From: Daniel Berger <djberg96@...>
Date: 2007-04-02T11:45:04+09:00
Subject: Re: Hacking mkmf.rb

On Apr 1, 4:34 pm, Timothy Hunter <TimHun...@nc.rr.com> wrote:
> I'm in the process of replacing RMagick's configure/make/make install
> process with a pure-Ruby solution using just setup.rb or RubyGems and
> extconf.rb. I've been able to successfully replace configure.ac with
> extconf.rb except for two things. First, mkmf.rb does not have a method
> that tests for the presence of a specific value in an enum. Second,
> mkmf.rb wants to put all its feature symbols (-DHAVE_SOMETHING) on the
> gcc command line but RMagick may have upwards of 100 such symbols and
> I'm afraid that that many will exceed some system's limit on the maximum
> length of a command's arguments. I'd rather put these symbols in a
> config.h file.

I requested have_enum_member two years ago:

http://rubyforge.org/tracker/index.php?func=detail&aid=1486&group_id=426&atid=1700.

That eventually turned into have_const:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/4430.

Note that "checking_for type" should be "checking_for const". I think
it just got lost in the shuffle. I'll bring it up again on ruby-core.

> So i've added two methods to my extconf.rb. (I've added them below). Any
> comments on the risks I'm introducing to my extconf.rb and how I might
> mitigate them? I've tested my extconf.rb with Ruby 1.8.2, 1.8.3, 1.8.4,
> 1.8.5, and 1.8.6. What about going forward? I would like to minimize the
> chances of my having to fix my extconf.rb when Ruby 1.8.7 comes out.
>
> (I learned that my extconf.rb is not compatible with Ruby 1.8.0 or
> 1.8.1, notably because have_library has a different signature in those
> releases. That's not a problem for me.)
>
> # Test for a specific value in an enum type
> def have_enum_value(enum, value, headers=nil, &b)
>   checking_for "#{enum}.#{value}" do
>     if try_compile(<<"SRC", &b)
> #{COMMON_HEADERS}
> #{cpp_include(headers)}
> /*top*/
> int main(){ #{enum} x = #{value}; x = x; return 0; }
> SRC
>       $defs.push(format("-DHAVE_%s", value.upcase))
>       true
>     else
>       false
>     end
>   end
> end
>
> # Create a config.h file from the $defs array.
> def create_config_file(file)
>   message "creating #{file}\n"
>   File.open(file, "w") do |f|
>     while (sym = $defs.shift)
>       define = sym.sub(/\A-D/, '#define ')
>       if define['=']
>         define['='] = ' '   # symbols with values
>       else
>         define << ' 1'      # symbols without values
>       end
>       f.puts define
>     end
>   end
> end

create_config_file looks reasonable to me.

Regards,

Dan