Refactor pkg/path.

pkg/path/lib/path.dart

Index: pkg/path/lib/path.dart
diff --git a/pkg/path/lib/path.dart b/pkg/path/lib/path.dart
index 5f469edd6a6e5b9e67cc4abd2d892a8e8405e89e..6f522c5bc7456bfe6f98d0fa112fc5544ddd5fc4 100644
--- a/pkg/path/lib/path.dart
+++ b/pkg/path/lib/path.dart
@@ -37,45 +37,47 @@
 ///
 /// If you want to work with paths for a specific platform regardless of the
 /// underlying platform that the program is running on, you can create a
-/// [Builder] and give it an explicit [Style]:
+/// [Context] and give it an explicit [Style]:
 ///
-///     var builder = new path.Builder(style: Style.windows);
-///     builder.join("directory", "file.txt");
+///     var context = new path.Context(style: Style.windows);
+///     context.join("directory", "file.txt");
 ///
 /// This will join "directory" and "file.txt" using the Windows path separator,
 /// even when the program is run on a POSIX machine.
 library path;
 
-/// A default builder for manipulating POSIX paths.
-final posix = new Builder(style: Style.posix);
+import 'src/context.dart';
+import 'src/style.dart';
 
-/// A default builder for manipulating Windows paths.
-final windows = new Builder(style: Style.windows);
+export 'src/context.dart';
+export 'src/path_exception.dart';
+export 'src/style.dart';
 
-/// A default builder for manipulating URLs.
-final url = new Builder(style: Style.url);
+/// A default context for manipulating POSIX paths.
+final posix = new Context(style: Style.posix);
 
-/// Inserts [length] elements in front of the [list] and fills them with the
-/// [fillValue].
-void _growListFront(List list, int length, fillValue) =>
-  list.insertAll(0, new List.filled(length, fillValue));
+/// A default context for manipulating Windows paths.
+final windows = new Context(style: Style.windows);
+
+/// A default context for manipulating URLs.
+final url = new Context(style: Style.url);
 
 /// The result of [Uri.base] last time the current working directory was
 /// calculated.
 ///
-/// This is used to invalidate [_cachedBuilder] when the working directory has
+/// This is used to invalidate [_cachedContext] when the working directory has
 /// changed since the last time a function was called.
 Uri _lastBaseUri;
 
-/// An internal builder for the current OS so we can provide a straight
+/// An internal context for the current OS so we can provide a straight
 /// functional interface and not require users to create one.
-Builder get _builder {
-  if (_cachedBuilder != null && Uri.base == _lastBaseUri) return _cachedBuilder;
+Context get _context {
+  if (_cachedContext != null && Uri.base == _lastBaseUri) return _cachedContext;
   _lastBaseUri = Uri.base;
-  _cachedBuilder = new Builder();
-  return _cachedBuilder;
+  _cachedContext = new Context();
+  return _cachedContext;
 }
-Builder _cachedBuilder;
+Context _cachedContext;
 
 /// Gets the path to the current working directory.
 ///
@@ -95,13 +97,15 @@ String get current {
 
 /// Gets the path separator for the current platform. This is `\` on Windows
 /// and `/` on other platforms (including the browser).
-String get separator => _builder.separator;
+String get separator => _context.separator;
 
-/// Converts [path] to an absolute path by resolving it relative to the current
-/// working directory. If [path] is already an absolute path, just returns it.
+/// Creates a new path by appending the given path parts to [current].
+/// Equivalent to [join()] with [current] as the first argument. Example:
 ///
-///     path.absolute('foo/bar.txt'); // -> /your/current/dir/foo/bar.txt
-String absolute(String path) => join(current, path);
+///     path.absolute('path', 'to/foo'); // -> '/your/current/dir/path/to/foo'
+String absolute(String part1, [String part2, String part3, String part4,
+            String part5, String part6, String part7]) =>
+  _context.absolute(part1, part2, part3, part4, part5, part6, part7);
 
 /// Gets the part of [path] after the last separator.
 ///
@@ -110,8 +114,8 @@ String absolute(String path) => join(current, path);
 ///
 /// Trailing separators are ignored.
 ///
-///     builder.basename('path/to/'); // -> 'to'
-String basename(String path) => _builder.basename(path);
+///     path.basename('path/to/'); // -> 'to'
+String basename(String path) => _context.basename(path);
 
 /// Gets the part of [path] after the last separator, and without any trailing
 /// file extension.
@@ -120,9 +124,9 @@ String basename(String path) => _builder.basename(path);
 ///
 /// Trailing separators are ignored.
 ///
-///     builder.basenameWithoutExtension('path/to/foo.dart/'); // -> 'foo'
+///     path.basenameWithoutExtension('path/to/foo.dart/'); // -> 'foo'
 String basenameWithoutExtension(String path) =>
-    _builder.basenameWithoutExtension(path);
+    _context.basenameWithoutExtension(path);
 
 /// Gets the part of [path] before the last separator.
 ///
@@ -131,7 +135,7 @@ String basenameWithoutExtension(String path) =>
 ///
 /// Trailing separators are ignored.
 ///
-///     builder.dirname('path/to/'); // -> 'path'
+///     path.dirname('path/to/'); // -> 'path'
 ///
 /// If an absolute path contains no directories, only a root, then the root
 /// is returned.
@@ -143,7 +147,7 @@ String basenameWithoutExtension(String path) =>
 ///
 ///     path.dirname('foo');  // -> '.'
 ///     path.dirname('');  // -> '.'
-String dirname(String path) => _builder.dirname(path);
+String dirname(String path) => _context.dirname(path);
 
