Initial Bazel file resolver support.

pkg/analyzer/lib/src/generated/bazel.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 analyzer.src.generated.bazel;
+
+import 'dart:core' hide Resource;
+
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/source_io.dart';
+
+/**
+ * Instances of the class `BazelFileUriResolver` resolve `file` URI's by first
+ * resolving file uri's in the expected way, and then by looking in the
+ * corresponding generated directories.
+ */
+class BazelFileUriResolver extends ResourceUriResolver {
+  /**
+   * The Bazel workspace directory.
+   */
+  final Folder _workspaceDir;
+
+  /**
+   * The build directories that relative `file` URI's should use to resolve
+   * relative URIs.
+   */
+  final List<Folder> _buildDirectories;
+
+  BazelFileUriResolver(
+      ResourceProvider provider, this._workspaceDir, this._buildDirectories)
+      : super(provider);
+
+  @override
+  Source resolveAbsolute(Uri uri, [Uri actualUri]) {
+    if (!ResourceUriResolver.isFileUri(uri)) {
+      return null;
+    }
+
+    File uriFile = provider.getFile(provider.pathContext.fromUri(uri));
+    if (uriFile.exists) {
+      return uriFile.createSource(actualUri ?? uri);
+    }
+
+    String relativeFromWorkspaceDir = _getPathFromWorkspaceDir(uri);
+    if (_buildDirectories.isEmpty || relativeFromWorkspaceDir.isEmpty) {
+      return null;
+    }
+
+    for (Folder buildDir in _buildDirectories) {
+      File file = buildDir.getChildAssumingFile(relativeFromWorkspaceDir);
+      if (file.exists) {
+        return file.createSource(actualUri ?? uri);
+      }
+    }
+    return null;
+  }
+
+  String _getPathFromWorkspaceDir(Uri uri) {
+    String uriPath = uri.path;
+    String workspacePath = _workspaceDir.path;
+
+    if (uriPath.startsWith(workspacePath) &&
+        workspacePath.length < uriPath.length) {
+      return uriPath.substring(workspacePath.length + 1);
+    }
+    return '';
+  }
+}