Few tweaks to the rakefile to permit native gems compilation with the proto files generation.

ruby/Gemfile.lock

 PATH
   remote: .
   specs:
-    google-protobuf (3.0.0.alpha.5.0)
+    google-protobuf (3.0.0.alpha.5.0.5)
 
 GEM
   remote: https://rubygems.org/

ruby/Rakefile

@@ -5,6 +5,38 @@ require "rake/testtask"
 
 spec = Gem::Specification.load("google-protobuf.gemspec")
 
+well_known_protos = %w[
+  google/protobuf/any.proto
+  google/protobuf/api.proto
+  google/protobuf/duration.proto
+  google/protobuf/empty.proto
+  google/protobuf/field_mask.proto
+  google/protobuf/source_context.proto
+  google/protobuf/struct.proto
+  google/protobuf/timestamp.proto
+  google/protobuf/type.proto
+  google/protobuf/wrappers.proto
+]
+
+# These are omitted for now because we don't support proto2.
+proto2_protos = %w[
+  google/protobuf/descriptor.proto
+  google/protobuf/compiler/plugin.proto
+]
+
+genproto_output = []
+
+unless ENV['IN_DOCKER'] == 'true'
+  well_known_protos.each do |proto_file|
+    input_file = "../src/" + proto_file
+    output_file = "lib/" + proto_file.sub(/\.proto$/, ".rb")
+    genproto_output << output_file
+    file output_file => input_file do |file_task|
+      sh "../src/protoc -I../src --ruby_out=lib #{input_file}"
+    end
+  end
+end
+
 if RUBY_PLATFORM == "java"
   if `which mvn` == ''
     raise ArgumentError, "maven needs to be installed"
@@ -30,38 +62,10 @@ else
 
   task 'gem:windows' do
     require 'rake_compiler_dock'
-    RakeCompilerDock.sh "bundle && rake cross native gem RUBY_CC_VERSION=2.3.0:2.2.2:2.1.6"
+    RakeCompilerDock.sh "bundle && IN_DOCKER=true rake cross native gem RUBY_CC_VERSION=2.3.0:2.2.2:2.1.5:2.0.0"
   end
-end
 
-well_known_protos = %w[
-  google/protobuf/any.proto
-  google/protobuf/api.proto
-  google/protobuf/duration.proto
-  google/protobuf/empty.proto
-  google/protobuf/field_mask.proto
-  google/protobuf/source_context.proto
-  google/protobuf/struct.proto
-  google/protobuf/timestamp.proto
-  google/protobuf/type.proto
-  google/protobuf/wrappers.proto
-]
-
-# These are omitted for now because we don't support proto2.
-proto2_protos = %w[
-  google/protobuf/descriptor.proto
-  google/protobuf/compiler/plugin.proto
-]
-
-genproto_output = []
-
-well_known_protos.each do |proto_file|
-  input_file = "../src/" + proto_file
-  output_file = "lib/" + proto_file.sub(/\.proto$/, ".rb")
-  genproto_output << output_file
-  file output_file => input_file do |file_task|
-    sh "../src/protoc -I../src --ruby_out=lib #{input_file}"
-  end
+  task 'gem:native' => [:genproto, 'gem:windows']
 end
 
 

ruby/google-protobuf.gemspec

 Gem::Specification.new do |s|
   s.name        = "google-protobuf"
-  s.version     = "3.0.0.alpha.5.0"
+  s.version     = "3.0.0.alpha.5.0.5"
   s.licenses    = ["BSD"]
   s.summary     = "Protocol Buffers"
   s.description = "Protocol Buffers are Google's data interchange format."