diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/vertex.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/vertex.rb
index 821f79871fa..41bc013143c 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/vertex.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/vertex.rb
@@ -130,11 +130,21 @@ def hash
       # dependency graph?
       # @return true iff there is a path following edges within this {#graph}
       def path_to?(other)
-        equal?(other) || successors.any? { |v| v.path_to?(other) }
+        _path_to?(other)
       end
 
       alias descendent? path_to?
 
+      # @param [Vertex] other the vertex to check if there's a path to
+      # @param [Set<Vertex>] visited the vertices of {#graph} that have been visited
+      # @return [Boolean] whether there is a path to `other` from `self`
+      def _path_to?(other, visited = Set.new)
+        return false unless visited.add?(self)
+        return true if equal?(other)
+        successors.any? { |v| v._path_to?(other, visited) }
+      end
+      protected :_path_to?
+
       # Is there a path from `other` to `self` following edges in the
       # dependency graph?
       # @return true iff there is a path following edges within this {#graph}
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb b/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb
index fb343250b13..ce0931f103b 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb
@@ -18,7 +18,7 @@ class NoSuchDependencyError < ResolverError
     # @param [Array<Object>] required_by @see {#required_by}
     def initialize(dependency, required_by = [])
       @dependency = dependency
-      @required_by = required_by
+      @required_by = required_by.uniq
       super()
     end
 
@@ -101,9 +101,14 @@ def message_with_trees(opts = {})
       printable_requirement = opts.delete(:printable_requirement) { proc { |req| req.to_s } }
       additional_message_for_conflict = opts.delete(:additional_message_for_conflict) { proc {} }
       version_for_spec = opts.delete(:version_for_spec) { proc(&:to_s) }
+      incompatible_version_message_for_conflict = opts.delete(:incompatible_version_message_for_conflict) do
+        proc do |name, _conflict|
+          %(#{solver_name} could not find compatible versions for #{possibility_type} "#{name}":)
+        end
+      end
 
       conflicts.sort.reduce(''.dup) do |o, (name, conflict)|
-        o << %(\n#{solver_name} could not find compatible versions for #{possibility_type} "#{name}":\n)
+        o << "\n" << incompatible_version_message_for_conflict.call(name, conflict) << "\n"
         if conflict.locked_requirement
           o << %(  In snapshot (#{name_for_locking_dependency_source}):\n)
           o << %(    #{printable_requirement.call(conflict.locked_requirement)}\n)
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb b/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb
index d9eee767ceb..73f8fbf2ac9 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb
@@ -2,5 +2,5 @@
 
 module Bundler::Molinillo
   # The version of Bundler::Molinillo.
-  VERSION = '0.6.5'.freeze
+  VERSION = '0.6.6'.freeze
 end