Fix sorting of utilities that share multiple candidates

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Don’t crash when important and parent selectors are equal in `@apply` ([#12112](https://github.com/tailwindlabs/tailwindcss/pull/12112))
 - Eliminate irrelevant rules when applying variants ([#12113](https://github.com/tailwindlabs/tailwindcss/pull/12113))
 - Improve RegEx parser, reduce possibilities as the key for arbitrary properties ([#12121](https://github.com/tailwindlabs/tailwindcss/pull/12121))
+- Fix sorting of utilities that share multiple candidates ([#12173](https://github.com/tailwindlabs/tailwindcss/pull/12173))
 
 ### Added
 

src/lib/generateRules.js

@@ -877,7 +877,7 @@ function getImportantStrategy(important) {
   }
 }
 
-function generateRules(candidates, context) {
+function generateRules(candidates, context, isSorting = false) {
   let allRules = []
   let strategy = getImportantStrategy(context.tailwindConfig.important)
 
@@ -912,7 +912,9 @@ function generateRules(candidates, context) {
         rule = container.nodes[0]
       }
 
-      let newEntry = [sort, rule]
+      // Note: We have to clone rules during sorting
+      // so we eliminate some shared mutable state
+      let newEntry = [sort, isSorting ? rule.clone() : rule]
       rules.add(newEntry)
       context.ruleCache.add(newEntry)
       allRules.push(newEntry)

src/lib/setupContextUtils.js

@@ -938,7 +938,7 @@ function registerPlugins(plugins, context) {
 
     // Sort all classes in order
     // Non-tailwind classes won't be generated and will be left as `null`
-    let rules = generateRules(new Set(sorted), context)
+    let rules = generateRules(new Set(sorted), context, true)
     rules = context.offsets.sort(rules)
 
     let idx = BigInt(parasiteUtilities.length)

tests/getSortOrder.test.js

@@ -178,3 +178,42 @@ it('sorts based on first occurrence of a candidate / rule', () => {
     expect(defaultSort(context.getClassOrder(input.split(' ')))).toEqual(output)
   }
 })
+
+it('Sorting is unchanged when multiple candidates share the same rule / object', () => {
+  let classes = [
+    ['x y', 'x y'],
+    ['a', 'a'],
+    ['x y', 'x y'],
+  ]
+
+  let config = {
+    theme: {},
+    plugins: [
+      function ({ addComponents }) {
+        addComponents({
+          '.x': { color: 'red' },
+          '.a': { color: 'red' },
+
+          // This rule matches both the candidate `a` and `y`
+          // When sorting x and y first we would keep that sort order
+          // Then sorting `a` we would end up replacing the candidate on the rule
+          // Thus causing `y` to no longer have a sort order causing it to be sorted
+          // first by accident
+          '.y .a': { color: 'red' },
+        })
+      },
+    ],
+  }
+
+  // Same context, different class lists
+  let context = createContext(resolveConfig(config))
+  for (const [input, output] of classes) {
+    expect(defaultSort(context.getClassOrder(input.split(' ')))).toEqual(output)
+  }
+
+  // Different context, different class lists
+  for (const [input, output] of classes) {
+    context = createContext(resolveConfig(config))
+    expect(defaultSort(context.getClassOrder(input.split(' ')))).toEqual(output)
+  }
+})