Check cycles in redirecting factories.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

Index: sdk/lib/_internal/compiler/implementation/elements/modelx.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index fda82a7406b554fd4bb58c354a211b9125d355f5..6f863955307fdc151c5db7824809c726c89a373a 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -1275,22 +1275,15 @@ class FunctionElementX extends ElementX implements FunctionElement {
 
   bool get isRedirectingFactory => defaultImplementation != this;
 
-  FunctionElement get redirectionTarget {
-    if (this == defaultImplementation) return this;
-    var target = defaultImplementation;
-    Set<Element> seen = new Set<Element>();
-    seen.add(target);
-    while (!target.isErroneous() && target != target.defaultImplementation) {
-      target = target.defaultImplementation;
-      if (seen.contains(target)) {
-        // TODO(ahe): This is expedient for now, but it should be
-        // checked by the resolver.  Keeping http://dartbug.com/3970
-        // open to track this.
-        throw new SpannableAssertionFailure(
-            target, 'redirecting factory leads to cycle');
-      }
-    }
-    return target;
+  /// This field is set by the post process queue when checking for cycles.
+  FunctionElement internalRedirectionTarget;
+  set redirectionTarget(FunctionElement constructor) {
+    assert(constructor != null && internalRedirectionTarget == null);
+    internalRedirectionTarget = constructor;
+  }
+  get redirectionTarget {
+    return internalRedirectionTarget != null ? internalRedirectionTarget
+                                             : defaultImplementation;

[ngeoffray, 2013/09/18 11:19:23]

This looks weird. Depending on the current stage of the compiler the element
model could return you something different? Can't you just return
internalRedirectionTarget and have the callers deal if it's null?

[karlklose, 2013/09/18 12:30:39]

Actually I can decide which of them to return independent of their value.

internalRedirectionTarget still changes during post-processing, but the getter
is only called in the backend.

   }
 
   InterfaceType computeTargetType(Compiler compiler,