diff --git a/package-lock.json b/package-lock.json
index 4b3470d1c..3c441984f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2128,6 +2128,10 @@
"resolved": "plugins/postcss-stepped-value-functions",
"link": true
},
+ "node_modules/@csstools/postcss-system-ui-font-family": {
+ "resolved": "plugins/postcss-system-ui-font-family",
+ "link": true
+ },
"node_modules/@csstools/postcss-tape": {
"resolved": "packages/postcss-tape",
"link": true
@@ -12028,6 +12032,30 @@
"postcss": "^8.4"
}
},
+ "plugins/postcss-system-ui-font-family": {
+ "name": "@csstools/postcss-system-ui-font-family",
+ "version": "0.0.0",
+ "funding": [
+ {
+ "type": "github",
+ "url": "https://github.com/sponsors/csstools"
+ },
+ {
+ "type": "opencollective",
+ "url": "https://opencollective.com/csstools"
+ }
+ ],
+ "license": "MIT-0",
+ "devDependencies": {
+ "@csstools/postcss-tape": "*"
+ },
+ "engines": {
+ "node": ">=18"
+ },
+ "peerDependencies": {
+ "postcss": "^8.4"
+ }
+ },
"plugins/postcss-text-decoration-shorthand": {
"name": "@csstools/postcss-text-decoration-shorthand",
"version": "4.0.3",
diff --git a/plugins/postcss-system-ui-font-family/.gitignore b/plugins/postcss-system-ui-font-family/.gitignore
new file mode 100644
index 000000000..e5b28db4a
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/.gitignore
@@ -0,0 +1,6 @@
+node_modules
+package-lock.json
+yarn.lock
+*.result.css
+*.result.css.map
+*.result.html
diff --git a/plugins/postcss-system-ui-font-family/.nvmrc b/plugins/postcss-system-ui-font-family/.nvmrc
new file mode 100644
index 000000000..28d6ff1c8
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/.nvmrc
@@ -0,0 +1 @@
+v25.1.0
diff --git a/plugins/postcss-system-ui-font-family/CHANGELOG.md b/plugins/postcss-system-ui-font-family/CHANGELOG.md
new file mode 100644
index 000000000..90950723c
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Changes to PostCSS System UI Font Family
+
+### Unreleased (major)
+
+- Initial version
diff --git a/plugins/postcss-system-ui-font-family/INSTALL.md b/plugins/postcss-system-ui-font-family/INSTALL.md
new file mode 100644
index 000000000..0d30ea33f
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/INSTALL.md
@@ -0,0 +1,235 @@
+# Installing PostCSS System UI Font Family
+
+[PostCSS System UI Font Family] runs in all Node environments, with special instructions for:
+
+- [Node](#node)
+- [PostCSS CLI](#postcss-cli)
+- [PostCSS Load Config](#postcss-load-config)
+- [Webpack](#webpack)
+- [Next.js](#nextjs)
+- [Gulp](#gulp)
+- [Grunt](#grunt)
+
+
+
+## Node
+
+Add [PostCSS System UI Font Family] to your project:
+
+```bash
+npm install postcss @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use it as a [PostCSS] plugin:
+
+```js
+// commonjs
+const postcss = require('postcss');
+const postcssSystemUIFontFamily = require('@csstools/postcss-system-ui-font-family');
+
+postcss([
+ postcssSystemUIFontFamily(/* pluginOptions */)
+]).process(YOUR_CSS /*, processOptions */);
+```
+
+```js
+// esm
+import postcss from 'postcss';
+import postcssSystemUIFontFamily from '@csstools/postcss-system-ui-font-family';
+
+postcss([
+ postcssSystemUIFontFamily(/* pluginOptions */)
+]).process(YOUR_CSS /*, processOptions */);
+```
+
+## PostCSS CLI
+
+Add [PostCSS CLI] to your project:
+
+```bash
+npm install postcss-cli @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use [PostCSS System UI Font Family] in your `postcss.config.js` configuration file:
+
+```js
+const postcssSystemUIFontFamily = require('@csstools/postcss-system-ui-font-family');
+
+module.exports = {
+ plugins: [
+ postcssSystemUIFontFamily(/* pluginOptions */)
+ ]
+}
+```
+
+## PostCSS Load Config
+
+If your framework/CLI supports [`postcss-load-config`](https://github.com/postcss/postcss-load-config).
