Analyzed CyclicErrors: report the correct symbol

Make reports about cycleSym not tree.name. We need then to use flagsUNSAFE, see
description.

* Store cycleSym in all relevant errors
* Mention cycleSym instead of tree.name in errors

Tests pass, and have the correct expectations both for `tree.name` and
`cycleSym.name`, tho we just show `cycleSym.name` and `tree.name` is less
accurate.

But at this point, I might be able to stop using `tree.name` altogether.

Author: Blaisorblade

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

@@ -109,6 +109,12 @@ class CyclicReference private (val denot: SymDenotation) extends TypeError {
   override def toMessage(implicit ctx: Context): Message = {
     val cycleSym = denot.symbol
 
+    // cycleSym.flags would try completing denot and would fail, but here we can use flagsUNSAFE to detect flags
+    // set by the parser.
+    val unsafeFlags = cycleSym.flagsUNSAFE
+    val isMethod = unsafeFlags.is(Method)
+    val isVal = !isMethod && cycleSym.isTerm
+
     /* This CyclicReference might have arisen from asking for `m`'s type while trying to infer it.
      * To try to diagnose this, walk the context chain searching for context in
      * Mode.InferringReturnType for the innermost member without type
@@ -117,13 +123,15 @@ class CyclicReference private (val denot: SymDenotation) extends TypeError {
     def errorMsg(cx: Context): Message = {
       if (cx.mode is Mode.InferringReturnType) {
         cx.tree match {
-          case tree: untpd.ValOrDefDef if inImplicitSearch && !tree.tpt.typeOpt.exists =>
-            // Can happen in implicit defs (#4709) or outside (#3253).
-            TermMemberNeedsResultTypeForImplicitSearch(cycleSym)
-          case tree: untpd.DefDef if !tree.tpt.typeOpt.exists =>
-            OverloadedOrRecursiveMethodNeedsResultType(tree.name)
-          case tree: untpd.ValDef if !tree.tpt.typeOpt.exists =>
-            RecursiveValueNeedsResultType(tree.name)
+          case tree: untpd.ValOrDefDef if !tree.tpt.typeOpt.exists =>
+            if (inImplicitSearch)
+              TermMemberNeedsResultTypeForImplicitSearch(tree.name, cycleSym)
+            else if (isMethod)
+              OverloadedOrRecursiveMethodNeedsResultType(tree.name, cycleSym)
+            else if (isVal)
+              RecursiveValueNeedsResultType(tree.name, cycleSym)
+            else
+              errorMsg(cx.outer)
           case _ =>
             errorMsg(cx.outer)
         }

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

@@ -1260,27 +1260,27 @@ object messages {
            |""".stripMargin
   }
 
-  case class OverloadedOrRecursiveMethodNeedsResultType(method: Names.Name)(implicit ctx: Context)
+  case class OverloadedOrRecursiveMethodNeedsResultType(methodName: Names.TermName, cycleSym: Symbol)(implicit ctx: Context)
   extends Message(OverloadedOrRecursiveMethodNeedsResultTypeID) {
     val kind = "Syntax"
-    val msg = hl"""overloaded or recursive method ${method} needs return type"""
+    val msg = hl"""overloaded or recursive ${cycleSym} needs return type"""
     val explanation =
-      hl"""Case 1: ${method} is overloaded
-          |If there are multiple methods named `${method}` and at least one definition of
+      hl"""Case 1: ${cycleSym} is overloaded
+          |If there are multiple methods named `${cycleSym}` and at least one definition of
           |it calls another, you need to specify the calling method's return type.
           |
-          |Case 2: ${method} is recursive
-          |If `${method}` calls itself on any path (even through mutual recursion), you need to specify the return type
-          |of `${method}` or of a definition it's mutually recursive with.
+          |Case 2: ${cycleSym} is recursive
+          |If `${cycleSym}` calls itself on any path (even through mutual recursion), you need to specify the return type
+          |of `${cycleSym}` or of a definition it's mutually recursive with.
           |""".stripMargin
   }
 
