Migrate arbitrary values to bare values (#14669)

This PR adds a codemod that can convert arbitrary values to the cleaner
bare values if we can.

For example, some classes use arbitrary values such as `col-start-[16]`,
but in v4 we have bare values for some plugins that don't really need to
adhere to your design system.

In this case, we can convert `col-start-[16]` to just `col-start-16`.

Another use case is for utilities that use fractions. For example the
`aspect-*` plugin.

A custom aspect ratio such as `aspect-[16/9]` can be converted to
`aspect-16/9`.

There are some rules attached to this migration:

1. We can only migrate arbitrary values that is a single positive
integer, or an arbitrary value that is a fraction where the numerator
and denominator are both positive integers.
2. We make sure that some CSS can be generated once its converted to a
bare value.

Author: RobinMalfait

Diff for: CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - _Upgrade (experimental)_: Migrate `@media screen(…)` when running codemods ([#14603](https://github.com/tailwindlabs/tailwindcss/pull/14603))
 - _Upgrade (experimental)_: Inject `@config "…"` when a `tailwind.config.{js,ts,…}` is detected ([#14635](https://github.com/tailwindlabs/tailwindcss/pull/14635))
 - _Upgrade (experimental)_: Migrate `aria-*`, `data-*`, and `supports-*` variants from arbitrary values to bare values ([#14644](https://github.com/tailwindlabs/tailwindcss/pull/14644))
+- _Upgrade (experimental)_: Migrate arbitrary values to bare values ([#14669](https://github.com/tailwindlabs/tailwindcss/pull/14669))
 
 ### Fixed
 

Diff for: packages/@tailwindcss-upgrade/src/template/codemods/arbitrary-value-to-bare-value.test.ts

@@ -3,6 +3,24 @@ import { expect, test } from 'vitest'
 import { arbitraryValueToBareValue } from './arbitrary-value-to-bare-value'
 
 test.each([
+  ['aspect-[12/34]', 'aspect-12/34'],
+  ['aspect-[1.2/34]', 'aspect-[1.2/34]'],
+  ['col-start-[7]', 'col-start-7'],
+  ['flex-[2]', 'flex-2'], // `flex` is implemented as static and functional utilities
+
+  // Only 50-200% (inclusive) are valid:
+  // https://developer.mozilla.org/en-US/docs/Web/CSS/font-stretch#percentage
+  ['font-stretch-[50%]', 'font-stretch-50%'],
+  ['font-stretch-[50.5%]', 'font-stretch-[50.5%]'],
+  ['font-stretch-[201%]', 'font-stretch-[201%]'],
+  ['font-stretch-[49%]', 'font-stretch-[49%]'],
+  // Should stay as-is
+  ['font-stretch-[1/2]', 'font-stretch-[1/2]'],
+
+  // This test in itself is a bit flawed because `text-[1/2]` currently
+  // generates something. Converting it to `text-1/2` doesn't produce anything.
+  ['text-[1/2]', 'text-[1/2]'],
+
   ['data-[selected]:flex', 'data-selected:flex'],
   ['data-[foo=bar]:flex', 'data-[foo=bar]:flex'],
 
@@ -22,6 +40,10 @@ test.each([
   ['group-has-aria-[selected]:flex', 'group-has-aria-[selected]:flex'],
 
   ['max-lg:hover:data-[selected]:flex!', 'max-lg:hover:data-selected:flex!'],
+  [
+    'data-[selected]:aria-[selected="true"]:aspect-[12/34]',
+    'data-selected:aria-selected:aspect-12/34',
+  ],
 ])('%s => %s', async (candidate, result) => {
   let designSystem = await __unstable__loadDesignSystem('@import "tailwindcss";', {
     base: __dirname,

Diff for: packages/@tailwindcss-upgrade/src/template/codemods/arbitrary-value-to-bare-value.ts

@@ -1,6 +1,7 @@
 import type { Config } from 'tailwindcss'
 import { parseCandidate, type Candidate, type Variant } from '../../../../tailwindcss/src/candidate'
 import type { DesignSystem } from '../../../../tailwindcss/src/design-system'
+import { isPositiveInteger } from '../../../../tailwindcss/src/utils/infer-data-type'
 import { segment } from '../../../../tailwindcss/src/utils/segment'
 import { printCandidate } from '../candidates'
 
@@ -12,6 +13,74 @@ export function arbitraryValueToBareValue(
   for (let candidate of parseCandidate(rawCandidate, designSystem)) {
     let clone = structuredClone(candidate)
     let changed = false
+
+    // Convert font-stretch-* utilities
+    if (
+      clone.kind === 'functional' &&
+      clone.value?.kind === 'arbitrary' &&
+      clone.value.dataType === null &&
+      clone.root === 'font-stretch'
+    ) {
+      if (clone.value.value.endsWith('%') && isPositiveInteger(clone.value.value.slice(0, -1))) {
+        let percentage = parseInt(clone.value.value)
+        if (percentage >= 50 && percentage <= 200) {
+          changed = true
+          clone.value = {
+            kind: 'named',
+            value: clone.value.value,
+            fraction: null,
+          }
+        }
+      }
+    }
+
+    // Convert arbitrary values with positive integers to bare values
+    // Convert arbitrary values with fractions to bare values
+    else if (
+      clone.kind === 'functional' &&
+      clone.value?.kind === 'arbitrary' &&
+      clone.value.dataType === null
+    ) {
+      let parts = segment(clone.value.value, '/')
+      if (parts.every((part) => isPositiveInteger(part))) {
+        changed = true
+
+        let currentValue = clone.value
+        let currentModifier = clone.modifier
+
+        // E.g.: `col-start-[12]`
+        //                   ^^
+        if (parts.length === 1) {
+          clone.value = {
+            kind: 'named',
+            value: clone.value.value,
+            fraction: null,
+          }
+        }
+
+        // E.g.: `aspect-[12/34]`
+        //                ^^ ^^
+        else {
+          clone.value = {
+            kind: 'named',
+            value: parts[0],
+            fraction: clone.value.value,
+          }
+          clone.modifier = {
+            kind: 'named',
+            value: parts[1],
+          }
+        }
+
+        // Double check that the new value compiles correctly
+        if (designSystem.compileAstNodes(clone).length === 0) {
+          clone.value = currentValue
+          clone.modifier = currentModifier
+          changed = false
+        }
+      }
+    }
+
     for (let variant of variants(clone)) {
       // Convert `data-[selected]` to `data-selected`
       if (