+
+```bash
+npm install @csstools/postcss-system-ui-font-family --save-dev
+```
+
+`package.json`:
+
+```json
+{
+ "postcss": {
+ "plugins": {
+ "@csstools/postcss-system-ui-font-family": {}
+ }
+ }
+}
+```
+
+`.postcssrc.json`:
+
+```json
+{
+ "plugins": {
+ "@csstools/postcss-system-ui-font-family": {}
+ }
+}
+```
+
+_See the [README of `postcss-load-config`](https://github.com/postcss/postcss-load-config#usage) for more usage options._
+
+## Webpack
+
+_Webpack version 5_
+
+Add [PostCSS Loader] to your project:
+
+```bash
+npm install postcss-loader @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use [PostCSS System UI Font Family] in your Webpack configuration:
+
+```js
+module.exports = {
+ module: {
+ rules: [
+ {
+ test: /\.css$/i,
+ use: [
+ "style-loader",
+ {
+ loader: "css-loader",
+ options: { importLoaders: 1 },
+ },
+ {
+ loader: "postcss-loader",
+ options: {
+ postcssOptions: {
+ plugins: [
+ // Other plugins,
+ [
+ "@csstools/postcss-system-ui-font-family",
+ {
+ // Options
+ },
+ ],
+ ],
+ },
+ },
+ },
+ ],
+ },
+ ],
+ },
+};
+```
+
+## Next.js
+
+Read the instructions on how to [customize the PostCSS configuration in Next.js](https://nextjs.org/docs/advanced-features/customizing-postcss-config)
+
+```bash
+npm install @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use [PostCSS System UI Font Family] in your `postcss.config.json` file:
+
+```json
+{
+ "plugins": [
+ "@csstools/postcss-system-ui-font-family"
+ ]
+}
+```
+
+```json5
+{
+ "plugins": [
+ [
+ "@csstools/postcss-system-ui-font-family",
+ {
+ // Optionally add plugin options
+ }
+ ]
+ ]
+}
+```
+
+## Gulp
+
+Add [Gulp PostCSS] to your project:
+
+```bash
+npm install gulp-postcss @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use [PostCSS System UI Font Family] in your Gulpfile:
+
+```js
+const postcss = require('gulp-postcss');
+const postcssSystemUIFontFamily = require('@csstools/postcss-system-ui-font-family');
+
+gulp.task('css', function () {
+ var plugins = [
+ postcssSystemUIFontFamily(/* pluginOptions */)
+ ];
+
+ return gulp.src('./src/*.css')
+ .pipe(postcss(plugins))
+ .pipe(gulp.dest('.'));
+});
+```
+
+## Grunt
+
+Add [Grunt PostCSS] to your project:
+
+```bash
+npm install grunt-postcss @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use [PostCSS System UI Font Family] in your Gruntfile:
+
+```js
+const postcssSystemUIFontFamily = require('@csstools/postcss-system-ui-font-family');
+
+grunt.loadNpmTasks('grunt-postcss');
+
+grunt.initConfig({
+ postcss: {
+ options: {
+ processors: [
+ postcssSystemUIFontFamily(/* pluginOptions */)
+ ]
+ },
+ dist: {
+ src: '*.css'
+ }
+ }
+});
+```
+
+[Gulp PostCSS]: https://github.com/postcss/gulp-postcss
+[Grunt PostCSS]: https://github.com/nDmitry/grunt-postcss
+[PostCSS]: https://github.com/postcss/postcss
+[PostCSS CLI]: https://github.com/postcss/postcss-cli
+[PostCSS Loader]: https://github.com/postcss/postcss-loader
+[PostCSS System UI Font Family]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-system-ui-font-family
+[Next.js]: https://nextjs.org
diff --git a/plugins/postcss-system-ui-font-family/LICENSE.md b/plugins/postcss-system-ui-font-family/LICENSE.md
new file mode 100644
index 000000000..e8ae93b9f
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/LICENSE.md
@@ -0,0 +1,18 @@
+MIT No Attribution (MIT-0)
+
+Copyright © CSSTools Contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the “Software”), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/plugins/postcss-system-ui-font-family/README.md b/plugins/postcss-system-ui-font-family/README.md
new file mode 100644
index 000000000..c51f26dd4
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/README.md
@@ -0,0 +1,91 @@
+# PostCSS System UI Font Family [
][PostCSS]
+
+[
][npm-url] [
][cli-url] [
][discord]
[
][css-url] [
][css-url]
+
+```bash
+npm install @csstools/postcss-system-ui-font-family --save-dev
+```
+
+[PostCSS System UI Font Family] lets you use the `system-ui` keyword following the [CSS Fonts 4 Specification].
