1 files changed, 56 insertions, 0 deletions
diff --git a/jni/ruby/lib/rake/invocation_chain.rb b/jni/ruby/lib/rake/invocation_chain.rb
new file mode 100644
index 0000000..5406289
--- /dev/null
+++ b/jni/ruby/lib/rake/invocation_chain.rb
@@ -0,0 +1,56 @@
+module Rake
+
+  # InvocationChain tracks the chain of task invocations to detect
+  # circular dependencies.
+  class InvocationChain < LinkedList
+
+    # Is the invocation already in the chain?
+    def member?(invocation)
+      head == invocation || tail.member?(invocation)
+    end
+
+    # Append an invocation to the chain of invocations. It is an error
+    # if the invocation already listed.
+    def append(invocation)
+      if member?(invocation)
+        fail RuntimeError, "Circular dependency detected: #{to_s} => #{invocation}"
+      end
+      conj(invocation)
+    end
+
+    # Convert to string, ie: TOP => invocation => invocation
+    def to_s
+      "#{prefix}#{head}"
+    end
+
+    # Class level append.
+    def self.append(invocation, chain)
+      chain.append(invocation)
+    end
+
+    private
+
+    def prefix
+      "#{tail} => "
+    end
+
+    # Null object for an empty chain.
+    class EmptyInvocationChain < LinkedList::EmptyLinkedList
+      @parent = InvocationChain
+
+      def member?(obj)
+        false
+      end
+
+      def append(invocation)
+        conj(invocation)
+      end
+
+      def to_s
+        "TOP"
+      end
+    end
+
+    EMPTY = EmptyInvocationChain.new
+  end
+end