Add support for building precompiled gems

Running `rake gem:native` will attempt to cross-compile gems
for the following platforms:

-  aarch64-linux
-  arm64-darwin
-  x86_64-darwin
-  x86_64-linux

`rake gem:<platform>` also will compile one specific platform. For
 example: `rake gem:arm64-darwin`.

Rakefile

@@ -1,5 +1,8 @@
+# frozen_string_literal: true
+
 require 'rake/extensiontask'
 require 'rspec/core/rake_task'
+require 'rake_compiler_dock'
 
 CLEAN.include FileList['**/*{.o,.so,.dylib,.bundle}'],
               FileList['**/extconf.h'],
@@ -14,17 +17,65 @@ CLOBBER.add("ports/*").exclude(%r{ports/archives$})
 
 RE2_GEM_SPEC = Gem::Specification.load('re2.gemspec')
 
-Rake::ExtensionTask.new('re2')
-
 Gem::PackageTask.new(RE2_GEM_SPEC) do |p|
   p.need_zip = false
   p.need_tar = false
 end
 
+CROSS_RUBY_VERSIONS = %w[3.2.0 3.1.0 3.0.0 2.7.0].join(':')
+CROSS_RUBY_PLATFORMS = %w[
+  aarch64-linux
+  arm64-darwin
+  x86_64-darwin
+  x86_64-linux
+].freeze
+
+ENV['RUBY_CC_VERSION'] = CROSS_RUBY_VERSIONS
+
+Rake::ExtensionTask.new('re2', RE2_GEM_SPEC) do |e|
+  e.cross_compile = true
+  e.cross_config_options << '--enable-cross-build'
+  e.config_options << '--disable-system-libraries'
+  e.cross_platform = CROSS_RUBY_PLATFORMS
+  e.cross_compiling do |spec|
+    spec.files.reject! { |path| File.fnmatch?('ports/*', path) }
+    spec.dependencies.reject! { |dep| dep.name == 'mini_portile2' }
+  end
+end
+
 RSpec::Core::RakeTask.new(:spec)
 
-def gem_build_path
-  File.join 'pkg', RE2_GEM_SPEC.full_name
+namespace 'gem' do
+  def gem_builder(platform)
+    # use Task#invoke because the pkg/*gem task is defined at runtime
+    Rake::Task["native:#{platform}"].invoke
+    Rake::Task["pkg/#{RE2_GEM_SPEC.full_name}-#{Gem::Platform.new(platform)}.gem"].invoke
+  end
+
+  CROSS_RUBY_PLATFORMS.each do |platform|
+    # The Linux x86 image (ghcr.io/rake-compiler/rake-compiler-dock-image:1.3.0-mri-x86_64-linux)
+    # is based on CentOS 7 and has two versions of cmake installed:
+    # a 2.8 version in /usr/bin and a 3.25 in /usr/local/bin. The latter is needed by abseil.
+    cmake = platform == 'x86_64-linux' ? '/usr/local/bin/cmake' : 'cmake'
+    desc "build native gem for #{platform} platform"
+    task platform do
+      RakeCompilerDock.sh <<~SCRIPT, platform: platform, verbose: true
+        gem install bundler --no-document &&
+        bundle &&
+        CMAKE=#{cmake} bundle exec rake gem:#{platform}:builder MAKE='nice make -j`nproc`'
+      SCRIPT
+    end
+
+    namespace platform do
+      desc "build native gem for #{platform} platform (guest container)"
+      task 'builder' do
+        gem_builder(platform)
+      end
+    end
+  end
+
+  desc 'build all native gems'
+  task 'native' => CROSS_RUBY_PLATFORMS
 end
 
 def add_file_to_gem(relative_source_path)
@@ -38,6 +89,10 @@ def add_file_to_gem(relative_source_path)
   RE2_GEM_SPEC.files << relative_source_path
 end
 
+def gem_build_path
+  File.join 'pkg', RE2_GEM_SPEC.full_name
+end
+
 def add_vendored_libraries
   dependencies = YAML.load_file(File.join(File.dirname(__FILE__), 'dependencies.yml'))
   abseil_archive = File.join('ports', 'archives', "#{dependencies['abseil']['version']}.tar.gz")

lib/re2.rb

@@ -3,5 +3,11 @@
 #
 # Copyright (c) 2010-2014, Paul Mucur (http://mudge.name)
 # Released under the BSD Licence, please see LICENSE.txt
-require "re2.so"
+begin
+  ::RUBY_VERSION =~ /(\d+\.\d+)/
+  require_relative "#{Regexp.last_match(1)}/re2.so"
+rescue LoadError
+  require 're2.so'
+end
+
 require "re2/scanner"

re2.gemspec

@@ -27,7 +27,8 @@ Gem::Specification.new do |s|
     "spec/re2/set_spec.rb",
     "spec/re2/scanner_spec.rb"
   ]
-  s.add_development_dependency("rake-compiler", "~> 0.9")
+  s.add_development_dependency "rake-compiler", "~> 1.2.1"
+  s.add_development_dependency "rake-compiler-dock", "~> 1.3.0"
   s.add_development_dependency("rspec", "~> 3.2")
   s.add_runtime_dependency("mini_portile2", "~> 2.8.2") # keep version in sync with extconf.rb
 end