Add bounds check in scope lookup (issue 26633)

pkg/analyzer/test/generated/resolver_test.dart

Index: pkg/analyzer/test/generated/resolver_test.dart
diff --git a/pkg/analyzer/test/generated/resolver_test.dart b/pkg/analyzer/test/generated/resolver_test.dart
index 11eee0be474ebcd0234f35c4e42aff557bb072db..102956ae860a7fdacc0d565196d82cb2b2a17888 100644
--- a/pkg/analyzer/test/generated/resolver_test.dart
+++ b/pkg/analyzer/test/generated/resolver_test.dart
@@ -42,6 +42,7 @@ main() {
   runReflectiveTests(ErrorResolverTest);
   runReflectiveTests(LibraryImportScopeTest);
   runReflectiveTests(LibraryScopeTest);
+  runReflectiveTests(PrefixedNamespaceTest);
   runReflectiveTests(ScopeTest);
   runReflectiveTests(StrictModeTest);
   runReflectiveTests(SubtypeManagerTest);
@@ -535,6 +536,35 @@ class LibraryScopeTest extends ResolverTestCase {
   }
 }
 
+@reflectiveTest
+class PrefixedNamespaceTest extends ResolverTestCase {
+  void test_lookup_missing() {
+    ClassElement element = ElementFactory.classElement2('A');
+    PrefixedNamespace namespace = new PrefixedNamespace('p', _toMap([element]));
+    expect(namespace.get('p.B'), isNull);
+  }
+
+  void test_lookup_missing_matchesPrefix() {
+    ClassElement element = ElementFactory.classElement2('A');
+    PrefixedNamespace namespace = new PrefixedNamespace('p', _toMap([element]));
+    expect(namespace.get('p'), isNull);
+  }
+
+  void test_lookup_valid() {
+    ClassElement element = ElementFactory.classElement2('A');
+    PrefixedNamespace namespace = new PrefixedNamespace('p', _toMap([element]));
+    expect(namespace.get('p.A'), same(element));
+  }
+
+  HashMap<String, Element> _toMap(List<Element> elements) {
+    HashMap<String, Element> map = new HashMap<String, Element>();
+    for (Element element in elements) {
+      map[element.name] = element;
+    }
+    return map;
+  }
+}
+
 class Scope_EnclosedScopeTest_test_define_duplicate extends Scope {
   GatheringErrorListener listener;