 /// Gets the file extension of [path]: the portion of [basename] from the last
 /// `.` to the end (including the `.` itself).
@@ -158,7 +162,7 @@ String dirname(String path) => _builder.dirname(path);
 ///
 ///     path.extension('~/.bashrc');    // -> ''
 ///     path.extension('~/.notes.txt'); // -> '.txt'
-String extension(String path) => _builder.extension(path);
+String extension(String path) => _context.extension(path);
 
 // TODO(nweiz): add a UNC example for Windows once issue 7323 is fixed.
 /// Returns the root of [path], if it's absolute, or the empty string if it's
@@ -176,7 +180,7 @@ String extension(String path) => _builder.extension(path);
 ///     path.rootPrefix('path/to/foo'); // -> ''
 ///     path.rootPrefix('http://dartlang.org/path/to/foo');
 ///       // -> 'http://dartlang.org'
-String rootPrefix(String path) => _builder.rootPrefix(path);
+String rootPrefix(String path) => _context.rootPrefix(path);
 
 /// Returns `true` if [path] is an absolute path and `false` if it is a
 /// relative path.
@@ -190,13 +194,13 @@ String rootPrefix(String path) => _builder.rootPrefix(path);
 /// relative to the root of the current URL. Since root-relative paths are still
 /// absolute in every other sense, [isAbsolute] will return true for them. They
 /// can be detected using [isRootRelative].
-bool isAbsolute(String path) => _builder.isAbsolute(path);
+bool isAbsolute(String path) => _context.isAbsolute(path);
 
 /// Returns `true` if [path] is a relative path and `false` if it is absolute.
 /// On POSIX systems, absolute paths start with a `/` (forward slash). On
 /// Windows, an absolute path starts with `\\`, or a drive letter followed by
 /// `:/` or `:\`.
-bool isRelative(String path) => _builder.isRelative(path);
+bool isRelative(String path) => _context.isRelative(path);
 
 /// Returns `true` if [path] is a root-relative path and `false` if it's not.
 ///
@@ -206,7 +210,7 @@ bool isRelative(String path) => _builder.isRelative(path);
 /// can be detected using [isRootRelative].
 ///
 /// No POSIX and Windows paths are root-relative.
-bool isRootRelative(String path) => _builder.isRootRelative(path);
+bool isRootRelative(String path) => _context.isRootRelative(path);
 
 /// Joins the given path parts into a single path using the current platform's
 /// [separator]. Example:
@@ -223,7 +227,7 @@ bool isRootRelative(String path) => _builder.isRootRelative(path);
 ///     path.join('path', '/to', 'foo'); // -> '/to/foo'
 String join(String part1, [String part2, String part3, String part4,
             String part5, String part6, String part7, String part8]) =>
-  _builder.join(part1, part2, part3, part4, part5, part6, part7, part8);
+  _context.join(part1, part2, part3, part4, part5, part6, part7, part8);
 
 /// Joins the given path parts into a single path using the current platform's
 /// [separator]. Example:
@@ -240,7 +244,7 @@ String join(String part1, [String part2, String part3, String part4,
 ///     path.joinAll(['path', '/to', 'foo']); // -> '/to/foo'
 ///
 /// For a fixed number of parts, [join] is usually terser.
-String joinAll(Iterable<String> parts) => _builder.joinAll(parts);
+String joinAll(Iterable<String> parts) => _context.joinAll(parts);
 
 // TODO(nweiz): add a UNC example for Windows once issue 7323 is fixed.
 /// Splits [path] into its components using the current platform's [separator].
@@ -263,13 +267,13 @@ String joinAll(Iterable<String> parts) => _builder.joinAll(parts);
 ///     // Browser
 ///     path.split('http://dartlang.org/path/to/foo');
 ///       // -> ['http://dartlang.org', 'path', 'to', 'foo']
-List<String> split(String path) => _builder.split(path);
+List<String> split(String path) => _context.split(path);
 
 /// Normalizes [path], simplifying it by handling `..`, and `.`, and
 /// removing redundant path separators whenever possible.
 ///
 ///     path.normalize('path/./to/..//file.text'); // -> 'path/file.txt'
-String normalize(String path) => _builder.normalize(path);
+String normalize(String path) => _context.normalize(path);
 
 /// Attempts to convert [path] to an equivalent relative path from the current
 /// directory.
@@ -299,19 +303,19 @@ String normalize(String path) => _builder.normalize(path);
 ///     path.relative('http://dartlang.org', from: 'http://pub.dartlang.org');
 ///       // -> 'http://dartlang.org'
 String relative(String path, {String from}) =>
-    _builder.relative(path, from: from);
+    _context.relative(path, from: from);
 
 /// Returns `true` if [child] is a path beneath `parent`, and `false` otherwise.
 ///
 ///     path.isWithin('/root/path', '/root/path/a'); // -> true
 ///     path.isWithin('/root/path', '/root/other'); // -> false
 ///     path.isWithin('/root/path', '/root/path') // -> false
-bool isWithin(String parent, String child) => _builder.isWithin(parent, child);
+bool isWithin(String parent, String child) => _context.isWithin(parent, child);
 
 /// Removes a trailing extension from the last part of [path].
 ///
 ///     withoutExtension('path/to/foo.dart'); // -> 'path/to/foo'
-String withoutExtension(String path) => _builder.withoutExtension(path);
+String withoutExtension(String path) => _context.withoutExtension(path);
 
 /// Returns the path represented by [uri].
 ///
@@ -329,7 +333,7 @@ String withoutExtension(String path) => _builder.withoutExtension(path);
 ///     // URL
 ///     path.fromUri(Uri.parse('http://dartlang.org/path/to/foo'))
 ///       // -> 'http://dartlang.org/path/to/foo'
-String fromUri(Uri uri) => _builder.fromUri(uri);
+String fromUri(Uri uri) => _context.fromUri(uri);
 
