Cross Compile looks for Ruby headers in the wrong directory

[ParadoxV5]

mkmf.rb can't find header files for ruby at <absolute/path/to/config/`tmp_dir`>/<`cross_platform`>/<`name`>/include/ruby.h

You might have to install separate package for the ruby development
environment, ruby-dev or ruby-devel for example.

Edit: It could be that I used my existing RubyIntaller2 prebuild instead of letting rake-compiler rebuild the entire Ruby from source.

Analysis

Cross Compile currently works by replacing RbConfig::CONFIG with a fake.rb script in the $LOAD_PATH. This fake.rb copy-pastes the the target platform’s rbconfig.rb verbatim.

rake-compiler/lib/rake/extensiontask.rb

Lines 415 to 435 in 9baeced

	# copy the rbconfig from the cross-ruby location and
	# genearte fake.rb for different ruby versions
	file "#{tmp_path}/fake.rb" => [rbconfig_file] do |t|
	File.open(t.name, 'w') do |f|
	# Keep the original RbConfig::CONFIG["ENABLE_SHARED"] to use
	# the same RubyGems extension directory. See also
	# Gem::BasicSpecificaion#extenions_dir and
	# Gem.extension_api_version.
	#
	# if RbConfig::CONFIG["ENABLE_SHARED"] == "no"
	# "extensions/x86_64-linux/2.5.0-static"
	# else
	# "extensions/x86_64-linux/2.5.0"
	# end
	f.puts("require 'rbconfig'")
	f.puts("original_enable_shared = RbConfig::CONFIG['ENABLE_SHARED']")
	f.puts(fake_rb(for_platform, ruby_ver))
	f.puts(File.read(t.prerequisites.first))
	f.puts("RbConfig::CONFIG['ENABLE_SHARED'] = original_enable_shared")
	end
	end

However, rbconfig.rb begins with this for RubyIntaller2:

# Ruby installed directory.
TOPDIR = File.dirname(__FILE__).chomp!("/lib/ruby/3.3.0/x64-mingw-ucrt")

Same for Ubuntu, for that matter:

# Ruby installed directory.
TOPDIR = File.dirname(__FILE__).chomp!("/lib/ruby/3.3.0/x86_64-linux")

With __FILE__ being /path/to/project/tmp/fake.rb rather than /path/to/target/ruby/rbconfig.rb, RbConfig::TOPDIR becomes nil and leads to a cascade of fallbacks.

[kou]

Do you want to cross compile on Windows?

[ParadoxV5]

I want(ed) to cross compile from WSL Ubuntu to Windows.

[kou]

Could you show all command lines you used for it? (How to reproduce this?)

[ParadoxV5]

1. Download and extract https://github.com/oneclick/rubyinstaller2/releases/download/RubyInstaller-3.3.0-1/rubyinstaller-3.3.0-1-x64.7z
2. ~/.rake-compiler/config.yml:

   ---
   rbconfig-x64-mingw-3.3.0: /path/to/ruby33/ruby/lib/ruby/3.3.0/x64-mingw-ucrt/rbconfig.rb

3. Skip rake-compile, go straight to rake cross compile

[kou]

Thanks.
The usage isn't supported.