Package map processing abstraction.

pkg/analyzer/lib/src/context/context_factory.dart

Index: pkg/analyzer/lib/src/context/context_factory.dart
diff --git a/pkg/analyzer/lib/src/context/context_factory.dart b/pkg/analyzer/lib/src/context/context_factory.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4bb877db057aacc72b252748b2902aad3cc6561b
--- /dev/null
+++ b/pkg/analyzer/lib/src/context/context_factory.dart
@@ -0,0 +1,137 @@
+// 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 analyzer.src.context_factory;
+
+import 'dart:convert';
+import 'dart:core' hide Resource;
+
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/src/generated/sdk.dart';
+import 'package:yaml/yaml.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'dart:io' as io;
+
+/// (Placeholder)
+abstract class ContextFactory {
+  /// Create an analysis context for the given [source] directory or file, with
+  /// the given [defaultOptions].
+  AnalysisContext createContext(
+      io.FileSystemEntity source, AnalysisOptions defaultOptions);
+}
+
+/// Processes package maps, extracting SDK embedders and extenders, creating a
+/// consolidated [libraryMap].
+class PackageMapProcessor {
+  static const String _EMBEDDED_LIB_MAP_KEY = 'embedded_libs';
+  static const String _EMBEDDER_FILE_NAME = '_embedder.yaml';
+  static const String _SDK_EXT_NAME = '_sdkext';
+
+  /// Map of processed embedder libraries.
+  final LibraryMap embeddedLibraries = new LibraryMap();
+
+  /// Map of processed SDK extension libraries.
+  final LibraryMap extendedLibraries = new LibraryMap();
+
+  /// Combined map of processed libraries.
+  LibraryMap get libraryMap {
+    LibraryMap libraryMap = new LibraryMap();
+    for (String uri in embeddedLibraries.uris) {
+      libraryMap.setLibrary(uri, embeddedLibraries.getLibrary(uri));
+    }
+    // Extenders extend but do not override.
+    for (String uri in extendedLibraries.uris) {

[Brian Wilkerson, 2016/06/07 20:48:48]

It would be more efficient to add the extensions to the map first, then override
them from the embedded libraries.

[pquitslund, 2016/06/07 20:59:58]

Done.

+      if (embeddedLibraries.getLibrary(uri) == null) {
+        libraryMap.setLibrary(uri, extendedLibraries.getLibrary(uri));
+      }
+    }
+    return libraryMap;
+  }
+
+  /// Create a processor for the given [packageMap].
+  PackageMapProcessor(Map<String, List<Folder>> packageMap) {
+    packageMap?.forEach(_processPackage);
+  }
+
+  /// Whether the package map contains an SDK embedder.
+  bool get hasEmbedder => embeddedLibraries.size() > 0;
+
+  /// Whether the package map contains an SDK extension.
+  bool get hasSdkExtension => extendedLibraries.size() > 0;
+
+  void _processEmbedderYaml(String embedderYaml, Folder libDir) {
+    try {
+      YamlNode map = loadYaml(embedderYaml);
+      if (map is YamlMap) {
+        YamlNode embedded_libs = map[_EMBEDDED_LIB_MAP_KEY];
+        if (embedded_libs is YamlMap) {
+          embedded_libs.forEach(
+              (k, v) => _processMapping(embeddedLibraries, k, v, libDir));
+        }
+      }
+    } catch (_) {
+      // Ignored.
+    }
+  }
+
+  void _processMapping(
+      LibraryMap libraryMap, String name, String file, Folder libDir) {
+    if (!_hasDartPrefix(name)) {
+      // SDK libraries must begin with 'dart:'.
+      return;
+    }
+    if (libraryMap.getLibrary(name) != null) {
+      // Libraries can't be redefined.
+      return;
+    }
+    String libPath = libDir.canonicalizePath(file);
+    SdkLibraryImpl library = new SdkLibraryImpl(name)..path = libPath;
+    libraryMap.setLibrary(name, library);
+  }
+
+  void _processPackage(String name, List<Folder> libDirs) {
+    for (Folder libDir in libDirs) {
+      String embedderYaml = _readEmbedderYaml(libDir);
+      if (embedderYaml != null) {
+        _processEmbedderYaml(embedderYaml, libDir);
+      }
+      String sdkExt = _readDotSdkExt(libDir);
+      if (sdkExt != null) {
+        _processSdkExt(sdkExt, libDir);
+      }
+    }
+  }
+
+  void _processSdkExt(String sdkExtJSON, Folder libDir) {
+    try {
+      var sdkExt = JSON.decode(sdkExtJSON);
+      if (sdkExt is Map) {
+        sdkExt.forEach(
+            (k, v) => _processMapping(extendedLibraries, k, v, libDir));
+      }
+    } catch (_) {
+      // Ignored.
+    }
+  }
+
+  static bool _hasDartPrefix(String uri) =>
+      uri.startsWith(DartSdk.DART_LIBRARY_PREFIX);
+
+  static String _readDotSdkExt(Folder libDir) =>
+      _safeRead(libDir.getChild(_SDK_EXT_NAME));
+
+  static String _readEmbedderYaml(Folder libDir) =>
+      _safeRead(libDir.getChild(_EMBEDDER_FILE_NAME));
+
+  static String _safeRead(Resource file) {
+    try {
+      if (file is File) {
+        return file.readAsStringSync();
+      }
+    } on FileSystemException {
+      // File can't be read.
+    }
+    return null;
+  }
+}