Added .packages, packages/ discovery.

lib/packages_file.dart

Index: lib/packages_file.dart
diff --git a/lib/packages_file.dart b/lib/packages_file.dart
new file mode 100644
index 0000000000000000000000000000000000000000..48c2334e0d134ceb12421586eb8dfdd42f1279a4
--- /dev/null
+++ b/lib/packages_file.dart
@@ -0,0 +1,172 @@
+// Copyright (c) 2015, 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 package_config.packages_file;
+
+import "package:charcode/ascii.dart";
+import "src/util.dart" show isIdentifier;
+
+/// Parses a `.packages` file into a map from package name to base URI.
+///
+/// The [source] is the byte content of a `.packages` file, assumed to be
+/// UTF-8 encoded. In practice, all sinficant parts of the file must be ASCII,
+/// so Latin-1 or Windows-1252 encoding will also work fine.
+///
+/// If the file content is available as a string, its [String.codeUnits] can
+/// be used as the `source` argument of this function.
+///
+/// The [baseLocation] is used as a base URI to resolve all relative
+/// URI references against.
+/// If the content was read from a file, `baseLocation` should be the
+/// location of that file.
+///
+/// Returns a simple mapping from package name to package location.
+Map<String, Uri> parse(List<int> source, Uri baseLocation) {
+  int index = 0;
+  Map<String, Uri> result = <String, Uri>{};
+  while (index < source.length) {
+    bool isComment = false;
+    int start = index;
+    int eqIndex = -1;
+    int end = source.length;
+    int char = source[index++];
+    if (char == $cr || char == $lf) {
+      continue;
+    }
+    if (char == $equal) {
+      throw new FormatException("Missing package name", source, index - 1);
+    }
+    isComment = char == $hash;
+    while (index < source.length) {
+      char = source[index++];
+      if (char == $equal && eqIndex < 0) {
+        eqIndex = index - 1;
+      } else if (char == $cr || char == $lf) {
+        end = index - 1;
+        break;
+      }
+    }
+    if (isComment) continue;
+    if (eqIndex < 0) {
+      throw new FormatException("No '=' on line", source, index - 1);
+    }
+    var packageName = new String.fromCharCodes(source, start, eqIndex);
+    if (!isIdentifier(packageName)) {
+      throw new FormatException("Not a valid package name", packageName, 0);
+    }
+    var packageUri = new String.fromCharCodes(source, eqIndex + 1, end);
+    var packageLocation = Uri.parse(packageUri);
+    if (!packageLocation.path.endsWith('/')) {
+      packageLocation =
+          packageLocation.replace(path: packageLocation.path + "/");
+    }
+    packageLocation = baseLocation.resolveUri(packageLocation);
+    if (result.containsKey(packageName)) {
+      throw new FormatException(
+          "Same package name occured twice.", source, start);
+    }
+    result[packageName] = packageLocation;
+  }
+  return result;
+}
+
+/// Writes the mapping to a [StringSink].
+///
+/// If [comment] is provided, the output will contain this comment
+/// with `#` in front of each line.
+///
+/// If [baseUri] is provided, package locations will be made relative
+/// to the base URI, if possible, before writing.
+void write(StringSink output, Map<String, Uri> packageMapping,
+           {Uri baseUri, String comment}) {
+  if (baseUri != null && !baseUri.isAbsolute) {
+    throw new ArgumentError.value(baseUri, "baseUri", "Must be absolute");
+  }
+
+  if (comment != null) {
+    for (var commentLine in comment.split('\n')) {
+      output.write('#');
+      output.writeln(commentLine);
+    }
+  } else {
+    output.write("# generated by package:package_config at ");
+    output.write(new DateTime.now());
+    output.writeln();
+  }
+
+  packageMapping.forEach((String packageName, Uri uri) {
+    // Validate packageName.
+    if (!isIdentifier(packageName)) {
+      throw new ArgumentError('"$packageName" is not a valid package name');
+    }
+    output.write(packageName);
+    output.write('=');
+    // If baseUri provided, make uri relative.
+    if (baseUri != null) {
+      uri = _relativize(uri, baseUri);
+    }
+    output.write(uri);
+    if (!uri.path.endsWith('/')) {
+      output.write('/');
+    }
+    output.writeln();
+  });
+}
+
+/// Attempts to return a relative URI for [uri].
+///
+/// The result URI satisfies `baseUri.resolveUri(result) == uri`,
+/// but may be relative.
+/// The `baseUri` must be absolute.
+Uri _relativize(Uri uri, Uri baseUri) {
+  assert(!baseUri.isAbsolute);
+  if (uri.hasQuery || uri.hasFragment) {
+    uri = new Uri(
+        scheme: uri.scheme,
+        userInfo: uri.hasAuthority ? uri.userInfo : null,
+        host: uri.hasAuthority ? uri.host : null,
+        port: uri.hasAuthority ? uri.port : null,
+        path: uri.path);
+  }
+
+  // Already relative. We assume the caller knows what they are doing.
+  if (!uri.isAbsolute) return uri;
+
+  if (baseUri.scheme != uri.scheme) {
+    return uri;
+  }
+
+  // If authority differs, we could remove the scheme, but it's not worth it.
+  if (uri.hasAuthority != baseUri.hasAuthority) return uri;
+  if (uri.hasAuthority) {
+    if (uri.userInfo != baseUri.userInfo ||
+        uri.host.toLowerCase() != baseUri.host.toLowerCase() ||
+        uri.port != baseUri.port) {
+      return uri;
+    }
+  }
+
+  baseUri = baseUri.normalizePath();
+  List<String> base = baseUri.pathSegments.toList();
+  if (base.isNotEmpty) {
+    base = new List<String>.from(base)..removeLast();
+  }
+  uri = uri.normalizePath();
+  List<String> target = uri.pathSegments.toList();
+  int index = 0;
+  while (index < base.length && index < target.length) {
+    if (base[index] != target[index]) {
+      break;
+    }
+    index++;
+  }
+  if (index == base.length) {
+    return new Uri(path: target.skip(index).join('/'));
+  } else if (index > 0) {
+    return new Uri(
+        path: '../' * (base.length - index) + target.skip(index).join('/'));
+  } else {
+    return uri;
+  }
+}