ensure we re-print the candidate in case it didn't change

When printing a candidate, we do some optimizations already, such as:

- `bg-[var(--foo)]` -> `bg-(--foo)`
- `bg-[rgb(0,_0,_0)]` -> `bg-[rgb(0,0,0)]`

Consistency in your project will reduce the file size.

We parse and reprint the candidate if nothing changed during migrations
because we don't have dedicated migrations for them.

So (a lot) of these classes weren't fully updated to the v4 flavor of
the classes.

Luckily re-parsing the candidate is fast because we are re-using the
design system which means that we have a cached version of the
candidate.

Author: RobinMalfait

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

@@ -1,9 +1,10 @@
 import fs from 'node:fs/promises'
 import path, { extname } from 'node:path'
+import { parseCandidate } from '../../../../tailwindcss/src/candidate'
 import type { Config } from '../../../../tailwindcss/src/compat/plugin-api'
 import type { DesignSystem } from '../../../../tailwindcss/src/design-system'
 import { spliceChangesIntoString, type StringChange } from '../../utils/splice-changes-into-string'
-import { extractRawCandidates } from './candidates'
+import { extractRawCandidates, printCandidate } from './candidates'
 import { migrateArbitraryValueToBareValue } from './migrate-arbitrary-value-to-bare-value'
 import { migrateAutomaticVarInjection } from './migrate-automatic-var-injection'
 import { migrateBgGradient } from './migrate-bg-gradient'
@@ -56,9 +57,22 @@ export async function migrateCandidate(
     end: number
   },
 ): Promise<string> {
+  let original = rawCandidate
   for (let migration of DEFAULT_MIGRATIONS) {
     rawCandidate = await migration(designSystem, userConfig, rawCandidate, location)
   }
+
+  // If nothing changed, let's parse it again and re-print it. This will migrate
+  // pretty print candidates to the new format. If it did change, we already had
+  // to re-print it.
+  //
+  // E.g.: `bg-red-500/[var(--my-opacity)]` -> `bg-red-500/(--my-opacity)`
+  if (rawCandidate === original) {
+    for (let candidate of parseCandidate(rawCandidate, designSystem)) {
+      return printCandidate(designSystem, candidate)
+    }
+  }
+
   return rawCandidate
 }