Handle fields with initializers in constant constructors.

pkg/compiler/lib/src/elements/modelx.dart

 // Copyright (c) 2013, 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.
 
 library elements.modelx;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
 import '../common/resolution.dart' show Resolution, ParsingContext;
 import '../compiler.dart' show Compiler;
@@ skipping 1407 matching lines @@
       ConstantVariableMixin originVariable = origin;
       originVariable.constant = value;
       return;
     }
     if (constantCache != null &&
         constantCache.kind == ConstantExpressionKind.ERRONEOUS) {
       // TODO(johnniwinther): Find out why we sometimes compute a non-erroneous
       // constant for a variable already known to be erroneous.
       return;
     }
-    assert(invariant(this, constantCache == null || constantCache == value,
-        message: "Constant has already been computed for $this. "
-            "Existing constant: "
-            "${constantCache != null ? constantCache.toStructuredText() : ''}, "
-            "New constant: ${value != null ? value.toStructuredText() : ''}."));
+    if (constantCache != null && constantCache != value) {
+      // Allow setting the constant as erroneous. Constants computed during
+      // resolution are locally valid but might be effectively erroneous. For
+      // instance `a ? true : false` where a is `const a = m()`. Since `a` is
+      // declared to be constant, the conditional is assumed valid, but when
+      // computing the value we see that it isn't.
+      // TODO(johnniwinther): Remove this exception when all constant
+      // expressions are computed during resolution.
+      assert(invariant(
+          this, value == null || value.kind == ConstantExpressionKind.ERRONEOUS,
+          message: "Constant has already been computed for $this. "
+              "Existing constant: "
+              "${constantCache != null ? constantCache.toStructuredText() : ''}"
+              ", New constant: "
+              "${value != null ? value.toStructuredText() : ''}."));
+    }
     constantCache = value;
   }
 }
 
 abstract class VariableElementX extends ElementX
     with AstElementMixin, ConstantVariableMixin
     implements VariableElement {
   final Token token;
   final VariableList variables;
   VariableDefinitions definitionsCache;
@@ skipping 1864 matching lines @@
       body = node.asFunctionExpression().body;
     }
     return new ParsedResolvedAst(
         declaration,
         node,
         body,
         definingElement.treeElements,
         definingElement.compilationUnit.script.resourceUri);
   }
 }