Link C/C++ stlib statically for binary gems

Also:
1. Compile via `mkmf` instead of libsass's own Makefile.
   This is necessary to make cross-compilation work (rake-compiler hooks
   into mkmf).
2. Do not use per-ruby versions of `libsass.so`. It is unnecessary,
   because `libsass.so` is Ruby-agnostic (the FFI gem is used instead to
   use it from any Ruby version).
3. Add VERSION file to the non-precompiled gem.
4. Clean before every build.

.gitignore

@@ -15,3 +15,4 @@
 *.gem
 mkmf.log
 vendor/bundle
+/ext/Makefile

Rakefile

@@ -10,19 +10,36 @@ Rake::ExtensionTask.new('libsass', gem_spec) do |ext|
   ext.lib_dir = 'lib/sassc'
   ext.cross_compile = true
   ext.cross_platform = %w[x86-mingw32 x64-mingw32 x86-linux x86_64-linux]
+
+  # Link C++ stdlib statically when building binary gems.
+  ext.cross_config_options << '--enable-static-stdlib'
+
   ext.cross_compiling do |spec|
     spec.files.reject! { |path| File.fnmatch?('ext/*', path) }
+
+
+    # Reset the required ruby version requirements.
+    # This is set by rake-compiler, but the shared library here is Ruby-agnostic.
+    spec.required_ruby_version = gem_spec.required_ruby_version
   end
 end
 
 desc 'Compile all native gems via rake-compiler-dock (Docker)'
 task 'gem:native' do
   require 'rake_compiler_dock'
-  RakeCompilerDock.sh "bundle && gem i rake --no-document && "\
-                      "rake cross native gem MAKE='nice make -j`nproc`' "\
-                      "RUBY_CC_VERSION=2.6.0:2.5.0:2.4.0:2.3.0"
+
+  # The RUBY_CC_VERSION here doesn't matter for the final package.
+  # Only one version should be specified, as the shared library is Ruby-agnostic.
+  #
+  # g++-multilib is installed for 64->32-bit cross-compilation.
+  RakeCompilerDock.sh "sudo apt-get install -y g++-multilib && bundle && gem i rake --no-document && "\
+                      "rake clean && rake cross native gem MAKE='nice make -j`nproc`' "\
+                      "RUBY_CC_VERSION=2.6.0 CLEAN=1"
 end
 
+CLEAN.include 'tmp', 'pkg', 'lib/sassc/libsass.so', 'ext/libsass/VERSION',
+              'ext/*.{o,so,bundle}', 'ext/Makefile'
+
 desc "Run all tests"
 task test: 'compile:libsass' do
   $LOAD_PATH.unshift('lib', 'test')

ext/depend

@@ -0,0 +1,4 @@
+# Replaces default mkmf dependencies. Default mkmf dependencies include all libruby headers.
+# We don't need libruby and some of these headers are missing on JRuby (breaking compilation there).
+$(OBJS): $(HDRS)
+

ext/extconf.rb

@@ -10,30 +10,63 @@
     fail 'Could not fetch libsass'
 end
 
-# Only needed because rake-compiler expects `.bundle` on macOS:
-# https://github.com/rake-compiler/rake-compiler/blob/9f15620e7db145d11ae2fc4ba032367903f625e3/features/support/platform_extension_helpers.rb#L5
-dl_ext = (RUBY_PLATFORM =~ /darwin/ ? 'bundle' : 'so')
+require 'mkmf'
 
-File.write 'Makefile', <<-MAKEFILE
-ifndef DESTDIR
-	LIBSASS_OUT = #{gem_root}/lib/sassc/libsass.#{dl_ext}
-else
-	LIBSASS_OUT = $(DESTDIR)$(PREFIX)/libsass.#{dl_ext}
-endif
+$CXXFLAGS << ' -std=c++11'
 
-SUB_DIR := #{libsass_dir}
+# Link stdlib statically when building binary gems.
+if enable_config('static-stdlib')
+  $LDFLAGS << ' -static-libgcc -static-libstdc++'
+end
+
+# Disable noisy compilation warnings.
+$warnflags = ''
+$CFLAGS.gsub!(/[\s+](-ansi|-std=[^\s]+)/, '')
+
+dir_config 'libsass'
+
+libsass_version = Dir.chdir(libsass_dir) do
+  if File.exist?('VERSION')
+    File.read('VERSION').chomp
+  elsif File.exist?('.git')
+    ver = %x[git describe --abbrev=4 --dirty --always --tags].chomp
+    File.write('VERSION', ver)
+    ver
+  end
+end
+
+if libsass_version
+  libsass_version_def = %Q{ -DLIBSASS_VERSION='"#{libsass_version}"'}
+  $CFLAGS << libsass_version_def
+  $CXXFLAGS << libsass_version_def
+end
+
+$INCFLAGS << " -I$(srcdir)/libsass/include"
+$VPATH << "$(srcdir)/libsass/src"
+Dir.chdir(__dir__) do
+  $VPATH += Dir['libsass/src/*/'].map { |p| "$(srcdir)/#{p}" }
+  $srcs = Dir['libsass/src/**/*.{c,cpp}']
+end
 
