fix(tailwindcss-patch): getClassSetSync() returning an empty set

Author: sonofmagic

.changeset/reliable-otters-ring.md

@@ -0,0 +1,5 @@
+---
+'tailwindcss-patch': patch
+---
+
+Fix `getClassSetSync()` returning an empty set before Tailwind v3 contexts are ready so runtime collectors fall back to the async extraction path instead of skipping class discovery.

packages/tailwindcss-patch/src/api/tailwindcss-patcher.ts

@@ -150,15 +150,6 @@ export class TailwindcssPatcher {
     return collectClassesFromContexts(contexts, this.options.filter)
   }
 
-  private collectClassSetSync(): Set<string> {
-    if (this.majorVersion === 4) {
-      throw new Error('getClassSetSync is not supported for Tailwind CSS v4 projects. Use getClassSet instead.')
-    }
-
-    const contexts = this.getContexts()
-    return collectClassesFromContexts(contexts, this.options.filter)
-  }
-
   private async mergeWithCache(set: Set<string>) {
     if (!this.options.cache.enabled) {
       return set
@@ -213,9 +204,18 @@ export class TailwindcssPatcher {
     return this.mergeWithCache(set)
   }
 
-  getClassSetSync() {
-    const set = this.collectClassSetSync()
-    return this.mergeWithCacheSync(set)
+  getClassSetSync(): Set<string> | undefined {
+    if (this.majorVersion === 4) {
+      throw new Error('getClassSetSync is not supported for Tailwind CSS v4 projects. Use getClassSet instead.')
+    }
+
+    const contexts = this.getContexts()
+    const set = collectClassesFromContexts(contexts, this.options.filter)
+    const merged = this.mergeWithCacheSync(set)
+    if (contexts.length === 0 && merged.size === 0) {
+      return undefined
+    }
+    return merged
   }
 
   async extract(options?: { write?: boolean }): Promise<ExtractResult> {

packages/tailwindcss-patch/test/api.tailwindcss-patcher.test.ts

@@ -128,8 +128,9 @@ describe('TailwindcssPatcher', () => {
 
     const result = patcher.getClassSetSync()
 
-    expect(result.has('foo')).toBe(true)
-    expect(result.has('bar')).toBe(true)
+    expect(result).toBeDefined()
+    expect(result?.has('foo')).toBe(true)
+    expect(result?.has('bar')).toBe(true)
     expect(fs.pathExistsSync(cacheFile)).toBe(true)
     const cacheContent = fs.readJSONSync(cacheFile)
     expect(cacheContent).toEqual(expect.arrayContaining(['foo', 'bar']))
@@ -161,7 +162,37 @@ describe('TailwindcssPatcher', () => {
 
     const result = patcher.getClassSetSync()
 
-    expect(result.size).toBe(1)
-    expect(result.has('cached-class')).toBe(true)
+    expect(result).toBeDefined()
+    expect(result?.size).toBe(1)
+    expect(result?.has('cached-class')).toBe(true)
+  })
+
+  it('defers synchronous class access until runtime contexts are populated', async () => {
+    const tooltipClass = 'text-[#123456]'
+    const contexts: any[] = []
+
+    const patcher = new TailwindcssPatcher({
+      overwrite: false,
+      cache: false,
+      tailwind: {
+        packageName: 'tailwindcss-3',
+        version: 3,
+      },
+    })
+
+    vi.spyOn(patcher, 'getContexts').mockImplementation(() => contexts)
+    vi.spyOn(patcher as any, 'runTailwindBuildIfNeeded').mockImplementation(async () => {
+      contexts.push({
+        classCache: new Map([[tooltipClass, []]]),
+      })
+    })
+
+    expect(patcher.getClassSetSync()).toBeUndefined()
+
+    const { classSet } = await patcher.extract({ write: false })
+    expect(classSet?.has(tooltipClass)).toBe(true)
+
+    const syncSet = patcher.getClassSetSync()
+    expect(syncSet?.has(tooltipClass)).toBe(true)
   })
 })