Add support for .sdkext file to analysis server

pkg/analysis_server/lib/src/sdk_ext.dart

+// Copyright (c) 2015, 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 analysis_server.src.sdk_ext;
+
+import 'dart:async';
+import 'dart:collection';
+import 'dart:convert';
+import 'dart:core' hide Resource;
+
+import 'package:analysis_server/uri/resolver_provider.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/source/package_map_resolver.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/java_io.dart' show JavaFile;
+import 'package:analyzer/src/generated/source_io.dart' show FileBasedSource;
+
+/// Given a packageMap (see [PackageMapProvider]), check in each package's lib
+/// directory for the existence of a `.sdkext` file. This file must contain a
+/// JSON encoded map. Each key in the map is a `dart:` library name. Each value
+/// is a path (relative to the directory containing `.sdkext`) to a dart script
+/// for the given library. For example:
+/// {
+///   "dart:sky": "../sdk_ext/dart_sky.dart"
+/// }
+///
+/// If a key doesn't begin with `dart:` it is ignored.
+class SdkExtUriResolver extends UriResolver {

[Brian Wilkerson, 2015/07/07 22:10:18]

The lack of an implementation of restoreAbsolute will probably cause problems.
We use that to method to get back to a string like "dart:sky" for the purposes
of inserting import statements, refactorings, etc. (Though now that I'm thinking
about it, we might be able to get rid of that method at this point.) Still, we
probably ought to implement it until we can fix the callers.

[Cutch, 2015/07/08 14:18:17]

I've implemented this and added tests but I'll note that both |DartUriResolver|
and |CustomUriResolver| lack implementations of restoreAbsolute. I wonder if
this is already unused?

[Brian Wilkerson, 2015/07/08 14:48:28]

It's used in 5 places in the analysis server. I'm not sure why it isn't
implemented in those places.

+  static const String DOT_SDK_EXT_NAME = '.sdkext';
+  static const String DART_COLON_PREFIX = 'dart:';
+
+  final Map<String, String> _urlMappings = <String,String>{};
+
+  /// Construct a [SdkExtUriResolver] from a package map
+  /// (see [PackageMapProvider]).
+  SdkExtUriResolver(Map<String, List<Folder>> packageMap) {
+    if (packageMap == null) {
+      return;
+    }
+    packageMap.forEach(_processPackage);
+  }
+
+  /// Programmatically add a new SDK extension given a JSON description
+  /// ([sdkExtJSON]) and a lib directory ([libDir]).
+  void addSdkExt(String sdkExtJSON, Folder libDir) {
+    _processSdkExt(sdkExtJSON, libDir);
+  }
+
+  /// Return the path mapping for [libName] or null if there is none.
+  String operator[](String libName) => _urlMappings[libName];
+
+  /// Number of sdk extensions.
+  int get length => _urlMappings.length;
+
+  @override
+  Source resolveAbsolute(Uri uri) {
+    String mapping = _urlMappings[uri.toString()];
+    if (mapping == null) return null;
+    Uri fileUri = new Uri.file(mapping);
+    if (!fileUri.isAbsolute) return null;
+
+    JavaFile javaFile = new JavaFile.fromUri(fileUri);
+    return new FileBasedSource(javaFile, uri);
+  }
+
+  /// Given a package [name] and a list of folders ([libDirs]),
+  /// add any found sdk extensions.
+  void _processPackage(String name, List<Folder> libDirs) {
+    for (var libDir in libDirs) {
+      var sdkExt = _readDotSdkExt(libDir);
+      if (sdkExt != null) {
+        _processSdkExt(sdkExt, libDir);
+      }
+    }
+  }
+
+  /// Read the contents of [libDir]/[DOT_SDK_EXT_NAME] as a string.
+  /// Returns null if the file doesn't exist.
+  String _readDotSdkExt(Folder libDir) {
+    var file = libDir.getChild(DOT_SDK_EXT_NAME);
+    try {
+      return file.readAsStringSync();
+    } on FileSystemException catch (e) {
+      // File can't be read.
+      return null;
+    }
+  }
+
+  /// Given the JSON for an SDK extension ([sdkExtJSON]) and a folder
+  /// ([libDir]), setup the uri mapping.
+  void _processSdkExt(String sdkExtJSON, Folder libDir) {
+    var sdkExt;
+    try {
+      sdkExt = JSON.decode(sdkExtJSON);
+    } catch (e) {
+      return;
+    }
+    if ((sdkExt == null) || (sdkExt is! Map)) {
+      return;
+    }
+    sdkExt.forEach((k, v) => _processSdkExtension(k, v, libDir));
+  }
+
+  /// Install the mapping from [name] to [libDir]/[file].
+  void _processSdkExtension(String name, String file, Folder libDir) {
+    if (!name.startsWith(DART_COLON_PREFIX)) {
+      // SDK extensions must begin with 'dart:'.
+      return;
+    }
+    var key = name;
+    var value = libDir.canonicalizePath(file);
+    _urlMappings[key] = value;
+  }
+}