useLayeredStyles (CSS)

Language CSS

Summary

Rule available since: v2.5.13
Diagnostic Category: lint/nursery/useLayeredStyles
This rule doesn’t have a fix.
The default severity of this rule is warning.
Sources:
- Inspired from css/use-layers

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "useLayeredStyles": "error"
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      }
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    }
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  }
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}

Description

Enforce style rules to be defined within a cascade layer.

This rule reports style rules that are not contained within a cascade layer (@layer). Rules outside of a cascade layer (excluding !important) always take precedence over layered rules, making the cascade more difficult to predict and override.

SCSS limitations

Layer membership is determined from the authored ancestors of a style rule. SCSS mixins and includes are not expanded, so a rule in a mixin is checked at its definition site rather than at the layer where the mixin may be included.

Examples

Invalid

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.my-style {
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  color: red;
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}

code-block.css:1:1 lint/nursery/useLayeredStyles ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This style rule is defined outside of a cascade layer.
  
  > 1 │ .my-style {
      │ ^^^^^^^^^^^
  > 2 │   color: red;
  > 3 │ }
      │ ^
    4 │ 
  
  ℹ Style rules outside a cascade layer always take precedence over layered styles, which makes the cascade harder to predict and override.
  
  ℹ Wrap the style rule in a @layer block to control its place in the cascade.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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@media (min-width: 600px) {
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  .my-style {
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    color: red;
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  }
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}

code-block.css:2:3 lint/nursery/useLayeredStyles ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This style rule is defined outside of a cascade layer.
  
    1 │ @media (min-width: 600px) {
  > 2 │   .my-style {
      │   ^^^^^^^^^^^
  > 3 │     color: red;
  > 4 │   }
      │   ^
    5 │ }
    6 │ 
  
  ℹ Style rules outside a cascade layer always take precedence over layered styles, which makes the cascade harder to predict and override.
  
  ℹ Wrap the style rule in a @layer block to control its place in the cascade.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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@import "foo.css";

code-block.css:1:2 lint/nursery/useLayeredStyles ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This import is defined outside of a cascade layer.
  
  > 1 │ @import "foo.css";
      │  ^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Imported styles without a cascade layer always take precedence over layered styles, which makes the cascade harder to predict and override.
  
  ℹ Add the layer keyword after the import to control its place in the cascade.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

Valid

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@layer {
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  .my-style {
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    color: red;
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  }
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}

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@layer base {
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  .my-style {
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    color: red;
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  }
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}

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@layer base {
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  @media (min-width: 600px) {
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    .my-style {
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      color: red;
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    }
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  }
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}

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@import "foo.css" layer;

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@import "foo.css" layer(base);

Options

`requireImportLayers`

Whether @import rules must specify a cascade layer.

When set to false, @import rules without a layer keyword are allowed.

Default: true

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "useLayeredStyles": {
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          "level": "on",
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          "options": {
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            "requireImportLayers": false
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          }
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        }
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      }
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    }
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  }
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}

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@import "foo.css";