Try to canonicalize any arbitrary utility to a bare value

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Preserve case of theme keys from JS configs and plugins ([#19337](https://github.com/tailwindlabs/tailwindcss/pull/19337))
 - Write source maps correctly on the CLI when using `--watch` ([#19373](https://github.com/tailwindlabs/tailwindcss/pull/19373))
 - Upgrade: Handle `future` and `experimental` config keys ([#19344](https://github.com/tailwindlabs/tailwindcss/pull/19344))
+- Try to canonicalize any arbitrary utility to a bare value ([#19379](https://github.com/tailwindlabs/tailwindcss/pull/19379))
 
 ### Added
 

packages/tailwindcss/src/canonicalize-candidates.test.ts

@@ -530,8 +530,24 @@ describe.each([['default'], ['with-variant'], ['important'], ['prefix']])('%s',
       // Default spacing scale
       ['w-[64rem]', 'w-256', '0.25rem'],
 
+      // Non-suggested numbers
+      ['gap-[7.25rem]', 'gap-29', '0.25rem'],
+      ['gap-[calc(7rem+0.25rem)]', 'gap-29', '0.25rem'],
+      ['gap-[116px]', 'gap-29', '0.25rem'],
+
+      // Non-suggested numbers, with the same spacing scale with different
+      // units
+      ['gap-[7.25rem]', 'gap-29', '4px'],
+      ['gap-[calc(7rem+0.25rem)]', 'gap-29', '4px'],
+      ['gap-[116px]', 'gap-29', '4px'],
+
+      // Non-suggested numbers, with a different spacing scale
+      ['gap-[7.25rem]', 'gap-116', '1px'],
+      ['gap-[calc(7rem+0.25rem)]', 'gap-116', '1px'],
+      ['gap-[116px]', 'gap-116', '1px'],
+
       // Keep arbitrary value if units are different
-      ['w-[124px]', 'w-[124px]', '0.25rem'],
+      ['w-[124px]', 'w-31', '0.25rem'],
 
       // Keep arbitrary value if bare value doesn't fit in steps of .25
       ['w-[0.123rem]', 'w-[0.123rem]', '0.25rem'],

packages/tailwindcss/src/canonicalize-candidates.ts

@@ -990,6 +990,43 @@ function arbitraryUtilities(candidate: Candidate, options: InternalCanonicalizeO
         candidate.kind === 'arbitrary' ? candidate.value : (candidate.value?.value ?? null)
       if (value === null) return
 
+      // Try to canonicalize any incoming arbitrary value. Canonicalization of
+      // `rem` and `px` values will be converted to `px`, so we have to
+      // canonicalize the spacing multiplier as well.
+      if (
+        options.signatureOptions.rem !== null &&
+        candidate.kind === 'functional' &&
+        candidate.value?.kind === 'arbitrary'
+      ) {
+        let spacingMultiplier = designSystem.resolveThemeValue('--spacing')
+        if (spacingMultiplier !== undefined) {
+          // Canonicalizing the spacing multiplier allows us to handle both
+          // `--spacing: 0.25rem` and `--spacing: 4px` values correctly.
+          let canonicalizedSpacingMultiplier = constantFoldDeclaration(
+            spacingMultiplier,
+            options.signatureOptions.rem,
+          )
+          if (canonicalizedSpacingMultiplier !== null) {
+            let canonicalizedValue = constantFoldDeclaration(value, options.signatureOptions.rem)
+            let valueDimension = dimensions.get(canonicalizedValue)
+            let spacingMultiplierDimension = dimensions.get(canonicalizedSpacingMultiplier)
+            if (
+              valueDimension &&
+              spacingMultiplierDimension &&
+              valueDimension[1] === spacingMultiplierDimension[1] && // Ensure the units match
+              spacingMultiplierDimension[0] !== 0
+            ) {
+              let bareValue = `${valueDimension[0] / spacingMultiplierDimension[0]}`
+              if (isValidSpacingMultiplier(bareValue)) {
+                yield Object.assign({}, candidate, {
+                  value: { kind: 'named', value: bareValue, fraction: null },
+                })
+              }
+            }
+          }
+        }
+      }
+
       let spacingMultiplier = designSystem.storage[SPACING_KEY]?.get(value) ?? null
       let rootPrefix = ''
       if (spacingMultiplier !== null && spacingMultiplier < 0) {