[rubygems/rubygems] Skip nil-value keys to make metadata reproducible

Nil-value keys in a mapping end with a space or not depending on
libyaml versions, and result metadata are different per platforms.
This commit makes to skip such keys to make metadata reproducible
accross platforms.

https://github.com/rubygems/rubygems/commit/74b4db8d30

lib/rubygems/psych_tree.rb

@@ -14,6 +14,10 @@ module Gem
         @emitter.scalar str, nil, nil, false, true, quote
       end
 
+      def visit_Hash(o)
+        super(o.dup.delete_if {|_, v| v.nil? })
+      end
+
       # Noop this out so there are no anchors
       def register(target, obj)
       end

lib/rubygems/specification.rb

@@ -1890,7 +1890,8 @@ class Gem::Specification < Gem::BasicSpecification
 
     attributes = @@attributes.map(&:to_s) - %w[name version platform]
     attributes.each do |name|
-      coder.add name, instance_variable_get("@#{name}")
+      value = instance_variable_get("@#{name}")
+      coder.add name, value unless value.nil?
     end
   end
 

test/rubygems/test_gem_specification.rb

@@ -2517,6 +2517,26 @@ end
     assert_match(/^platform: ruby$/, @a1.to_yaml)
   end
 
+  def test_to_yaml_no_autorequire
+    yaml_str = @a1.to_yaml
+
+    refute_match(/^autorequire:/, yaml_str)
+  end
+
+  def test_to_yaml_no_signing_key
+    @a1.signing_key = nil
+    yaml_str = @a1.to_yaml
+
+    refute_match(/^signing_key:/, yaml_str)
+  end
+
+  def test_to_yaml_no_post_install_message
+    @a1.post_install_message = nil
+    yaml_str = @a1.to_yaml
+
+    refute_match(/^post_install_message:/, yaml_str)
+  end
+
   def test_validate
     util_setup_validate