Compile Less Files with Source Maps

Compile LESS files with source maps

Update: New shortest answer

The docs have been updated! As new features hit LESS, sometimes the docs lag behind a bit, so if you're looking for bleeding-edge features, you're still probably better off running lessc (see longer answer) and checking what pops out of the help text.

http://lesscss.org/usage/

Short answer

You're looking for any number of the following options from the command line:

--source-map[=FILENAME]  Outputs a v3 sourcemap to the filename (or output filename.map)
--source-map-rootpath=X  adds this path onto the sourcemap filename and less file paths
--source-map-basepath=X  Sets sourcemap base path, defaults to current working directory.
--source-map-less-inline puts the less files into the map instead of referencing them
--source-map-map-inline  puts the map (and any less files) into the output css file
--source-map-url=URL     the complete url and filename put in the less file

As I write this I'm not aware of any GUI options that generate maps (source maps were only added to LESS in the last few months) -- sorry to not have any better news. I'm sure they'll add support in as they update over the next year.

Longer answer

If you run lessc from the command line without any parameters it will give you all the options. (In my experience, this is more up to date than their documentation, so it'll at least get you pointed in the right direction.) with all the most recent map stuff included.

The easiest combo to use for dev is --source-map-less-inline --source-map-map-inline as that will give you your source maps embedded in your output css.

If you'd like to add a separate map file, you can use --source-map which, from my.less will output my.css and my.css.map

For reference: when I run my copy (v 1.6.1 at the moment) I get

usage: lessc [option option=parameter ...] <source> [destination]

If source is set to `-' (dash or hyphen-minus), input is read from stdin.
options:
  -h, --help               Print help (this message) and exit.
  --include-path=PATHS     Set include paths. Separated by `:'. Use `;' on Windows.
  -M, --depends            Output a makefile import dependency list to stdout
  --no-color               Disable colorized output.
  --no-ie-compat           Disable IE compatibility checks.
  --no-js                  Disable JavaScript in less files
  -l, --lint               Syntax check only (lint).
  -s, --silent             Suppress output of error messages.
  --strict-imports         Force evaluation of imports.
  --insecure               Allow imports from insecure https hosts.
  -v, --version            Print version number and exit.
  -x, --compress           Compress output by removing some whitespaces.
  --clean-css              Compress output using clean-css
  --clean-option=opt:val   Pass an option to clean css, using CLI arguments from
                           https://github.com/GoalSmashers/clean-css e.g.
                           --clean-option=--selectors-merge-mode:ie8
                           and to switch on advanced use --clean-option=--advanced
  --source-map[=FILENAME]  Outputs a v3 sourcemap to the filename (or output filename.map)
  --source-map-rootpath=X  adds this path onto the sourcemap filename and less file paths
  --source-map-basepath=X  Sets sourcemap base path, defaults to current working directory.
  --source-map-less-inline puts the less files into the map instead of referencing them
  --source-map-map-inline  puts the map (and any less files) into the output css file
  --source-map-url=URL     the complete url and filename put in the less file
  -rp, --rootpath=URL      Set rootpath for url rewriting in relative imports and urls.
                           Works with or without the relative-urls option.
  -ru, --relative-urls     re-write relative urls to the base less file.
  -sm=on|off               Turn on or off strict math, where in strict mode, math
  --strict-math=on|off     requires brackets. This option may default to on and then
                           be removed in the future.
  -su=on|off               Allow mixed units, e.g. 1px+1em or 1px*1px which have units
  --strict-units=on|off    that cannot be represented.
  --global-var='VAR=VALUE' Defines a variable that can be referenced by the file.
  --modify-var='VAR=VALUE' Modifies a variable already declared in the file.

-------------------------- Deprecated ----------------
  -O0, -O1, -O2            Set the parser's optimization level. The lower
                           the number, the less nodes it will create in the
                           tree. This could matter for debugging, or if you
                           want to access the individual nodes in the tree.
  --line-numbers=TYPE      Outputs filename and line numbers.
                           TYPE can be either 'comments', which will output
                           the debug info within comments, 'mediaquery'
                           that will output the information within a fake
                           media query which is compatible with the SASS
                           format, and 'all' which will do both.
  --verbose                Be verbose.

