1 files changed, 51 insertions, 0 deletions
diff --git a/ruby_1_9_3/lib/rake/invocation_chain.rb b/ruby_1_9_3/lib/rake/invocation_chain.rb
new file mode 100644
index 0000000000..8a01ab4c29
--- /dev/null
+++ b/ruby_1_9_3/lib/rake/invocation_chain.rb
@@ -0,0 +1,51 @@
+module Rake
+
+  ####################################################################
+  # InvocationChain tracks the chain of task invocations to detect
+  # circular dependencies.
+  class InvocationChain
+    def initialize(value, tail)
+      @value = value
+      @tail = tail
+    end
+
+    def member?(obj)
+      @value == obj || @tail.member?(obj)
+    end
+
+    def append(value)
+      if member?(value)
+        fail RuntimeError, "Circular dependency detected: #{to_s} => #{value}"
+      end
+      self.class.new(value, self)
+    end
+
+    def to_s
+      "#{prefix}#{@value}"
+    end
+
+    def self.append(value, chain)
+      chain.append(value)
+    end
+
+    private
+
+    def prefix
+      "#{@tail.to_s} => "
+    end
+
+    class EmptyInvocationChain
+      def member?(obj)
+        false
+      end
+      def append(value)
+        InvocationChain.new(value, self)
+      end
+      def to_s
+        "TOP"
+      end
+    end
+
+    EMPTY = EmptyInvocationChain.new
+  end
+end