Fixing Mac build for Ruby.

Rakefile

@@ -3,6 +3,7 @@ require 'rake/extensiontask'
 require 'rspec/core/rake_task'
 require 'rubocop/rake_task'
 require 'bundler/gem_tasks'
+require 'fileutils'
 
 load 'tools/distrib/docker_for_windows.rb'
 
@@ -26,11 +27,7 @@ Rake::ExtensionTask.new('grpc_c', spec) do |ext|
   ext.cross_platform = [
     'x86-mingw32', 'x64-mingw32',
     'x86_64-linux', 'x86-linux',
-    'x86_64-darwin-11',
-    'x86_64-darwin-12',
-    'x86_64-darwin-13',
-    'x86_64-darwin-14',
-    'x86_64-darwin-15'
+    'universal-darwin'
   ]
   ext.cross_compiling do |spec|
     spec.files = %w( etc/roots.pem grpc_c.32.ruby grpc_c.64.ruby )
@@ -103,7 +100,14 @@ desc 'Build the native gem file under rake_compiler_dock'
 task 'gem:native' do
   verbose = ENV['V'] || '0'
 
-  docker_for_windows "bundle && rake cross native gem RUBY_CC_VERSION=2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose}"
+  if RUBY_PLATFORM =~ /darwin/
+    FileUtils.touch 'grpc_c.32.ruby'
+    FileUtils.touch 'grpc_c.64.ruby'
+    system "rake cross native gem RUBY_CC_VERSION=2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose}"
+  else
+    Rake::Task['dlls'].execute
+    docker_for_windows "bundle && rake cross native gem RUBY_CC_VERSION=2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose}"
+  end
 end
 
 # Define dependencies between the suites.
@@ -113,8 +117,6 @@ task 'suite:bidi' => 'suite:wrapper'
 task 'suite:server' => 'suite:wrapper'
 task 'suite:pb' => 'suite:server'
 
-task 'gem:native' => 'dlls'
-
 desc 'Compiles the gRPC extension then runs all the tests'
 task all: ['suite:idiomatic', 'suite:bidi', 'suite:pb', 'suite:server']
 task default: :all

src/ruby/ext/grpc/extconf.rb

@@ -66,6 +66,8 @@ else
   grpc_lib_dir = File.join(grpc_root, 'libs', grpc_config)
 end
 
+ENV['MACOSX_DEPLOYMENT_TARGET'] = '10.7'
+
 unless File.exist?(File.join(grpc_lib_dir, 'libgrpc.a')) or windows
   ENV['AR'] = RbConfig::CONFIG['AR'] + ' rcs'
   ENV['CC'] = RbConfig::CONFIG['CC']

src/ruby/ext/grpc/rb_channel.c

@@ -229,7 +229,7 @@ static VALUE grpc_rb_channel_watch_connectivity_state(VALUE self,
   }
   grpc_channel_watch_connectivity_state(
       ch,
-      NUM2LONG(last_state),
+      (grpc_connectivity_state)NUM2LONG(last_state),
       grpc_rb_time_timeval(deadline, /* absolute time */ 0),
       cq,
       ROBJECT(tag));

src/ruby/ext/grpc/rb_server_credentials.c

@@ -177,7 +177,7 @@ static VALUE grpc_rb_server_credentials_init(VALUE self, VALUE pem_root_certs,
   VALUE key = Qnil;
   VALUE key_cert = Qnil;
   int auth_client = 0;
-  int num_key_certs = 0;
+  long num_key_certs = 0;
   int i;
 
   if (NIL_P(force_client_auth) ||