Make apply proxies work with overloaded ctors (#19464)

Fixes #19201

Author: odersky

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

@@ -4298,8 +4298,12 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       case _ =>
     }
 
-    /** Convert constructor proxy reference to a new expression */
-    def newExpr =
+    /** If `tree` is a constructor proxy reference, convert it to a `new` expression,
+     *  otherwise return EmptyTree.
+     */
+    def newExpr(tree: Tree): Tree =
+      val ctorResultType = applyProxyResultType(tree)
+      if !ctorResultType.exists then return EmptyTree
       val qual = qualifier(tree)
       val tpt = qual match
         case Ident(name) =>
@@ -4310,17 +4314,27 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           cpy.Ident(qual)(qual.symbol.name.sourceModuleName.toTypeName)
         case _ =>
           errorTree(tree, em"cannot convert from $tree to an instance creation expression")
-      val tycon = tree.tpe.widen.finalResultType.underlyingClassRef(refinementOK = false)
+      val tycon = ctorResultType.underlyingClassRef(refinementOK = false)
       typed(
         untpd.Select(
           untpd.New(untpd.TypedSplice(tpt.withType(tycon))),
           nme.CONSTRUCTOR),
         pt)
         .showing(i"convert creator $tree -> $result", typr)
 
-    def isApplyProxy(tree: Tree) = tree match
-      case Select(_, nme.apply) => tree.symbol.isAllOf(ApplyProxyFlags)
-      case _ => false
+    /** If `tree` is a constructor proxy reference, return the type it constructs,
+     *  otherwise return NoType.
+     */
+    def applyProxyResultType(tree: Tree): Type = tree match
+      case Select(_, nme.apply) =>
+        // can't use tree.symbol and tree.tpe.widen.finalResultType, because when overloaded
+        // tree.symbol is NoSymbol (via MultiDenotation.symbol) and tree.tpe won't widen.
+        tree.denot.altsWith(_.isAllOf(ApplyProxyFlags)) match
+          case denot :: _ =>
+            // any of the constructors will do, in order to get the result type, so using the first one
+            denot.info.widen.finalResultType
+          case _ => NoType
+      case _ => NoType
 
     tree match {
       case _: MemberDef | _: PackageDef | _: Import | _: WithoutTypeOrPos[?] | _: Closure => tree
@@ -4334,7 +4348,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             if needsTupledDual(ref, pt) && Feature.autoTuplingEnabled =>
               adapt(tree, pt.tupledDual, locked)
             case _ =>
-              adaptOverloaded(ref)
+              newExpr(tree).orElse(adaptOverloaded(ref))
           }
         case poly: PolyType
         if !(ctx.mode is Mode.Type) && dummyTreeOfType.unapply(tree).isEmpty =>
@@ -4343,22 +4357,21 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             // Test case was but i18695.scala, but it got fixed by a different tweak in #18719.
             // We leave test for this condition in as a defensive measure in case
             // it arises somewhere else.
-          if isApplyProxy(tree) then newExpr
-          else if pt.isInstanceOf[PolyProto] then tree
-          else
-            var typeArgs = tree match
-              case Select(qual, nme.CONSTRUCTOR) => qual.tpe.widenDealias.argTypesLo.map(TypeTree(_))
-              case _ => Nil
-            if typeArgs.isEmpty then typeArgs = constrained(poly, tree)._2.map(_.wrapInTypeTree(tree))
-            convertNewGenericArray(readapt(tree.appliedToTypeTrees(typeArgs)))
+          newExpr(tree).orElse:
+            if pt.isInstanceOf[PolyProto] then tree
+            else
+              var typeArgs = tree match
+                case Select(qual, nme.CONSTRUCTOR) => qual.tpe.widenDealias.argTypesLo.map(TypeTree(_))
+                case _ => Nil
+              if typeArgs.isEmpty then typeArgs = constrained(poly, tree)._2.map(_.wrapInTypeTree(tree))
+              convertNewGenericArray(readapt(tree.appliedToTypeTrees(typeArgs)))
         case wtp =>
           val isStructuralCall = wtp.isValueType && isStructuralTermSelectOrApply(tree)
           if (isStructuralCall)
             readaptSimplified(handleStructural(tree))
           else pt match {
             case pt: FunProto =>
-              if isApplyProxy(tree) then newExpr
-              else adaptToArgs(wtp, pt)
+              newExpr(tree).orElse(adaptToArgs(wtp, pt))
             case pt: PolyProto if !wtp.isImplicitMethod =>
               tryInsertApplyOrImplicit(tree, pt, locked)(tree) // error will be reported in typedTypeApply
             case _ =>

tests/pos/i19201.scala

@@ -0,0 +1,12 @@
+class Person(
+    val firstName: String,
+    val lastName: String,
+    val birthYear: Int = -1,
+    val address: String = ""
+):
+  // Works if remove this constructor
+  def this() = this("John", "Doe")
+
+class Test:
+  def p1 = Person("First", "Last") // was: Type Error: none of the overloads.. match arguments
+  def p2 = Person("Josh", "Joe", 1912, "Main Street")