 /// Returns the URI that represents [path].
 ///
@@ -352,898 +356,4 @@ String fromUri(Uri uri) => _builder.fromUri(uri);
 ///
 ///     path.toUri('path/to/foo')
 ///       // -> Uri.parse('path/to/foo')
-Uri toUri(String path) => _builder.toUri(path);
-
-/// Validates that there are no non-null arguments following a null one and
-/// throws an appropriate [ArgumentError] on failure.
-_validateArgList(String method, List<String> args) {
-  for (var i = 1; i < args.length; i++) {
-    // Ignore nulls hanging off the end.
-    if (args[i] == null || args[i - 1] != null) continue;
-
-    var numArgs;
-    for (numArgs = args.length; numArgs >= 1; numArgs--) {
-      if (args[numArgs - 1] != null) break;
-    }
-
-    // Show the arguments.
-    var message = new StringBuffer();
-    message.write("$method(");
-    message.write(args.take(numArgs)
-        .map((arg) => arg == null ? "null" : '"$arg"')
-        .join(", "));
-    message.write("): part ${i - 1} was null, but part $i was not.");
-    throw new ArgumentError(message.toString());
-  }
-}
-
-/// An instantiable class for manipulating paths. Unlike the top-level
-/// functions, this lets you explicitly select what platform the paths will use.
-class Builder {
-  /// Creates a new path builder for the given style and root directory.
-  ///
-  /// If [style] is omitted, it uses the host operating system's path style. If
-  /// only [root] is omitted, it defaults ".". If *both* [style] and [root] are
-  /// omitted, [root] defaults to the current working directory.
-  ///
-  /// On the browser, the path style is [Style.url]. In Dartium, [root] defaults
-  /// to the current URL. When using dart2js, it currently defaults to `.` due
-  /// to technical constraints.
-  factory Builder({Style style, String root}) {
-    if (root == null) {
-      if (style == null) {
-        root = current;
-      } else {
-        root = ".";
-      }
-    }
-
-    if (style == null) style = Style.platform;
-
-    return new Builder._(style, root);
-  }
-
-  Builder._(this.style, this.root);
-
-  /// The style of path that this builder works with.
-  final Style style;
-
-  /// The root directory that relative paths will be relative to.
-  final String root;
-
-  /// Gets the path separator for the builder's [style]. On Mac and Linux,
-  /// this is `/`. On Windows, it's `\`.
-  String get separator => style.separator;
-
-  /// Gets the part of [path] after the last separator on the builder's
-  /// platform.
-  ///
-  ///     builder.basename('path/to/foo.dart'); // -> 'foo.dart'
-  ///     builder.basename('path/to');          // -> 'to'
-  ///
-  /// Trailing separators are ignored.
-  ///
-  ///     builder.basename('path/to/'); // -> 'to'
-  String basename(String path) => _parse(path).basename;
-
-  /// Gets the part of [path] after the last separator on the builder's
-  /// platform, and without any trailing file extension.
-  ///
-  ///     builder.basenameWithoutExtension('path/to/foo.dart'); // -> 'foo'
-  ///
-  /// Trailing separators are ignored.
-  ///
-  ///     builder.basenameWithoutExtension('path/to/foo.dart/'); // -> 'foo'
-  String basenameWithoutExtension(String path) =>
-    _parse(path).basenameWithoutExtension;
-
-  /// Gets the part of [path] before the last separator.
-  ///
-  ///     builder.dirname('path/to/foo.dart'); // -> 'path/to'
-  ///     builder.dirname('path/to');          // -> 'path'
-  ///
-  /// Trailing separators are ignored.
-  ///
-  ///     builder.dirname('path/to/'); // -> 'path'
-  String dirname(String path) {
-    var parsed = _parse(path);
-    parsed.removeTrailingSeparators();
-    if (parsed.parts.isEmpty) return parsed.root == null ? '.' : parsed.root;
-    if (parsed.parts.length == 1) {
-      return parsed.root == null ? '.' : parsed.root;
-    }
-    parsed.parts.removeLast();
-    parsed.separators.removeLast();
-    parsed.removeTrailingSeparators();
-    return parsed.toString();
-  }
-
-  /// Gets the file extension of [path]: the portion of [basename] from the last
-  /// `.` to the end (including the `.` itself).
-  ///
-  ///     builder.extension('path/to/foo.dart'); // -> '.dart'
-  ///     builder.extension('path/to/foo'); // -> ''
-  ///     builder.extension('path.to/foo'); // -> ''
-  ///     builder.extension('path/to/foo.dart.js'); // -> '.js'
-  ///
-  /// If the file name starts with a `.`, then it is not considered an
-  /// extension:
-  ///
-  ///     builder.extension('~/.bashrc');    // -> ''
-  ///     builder.extension('~/.notes.txt'); // -> '.txt'
-  String extension(String path) => _parse(path).extension;
-
-  // TODO(nweiz): add a UNC example for Windows once issue 7323 is fixed.
-  /// Returns the root of [path], if it's absolute, or an empty string if it's
-  /// relative.
-  ///
-  ///     // Unix
-  ///     builder.rootPrefix('path/to/foo'); // -> ''
-  ///     builder.rootPrefix('/path/to/foo'); // -> '/'
-  ///
-  ///     // Windows
-  ///     builder.rootPrefix(r'path\to\foo'); // -> ''
-  ///     builder.rootPrefix(r'C:\path\to\foo'); // -> r'C:\'
-  ///
-  ///     // URL
-  ///     builder.rootPrefix('path/to/foo'); // -> ''
-  ///     builder.rootPrefix('http://dartlang.org/path/to/foo');
-  ///       // -> 'http://dartlang.org'
-  String rootPrefix(String path) {
-    var root = _parse(path).root;
-    return root == null ? '' : root;
-  }
-
-  /// Returns `true` if [path] is an absolute path and `false` if it is a
-  /// relative path.
-  ///
-  /// On POSIX systems, absolute paths start with a `/` (forward slash). On
