Use URIs rather than paths in front end API.

pkg/front_end/lib/compiler_options.dart

Index: pkg/front_end/lib/compiler_options.dart
diff --git a/pkg/front_end/lib/compiler_options.dart b/pkg/front_end/lib/compiler_options.dart
index 5230f4e47fb31f7025e7d65351f99091280f44a6..731344c03dcddfc9e64a45088f062813dbcf9b95 100644
--- a/pkg/front_end/lib/compiler_options.dart
+++ b/pkg/front_end/lib/compiler_options.dart
@@ -18,13 +18,13 @@ typedef void ErrorHandler(CompilationError error);
 ///
 /// Not intended to be implemented or extended by clients.
 class CompilerOptions {
-  /// The path to the Dart SDK.
+  /// The URI of the root of the Dart SDK (typically a "file:" URI).
   ///
   /// If `null`, the SDK will be searched for using
   /// [Platform.resolvedExecutable] as a starting point.
   ///
   /// This option is mutually exclusive with [sdkSummary].
-  String sdkPath;
+  Uri sdkRoot;
 
   /// Callback to which compilation errors should be delivered.
   ///
@@ -32,56 +32,58 @@ class CompilerOptions {
   /// type [CompilationError].
   ErrorHandler onError = defaultErrorHandler;
 
-  /// Path to the ".packages" file.
+  /// URI of the ".packages" file (typically a "file:" URI).
   ///
   /// If `null`, the ".packages" file will be found via the standard
   /// package_config search algorithm.
   ///
-  /// If the empty string, no packages file will be used.
-  String packagesFilePath;
+  /// If the URI's path component is empty (e.g. `new Uri()`), no packages file
+  /// will be used.
+  Uri packagesFileUri;
 
-  /// Paths to the input summary files (excluding the SDK summary).  These files
-  /// should all be linked summaries.  They should also be closed, in the sense
-  /// that any libraries they reference should also appear in [inputSummaries]
-  /// or [sdkSummary].
-  List<String> inputSummaries = [];
+  /// URIs of input summary files (excluding the SDK summary; typically these
+  /// will be "file:" URIs).  These files should all be linked summaries.  They
+  /// should also be closed, in the sense that any libraries they reference
+  /// should also appear in [inputSummaries] or [sdkSummary].
+  List<Uri> inputSummaries = [];
 
-  /// Path to the SDK summary file.
+  /// URI of the SDK summary file (typically a "file:" URI).
   ///
   /// This should be a linked summary.  If `null`, the SDK summary will be
-  /// searched for at a default location within [sdkPath].
+  /// searched for at a default location within [sdkRoot].
   ///
-  /// This option is mutually exclusive with [sdkPath].  TODO(paulberry): if the
+  /// This option is mutually exclusive with [sdkRoot].  TODO(paulberry): if the
   /// VM does not contain a pickled copy of the SDK, we might need to change
   /// this.
-  String sdkSummary;
+  Uri sdkSummary;
 
   /// URI override map.
   ///
-  /// This is a map from Uri to file path.  Any URI override listed in this map
-  /// takes precedence over the URI resolution that would be implied by the
-  /// packages file (see [packagesFilePath]) and/or [bazelRoots].
+  /// This is a map from URIs that might appear in import/export/part statements
+  /// to URIs that should be used to locate the corresponding files in the
+  /// [fileSystem].  Any URI override listed in this map takes precedence over
+  /// the URI resolution that would be implied by the packages file (see
+  /// [packagesFileUri]) and/or [multiRoots].
   ///
   /// If a URI is not listed in this map, then the normal URI resolution
   /// algorithm will be used.
   ///
   /// TODO(paulberry): transition analyzer and dev_compiler to use the
-  /// "file:///bazel-root" mechanism, and then remove this.
+  /// "multi-root:" mechanism, and then remove this.
   @deprecated
-  Map<Uri, String> uriOverride = {};
+  Map<Uri, Uri> uriOverride = {};
 
-  /// Bazel roots.
+  /// Multi-roots.
   ///
-  /// Any Uri that resolves to "file:///bazel-root/$rest" will be searched for
-  /// at "$root/$rest" ("$root\\$rest" in Windows), where "$root" is drawn from
-  /// this list.  If the file is not found at any of those locations, the URI
-  /// "file:///bazel-root/$rest" will be used directly.
+  /// Any Uri that resolves to "multi-root:///$rest" will be searched for
+  /// at "$root/$rest", where "$root" is drawn from this list.
   ///
-  /// Intended use: if the Bazel workspace is located at path "$workspace", this
-  /// could be set to `['$workspace', '$workspace/bazel-bin',
-  /// '$workspace/bazel-genfiles']`, effectively overlaying source and generated
-  /// files.
-  List<String> bazelRoots = [];
+  /// Intended use: if the user has a Bazel workspace located at path
+  /// "$workspace", this could be set to the file URIs corresponding to the
+  /// paths for "$workspace", "$workspace/bazel-bin",
+  /// and "$workspace/bazel-genfiles", effectively overlaying source and
+  /// generated files.
+  List<Uri> multiRoots = [];
 
   /// Sets the platform bit, which determines which patch files should be
   /// applied to the SDK.
@@ -99,7 +101,7 @@ class CompilerOptions {
   ///
   /// All file system access performed by the front end goes through this
   /// mechanism, with one exception: if no value is specified for
-  /// [packagesFilePath], the packages file is located using the actual physical
+  /// [packagesFileUri], the packages file is located using the actual physical
   /// file system.  TODO(paulberry): fix this.
   FileSystem fileSystem = PhysicalFileSystem.instance;