cross.rake

require 'rake/tasklib'
require 'rake/clean'

##
# Creates a cross-compiled library that mruby-cli can use to link with
# each cross-built command.
#
#   CrossLibrary.new "curl" do |cross|
#     cross.release_name = "curl-7.28.0"
#     cross.url = "https://curl.example/download/#{cross.release}.tar.gz"
#   end
#
# You must also add the cross-compiled include and library paths to your
# build_config.rb:
#
#   MRuby::Build.new do |conf|
#     # …
#
#     conf.cc.include_paths     << "cross/#{name}/include"
#     conf.linker.library_paths << "cross/#{name}/lib"
#
#     # …

class CrossLibrary < Rake::TaskLib

  ##
  # Extra flags to send to `configure` when building this library.
  #
  # These must be specified as an Array:
  #
  #   cross.configure_flags << '--without-ssl' << '--without-zlib'

  attr_reader :configure_flags

  ##
  # The name of the mrbgem that depends upon this library.
  #
  # This allows the Rakefile to cross-compile the library when it is needed.

  attr_accessor :mrbgem_name

  ##
  # The name of this release package.
  #
  # This must uniquely identify this release amongst other libraries of the
  # same name.  Usually this will include the library name and a release
  # version.
  #
  #   cross.release_name = "curl-7.28.0"

  attr_accessor :release_name

  ##
  # The URL where this release can be downloaded.
  #
  # The value should include #release_name in the URL.
  #
  #   cross.release_name = "curl-7.28.0"
  #   cross.url = "https://curl.example/download/#{cross.release}.tar.gz"

  attr_accessor :url

  def initialize(library, mrbgem_name: "mruby-#{library}", &block)
    @library     = library
    @mrbgem_name = "mruby-#{library}"

    @configure_flags = []

    # Used to re-run configure when the defining rake file changes
    @task_source = block.source_location.first

    default_flags = MRuby.targets['host'].cc.flags

    targets = MRuby.targets.map do |name, build|
      cflags = build.cc.flags - default_flags

      env = {}
      env['CC']     = build.cc.command
      env['CFLAGS'] = cflags.join ' ' unless cflags.empty?

      [name, env]
    end

    @targets = Hash[targets]

    yield self

    raise ArgumentError, "you must set release_name" unless @release_name
    raise ArgumentError, "you must set url"          unless @url

    @tarball    = File.basename @url
    @download   = "tmp/#{@tarball}"
    @source_dir = "tmp/#{@release_name}"

    define
  end

  ##
  # Defines compilation tasks for cross-compiling on +host+.  Use +env+ to set
  # environment details for the cross-compiled environment (CC, etc).
  #
  # The targets and environment are automatically determined from your
  # build_config.rb so you should not need to edit these values.
  #
  #   compile_tasks 'x86_64-pc-linux-gnu'
  #   compile_tasks 'i686-pc-linux-gnu',     CFLAGS: '-m32'
  #   compile_tasks 'x86_64-apple-darwin14', CC: 'x86_64-apple-darwin14-clang'
  #   compile_tasks 'i386-apple-darwin14',   CC: 'i386-apple-darwin14-clang'

  def compile_tasks(host, env)
    task_name = "#{@library}:#{host}"

    # task environment

    build_dir   = File.join 'tmp', @library, 'build', host
    configure   = File.join @source_dir, 'configure'
    configure   = File.expand_path configure
    install_dir = File.expand_path "cross/#{host}"

    makefile  = File.join build_dir, 'Makefile'
    library_a = File.join install_dir, 'lib', "lib#{@library}.a"

    mruby_build = MRuby.targets[host]
    mrbgem      = mruby_build.gems.find { |gem| gem.name == @mrbgem_name }
    mrbgem_srcs = Rake::FileList["#{mrbgem.dir}/src/*.{c,cpp,cxx,cc,m,asm,s,S}"]

    # define tasks

    CLOBBER << install_dir

    directory build_dir
    CLEAN << build_dir

    file makefile => [build_dir, @source_dir, @task_source, __FILE__] do
      configure_command = [
        configure,
        '--prefix', install_dir,
      ]

      if host != 'host' then
        configure_command << '--host' << host
      end

      configure_command.concat configure_flags

      cd build_dir do
        with_env env do
          sh(*configure_command)
        end
      end
    end

    file library_a => makefile do
      cd build_dir do
        sh 'make'
        sh 'make', 'install'
      end
    end

    mrbgem_srcs.each do |src|
      file src => library_a
    end

    desc "Build #{@library} for #{host}"
    task task_name => library_a

    task "#{@library}:compile" => task_name

    task_name
  end

  ##
  # Defines all necessary tasks for cross-compiling a library.

  def define
    directory 'tmp'
    CLEAN << 'tmp'

    file @download => 'tmp' do
      sh 'curl', '-s', '-L',
         '--fail', '--retry', '3', '--retry-delay', '1',
         '-o', @download,
         @url
    end
    CLEAN << @download

    directory @source_dir => @download do
      sh 'tar', 'xzf', @download, '-C', 'tmp'
    end
    CLEAN << @source_dir

    desc 'Cross-compile curl for all platforms'
    task "#{@library}:compile"

    @targets.each do |target, env|
      compile_tasks target, env
    end

    task compile: "#{@library}:compile"
  end

  def with_env(env)
    orig_env = {}

    env.each do |key, value|
      key = key.to_s
      orig_env[key] = ENV[key] if ENV.include? key
      ENV[key] = value
    end

    begin
      yield
    ensure
      env.each_key do |key|
        ENV.delete key.to_s
      end

      orig_env.each do |key, value|
        ENV[key] = value
      end
    end
  end
end