+
+```css
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: system-ui;
+ --font-family: system-ui;
+}
+
+/* becomes */
+
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ --font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+}
+```
+
+## Usage
+
+Add [PostCSS System UI Font Family] to your project:
+
+```bash
+npm install postcss @csstools/postcss-system-ui-font-family --save-dev
+```
+
+Use it as a [PostCSS] plugin:
+
+```js
+const postcss = require('postcss');
+const postcssSystemUIFontFamily = require('@csstools/postcss-system-ui-font-family');
+
+postcss([
+ postcssSystemUIFontFamily(/* pluginOptions */)
+]).process(YOUR_CSS /*, processOptions */);
+```
+
+[PostCSS System UI Font Family] runs in all Node environments, with special
+instructions for:
+
+- [Node](INSTALL.md#node)
+- [PostCSS CLI](INSTALL.md#postcss-cli)
+- [PostCSS Load Config](INSTALL.md#postcss-load-config)
+- [Webpack](INSTALL.md#webpack)
+- [Next.js](INSTALL.md#nextjs)
+- [Gulp](INSTALL.md#gulp)
+- [Grunt](INSTALL.md#grunt)
+
+## Options
+
+### preserve
+
+The `preserve` option determines whether the original notation
+is preserved. By default, it is preserved.
+
+```js
+postcssSystemUIFontFamily({ preserve: false })
+```
+
+```css
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: system-ui;
+ --font-family: system-ui;
+}
+
+/* becomes */
+
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: -apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ --font-family: -apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+}
+```
+
+[cli-url]: https://github.com/csstools/postcss-plugins/actions/workflows/test.yml?query=workflow/test
+[css-url]: https://cssdb.org/#system-ui-font-family
+[discord]: https://discord.gg/bUadyRwkJS
+[npm-url]: https://www.npmjs.com/package/@csstools/postcss-system-ui-font-family
+
+[PostCSS]: https://github.com/postcss/postcss
+[PostCSS System UI Font Family]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-system-ui-font-family
+[CSS Fonts 4 Specification]: https://drafts.csswg.org/css-fonts-4/#system-ui-def
diff --git a/plugins/postcss-system-ui-font-family/api-extractor.json b/plugins/postcss-system-ui-font-family/api-extractor.json
new file mode 100644
index 000000000..42058be51
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/api-extractor.json
@@ -0,0 +1,4 @@
+{
+ "$schema": "https://developer.microsoft.com/json-schemas/api-extractor/v7/api-extractor.schema.json",
+ "extends": "../../api-extractor.json"
+}
diff --git a/plugins/postcss-system-ui-font-family/dist/index.cjs b/plugins/postcss-system-ui-font-family/dist/index.cjs
new file mode 100644
index 000000000..090961a2a
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/dist/index.cjs
@@ -0,0 +1 @@
+"use strict";var e=require("@csstools/css-parser-algorithms"),s=require("@csstools/css-tokenizer");const t=/^font(?:-family)?$/i,o=["system-ui","-apple-system","Segoe UI","Roboto","Ubuntu","Cantarell","Noto Sans","sans-serif"];const n=o.join(","),creator=r=>{const i=Object.assign({preserve:!0},r);return{postcssPlugin:"postcss-system-ui-font-family",Declaration(r){if(!r.variable&&!t.test(r.prop))return;if(r.value.includes(n))return;const a=r.value,l=s.tokenize({css:a}),u=e.parseCommaSeparatedListOfComponentValues(l),c=new Map;let p=-1;e:for(let t=0;t!("system-ui"!==e||!v)||!m.has(e)).map(t=>[new e.TokenNode([s.TokenType.Ident,t,-1,-1,{value:t}])]));var m,v;if(0===f.length)return;u.splice(p,1,...f);const d=e.stringify(u);d!==a&&(r.cloneBefore({prop:r.prop,value:d}),r.remove())}}};creator.postcss=!0,module.exports=creator;
diff --git a/plugins/postcss-system-ui-font-family/dist/index.d.ts b/plugins/postcss-system-ui-font-family/dist/index.d.ts
