Breaking Change: Invalid Combinators

Sass has historically been very permissive about the use of leading, trailing, and repeated combinators in selectors. These combinators are being deprecated except where they’re useful for nesting.

Sass has historically supported three invalid uses of combinators:

  • Leading combinators, as in + .error {color: red}.

  • Trailing combinators, as in .error + {color: red}.

  • Repeated combinators, as in div > > .error {color: red}.

None of these are valid CSS, and all of them will cause browsers to ignore the style rule in question. Supporting them added a substantial amount of complexity to Sass’s implementation, and made it particularly difficult to fix various bugs related to the @extend rule. As such, we made the decision to remove support for these uses.

There is one major exception: leading and trailing combinators may still be used for nesting purposes. For example, the following is still very much supported:

SCSS Syntax

.sidebar > {
  .error {
    color: red;
  }
}

Sass Syntax

.sidebar >
  .error
    color: red

CSS Output

.sidebar > .error {
  color: red;
}

Sass will only produce an error if a selector still has a leading or trailing combinator after nesting is resolved. Repeated combinators, on the other hand, will always be errors.

To make sure existing stylesheets who (likely accidentally) contain invalid combinators, we’ll support a transition period until the next major release of Dart Sass.

Transition PeriodTransition Period permalink

Compatibility:
Dart Sass
since 1.54.0
LibSass
✗
Ruby Sass
✗

First, we’ll emit deprecation warnings for all double combinators, as well as leading or trailing combinators that end up in selectors after nesting is resolved.

💡 Fun fact:

Remember, you can silence deprecation warnings from libraries you don’t control! If you’re using the command-line interface you can pass the --quiet-deps flag, and if you’re using the JavaScript API you can set the quietDeps option to true.

In addition, we’ll immediately start omitting selectors that we know to be invalid CSS from the compiled CSS, with one exception: we won’t omit selectors that begin with a leading combinator, since they may be used from a nested @import rule or meta.load-css() mixin. However, we don’t encourage this pattern and will drop support for it in Dart Sass 2.0.0.