-  /// Windows, an absolute path starts with `\\`, or a drive letter followed by
-  /// `:/` or `:\`. For URLs, absolute paths either start with a protocol and
-  /// optional hostname (e.g. `http://dartlang.org`, `file://`) or with a `/`.
-  ///
-  /// URLs that start with `/` are known as "root-relative", since they're
-  /// relative to the root of the current URL. Since root-relative paths are
-  /// still absolute in every other sense, [isAbsolute] will return true for
-  /// them. They can be detected using [isRootRelative].
-  bool isAbsolute(String path) => _parse(path).isAbsolute;
-
-  /// Returns `true` if [path] is a relative path and `false` if it is absolute.
-  /// On POSIX systems, absolute paths start with a `/` (forward slash). On
-  /// Windows, an absolute path starts with `\\`, or a drive letter followed by
-  /// `:/` or `:\`.
-  bool isRelative(String path) => !this.isAbsolute(path);
-
-  /// Returns `true` if [path] is a root-relative path and `false` if it's not.
-  ///
-  /// URLs that start with `/` are known as "root-relative", since they're
-  /// relative to the root of the current URL. Since root-relative paths are
-  /// still absolute in every other sense, [isAbsolute] will return true for
-  /// them. They can be detected using [isRootRelative].
-  ///
-  /// No POSIX and Windows paths are root-relative.
-  bool isRootRelative(String path) => _parse(path).isRootRelative;
-
-  /// Joins the given path parts into a single path. Example:
-  ///
-  ///     builder.join('path', 'to', 'foo'); // -> 'path/to/foo'
-  ///
-  /// If any part ends in a path separator, then a redundant separator will not
-  /// be added:
-  ///
-  ///     builder.join('path/', 'to', 'foo'); // -> 'path/to/foo
-  ///
-  /// If a part is an absolute path, then anything before that will be ignored:
-  ///
-  ///     builder.join('path', '/to', 'foo'); // -> '/to/foo'
-  ///
-  String join(String part1, [String part2, String part3, String part4,
-              String part5, String part6, String part7, String part8]) {
-    var parts = [part1, part2, part3, part4, part5, part6, part7, part8];
-    _validateArgList("join", parts);
-    return joinAll(parts.where((part) => part != null));
-  }
-
-  /// Joins the given path parts into a single path. Example:
-  ///
-  ///     builder.joinAll(['path', 'to', 'foo']); // -> 'path/to/foo'
-  ///
-  /// If any part ends in a path separator, then a redundant separator will not
-  /// be added:
-  ///
-  ///     builder.joinAll(['path/', 'to', 'foo']); // -> 'path/to/foo
-  ///
-  /// If a part is an absolute path, then anything before that will be ignored:
-  ///
-  ///     builder.joinAll(['path', '/to', 'foo']); // -> '/to/foo'
-  ///
-  /// For a fixed number of parts, [join] is usually terser.
-  String joinAll(Iterable<String> parts) {
-    var buffer = new StringBuffer();
-    var needsSeparator = false;
-    var isAbsoluteAndNotRootRelative = false;
-
-    for (var part in parts.where((part) => part != '')) {
-      if (this.isRootRelative(part) && isAbsoluteAndNotRootRelative) {
-        // If the new part is root-relative, it preserves the previous root but
-        // replaces the path after it.
-        var parsed = _parse(part);
-        parsed.root = this.rootPrefix(buffer.toString());
-        if (parsed.root.contains(style.needsSeparatorPattern)) {
-          parsed.separators[0] = style.separator;
-        }
-        buffer.clear();
-        buffer.write(parsed);
-      } else if (this.isAbsolute(part)) {
-        isAbsoluteAndNotRootRelative = !this.isRootRelative(part);
-        // An absolute path discards everything before it.
-        buffer.clear();
-        buffer.write(part);
-      } else {
-        if (part.length > 0 && part[0].contains(style.separatorPattern)) {
-          // The part starts with a separator, so we don't need to add one.
-        } else if (needsSeparator) {
-          buffer.write(separator);
-        }
-
-        buffer.write(part);
-      }
-
-      // Unless this part ends with a separator, we'll need to add one before
-      // the next part.
-      needsSeparator = part.contains(style.needsSeparatorPattern);
-    }
-
-    return buffer.toString();
-  }
-
-  // TODO(nweiz): add a UNC example for Windows once issue 7323 is fixed.
-  /// Splits [path] into its components using the current platform's
-  /// [separator]. Example:
-  ///
-  ///     builder.split('path/to/foo'); // -> ['path', 'to', 'foo']
-  ///
-  /// The path will *not* be normalized before splitting.
-  ///
-  ///     builder.split('path/../foo'); // -> ['path', '..', 'foo']
-  ///
-  /// If [path] is absolute, the root directory will be the first element in the
-  /// array. Example:
-  ///
-  ///     // Unix
-  ///     builder.split('/path/to/foo'); // -> ['/', 'path', 'to', 'foo']
-  ///
-  ///     // Windows
-  ///     builder.split(r'C:\path\to\foo'); // -> [r'C:\', 'path', 'to', 'foo']
-  List<String> split(String path) {
-    var parsed = _parse(path);
-    // Filter out empty parts that exist due to multiple separators in a row.
-    parsed.parts = parsed.parts.where((part) => !part.isEmpty)
-                               .toList();
-    if (parsed.root != null) parsed.parts.insert(0, parsed.root);
-    return parsed.parts;
-  }
-
-  /// Normalizes [path], simplifying it by handling `..`, and `.`, and
-  /// removing redundant path separators whenever possible.
-  ///
-  ///     builder.normalize('path/./to/..//file.text'); // -> 'path/file.txt'
-  String normalize(String path) {
