A subspec always depends on the parent spec if the parent spec is a Subspec too.

lib/cocoapods/specification.rb

@@ -395,7 +395,10 @@ module Pod
         @dependencies, @resources, @clean_paths, @subspecs = [], [], [], []
         @xcconfig = Xcodeproj::Config.new
 
-        self.part_of = top_level_parent.name, top_level_parent.version
+        # A subspec is _always_ part of the source of its top level spec.
+        self.part_of = top_level_parent.name, version
+        # A subspec has a dependency on the parent if the parent is a subspec too.
+        dependency(@parent.name, version) if @parent.is_a?(Subspec)
 
         yield self if block_given?
       end
@@ -416,6 +419,10 @@ module Pod
         @summary ? @summary : top_level_parent.summary
       end
 
+      def version
+        top_level_parent.version
+      end
+
       def source
         top_level_parent.source
       end

master @ d0a5f7b8

-Subproject commit 4d304b8066a9c1d1156412d882de60eeca625659
+Subproject commit d0a5f7b8b29c6cc81ff28760d756e5fb300a9e7f

spec/unit/specification_spec.rb

@@ -313,6 +313,12 @@ describe "A Pod::Specification subspec" do
     @spec.subspecs.first.subspecs.first.part_of.should == dependency
   end
 
+  it "depends on the parent spec, if it is a subspec" do
+    dependency = Pod::Dependency.new('MainSpec', '1.2.3').tap { |d| d.only_part_of_other_pod = true }
+    @spec.subspecs.first.dependencies.should == [dependency]
+    @spec.subspecs.first.subspecs.first.dependencies.should == [dependency, Pod::Dependency.new('MainSpec/FirstSubSpec', '1.2.3')]
+  end
+
   it "automatically forwards undefined attributes to the top level parent" do
     @spec.subspecs.first.summary.should        == @spec.summary
     @spec.subspecs.first.source.should         == @spec.source