Migrate legacy classes to the v4 alternative (#14643)

This PR adds a mapping from legacy classes to new classes. For example,
the `flex-shrink-0` is still used in our projects, but is deprecated in
v3.

The migration does a tiny bit of parsing because we can't rely on
`designSystem.parseCandidate(…)` because this requires the utility to be
defined which is not the case for legacy classes.

This migration runs _after_ the migration where we handle prefixes, so
we don't have to worry about that. We do have to worry about the `!`
location, because the `important` migration also relies on the
`designSystem`.

| Old                 | New                    |
| ------------------- | ---------------------- |
| `overflow-clip`     | `text-clip`            |
| `overflow-ellipsis` | `text-ellipsis`        |
| `flex-grow-0`       | `grow-0`               |
| `flex-shrink-0`     | `shrink-0`             |
| `decoration-clone`  | `box-decoration-clone` |
| `decoration-slice`  | `box-decoration-slice` |

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Support `keyframes` in JS config file themes ([#14594](https://github.com/tailwindlabs/tailwindcss/pull/14594))
 - _Upgrade (experimental)_: Migrate v3 PostCSS setups to v4 in some cases ([#14612](https://github.com/tailwindlabs/tailwindcss/pull/14612))
 - _Upgrade (experimental)_: The upgrade tool now automatically discovers your JavaScript config ([#14597](https://github.com/tailwindlabs/tailwindcss/pull/14597))
+- _Upgrade (experimental)_: Migrate legacy classes to the v4 alternative ([#14643](https://github.com/tailwindlabs/tailwindcss/pull/14643))
 
 ### Fixed
 

packages/@tailwindcss-upgrade/src/template/candidates.ts

@@ -5,9 +5,10 @@ import type { DesignSystem } from '../../../tailwindcss/src/design-system'
 
 export async function extractRawCandidates(
   content: string,
+  extension: string = 'html',
 ): Promise<{ rawCandidate: string; start: number; end: number }[]> {
   let scanner = new Scanner({})
-  let result = scanner.getCandidatesWithPositions({ content, extension: 'html' })
+  let result = scanner.getCandidatesWithPositions({ content, extension })
 
   let candidates: { rawCandidate: string; start: number; end: number }[] = []
   for (let { candidate: rawCandidate, position: start } of result) {

packages/@tailwindcss-upgrade/src/template/codemods/simple-legacy-classes.test.ts

@@ -0,0 +1,22 @@
+import { __unstable__loadDesignSystem } from '@tailwindcss/node'
+import { expect, test } from 'vitest'
+import { simpleLegacyClasses } from './simple-legacy-classes'
+
+test.each([
+  ['overflow-clip', 'text-clip'],
+  ['overflow-ellipsis', 'text-ellipsis'],
+  ['flex-grow-0', 'grow-0'],
+  ['flex-shrink-0', 'shrink-0'],
+  ['decoration-clone', 'box-decoration-clone'],
+  ['decoration-slice', 'box-decoration-slice'],
+
+  ['max-lg:hover:decoration-slice', 'max-lg:hover:box-decoration-slice'],
+  ['max-lg:hover:decoration-slice!', 'max-lg:hover:box-decoration-slice!'],
+  ['max-lg:hover:!decoration-slice', 'max-lg:hover:box-decoration-slice!'],
+])('%s => %s', async (candidate, result) => {
+  let designSystem = await __unstable__loadDesignSystem('@import "tailwindcss";', {
+    base: __dirname,
+  })
+
+  expect(simpleLegacyClasses(designSystem, {}, candidate)).toEqual(result)
+})

packages/@tailwindcss-upgrade/src/template/codemods/simple-legacy-classes.ts

@@ -0,0 +1,41 @@
+import type { Config } from 'tailwindcss'
+import type { DesignSystem } from '../../../../tailwindcss/src/design-system'
+import { printCandidate } from '../candidates'
+
+// Classes that used to exist in Tailwind CSS v3, but do not exist in Tailwind
+// CSS v4 anymore.
+const LEGACY_CLASS_MAP = {
+  'overflow-clip': 'text-clip',
+  'overflow-ellipsis': 'text-ellipsis',
+  'flex-grow-0': 'grow-0',
+  'flex-shrink-0': 'shrink-0',
+  'decoration-clone': 'box-decoration-clone',
+  'decoration-slice': 'box-decoration-slice',
+}
+
+const SEEDED = new WeakSet<DesignSystem>()
+
+export function simpleLegacyClasses(
+  designSystem: DesignSystem,
+  _userConfig: Config,
+  rawCandidate: string,
+): string {
+  // Prepare design system with the legacy classes
+  if (!SEEDED.has(designSystem)) {
+    for (let old in LEGACY_CLASS_MAP) {
+      designSystem.utilities.static(old, () => [])
+    }
+    SEEDED.add(designSystem)
+  }
+
+  for (let candidate of designSystem.parseCandidate(rawCandidate)) {
+    if (candidate.kind === 'static' && Object.hasOwn(LEGACY_CLASS_MAP, candidate.root)) {
+      return printCandidate(designSystem, {
+        ...candidate,
+        root: LEGACY_CLASS_MAP[candidate.root as keyof typeof LEGACY_CLASS_MAP],
+      })
+    }
+  }
+
+  return rawCandidate
+}

packages/@tailwindcss-upgrade/src/template/migrate.ts

@@ -7,6 +7,7 @@ import { automaticVarInjection } from './codemods/automatic-var-injection'
 import { bgGradient } from './codemods/bg-gradient'
 import { important } from './codemods/important'
 import { prefix } from './codemods/prefix'
+import { simpleLegacyClasses } from './codemods/simple-legacy-classes'
 import { variantOrder } from './codemods/variant-order'
 
 export type Migration = (
@@ -20,6 +21,7 @@ export const DEFAULT_MIGRATIONS: Migration[] = [
   important,
   automaticVarInjection,
   bgGradient,
+  simpleLegacyClasses,
   variantOrder,
 ]