Add bare value support for auto-rows-* and auto-cols-*

[RobinMalfait]

This PR adds bare value support for auto-rows-* and auto-cols-*.

We first introduced auto-rows-auto, auto-rows-min, auto-rows-max and auto-rows-fr (same for auto-cols-*) back in Tailwind CSS v1.9 (https://v1.tailwindcss.com/docs/grid-auto-rows#app) but we haven't touched it since.

This PR now adds support for bare values that use the spacing scale. That means that you can now use auto-rows-12 or auto-cols-12 which will result in the following CSS:

.auto-cols-12 {
  grid-auto-columns: calc(var(--spacing) * 12);
}
.auto-rows-12 {
  grid-auto-rows: calc(var(--spacing) * 12);
}

We could also add support for percentage based values. The only question is what the syntax should be. This can either be auto-rows-3/4 or auto-rows-75%.

For the fraction case, we already have w-3/4 and aspect-3/4 even though they both have a different value as a result:

.aspect-3\/4 {
  aspect-ratio: 3/4;
}
.w-3\/4 {
  width: calc(3 / 4 * 100%);
}

We also have some precedence for the % value as well, e.g. via-10% for gradient color stops.

I think I would personally towards the auto-rows-75% value instead of auto-rows-3/4. The fraction syntax works great for aspect ratio because that's literally what it is (aspect-16/9). The fraction also works great for widths, because you typically have 2 elements next to each other:

<div>
  <div class="w-1/3"></div>
  <div class="w-2/3"></div>
</div>

Since you only use the auto-rows-* once on a parent element, I think the auto-rows-75% makes a bit more sense than auto-rows-3/4 since there is no other element (at least not that I can think of).

TODO

• Support percentages?
  • Syntax A: auto-rows-3/4
  • Syntax B: auto-rows-75%
  • Syntax C: support both, but that seems silly

Percentage support isn't a blocker for this PR, since you can always use auto-rows-[75%] if you want

Test plan

1. Added a test to prove that this works
2. Existing tests still pass

Requested by: #20225

[greptile-apps]

Confidence Score: 5/5

Small, well-contained addition that follows the established spacing utility pattern exactly — safe to merge.

The bare-value handler uses the correct validator (isValidSpacingMultiplier) and properly guards on --spacing being present in the theme before emitting a value, which is identical to how every other spacing utility (w-*, h-*, m-*, etc.) is implemented. The test snapshots confirm correct CSS output and the change touches only the two target utilities.

No files require special attention.

_{Reviews (3): Last reviewed commit: "use `isValidSpacingMultiplier`" | Re-trigger Greptile}

[coderabbitai]

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📒 Files selected for processing (3)

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

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• CHANGELOG.md

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

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

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Walkthrough

This PR introduces support for bare numeric spacing values in auto-cols-* and auto-rows-* utilities. The implementation adds handleBareValue handlers to both utilities in utilities.ts that accept positive integers and emit --spacing(<value>) calculations when theme resolution does not provide a value. Tests are updated to verify the feature works with a custom theme spacing token, and a changelog entry documents the addition.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding bare value support for auto-rows-* and auto-cols-* utilities, which is the primary objective of the changeset.
Description check	✅ Passed	The description clearly explains the changes, provides context about previous functionality, shows concrete examples of the new feature, and discusses future considerations with a test plan.
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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