Revert "Switch FE to use the libraries.json format."

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

 // Copyright (c) 2016, 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 fasta.uri_translator_impl;
 
-import 'package:front_end/src/base/libraries_specification.dart'
-    show TargetLibrariesSpecification;
+import 'dart:async' show Future;
+import 'dart:convert' show JSON;
+
+import 'package:front_end/file_system.dart'
+    show FileSystem, FileSystemException;
 import 'package:front_end/src/fasta/compiler_context.dart' show CompilerContext;
 import 'package:front_end/src/fasta/fasta_codes.dart';
 import 'package:front_end/src/fasta/severity.dart' show Severity;
 import 'package:front_end/src/fasta/uri_translator.dart';
+import 'package:package_config/packages_file.dart' as packages_file show parse;
 import 'package:package_config/packages.dart' show Packages;
+import 'package:package_config/src/packages_impl.dart' show MapPackages;
+
+import 'deprecated_problems.dart' show deprecated_inputError;
+
+/// Read the JSON file with defined SDK libraries from the given [uri] in the
+/// [fileSystem] and return the mapping from parsed Dart library names (e.g.
+/// `math`) to file URIs.
+Future<Map<String, Uri>> computeDartLibraries(
+    FileSystem fileSystem, Uri uri) async {
+  if (uri == null) return const <String, Uri>{};
+  Map<String, String> libraries = JSON
+      .decode(await fileSystem.entityForUri(uri).readAsString())["libraries"];
+  Map<String, Uri> result = <String, Uri>{};
+  libraries.forEach((String name, String path) {
+    result[name] = uri.resolveUri(new Uri.file(path));
+  });
+  return result;
+}
+
+Future<Map<String, List<Uri>>> computeDartPatches(
+    FileSystem fileSystem, Uri uri) async {
+  // TODO(ahe): Read patch information.
+  return const <String, List<Uri>>{};
+}
 
 /// Implementation of [UriTranslator] for absolute `dart` and `package` URIs.
 class UriTranslatorImpl implements UriTranslator {
-  /// Library information for platform libraries.
-  final TargetLibrariesSpecification dartLibraries;
+  /// Mapping from Dart library names (e.g. `math`) to file URIs.
+  final Map<String, Uri> dartLibraries;
+
+  // TODO(ahe): We probably want this to be `Map<String, Uri>`, that is, just
+  // one patch library (with parts).
+  /// Mapping from Dart library names to the file URIs of patches to apply.
+  final Map<String, List<Uri>> dartPatches;
 
   /// Mapping from package names (e.g. `angular`) to the file URIs.
   final Packages packages;
 
-  UriTranslatorImpl(this.dartLibraries, this.packages);
+  UriTranslatorImpl(this.dartLibraries, this.dartPatches, this.packages);
 
   @override
-  List<Uri> getDartPatches(String libraryName) =>
-      dartLibraries.libraryInfoFor(libraryName)?.patches;
+  List<Uri> getDartPatches(String libraryName) => dartPatches[libraryName];
 
   @override
   bool isPlatformImplementation(Uri uri) {
     if (uri.scheme != "dart") return false;
     String path = uri.path;
-    return dartLibraries.libraryInfoFor(path) == null || path.startsWith("_");
+    return dartLibraries[path] == null || path.startsWith("_");
   }
 
   @override
   // TODO(sigmund, ahe): consider expanding this API to include an error
   // callback, so we can provide an error location when one is available. For
   // example, if the error occurs in an `import`.
   Uri translate(Uri uri) {
     if (uri.scheme == "dart") return _translateDartUri(uri);
     if (uri.scheme == "package") return _translatePackageUri(uri);
     return null;
   }
 
   /// Return the file URI that corresponds to the given `dart` URI, or `null`
   /// if there is no corresponding Dart library registered.
   Uri _translateDartUri(Uri uri) {
     if (!uri.isScheme('dart')) return null;
     String path = uri.path;
 
     int index = path.indexOf('/');
-    if (index == -1) return dartLibraries.libraryInfoFor(path)?.uri;
+    if (index == -1) return dartLibraries[path];
 
     String libraryName = path.substring(0, index);
     String relativePath = path.substring(index + 1);
-    Uri libraryFileUri = dartLibraries.libraryInfoFor(libraryName).uri;
+    Uri libraryFileUri = dartLibraries[libraryName];
     return libraryFileUri?.resolve(relativePath);
   }
 
   /// Return the file URI that corresponds to the given `package` URI, or
   /// `null` if the `package` [uri] format is invalid, or there is no
   /// corresponding package registered.
   Uri _translatePackageUri(Uri uri) {
     try {
       // TODO(sigmund): once we remove the `parse` API, we can ensure that
       // packages will never be null and get rid of `?` below.
       return packages?.resolve(uri, notFound: _packageUriNotFound);
     } on ArgumentError catch (e) {
       // TODO(sigmund): catch a more precise error when
       // https://github.com/dart-lang/package_config/issues/40 is fixed.
       CompilerContext.current.reportWithoutLocation(
           templateInvalidPackageUri.withArguments(uri, '$e'), Severity.error);
       return null;
     }
   }
 
   static Uri _packageUriNotFound(Uri uri) {
     String name = uri.pathSegments.first;
     CompilerContext.current.reportWithoutLocation(
         templatePackageNotFound.withArguments(name, uri), Severity.error);
     // TODO(sigmund, ahe): ensure we only report an error once,
     // this null result will likely cause another error further down in the
     // compiler.
     return null;
   }
+
+  static Future<UriTranslator> parse(FileSystem fileSystem, Uri sdk,
+      {Uri packages}) async {
+    Uri librariesJson = sdk?.resolve("lib/libraries.json");
+
+    // TODO(ahe): Provide a value for this file.
+    Uri patches = null;
+
+    packages ??= Uri.base.resolve(".packages");
+
+    List<int> bytes;
+    try {
+      bytes = await fileSystem.entityForUri(packages).readAsBytes();
+    } on FileSystemException catch (e) {
+      deprecated_inputError(packages, -1, e.message);
+    }
+
+    Packages parsedPackages;
+    try {
+      parsedPackages = new MapPackages(packages_file.parse(bytes, packages));
+    } on FormatException catch (e) {
+      return deprecated_inputError(packages, e.offset, e.message);
+    }
+
+    var dartLibraries = await computeDartLibraries(fileSystem, librariesJson);
+    return new UriTranslatorImpl(dartLibraries,
+        await computeDartPatches(fileSystem, patches), parsedPackages);
+  }
 }