new file mode 100644
index 000000000..03cfbc7b1
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/dist/index.d.ts
@@ -0,0 +1,12 @@
+import type { PluginCreator } from 'postcss';
+
+declare const creator: PluginCreator;
+export default creator;
+
+/** postcss-system-ui-font-family plugin options */
+export declare type pluginOptions = {
+ /** Preserve the original notation. default: true */
+ preserve?: boolean;
+};
+
+export { }
diff --git a/plugins/postcss-system-ui-font-family/dist/index.mjs b/plugins/postcss-system-ui-font-family/dist/index.mjs
new file mode 100644
index 000000000..aaab436a7
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/dist/index.mjs
@@ -0,0 +1 @@
+import{parseCommaSeparatedListOfComponentValues as e,isWhiteSpaceOrCommentNode as s,isTokenNode as t,stringify as o,TokenNode as n}from"@csstools/css-parser-algorithms";import{tokenize as r,isTokenIdent as i,TokenType as l}from"@csstools/css-tokenizer";const a=/^font(?:-family)?$/i,c=["system-ui","-apple-system","Segoe UI","Roboto","Ubuntu","Cantarell","Noto Sans","sans-serif"];const u=c.join(","),creator=p=>{const f=Object.assign({preserve:!0},p);return{postcssPlugin:"postcss-system-ui-font-family",Declaration(p){if(!p.variable&&!a.test(p.prop))return;if(p.value.includes(u))return;const m=p.value,v=r({css:m}),g=e(v),y=new Map;let h=-1;e:for(let e=0;e!("system-ui"!==e||!j)||!d.has(e)).map(e=>[new n([l.Ident,e,-1,-1,{value:e}])]));var d,j;if(0===b.length)return;g.splice(h,1,...b);const w=o(g);w!==m&&(p.cloneBefore({prop:p.prop,value:w}),p.remove())}}};creator.postcss=!0;export{creator as default};
diff --git a/plugins/postcss-system-ui-font-family/docs/README.md b/plugins/postcss-system-ui-font-family/docs/README.md
new file mode 100644
index 000000000..846d3048b
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/docs/README.md
@@ -0,0 +1,54 @@
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+[] lets you use the `system-ui` keyword following the [CSS Fonts 4 Specification].
+
+```css
+
+
+/* becomes */
+
+
+```
+
+
+
+
+
+## Options
+
+### preserve
+
+The `preserve` option determines whether the original notation
+is preserved. By default, it is preserved.
+
+```js
+({ preserve: false })
+```
+
+```css
+
+
+/* becomes */
+
+
+```
+
+
+[CSS Fonts 4 Specification]:
diff --git a/plugins/postcss-system-ui-font-family/package.json b/plugins/postcss-system-ui-font-family/package.json
new file mode 100644
index 000000000..0db0a13a7
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/package.json
@@ -0,0 +1,87 @@
+{
+ "name": "@csstools/postcss-system-ui-font-family",
+ "description": "Use the `system-ui` keyword",
+ "version": "0.0.0",
+ "contributors": [
+ {
+ "name": "Antonio Laguna",
+ "email": "antonio@laguna.es",
+ "url": "https://antonio.laguna.es"
+ },
+ {
+ "name": "Romain Menke",
+ "email": "romainmenke@gmail.com"
+ }
+ ],
+ "license": "MIT-0",
+ "funding": [
+ {
+ "type": "github",
+ "url": "https://github.com/sponsors/csstools"
+ },
+ {
+ "type": "opencollective",
+ "url": "https://opencollective.com/csstools"
+ }
+ ],
+ "engines": {
+ "node": ">=18"
+ },
+ "type": "module",
+ "main": "dist/index.cjs",
+ "module": "dist/index.mjs",
+ "exports": {
+ ".": {
+ "import": {
+ "types": "./dist/index.d.ts",
+ "default": "./dist/index.mjs"
+ },
+ "require": {
+ "default": "./dist/index.cjs"
+ }
+ }
+ },
+ "files": [
+ "CHANGELOG.md",
+ "LICENSE.md",
+ "README.md",
+ "dist"
+ ],
+ "dependencies": {
+ "@csstools/css-parser-algorithms": "^3.0.5",
+ "@csstools/css-tokenizer": "^3.0.4"
+ },
+ "peerDependencies": {
+ "postcss": "^8.4"
+ },
+ "devDependencies": {
+ "@csstools/postcss-tape": "*"
+ },
+ "scripts": {