-  case class RecursiveValueNeedsResultType(value: Names.TermName)(implicit ctx: Context)
+  case class RecursiveValueNeedsResultType(valName: Names.TermName, cycleSym: Symbol)(implicit ctx: Context)
   extends Message(RecursiveValueNeedsResultTypeID) {
     val kind = "Syntax"
-    val msg = hl"""recursive value ${value} needs type"""
+    val msg = hl"""recursive ${cycleSym} needs type"""
     val explanation =
-      hl"""The definition of `${value}` is recursive and you need to specify its type.
+      hl"""The definition of `${cycleSym}` is recursive and you need to specify its type.
           |""".stripMargin
   }
 
@@ -2111,13 +2111,13 @@ object messages {
   }
 
   // Relative of CyclicReferenceInvolvingImplicit and RecursiveValueNeedsResultType
-  case class TermMemberNeedsResultTypeForImplicitSearch(cycleSym: Symbol)(implicit ctx: Context)
+  case class TermMemberNeedsResultTypeForImplicitSearch(memberName: Names.TermName, cycleSym: Symbol)(implicit ctx: Context)
     extends Message(TermMemberNeedsNeedsResultTypeForImplicitSearchID) {
     val kind = "Syntax"
     val msg = hl"""$cycleSym needs result type because its right-hand side attempts implicit search"""
     val explanation =
       hl"""|The right hand-side of $cycleSym's definition requires an implicit search at the highlighted position.
-           |To avoid this error, give `${cycleSym.name}` an explicit type.
+           |To avoid this error, give `$cycleSym` an explicit type.
            |""".stripMargin
   }
 }

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

@@ -207,8 +207,9 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
 
       assertMessageCount(1, messages)
-      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
-      assertEquals("foo", tree.show)
+      val OverloadedOrRecursiveMethodNeedsResultType(methodName, cycleSym) :: Nil = messages
+      assertEquals("foo", methodName.show)
+      assertEquals("foo", cycleSym.name.show)
     }
 
   @Test def recursiveMethodNeedsReturnType =
@@ -223,8 +224,9 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
 
       assertMessageCount(1, messages)
-      val OverloadedOrRecursiveMethodNeedsResultType(tree) :: Nil = messages
-      assertEquals("i", tree.show)
+      val OverloadedOrRecursiveMethodNeedsResultType(methodName, cycleSym) :: Nil = messages
+      assertEquals("i", methodName.show)
+      assertEquals("i", cycleSym.name.show)
     }
 
   @Test def recursiveValueNeedsReturnType =
@@ -239,10 +241,29 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
 
       assertMessageCount(1, messages)
-      val RecursiveValueNeedsResultType(tree) :: Nil = messages
-      assertEquals("i", tree.show)
+      val RecursiveValueNeedsResultType(valName, cycleSym) :: Nil = messages
+      assertEquals("i", valName.show)
+      assertEquals("i", cycleSym.name.show)
     }
 
+  @Test def recursiveValueNeedsReturnType2 =
+    checkMessagesAfter(FrontEnd.name) {
+      """
+        |class Scope() {
+        |  lazy val i = j + 5
+        |  lazy val j = i
+        |}
+      """.stripMargin
+    }
+      .expect { (ictx, messages) =>
+        implicit val ctx: Context = ictx
+
+        assertMessageCount(1, messages)
+        val RecursiveValueNeedsResultType(valName, cycleSym) :: Nil = messages
+        assertEquals("j", valName.show)
+        assertEquals("i", cycleSym.name.show)
+      }
+
   @Test def cyclicReferenceInvolving =
     checkMessagesAfter(FrontEnd.name) {
       """
@@ -290,8 +311,9 @@ class ErrorMessagesTests extends ErrorMessagesTest {
         implicit val ctx: Context = ictx
 
         assertMessageCount(1, messages)
-        val OverloadedOrRecursiveMethodNeedsResultType(name) :: Nil = messages
-        assertEquals("even", name.show)
+        val OverloadedOrRecursiveMethodNeedsResultType(methodName, cycleSym) :: Nil = messages
+        assertEquals("even", methodName.show)
+        assertEquals("odd", cycleSym.name.show)
       }
 
