ruby: build native Darwin gems using rake-compiler-dock

Please note that this work simplifies the Darwin rubygem build,
and addresses inconsistencies in packaging that result in issues
like grpc#25060, but introduces some notable changes:

- ships "x86_64-darwin" and "arm64-darwin" platform gems
- stops shipping "universal-darwin" platform gem
- drop support for i386 darwin

It's unclear to me whether grpc should continue to support i386
Darwin, and so I'm open to learning more about this.

Related to:

- grpc#25429
- grpc#25755
- grpc#25756

Rakefile

@@ -23,20 +23,15 @@ end
 
 # Add the extension compiler task
 Rake::ExtensionTask.new('grpc_c', spec) do |ext|
-  unless RUBY_PLATFORM =~ /darwin/
-    # TODO: also set "no_native to true" for mac if possible. As is,
-    # "no_native" can only be set if the RUBY_PLATFORM doing
-    # cross-compilation is contained in the "ext.cross_platform" array.
-    ext.no_native = true
-  end
+  ext.no_native = true
   ext.source_pattern = '**/*.{c,h}'
   ext.ext_dir = File.join('src', 'ruby', 'ext', 'grpc')
   ext.lib_dir = File.join('src', 'ruby', 'lib', 'grpc')
   ext.cross_compile = true
   ext.cross_platform = [
     'x86-mingw32', 'x64-mingw32',
     'x86_64-linux', 'x86-linux',
-    'universal-darwin'
+    'x86_64-darwin', 'arm64-darwin',
   ]
   ext.cross_compiling do |spec|
     spec.files = %w( etc/roots.pem grpc_c.32.ruby grpc_c.64.ruby )
@@ -123,40 +118,32 @@ task 'gem:native' do
   grpc_config = ENV['GRPC_CONFIG'] || 'opt'
   ruby_cc_versions = ['3.0.0', '2.7.0', '2.6.0', '2.5.0', '2.4.0'].join(':')
 
-  if RUBY_PLATFORM =~ /darwin/
-    FileUtils.touch 'grpc_c.32.ruby'
-    FileUtils.touch 'grpc_c.64.ruby'
-    unless '2.5' == /(\d+\.\d+)/.match(RUBY_VERSION).to_s
-      fail "rake gem:native (the rake task to build the binary packages) is being " \
-        "invoked on macos with ruby #{RUBY_VERSION}. The ruby macos artifact " \
-        "build should be running on ruby 2.5."
-    end
-    system "rake cross native gem RUBY_CC_VERSION=#{ruby_cc_versions} V=#{verbose} GRPC_CONFIG=#{grpc_config}"
-  else
-    Rake::Task['dlls'].execute
-    ['x86-mingw32', 'x64-mingw32'].each do |plat|
-      run_rake_compiler plat, <<-EOT
-        gem update --system --no-document && \
-        bundle && \
-        rake native:#{plat} pkg/#{spec.full_name}-#{plat}.gem pkg/#{spec.full_name}.gem \
-          RUBY_CC_VERSION=#{ruby_cc_versions} \
-          V=#{verbose} \
-          GRPC_CONFIG=#{grpc_config}
-      EOT
-    end
-    # Truncate grpc_c.*.ruby files because they're for Windows only.
-    File.truncate('grpc_c.32.ruby', 0)
-    File.truncate('grpc_c.64.ruby', 0)
-    ['x86_64-linux', 'x86-linux'].each do |plat|
-      run_rake_compiler plat, <<-EOT
-        gem update --system --no-document && \
-        bundle && \
-        rake native:#{plat} pkg/#{spec.full_name}-#{plat}.gem pkg/#{spec.full_name}.gem \
-          RUBY_CC_VERSION=#{ruby_cc_versions} \
-          V=#{verbose} \
-          GRPC_CONFIG=#{grpc_config}
-      EOT
-    end
+  FileUtils.touch 'grpc_c.32.ruby'
+  FileUtils.touch 'grpc_c.64.ruby'
+  Rake::Task['dlls'].execute
+  ['x86-mingw32', 'x64-mingw32'].each do |plat|
+    run_rake_compiler plat, <<-EOT
+      gem update --system --no-document && \
+      bundle && \
+      rake native:#{plat} pkg/#{spec.full_name}-#{plat}.gem pkg/#{spec.full_name}.gem \
+        RUBY_CC_VERSION=#{ruby_cc_versions} \
+        V=#{verbose} \
+        GRPC_CONFIG=#{grpc_config}
+    EOT
+  end
+
+  # Truncate grpc_c.*.ruby files because they're for Windows only.
+  File.truncate('grpc_c.32.ruby', 0)
+  File.truncate('grpc_c.64.ruby', 0)
+  ['x86_64-linux', 'x86-linux', 'x86_64-darwin', 'arm64-darwin'].each do |plat|
+    run_rake_compiler plat, <<-EOT
+      gem update --system --no-document && \
+      bundle && \
+      rake native:#{plat} pkg/#{spec.full_name}-#{plat}.gem pkg/#{spec.full_name}.gem \
+        RUBY_CC_VERSION=#{ruby_cc_versions} \
+        V=#{verbose} \
+        GRPC_CONFIG=#{grpc_config}
+    EOT
   end
 end
 

src/ruby/ext/grpc/extconf.rb

@@ -37,24 +37,11 @@
     ENV['LD'] = ENV['CC']
 end
 
-if RUBY_PLATFORM =~ /darwin/
-  ENV['AR'] = 'libtool'
-  ENV['ARFLAGS'] = '-o'
- end
-
 ENV['EMBED_OPENSSL'] = 'true'
 ENV['EMBED_ZLIB'] = 'true'
 ENV['EMBED_CARES'] = 'true'
 
 ENV['ARCH_FLAGS'] = RbConfig::CONFIG['ARCH_FLAG']
-if RUBY_PLATFORM =~ /darwin/
-  if RUBY_PLATFORM =~ /arm64/
-    ENV['ARCH_FLAGS'] = '-arch arm64'
-  else
-    ENV['ARCH_FLAGS'] = '-arch i386 -arch x86_64'
-  end
-end
-
 ENV['CPPFLAGS'] = '-DGPR_BACKWARDS_COMPATIBILITY_MODE'
 
 output_dir = File.expand_path(RbConfig::CONFIG['topdir'])
@@ -100,7 +87,7 @@
 create_makefile(output)
 
 strip_tool = RbConfig::CONFIG['STRIP']
-strip_tool = 'strip -x' if RUBY_PLATFORM =~ /darwin/
+strip_tool += ' -x' if RUBY_PLATFORM =~ /darwin/
 
 if grpc_config == 'opt'
   File.open('Makefile.new', 'w') do |o|

third_party/rake-compiler-dock/rake_arm64-darwin/Dockerfile

@@ -0,0 +1 @@
+FROM larskanis/rake-compiler-dock-mri-arm64-darwin:1.1.0

third_party/rake-compiler-dock/rake_x86_64-darwin/Dockerfile

@@ -0,0 +1 @@
+FROM larskanis/rake-compiler-dock-mri-x86_64-darwin:1.1.0