Add * variant for targeting direct children (#12551)

* add `*` as child variant

* add `*` as allowed variant character

* update test to reflect Lightning CSS output

* add `childVariant` test

* Update changelog

---------

Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
Co-authored-by: Gregor Kaczmarczyk <github@aggreggator.de>

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `forced-colors` variant ([#11694](https://github.com/tailwindlabs/tailwindcss/pull/11694))
 - Add `appearance-auto` utility ([#12404](https://github.com/tailwindlabs/tailwindcss/pull/12404))
 - Add logical property values for `float` and `clear` utilities ([#12480](https://github.com/tailwindlabs/tailwindcss/pull/12480))
+- Add `*` variant for targeting direct children ([#12551](https://github.com/tailwindlabs/tailwindcss/pull/12551))
 - [Oxide] New Rust template parsing engine ([#10252](https://github.com/tailwindlabs/tailwindcss/pull/10252))
 - [Oxide] Support `@import "tailwindcss"` using top-level `index.css` file ([#11205](https://github.com/tailwindlabs/tailwindcss/pull/11205), ([#11260](https://github.com/tailwindlabs/tailwindcss/pull/11260)))
 - [Oxide] Use `lightningcss` for nesting and vendor prefixes in PostCSS plugin ([#10399](https://github.com/tailwindlabs/tailwindcss/pull/10399))

oxide/crates/core/src/parser.rs

@@ -412,7 +412,7 @@ impl<'a> Extractor<'a> {
             }
 
             // Allowed first characters.
-            b'@' | b'!' | b'-' | b'<' | b'>' | b'0'..=b'9' | b'a'..=b'z' | b'A'..=b'Z' => {
+            b'@' | b'!' | b'-' | b'<' | b'>' | b'0'..=b'9' | b'a'..=b'z' | b'A'..=b'Z' | b'*' => {
                 // TODO: A bunch of characters that we currently support but maybe we only want it behind
                 // a flag. E.g.: '<sm'
                 // | '$' | '^' | '_'
@@ -473,7 +473,7 @@ impl<'a> Extractor<'a> {
             b'%' => return ParseAction::Skip,
 
             // < and > can only be part of a variant and only be the first or last character
-            b'<' | b'>' => {
+            b'<' | b'>' | b'*' => {
                 // Can only be the first or last character
                 // E.g.:
                 // - <sm:underline
@@ -797,6 +797,15 @@ mod test {
         assert_eq!(candidates, vec!["hover:underline"]);
     }
 
+    #[test]
+    fn it_can_parse_start_variants() {
+        let candidates = run("*:underline", false);
+        assert_eq!(candidates, vec!["*:underline"]);
+
+        let candidates = run("hover:*:underline", false);
+        assert_eq!(candidates, vec!["hover:*:underline"]);
+    }
+
     #[test]
     fn it_can_parse_simple_candidates_with_stacked_variants() {
         let candidates = run("focus:hover:underline", false);

src/corePlugins.js

@@ -24,6 +24,9 @@ import { normalize } from './util/dataTypes'
 import { INTERNAL_FEATURES } from './lib/setupContextUtils'
 
 export let variantPlugins = {
+  childVariant: ({ addVariant }) => {
+    addVariant('*', '& > *')
+  },
   pseudoElementVariants: ({ addVariant }) => {
     addVariant('first-letter', '&::first-letter')
     addVariant('first-line', '&::first-line')

src/lib/setupContextUtils.js

@@ -746,6 +746,7 @@ function resolvePlugins(context, root) {
   // TODO: This is a workaround for backwards compatibility, since custom variants
   // were historically sorted before screen/stackable variants.
   let beforeVariants = [
+    variantPlugins['childVariant'],
     variantPlugins['pseudoElementVariants'],
     variantPlugins['pseudoClassVariants'],
     variantPlugins['hasVariants'],

tests/plugins/variants/__snapshots__/childVariant.test.js.snap

@@ -0,0 +1,9 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`should test the 'childVariant' plugin 1`] = `
+"
+.\\*\\:flex > * {
+  display: flex;
+}
+"
+`;

tests/plugins/variants/childVariant.test.js

@@ -0,0 +1,3 @@
+import { quickVariantPluginTest } from '../../util/run'
+
+quickVariantPluginTest('childVariant').toMatchSnapshot()

tests/variants.test.js

@@ -1167,3 +1167,36 @@ test('stacking dark and rtl variants with pseudo elements', async () => {
     }
   `)
 })
+
+test('* is matched by the parser as the children variant', async () => {
+  let config = {
+    content: [
+      {
+        raw: html`
+          <div class="*:italic" />
+          <div class="*:hover:italic" />
+          <div class="hover:*:italic" />
+          <div class="data-[slot=label]:*:hover:italic" />
+          <div class="[&_p]:*:hover:italic" />
+        `,
+      },
+    ],
+    corePlugins: { preflight: false },
+  }
+
+  let input = css`
+    @tailwind utilities;
+  `
+
+  let result = await run(input, config)
+
+  expect(result.css).toMatchFormattedCss(css`
+    .\*\:italic > *,
+    .\*\:hover\:italic:hover > *,
+    .hover\:\*\:italic > :hover,
+    .data-\[slot\=label\]\:\*\:hover\:italic:hover > [data-slot='label'],
+    .\[\&_p\]\:\*\:hover\:italic:hover > * p {
+      font-style: italic;
+    }
+  `)
+})