fix(react-native): fall back to Platform for $os_name and $os_version

.changeset/rn-os-name-platform-fallback.md

@@ -0,0 +1,5 @@
+---
+'posthog-react-native': patch
+---
+
+Fix events missing `$os_name` and `$os_version` in apps that use neither `expo-device` nor `react-native-device-info`.

packages/react-native/src/native-deps.tsx

@@ -9,6 +9,7 @@ import { PostHogCustomAppProperties, PostHogCustomStorage } from './types'
 import { OptionalReactNativeLocalize } from './optional/OptionalReactNativeLocalize'
 import { OptionalExpoFileSystemLegacy } from './optional/OptionalExpoFileSystemLegacy'
 import { detectDeviceType } from '@posthog/core'
+import { Platform } from 'react-native'
 
 const getDeviceType = (): string => {
   let deviceType = 'Mobile'
@@ -76,6 +77,10 @@ export const getAppProperties = (): PostHogCustomAppProperties => {
     properties.$is_emulator = OptionalReactNativeDeviceInfo.isEmulatorSync()
   }
 
+  if (!properties.$os_name) {
+    Object.assign(properties, getPlatformOSProperties())
+  }
+
   if (OptionalExpoLocalization) {
     // expo-localization >= 14 use functions to get these results, older versions use JS getters
     // https://github.com/expo/expo/blob/sdk-54/packages/expo-localization/CHANGELOG.md#1400--2022-10-25
@@ -131,6 +136,25 @@ export const getAppProperties = (): PostHogCustomAppProperties => {
   return properties
 }
 
+type PlatformConstants = { Release?: string; systemName?: string }
+
+// Reads the OS from React Native's own Platform module, matching what posthog-android and posthog-ios report.
+const getPlatformOSProperties = (): Pick<PostHogCustomAppProperties, '$os_name' | '$os_version'> => {
+  try {
+    const os = getPlatformOS()
+    const constants = (Platform as { constants?: PlatformConstants }).constants
+    const version = Platform.Version !== undefined ? String(Platform.Version) : undefined
+    if (os === 'android') {
+      // Platform.Version is the API level on Android; Release is the user-facing OS version
+      return { $os_name: 'Android', $os_version: constants?.Release ?? version }
+    }
+    if (os === 'ios') {
+      return { $os_name: constants?.systemName ?? 'iOS', $os_version: version }
+    }
+  } catch {}
+  return {}
+}
+
 // react-native-device-info returns 'unknown' if the property is not available (Web target)
 const returnPropertyIfNotUnknown = (value: string | null): string | null => {
   if (value !== 'unknown') {

packages/react-native/test/native-deps-os.spec.ts

@@ -0,0 +1,45 @@
+import { Platform } from 'react-native'
+import { getAppProperties } from '../src/native-deps'
+
+vi.mock('../src/optional/OptionalExpoDevice', () => ({ OptionalExpoDevice: undefined }))
+vi.mock('../src/optional/OptionalExpoApplication', () => ({ OptionalExpoApplication: undefined }))
+vi.mock('../src/optional/OptionalReactNativeDeviceInfo', () => ({ OptionalReactNativeDeviceInfo: undefined }))
+
+const platform = Platform as unknown as { OS: string; Version: string | number; constants?: unknown }
+
+describe('getAppProperties OS fallback without a device-info library', () => {
+  const original = { OS: platform.OS, Version: platform.Version }
+
+  afterEach(() => {
+    platform.OS = original.OS
+    platform.Version = original.Version
+    delete platform.constants
+  })
+
+  it('reports Android with the release version, not the API level', () => {
+    platform.OS = 'android'
+    platform.Version = 36
+    platform.constants = { Release: '16' }
+    expect(getAppProperties()).toMatchObject({ $os_name: 'Android', $os_version: '16' })
+  })
+
+  it('reports the iOS system name and version', () => {
+    platform.OS = 'ios'
+    platform.Version = '18.2'
+    platform.constants = { systemName: 'iPadOS' }
+    expect(getAppProperties()).toMatchObject({ $os_name: 'iPadOS', $os_version: '18.2' })
+  })
+
+  it('defaults the iOS name when the platform constants omit it', () => {
+    platform.OS = 'ios'
+    platform.Version = '18.2'
+    expect(getAppProperties()).toMatchObject({ $os_name: 'iOS', $os_version: '18.2' })
+  })
+
+  it('leaves OS properties unset on web', () => {
+    platform.OS = 'web'
+    const properties = getAppProperties()
+    expect(properties).not.toHaveProperty('$os_name')
+    expect(properties).not.toHaveProperty('$os_version')
+  })
+})