From 970ff521621f820dc08f57d998c269096fba7176 Mon Sep 17 00:00:00 2001
From: Jordan Pittman <jordan@cryptica.me>
Date: Tue, 21 Oct 2025 16:06:02 -0400
Subject: [PATCH 1/2] Discard candidates with an empty data type

---
 packages/tailwindcss/src/candidate.test.ts | 8 ++++++++
 packages/tailwindcss/src/candidate.ts      | 4 +++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/packages/tailwindcss/src/candidate.test.ts b/packages/tailwindcss/src/candidate.test.ts
index 3d4aa983b2a0..53d21dda695f 100644
--- a/packages/tailwindcss/src/candidate.test.ts
+++ b/packages/tailwindcss/src/candidate.test.ts
@@ -1776,6 +1776,14 @@ it('should not parse compound group with a non-compoundable variant', () => {
   expect(run('group-*:flex', { utilities, variants })).toMatchInlineSnapshot(`[]`)
 })
 
+it('empty data types are invalid', () => {
+  let utilities = new Utilities()
+  utilities.functional('bg', () => [])
+  let variants = new Variants()
+
+  expect(run('bg-[:foo]', { utilities, variants })).toMatchInlineSnapshot(`[]`)
+})
+
 it('should parse a variant containing an arbitrary string with unbalanced parens, brackets, curlies and other quotes', () => {
   let utilities = new Utilities()
   utilities.static('flex', () => [])
diff --git a/packages/tailwindcss/src/candidate.ts b/packages/tailwindcss/src/candidate.ts
index c081c3b472b8..fa8cd3047e6d 100644
--- a/packages/tailwindcss/src/candidate.ts
+++ b/packages/tailwindcss/src/candidate.ts
@@ -554,7 +554,7 @@ export function* parseCandidate(input: string, designSystem: DesignSystem): Iter
         if (!isValidArbitrary(arbitraryValue)) continue
 
         // Extract an explicit typehint if present, e.g. `bg-[color:var(--my-var)])`
-        let typehint = ''
+        let typehint: string | null = null
         for (let i = 0; i < arbitraryValue.length; i++) {
           let code = arbitraryValue.charCodeAt(i)
 
@@ -580,6 +580,8 @@ export function* parseCandidate(input: string, designSystem: DesignSystem): Iter
           continue
         }
 
+        if (typehint === '') continue
+
         candidate.value = {
           kind: 'arbitrary',
           dataType: typehint || null,

From f261c6ec08e3bfe184c8875ddbeddeaff2bb3bed Mon Sep 17 00:00:00 2001
From: Jordan Pittman <jordan@cryptica.me>
Date: Tue, 21 Oct 2025 16:49:30 -0400
Subject: [PATCH 2/2] Update changelog

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5292d918cc87..375288258a2d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - _Experimental_: Add `@container-size` utility ([#18901](https://github.com/tailwindlabs/tailwindcss/pull/18901))
 
+### Fixed
+
+- Discard candidates with an empty data type ([#19172](https://github.com/tailwindlabs/tailwindcss/pull/19172))
+
 ## [4.1.15] - 2025-10-20
 
 ### Fixed