Auto merge of #4972 - bundler:seg-molinillo-0.5.1, r=indirect

Update vendored Molinillo to 0.5.1

See https://github.com/CocoaPods/Molinillo/releases/0.5.1

I'd love this to be a 1.13.1

(cherry picked from commit ffbb417d22592fe3b0a6e5f6008fc7eee491b027)

2 files changed, 9 insertions, 3 deletions

diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb b/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb
index c44da1ce3e..f840e7ea30 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/gem_metadata.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 module Bundler::Molinillo
   # The version of Bundler::Molinillo.
-  VERSION = '0.5.0'.freeze
+  VERSION = '0.5.1'.freeze
 end
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb b/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb
index 5707e890b7..1890d95a56 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb
@@ -184,6 +184,8 @@ module Bundler::Molinillo
           raise VersionConflict.new(c) unless state
           activated.rewind_to(sliced_states.first || :initial_state) if sliced_states
           state.conflicts = c
+          index = states.size - 1
+          @parent_of.reject! { |_, i| i >= index }
         end
       end
 
@@ -209,7 +211,10 @@ module Bundler::Molinillo
       # @return [Object] the requirement that led to `requirement` being added
       #   to the list of requirements.
       def parent_of(requirement)
-        @parent_of[requirement]
+        return unless requirement
+        return unless index = @parent_of[requirement]
+        return unless parent_state = @states[index]
+        parent_state.requirement
       end
 
       # @return [Object] the requirement that led to a version of a possibility
@@ -418,7 +423,8 @@ module Bundler::Molinillo
         debug(depth) { "Requiring nested dependencies (#{nested_dependencies.join(', ')})" }
         nested_dependencies.each do |d|
           activated.add_child_vertex(name_for(d), nil, [name_for(activated_spec)], d)
-          @parent_of[d] = requirement
+          parent_index = states.size - 1
+          @parent_of[d] ||= parent_index
         end
 
         push_state_for_requirements(requirements + nested_dependencies, !nested_dependencies.empty?)