fix(canonicalize): prevent collapse cache pollution across calls

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

@@ -1163,3 +1163,46 @@ describe('options', () => {
     expect(designSystem.canonicalizeCandidates(['m-[16px]'])).toEqual(['m-[16px]']) // Ensure options don't influence shared state
   })
 })
+
+// https://github.com/schoero/eslint-plugin-better-tailwindcss/issues/321
+test('a subset of classes should be canonicalizable', { timeout }, async () => {
+  let designSystem = await designSystems.get(__dirname).get(css`
+    @import 'tailwindcss';
+  `)
+
+  let options: CanonicalizeOptions = {
+    collapse: true,
+    logicalToPhysical: true,
+    rem: 16,
+  }
+
+  expect(
+    designSystem.canonicalizeCandidates(['underline', 'h-4', 'w-4', 'text-sm'], options),
+  ).toEqual(['underline', 'text-sm', 'size-4'])
+})
+
+test('collapse canonicalization is not affected by previous calls', { timeout }, async () => {
+  let designSystem = await designSystems.get(__dirname).get(css`
+    @import 'tailwindcss';
+  `)
+
+  let options: CanonicalizeOptions = {
+    collapse: true,
+    logicalToPhysical: true,
+    rem: 16,
+  }
+
+  let target = ['underline', 'h-4', 'w-4']
+
+  expect(designSystem.canonicalizeCandidates(target, options)).toEqual(['underline', 'size-4'])
+
+  designSystem.canonicalizeCandidates(['mb-4', 'text-sm'], options)
+  designSystem.canonicalizeCandidates(['underline', 'mb-4'], options)
+
+  expect(designSystem.canonicalizeCandidates(target, options)).toEqual(['underline', 'size-4'])
+  expect(designSystem.canonicalizeCandidates(target.concat('text-sm'), options)).toEqual([
+    'underline',
+    'text-sm',
+    'size-4',
+  ])
+})

packages/tailwindcss/src/canonicalize-candidates.ts

@@ -315,7 +315,9 @@ function collapseCandidates(options: InternalCanonicalizeOptions, candidates: st
     // E.g.: `margin-top` → `mt-1`, `my-1`, `m-1`
     let otherUtilities = candidatePropertiesValues.map((propertyValues) => {
       let result: Set<string> | null = null
-      for (let property of propertyValues.keys()) {
+      for (let [property, values] of propertyValues.entries()) {
+        if (values.size === 0) continue
+
         let otherUtilities = new Set<string>()
         for (let group of staticUtilities.get(property).values()) {
           for (let candidate of group) {
@@ -330,7 +332,7 @@ function collapseCandidates(options: InternalCanonicalizeOptions, candidates: st
         // all intersections with an empty set will remain empty.
         if (result!.size === 0) return result!
       }
-      return result!
+      return result ?? new Set<string>()
     })
 
     // Link each candidate that could be linked via another utility