Fix utility staticValues shadowed by fallback theme namespaces

[koreahghg]

Summary

Some functional utilities resolve their value against two theme namespaces: their own dedicated one, and a shared fallback used by many unrelated utilities (e.g. leading uses ['--leading', '--spacing'], columns uses ['--columns', '--container'], backdrop-blur uses ['--backdrop-blur', '--blur']). These utilities also define staticValues for special keywords like none/auto.

The staticValues fallback only kicked in when the theme resolved to nothing at all across every key in themeKeys. This means a same-named custom theme value defined for a completely different, unrelated utility silently wins over the intended static value:

@theme {
  --spacing-none: 0; /* meant for spacing utilities, e.g. p-none */
}

<p class="leading-none">...</p>
<!-- outputs line-height: var(--spacing-none) → 0, instead of the intended line-height: 1 -->

This fixes #19722 (leading-none shadowed by a custom --spacing-none), and also fixes two more previously unreported instances of the exact same root cause:

• columns-auto shadowed by a custom --container-auto (outputs columns: 500px instead of columns: auto)
• backdrop-blur-none shadowed by a custom --blur-none (doesn't properly reset the backdrop blur)

Fix: functionalUtility() now also resolves the candidate against just the utility's own dedicated namespace (themeKeys[0]). A staticValues entry is only shadowed if that resolution (not the combined fallback resolution) finds a value — i.e. only when the utility's own namespace defines something for that name. A same-named value that only exists in a shared fallback namespace no longer suppresses the static value.

Test plan

• Added regression tests in utilities.test.ts for all three affected utilities (leading-none, columns-auto, backdrop-blur-none), each reproducing the shadowing with a colliding custom theme value and asserting the correct static output.
• pnpm vitest run packages/tailwindcss/src — all 5007 tests pass (1 pre-existing skip), no regressions from this change.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between 90f8ff4 and 8776458.

📒 Files selected for processing (2)

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

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Walkthrough

Updated functionalUtility to distinguish a utility’s primary theme namespace from fallback namespaces when resolving candidate values. Static values remain available unless the primary namespace defines the candidate. Added regression tests for columns-auto, backdrop-blur-none, and leading-none with customized related theme variables.

Merge Risk: ⚪ Minimal · up to 87764

This localized fix corrects static utility values that could be shadowed by unrelated fallback theme values, with regression coverage for the affected cases; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the fix for static utility values being shadowed by fallback theme namespaces.
Description check	✅ Passed	The description directly explains the bug, the implementation, the affected utilities, and the regression tests.
Linked Issues check	✅ Passed	The change fixes issue #19722 and preserves static leading-none output while retaining fallback support for numeric leading values.
Out of Scope Changes check	✅ Passed	The code and test changes are limited to the linked issue and its directly related fallback-namespace regressions.

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The precedence adjustment is limited to the three intended multi-namespace utilities with static values, and the additional theme lookup is side-effect-free.

_{Reviews (1): Last reviewed commit: "Fix staticValues being shadowed by unrel..." | Re-trigger Greptile}

[koreahghg]

Closing this — I hadn't seen #19773 and #20394 when I opened this. This PR uses the same approach as #19773 (treating themeKeys[0] as the utility's own namespace generically in functionalUtility), which was already flagged as an overreach in the discussion on #19722 (it doesn't hold for utilities like min-h where more than one key is legitimately utility-specific, not just a generic fallback like --spacing).

#20394's scoped, opt-in approach (fallbackThemeKeys) looks like the right pattern here. I'll follow up separately, scoped just to the columns-auto/--container-auto and backdrop-blur-none/--blur-none cases, which aren't covered by #20394 since those utilities don't go through spacingUtility().