Sort class lists deterministically for Prettier plugin (#10672)

* Ensure class sorting is deterministic for Prettier

* Update changelog

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Disallow multiple selectors in arbitrary variants ([#10655](https://github.com/tailwindlabs/tailwindcss/pull/10655))
+- Sort class lists deterministically for Prettier plugin ([#10672](https://github.com/tailwindlabs/tailwindcss/pull/10672))
 
 ### Changed
 

src/lib/setupContextUtils.js

@@ -931,12 +931,19 @@ function registerPlugins(plugins, context) {
     prefix(context, 'peer'),
   ]
   context.getClassOrder = function getClassOrder(classes) {
+    // Sort classes so they're ordered in a deterministic manner
+    let sorted = [...classes].sort((a, z) => {
+      if (a === z) return 0
+      if (a < z) return -1
+      return 1
+    })
+
     // Non-util classes won't be generated, so we default them to null
-    let sortedClassNames = new Map(classes.map((className) => [className, null]))
+    let sortedClassNames = new Map(sorted.map((className) => [className, null]))
 
     // Sort all classes in order
     // Non-tailwind classes won't be generated and will be left as `null`
-    let rules = generateRules(new Set(classes), context)
+    let rules = generateRules(new Set(sorted), context)
     rules = context.offsets.sort(rules)
 
     let idx = BigInt(parasiteUtilities.length)

tests/getSortOrder.test.js

@@ -51,7 +51,7 @@ crosscheck(() => {
     ['px-3 focus:hover:p-3 hover:p-1 py-3', 'px-3 py-3 hover:p-1 focus:hover:p-3'],
 
     // Utitlies with important
-    ['px-3 !py-4', 'px-3 !py-4'],
+    ['px-3 !py-4', '!py-4 px-3'],
     ['!py-4 px-3', '!py-4 px-3'],
 
     // Components with variants
@@ -89,7 +89,7 @@ crosscheck(() => {
     ],
 
     // Utitlies with important
-    ['tw-px-3 !tw-py-4', 'tw-px-3 !tw-py-4'],
+    ['tw-px-3 !tw-py-4', '!tw-py-4 tw-px-3'],
     ['!tw-py-4 tw-px-3', '!tw-py-4 tw-px-3'],
 
     // Components with variants
@@ -115,4 +115,31 @@ crosscheck(() => {
       expect(defaultSort(context.getClassOrder(input.split(' ')))).toEqual(output)
     }
   )
+
+  it('sorts classes deterministically across multiple class lists', () => {
+    let classes = [
+      [
+        'a-class px-3 p-1 b-class py-3 bg-red-500 bg-blue-500',
+        'a-class b-class bg-blue-500 bg-red-500 p-1 px-3 py-3',
+      ],
+      [
+        'px-3 b-class p-1 py-3 bg-blue-500 a-class bg-red-500',
+        'b-class a-class bg-blue-500 bg-red-500 p-1 px-3 py-3',
+      ],
+    ]
+
+    let config = {}
+
+    // 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)
+    }
+  })
 })