• #3811 add support for container queries (@puckowski)
• #3761 fix faulty source map generation with variables in selectors, fixes #3567 (@pgoldberg)
• #3700 parsing variables fail when there is no trailing semicolon (@b-kelly)
• #3719 modify this pointer so that it is not empty. (@lumburr)
• #3649 fixes #2991 empty @media queries generated when compiling less file with (reference) to bootstrap (@MoonCoral)

• #3673 Feat: add support for case-insensitive attribute selectors (#3673) (@iChenLei)
• #3710 Feat: add disablePluginRule flag for render() options (#3710) (@broofa @edhgoose)
• #3656 Fix #3655 for param tag is null (#3658) (@langren1353)
• #3658 Fix #3646 forcefully change unsupported input to strings (#3658) (@gzb1128)
• #3668 Fix change keyword plugin and import regexp (#3668) (@iChenLei)
• #3613 Fix #3591: refactor debugInfo from class to function (#3613) (@drdevlin)
• #3716 Fix https failures on macOS (#3716) (@joeyparrish)

• #3602 Fix currentFileInfo and index properties on nodes (#3602) (@bjpbakker)
• #3626 Fix #3616 IfStatement requires double parentheses when dividing (#3626) (@iChenLei)
• #3630 Fix needle dependency warning typo. (#3630) (@cjwilsontech)

• #3597 Fix expected response when there's a socket error (#3597) (@zxfrank)
• #3589 Fixes #3586 (#3589) (@matthew-dean)

Mixin parentheses requirement removed

This was maybe too big a change without some kind of deprecation or conversion. So for this version, this works again:

.mixin;

• #3582 Fix #3576 import redirects. Replace native-request with needle. (#3582) (@zaquest)
• #3583 Update rollup and other build dependencies (#3583) (@pravi)
• #3588 Roll back paren requirement on mixin calls (#3588) (@matthew-dean)

This release has 2 breaking changes:

Parentheses required for mixin calls

This aligns it with syntax for calling detached rulesets.

Example

.mixin() {}
.mixin;  // error in 4.0

Parens-division now the default math setting

Parentheses are required (by default) around division-like expressions, to force math evaluation.

Example:

@ratio_large: 16;
@ratio_small: 9;

/** The following will produce `device-aspect-ratio: 1.77777778` by default in 3.x */
@media all and (device-aspect-ratio: @ratio_large / @ratio_small) {
   .body { max-width: 800px; }
}

Produces:

@media all and (device-aspect-ratio: 16 / 9) {
  .body {
    max-width: 800px;
  }
}

You can, of course, get old math behavior. See: http://lesscss.org/usage/#less-options-math

What's New

• min() / max() functions can pass-through if it cannot be evaluated in Less
• isdefined() can be used to test if variables are defined (e.g. isdefined(@unknown))
• New rgb color syntax supported (e.g. rgb(0 128 255 / 50%))

• Support for plugins that pre-process (to add libraries silently etc.)
• Empty sourcemaps now work
• Extract and Length functions now ignore comments in a list (more work to come to fix the general problem)
• fragment urls are treated absolute since they refer to the html document
• Extends on a selector joined with & now work better
• Nested mixins work better with !important (regression in 2.3.0)
• The promise dependency is now actually optional (introduced in 2.0.0)
• Files with just \r newlines now process ok (regression in 2.0.0)
• When strict units is off and the unit is 1/x, (e.g. 1 / 12px) the unit output is x, previously nothing (regression in 2.0.0)

• supports the scoped @plugin directive to load function plugins
• All directives are bubbled (e.g. supports), not just media
• Performance improvements to the parser - should help non-chrome browsers with very large less files to be a lot quicker.
• the image size function respects include paths like other file functions
• colour functions take a relative argument that applies percentages relatively instead of absolutely
• include paths now allows : as a separator on windows (recognising and not splitting drive names by the backslash)
• @import (css) does not pull the directive above comments
• Fix for import statements without quotes sometimes causing issues
• replace supports dimensions and colours
• the browser field is set in the package.json for use with browserify
• another fix to support paths being passed as a string instead of an array
• detached rulesets can be used as default arguments
• Fix a lot of false warnings about extends
• errors written to stderr more consistently
• consistently keep units if strict units is off
• Better support for comments in function all arguments

• Fix problems with less being async in some browsers
• Minor fix only likely to affect programmatic usage of ruleset find
• Fix error when a namespaced mixin is invoked in global scope