From 34e3508cccbbcc49554a4c5b13419769cc3c7bf9 Mon Sep 17 00:00:00 2001
From: Enno Runne <enno@runne.net>
Date: Sat, 4 Mar 2017 16:32:33 +0100
Subject: Explanations for recursive/cyclic type requirements

---
 .../tools/dotc/reporting/diagnostic/messages.scala | 44 ++++++++--------
 .../tools/dotc/reporting/ErrorMessagesTests.scala  | 58 ++++++++++++++++++++++
 2 files changed, 81 insertions(+), 21 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
index f2f69b6cc..9d899923b 100644
--- a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
@@ -1146,46 +1146,48 @@ object messages {
            |""".stripMargin
   }
 
+  case class AnnotatedPrimaryConstructorRequiresModifierOrThis(cls: Name)(implicit ctx: Context)
+  extends Message(AnnotatedPrimaryConstructorRequiresModifierOrThisID) {
+    val kind = "Syntax"
+    val msg = hl"""${"private"}, ${"protected"}, or ${"this"} expected for annotated primary constructor"""
+    val explanation =
+      hl"""|When using annotations with a primary constructor of a class,
+           |the annotation must be followed by an access modifier
+           |(${"private"} or ${"protected"}) or ${"this"}.
+           |
+           |For example:
+           |  ${"class Sample @deprecated this(param: Parameter) { ..."}
+           |                           ^^^^
+           |""".stripMargin
+  }
+
   case class OverloadedOrRecursiveMethodNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
   extends Message(OverloadedOrRecursiveMethodNeedsResultTypeID) {
     val kind = "Syntax"
     val msg = hl"""overloaded or recursive method ${tree} needs result type"""
     val explanation =
-      hl"""
-          |
-        """.stripMargin
+      hl"""|${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 RecursiveValueNeedsResultType(tree: Names.TermName)(implicit ctx: Context)
-    extends Message(RecursiveValueNeedsResultTypeID) {
+  extends Message(RecursiveValueNeedsResultTypeID) {
     val kind = "Syntax"
     val msg = hl"""recursive value ${tree.name} needs type"""
     val explanation =
-      hl"""""".stripMargin
+      hl"""|The definition of `${tree.name}` is recursive and you need to specify its type.
+         """.stripMargin
   }
 
   case class CyclicReferenceInvolvingImplicit(cycleSym: Symbol)(implicit ctx: Context)
-    extends Message(CyclicReferenceInvolvingImplicitID) {
+  extends Message(CyclicReferenceInvolvingImplicitID) {
     val kind = "Syntax"
     val msg = hl"""cyclic reference involving implicit $cycleSym"""
     val explanation =
       hl"""|This happens when the right hand-side of $cycleSym's definition involves an implicit search.
-           |To avoid the error, give $cycleSym an explicit type.
+           |To avoid this error, give `${cycleSym.name}` an explicit type.
            |""".stripMargin
   }
 
-  case class AnnotatedPrimaryConstructorRequiresModifierOrThis(cls: Name)(implicit ctx: Context)
-    extends Message(AnnotatedPrimaryConstructorRequiresModifierOrThisID) {
-    val kind = "Syntax"
-    val msg = hl"""${"private"}, ${"protected"}, or ${"this"} expected for annotated primary constructor"""
-    val explanation =
-      hl"""|When using annotations with a primary constructor of a class,
-           |the annotation must be followed by an access modifier
-           |(${"private"} or ${"protected"}) or ${"this"}.
-           |
-           |For example:
-           |  ${"class Sample @deprecated this(param: Parameter) { ..."}
-           |                           ^^^^
-           |""".stripMargin
-  }
 }
diff --git a/compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala b/compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala
index d6e687a1e..257d40bb0 100644
--- a/compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala
+++ b/compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala
@@ -212,4 +212,62 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       val AnnotatedPrimaryConstructorRequiresModifierOrThis(cls) :: Nil = messages
       assertEquals("AnotherClass", cls.show)
     }
+
+  @Test def overloadedMethodNeedsReturnType =
+    checkMessagesAfter("frontend") {
+      """
+        |class Scope() {
+        |  def foo(i: Int) = foo(i.toString)
+        |  def foo(s: String) = s
+        |}
+      """.stripMargin
+    }
+    .expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+      val defn = ictx.definitions
+
+      assertMessageCount(1, messages)
+      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
+      assertEquals("foo", tree.show)
+    }
+
+  @Test def recursiveValueNeedsReturnType =
+    checkMessagesAfter("frontend") {
+      """
+        |class Scope() {
+        |  lazy val i = i + 5
+        |}
+      """.stripMargin
+    }
+    .expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+      val defn = ictx.definitions
+
+      assertMessageCount(1, messages)
+      val RecursiveValueNeedsResultType(tree) :: Nil = messages
+      assertEquals("i", tree.show)
+    }
+
+  @Test def cyclicReferenceInvolvingImplicit =
+    checkMessagesAfter("frontend") {
+      """
+        |object implicitDefs {
+        |  def foo(implicit x: String) = 1
+        |  def bar() = {
+        |    implicit val x = foo
+        |    x
+        |  }
+        |}
+      """.stripMargin
+    }
+    .expect { (ictx, messages) =>
+      implicit val ctx: Context = ictx
+      val defn = ictx.definitions
+
+      assertMessageCount(1, messages)
+      val CyclicReferenceInvolvingImplicit(tree) :: Nil = messages
+      assertEquals("x", tree.name.show)
+    }
+
+
 }
-- 
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