+ "build": "rollup -c ../../rollup/default.mjs",
+ "docs": "node ../../.github/bin/generate-docs/install.mjs && node ../../.github/bin/generate-docs/readme.mjs",
+ "lint": "node ../../.github/bin/format-package-json.mjs",
+ "prepublishOnly": "npm run build && npm run test",
+ "test": "node --test",
+ "test:rewrite-expects": "REWRITE_EXPECTS=true node --test"
+ },
+ "homepage": "https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-system-ui-font-family#readme",
+ "repository": {
+ "type": "git",
+ "url": "git+https://github.com/csstools/postcss-plugins.git",
+ "directory": "plugins/postcss-system-ui-font-family"
+ },
+ "bugs": "https://github.com/csstools/postcss-plugins/issues",
+ "keywords": [
+ "postcss-plugin"
+ ],
+ "csstools": {
+ "cssdbId": "system-ui-font-family",
+ "exportName": "postcssSystemUIFontFamily",
+ "humanReadableName": "PostCSS System UI Font Family",
+ "specUrl": "https://drafts.csswg.org/css-fonts-4/#system-ui-def"
+ },
+ "volta": {
+ "extends": "../../package.json"
+ }
+}
diff --git a/plugins/postcss-system-ui-font-family/src/index.ts b/plugins/postcss-system-ui-font-family/src/index.ts
new file mode 100644
index 000000000..976bcbe63
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/src/index.ts
@@ -0,0 +1,130 @@
+import type { ComponentValue} from '@csstools/css-parser-algorithms';
+import { isTokenNode, isWhiteSpaceOrCommentNode, parseCommaSeparatedListOfComponentValues, stringify, TokenNode } from '@csstools/css-parser-algorithms';
+import { isTokenIdent, tokenize, TokenType } from '@csstools/css-tokenizer';
+import type { PluginCreator } from 'postcss';
+
+/** postcss-system-ui-font-family plugin options */
+export type pluginOptions = {
+ /** Preserve the original notation. default: true */
+ preserve?: boolean,
+};
+
+const PROPERTY_REGEX = /^font(?:-family)?$/i;
+
+const systemUiFamilies = [
+ 'system-ui',
+ /* macOS 10.11-10.12 */ '-apple-system',
+ /* Windows 6+ */ 'Segoe UI',
+ /* Android 4+ */ 'Roboto',
+ /* Ubuntu 10.10+ */ 'Ubuntu',
+ /* Gnome 3+ */ 'Cantarell',
+ /* KDE Plasma 5+ */ 'Noto Sans',
+ /* fallback */ 'sans-serif',
+];
+
+function systemUIFamiliesAsComponentValues(existingSet: Map, preserve: boolean): Array> {
+ return systemUiFamilies.filter((family) => {
+ if (family === 'system-ui' && preserve) {
+ return true;
+ }
+
+ return !existingSet.has(family)
+ }).map((family) => {
+ return [
+ new TokenNode([TokenType.Ident, family, -1, -1, { value: family }]),
+ ]
+ });
+}
+
+const systemUIFamiliesList = systemUiFamilies.join(',');
+
+const creator: PluginCreator = (opts?: pluginOptions) => {
+ const options: pluginOptions = Object.assign(
+ {
+ preserve: true,
+ },
+ opts,
+ );
+
+ return {
+ postcssPlugin: 'postcss-system-ui-font-family',
+ Declaration(decl): void {
+ if (!decl.variable && !PROPERTY_REGEX.test(decl.prop)) {
+ return;
+ }
+
+ if (decl.value.includes(systemUIFamiliesList)) {
+ return;
+ }
+
+ const originalValue = decl.value;
+
+ const tokens = tokenize({ css: originalValue });
+ const componentValuesList = parseCommaSeparatedListOfComponentValues(tokens)
+
+ const foundFamilies = new Map()
+ let symstemUI_Index = -1;
+
+ TOP_LEVEL:
+ for (let i = 0; i < componentValuesList.length; i++) {
+ const componentValues = componentValuesList[i];
+
+ const fontFamilyParts = [];
+
+ for (let j = 0; j < componentValues.length; j++) {
+ const componentValue = componentValues[j];
+ if (isWhiteSpaceOrCommentNode(componentValue)) {
+ continue;
+ }
+
+ if (!isTokenNode(componentValue)) {
+ continue TOP_LEVEL;
+ }
+
+ const token = componentValue.value;
+ if (!isTokenIdent(token)) {
+ continue TOP_LEVEL;
+ }
+
+ if (token[4].value.toLowerCase() === 'system-ui') {
+ symstemUI_Index = i;
