Error when trying to use grunt-contrib-uglify: “src files were empty”

Question

I have the following Gruntfile.js :

module.exports = function(grunt) {
  var config = {
    pkg: grunt.file.readJSON('package.json'),

    /* Some other tasks... */

    uglify: {
      options: {
        banner: '/*! <%= pkg.name %> <%= grunt.template.today("yyyy-mm-dd") %> */\n'
      },
      def: {
        files: {
          'out/src.js': 'out/src.min.js'
        }
      }
    }
  };

  grunt.initConfig(config);
  grunt.loadNpmTasks('grunt-contrib-uglify');

  grunt.registerTask('default', [/* <other-tasks>, */ 'uglify:def']);
};

Folder structure is as follows:

project
  |
  +-out (folder)
  +-Gruntfile.js

Important: I run grunt from the project folder .

When running grunt , there is a task before uglify:def which is responsible for generating src.js into project/out .

When I run grunt I can see src.js being generated into project/out , but when Grunt runs uglisy:def I get the following error:

Running "uglify:def" (uglify) task.

Destination out/src.js not written because src files were empty.

No files created.

What am i doing wrong?

Log

When running with --verbose I get:

Running "uglify:def" (uglify) task
Verifying property uglify.def exists in config...OK
Files: [no src] -> out/src.js
Options: banner="/*! My Pack 2015-07-19 */\r\n", footer="", compress={"warnings":false}, mangle={}, beautify=false, report="
min", expression=false, maxLineLen=32000, ASCIIOnly=false, screwIE8=false, quoteStyle=0
>> Destination out/src.js not written because src files were empty.
>> No files created.

Answer 1

I've a configuration like the following, and it works fine for me.

    // uglify javascript
    uglify: {
        dev: {
            options: {
                mangle: true
            },
            files: {
                'js/dest.min.js': 'js/source.js'
            }
        }
    },

Probably you confused the destination with the source. Try to switch them.

Answer 2

It were happening due to, you are not registering above given tasks.

OK, lets start with concatenation in grunt:

concat: {
    css: {
        src: ['./assets/css/*.css', './assets/css/**/*.css'],
        dest: './dist/css/style.css'
    },
    js: {
        src: ['./assets/js/*.js', './assets/js/**/*.js'],
        dest: './dist/js/script.js'
    }
},

so, this concat is supposed to collect all css files from above given url / directories and concatenate to given destination in one place and so with js .

this will be simple concatenated style.css and script.js at dest destination directory.

but it won't work, till you not register this concat task inside below line:

grunt.registerTask('default', ['concat', 'cssmin', 'uglify']);

So, till concat will not concatenate those files in dest directory, how the uglify will collect and work!

Conclusion: task won't get execute till you not mention them inside grunt.registerTask function.

Answer 3

My problem was that the path to my source file was incorrect. So it wasn't so much that the file is "empty" but that it can't be found.