   @Test def mutualRecursion_i2001a =
@@ -312,13 +334,37 @@ class ErrorMessagesTests extends ErrorMessagesTest {
         implicit val ctx: Context = ictx
 
         assertMessageCount(1, messages)
-        val OverloadedOrRecursiveMethodNeedsResultType(denot) :: Nil = messages
+        val OverloadedOrRecursiveMethodNeedsResultType(methodName, cycleSym) :: Nil = messages
         // Not ideal behavior
-        assertEquals("foo", denot.show)
+        assertEquals("foo", methodName.show)
+        assertEquals("odd", cycleSym.name.show)
       }
 
+  @Test def mutualRecursion_i2001b =
+    checkMessagesAfter(FrontEnd.name) {
+      """
+        |class A {
+        |  def odd(x: Int) = if (x == 0) false else !even(x-1)
+        |  def even(x: Int) = {
+        |    val foo = {
+        |      if (x == 0) true else !odd(x-1) // error: overloaded or recursive method needs result type
+        |    }
+        |    false
+        |  }
+        |}
+      """.stripMargin
+    }
+      .expect { (ictx, messages) =>
+        implicit val ctx: Context = ictx
+
+        assertMessageCount(1, messages)
+        val OverloadedOrRecursiveMethodNeedsResultType(methodName, cycleSym) :: Nil = messages
+        // Not ideal behavior
+        assertEquals("foo", methodName.show)
+        assertEquals("odd", cycleSym.name.show)
+      }
 
-  @Test def termMemberNeedsNeedsResultTypeForImplicitSearch =
+  @Test def termMemberNeedsResultTypeForImplicitSearch =
     checkMessagesAfter(FrontEnd.name) {
       """
         |object implicitDefs {
@@ -334,8 +380,9 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
 
       assertMessageCount(1, messages)
-      val TermMemberNeedsResultTypeForImplicitSearch(tree) :: Nil = messages
-      assertEquals("x", tree.name.show)
+      val TermMemberNeedsResultTypeForImplicitSearch(memberName, cycleSym) :: Nil = messages
+      assertEquals("x", cycleSym.name.show)
+      assertEquals("x", memberName.show)
     }
 
   @Test def implicitSearchForcesImplicitRetType_i4709 =
@@ -359,8 +406,9 @@ class ErrorMessagesTests extends ErrorMessagesTest {
       implicit val ctx: Context = ictx
 
       assertMessageCount(1, messages)
-      val TermMemberNeedsResultTypeForImplicitSearch(tree) :: Nil = messages
-      assertEquals("ctx", tree.name.show)
+      val TermMemberNeedsResultTypeForImplicitSearch(memberName, cycleSym) :: Nil = messages
+      assertEquals("ctx", memberName.show)
+      assertEquals("ctx", cycleSym.name.show)
     }
 
   @Test def implicitSearchForcesNonImplicitRetTypeOnExplicitImport_i3253 =
@@ -377,8 +425,9 @@ class ErrorMessagesTests extends ErrorMessagesTest {
         implicit val ctx: Context = ictx
 
         assertMessageCount(1, messages)
-        val TermMemberNeedsResultTypeForImplicitSearch(tree) :: Nil = messages
-        assertEquals("test", tree.name.show)
+        val TermMemberNeedsResultTypeForImplicitSearch(memberName, cycleSym) :: Nil = messages
+        assertEquals("test", memberName.show)
+        assertEquals("test", cycleSym.name.show)
       }
 
   @Test def superQualMustBeParent =

tests/neg/i2001b.scala

@@ -0,0 +1,9 @@
+class A {
+  def odd(x: Int) = if (x == 0) false else !even(x-1)
+  def even(x: Int) = {
+    val foo = {
+      if (x == 0) true else !odd(x-1) // error: overloaded or recursive method needs result type
+    }
+    false
+  }
+}