merge revision(s) 53707,53708,53709,53712,53777,53781: [Backport #12326]

* lib/rubygems.rb, lib/rubygems/*, test/rubygems/*: Update rubygems-2.5.2.
	  It supports to enable frozen string literal and add `--norc` option for
	  disable to `.gemrc` configuration.
	  See 2.5.2 release notes for other fixes and enhancements.
	  a8aa3bac72/History.txt (L3)

	* lib/rubygems/specification.rb: `coding` is affect only first line except
	  shebang.

	* lib/rubygems/package.rb, lib/rubygems/package/*: ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@56003 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/resolver/source_set.rb

@@ -0,0 +1,48 @@
+##
+# The SourceSet chooses the best available method to query a remote index.
+#
+# Kind off like BestSet but filters the sources for gems
+
+class Gem::Resolver::SourceSet < Gem::Resolver::Set
+
+  ##
+  # Creates a SourceSet for the given +sources+ or Gem::sources if none are
+  # specified.  +sources+ must be a Gem::SourceList.
+
+  def initialize
+    super()
+
+    @links = {}
+    @sets  = {}
+  end
+
+  def find_all req # :nodoc:
+    if set = get_set(req.dependency.name)
+      set.find_all req
+    else
+      []
+    end
+  end
+
+  # potentially no-op
+  def prefetch reqs # :nodoc:
+    reqs.each do |req|
+      if set = get_set(req.dependency.name)
+        set.prefetch reqs
+      end
+    end
+  end
+
+  def add_source_gem name, source
+    @links[name] = source
+  end
+
+private
+
+  def get_set(name)
+    link = @links[name]
+    @sets[link] ||= Gem::Source.new(link).dependency_resolver_set if link
+  end
+
+end
+