-    var parsed = _parse(path);
-    parsed.normalize();
-    return parsed.toString();
-  }
-
-  /// Creates a new path by appending the given path parts to the [root].
-  /// Equivalent to [join()] with [root] as the first argument. Example:
-  ///
-  ///     var builder = new Builder(root: 'root');
-  ///     builder.resolve('path', 'to', 'foo'); // -> 'root/path/to/foo'
-  String resolve(String part1, [String part2, String part3, String part4,
-              String part5, String part6, String part7]) {
-    return join(root, part1, part2, part3, part4, part5, part6, part7);
-  }
-
-  /// Attempts to convert [path] to an equivalent relative path relative to
-  /// [root].
-  ///
-  ///     var builder = new Builder(root: '/root/path');
-  ///     builder.relative('/root/path/a/b.dart'); // -> 'a/b.dart'
-  ///     builder.relative('/root/other.dart'); // -> '../other.dart'
-  ///
-  /// If the [from] argument is passed, [path] is made relative to that instead.
-  ///
-  ///     builder.relative('/root/path/a/b.dart',
-  ///         from: '/root/path'); // -> 'a/b.dart'
-  ///     builder.relative('/root/other.dart',
-  ///         from: '/root/path'); // -> '../other.dart'
-  ///
-  /// If [path] and/or [from] are relative paths, they are assumed to be
-  /// relative to [root].
-  ///
-  /// Since there is no relative path from one drive letter to another on
-  /// Windows, this will return an absolute path in that case.
-  ///
-  ///     builder.relative(r'D:\other', from: r'C:\other'); // -> 'D:\other'
-  ///
-  /// This will also return an absolute path if an absolute [path] is passed to
-  /// a builder with a relative [root].
-  ///
-  ///     var builder = new Builder(r'some/relative/path');
-  ///     builder.relative(r'/absolute/path'); // -> '/absolute/path'
-  ///
-  /// If [root] is relative, it may be impossible to determine a path from
-  /// [from] to [path]. For example, if [root] and [path] are "." and [from] is
-  /// "/", no path can be determined. In this case, a [PathException] will be
-  /// thrown.
-  String relative(String path, {String from}) {
-    from = from == null ? root : this.join(root, from);
-
-    // We can't determine the path from a relative path to an absolute path.
-    if (this.isRelative(from) && this.isAbsolute(path)) {
-      return this.normalize(path);
-    }
-
-    // If the given path is relative, resolve it relative to the root of the
-    // builder.
-    if (this.isRelative(path) || this.isRootRelative(path)) {
-      path = this.resolve(path);
-    }
-
-    // If the path is still relative and `from` is absolute, we're unable to
-    // find a path from `from` to `path`.
-    if (this.isRelative(path) && this.isAbsolute(from)) {
-      throw new PathException('Unable to find a path to "$path" from "$from".');
-    }
-
-    var fromParsed = _parse(from)..normalize();
-    var pathParsed = _parse(path)..normalize();
-
-    if (fromParsed.parts.length > 0 && fromParsed.parts[0] == '.') {
-      return pathParsed.toString();
-    }
-
-    // If the root prefixes don't match (for example, different drive letters
-    // on Windows), then there is no relative path, so just return the absolute
-    // one. In Windows, drive letters are case-insenstive and we allow
-    // calculation of relative paths, even if a path has not been normalized.
-    if (fromParsed.root != pathParsed.root &&
-        ((fromParsed.root ==  null || pathParsed.root == null) ||
-          fromParsed.root.toLowerCase().replaceAll('/', '\\') !=
-          pathParsed.root.toLowerCase().replaceAll('/', '\\'))) {
-      return pathParsed.toString();
-    }
-
-    // Strip off their common prefix.
-    while (fromParsed.parts.length > 0 && pathParsed.parts.length > 0 &&
-           fromParsed.parts[0] == pathParsed.parts[0]) {
-      fromParsed.parts.removeAt(0);
-      fromParsed.separators.removeAt(1);
-      pathParsed.parts.removeAt(0);
-      pathParsed.separators.removeAt(1);
-    }
-
-    // If there are any directories left in the from path, we need to walk up
-    // out of them. If a directory left in the from path is '..', it cannot
-    // be cancelled by adding a '..'.
-    if (fromParsed.parts.length > 0 && fromParsed.parts[0] == '..') {
-      throw new PathException('Unable to find a path to "$path" from "$from".');
-    }
-    _growListFront(pathParsed.parts, fromParsed.parts.length, '..');
-    pathParsed.separators[0] = '';
-    pathParsed.separators.insertAll(1,
-        new List.filled(fromParsed.parts.length, style.separator));
-
-    // Corner case: the paths completely collapsed.
-    if (pathParsed.parts.length == 0) return '.';
-
-    // Corner case: path was '.' and some '..' directories were added in front.
-    // Don't add a final '/.' in that case.
-    if (pathParsed.parts.length > 1 && pathParsed.parts.last == '.') {
-      pathParsed.parts.removeLast();
-      pathParsed.separators..removeLast()..removeLast()..add('');
-    }
-
-    // Make it relative.
-    pathParsed.root = '';
-    pathParsed.removeTrailingSeparators();
-
-    return pathParsed.toString();
-  }
-
-  /// Returns `true` if [child] is a path beneath `parent`, and `false`
-  /// otherwise.
-  ///
-  ///     path.isWithin('/root/path', '/root/path/a'); // -> true
-  ///     path.isWithin('/root/path', '/root/other'); // -> false
-  ///     path.isWithin('/root/path', '/root/path') // -> false
-  bool isWithin(String parent, String child) {
-    var relative;
-    try {
-      relative = this.relative(child, from: parent);
