Handle comparison of empty URIs (sdk/24126).

Fixes issue where `.packages` provides a key mapped to an empty value (#24126).

[email protected]

Review URL: https://codereview.chromium.org//1298393004 .

Author: pq

pkg/analyzer/lib/src/generated/utilities_dart.dart

@@ -9,6 +9,34 @@ library engine.utilities.dart;
 
 import 'java_core.dart';
 
+/**
+ * Check whether [uri1] starts with (or 'is prefixed by') [uri2] by checking
+ * path segments.
+ */
+bool startsWith(Uri uri1, Uri uri2) {
+  List<String> uri1Segments = uri1.pathSegments;
+  List<String> uri2Segments = uri2.pathSegments.toList();
+  // Punt if empty (https://github.com/dart-lang/sdk/issues/24126)
+  if (uri2Segments.isEmpty) {
+    return false;
+  }
+  // Trim trailing empty segments ('/foo/' => ['foo', ''])
+  if (uri2Segments.last == '') {
+    uri2Segments.removeLast();
+  }
+
+  if (uri2Segments.length > uri1Segments.length) {
+    return false;
+  }
+
+  for (int i = 0; i < uri2Segments.length; ++i) {
+    if (uri2Segments[i] != uri1Segments[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
 /**
  * The enumeration `ParameterKind` defines the different kinds of parameters. There are two
  * basic kinds of parameters: required and optional. Optional parameters are further divided into
@@ -38,27 +66,3 @@ class ParameterKind extends Enum<ParameterKind> {
   const ParameterKind(String name, int ordinal, this.isOptional)
       : super(name, ordinal);
 }
-
-/**
- * Check whether [uri1] starts with (or 'is prefixed by') [uri2] by checking
- * path segments.
- */
-bool startsWith(Uri uri1, Uri uri2) {
-  List<String> uri1Segments = uri1.pathSegments;
-  List<String> uri2Segments = uri2.pathSegments.toList();
-  // Trim trailing empty segments ('/foo/' => ['foo', ''])
-  if (uri2Segments.last == '') {
-    uri2Segments.removeLast();
-  }
-
-  if (uri2Segments.length > uri1Segments.length) {
-    return false;
-  }
-
-  for (int i = 0; i < uri2Segments.length; ++i) {
-    if (uri2Segments[i] != uri1Segments[i]) {
-      return false;
-    }
-  }
-  return true;
-}

pkg/analyzer/test/generated/source_factory_test.dart

@@ -171,6 +171,9 @@ foo:http://www.google.com
             isTrue);
         expect(utils.startsWith(Uri.parse('/foo/bar'), Uri.parse('/foo/b')),
             isFalse);
+        // Handle odd URIs (https://github.com/dart-lang/sdk/issues/24126)
+        expect(utils.startsWith(Uri.parse('/foo/bar'), Uri.parse('')), isFalse);
+        expect(utils.startsWith(Uri.parse(''), Uri.parse('/foo/bar')), isFalse);
       });
     });
   });