add build test using a build directory

build_tests/build_dir/build.rb

@@ -0,0 +1,5 @@
+Rscons::Environment.new do |env|
+  env.append('CPPPATH' => Dir['src/**/*/'])
+  env.build_dir('src', 'build')
+  env.Program('build_dir', Dir['src/**/*.c'])
+end

build_tests/build_dir/src/one/one.c

@@ -0,0 +1,6 @@
+#include "two.h"
+
+int main(int argc, char *argv[])
+{
+    two();
+}

build_tests/build_dir/src/two/two.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+#include "two.h"
+
+void two(void)
+{
+    printf("Hello from two()\n");
+}

build_tests/build_dir/src/two/two.h

@@ -0,0 +1,6 @@
+#ifndef TWO_H
+#define TWO_H
+
+void two(void);
+
+#endif

lib/rscons/builders/program.rb

@@ -18,12 +18,13 @@ module Rscons
         if source.has_suffix?([@env['OBJSUFFIX'], @env['LIBSUFFIX']])
           source
         else
-          o_file = source.set_suffix(@env['OBJSUFFIX', :string])
+          o_file = @env.get_build_fname(source, @env['OBJSUFFIX', :string])
           builder = @env.builders.values.find { |b| b.produces?(o_file, source) }
           builder or raise "No builder found to convert input source #{source.inspect} to an object file."
-          builder.run(o_file, [source], cache)
+          builder.run(o_file, [source], cache) or break
         end
       end
+      if sources
         vars = {
           'TARGET' => target,
           'SOURCES' => sources,
@@ -37,4 +38,5 @@ module Rscons
         target
       end
     end
+  end
 end

spec/build_tests_spec.rb

@@ -112,4 +112,11 @@ describe Rscons do
     lines = build_testdir
     lines.should == ['gcc -o simple simple.o -lc']
   end
+
+  it 'builds object files in a different build directory' do
+    lines = test_dir('build_dir')
+    `./build_dir`.should == "Hello from two()\n"
+    File.exists?('build/one/one.o').should be_true
+    File.exists?('build/two/two.o').should be_true
+  end
 end