2 files changed, 76 insertions, 4 deletions
diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index df1ba1e2ea..02bee5e369 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -1017,14 +1017,16 @@ trait Trees extends api.Trees { self: SymbolTable =>
   trait CannotHaveAttrs extends Tree {
     override def canHaveAttrs = false
 
-    private def unsupported(what: String, args: Any*) =
-      throw new UnsupportedOperationException(s"$what($args) inapplicable for "+self.toString)
+    private def requireLegal(value: Any, allowed: Any, what: String) =
+      require(value == allowed, s"can't set $what for $self to value other than $allowed")
 
     super.setPos(NoPosition)
-    override def setPos(pos: Position) = unsupported("setPos", pos)
+    override def setPos(pos: Position) = { requireLegal(pos, NoPosition, "pos"); this }
+    override def pos_=(pos: Position) = setPos(pos)
 
     super.setType(NoType)
-    override def tpe_=(t: Type) = if (t != NoType) unsupported("tpe_=", t)
+    override def setType(t: Type) = { requireLegal(t, NoType, "tpe"); this }
+    override def tpe_=(t: Type) = setType(t)
   }
 
   case object EmptyTree extends TermTree with CannotHaveAttrs { override def isEmpty = true; val asList = List(this) }
diff --git a/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala b/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala
new file mode 100644
index 0000000000..5867a9030b
--- /dev/null
+++ b/test/junit/scala/tools/nsc/symtab/CannotHaveAttrsTest.scala
@@ -0,0 +1,70 @@
+package scala.tools.nsc
+package symtab
+
+import org.junit.Assert._
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+import scala.tools.testing.AssertUtil.assertThrows
+import scala.reflect.internal.util.OffsetPosition
+
+@RunWith(classOf[JUnit4])
+class CannotHaveAttrsTest {
+  class CustomSymbolTable extends SymbolTableForUnitTesting {
+    object CHA extends CannotHaveAttrs {
+      def canEqual(that: Any): Boolean = ???
+      def productArity: Int = ???
+      def productElement(n: Int): Any = ???
+    }
+    val attrlessTrees = List(CHA, EmptyTree, emptyValDef, pendingSuperCall)
+  }
+  def withCtx(body: CustomSymbolTable => Unit) = body(new CustomSymbolTable)
+
+  @Test
+  def canHaveAttrsIsFalse = withCtx { st => import st._
+    attrlessTrees.foreach { t =>
+      assertFalse(t.canHaveAttrs)
+    }
+  }
+
+  @Test
+  def defaultPosAssignment = withCtx { st => import st._
+    attrlessTrees.foreach { t =>
+      assertEquals(t.pos, NoPosition)
+      t.pos = NoPosition
+      assertEquals(t.pos, NoPosition)
+      t.setPos(NoPosition)
+      assertEquals(t.pos, NoPosition)
+    }
+  }
+
+  @Test
+  def defaultTpeAssignment = withCtx { st => import st._
+    attrlessTrees.foreach { t =>
+      assertEquals(t.tpe, NoType)
+      t.tpe = NoType
+      assertEquals(t.tpe, NoType)
+      t.setType(NoType)
+      assertEquals(t.tpe, NoType)
+    }
+  }
+
+  @Test
+  def nonDefaultPosAssignmentFails = withCtx { st => import st._
+    val pos = new OffsetPosition(null, 0)
+    attrlessTrees.foreach { t =>
+      assertThrows[IllegalArgumentException] { t.pos = pos }
+      assertThrows[IllegalArgumentException] { t.setPos(pos) }
+    }
+  }
+
+  @Test
+  def nonDefaultTpeAssignmentFails = withCtx { st => import st._
+    val tpe = typeOf[Int]
+    attrlessTrees.foreach { t =>
+      assertThrows[IllegalArgumentException] { t.tpe = tpe }
+      assertThrows[IllegalArgumentException] { t.setType(tpe) }
+    }
+  }
+}