Breaking Change: meta.feature-exists()

The meta.feature-exists() function hasn’t had any new features added in a long time, and is now deprecated. Users should use other methods to determine if a new feature is available.

Historically, Sass used the meta.feature-exists() function (also available as the global feature-exists() function) to allow authors to detect whether various new language features were available when compiling stylesheets. However, as time has gone on it’s turned out that the vast majority of new Sass features are either possible to detect in a more straightforward way, or else aren’t very useful to detect at all.

This function is now deprecated and will be removed in Dart Sass 2.0.0. Since Dart Sass is now the only officially supported Sass implementation, and all versions of Dart Sass support all the features supported by meta.feature-exists(), all existing uses of it can safely be removed.

Many new features can be detected using meta.function-exists(), meta.mixin-exists(), or [meta.global-variable-exists()]. Others can be detected using expression-level syntax, such as using calc(1) == 1 to determine if the current version of Sass supports first-class calculations.

Transition PeriodTransition Period permalink

Dart Sass: since 1.78.0
LibSass: ✗
Ruby Sass: ✗

First, we’ll emit deprecation warnings for all usages of feature-exists.

In Dart Sass 2.0.0, meta.feature-exists() will no longer exist. Attempts to call it will throw an error, and attempts to call the global feature-exists() function will be treated as a plain CSS function call.

Can I Silence the Warnings?Can I Silence the Warnings? permalink

Sass provides a powerful suite of options for managing which deprecation warnings you see and when.

Terse and Verbose ModeTerse and Verbose Mode permalink

By default, Sass runs in terse mode, where it will only print each type of deprecation warning five times before it silences additional warnings. This helps ensure that users know when they need to be aware of an upcoming breaking change without creating an overwhelming amount of console noise.

If you run Sass in verbose mode instead, it will print every deprecation warning it encounters. This can be useful for tracking the remaining work to be done when fixing deprecations. You can enable verbose mode using the --verbose flag on the command line, or the verbose option in the JavaScript API.

⚠️ Heads up!

When running from the JS API, Sass doesn’t share any information across compilations, so by default it’ll print five warnings for each stylesheet that’s compiled. However, you can fix this by writing (or asking the author of your favorite framework’s Sass plugin to write) a custom Logger that only prints five errors per deprecation and can be shared across multiple compilations.

Silencing Deprecations in DependenciesSilencing Deprecations in Dependencies permalink

Sometimes, your dependencies have deprecation warnings that you can’t do anything about. You can silence deprecation warnings from dependencies while still printing them for your app using the --quiet-deps flag on the command line, or the quietDeps option in the JavaScript API.

For the purposes of this flag, a "dependency" is any stylesheet that’s not just a series of relative loads from the entrypoint stylesheet. This means anything that comes from a load path, and most stylesheets loaded through custom importers.

Silencing Specific DeprecationsSilencing Specific Deprecations permalink

If you know that one particular deprecation isn’t a problem for you, you can silence warnings for that specific deprecation using the --silence-deprecation flag on the command line, or the silenceDeprecations option in the JavaScript API.