Support relative paths in path dependencies.

utils/pub/path_source.dart

Index: utils/pub/path_source.dart
diff --git a/utils/pub/path_source.dart b/utils/pub/path_source.dart
index 123a3086c2ed0b3a8c5d546e6a12521cf3e897d2..b985a4afc8cd2461611c43f2303bab0af51dfd5a 100644
--- a/utils/pub/path_source.dart
+++ b/utils/pub/path_source.dart
@@ -25,46 +25,78 @@ class PathSource extends Source {
   Future<Pubspec> describe(PackageId id) {
     return defer(() {
       _validatePath(id.name, id.description);
-      return new Pubspec.load(id.name, id.description, systemCache.sources);
+      return new Pubspec.load(id.name, id.description["path"],
+          systemCache.sources);
     });
   }
 
-  Future<bool> install(PackageId id, String path) {
+  Future<bool> install(PackageId id, String destination) {
     return defer(() {
       try {
         _validatePath(id.name, id.description);
       } on FormatException catch(err) {
         return false;
       }
-      return createPackageSymlink(id.name, id.description, path);
+
+      return createPackageSymlink(id.name, destination, id.description["path"],
+          relative: id.description["relative"]);
     }).then((_) => true);
   }
 
-  void validateDescription(description, {bool fromLockFile: false}) {
+  /// Parses a path dependency. This takes in a path string and returns a map.
+  /// The "path" key will be the original path but resolves relative to the
+  /// containing path. The "relative" key will be `true` if the original path
+  /// was relative.
+  ///
+  /// A path coming from a pubspec is a simple string. From a lock file, it's
+  /// an expanded {"path": ..., "relative": ...} map.
+  dynamic parseDescription(String containingPath, description,
+                           {bool fromLockFile: false}) {
+    if (fromLockFile) {
+      if (description is! Map) {
+        throw new FormatException("The description must be a map.");
+      }
+
+      if (description["path"] is! String) {
+        throw new FormatException("The 'path' field of the description must "
+            "be a string.");
+      }
+
+      if (description["relative"] is! bool) {
+        throw new FormatException("The 'relative' field of the description "
+            "must be a boolean.");
+      }
+
+      return description;
+    }
+
     if (description is! String) {
       throw new FormatException("The description must be a path string.");
     }
-  }
 
-  /// Ensures that [dir] is a valid path. It must be an absolute path that
-  /// points to an existing directory. Throws a [FormatException] if the path
-  /// is invalid.
-  void _validatePath(String name, String dir) {
-    // Relative paths are not (currently) allowed because the user would expect
-    // them to be relative to the pubspec where the dependency appears. That in
-    // turn means that two pubspecs in different locations with the same
-    // relative path dependency could refer to two different packages. That
-    // violates pub's rule that a description should uniquely identify a
-    // package.
-    //
-    // At some point, we may want to loosen this, but it will mean tracking
-    // where a given PackageId appeared.
-    if (!path.isAbsolute(dir)) {
-      throw new FormatException(
-          "Path dependency for package '$name' must be an absolute path. "
-          "Was '$dir'.");
+    // Resolve the path relative to the containing file path, and remember
+    // whether the original path was relative or absolute.
+    bool isRelative = path.isRelative(description);
+    if (path.isRelative(description)) {
+      // Can't handle relative paths coming from pubspecs that are not on the
+      // local file system.
+      assert(containingPath != null);
+
+      description = path.join(path.dirname(containingPath), description);
     }
 
+    return {
+      "path": description,
+      "relative": isRelative
+    };
+  }
+
+  /// Ensures that [description] is a valid path description. It must be a map,
+  /// with a "path" key containing a path that points to an existing directory.
+  /// Throws a [FormatException] if the path is invalid.
+  void _validatePath(String name, description) {
+    var dir = description["path"];
+
     if (fileExists(dir)) {
       throw new FormatException(
           "Path dependency for package '$name' must refer to a "