If the grunt.file.copy optional process function returns false, the f…

…ile copy will be aborted.

docs/api_file.md

@@ -49,7 +49,7 @@ The `options` object has these possible properties:
 var options = {
   // If specified, the file contents will be parsed as `utf8` and passed into
   // the function, whose return value will be used as the destination file's
-  // contents.
+  // contents. If this function returns false, the file copy will be aborted.
   process: processFunction,
   // These optional wildcard patterns will be matched against the filepath using
   // grunt.file.isMatch. If a specified wildcard pattern matches, the file will

lib/grunt/file.js

@@ -201,7 +201,12 @@ file.copy = function(srcpath, destpath, options) {
       throw grunt.task.taskError('Error while processing "' + srcpath + '" file.', e);
     }
   }
-  file.write(destpath, src);
+  // Abort copy if the process function returns false.
+  if (src === false) {
+    grunt.verbose.writeln('Write aborted.');
+  } else {
+    file.write(destpath, src);
+  }
 };
 
 // Read a file, parse its contents, return an object.