handle nil in config options (broken in 1.2.2)

[flavorjones]

Context

In rake-compiler 1.2.1 and earlier, if an extension did something like this, rake-compiler handled it gracefully:

  Rake::ExtensionTask.new("gem", spec) do |ext|
    ext.config_options << ENV["EXTOPTS"] # this is probably going to be nil
  end

It is OK to do this because in 1.2.1 and earlier, the command array was executed as:

  sh cmd.join(' ')

However, this was changed in 1.2.2 to

  sh *cmd

which of course is preferable. However, this breaks extensions like nokogiri that do something silly like above.

Details

I've fixed Nokogiri (see sparklemotion/nokogiri#2894) but I do think that there may be other gems impacted by this change.

This PR does a few things:

• extract a method make_makefile_cmd so that we can unit test it
• backfill basic test coverage
• backfill test for The extra option including a space is splitted to execute the command. #215
• write a test for this nil case, and fix it by returning the result of cmd.compact

This is a big PR because of the extraction and test coverage. Please let me know if you would prefer this to be done a different way.

[kou]

Thanks!