Migrate [&>*] to * variant, and [&_*] to ** variant (#15022)

This PR adds a migration to convert the `[&>*]` variant to the `*`
variant. Additionally this PR also converts the `[&_*]` variant to the
`**` variant.

We use this variant in Catalyst for example, and now that the
specificity is the same as `*`, we can use the more modern syntax
instead.


# Test plan:

Running this on Catalyst results in a diff like:
<img width="615" alt="image"
src="https://github.com/user-attachments/assets/f384885e-cae1-4b6b-80ab-85f76fa89a33">

<img width="833" alt="image"
src="https://github.com/user-attachments/assets/8a185e1d-0f1b-4fe6-9e06-ca7597534398">


Note: the swapped order of variants is another codemod at work

---------

Co-authored-by: Adam Wathan <adam.wathan@gmail.com>

Author: RobinMalfait

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Reintroduce `max-w-screen-*` utilities that read from the `--breakpoint` namespace as deprecated utilities ([#15013](https://github.com/tailwindlabs/tailwindcss/pull/15013))
 - Support using CSS variables as arbitrary values without `var(…)` by using parentheses instead of square brackets (e.g. `bg-(--my-color)`) ([#15020](https://github.com/tailwindlabs/tailwindcss/pull/15020))
+- _Upgrade (experimental)_: Migrate `[&>*]` to the `*` variant ([#15022](https://github.com/tailwindlabs/tailwindcss/pull/15022))
+- _Upgrade (experimental)_: Migrate `[&_*]` to the `**` variant ([#15022](https://github.com/tailwindlabs/tailwindcss/pull/15022))
 
 ### Fixed
 

packages/@tailwindcss-upgrade/src/template/codemods/modernize-arbitrary-values.test.ts

@@ -9,8 +9,11 @@ test.each([
   ['[[data-visible]&]:flex', 'data-visible:flex'],
   ['[&>[data-visible]]:flex', '*:data-visible:flex'],
   ['[&_>_[data-visible]]:flex', '*:data-visible:flex'],
+  ['[&>*]:flex', '*:flex'],
+  ['[&_>_*]:flex', '*:flex'],
 
   ['[&_[data-visible]]:flex', '**:data-visible:flex'],
+  ['[&_*]:flex', '**:flex'],
 
   ['[&:first-child]:flex', 'first:flex'],
   ['[&:not(:first-child)]:flex', 'not-first:flex'],

packages/@tailwindcss-upgrade/src/template/codemods/modernize-arbitrary-values.ts

@@ -28,8 +28,41 @@ export function modernizeArbitraryValues(
 
       let prefixedVariant: Variant | null = null
 
-      // Track whether we need to add a `**:` variant
-      let addStarStarVariant = false
+      // `[&>*]` can be replaced with `*`
+      if (
+        // Only top-level, so `has-[&>*]` is not supported
+        parent === null &&
+        // [&_>_*]:flex
+        //  ^ ^ ^
+        ast.nodes[0].length === 3 &&
+        ast.nodes[0].nodes[0].type === 'nesting' &&
+        ast.nodes[0].nodes[0].value === '&' &&
+        ast.nodes[0].nodes[1].type === 'combinator' &&
+        ast.nodes[0].nodes[1].value === '>' &&
+        ast.nodes[0].nodes[2].type === 'universal'
+      ) {
+        changed = true
+        Object.assign(variant, designSystem.parseVariant('*'))
+        continue
+      }
+
+      // `[&_*]` can be replaced with `**`
+      if (
+        // Only top-level, so `has-[&_*]` is not supported
+        parent === null &&
+        // [&_*]:flex
+        //  ^ ^
+        ast.nodes[0].length === 3 &&
+        ast.nodes[0].nodes[0].type === 'nesting' &&
+        ast.nodes[0].nodes[0].value === '&' &&
+        ast.nodes[0].nodes[1].type === 'combinator' &&
+        ast.nodes[0].nodes[1].value === ' ' &&
+        ast.nodes[0].nodes[2].type === 'universal'
+      ) {
+        changed = true
+        Object.assign(variant, designSystem.parseVariant('**'))
+        continue
+      }
 
       // Handling a child combinator. E.g.: `[&>[data-visible]]` => `*:data-visible`
       if (