Compile less files with grunt-contrib-less won't work

The glob pattern js/base/*.css does not match any files, therefore there is no destination. Usually, tasks like this expect multiple inputs to combine into a single output. Also, bear in mind that less is a multi-task, and putting files as a child of less is not doing what you expect. (it is treating it as a target, not a src/dest map)

If you want a 1-1 transform of .less into .css, you can use dynamic expansion. (or you can define each src/dest pair manually, but who wants to do that?)

In your case:

less: {    options: {        paths: ['js/base']    },    // target name    src: {        // no need for files, the config below should work        expand: true,        cwd:    "js/base",        src:    "*.less",        ext:    ".css"    }}

I used Anthonies solution but stil had an error

Warning: Object true has no method indexOf

If I changed the order putting expand true as second it gave me the error

Unable to read "less" file

where "less" was the value of the first item in my list.

I solved it by changing files into an array like this:

less: {    options: {            paths: ["js/base"]        },        files: [{            expand: true,            cwd: "js/base",            src: ["**/*.less"],            dest: "js/base",            ext: ".css"        }]},

I used "grunt-contrib-less" : "^0.11.0"

This works for me, but modified to reflect this scenario:

less: {    options: {        paths: ["js/base"]    },    files: {        expand: true,        cwd: "js/base",        src: ["**/*.less"],        dest: "js/base",        ext: ".css"    }},