+            true
+          }
+
+      if ((implicitFun || caseCompanion) &&
           !isApplyProto(pt) &&
           pt != AssignProto &&
           !ctx.mode.is(Mode.Pattern) &&
@@ -3390,7 +3396,7 @@ class Typer extends Namer
             }
           adaptNoArgsUnappliedMethod(wtp, funExpected, arity)
         case _ =>
-          adaptNoArgsOther(wtp)
+          adaptNoArgsOther(wtp, functionExpected)
       }
     }