1 files changed, 34 insertions, 1 deletions
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb
index 31578bb5bf..d1d7045daf 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb
@@ -124,6 +124,7 @@ module Bundler::Molinillo
       dot.join("\n")
     end
 
+    # @param [DependencyGraph] other
     # @return [Boolean] whether the two dependency graphs are equal, determined
     #   by a recursive traversal of each {#root_vertices} and its
     #   {Vertex#successors}
@@ -190,7 +191,7 @@ module Bundler::Molinillo
     # @return [Edge] the added edge
     def add_edge(origin, destination, requirement)
       if destination.path_to?(origin)
-        raise CircularDependencyError.new([origin, destination])
+        raise CircularDependencyError.new(path(destination, origin))
       end
       add_edge_no_circular(origin, destination, requirement)
     end
@@ -219,5 +220,37 @@ module Bundler::Molinillo
     def add_edge_no_circular(origin, destination, requirement)
       log.add_edge_no_circular(self, origin.name, destination.name, requirement)
     end
+
+    # Returns the path between two vertices
+    # @raise [ArgumentError] if there is no path between the vertices
+    # @param [Vertex] from
+    # @param [Vertex] to
+    # @return [Array<Vertex>] the shortest path from `from` to `to`
+    def path(from, to)
+      distances = Hash.new(vertices.size + 1)
+      distances[from.name] = 0
+      predecessors = {}
+      each do |vertex|
+        vertex.successors.each do |successor|
+          if distances[successor.name] > distances[vertex.name] + 1
+            distances[successor.name] = distances[vertex.name] + 1
+            predecessors[successor] = vertex
+          end
+        end
+      end
+
+      path = [to]
+      while before = predecessors[to]
+        path << before
+        to = before
+        break if to == from
+      end
+
+      unless path.last.equal?(from)
+        raise ArgumentError, "There is no path from #{from.name} to #{to.name}"
+      end
+
+      path.reverse
+    end
   end
 end