Read SDK and patches from a JSON file.

pkg/front_end/lib/src/fasta/source/source_library_builder.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.source_library_builder;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
 import 'package:front_end/src/fasta/scanner/token.dart' show SymbolToken;
 
 import 'package:kernel/ast.dart' show ProcedureKind;
 
+import '../../base/resolve_relative_uri.dart' show resolveRelativeUri;
+
 import '../combinator.dart' show Combinator;
 
 import '../errors.dart' show inputError, internalError;
 
 import '../export.dart' show Export;
 
 import '../import.dart' show Import;
 
 import 'source_loader.dart' show SourceLoader;
 
@@ skipping 57 matching lines @@
   SourceLibraryBuilder.fromScopes(
       this.loader, this.fileUri, this.libraryDeclaration, this.importScope)
       : currentDeclaration = libraryDeclaration,
         super(
             fileUri, libraryDeclaration.toScope(importScope), new Scope.top());
 
   Uri get uri;
 
   bool get isPart => partOfName != null || partOfUri != null;
 
+  bool get isPatch;
+
   List<T> get types => libraryDeclaration.types;
 
   T addNamedType(String name, List<T> arguments, int charOffset);
 
   T addMixinApplication(T supertype, List<T> mixins, int charOffset);
 
   T addType(T type) {
     currentDeclaration.addType(type);
     return type;
   }
@@ skipping 43 matching lines @@
         prefix,
         combinators,
         charOffset,
         prefixCharOffset));
   }
 
   void addPart(List<MetadataBuilder> metadata, String path) {
     Uri resolvedUri;
     Uri newFileUri;
     if (uri.scheme == "dart") {
-      resolvedUri = new Uri(scheme: "dart", path: "${uri.path}/$path");
+      resolvedUri = resolveRelativeUri(uri, Uri.parse(path));
       newFileUri = fileUri.resolve(path);
     } else {
       resolvedUri = uri.resolve(path);
-
-      // TODO(ahe): This is wrong for package URIs.
-      newFileUri = fileUri.resolve(path);
+      if (uri.scheme != "package") {
+        newFileUri = fileUri.resolve(path);
+      }
     }
     parts
         .add(loader.read(resolvedUri, -1, fileUri: newFileUri, accessor: this));
   }
 
   void addPartOf(List<MetadataBuilder> metadata, String name, String uri) {
     partOfName = name;
     partOfUri = uri == null ? null : this.uri.resolve(uri);
   }
 
@@ skipping 397 matching lines @@
   /// synthesize type variables on the factory matching the class'.
   void addFactoryDeclaration(
       ProcedureBuilder procedure, DeclarationBuilder<T> factoryDeclaration) {
     factoryDeclarations[procedure] = factoryDeclaration;
   }
 
   Scope toScope(Scope parent) {
     return new Scope(members, setters, parent, isModifiable: false);
   }
 }