fix(canonicalize): collapse arbitrary values into shorthand utilities

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve canonicalizations for `tracking-*` utilities ([#19827](https://github.com/tailwindlabs/tailwindcss/pull/19827))
 - Fix crash due to invalid characters in candidate ([#19829](https://github.com/tailwindlabs/tailwindcss/pull/19829))
 - Ensure query params in imports are considered unique resources when using `@tailwindcss/webpack` ([#19723](https://github.com/tailwindlabs/tailwindcss/pull/19723))
+- Collapse arbitrary values into shorthand utilities during canonicalization ([#19837](https://github.com/tailwindlabs/tailwindcss/pull/19837))
 
 ## [4.2.2] - 2026-03-18
 

packages/tailwindcss/src/canonicalize-candidates.test.ts

@@ -1310,3 +1310,34 @@ test(
     )
   },
 )
+
+// https://github.com/tailwindlabs/tailwindcss/issues/19835
+test.each([
+  // Arbitrary values should be collapsed to another arbitrary value
+  [
+    ['px-[1.2rem]', 'py-[1.2rem]', 'text-left'],
+    ['text-left', 'p-[1.2rem]'],
+  ],
+
+  // Arbitrary values could also be collapsed into a bare value
+  [
+    ['px-[30.75rem]', 'py-[30.75rem]', 'text-left'],
+    ['text-left', 'p-123'],
+  ],
+])(
+  'collapse canonicalization works for arbitrary values',
+  { timeout },
+  async (candidates, expected) => {
+    let designSystem = await designSystems.get(__dirname).get(css`
+      @import 'tailwindcss';
+    `)
+
+    let options: CanonicalizeOptions = {
+      collapse: true,
+      logicalToPhysical: true,
+      rem: 16,
+    }
+
+    expect(designSystem.canonicalizeCandidates(candidates, options)).toEqual(expected)
+  },
+)

packages/tailwindcss/src/canonicalize-candidates.ts

@@ -321,10 +321,7 @@ function collapseCandidates(options: InternalCanonicalizeOptions, candidates: st
       if (relevantProperties.size === 0) return result
 
       for (let parsedCandidate of parseCandidate(designSystem, candidate)) {
-        if (
-          parsedCandidate.kind !== 'functional' ||
-          parsedCandidate.value?.kind !== 'named' // Necessary for bare values
-        ) {
+        if (parsedCandidate.kind !== 'functional' || parsedCandidate.value === null) {
           continue
         }