firebase-kit

Firebase in a Compose Multiplatform app (android, iosArm64, iosSimulatorArm64), as four capabilities an app takes one by one: crash reporting (Crashlytics), remote config with typed keys a feature owns, push (Cloud Messaging — token, topics, messages and taps), and sign-in with Google and Apple returning a Firebase ID token. Android uses the Firebase SDKs directly; iOS reaches the Firebase iOS SDK through Swift bridges the kit ships into the app's Xcode project. Firebase App Distribution lanes come with it.

enum class HomeFlags(override val key: String, override val default: Boolean) : RemoteConfigKey<Boolean> {
    SHOW_PROMO_BANNER("show_promo_banner", default = false),
}

class HomeViewModel(remoteConfig: RemoteConfig, private val crash: CrashReporter) : ViewModel() {
    val showBanner: Flow<Boolean> = remoteConfig.observe(HomeFlags.SHOW_PROMO_BANNER)
}

when (val result = socialSignIn.signInWithGoogle()) {
    is SignInResult.Success -> session.signIn(api.exchange(result.idToken))   // the backend's session
    SignInResult.Cancelled -> Unit
    is SignInResult.Failed -> crash.log(result.message)
}

Documentation

Read	For
this file	what is here and how it is built
firebase/README.md	setup (Gradle, Xcode, the bridges, the app delegate), then each capability task by task, App Distribution
firebase/DESIGN.md	why each part has its shape, and what changed from the apps it came from
skills/firebase-kit	the same for an agent working in an app that uses the kit

Installing

An application takes the kit by copy, not as a dependency: the code is copied into the app, renamed to the app's own package, and belongs to the app from then on. Nothing is published to a Maven repository.

With skill-manager

If you have access to the author's knowledge repository (github.com/Thernal/knowledge), its skill-manager skill does all of it — copy, rename, the skill, and later updates:

skillctl.sh kit install firebase-kit --package com.example.app --module :core:firebase --alias app \
    --framework ComposeApp --place ios/Firebase=iosApp/iosApp/Firebase

It copies the code parts of kit.yml renamed, places its files where the app keeps them (--place), installs the firebase-kit skill and records the copy in kits.lock. kit status then shows what changed upstream and what the app edited; kit update merges the kit's changes three ways, keeping the app's edits. The install prints what the app must provide (requires).

Without it

The same by hand, from a clone of this repository.

1. Copy the paths listed under code in kit.yml into the app, under the module path the app gives them: firebase/… → core/firebase/…; copy the paths under files where the app keeps such files (ios/Firebase, scripts/distribute-firebase.sh, fastlane/FirebaseFastfile, fastlane/.env.firebase.example, config/firebase). Note the commit you copied (git rev-parse HEAD) — updates start from it.

2. Rename in everything copied:

   In the kit	Becomes	Where
   io.thernal.firebasekit	the app's package, e.g. com.example.app	sources, build files; and the directories io/thernal/firebasekit
   :firebase: and ":firebase", projects.firebase.	the module path, e.g. :core:firebase:, projects.core.firebase.	build files
   libs.plugins.firebasekit.	the app's catalog alias, e.g. libs.plugins.app.	build files
   import SampleShared	import of the app's Kotlin framework	Swift files

   # in the app, after copying — perl, so it runs the same on macOS and Linux
   grep -rlI -e io.thernal.firebasekit -e io/thernal/firebasekit -e :firebase -e plugins.firebasekit. -e SampleShared core/firebase iosApp/iosApp/Firebase scripts/distribute-firebase.sh fastlane/FirebaseFastfile fastlane/.env.firebase.example config/firebase \
     | xargs perl -pi -e 's/\Qio.thernal.firebasekit\E/com.example.app/g; s{\Qio/thernal/firebasekit\E}{com/example/app}g; s/\Q:firebase:\E/:core:firebase:/g; s/"\Q:firebase\E"/":core:firebase"/g; s/projects\.\Qfirebase\E\./projects.core.firebase./g; s/libs\.plugins\.\Qfirebasekit\E\./libs.plugins.app./g; s/^(\s*(?:@\w+\s+)?)import \QSampleShared\E$/$1import ComposeApp/'
   find core/firebase -depth -type d -path '*/io/thernal/firebasekit' | while read -r d; do
     mkdir -p "${d%/io/thernal/firebasekit}/com/example" && mv "$d" "${d%/io/thernal/firebasekit}/com/example/app"
   done
   find core/firebase -depth -type d -empty -delete

3. Provide what the copy expects — the requires list in kit.yml: convention plugins (build-kit's, or the ones in this repository's build-logic/convention), catalog entries, settings — and, where listed, platform setup.

4. The skill (optional): copy skills/firebase-kit into the app's skills directory (.claude/skills/ for Claude Code), with the same renames, so an agent working in the app knows the kit.

5. Updates are yours to carry: git diff <the commit you copied> <a newer one> -- <the code paths> in the kit shows what changed; apply what you want, renamed the same way.

Layout

Part	Holds	Depends on
firebase/crash/{api,impl,wiring}	CrashReporter; Crashlytics	Crashlytics (Android)
firebase/config/{api,impl,wiring}	RemoteConfigKey<T>, ConfigKey, RemoteConfig, RemoteConfigSource; DefaultRemoteConfig, StaticRemoteConfigSource, the Firebase source	Remote Config (Android)
firebase/messaging/{api,impl,wiring}	PushMessage, PushMessaging, PushMessageStream; the Android messaging service, notification and PushIntents	Messaging, core, lifecycle-process (Android)
firebase/auth/{api,impl,wiring}	SocialSignIn, SignInResult; Credential Manager (Google) and Firebase's Apple flow	Auth, Credential Manager, Google ID, startup (Android)
firebase/bridge	the interfaces the Swift implements, FirebaseBridges, PushHub — exported into the iOS framework	messaging/api
firebase/testing	FakeCrashReporter, testRemoteConfig(), FakePushMessaging, FakePushMessageStream, FakeSocialSignIn	the apis
ios/Firebase	FirebaseKit.swift and one bridge per capability	Firebase iOS SDK, GoogleSignIn (SPM)
fastlane/FirebaseFastfile, scripts/distribute-firebase.sh, fastlane/.env.firebase.example	App Distribution lanes and their environment	fastlane, build-kit's make
config/firebase	example google-services.json and GoogleService-Info.plist, and what the kit reads from them	—
sample/{shared,android,ios}	one screen using all four	the kit — never copied

Building

./gradlew build

Every target, tests on the JVM host and the iOS simulator — remote config (defaults, activation, throttling, decoding, a failed fetch), the push token stream and taps kept until collected, the iOS bridges' adapters, sign-in results, the fakes, and a Metro graph that replaces Firebase with fixed values — Detekt, which fails on any finding, Android lint on the sample, and the sample's iOS framework link. No Firebase project is needed: the build never talks to Firebase.

The iOS sample compiles the Swift bridges against the Kotlin framework and the Firebase iOS SDK (fetched by Swift Package Manager on the first build):

xcodebuild -project sample/ios/Sample.xcodeproj -scheme Sample -sdk iphonesimulator \
  -destination 'generic/platform=iOS Simulator' build

No google-services.json or GoogleService-Info.plist is committed — config/firebase has examples of both. Without them the sample runs with Firebase unconfigured and every capability says so; put real ones at sample/android/google-services.json and sample/ios/Sample/GoogleService-Info.plist and it runs against that project.