Get rid of RootSource.

utils/pub/package.dart

Index: utils/pub/package.dart
diff --git a/utils/pub/package.dart b/utils/pub/package.dart
index 70f469c0ea6eb69b897cdf1dff427625bafd7fa4..8e0d39e4aeaa011507acbba3df41d246e58763cd 100644
--- a/utils/pub/package.dart
+++ b/utils/pub/package.dart
@@ -82,7 +82,8 @@ class PackageId implements Comparable {
   /// The name of the package being identified.
   final String name;
 
-  /// The [Source] used to look up this package given its [description].
+  /// The [Source] used to look up this package given its [description]. If
+  /// this is a root package ID, this will be `null`.

[Jennifer Messerly, 2013/01/24 23:24:37]

fwiw, I think Kathy suggested not using code font for `null`, as a general
desire to avoid too much code font. Up to you though. I might be misremembering
this.

[Bob Nystrom, 2013/01/25 18:22:50]

I think you're remembering right, though I personally do prefer using code font
for literals. I like a little visual style variation and I think code font can
be important to disambiguate use-mention in cases where a literal is a valid
word like "this".

   final Source source;
 
   /// The package's version.
@@ -96,8 +97,11 @@ class PackageId implements Comparable {
 
   PackageId(this.name, this.source, this.version, this.description);
 
+  /// Whether this ID identifies the root package.
+  bool get isRoot => source == null;
+
   int get hashCode => name.hashCode ^
-                      source.name.hashCode ^
+                      (source != null ? source.name.hashCode : 0) ^

[Jennifer Messerly, 2013/01/24 23:24:37]

Another idea here: you could make Source.hashCode return its name.hashCode:

    class Source { ...; int get hashCode => name.hashCode; }

Then change this one to be:

    int get hashCode => name.hashCode ^ source.hashCode ^ version.hashCode


That might be cleaner? Basically, exploit the fact that "null.hashCode" works in
Dart :)

[Bob Nystrom, 2013/01/25 18:22:50]

Great idea! Done.

                       version.hashCode;
 
   bool operator ==(other) {
@@ -106,11 +110,12 @@ class PackageId implements Comparable {
     // enough to uniquely identify the package and that we don't need to delve
     // into the description.
     return other.name == name &&
-           other.source.name == source.name &&
+           other.source == source &&

[Jennifer Messerly, 2013/01/24 23:24:37]

just checking, source already implements reasonable equality operator? Or do we
know that identity semantics work for it?

[Bob Nystrom, 2013/01/25 18:22:50]

I'm relying on identity here. Sources are effectively singletons and weird
things would happen if you had more than one source of the same type.

            other.version == version;
   }
 
   String toString() {
+    if (isRoot) return "$name $version (root)";
     if (source.isDefault) return "$name $version";
     return "$name $version from $source";
   }
@@ -141,7 +146,8 @@ class PackageRef {
   /// The name of the package being identified.
   final String name;
 
-  /// The [Source] used to look up the package.
+  /// The [Source] used to look up the package. If this refers to a root
+  /// package, this will be `null`.
   final Source source;
 
   /// The allowed package versions.
@@ -153,7 +159,20 @@ class PackageRef {
 
   PackageRef(this.name, this.source, this.constraint, this.description);
 
-  String toString() => "$name $constraint from $source ($description)";
+  /// Creates a reference to the given root package.
+  PackageRef.root(Package package)
+      : name = package.name,
+        source = null,
+        constraint = package.version,
+        description = package.name;
+
+  /// Whether this refers to the root package.
+  bool get isRoot => source == null;
+
+  String toString() {
+    if (isRoot) return "$name $constraint (root)";
+    return "$name $constraint from $source ($description)";
+  }
 
   /// Returns a [PackageId] generated from this [PackageRef] with the given
   /// concrete version.