Improved a cyclic reference error message.

"illegal cyclic reference involving value <import>" not
so useful.

Author: paulp

src/compiler/scala/tools/nsc/typechecker/TypeDiagnostics.scala

@@ -494,6 +494,11 @@ trait TypeDiagnostics {
     def cyclicReferenceMessage(sym: Symbol, tree: Tree) = condOpt(tree) {
       case ValDef(_, _, tpt, _) if tpt.tpe == null        => "recursive "+sym+" needs type"
       case DefDef(_, _, _, _, tpt, _) if tpt.tpe == null  => List(cyclicAdjective(sym), sym, "needs result type") mkString " "
+      case Import(expr, selectors)                        =>
+        ( "encountered unrecoverable cycle resolving import." +
+          "\nNote: this is often due in part to a class depending on a definition nested within its companion." +
+          "\nIf applicable, you may wish to try moving some members into another object."
+        )
     }
 
     /** Report a type error.
@@ -508,7 +513,11 @@ trait TypeDiagnostics {
 
       ex match {
         case CyclicReference(sym, info: TypeCompleter) =>
-          contextError(ex.pos, cyclicReferenceMessage(sym, info.tree) getOrElse ex.getMessage())
+          val pos = info.tree match {
+            case Import(expr, _)  => expr.pos
+            case _                => ex.pos
+          }
+          contextError(pos, cyclicReferenceMessage(sym, info.tree) getOrElse ex.getMessage())
 
           if (sym == ObjectClass)
             throw new FatalError("cannot redefine root "+sym)

test/files/neg/cyclics-import.check

@@ -0,0 +1,15 @@
+cyclics-import.scala:1: error: encountered unrecoverable cycle resolving import.
+Note: this is often due in part to a class depending on a definition nested within its companion.
+If applicable, you may wish to try moving some members into another object.
+import User.UserStatus._
+            ^
+cyclics-import.scala:12: error: not found: type Value
+    type UserStatus = Value
+                      ^
+cyclics-import.scala:14: error: not found: value Value
+    val Active = Value("1")
+                 ^
+cyclics-import.scala:15: error: not found: value Value
+    val Disabled = Value("2")
+                   ^
+four errors found

test/files/neg/cyclics-import.scala

@@ -0,0 +1,17 @@
+import User.UserStatus._
+
+class User {
+  var id: Int = 0
+  var email: String = null
+  var password: String = null
+  var userStatus: UserStatus = null
+}
+
+object User {
+  object UserStatus extends Enumeration {
+    type UserStatus = Value
+
+    val Active = Value("1")
+    val Disabled = Value("2")
+  }
+}

test/files/neg/t1845.check

@@ -1,4 +1,6 @@
-t1845.scala:9: error: illegal cyclic reference involving value <import>
-  val lexical = new StdLexical
-                    ^
+t1845.scala:6: error: encountered unrecoverable cycle resolving import.
+Note: this is often due in part to a class depending on a definition nested within its companion.
+If applicable, you may wish to try moving some members into another object.
+  import lexical._
+         ^
 one error found

test/files/neg/t2870.check

@@ -1,7 +1,9 @@
 t2870.scala:1: error: not found: type Jar (similar: Jars)
 class Jars(jar: Jar)
                 ^
-t2870.scala:6: error: illegal cyclic reference involving value <import>
-  val scala = fromClasspathString(javaClassPath) 
-                                  ^
+t2870.scala:4: error: encountered unrecoverable cycle resolving import.
+Note: this is often due in part to a class depending on a definition nested within its companion.
+If applicable, you may wish to try moving some members into another object.
+  import scala.util.Properties.javaClassPath
+                    ^
 two errors found