Report compile-time error if using `this` implicitly in initializers

pkg/compiler/lib/src/resolution/members.dart

Index: pkg/compiler/lib/src/resolution/members.dart
diff --git a/pkg/compiler/lib/src/resolution/members.dart b/pkg/compiler/lib/src/resolution/members.dart
index 652387b9ab146828326a32ce5cdb473311b9a15c..7aa3e1dcdf068bb5d1aceced24f1126deddaa1b7 100644
--- a/pkg/compiler/lib/src/resolution/members.dart
+++ b/pkg/compiler/lib/src/resolution/members.dart
@@ -2112,6 +2112,9 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
    * This field is updated when nested closures are visited.
    */
   Element enclosingElement;
+
+  /// Whether we are in a context where `this` is accessible (this will be false
+  /// in static contexts, factory methods, and field initializers).
   bool inInstanceContext;
   bool inCheckContext;
   bool inCatchBlock;
@@ -2304,6 +2307,19 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
               node, node.source, MessageKind.CANNOT_RESOLVE,
               {'name': node});
           registry.registerThrowNoSuchMethod();
+
+          // We also report an error within initializers because `this` is
+          // implicitly accessed when unqualified identifiers are not resolved.
+          // For details, see section 16.14.3 of the spec (2nd edition):
+          //   An unqualified invocation `i` of the form `id(a1, ...)`
+          //   ...
+          //   If `i` does not occur inside a top level or static function, `i`
+          //   is equivalent to `this.id(a1 , ...)`.
+          if ((enclosingElement.isInstanceMember && enclosingElement.isField) ||
+              (enclosingElement.isGenerativeConstructor)) {
+            compiler.reportError(

[Johnni Winther, 2015/04/10 07:55:50]

From a users perspective, it might be better to have a special message that
combines the information from CANNOT_RESOLVE and NO_INSTANCE_AVAILABLE for this
situation.

I you want to do that, you could add a named argument {bool reportError: false}
to [warnAndCreateErroneousElement] (and maybe name it to
`reportAndCreateErroneousElement`) and use the `reportError` to either call
`compiler.reportWarning` or `compiler.reportError`.

[Siggi Cherem (dart-lang), 2015/04/10 18:56:26]

I have it a try. WDYT?

+                node, MessageKind.NO_INSTANCE_AVAILABLE, {'name': node.source});
+          }
         }
       } else if (element.isErroneous) {
         // Use the erroneous element.