parse makefile depends generated by gcc

lib/rscons/builders/cc.rb

@@ -7,7 +7,8 @@ module Rscons
         'CPPFLAGS' => [],
         'OBJSUFFIX' => '.o',
         'CSUFFIX' => '.c',
-        'CCCOM' => ['$CC', '-c', '-o', '$TARGET', '$CPPFLAGS', '$CFLAGS', '$SOURCES']
+        'CCDEPGEN' => ['-MMD', '-MF', '$DEPFILE'],
+        'CCCOM' => ['$CC', '-c', '-o', '$TARGET', '$CCDEPGEN', '$CPPFLAGS', '$CFLAGS', '$SOURCES']
       }
     end
 
@@ -22,9 +23,15 @@ module Rscons
         vars = {
           'TARGET' => target,
           'SOURCES' => source,
+          'DEPFILE' => env.stem(target) + '.mf',
         }
         env.execute("CC #{target}", env['CCCOM'], vars)
-        Cache.open.register_build(target, [source])
+        deps = [source]
+        if File.exists?(vars['DEPFILE'])
+          deps += env.parse_makefile_deps(vars['DEPFILE'], target)
+          FileUtils.rm_f(vars['DEPFILE'])
+        end
+        Cache.open.register_build(target, deps.uniq)
       end
       target
     end

lib/rscons/environment.rb

@@ -107,5 +107,24 @@ module Rscons
         orig_method_missing(method, *args)
       end
     end
+
+    def parse_makefile_deps(mf, fname)
+      deps = []
+      buildup = ''
+      File.read(mf).each_line do |line|
+        if line =~ /^(.*)\\\s*$/
+          buildup += ' ' + $1
+        else
+          if line =~ /^(.*): (.*)$/
+            target, tdeps = $1.strip, $2
+            if target == fname
+              deps += tdeps.split(' ').map(&:strip)
+            end
+          end
+          buildup = ''
+        end
+      end
+      deps
+    end
   end
 end

spec/build_tests_spec.rb

@@ -49,7 +49,7 @@ describe Rscons do
   end
 
   it 'does not rebuild the program if no sources changed' do
-    $stdout.should_receive(:puts).once.with('gcc -c -o simple.o simple.c')
+    $stdout.should_receive(:puts).once.with("gcc -c -o simple.o -MMD -MF simple.mf simple.c")
     $stdout.should_receive(:puts).once.with('gcc -o simple simple.o')
     setup_testdir(['simple.c']) do
       env = Rscons::Environment.new