Do not rebuild targets when they are up to date

Store dependencies and file checksums in a cache file

lib/rscons/builders/cc.rb

@@ -17,14 +17,17 @@ module Rscons
     def run(env, target, source)
       raise "String expected, not #{source.inspect}" unless source.is_a?(String)
       o_file = "#{env.stem(source)}#{env['OBJSUFFIX']}"
-      command = [
-        env['CC'],
-        *env['CPPFLAGS'],
-        *env['CFLAGS'],
-        '-o', o_file,
-        source
-      ]
-      env.execute("CC #{o_file}", command)
+      unless Cache.open.up_to_date?(target, [source])
+        command = [
+          env['CC'],
+          *env['CPPFLAGS'],
+          *env['CFLAGS'],
+          '-o', o_file,
+          source
+        ]
+        env.execute("CC #{o_file}", command)
+        Cache.open.register_build(target, [source])
+      end
       o_file
     end
   end

lib/rscons/builders/program.rb

@@ -11,6 +11,7 @@ module Rscons
 
     def run(env, target, sources)
       sources = [sources] if sources.is_a?(String)
+      # convert sources to object file names
       sources = sources.map do |source|
         if source =~ /#{env['OBJSUFFIX']}$/ or source =~ /#{env['LIBSUFFIX']}$/
           source
@@ -24,15 +25,18 @@ module Rscons
           end
         end
       end
-      command = [
-        env['LD'] || env['CC'],
-        '-o', target,
-        *env['LDFLAGS'],
-        *sources,
-        *env['LIBPATHS'].map {|lp| "-L#{lp}"},
-        *env['LIBS'].map {|lib| "-l#{lib}"}
-      ]
-      env.execute("LINK #{target}", command)
+      unless Cache.open.up_to_date?(target, sources)
+        command = [
+          env['LD'] || env['CC'],
+          '-o', target,
+          *env['LDFLAGS'],
+          *sources,
+          *env['LIBPATHS'].map {|lp| "-L#{lp}"},
+          *env['LIBS'].map {|lib| "-l#{lib}"}
+        ]
+        env.execute("LINK #{target}", command)
+        Cache.open.register_build(target, sources)
+      end
       target
     end
   end