Breaking Change: Strict Function Units

Various built-in functions will become stricter in which units they allow and will handle those units more consistently. This makes Sass more compatible with the CSS spec and helps catch errors more quickly.

HueHue permalink

Compatibility:
Dart Sass
since 1.32.0
LibSass
✗
Ruby Sass
✗

When specifying a color’s hue, CSS allows any angle unit (deg, grad, rad, or turn). It also allows a unitless number, which is interpreted as deg. Historically, Sass has allowed any unit, and interpreted it as deg. This is particularly problematic because it meant that the valid CSS expression hsl(0.5turn, 100%, 50%) would be allowed by Sass but interpreted entirely wrong.

To fix this issue and bring Sass in line with the CSS spec, we’re making changes in multiple phases:

Phase 1Phase 1 permalink

Compatibility:
Dart Sass
since 1.32.0
LibSass
✗
Ruby Sass
✗

At first, Sass just emitted a deprecation warning if you passed a number with a unit other than deg as a hue to any function. Passing a unitless number is still allowed.

Phase 2Phase 2 permalink

Compatibility:
Dart Sass
since 1.52.1
LibSass
✗
Ruby Sass
✗

Next, we changed the way angle units are handled for hue parameters to match the CSS spec. This means that numbers with grad, rad, or turn units will be converted to deg: 0.5turn will be converted to 180deg, 100grad will be converted to 90deg, and so on.

Because this change is necessary to preserve CSS compatibility, according to the Dart Sass compatibility policy it was made with only a minor version bump. However, it changes as little behavior as possible to ensure that Sass interprets all valid CSS according to the CSS spec.

Phase 3Phase 3 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

Finally, in Dart Sass 2.0.0 color functions will throw errors if they’re passed a hue parameter with a non-angle unit. Unitless hues will still be allowed.

Saturation and LightnessSaturation and Lightness permalink

When specifying an HSL color’s saturation and lightness, CSS only allows % units. Even unitless numbers aren’t allowed (unlike for the hue). Historically, Sass has allowed any unit, and interpreted it as %. You could even write hsl(0, 100px, 50s) and Sass would return the color red.

To fix this issue and bring Sass in line with the CSS spec, we’re making changes in two phases:

Phase 1Phase 1 permalink

Compatibility:
Dart Sass
since 1.32.0
LibSass
✗
Ruby Sass
✗

Currently, Sass just emits a deprecation warning if you pass a number with no unit or a unit other than % as a lightness or saturation to any function.

Phase 2Phase 2 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

In Dart Sass 2.0.0 color functions will throw errors if they’re passed a saturation or lightness parameter with no unit or a non-% unit.

AlphaAlpha permalink

When specifying a color’s alpha value, CSS (as of Colors Level 4) allows either unitless values between 0 and 1 or % values between 0% and 100%. In most cases Sass follows this behavior, but the functions color.adjust() and color.change() have historically allowed any unit, and interpreted it as unitless. You could even write color.change(red, $alpha: 1%) and Sass would return the opaque color red.

To fix this issue and bring Sass in line with the CSS spec, we’re making changes in three phases:

Phase 1Phase 1 permalink

Compatibility:
Dart Sass
since 1.56.0
LibSass
✗
Ruby Sass
✗

Currently, Sass just emits a deprecation warning if you pass a number with any unit, including %, as an alpha value to color.change() or color.adjust().

Phase 2Phase 2 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

Next, we’ll change the way % units are handled for the alpha argument to color.change() and color.adjust(). Alphas with unit % will be divided by 100%, converting them to unitless numbers between 0 and 1.

Because this change is a bug fix that improves consistency with other Sass functions, it will be made with only a minor version bump. It will be changed at minimum three months after Phase 1 is released, to give users time to adjust their code and avoid the bug.

Phase 3Phase 3 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

Finally, in Dart Sass 2.0.0 color.change() and color.adjust() will throw errors if they’re passed an alpha parameter with a non-% unit. Unitless alphas will still be allowed.

math.random()math.random() permalink

The math.random() function has historically ignored units in $limit and returned a unitless value. For example math.random(100px) would drop "px" and return a value like 42.

A future version of Sass will stop ignoring units for the $limit argument and return a random integer with the same units.

SCSS Syntax

@use "sass:math";

// Future Sass, doesn't work yet!
@debug math.random(100px); // 42px

Sass Syntax

@use "sass:math"

// Future Sass, doesn't work yet!
@debug math.random(100px)  // 42px

Phase 1Phase 1 permalink

Compatibility:
Dart Sass
since 1.54.5
LibSass
✗
Ruby Sass
✗

Currently, Sass emits a deprecation warning if you pass a $limit with units to math.random().

Phase 2Phase 2 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

In Dart Sass 2.0.0, passing a $limit number with units will be an error.

Phase 3Phase 3 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

In a minor release after Dart Sass 2.0.0, passing a $limit number with units to the math.random() function will be allowed again. It will return a random integer the same units as $limit, instead of a unitless number.

WeightWeight permalink

The color.mix() function and color.invert() function have both historically ignored units in their $weight arguments, despite that argument conceptually representing a percentage. A future version of Sass will require the unit %.

Phase 1Phase 1 permalink

Compatibility:
Dart Sass
since 1.56.0
LibSass
✗
Ruby Sass
✗

Currently, Sass emits a deprecation warning if you pass a $weight with no units or with units other than % to color.mix() or color.invert().

Phase 2Phase 2 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

In Dart Sass 2.0.0, color.mix() and color.invert() will throw errors if they’re passed a $weight with no unit or a non-% unit.

IndexIndex permalink

The list.nth() function and list.set-nth() function have both historically ignored units in their $n arguments. A future version of Sass will forbid any units.

Phase 1Phase 1 permalink

Compatibility:
Dart Sass
since 1.56.0
LibSass
✗
Ruby Sass
✗

Currently, Sass emits a deprecation warning if you pass a $weight with no units or with units other than % to color.mix() or color.invert().

Phase 2Phase 2 permalink

Compatibility:
Dart Sass
✗
LibSass
✗
Ruby Sass
✗

In Dart Sass 2.0.0, list.nth() and list.set-nth() will throw errors if they’re passed an index $n with a unit.