Closes #1731 by fixing error message for overloaded method without re…

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

@@ -126,7 +126,7 @@ object Contexts {
     protected def sstate_=(sstate: SettingsState) = _sstate = sstate
     def sstate: SettingsState = _sstate
 
-    /** The current tree */
+    /** The current compilation unit */
     private[this] var _compilationUnit: CompilationUnit = _
     protected def compilationUnit_=(compilationUnit: CompilationUnit) = _compilationUnit = compilationUnit
     def compilationUnit: CompilationUnit = _compilationUnit

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

@@ -1209,20 +1209,29 @@ object messages {
            |""".stripMargin
   }
 
-  case class OverloadedOrRecursiveMethodNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
+  case class OverloadedOrRecursiveMethodNeedsResultType private (termName: String)(implicit ctx: Context)
   extends Message(OverloadedOrRecursiveMethodNeedsResultTypeID) {
     val kind = "Syntax"
-    val msg = hl"""overloaded or recursive method ${tree} needs return type"""
+    val msg = hl"""overloaded or recursive method $termName needs return type"""
     val explanation =
-      hl"""Case 1: ${tree} is overloaded
-          |If there are multiple methods named `${tree.name}` and at least one definition of
+      hl"""Case 1: $termName is overloaded
+          |If there are multiple methods named `$termName` and at least one definition of
           |it calls another, you need to specify the calling method's return type.
           |
-          |Case 2: ${tree} is recursive
-          |If `${tree.name}` calls itself on any path, you need to specify its return type.
+          |Case 2: $termName is recursive
+          |If `$termName` calls itself on any path, you need to specify its return type.
           |""".stripMargin
   }
 
+  object OverloadedOrRecursiveMethodNeedsResultType {
+    def apply[T >: Trees.Untyped](tree: NameTree[T])(implicit ctx: Context)
+    : OverloadedOrRecursiveMethodNeedsResultType =
+      OverloadedOrRecursiveMethodNeedsResultType(tree.name.show)(ctx)
+    def apply(symbol: Symbol)(implicit ctx: Context)
+    : OverloadedOrRecursiveMethodNeedsResultType =
+      OverloadedOrRecursiveMethodNeedsResultType(symbol.name.show)(ctx)
+  }
+
   case class RecursiveValueNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
   extends Message(RecursiveValueNeedsResultTypeID) {
     val kind = "Syntax"
@@ -1320,7 +1329,8 @@ object messages {
            |"""
   }
 
-  case class MethodDoesNotTakeParameters(tree: tpd.Tree, methPartType: Types.Type)(err: typer.ErrorReporting.Errors)(implicit ctx: Context)
+  case class MethodDoesNotTakeParameters(tree: tpd.Tree, methPartType: Types.Type)
+  (err: typer.ErrorReporting.Errors)(implicit ctx: Context)
   extends Message(MethodDoesNotTakeParametersId) {
     private val more = tree match {
       case Apply(_, _) => " more"

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

@@ -32,7 +32,7 @@ object ErrorReporting {
       if (cx.mode is Mode.InferringReturnType) {
         cx.tree match {
           case tree: untpd.DefDef if !tree.tpt.typeOpt.exists =>
-            OverloadedOrRecursiveMethodNeedsResultType(tree.name)
+            OverloadedOrRecursiveMethodNeedsResultType(tree)
           case tree: untpd.ValDef if !tree.tpt.typeOpt.exists =>
             RecursiveValueNeedsResultType(tree.name)
           case _ =>

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

@@ -1929,7 +1929,13 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
         else
           tree
       case _ => tryInsertApplyOrImplicit(tree, pt) {
-        errorTree(tree, MethodDoesNotTakeParameters(tree, methPart(tree).tpe)(err))
+        pt.resType match {
+          case IgnoredProto(WildcardType(optBounds))
+            if (optBounds == NoType) && (pt.args.size == tree.productArity) =>
+              errorTree(tree, OverloadedOrRecursiveMethodNeedsResultType(tree.symbol))
+          case resType =>
+            errorTree(tree, MethodDoesNotTakeParameters(tree, methPart(tree).tpe)(err))
+        }
       }
     }
 

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -200,7 +200,7 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       assertTrue("expected trait", isTrait)
     }
 
-  @Test def overloadedMethodNeedsReturnType =
+  @Test def overloadedMethodNeedsReturnType = {
     checkMessagesAfter("frontend") {
       """
         |class Scope() {
@@ -214,10 +214,25 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val defn = ictx.definitions
 
       assertMessageCount(1, messages)
-      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
-      assertEquals("foo", tree.show)
+      val OverloadedOrRecursiveMethodNeedsResultType(treeName) :: Nil = messages
+      assertEquals("foo", treeName)
     }
 
+
+    checkMessagesAfter("frontend") {
+      """
+        |case class Foo[T](x: T)
+        |object Foo { def apply[T]() = Foo(null.asInstanceOf[T]) }
+      """.stripMargin
+    }.expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+
+      assertMessageCount(1, messages)
+      val OverloadedOrRecursiveMethodNeedsResultType(treeName2) :: Nil = messages
+      assertEquals("Foo", treeName2)
+    }
+  }
+
   @Test def recursiveMethodNeedsReturnType =
     checkMessagesAfter("frontend") {
       """
@@ -231,8 +246,8 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val defn = ictx.definitions
 
       assertMessageCount(1, messages)
-      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
-      assertEquals("i", tree.show)
+      val OverloadedOrRecursiveMethodNeedsResultType(treeName) :: Nil = messages
+      assertEquals("i", treeName)
     }
 
   @Test def recursiveValueNeedsReturnType =