Merge pull request #195 from smarter/fix/singleton-cycles

Detect cycles involving types bounded by singleton types

Author: odersky

src/dotty/tools/dotc/typer/Checking.scala

@@ -105,6 +105,9 @@ object Checking {
     }
 
     def apply(tp: Type) = tp match {
+      case tp: TermRef =>
+        this(tp.info)
+        mapOver(tp)
       case tp @ RefinedType(parent, name) =>
         val parent1 = this(parent)
         val saved = cycleOK

test/dotc/tests.scala

@@ -100,6 +100,8 @@ class tests extends CompilerTest {
   @Test def neg_badAuxConstr = compileFile(negDir, "badAuxConstr", xerrors = 2)
   @Test def neg_typetest = compileFile(negDir, "typetest", xerrors = 1)
   @Test def neg_t1569_failedAvoid = compileFile(negDir, "t1569-failedAvoid", xerrors = 1)
+  @Test def neg_cycles = compileFile(negDir, "cycles", xerrors = 6)
+
   @Test def dotc = compileDir(dotcDir + "tools/dotc", twice)(allowDeepSubtypes)
   @Test def dotc_ast = compileDir(dotcDir + "tools/dotc/ast", twice)
   @Test def dotc_config = compileDir(dotcDir + "tools/dotc/config", twice)

tests/neg/cycles.scala

@@ -2,3 +2,28 @@ class Foo[T <: U, U <: T]
 
 class Bar[T >: T]
 
+class A {
+  val x: T = ???
+  type T <: x.type
+}
+
+class B {
+  type T <: x.type
+  val x: T = ???
+}
+
+class C {
+  val x: D#T = ???
+  class D {
+    type T <: x.type
+    val z: x.type = ???
+  }
+}
+
+class E {
+  class F {
+    type T <: x.type
+    val z: x.type = ???
+  }
+  val x: F#T = ???
+}