-libsass.#{dl_ext}:#{' clean' if ENV['CLEAN']}
-	$(MAKE) -C '$(SUB_DIR)' lib/libsass.so
-	cp '$(SUB_DIR)/lib/libsass.so' libsass.#{dl_ext}
-	strip -x libsass.#{dl_ext}
+MakeMakefile::LINK_SO << "\nstrip -x $@"
 
-install: libsass.#{dl_ext}
-	cp libsass.#{dl_ext} '$(LIBSASS_OUT)'
+# Don't link libruby.
+$LIBRUBYARG = nil
 
-clean:
-	$(MAKE) -C '$(SUB_DIR)' clean
-	rm -f '$(LIBSASS_OUT)' libsass.#{dl_ext}
+# Disable .def file generation for mingw, as it defines an
+# `Init_libsass` export which we don't have.
+MakeMakefile.send(:remove_const, :EXPORT_PREFIX)
+MakeMakefile::EXPORT_PREFIX = nil
+
+if RUBY_PLATFORM == 'java'
+  # COUTFLAG is not set correctly on jruby
+  # See https://github.com/jruby/jruby/issues/5749
+  MakeMakefile.send(:remove_const, :COUTFLAG)
+  MakeMakefile::COUTFLAG = '-o $(empty)'
+
+  # CCDLFLAGS is not set correctly on jruby
+  # See https://github.com/jruby/jruby/issues/5751
+  $CXXFLAGS << ' -fPIC'
+end
 
-.PHONY: clean install
-MAKEFILE
+create_makefile 'sassc/libsass'

lib/sassc/native.rb

@@ -10,12 +10,7 @@ module Native
     gem_root = spec.gem_dir
 
     dl_ext = (RUBY_PLATFORM =~ /darwin/ ? 'bundle' : 'so')
-    ruby_version_so_path = "#{gem_root}/lib/sassc/#{RUBY_VERSION[/\d+.\d+/]}/libsass.#{dl_ext}"
-    if File.exist?(ruby_version_so_path)
-      ffi_lib ruby_version_so_path
-    else
-      ffi_lib "#{gem_root}/lib/sassc/libsass.#{dl_ext}"
-    end
+    ffi_lib "#{gem_root}/lib/sassc/libsass.#{dl_ext}"
 
     require_relative "native/sass_value"
 

sassc.gemspec

@@ -40,18 +40,30 @@ Gem::Specification.new do |spec|
   gem_dir = File.expand_path(File.dirname(__FILE__)) + "/"
 
   libsass_dir = File.join(gem_dir, 'ext', 'libsass')
-  if !File.directory?(libsass_dir)
-    $stderr.puts "Error: ext/libsass not checked out. Please run:\n\n"\
-                 "  git submodule update --init"
-    exit 1
+  if !File.directory?(libsass_dir) ||
+      # '.', '..', and possibly '.git' from a failed checkout:
+      Dir.entries(libsass_dir).size <= 3
+    Dir.chdir(__dir__) { system('git submodule update --init') } or
+        fail 'Could not fetch libsass'
+  end
+
+  # Write a VERSION file for non-binary gems (for `SassC::Native.version`).
+  if !File.exist?(File.join(libsass_dir, 'VERSION'))
+    libsass_version = Dir.chdir(libsass_dir) do
+      %x[git describe --abbrev=4 --dirty --always --tags].chomp
+    end
+    File.write(File.join(libsass_dir, 'VERSION'), libsass_version)
   end
 
   Dir.chdir(libsass_dir) do
     submodule_relative_path = File.join('ext', 'libsass')
+    skip_re = %r{(^("?test|docs|script)/)|\.md$|\.yml$}
+    only_re = %r{\.[ch](pp)?$}
     `git ls-files`.split($\).each do |filename|
-      next if filename =~ %r{(^("?test|docs|script)/)|\.md$|\.yml$}
+      next if filename =~ skip_re || filename !~ only_re
       spec.files << File.join(submodule_relative_path, filename)
     end
+    spec.files << File.join(submodule_relative_path, 'VERSION')
   end
 
 end