-    } on PathException catch (_) {
-      // If no relative path from [parent] to [child] is found, [child]
-      // definitely isn't a child of [parent].
-      return false;
-    }
-
-    var parts = this.split(relative);
-    return this.isRelative(relative) && parts.first != '..' &&
-        parts.first != '.';
-  }
-
-  /// Removes a trailing extension from the last part of [path].
-  ///
-  ///     builder.withoutExtension('path/to/foo.dart'); // -> 'path/to/foo'
-  String withoutExtension(String path) {
-    var parsed = _parse(path);
-
-    for (var i = parsed.parts.length - 1; i >= 0; i--) {
-      if (!parsed.parts[i].isEmpty) {
-        parsed.parts[i] = parsed.basenameWithoutExtension;
-        break;
-      }
-    }
-
-    return parsed.toString();
-  }
-
-  /// Returns the path represented by [uri].
-  ///
-  /// For POSIX and Windows styles, [uri] must be a `file:` URI. For the URL
-  /// style, this will just convert [uri] to a string.
-  ///
-  ///     // POSIX
-  ///     builder.fromUri(Uri.parse('file:///path/to/foo'))
-  ///       // -> '/path/to/foo'
-  ///
-  ///     // Windows
-  ///     builder.fromUri(Uri.parse('file:///C:/path/to/foo'))
-  ///       // -> r'C:\path\to\foo'
-  ///
-  ///     // URL
-  ///     builder.fromUri(Uri.parse('http://dartlang.org/path/to/foo'))
-  ///       // -> 'http://dartlang.org/path/to/foo'
-  String fromUri(Uri uri) => style.pathFromUri(uri);
-
-  /// Returns the URI that represents [path].
-  ///
-  /// For POSIX and Windows styles, this will return a `file:` URI. For the URL
-  /// style, this will just convert [path] to a [Uri].
-  ///
-  ///     // POSIX
-  ///     builder.toUri('/path/to/foo')
-  ///       // -> Uri.parse('file:///path/to/foo')
-  ///
-  ///     // Windows
-  ///     builder.toUri(r'C:\path\to\foo')
-  ///       // -> Uri.parse('file:///C:/path/to/foo')
-  ///
-  ///     // URL
-  ///     builder.toUri('http://dartlang.org/path/to/foo')
-  ///       // -> Uri.parse('http://dartlang.org/path/to/foo')
-  Uri toUri(String path) {
-    if (isRelative(path)) {
-      return style.relativePathToUri(path);
-    } else {
-      return style.absolutePathToUri(join(root, path));
-    }
-  }
-
-  _ParsedPath _parse(String path) {
-    var before = path;
-
-    // Remove the root prefix, if any.
-    var root = style.getRoot(path);
-    var isRootRelative = style.getRelativeRoot(path) != null;
-    if (root != null) path = path.substring(root.length);
-
-    // Split the parts on path separators.
-    var parts = [];
-    var separators = [];
-
-    var firstSeparator = style.separatorPattern.matchAsPrefix(path);
-    if (firstSeparator != null) {
-      separators.add(firstSeparator[0]);
-      path = path.substring(firstSeparator[0].length);
-    } else {
-      separators.add('');
-    }
-
-    var start = 0;
-    for (var match in style.separatorPattern.allMatches(path)) {
-      parts.add(path.substring(start, match.start));
-      separators.add(match[0]);
-      start = match.end;
-    }
-
-    // Add the final part, if any.
-    if (start < path.length) {
-      parts.add(path.substring(start));
-      separators.add('');
-    }
-
-    return new _ParsedPath(style, root, isRootRelative, parts, separators);
-  }
-}
-
-/// An enum type describing a "flavor" of path.
-abstract class Style {
-  /// POSIX-style paths use "/" (forward slash) as separators. Absolute paths
-  /// start with "/". Used by UNIX, Linux, Mac OS X, and others.
-  static final posix = new _PosixStyle();
-
-  /// Windows paths use "\" (backslash) as separators. Absolute paths start with
-  /// a drive letter followed by a colon (example, "C:") or two backslashes
-  /// ("\\") for UNC paths.
-  // TODO(rnystrom): The UNC root prefix should include the drive name too, not
-  // just the "\\".
-  static final windows = new _WindowsStyle();
-
-  /// URLs aren't filesystem paths, but they're supported to make it easier to
-  /// manipulate URL paths in the browser.
-  ///
-  /// URLs use "/" (forward slash) as separators. Absolute paths either start
-  /// with a protocol and optional hostname (e.g. `http://dartlang.org`,
-  /// `file://`) or with "/".
-  static final url = new _UrlStyle();
-
-  /// The style of the host platform.
-  ///
-  /// When running on the command line, this will be [windows] or [posix] based
-  /// on the host operating system. On a browser, this will be [url].
-  static final platform = _getPlatformStyle();
-
-  /// Gets the type of the host platform.
-  static Style _getPlatformStyle() {
-    // If we're running a Dart file in the browser from a `file:` URI,
-    // [Uri.base] will point to a file. If we're running on the standalone,
-    // it will point to a directory. We can use that fact to determine which
-    // style to use.
-    if (Uri.base.scheme != 'file') return Style.url;
-    if (!Uri.base.path.endsWith('/')) return Style.url;
-    if (new Uri(path: 'a/b').toFilePath() == 'a\\b') return Style.windows;
-    return Style.posix;
-  }
-
-  /// The name of this path style. Will be "posix" or "windows".
-  String get name;
-
-  /// The path separator for this style. On POSIX, this is `/`. On Windows,
-  /// it's `\`.
-  String get separator;
-
-  /// The [Pattern] that can be used to match a separator for a path in this
-  /// style. Windows allows both "/" and "\" as path separators even though "\"
-  /// is the canonical one.
-  Pattern get separatorPattern;
-
-  /// The [Pattern] that matches path components that need a separator after
-  /// them.
-  ///
