The Sass @error Directive

Sass offers several built-in directives to help developers manage their styles more effectively. One of these directives is the @error directive, which can be used to display the value of a SassScript expression as an error.

When the @error directive is used, Sass immediately stops the compilation and displays an error message carrying the value of the SassScript expression used in the @error directive. This instructs the preprocessor to stop translating the SASS/SCSS to CSS if it encounters a certain condition.

For example, imagine you're writing a mixin for a button and you only want it to accept certain values:

@mixin button-type($type) {
  @if ($type != 'primary' and $type != 'secondary') {
    @error "Unknown button type '#{$type}'.";
  }
  ...
}

If you try to use this mixin with an unsupported button type, like:

.button {
  @include button-type('fancy');
}

Sass will stop compilation and throw an error:

Error: Unknown button type 'fancy'.

This helps quickly identify the source of the problem and allows for faster debugging. While @warn directive may also communicate errors or potential issues, it only logs a warning in the terminal but does not interrupt the compilation like the @error directive does. The @at-root directive, on the other hand, is used to force a block of declarations or a rule to the root of a document.

As a best practice, use the @error directive whenever you want to ensure code doesn't compile unless certain conditions are met. It can be especially useful for libraries or shared code where you want to enforce specific constraints or requirements. Remember, well-placed error reporting can save a lot of debugging time down the road.