Improve the detection lockfile freshness.

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 94c574b2ae1de6bbc2e663d6a702e165b93a3c87..9726a105cc14d807b420df22f1e33eb742c50d91 100644
--- a/lib/src/lock_file.dart
+++ b/lib/src/lock_file.dart
@@ -25,19 +25,29 @@ class LockFile {
   /// The packages this lockfile pins.
   final Map<String, PackageId> packages;
 
-  /// Creates a new lockfile containing [ids].
-  factory LockFile(Iterable<PackageId> ids, SourceRegistry sources) {
-    var packages = new Map.fromIterable(
-        ids.where((id) => !id.isRoot),
-        key: (id) => id.name);
-    return new LockFile._(packages, sources);
-  }
+  /// The intersection of all SDK constraints for all locked packages.
+  final VersionConstraint sdkConstraint;
 
-  LockFile._(Map<String, PackageId> packages, this._sources)
+  /// Creates a new lockfile containing [ids].
+  ///
+  /// If passed, [sdkConstraint] represents the intersection of all SKD
+  /// constraints for all locked packages. It defaults to
+  /// [VersionConstraint.any].
+  LockFile(Iterable<PackageId> ids, SourceRegistry sources,
+          {VersionConstraint sdkConstraint})
+      : this._(
+          new Map.fromIterable(
+              ids.where((id) => !id.isRoot),
+              key: (id) => id.name),
+          sdkConstraint ?? VersionConstraint.any,
+          sources);
+
+  LockFile._(Map<String, PackageId> packages, this.sdkConstraint, this._sources)
       : packages = new UnmodifiableMapView(packages);
 
   LockFile.empty(this._sources)
-      : packages = const {};
+      : packages = const {},
+        sdkConstraint = VersionConstraint.any;
 
   /// Loads a lockfile from [filePath].
   factory LockFile.load(String filePath, SourceRegistry sources) {
@@ -55,8 +65,6 @@ class LockFile {
   /// `null`.
   static LockFile _parse(String filePath, String contents,
       SourceRegistry sources) {
-    var packages = {};
-
     if (contents.trim() == '') return new LockFile.empty(sources);
 
     var sourceUrl;
@@ -65,6 +73,19 @@ class LockFile {
 
     _validate(parsed is Map, 'The lockfile must be a YAML mapping.', parsed);
 
+    var sdkConstraint = VersionConstraint.any;
+    var sdkConstraintText = parsed['sdk'];
+    if (sdkConstraintText != null) {
+      _validate(sdkConstraintText is String, 'The "sdk" field must be a string.',

[Bob Nystrom, 2015/12/21 20:55:03]

Long line.

[nweiz, 2016/01/04 23:27:29]

Done.

+          parsed.nodes['sdk']);
+
+      sdkConstraint = _wrapFormatException(
+          'version constraint',
+          parsed.nodes['sdk'],
+          () => new VersionConstraint.parse(sdkConstraintText));
+    }
+
+    var packages = {};
     var packageEntries = parsed['packages'];
     if (packageEntries != null) {
       _validate(packageEntries is Map, 'The "packages" field must be a map.',
@@ -103,7 +124,22 @@ class LockFile {
       });
     }
 
-    return new LockFile._(packages, sources);
+    return new LockFile._(packages, sdkConstraint, sources);
+  }
+
+  /// Runs [fn] and wraps any [FormatException] it throws in a
+  /// [SourceSpanFormatException].
+  ///
+  /// [description] should be a noun phrase that describes whatever's being
+  /// parsed or processed by [fn]. [span] should be the location of whatever's
+  /// being processed within the pubspec.
+  static _wrapFormatException(String description, SourceSpan span, fn()) {
+    try {
+      return fn();
+    } on FormatException catch (e) {
+      throw new SourceSpanFormatException(
+          'Invalid $description: ${e.message}', span);
+    }
   }

[Bob Nystrom, 2015/12/21 20:55:03]

Do we do this elsewhere? Maybe move it into utils?

[nweiz, 2016/01/04 23:27:29]

We do something similar in pubspec.dart, but it throws a different type of
exception so we wouldn't be able to re-use code.

 
   /// If [condition] is `false` throws a format error with [message] for [node].
@@ -121,7 +157,7 @@ class LockFile {
 
     var packages = new Map.from(this.packages);
     packages[id.name] = id;
-    return new LockFile._(packages, _sources);
+    return new LockFile._(packages, sdkConstraint, _sources);
   }
 
   /// Returns a copy of this LockFile with a package named [name] removed.
@@ -132,7 +168,7 @@ class LockFile {
 
     var packages = new Map.from(this.packages);
     packages.remove(name);
-    return new LockFile._(packages, _sources);
+    return new LockFile._(packages, sdkConstraint, _sources);
   }
 
   /// Returns the contents of the `.packages` file generated from this lockfile.
@@ -161,22 +197,23 @@ class LockFile {
   /// properly serialize package descriptions.
   String serialize(String packageDir) {
     // Convert the dependencies to a simple object.
-    var data = {};
+    var packageMap = {};
     packages.forEach((name, package) {
       var description = _sources[package.source]
           .serializeDescription(packageDir, package.description);
 
-      data[name] = {
+      packageMap[name] = {
         'version': package.version.toString(),
         'source': package.source,
         'description': description
       };
     });
 
+    var data = {'sdk': sdkConstraint.toString(), 'packages': packageMap};
     return """
 # Generated by pub
 # See http://pub.dartlang.org/doc/glossary.html#lockfile
-${yamlToString({'packages': data})}
+${yamlToString(data)}
 """;
   }
 }