Fix generation of utilities that use slashes in arbitrary modifiers (#12515)

* Fix support for slashes in arbitrary modifiers

* Update changelog

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve types for `resolveConfig` ([#12272](https://github.com/tailwindlabs/tailwindcss/pull/12272))
 - Ensure configured `font-feature-settings` for `mono` are included in Preflight ([#12342](https://github.com/tailwindlabs/tailwindcss/pull/12342))
 - Don't crash when given applying a variant to a negated version of a simple utility ([#12514](https://github.com/tailwindlabs/tailwindcss/pull/12514))
+- Fix support for slashes in arbitrary modifiers ([#12515](https://github.com/tailwindlabs/tailwindcss/pull/12515))
 
 ## [3.3.5] - 2023-10-25
 

src/util/pluginUtils.js

@@ -88,6 +88,22 @@ function isArbitraryValue(input) {
 function splitUtilityModifier(modifier) {
   let slashIdx = modifier.lastIndexOf('/')
 
+  // If the `/` is inside an arbitrary, we want to find the previous one if any
+  // This logic probably isn't perfect but it should work for most cases
+  let arbitraryStartIdx = modifier.lastIndexOf('[', slashIdx)
+  let arbitraryEndIdx = modifier.indexOf(']', slashIdx)
+
+  let isNextToArbitrary = modifier[slashIdx - 1] === ']' || modifier[slashIdx + 1] === '['
+
+  // Backtrack to the previous `/` if the one we found was inside an arbitrary
+  if (!isNextToArbitrary) {
+    if (arbitraryStartIdx !== -1 && arbitraryEndIdx !== -1) {
+      if (arbitraryStartIdx < slashIdx && slashIdx < arbitraryEndIdx) {
+        slashIdx = modifier.lastIndexOf('/', arbitraryStartIdx)
+      }
+    }
+  }
+
   if (slashIdx === -1 || slashIdx === modifier.length - 1) {
     return [modifier, undefined]
   }

tests/arbitrary-values.test.js

@@ -654,6 +654,21 @@ crosscheck(({ stable, oxide }) => {
   })
 })
 
+it('should support slashes in arbitrary modifiers', () => {
+  let config = {
+    content: [{ raw: html`<div class="text-lg/[calc(50px/1rem)]"></div>` }],
+  }
+
+  return run('@tailwind utilities', config).then((result) => {
+    return expect(result.css).toMatchFormattedCss(css`
+      .text-lg\/\[calc\(50px\/1rem\)\] {
+        font-size: 1.125rem;
+        line-height: calc(50px / 1rem);
+      }
+    `)
+  })
+})
+
 it('should not insert spaces around operators inside `env()`', () => {
   let config = {
     content: [{ raw: html`<div class="grid-cols-[calc(env(safe-area-inset-bottom)+1px)]"></div>` }],