-  /// Windows and POSIX styles just need separators when the previous component
-  /// doesn't already end in a separator, but the URL always needs to place a
-  /// separator between the root and the first component, even if the root
-  /// already ends in a separator character. For example, to join "file://" and
-  /// "usr", an additional "/" is needed (making "file:///usr").
-  Pattern get needsSeparatorPattern;
-
-  /// The [Pattern] that can be used to match the root prefix of an absolute
-  /// path in this style.
-  Pattern get rootPattern;
-
-  /// The [Pattern] that can be used to match the root prefix of a root-relative
-  /// path in this style.
-  ///
-  /// This can be null to indicate that this style doesn't support root-relative
-  /// paths.
-  final Pattern relativeRootPattern = null;
-
-  /// A [Builder] that uses this style.
-  Builder get builder => new Builder(style: this);
-
-  /// Gets the root prefix of [path] if path is absolute. If [path] is relative,
-  /// returns `null`.
-  String getRoot(String path) {
-    // TODO(rnystrom): Use firstMatch() when #7080 is fixed.
-    var matches = rootPattern.allMatches(path);
-    if (matches.isNotEmpty) return matches.first[0];
-    return getRelativeRoot(path);
-  }
-
-  /// Gets the root prefix of [path] if it's root-relative.
-  ///
-  /// If [path] is relative or absolute and not root-relative, returns `null`.
-  String getRelativeRoot(String path) {
-    if (relativeRootPattern == null) return null;
-    // TODO(rnystrom): Use firstMatch() when #7080 is fixed.
-    var matches = relativeRootPattern.allMatches(path);
-    if (matches.isEmpty) return null;
-    return matches.first[0];
-  }
-
-  /// Returns the path represented by [uri] in this style.
-  String pathFromUri(Uri uri);
-
-  /// Returns the URI that represents the relative path made of [parts].
-  Uri relativePathToUri(String path) =>
-      new Uri(pathSegments: builder.split(path));
-
-  /// Returns the URI that represents [path], which is assumed to be absolute.
-  Uri absolutePathToUri(String path);
-
-  String toString() => name;
-}
-
-/// The style for POSIX paths.
-class _PosixStyle extends Style {
-  _PosixStyle();
-
-  final name = 'posix';
-  final separator = '/';
-  final separatorPattern = new RegExp(r'/');
-  final needsSeparatorPattern = new RegExp(r'[^/]$');
-  final rootPattern = new RegExp(r'^/');
-
-  String pathFromUri(Uri uri) {
-    if (uri.scheme == '' || uri.scheme == 'file') {
-      return Uri.decodeComponent(uri.path);
-    }
-    throw new ArgumentError("Uri $uri must have scheme 'file:'.");
-  }
-
-  Uri absolutePathToUri(String path) {
-    var parsed = builder._parse(path);
-    if (parsed.parts.isEmpty) {
-      // If the path is a bare root (e.g. "/"), [components] will
-      // currently be empty. We add two empty components so the URL constructor
-      // produces "file:///", with a trailing slash.
-      parsed.parts.addAll(["", ""]);
-    } else if (parsed.hasTrailingSeparator) {
-      // If the path has a trailing slash, add a single empty component so the
-      // URI has a trailing slash as well.
-      parsed.parts.add("");
-    }
-
-    return new Uri(scheme: 'file', pathSegments: parsed.parts);
-  }
-}
-
-/// The style for Windows paths.
-class _WindowsStyle extends Style {
-  _WindowsStyle();
-
-  final name = 'windows';
-  final separator = '\\';
-  final separatorPattern = new RegExp(r'[/\\]');
-  final needsSeparatorPattern = new RegExp(r'[^/\\]$');
-  final rootPattern = new RegExp(r'^(\\\\[^\\]+\\[^\\/]+|[a-zA-Z]:[/\\])');
-
-  // Matches a back or forward slash that's not followed by another back or
-  // forward slash.
-  final relativeRootPattern = new RegExp(r"^[/\\](?![/\\])");
-
-  String pathFromUri(Uri uri) {
-    if (uri.scheme != '' && uri.scheme != 'file') {
-      throw new ArgumentError("Uri $uri must have scheme 'file:'.");
-    }
-
-    var path = uri.path;
-    if (uri.host == '') {
-      // Drive-letter paths look like "file:///C:/path/to/file". The
-      // replaceFirst removes the extra initial slash.
-      if (path.startsWith('/')) path = path.replaceFirst("/", "");
-    } else {
-      // Network paths look like "file://hostname/path/to/file".
-      path = '\\\\${uri.host}$path';
-    }
-    return Uri.decodeComponent(path.replaceAll("/", "\\"));
-  }
-
-  Uri absolutePathToUri(String path) {
-    var parsed = builder._parse(path);
-    if (parsed.root.startsWith(r'\\')) {
-      // Network paths become "file://server/share/path/to/file".
-
-      // The root is of the form "\\server\share". We want "server" to be the
-      // URI host, and "share" to be the first element of the path.
-      var rootParts = parsed.root.split('\\').where((part) => part != '');
-      parsed.parts.insert(0, rootParts.last);
-
-      if (parsed.hasTrailingSeparator) {
-        // If the path has a trailing slash, add a single empty component so the
-        // URI has a trailing slash as well.
-        parsed.parts.add("");
-      }
-
-      return new Uri(scheme: 'file', host: rootParts.first,
-          pathSegments: parsed.parts);
-    } else {
-      // Drive-letter paths become "file:///C:/path/to/file".
-
-      // If the path is a bare root (e.g. "C:\"), [parsed.parts] will currently
-      // be empty. We add an empty component so the URL constructor produces
-      // "file:///C:/", with a trailing slash. We also add an empty component if
-      // the URL otherwise has a trailing slash.
-      if (parsed.parts.length == 0 || parsed.hasTrailingSeparator) {
-        parsed.parts.add("");
