Analysis of overloaded or recursive is harder than expected

Fall-back to reporting "overloaded or recursive needs type".

Author: ennru

compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java

@@ -52,8 +52,7 @@ public enum ErrorMessageID {
     MixedLeftAndRightAssociativeOpsID,
     CantInstantiateAbstractClassOrTraitID,
     AnnotatedPrimaryConstructorRequiresModifierOrThisID,
-    OverloadedMethodNeedsResultTypeID,
-    RecursiveMethodNeedsResultTypeID,
+    OverloadedOrRecursiveMethodNeedsResultTypeID,
     RecursiveValueNeedsResultTypeID,
     CyclicReferenceInvolvingID,
     CyclicReferenceInvolvingImplicitID,

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

@@ -1162,32 +1162,27 @@ object messages {
            |""".stripMargin
   }
 
-  case class OverloadedMethodNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
-  extends Message(OverloadedMethodNeedsResultTypeID) {
+  case class OverloadedOrRecursiveMethodNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
+  extends Message(OverloadedOrRecursiveMethodNeedsResultTypeID) {
     val kind = "Syntax"
-    val msg = hl"""overloaded method ${tree} needs result type"""
+    val msg = hl"""overloaded or recursive method ${tree} needs return type"""
     val explanation =
-      hl"""|${tree} is overloaded and at least one definition of it calls another.
-           |You need to specify the calling method's return type.
-         """.stripMargin
-  }
-
-  case class RecursiveMethodNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
-  extends Message(RecursiveMethodNeedsResultTypeID) {
-    val kind = "Syntax"
-    val msg = hl"""recursive method ${tree} needs result type"""
-    val explanation =
-      hl"""|The definition of `${tree.name}` is recursive and you need to specify its type.
-         """.stripMargin
+      hl"""Case 1: ${tree} is overloaded
+          |If there are multiple methods named `${tree.name}` 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.
+          |""".stripMargin
   }
 
   case class RecursiveValueNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
   extends Message(RecursiveValueNeedsResultTypeID) {
     val kind = "Syntax"
     val msg = hl"""recursive value ${tree.name} needs type"""
     val explanation =
-      hl"""|The definition of `${tree.name}` is recursive and you need to specify its type.
-         """.stripMargin
+      hl"""The definition of `${tree.name}` is recursive and you need to specify its type.
+          |""".stripMargin
   }
 
   case class CyclicReferenceInvolving(denot: SymDenotation)(implicit ctx: Context)

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

@@ -32,10 +32,7 @@ object ErrorReporting {
       if (cx.mode is Mode.InferringReturnType) {
         cx.tree match {
           case tree: untpd.DefDef if !tree.tpt.typeOpt.exists =>
-            // TODO: analysis if tree is an overloaded method (or directly recursive)
-            val overloaded = true
-            if (overloaded) OverloadedMethodNeedsResultType(tree.name)
-            else RecursiveMethodNeedsResultType(tree.name)
+            OverloadedOrRecursiveMethodNeedsResultType(tree.name)
           case tree: untpd.ValDef if !tree.tpt.typeOpt.exists =>
             RecursiveValueNeedsResultType(tree.name)
           case _ =>

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

@@ -227,11 +227,11 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val defn = ictx.definitions
 
       assertMessageCount(1, messages)
-      val OverloadedMethodNeedsResultType(tree) :: Nil = messages
+      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
       assertEquals("foo", tree.show)
     }
 
-  @Test @Ignore def recursiveMethodNeedsReturnType =
+  @Test def recursiveMethodNeedsReturnType =
     checkMessagesAfter("frontend") {
       """
         |class Scope() {
@@ -244,7 +244,7 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val defn = ictx.definitions
 
       assertMessageCount(1, messages)
-      val RecursiveMethodNeedsResultType(tree) :: Nil = messages
+      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
       assertEquals("i", tree.show)
     }