add Util module and Util.make_relative_path()

lib/rscons.rb

@@ -8,6 +8,7 @@ require_relative "rscons/environment"
 require_relative "rscons/job_set"
 require_relative "rscons/script"
 require_relative "rscons/threaded_command"
+require_relative "rscons/util"
 require_relative "rscons/varset"
 require_relative "rscons/version"
 

lib/rscons/environment.rb

@@ -265,15 +265,7 @@ module Rscons
         end
       end
       unless found_match
-        if Rscons.absolute_path?(build_fname)
-          if build_fname =~ %r{^(\w):(.*)$}
-            build_fname = "#{@build_root}#{extra_path}/_#{$1}#{$2}"
-          else
-            build_fname = "#{@build_root}#{extra_path}/_#{build_fname}"
-          end
-        elsif !build_fname.start_with?("#{@build_root}/")
-          build_fname = "#{@build_root}#{extra_path}/#{build_fname}"
-        end
+        build_fname = "#{@build_root}#{extra_path}/#{Util.make_relative_path(build_fname)}"
       end
       build_fname.gsub('\\', '/')
     end

lib/rscons/util.rb

@@ -0,0 +1,26 @@
+module Rscons
+  module Util
+    class << self
+
+      # Make a relative path corresponding to a possibly absolute one.
+      #
+      # @param path [String]
+      #   Input path that is possibly absolute.
+      #
+      # @return [String]
+      #   Relative path.
+      def make_relative_path(path)
+        if Rscons.absolute_path?(path)
+          if path =~ %r{^(\w):(.*)$}
+            "_#{$1}#{$2}"
+          else
+            "_#{path}"
+          end
+        else
+          path
+        end
+      end
+
+    end
+  end
+end