Fix resolveRelativeUri() to handle correctly empty contained Uri(s).

pkg/analyzer/test/generated/all_the_rest_test.dart

 // Copyright (c) 2014, 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 analyzer.test.generated.all_the_rest_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 4384 matching lines @@
         new FileBasedSource(file, parseUriWithException("dart:core"));
     expect(source, isNotNull);
     expect(source.fullName, file.getAbsolutePath());
     expect(source.isInSystemLibrary, isTrue);
   }
 }
 
 @reflectiveTest
 class ResolveRelativeUriTest {
   void test_resolveRelative_dart_dartUri() {
-    Uri uri = parseUriWithException('dart:foo');
-    Uri relative = resolveRelativeUri(uri, parseUriWithException('dart:bar'));
-    expect(relative, isNotNull);
-    expect(relative.toString(), 'dart:bar');
+    _assertResolve('dart:foo', 'dart:bar', 'dart:bar');
   }
 
   void test_resolveRelative_dart_fileName() {
-    Uri uri = parseUriWithException("dart:test");
-    Uri relative = resolveRelativeUri(uri, parseUriWithException("lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "dart:test/lib.dart");
+    _assertResolve('dart:test', 'lib.dart', 'dart:test/lib.dart');
   }
 
   void test_resolveRelative_dart_filePath() {
-    Uri uri = parseUriWithException("dart:test");
-    Uri relative = resolveRelativeUri(uri, parseUriWithException("c/lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "dart:test/c/lib.dart");
+    _assertResolve('dart:test', 'c/lib.dart', 'dart:test/c/lib.dart');
   }
 
   void test_resolveRelative_dart_filePathWithParent() {
-    Uri uri = parseUriWithException("dart:test/b/test.dart");
-    Uri relative =
-        resolveRelativeUri(uri, parseUriWithException("../c/lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "dart:test/c/lib.dart");
+    _assertResolve(
+        'dart:test/b/test.dart', '../c/lib.dart', 'dart:test/c/lib.dart');
   }
 
   void test_resolveRelative_package_dartUri() {
-    Uri uri = parseUriWithException('package:foo/bar.dart');
-    Uri relative = resolveRelativeUri(uri, parseUriWithException('dart:test'));
-    expect(relative, isNotNull);
-    expect(relative.toString(), 'dart:test');
+    _assertResolve('package:foo/bar.dart', 'dart:test', 'dart:test');
+  }
+
+  void test_resolveRelative_package_emptyPath() {
+    _assertResolve('package:foo/bar.dart', '', 'package:foo/bar.dart');
   }
 
   void test_resolveRelative_package_fileName() {
-    Uri uri = parseUriWithException("package:b/test.dart");
-    Uri relative = resolveRelativeUri(uri, parseUriWithException("lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "package:b/lib.dart");
+    _assertResolve('package:b/test.dart', 'lib.dart', 'package:b/lib.dart');
   }
 
   void test_resolveRelative_package_fileNameWithoutPackageName() {
-    Uri uri = parseUriWithException("package:test.dart");
-    Uri relative = resolveRelativeUri(uri, parseUriWithException("lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "package:lib.dart");
+    _assertResolve('package:test.dart', 'lib.dart', 'package:lib.dart');
   }
 
   void test_resolveRelative_package_filePath() {
-    Uri uri = parseUriWithException("package:b/test.dart");
-    Uri relative = resolveRelativeUri(uri, parseUriWithException("c/lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "package:b/c/lib.dart");
+    _assertResolve('package:b/test.dart', 'c/lib.dart', 'package:b/c/lib.dart');
   }
 
   void test_resolveRelative_package_filePathWithParent() {
-    Uri uri = parseUriWithException("package:a/b/test.dart");
-    Uri relative =
-        resolveRelativeUri(uri, parseUriWithException("../c/lib.dart"));
-    expect(relative, isNotNull);
-    expect(relative.toString(), "package:a/c/lib.dart");
+    _assertResolve(
+        'package:a/b/test.dart', '../c/lib.dart', 'package:a/c/lib.dart');
+  }
+
+  void _assertResolve(String baseStr, String containedStr, String expectedStr) {
+    Uri base = Uri.parse(baseStr);

[Paul Berry, 2016/08/12 17:51:18]

I'm curious what the motivation was for using Uri.parse instead of
parseUriWithException (as the code previously did)

[scheglov, 2016/08/12 17:58:06]

To allow parsing empty Uri.

+    Uri contained = Uri.parse(containedStr);
+    Uri result = resolveRelativeUri(base, contained);
+    expect(result, isNotNull);
+    expect(result.toString(), expectedStr);
   }
 }
 
 @reflectiveTest
 class SDKLibrariesReaderTest extends EngineTestCase {
   void test_readFrom_dart2js() {
     LibraryMap libraryMap = new SdkLibrariesReader(true).readFromFile(
         FileUtilities2.createFile("/libs.dart"),
         r'''
 final Map<String, LibraryInfo> LIBRARIES = const <String, LibraryInfo> {
@@ skipping 73 matching lines @@
     expect(UriKind.fromEncoding(0x70), same(UriKind.PACKAGE_URI));
     expect(UriKind.fromEncoding(0x58), same(null));
   }
 
   void test_getEncoding() {
     expect(UriKind.DART_URI.encoding, 0x64);
     expect(UriKind.FILE_URI.encoding, 0x66);
     expect(UriKind.PACKAGE_URI.encoding, 0x70);
   }
 }