Added .packages, packages/ discovery.

lib/src/util.dart

Index: lib/src/util.dart
diff --git a/lib/src/util.dart b/lib/src/util.dart
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index 0000000000000000000000000000000000000000..76bd1d6e566a464f158cb365df2dffdc58e70a74
--- /dev/null
+++ b/lib/src/util.dart
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+// 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.
+
+/// Utility methods used by more than one library in the package.
+library package_config.util;
+
+import "package:charcode/ascii.dart";
+
+/// Tests whether something is a valid Dart identifier/package name.
+bool isIdentifier(String string) {
+  if (string.isEmpty) return false;
+  int firstChar = string.codeUnitAt(0);
+  int firstCharLower = firstChar |= 0x20;
+  if (firstCharLower < $a || firstCharLower > $z) {
+    if (firstChar != $_ && firstChar != $$) return false;
+  }
+  for (int i = 1; i < string.length; i++) {
+    int char = string.codeUnitAt(i);
+    int charLower = char | 0x20;
+    if (charLower < $a || charLower > $z) {    // Letters.
+      if ((char ^ 0x30) <= 9) continue;        // Digits.
+      if (char == $_ || char == $$) continue;  // $ and _
+      if (firstChar != $_ && firstChar != $$) return false;
+    }
+  }
+  return true;
+}
+
+
+/// Validate that a Uri is a valid package:URI.
+String checkValidPackageUri(Uri packageUri) {
+  if (packageUri.scheme != "package") {
+    throw new ArgumentError.value(packageUri, "packageUri",
+                                  "Not a package: URI");
+  }
+  if (packageUri.hasAuthority) {
+    throw new ArgumentError.value(packageUri, "packageUri",
+                                  "Package URIs must not have a host part");
+  }
+  if (packageUri.hasQuery) {
+    // A query makes no sense if resolved to a file: URI.
+    throw new ArgumentError.value(packageUri, "packageUri",
+                                  "Package URIs must not have a query part");
+  }
+  if (packageUri.hasFragment) {
+    // We could leave the fragment after the URL when resolving,
+    // but it would be odd if "package:foo/foo.dart#1" and
+    // "package:foo/foo.dart#2" were considered different libraries.
+    // Keep the syntax open in case we ever get multiple libraries in one file.
+    throw new ArgumentError.value(packageUri, "packageUri",
+                                  "Package URIs must not have a fragment part");
+  }
+  if (packageUri.path.startsWith('/')) {
+    throw new ArgumentError.value(packageUri, "packageUri",
+                                  "Package URIs must not start with a '/'");
+  }
+  int firstSlash = packageUri.path.indexOf('/');
+  if (firstSlash == -1) {
+    throw new ArgumentError.value(packageUri, "packageUri",
+        "Package URIs must start with the package name followed by a '/'");
+  }
+  String packageName = packageUri.path.substring(0, firstSlash);
+  if (!isIdentifier(packageName)) {
+    throw new ArgumentError.value(packageUri, "packageUri",
+        "Package names must be valid identifiers");
+  }
+  return packageName;
+}