+ }
+
+ fontFamilyParts.push(token[4].value);
+ }
+
+ const fontFamily = fontFamilyParts.join(' ');
+ if (systemUiFamilies.includes(fontFamily)) {
+ foundFamilies.set(fontFamily, i)
+ }
+ }
+
+ if (symstemUI_Index === -1) {
+ return;
+ }
+
+ const replacements = systemUIFamiliesAsComponentValues(foundFamilies, !!options.preserve);
+ if (replacements.length === 0) {
+ return;
+ }
+
+ componentValuesList.splice(symstemUI_Index, 1, ...replacements);
+
+ const modified = stringify(componentValuesList);
+ if (modified === originalValue) {
+ return;
+ }
+
+ decl.cloneBefore({
+ prop: decl.prop,
+ value: modified,
+ });
+
+ decl.remove();
+ },
+ };
+};
+
+creator.postcss = true;
+
+export default creator;
diff --git a/plugins/postcss-system-ui-font-family/test/_import.mjs b/plugins/postcss-system-ui-font-family/test/_import.mjs
new file mode 100644
index 000000000..2dba7d5ec
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/_import.mjs
@@ -0,0 +1,10 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import plugin from '@csstools/postcss-system-ui-font-family';
+
+test('import', () => {
+ plugin();
+ assert.ok(plugin.postcss, 'should have "postcss flag"');
+ assert.equal(typeof plugin, 'function', 'should return a function');
+});
+
diff --git a/plugins/postcss-system-ui-font-family/test/_require.cjs b/plugins/postcss-system-ui-font-family/test/_require.cjs
new file mode 100644
index 000000000..6ac2f679c
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/_require.cjs
@@ -0,0 +1,9 @@
+const assert = require('node:assert/strict');
+const test = require('node:test');
+const plugin = require('@csstools/postcss-system-ui-font-family');
+
+test('require', () => {
+ plugin();
+ assert.ok(plugin.postcss, 'should have "postcss flag"');
+ assert.equal(typeof plugin, 'function', 'should return a function');
+});
diff --git a/plugins/postcss-system-ui-font-family/test/_tape.mjs b/plugins/postcss-system-ui-font-family/test/_tape.mjs
new file mode 100644
index 000000000..5b56ff664
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/_tape.mjs
@@ -0,0 +1,17 @@
+import { postcssTape } from '@csstools/postcss-tape';
+import plugin from '@csstools/postcss-system-ui-font-family';
+
+postcssTape(plugin)({
+ basic: {
+ message: 'supports basic usage',
+ },
+ 'examples/example': {
+ message: 'minimal example',
+ },
+ 'examples/example:preserve-false': {
+ message: 'minimal example',
+ options: {
+ preserve: false,
+ },
+ },
+});
diff --git a/plugins/postcss-system-ui-font-family/test/basic.css b/plugins/postcss-system-ui-font-family/test/basic.css
new file mode 100644
index 000000000..e1aabc468
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/basic.css
@@ -0,0 +1,27 @@
+.foo {
+ font: italic bold 12px/30px system-ui, Helvetica Neue, sans-serif;
+ font: italic bold 12px/30px system-ui, sans-serif;
+ font: italic bold 12px/30px sans-serif;
+ font-family: system-ui, Helvetica Neue, sans-serif;
+ font-family: system-ui, sans-serif;
+ font-family: system-ui;
+ font-family: "Droid Sans", system-ui, sans-serif;
+ --font-family: system-ui;
+}
+
+.ignore {
+ font-family: sans-serif;
+}
+
+.ignore {
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ font-family: system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans, sans-serif;
+}
+
+.tab-between-idents {
+ font-family: system-ui, Segoe UI;
+}
+
+.comment-between-idents {
+ font-family: system-ui, Segoe /* foo */UI;
+}
diff --git a/plugins/postcss-system-ui-font-family/test/basic.expect.css b/plugins/postcss-system-ui-font-family/test/basic.expect.css
new file mode 100644
index 000000000..f04ac87b5
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/basic.expect.css
@@ -0,0 +1,27 @@
