add Rscons.command_executer to determine command executer

Use "env" to execute commands when in MSYS on Windows

lib/rscons.rb

@@ -83,6 +83,33 @@ module Rscons
         end
       end
   end
+
+  # Return an Array containing a command used to execute commands.
+  #
+  # This will normally be an empty Array, but on Windows if Rscons detects
+  # that it is running in MSYS then ["env"] will be returned.
+  #
+  # @return [Array<String>] Command used to execute commands.
+  def self.command_executer
+    @@command_executer ||=
+      if Object.const_get("RUBY_PLATFORM") =~ /mingw/
+        if ENV.keys.find {|key| key =~ /MSYS/}
+          begin
+            if IO.popen(["env", "echo", "success"]) {|io| io.read.strip} == "success"
+              ["env"]
+            end
+          rescue
+          end
+        end
+      end || []
+  end
+
+  # Set the command executer array.
+  #
+  # @param val [Array<String>] Command used to execute commands.
+  def self.command_executer=(val)
+    @@command_executer = val
+  end
 end
 
 # Unbuffer $stdout

lib/rscons/environment.rb

@@ -245,7 +245,7 @@ module Rscons
       end
       env_args = options[:env] ? [options[:env]] : []
       options_args = options[:options] ? [options[:options]] : []
-      system(*env_args, *command, *options_args).tap do |result|
+      system(*env_args, *Rscons.command_executer, *command, *options_args).tap do |result|
         unless result or @echo == :command
           $stdout.write "Failed command was: "
           print_command.call

spec/rscons_spec.rb

@@ -66,4 +66,50 @@ describe Rscons do
       expect(Rscons.get_system_shell).to eq(["sh", "-c"])
     end
   end
+
+  context "command executer" do
+    describe ".command_executer" do
+      before(:each) do
+        Rscons.class_variable_set(:@@command_executer, nil)
+      end
+
+      after(:each) do
+        Rscons.class_variable_set(:@@command_executer, nil)
+      end
+
+      it "returns ['env'] if mingw platform in MSYS and 'env' works" do
+        Object.should_receive(:const_get).and_return("x86-mingw")
+        ENV.should_receive(:keys).and_return(["MSYSCON"])
+        io = StringIO.new("success\n")
+        IO.should_receive(:popen).with(["env", "echo", "success"]).and_yield(io)
+        expect(Rscons.command_executer).to eq(["env"])
+      end
+
+      it "returns [] if mingw platform in MSYS and 'env' does not work" do
+        Object.should_receive(:const_get).and_return("x86-mingw")
+        ENV.should_receive(:keys).and_return(["MSYSCON"])
+        IO.should_receive(:popen).with(["env", "echo", "success"]).and_raise "ENOENT"
+        expect(Rscons.command_executer).to eq([])
+      end
+
+      it "returns [] if mingw platform not in MSYS" do
+        Object.should_receive(:const_get).and_return("x86-mingw")
+        ENV.should_receive(:keys).and_return(["COMSPEC"])
+        expect(Rscons.command_executer).to eq([])
+      end
+
+      it "returns [] if not mingw platform" do
+        Object.should_receive(:const_get).and_return("x86-linux")
+        expect(Rscons.command_executer).to eq([])
+      end
+    end
+
+    describe ".command_executer=" do
+      it "overrides the value of @@command_executer" do
+        Rscons.class_variable_set(:@@command_executer, ["env"])
+        Rscons.command_executer = []
+        expect(Rscons.class_variable_get(:@@command_executer)).to eq([])
+      end
+    end
+  end
 end