Don't emit utilities that resolve a theme value when an unsupported modifier is used

[webdevelopersrinu]

Summary

Modifiers on functional utilities that resolve a named theme value are silently
dropped instead of invalidating the candidate. For example, with the default theme:

• rounded-sm/[5] emits the same CSS as rounded-sm (the [5] is ignored)
• shadow-sm/foo, inset-shadow-sm/foo, text-shadow/foo, and drop-shadow/foo
  emit the full shadow CSS with the invalid foo modifier ignored

This is inconsistent with how every sibling code path behaves: rounded/foo,
rounded-[4px]/foo, rounded-sm/5, and drop-shadow-xl/foo all correctly
produce no output, because those paths check candidate.modifier.

This PR adds the missing guards:

• In the generic functionalUtility handler, a candidate whose named value
  resolves from the theme now rejects modifiers (except fractions like w-1/2,
  where the modifier is part of the resolved value).
• The shadow, inset-shadow, and text-shadow utilities now apply the same
  if (candidate.modifier && !alpha) return guard in their default-value,
  arbitrary-value, and named-size branches that drop-shadow already applies,
  and drop-shadow gets it in its default-value branch too.

Existing tests asserting candidates like drop-shadow/foo produce no output were
passing for the wrong reason: they run without a theme, so the theme lookup fails
before the modifier is ever considered. The new tests provide a theme so the
invalid modifier is what invalidates the candidate.

Test plan

• Added assertions to the rounded, filter, shadow, inset-shadow, and
  text-shadow tests that compile candidates with invalid modifiers against a
  theme that defines the relevant values, and expect no output. All of them fail
  without the fix.
• pnpm vitest run packages/tailwindcss/src/utilities.test.ts — 398 passed.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains, and the previously reported changelog placeholder has been replaced with the correct PR link.

_{Reviews (5): Last reviewed commit: "update CHANGELOG" | Re-trigger Greptile}

[coderabbitai]

Walkthrough

Functional utilities now reject unsupported modifiers on resolved theme values unless the value is a fraction. Stroke-width resolution applies the same validation. Drop-shadow, text-shadow, shadow, and inset-shadow utilities reject invalid opacity modifiers across default, arbitrary, named, and theme-backed values. Tests cover these cases, and the changelog documents the fix.

Merge Risk: ⚪ Minimal · up to 0f5aa

The change prevents unsupported modifiers from emitting utilities. One arbitrary text-shadow case could use an additional regression test, but no actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: rejecting utilities when unsupported modifiers would otherwise be ignored.
Description check	✅ Passed	The description directly explains the modifier validation changes, affected utilities, test coverage, and test results.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: c7681f73-63e3-4892-ad83-9c6455b8d6d7

📥 Commits

Reviewing files that changed from the base of the PR and between 021b7fe and 1633e01.

📒 Files selected for processing (3)

• CHANGELOG.md
• packages/tailwindcss/src/utilities.test.ts
• packages/tailwindcss/src/utilities.ts

[RobinMalfait]

Thanks!

I updated the tests to make them part of the existing section where we expect the tests to fail.
I also added a missing case for the stroke-* utilities, because stroke-2/foo would also compiler otherwise.

Last but not least, I also split up your commit, just so I could easily verify that the tests were indeed failing before applying the fix.

Thanks again!

[coderabbitai]

Actionable comments posted: 1

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 537d3b07-3e72-41f4-99c0-e4cbb8a3d5fb

📥 Commits

Reviewing files that changed from the base of the PR and between d979c6d and 0f5aa7a.

📒 Files selected for processing (3)

• CHANGELOG.md
• packages/tailwindcss/src/utilities.test.ts
• packages/tailwindcss/src/utilities.ts

🚧 Files skipped from review as they are similar to previous changes (2)

• CHANGELOG.md
• packages/tailwindcss/src/utilities.ts

[coderabbitai]

📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win

Test an arbitrary text-shadow value with a slash modifier.

-text-shadow-[var(--value)] only tests negation. It does not execute the arbitrary-value branch with candidate.modifier set. Add text-shadow-[var(--value)]/foo so this test fails if unsupported modifiers are accepted again.

Proposed test case

         '-text-shadow-[var(--value)]',
         'text-shadow/foo',
         'text-shadow-sm/foo',
+        'text-shadow-[var(--value)]/foo',

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	'-text-shadow-[var(--value)]',
	'text-shadow/foo',
	'text-shadow-sm/foo',
	],
	'-text-shadow-[var(--value)]',
	'text-shadow/foo',
	'text-shadow-sm/foo',
	'text-shadow-[var(--value)]/foo',
	],

[webdevelopersrinu]

Thank you @RobinMalfait for the quick review and merge, and for tidying up the test organization noted for next time. This was my first contribution to Tailwind CSS and the experience was great.