Fix usage of UNKNOWN/CONFLICTING types for union.

lib/compiler/implementation/compiler.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 final bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 107 matching lines @@
       fields[field] = propagatedType;
     } else {
       fields[field] = fields[field].union(propagatedType);
     }
   }
 
   HType typeFromInitializersSoFar(Element field) {
     assert(field.isField());
     assert(field.enclosingElement.isClass());
     if (!fieldInitializers.containsKey(field.enclosingElement)) {
-      return HType.UNKNOWN;
+      return HType.CONFLICTING;
     }
     Map<Element, HType> fields = fieldInitializers[field.enclosingElement];
     return fields[field];
   }
 
   void updateFieldConstructorSetters(Element field, HType type) {
     assert(field.isField());
     assert(field.enclosingElement.isClass());
     Map<Element, HType> fields =
         fieldConstructorSetters.putIfAbsent(
           field.enclosingElement, () => new Map<Element, HType>());
     if (!fields.containsKey(field)) {
       fields[field] = type;
     } else {
       fields[field] = fields[field].union(type);
     }
   }
 
   // Check if this field is set in the constructor body.
   bool hasConstructorBodyFieldSetter(Element field) {
     if (!fieldConstructorSetters.containsKey(field.enclosingElement)) {
       return false;
     }
     return fieldConstructorSetters[field.enclosingElement][field] != null;
   }
 
   // Provide an optimistic estimate of the type of a field after construction.
+  // If the constructor body has setters for fields returns HType.UNKNOWN.
   // This only takes the initializer lists and field assignments in the
   // constructor body into account. The constructor body might have method calls
   // that could alter the field.
   HType optimisticFieldTypeAfterConstruction(Element field) {
     assert(field.isField());
     assert(field.enclosingElement.isClass());
 
     if (hasConstructorBodyFieldSetter(field)) {
-      // If there are field setters for this field in some constructor only one
-      // constructor then the type set will be the field type after
-      // construction.
-      if (field.enclosingElement.constructors.length == 1) {
+      // If there are field setters but there is only constructor then the type
+      // of the field is determined by the assignments in the constructor
+      // body.
+      ClassElement classElement = field.enclosingElement;
+      if (classElement.constructors.length == 1) {
         return fieldConstructorSetters[field.enclosingElement][field];
       } else {
         return HType.UNKNOWN;
       }
     } else if (fieldInitializers.containsKey(field.enclosingElement)) {
       HType type = fieldInitializers[field.enclosingElement][field];
-      return type == null ? HType.UNKNOWN : type;
+      return type == null ? HType.CONFLICTING : type;
     } else {
-      return HType.UNKNOWN;
+      return HType.CONFLICTING;
     }
   }
 
   void updateFieldSetters(Element field, HType type) {
     assert(field.isField());
     assert(field.enclosingElement.isClass());
     Map<Element, HType> fields =
         fieldSettersType.putIfAbsent(
           field.enclosingElement, () => new Map<Element, HType>());
     if (!fields.containsKey(field)) {
       fields[field] = type;
     } else {
       fields[field] = fields[field].union(type);
     }
   }
 
   // Returns the type that field setters are setting the field to based on what
   // have been seen during compilation so far.
   HType fieldSettersTypeSoFar(Element field) {
     assert(field.isField());
     assert(field.enclosingElement.isClass());
     if (!fieldSettersType.containsKey(field.enclosingElement)) {
-      return HType.UNKNOWN;
+      return HType.CONFLICTING;
     }
     Map<Element, HType> fields = fieldSettersType[field.enclosingElement];
-    if (!fields.containsKey(field)) return HType.UNKNOWN;
+    if (!fields.containsKey(field)) return HType.CONFLICTING;
     return fields[field];
   }
 }
 
 class Compiler implements DiagnosticListener {
   final Map<String, LibraryElement> libraries;
   int nextFreeClassId = 0;
   World world;
   String assembledCode;
   Namer namer;
@@ skipping 830 matching lines @@
                      f(int beginOffset, int endOffset)) {
     final beginOffset = begin.charOffset;
     final endOffset = end.charOffset + end.slowCharCount;
 
     // [begin] and [end] might be the same for the same empty token. This
     // happens for instance when scanning '$$'.
     assert(endOffset >= beginOffset);
     return f(beginOffset, endOffset);
   }
 }