+.foo {
+ font: italic bold 12px/30px system-ui, Helvetica Neue, sans-serif;
+ font: italic bold 12px/30px system-ui, sans-serif;
+ font: italic bold 12px/30px sans-serif;
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans, Helvetica Neue, sans-serif;
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans, sans-serif;
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ font-family: "Droid Sans",system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans, sans-serif;
+ --font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+}
+
+.ignore {
+ font-family: sans-serif;
+}
+
+.ignore {
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ font-family: system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans, sans-serif;
+}
+
+.tab-between-idents {
+ font-family: system-ui,-apple-system,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif, Segoe UI;
+}
+
+.comment-between-idents {
+ font-family: system-ui,-apple-system,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif, Segoe UI;
+}
diff --git a/plugins/postcss-system-ui-font-family/test/examples/example.css b/plugins/postcss-system-ui-font-family/test/examples/example.css
new file mode 100644
index 000000000..6bea38d75
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/examples/example.css
@@ -0,0 +1,5 @@
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: system-ui;
+ --font-family: system-ui;
+}
diff --git a/plugins/postcss-system-ui-font-family/test/examples/example.expect.css b/plugins/postcss-system-ui-font-family/test/examples/example.expect.css
new file mode 100644
index 000000000..3d70d1092
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/examples/example.expect.css
@@ -0,0 +1,5 @@
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ --font-family: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+}
diff --git a/plugins/postcss-system-ui-font-family/test/examples/example.preserve-false.expect.css b/plugins/postcss-system-ui-font-family/test/examples/example.preserve-false.expect.css
new file mode 100644
index 000000000..f4a483f7a
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/test/examples/example.preserve-false.expect.css
@@ -0,0 +1,5 @@
+.foo {
+ font: italic bold 12px/30px system-ui;
+ font-family: -apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+ --font-family: -apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
+}
diff --git a/plugins/postcss-system-ui-font-family/tsconfig.json b/plugins/postcss-system-ui-font-family/tsconfig.json
new file mode 100644
index 000000000..500af6d26
--- /dev/null
+++ b/plugins/postcss-system-ui-font-family/tsconfig.json
@@ -0,0 +1,10 @@
+{
+ "extends": "../../tsconfig.json",
+ "compilerOptions": {
+ "outDir": "dist",
+ "declarationDir": ".",
+ "strict": true
+ },
+ "include": ["./src/**/*"],
+ "exclude": ["dist"]
+}
diff --git a/rollup/configs/externals.mjs b/rollup/configs/externals.mjs
index 03066bdc5..352c46f99 100644
--- a/rollup/configs/externals.mjs
+++ b/rollup/configs/externals.mjs
@@ -61,6 +61,7 @@ export const externalsForCLI = [
'@csstools/postcss-scope-pseudo-class',
'@csstools/postcss-sign-functions',
'@csstools/postcss-stepped-value-functions',
+ '@csstools/postcss-system-ui-font-family',
'@csstools/postcss-text-decoration-shorthand',
'@csstools/postcss-trigonometric-functions',
'@csstools/postcss-unset-value',
@@ -169,6 +170,7 @@ export const externalsForPlugin = [
'@csstools/postcss-scope-pseudo-class',
'@csstools/postcss-sign-functions',
'@csstools/postcss-stepped-value-functions',
+ '@csstools/postcss-system-ui-font-family',
'@csstools/postcss-text-decoration-shorthand',
'@csstools/postcss-trigonometric-functions',
'@csstools/postcss-unset-value',