Use URIs rather than paths in front end API.

pkg/front_end/lib/compiler_options.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 front_end.compiler_options;
 
 import 'compilation_error.dart';
 import 'file_system.dart';
 import 'physical_file_system.dart';
 
 /// Default error handler used by [CompielerOptions.onError].
 void defaultErrorHandler(CompilationError error) => throw error;
 
 /// Callback used to report errors encountered during compilation.
 typedef void ErrorHandler(CompilationError error);
 
 /// Front-end options relevant to compiler back ends.
 ///
 /// Not intended to be implemented or extended by clients.
 class CompilerOptions {
-  /// The path to the Dart SDK.
+  /// The URI 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 sdkPath;

[danrubel, 2017/01/08 17:07:38]

Since this is no longer a path, perhaps rename sdkPath to sdkRoot? sdkUri?

[Paul Berry, 2017/01/09 17:24:42]

Done.

 
   /// Callback to which compilation errors should be delivered.
   ///
   /// By default, the first error will be reported by throwing an exception of
   /// 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 packagesFilePath;

[danrubel, 2017/01/08 17:07:38]

Same as above... packagesFileUri?

[Paul Berry, 2017/01/09 17:24:42]

Done.

 
-  /// 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].
   ///
   /// This option is mutually exclusive with [sdkPath].  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
+  /// [packagesFilePath]) 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 = [];
+  /// 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.
   ///
   /// The value should be a power of two, and should match the `PLATFORM` bit
   /// flags in sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart.  If
   /// zero, no patch files will be applied.
   int platformBit;
 
   /// The declared variables for use by configurable imports and constant
@@ skipping 19 matching lines @@
   /// that will be compiled are listed explicitly and all other dependencies
   /// are covered by summary files.
   ///
   /// When this option is true, these APIs will treat any dependency that is
   /// not described in a summary as if it was explictly listed as an input.
   bool chaseDependencies = false;
 
   /// Whether to intepret Dart sources in strong-mode.
   bool strongMode = true;
 }