fix: send $groupidentify for new groups even without properties (core SDK)

.changeset/gentle-foxes-rest.md

@@ -0,0 +1,5 @@
+---
+'@posthog/core': patch
+---
+
+fix: send $groupidentify for new groups even when no properties are provided

packages/core/src/__tests__/posthog.featureflags.spec.ts

@@ -728,8 +728,19 @@ describe('PostHog Feature Flags v4', () => {
       it('should reload if groups are set', async () => {
         posthog.group('my-group', 'is-great')
         await waitForPromises()
-        expect(mocks.fetch).toHaveBeenCalledTimes(2)
-        expect(JSON.parse((mocks.fetch.mock.calls[1][1].body as string) || '')).toMatchObject({
+        // 3 calls: 1 for flags reload, 1 for $groupidentify batch, 1 for flags decide
+        expect(mocks.fetch).toHaveBeenCalledTimes(3)
+        // The flags reload call contains the group
+        const flagsCall = mocks.fetch.mock.calls.find((call) => {
+          try {
+            const body = JSON.parse((call[1].body as string) || '')
+            return body.groups?.['my-group'] === 'is-great'
+          } catch {
+            return false
+          }
+        })
+        expect(flagsCall).toBeDefined()
+        expect(JSON.parse((flagsCall![1].body as string) || '')).toMatchObject({
           groups: { 'my-group': 'is-great' },
         })
       })

packages/core/src/__tests__/posthog.featureflags.v1.spec.ts

@@ -411,8 +411,19 @@ describe('PostHog Feature Flags v1', () => {
       it('should reload if groups are set', async () => {
         posthog.group('my-group', 'is-great')
         await waitForPromises()
-        expect(mocks.fetch).toHaveBeenCalledTimes(2)
-        expect(JSON.parse((mocks.fetch.mock.calls[1][1].body as string) || '')).toMatchObject({
+        // 3 calls: 1 for flags reload, 1 for $groupidentify batch, 1 for flags decide
+        expect(mocks.fetch).toHaveBeenCalledTimes(3)
+        // The flags reload call contains the group
+        const flagsCall = mocks.fetch.mock.calls.find((call) => {
+          try {
+            const body = JSON.parse((call[1].body as string) || '')
+            return body.groups?.['my-group'] === 'is-great'
+          } catch {
+            return false
+          }
+        })
+        expect(flagsCall).toBeDefined()
+        expect(JSON.parse((flagsCall![1].body as string) || '')).toMatchObject({
           groups: { 'my-group': 'is-great' },
         })
       })

packages/core/src/__tests__/posthog.groups.spec.ts

@@ -64,6 +64,79 @@ describe('PostHog Core', () => {
         ],
       })
     })
+
+    it('should call groupIdentify for a new group even without properties', async () => {
+      posthog.group('other', 'team')
+      await waitForPromises()
+
+      expect(mocks.fetch).toHaveBeenCalledTimes(2) // 1 for flags, 1 for groupIdentify
+      const batchCall = mocks.fetch.mock.calls[1]
+      expect(batchCall[0]).toEqual('https://us.i.posthog.com/batch/')
+      expect(parseBody(batchCall)).toMatchObject({
+        batch: [
+          {
+            event: '$groupidentify',
+            distinct_id: posthog.getDistinctId(),
+            properties: {
+              $group_type: 'other',
+              $group_key: 'team',
+            },
+            type: 'capture',
+          },
+        ],
+      })
+    })
+
+    it('should not call groupIdentify when group already exists with same key and no properties', async () => {
+      posthog.group('other', 'team')
+      await waitForPromises()
+      mocks.fetch.mockClear()
+
+      posthog.group('other', 'team')
+      await waitForPromises()
+
+      // No new fetch calls for groupIdentify (only flags reload if needed)
+      const groupIdentifyCalls = mocks.fetch.mock.calls.filter((call) => {
+        try {
+          const body = parseBody(call)
+          return body.batch?.some((e: any) => e.event === '$groupidentify')
+        } catch {
+          return false
+        }
+      })
+      expect(groupIdentifyCalls).toHaveLength(0)
+    })
+
+    it('should call groupIdentify for an existing group when properties are provided', async () => {
+      posthog.group('other', 'team')
+      await waitForPromises()
+      mocks.fetch.mockClear()
+
+      posthog.group('other', 'team', { name: 'My Team' })
+      await waitForPromises()
+
+      const groupIdentifyCalls = mocks.fetch.mock.calls.filter((call) => {
+        try {
+          const body = parseBody(call)
+          return body.batch?.some((e: any) => e.event === '$groupidentify')
+        } catch {
+          return false
+        }
+      })
+      expect(groupIdentifyCalls).toHaveLength(1)
+      expect(parseBody(groupIdentifyCalls[0])).toMatchObject({
+        batch: [
+          {
+            event: '$groupidentify',
+            properties: {
+              $group_type: 'other',
+              $group_key: 'team',
+              $group_set: { name: 'My Team' },
+            },
+          },
+        ],
+      })
+    })
   })
 
   describe('groupIdentify', () => {

packages/core/src/posthog-core.ts

@@ -443,11 +443,17 @@ export abstract class PostHogCore extends PostHogCoreStateless {
     options?: PostHogCaptureOptions
   ): void {
     this.wrap(() => {
+      const existingGroups = (this.props.$groups as PostHogGroupProperties) || {}
+      const isNewGroup = existingGroups[groupType] !== groupKey
+
       this.groups({
         [groupType]: groupKey,
       })
 
-      if (groupProperties) {
+      // Send $groupidentify when the group is new/changed OR when properties
+      // are provided. Skip only when the group already exists with the same
+      // key and no new properties are being set.
+      if (isNewGroup || groupProperties) {
         this.groupIdentify(groupType, groupKey, groupProperties, options)
       }
     })