Make LockFile immutable.

lib/src/lock_file.dart

Index: lib/src/lock_file.dart
diff --git a/lib/src/lock_file.dart b/lib/src/lock_file.dart
index 99b233276294f5baeeffa3de32bbfadd9b67f9da..21a40e722f5bde4cbf48b267dae78b2487695a07 100644
--- a/lib/src/lock_file.dart
+++ b/lib/src/lock_file.dart
@@ -4,6 +4,8 @@
 
 library pub.lock_file;
 
+import 'dart:collection';
+
 import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:source_span/source_span.dart';
@@ -16,23 +18,45 @@ import 'utils.dart';
 
 /// A parsed and validated `pubspec.lock` file.
 class LockFile {
+  /// The source registry with which the lock file's IDs are interpreted.
+  ///
+  /// This is `null` for an empty lock file, since there are no IDs to
+  /// interpret.
+  final SourceRegistry _sources;
+
   /// The packages this lockfile pins.
-  Map<String, PackageId> packages;
+  final Map<String, PackageId> packages;
 
   /// Creates a new lockfile containing [ids].
-  factory LockFile(List<PackageId> ids) {
-    var lockFile = new LockFile.empty();
+  ///
+  /// Throws an [ArgumentError] if any package has an undefined source according
+  /// to [sources] or an unresolved ID according to [Source.isResolved].
+  factory LockFile(Iterable<PackageId> ids, SourceRegistry sources) {
+    var packages = {};
     for (var id in ids) {
-      if (!id.isRoot) lockFile.packages[id.name] = id;
+      if (id.isRoot) continue;
+
+      var source = sources[id.source];
+      if (source == null) {
+        throw new ArgumentError('Undefined source "$source" for package "$id".');

[Bob Nystrom, 2015/08/07 21:50:56]

Long line.

Also, does this do the right thing on old lock files that may still have SDK
sources? Do we care? The rest of pub has the concept of an "unknown" source to
handle this. Should we do that here?

[nweiz, 2015/08/07 22:16:07]

Done.
Removed. I had forgotten about UnknownSource. That means that this will never
return null anyway.

+      }
+
+      if (!source.isResolved(id)) {
+        throw new ArgumentError('ID "$id" is not resolved.');
+      }
+
+      packages[id.name] = id;
     }
 
-    return lockFile;
+    return new LockFile._(packages, sources);
   }
 
-  LockFile._(this.packages);
+  LockFile._(Map<String, PackageId> packages, this._sources)
+      : packages = new UnmodifiableMapView(packages);
 
   LockFile.empty()
-    : packages = <String, PackageId>{};
+      : packages = const {},
+        _sources = null;
 
   /// Loads a lockfile from [filePath].
   factory LockFile.load(String filePath, SourceRegistry sources) {
@@ -50,7 +74,7 @@ class LockFile {
   /// `null`.
   static LockFile _parse(String filePath, String contents,
       SourceRegistry sources) {
-    var packages = <String, PackageId>{};
+    var packages = {};
 
     if (contents.trim() == '') return new LockFile.empty();
 
@@ -100,7 +124,7 @@ class LockFile {
       });
     }
 
-    return new LockFile._(packages);
+    return new LockFile._(packages, sources);
   }
 
   /// If [condition] is `false` throws a format error with [message] for [node].
@@ -113,12 +137,12 @@ class LockFile {
   ///
   /// [packageDir] is the containing directory of the root package, used to
   /// properly serialize package descriptions.
-  String serialize(String packageDir, SourceRegistry sources) {
+  String serialize(String packageDir) {
     // Convert the dependencies to a simple object.
     var data = {};
     packages.forEach((name, package) {
-      var description = sources[package.source].serializeDescription(packageDir,
-          package.description);
+      var description = _sources[package.source]
+          .serializeDescription(packageDir, package.description);
 
       data[name] = {
         'version': package.version.toString(),