Local declarations take precedence over exports.

pkg/front_end/lib/src/fasta/builder/library_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/library_builder.dart b/pkg/front_end/lib/src/fasta/builder/library_builder.dart
index e3067aa8ccbf980457e61dbfc39343eb82734d3b..ec866a9ee1e4a64e0076b2ba39ffea07ffb29729 100644
--- a/pkg/front_end/lib/src/fasta/builder/library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/library_builder.dart
@@ -98,6 +98,11 @@ abstract class LibraryBuilder<T extends TypeBuilder, R> extends Builder {
     Builder existing = map[name];
     if (existing == member) return false;
     if (existing != null) {
+      // For each entry mapping key `k` to declaration `d` in `NS` an entry
+      // mapping `k` to `d` is added to the exported namespace of `L` unless a
+      // top-level declaration with the name `k` exists in `L`.
+      if (existing.parent == this) return false;

[ahe, 2017/05/22 11:39:45]

buildAmbiguousBuilder should take care of this.

[scheglov, 2017/05/22 18:35:24]

Ah, I see now.
https://codereview.chromium.org/2893383002

+
       Builder result =
           buildAmbiguousBuilder(name, existing, member, -1, isExport: true);
       map[name] = result;