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.
This was my first contribution to Tailwind CSS and the experience was great.