Grunt/lessc error on fresh checkout

[msmithpq]

I don't seem to be able to run the less or grunt command without getting an error. Even on a freshly checked out version of the repo. When I run either one of them (lessc or grunt) I get an error of:

Grunt
src/themes/main.less: [L42:C1] Operation on an invalid type

Lessc
SyntaxError: Operation on an invalid type in /src/themes/proton/main.less on line 100, column 2:
99 .jstree-@{theme-name} {
100 .jstree-theme(22px, "@{image-path}32px", 32px);
101 &.jstree-rtl .jstree-node {

I'm apologize if this is a simple problem. I'm not familiar enough with less to diagnose it and I google wasn't much help.

[spadged]

I don't know if you solved this issue, but I came accross this today while trying to compile jstree with LESS v4.1.1, rolling back to LESS version v3.0.1 made the issue go away for me.

It appears that a breaking change introduced since v3.0.1 (no idea what that is though) which means that this theme needs to be updated to work with less v4.

Looking at the source of this theme, the package.json has a dependency on grunt-contrib-less v0.8.2 which in turn is using less v1.5.0.