[CFE] Get fragment from default package - use language version if any

Language versioning specifies that an empty-name-entry in .packages
specifies a sort of "default package" that a non-package file should
pretend to be a part of "for any purpose where that matters,
including choosing the default language level."

Change-Id: I16f4b2f5e4d3ca1e82d2189321e2be5c43e3b260
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112089
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

DEPS

@@ -107,7 +107,7 @@ vars = {
   "mustache_tag" : "5e81b12215566dbe2473b2afd01a8a8aedd56ad9",
   "oauth2_tag": "1.2.1",
   "observatory_pub_packages_rev": "0894122173b0f98eb08863a7712e78407d4477bc",
-  "package_config_tag": "1.0.5",
+  "package_config_tag": "2453cd2e78c2db56ee2669ced17ce70dd00bf576", # should be 1.1.0
   "package_resolver_tag": "1.0.10",
   "path_tag": "1.6.2",
   "pedantic_tag": "v1.8.0",

pkg/analyzer/test/src/context/source_test.dart

@@ -58,4 +58,19 @@ class _MockPackages implements Packages {
   Uri resolve(Uri packageUri, {Uri notFound(Uri packageUri)}) {
     fail('Unexpected invocation of resolve');
   }
+
+  @override
+  String get defaultPackageName {
+    fail('Unexpected invocation of defaultPackageName');
+  }
+
+  @override
+  String libraryMetadata(Uri libraryUri, String key) {
+    fail('Unexpected invocation of libraryMetadata');
+  }
+
+  @override
+  String packageMetadata(String packageName, String key) {
+    fail('Unexpected invocation of packageMetadata');
+  }
 }

pkg/front_end/lib/src/base/processed_options.dart

@@ -494,7 +494,8 @@ class ProcessedOptions {
     if (contents != null) {
       _packagesUri = file;
       try {
-        Map<String, Uri> map = package_config.parse(contents, file);
+        Map<String, Uri> map =
+            package_config.parse(contents, file, allowDefaultPackage: true);
         return new MapPackages(map);
       } on FormatException catch (e) {
         report(

pkg/front_end/lib/src/fasta/loader.dart

@@ -118,6 +118,9 @@ abstract class Loader {
 
           default:
             fileUri = uri;
+            // Check for empty package name entry (redirecting to package name
+            // from which we should get the fragment part).
+            packageFragment = target.uriTranslator?.getDefaultPackageFragment();
             break;
         }
       }

pkg/front_end/lib/src/fasta/uri_translator.dart

@@ -50,6 +50,16 @@ class UriTranslator {
     return packageBaseUri.fragment;
   }
 
+  /// Get the fragment for the package specified as the default package, if any.
+  String getDefaultPackageFragment() {
+    Uri emptyPackageRedirect = packages.asMap()[""];
+    if (emptyPackageRedirect == null) return null;
+    String packageName = emptyPackageRedirect.toString();
+    Uri packageBaseUri = packages.asMap()[packageName];
+    if (packageBaseUri == null) return null;
+    return packageBaseUri.fragment;
+  }
+
   bool isLibrarySupported(String libraryName) {
     // TODO(sigmund): change this to `?? false` when all backends provide the
     // `libraries.json` file by default (Issue #32657).

pkg/front_end/pubspec.yaml

@@ -9,7 +9,7 @@ environment:
   sdk: '>=2.2.2 <3.0.0'
 dependencies:
   kernel: 0.3.22
-  package_config: '^1.0.1'
+  package_config: '^1.1.0'
   path: '^1.3.9'
   yaml: '^2.1.12'
 dev_dependencies:

pkg/front_end/test/language_versioning/data/package_non_package_default_version/.packages

@@ -0,0 +1,2 @@
+foo:lib/#dart=2.5.3-dev.2
+:foo

pkg/front_end/test/language_versioning/data/package_non_package_default_version/lib/foo.dart

@@ -0,0 +1,9 @@
+// Copyright (c) 2019, 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: languageVersion=2.5*/
+
+foo() {
+  print("Hello from foo!");
+}

pkg/front_end/test/language_versioning/data/package_non_package_default_version/main.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2019, 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.
+
+import 'package:foo/foo.dart';
+
+// Version comes from "default package" in .packages.
+
+/*library: languageVersion=2.5*/
+
+main() {
+  foo();
+}

pkg/front_end/test/language_versioning/data/package_non_package_default_version/pubspec.yaml

@@ -0,0 +1,5 @@
+# Copyright (c) 2019, 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.
+
+# Analyzer workaround, see https://github.com/dart-lang/sdk/issues/37513