How to configure sourceMaps for LESS using Grunt? - css

Question

I'm using grunt 0.4.2 and grunt-contrib-less 0.9.0. I want my LESS to be compiled into CSS with support for source maps.
My LESS files are in public/less, and the main one is called main.less.
The compiling of public/less/main.less into public/css/main.css works, but source maps don't work.
What is wrong with my Grunt config below?
{
less: {
dev: {
options: {
compress: true,
yuicompress: true,
optimization: 2,
sourceMap: true,
sourceMapFilename: "public/css/main.css.source-map.json", //Write the source map to a separate file with the given filename.
sourceMapBasepath: "public/less", //Sets the base path for the Less file paths in the source map.
sourceMapRootpath: "/"//Adds this path onto the Less file paths in the source map.
},
files: {
"public/css/main.css": "public/less/main.less"
}
}
},
watch: {
styles: {
files: ["public/less/*"],
tasks: ['less'],
options: {
livereload: true,
nospaces: true
}
}
}
}
I don't want to have my CSS created in my /public/less folder; I want to put it into /public/css. Otherwise, I could use this other config, which works:
{
less: {
dev: {
options: {
compress: true,
yuicompress: true,
optimization: 2,
sourceMap: true,
sourceMapFilename: "public/less/main.css.map", //I DO NOT WANT THE CSS MAP HERE
sourceMapBasepath: "public/less", //Sets the base path for the Less file paths in the source map.
},
files: {
"public/less/main.css": "public/less/main.less"//I DO NOT WANT THE CSS HERE
}
}
},
watch: {
styles: {
files: ["public/less/*"],
tasks: ['less'],
options: {
livereload: true,
nospaces: true
}
}
}
}

Answer 1

I found the LESS site documentation to be more clear regarding params used by grunt-contrib-less.
LESS: Command Line Usage
http://lesscss.org/usage/#command-line-usage-installing-lessc
NPM: grunt-contrib-less
https://www.npmjs.org/package/grunt-contrib-less
File structure:
laravel/gruntfile.js
laravel/public/less/main.less
laravel/public/css/main.css
laravel/public/css/main.css.map
File 'main.css.map' note:
If you wish, you can rename to: main.css.source-map.json
I guess you have some server rule setup that doesn't server *.map files properly from the 'css' folder
Compression notes:
cleancss: true = will remove sourceMappingURL comment from main.css
yuicompress: true = will NOT remove sourceMappingURL comment from main.css
Gruntfile.js
less: {
dev: {
options: {
compress: true,
yuicompress: true,
optimization: 2,
sourceMap: true,
sourceMapFilename: 'public/css/main.css.map', // where file is generated and located
sourceMapURL: '/css/main.css.map', // the complete url and filename put in the compiled css file
sourceMapBasepath: 'public', // Sets sourcemap base path, defaults to current working directory.
sourceMapRootpath: '/', // adds this path onto the sourcemap filename and less file paths
},
files: {
'public/css/main.css': 'public/less/main.less',
}
}
},
watch: {
styles: {
files: ["public/less/*"],
tasks: ['less'],
options: {
livereload: true,
nospaces: true
}
}
},
laravel/public/css/main.css
.class{ compiled css here } /*# sourceMappingURL=/css/main.css.map */
laravel/public/css/main.css.map
{"version":3,"sources":["/less/main.less"], etc...

Answer 2

If you're still having trouble with it try setting the SourceMapURL to the full path, for example:
http://www.yourdomain.com/assets/css/styles.css.map
Obviously this is a bit of a pain as it's not relative, so when you move your site it will need to be changed. I had the same issue as you and this got it working for me.
Another point I discovered is that you cannot load the SourceMaps from the file system. It has to be from a web server. To get around the file system issue I believe you can inline the SourceMap.
This thread on GitHub has a lot of information.
https://github.com/less/less.js/issues/1050#issuecomment-25621390