Read SDK and patches from a JSON file.

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

Index: pkg/front_end/lib/src/fasta/source/source_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
index ed7f26b85d0d9ca0add68be9e15a7eb47d022f45..b5a21fb4651e5d11b966f64ffffd0261f606939c 100644
--- a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
@@ -10,6 +10,8 @@ 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;
@@ -87,6 +89,8 @@ abstract class SourceLibraryBuilder<T extends TypeBuilder, R>
 
   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);
@@ -150,13 +154,13 @@ abstract class SourceLibraryBuilder<T extends TypeBuilder, R>
     Uri resolvedUri;
     Uri newFileUri;

[Siggi Cherem (dart-lang), 2017/05/24 16:24:04]

when newFileUri is null is the underlying loader doing the translation from
resolvedUri? If so, and if you are adopting the analyzer-style to translate
dart-uris, then we could drop this argument entirely.

[ahe, 2017/05/24 16:51:41]

I'm not adopting the analyzer style. I'm accepting that it exists, and making
sure that it remains supported by using resolveRelativeUri to compute unique
names for the parts instead of it being an accident.

     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));