-      }
-
-      // Get rid of the trailing "\" in "C:\" because the URI constructor will
-      // add a separator on its own.
-      parsed.parts.insert(0, parsed.root.replaceAll(separatorPattern, ""));
-
-      return new Uri(scheme: 'file', pathSegments: parsed.parts);
-    }
-  }
-}
-
-/// The style for URL paths.
-class _UrlStyle extends Style {
-  _UrlStyle();
-
-  final name = 'url';
-  final separator = '/';
-  final separatorPattern = new RegExp(r'/');
-  final needsSeparatorPattern = new RegExp(
-      r"(^[a-zA-Z][-+.a-zA-Z\d]*://|[^/])$");
-  final rootPattern = new RegExp(r"[a-zA-Z][-+.a-zA-Z\d]*://[^/]*");
-  final relativeRootPattern = new RegExp(r"^/");
-
-  String pathFromUri(Uri uri) => uri.toString();
-
-  Uri relativePathToUri(String path) => Uri.parse(path);
-  Uri absolutePathToUri(String path) => Uri.parse(path);
-}
-
-// TODO(rnystrom): Make this public?
-class _ParsedPath {
-  /// The [Style] that was used to parse this path.
-  Style style;
-
-  /// The absolute root portion of the path, or `null` if the path is relative.
-  /// On POSIX systems, this will be `null` or "/". On Windows, it can be
-  /// `null`, "//" for a UNC path, or something like "C:\" for paths with drive
-  /// letters.
-  String root;
-
-  /// Whether this path is root-relative.
-  ///
-  /// See [Builder.isRootRelative].
-  bool isRootRelative;
-
-  /// The path-separated parts of the path. All but the last will be
-  /// directories.
-  List<String> parts;
-
-  /// The path separators preceding each part.
-  ///
-  /// The first one will be an empty string unless the root requires a separator
-  /// between it and the path. The last one will be an empty string unless the
-  /// path ends with a trailing separator.
-  List<String> separators;
-
-  /// The file extension of the last non-empty part, or "" if it doesn't have
-  /// one.
-  String get extension => _splitExtension()[1];
-
-  /// `true` if this is an absolute path.
-  bool get isAbsolute => root != null;
-
-  _ParsedPath(this.style, this.root, this.isRootRelative, this.parts,
-      this.separators);
-
-  String get basename {
-    var copy = this.clone();
-    copy.removeTrailingSeparators();
-    if (copy.parts.isEmpty) return root == null ? '' : root;
-    return copy.parts.last;
-  }
-
-  String get basenameWithoutExtension => _splitExtension()[0];
-
-  bool get hasTrailingSeparator =>
-      !parts.isEmpty && (parts.last == '' || separators.last != '');
-
-  void removeTrailingSeparators() {
-    while (!parts.isEmpty && parts.last == '') {
-      parts.removeLast();
-      separators.removeLast();
-    }
-    if (separators.length > 0) separators[separators.length - 1] = '';
-  }
-
-  void normalize() {
-    // Handle '.', '..', and empty parts.
-    var leadingDoubles = 0;
-    var newParts = [];
-    for (var part in parts) {
-      if (part == '.' || part == '') {
-        // Do nothing. Ignore it.
-      } else if (part == '..') {
-        // Pop the last part off.
-        if (newParts.length > 0) {
-          newParts.removeLast();
-        } else {
-          // Backed out past the beginning, so preserve the "..".
-          leadingDoubles++;
-        }
-      } else {
-        newParts.add(part);
-      }
-    }
-
-    // A relative path can back out from the start directory.
-    if (!isAbsolute) {
-      _growListFront(newParts, leadingDoubles, '..');
-    }
-
-    // If we collapsed down to nothing, do ".".
-    if (newParts.length == 0 && !isAbsolute) {
-      newParts.add('.');
-    }
-
-    // Canonicalize separators.
-    var newSeparators = new List.generate(
-        newParts.length, (_) => style.separator, growable: true);
-    newSeparators.insert(0,
-        isAbsolute && newParts.length > 0 &&
-                root.contains(style.needsSeparatorPattern) ?
-            style.separator : '');
-
-    parts = newParts;
-    separators = newSeparators;
-
-    // Normalize the Windows root if needed.
-    if (root != null && style == Style.windows) {
-      root = root.replaceAll('/', '\\');
-    }
-    removeTrailingSeparators();
-  }
-
-  String toString() {
-    var builder = new StringBuffer();
-    if (root != null) builder.write(root);
-    for (var i = 0; i < parts.length; i++) {
-      builder.write(separators[i]);
-      builder.write(parts[i]);
-    }
-    builder.write(separators.last);
-
-    return builder.toString();
-  }
-
-  /// Splits the last non-empty part of the path into a `[basename, extension`]
-  /// pair.
-  ///
-  /// Returns a two-element list. The first is the name of the file without any
-  /// extension. The second is the extension or "" if it has none.
-  List<String> _splitExtension() {
-    var file = parts.lastWhere((p) => p != '', orElse: () => null);
-
-    if (file == null) return ['', ''];
-    if (file == '..') return ['..', ''];
-
-    var lastDot = file.lastIndexOf('.');
-
-    // If there is no dot, or it's the first character, like '.bashrc', it
-    // doesn't count.
-    if (lastDot <= 0) return [file, ''];
-
-    return [file.substring(0, lastDot), file.substring(lastDot)];
-  }
-
-  _ParsedPath clone() => new _ParsedPath(
-      style, root, isRootRelative,
-      new List.from(parts), new List.from(separators));
-}
-
-/// An exception class that's thrown when a path operation is unable to be
-/// computed accurately.
-class PathException implements Exception {
-  String message;
-
-  PathException(this.message);
-
-  String toString() => "PathException: $message";
-}
+Uri toUri(String path) => _context.toUri(path);