feat: add support for @starting-style at-rule

.changeset/ten-pens-refuse.md

@@ -0,0 +1,6 @@
+---
+'@compiled/babel-plugin': minor
+'@compiled/css': minor
+---
+
+Added support for the @starting-style at-rule.

package.json

@@ -88,6 +88,7 @@
     "@typescript-eslint/parser": "^6.21.0",
     "@typescript-eslint/utils": "^6.21.0",
     "babel-loader": "^9.1.2",
+    "csstype": "^3.1.3",
     "eslint": "^8.57.1",
     "eslint-plugin-import": "^2.31.0",
     "eslint-plugin-json-files": "^2.2.0",

packages/babel-plugin/src/css-map/__tests__/at-rules-and-selectors.test.ts

@@ -277,6 +277,35 @@ describe('css map advanced functionality (at rules, selectors object)', () => {
     }
   });
 
+  // TODO: add a unit test for the `@starting-style` at-rule when it is NOT nested. This is currently not working as
+  // Compiled only supports processing at-rules that have two "halves", e.g. `@media screen`
+  // When nested, the at-rule is not processed like an at-rule - it is processed like a CSS selector.
+  it('should parse the @starting-style at-rule when nested', () => {
+    const actual = transform(`
+        import { cssMap } from '@compiled/react';
+
+        const styles = cssMap({
+          success: {
+            color: 'red',
+            '@media (prefers-reduced-motion: no-preference)': {
+              '@starting-style': {
+                color: 'blue'
+              },
+            },
+          },
+        });
+
+        ${EXAMPLE_USAGE}
+      `);
+
+    expect(actual).toIncludeMultiple([
+      '._syaz5scu{color:red}',
+      '@media (prefers-reduced-motion:no-preference){@starting-style{._ff1013q2{color:blue}}}',
+
+      'const styles={success:"_syaz5scu _ff1013q2"}',
+    ]);
+  });
+
   it('should error if more than one selectors key passed', () => {
     expect(() => {
       transform(`

packages/babel-plugin/src/utils/css-map.ts

@@ -20,7 +20,9 @@ const atRules: Record<AtRules, boolean> = {
   '@namespace': true,
   '@page': true,
   '@property': true,
+  '@scope': true,
   '@scroll-timeline': true,
+  '@starting-style': true,
   '@supports': true,
   '@viewport': true,
 };

packages/css/src/plugins/__tests__/atomicify-rules.test.ts

@@ -384,10 +384,14 @@ describe('atomicify rules', () => {
       @supports selector(h2 > p) {
         color: pink;
       }
+
+      @starting-style {
+        color: green;
+      }
     `;
 
     expect(actual).toMatchInlineSnapshot(
-      `"@container (width > 300px){._eq985scu h2{color:red}}@when font-tech(color-COLRv1) and font-tech(variations){@font-face{font-family:test;src:url(test.woff2)}}@else font-tech(color-SVG){@font-face{font-family:test;src:url(test2.woff2)}}@else{@font-face{font-family:test;src:url(test3.woff2)}}@-moz-document url-prefix(){._qral13q2{color:blue}}@layer state{._8tgm6x50{background-color:brown}}@media (min-width: 30rem){._hi7c1ule{display:block}._1l5zgktf{font-size:20px}}@supports selector(h2 > p){._1ll732ev{color:pink}}"`
+      `"@container (width > 300px){._eq985scu h2{color:red}}@when font-tech(color-COLRv1) and font-tech(variations){@font-face{font-family:test;src:url(test.woff2)}}@else font-tech(color-SVG){@font-face{font-family:test;src:url(test2.woff2)}}@else{@font-face{font-family:test;src:url(test3.woff2)}}@-moz-document url-prefix(){._qral13q2{color:blue}}@layer state{._8tgm6x50{background-color:brown}}@media (min-width: 30rem){._hi7c1ule{display:block}._1l5zgktf{font-size:20px}}@supports selector(h2 > p){._1ll732ev{color:pink}}@starting-style{._p77hbf54{color:green}}"`
     );
   });
 

packages/css/src/plugins/atomicify-rules.ts

@@ -188,6 +188,7 @@ const canAtomicifyAtRule = (node: AtRule): boolean => {
     'else',
     'layer',
     'media',
+    'starting-style',
     'supports',
     'when',
   ];

packages/css/src/transform.ts

@@ -42,7 +42,17 @@ export const transformCss = (
       discardEmptyRules(),
       parentOrphanedPseudos(),
       nested({
-        bubble: ['container', '-moz-document', 'layer', 'else', 'when'],
+        bubble: [
+          'container',
+          '-moz-document',
+          'layer',
+          'else',
+          'when',
+          // postcss-nested bubbles `starting-style` by default in versions from 6.0.2 onwards:
+          // https://github.com/postcss/postcss-nested?tab=readme-ov-file#bubble
+          // When we upgrade to a version that includes this change, we can remove this from the list.
+          'starting-style',
+        ],
         unwrap: ['color-profile', 'counter-style', 'font-palette-values', 'page', 'property'],
       }),
       ...normalizeCSS(opts),

yarn.lock

@@ -7600,10 +7600,10 @@ cssstyle@^2.3.0:
   dependencies:
     cssom "~0.3.6"
 
-csstype@^3.0.2, csstype@^3.1.2:
-  version "3.1.2"
-  resolved "https://registry.yarnpkg.com/csstype/-/csstype-3.1.2.tgz#1d4bf9d572f11c14031f0436e1c10bc1f571f50b"
-  integrity sha512-I7K1Uu0MBPzaFKg4nI5Q7Vs2t+3gWWW648spaF+Rg7pI9ds18Ugn+lvg4SHczUdKlHI5LWBXyqfS8+DufyBsgQ==
+csstype@^3.0.2, csstype@^3.1.2, csstype@^3.1.3:
+  version "3.1.3"
+  resolved "https://registry.yarnpkg.com/csstype/-/csstype-3.1.3.tgz#d80ff294d114fb0e6ac500fbf85b60137d7eff81"
+  integrity sha512-M1uQkMl8rQK/szD0LNhtqxIPLpimGm8sOBwU7lLnCpSbTyY3yeU1Vc7l4KT5zT4s/yOxHH5O7tIuuLOCnLADRw==
 
 csv-generate@^3.4.3:
   version "3.4.3"