Add BazelPackageUriResolver with resolveAbsolute().

pkg/analyzer/lib/src/generated/bazel.dart

Index: pkg/analyzer/lib/src/generated/bazel.dart
diff --git a/pkg/analyzer/lib/src/generated/bazel.dart b/pkg/analyzer/lib/src/generated/bazel.dart
index 4f4f019966bcb53dc1c4b17536af6c08771bfc6e..ed2b11afac432d4f099fb1a93f8a7d48fbe9f2c2 100644
--- a/pkg/analyzer/lib/src/generated/bazel.dart
+++ b/pkg/analyzer/lib/src/generated/bazel.dart
@@ -4,6 +4,7 @@
 
 library analyzer.src.generated.bazel;
 
+import 'dart:collection';
 import 'dart:core';
 
 import 'package:analyzer/file_system/file_system.dart';
@@ -38,6 +39,42 @@ class BazelFileUriResolver extends ResourceUriResolver {
 }
 
 /**
+ * The [UriResolver] that can resolve `package` URIs in [BazelWorkspace].
+ */
+class BazelPackageUriResolver extends UriResolver {
+  final BazelWorkspace workspace;
+
+  /**
+   * The cache of absolute [Uri]s to [Source]s mappings.
+   */
+  final Map<Uri, Source> _sourceCache = new HashMap<Uri, Source>();
+
+  BazelPackageUriResolver(this.workspace);
+
+  @override
+  Source resolveAbsolute(Uri uri, [Uri actualUri]) {
+    return _sourceCache.putIfAbsent(uri, () {
+      _BazelPackageUri bazelUri = _BazelPackageUri.parse(uri);
+      if (bazelUri == null) {
+        return null;
+      }
+      if (bazelUri.packageName.indexOf('.') == -1) {
+        String path = '${workspace.root}/third_party/dart/'
+            '${bazelUri.packageName}/lib/${bazelUri.libPath}';
+        File file = workspace.getFile(path);
+        return file?.createSource(uri);
+      } else {
+        String packagePath = bazelUri.packageName
+            .replaceAll('.', workspace.provider.pathContext.separator);
+        String path = '${workspace.root}/$packagePath/lib/${bazelUri.libPath}';
+        File file = workspace.findFile(path);
+        return file?.createSource(uri);
+      }
+    });
+  }
+}
+
+/**
  * Information about a Bazel workspace.
  */
 class BazelWorkspace {
@@ -165,4 +202,74 @@ class BazelWorkspace {
       return null;
     }
   }
+
+  /**
+   * Return the file with the given [absolutePath] in the workspace [root].
+   * The file is returned even if it does not exist. Return `null` if the given
+   * [absolutePath] is not in the workspace [root].
+   */
+  File getFile(String absolutePath) {
+    if (provider.pathContext.isWithin(root, absolutePath)) {
+      return provider.getFile(absolutePath);
+    }
+    return null;
+  }
+}
+
+/**
+ * A `package` URI that has been parsed according to Bazel rules.
+ *
+ * For example, "package:dart.tools.analyzer/src/foo.dart" will be split
+ * into "dart.tools.analyzer" (the package) and "src/foo.dart" (the suffix).
+ */
+class _BazelPackageUri {

[Brian Wilkerson, 2016/10/06 21:55:52]

This class seems like overkill because it does so little.

In addition, it isn't actually specific to Bazel. The way it splits the package
name and lib path are the same as is done for all package: URIs, so we might
want to rename it. Or get rid of it, given that we don't have a wrapper class
for the PackageMapUriResolver.

[scheglov, 2016/10/07 16:02:42]

Done.

+  /**
+   * The name of the package being imported or exported.
+   *
+   * For example, if the URI is "package:foo.bar/baz.dart" then the
+   * packageName is "foo.bar".
+   */
+  final String packageName;
+
+  /**
+   * The path from the `lib` folder for the package to the file.
+   *
+   * For example, if the URI is "package:foo/bar/baz.dart" then the
+   * suffix is "bar/baz.dart".
+   */
+  final String libPath;
+
+  _BazelPackageUri(this.packageName, this.libPath);
+
+  @override
+  String toString() => toUri().toString();
+
+  /**
+   * Return the reconstituted `package` URI.
+   */
+  Uri toUri() {
+    return new Uri(scheme: 'package', path: '$packageName/$libPath');
+  }
+
+  /**
+   * Parses a Dart `package` URI according to Bazel rules.
+   *
+   * Returns `null` if it's not a valid Bazel `package` URI.
+   */
+  static _BazelPackageUri parse(Uri uri) {
+    if (uri.scheme != 'package') {
+      return null;
+    }
+    String path = uri.path;
+    int slash = path.indexOf('/');
+
+    // If the path either starts with a slash or has no slash, it is invalid.
+    if (slash < 1) {
+      return null;
+    }
+
+    String packageName = path.substring(0, slash);
+    String suffix = path.substring(slash + 1);
+    return new _BazelPackageUri(packageName, suffix);
+  }
 }