How to have sourcemaps include all my LESS files with gulp

As far as i understand your configuration generate the following sourcemap code:

/*# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIm1haW4ubGVzcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFFQTtFQUNFLHlCQUFBIiwiZmlsZSI6Im1haW4uY3NzIiwic291cmNlc0NvbnRlbnQiOlsiQGltcG9ydCAndmFycyc7XG5cbmJvZHl7XG4gIGJhY2tncm91bmQtY29sb3I6IEBibGF1O1xufVxuIl0sInNvdXJjZVJvb3QiOiIvc291cmNlLyJ9 */

The encoded version:

{"version":3,"sources":["main.less"],"names":[],"mappings":"AAEA;EACE,yBAAA","file":"main.css","sourcesContent":["@import 'vars';\n\nbody{\n  background-color: @blau;\n}\n"],"sourceRoot":"/source/"}

Your vars.less does not generate any output to the CSS and so should not included in the sourcemap.

As soon as your vars.less generates output, for instance add .selector {p:1;} at the end of this file, the file will also be included in the source map:

{"version":3,"sources":["vars.less","main.less"],"names":[],"mappings":"AACA;EAAW,IAAA;;ACCX;EACE,yBAAA","file":"main.css","sourcesContent":["@blau : #6621ab;\n.selector {p:1;}\n","@import 'vars';\n\nbody{\n  background-color: @blau;\n}\n"],"sourceRoot":"/source/"}

Notice that the lessc compiler has different option for source maps:

  --source-map[=FILENAME]  Outputs a v3 sourcemap to the filename (or output filename.map)
  --source-map-rootpath=X  adds this path onto the sourcemap filename and less file paths
  --source-map-basepath=X  Sets sourcemap base path, defaults to current working directory.
  --source-map-less-inline puts the less files into the map instead of referencing them
  --source-map-map-inline  puts the map (and any less files) into the output css file
  --source-map-url=URL     the complete url and filename put in the less file

The gulp-sourcemaps outputs the same result as compiling with both the --source-map-less-inline and --source-map-map-inline options

Output multiple LESS source maps with Grunt?

The crummy brute-force method is to simply define a second build process and make sure that your build processes call both less.development1 and less.development2:

less: {
    "development1": {
        options: {
            compress: true,
            yuicompress: true,
            optimization: 2,
            sourceMap: true,
            sourceMapFilename: "<%= yeoman.app %>/live_preview/b/css/theme.css.map"

        },
        files: {
            // target.css file: source.less file
            "<%= yeoman.app %>/live_preview/b/css/theme.css": "<%= yeoman.app %>/less/theme.less"
        }
    },
    "development2": {
        options: {
            compress: true,
            yuicompress: true,
            optimization: 2,
            sourceMap: true,
            sourceMapFilename: "<%= yeoman.app %>/live_preview/b/css/main.css.map"

        },
        files: {
            // target.css file: source.less file
            "<%= yeoman.app %>/live_preview/b/css/main.css": "<%= yeoman.app %>/less/main.less"
        }
    }
}

How to configure sourceMaps for LESS using Grunt?

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...

Is there any way to compile less files with @imports and concatenate them with Gulp, all in the same stream?

You simply need to specify the paths option for gulp-less to tell it where it should start searching for files specified with @import directives.

For e.g., in widgets.less, its trying to find

• support-tickets.less
• comments.less
• article-comments.less

• etc..

  in Library/WebServer/Documents/qjt2015/trunk/styles/less/ (see the error message that you posted) but I believe it should be in Library/WebServer/Documents/qjt2015/trunk/styles/less/widgets/ (relative to your widgets.less file)

Simply set the path(s) like so:

gulp.task('buildStyles', function() { 
  return gulp.src([
     // ...
  ])
  // ... other gulp tasks here
  .pipe(less({
     paths: [
       '/Library/WebServer/Documents/qjt2015/trunk/styles/less/',
       '/Library/WebServer/Documents/qjt2015/trunk/styles/less/widgets/',
       '/Library/WebServer/Documents/qjt2015/trunk/styles/less/pages/',
       // add additional paths here for less to find imports in
       // less will tell you which import files it can't find, so simply tell it where to find them.

     ]
  ))
  .pipe(concat('allmin.css'))
  // ...
});

```

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