Meshtastic-Android/docs/decisions/koin-migration.md

Decision: Hilt → Koin Migration

Date: 2026-02-20 to 2026-03-09 | Status: Complete

Context

Hilt (Dagger) was the strongest remaining barrier to KMP adoption — it requires Android-specific annotation processing and can't run in commonMain.

Decision

Migrated to Koin 4.2.0-RC1 with the K2 Compiler Plugin (io.insert-koin.compiler.plugin) and later upgraded to 0.4.0.

Key choices:

• @KoinViewModel replaces @HiltViewModel; koinViewModel() replaces hiltViewModel()
• @Module + @ComponentScan in commonMain modules (valid 2026 KMP pattern)
• @KoinWorker replaces @HiltWorker for WorkManager
• @InjectedParam replaces @Assisted for factory patterns
• Root graph assembly centralized in AppKoinModule; shared modules expose annotated definitions
• Koin 0.4.0 A1 Compile Safety Disabled: Meshtastic heavily utilizes dependency inversion across KMP modules (e.g., interfaces defined in core:repository are implemented in core:data). Koin 0.4.0's per-module A1 validation strictly enforces that all dependencies must be explicitly provided or included locally, breaking this clean architecture. We have globally disabled A1 compileSafety in KoinConventionPlugin to properly rely on Koin's A3 full-graph validation at the composition root (startKoin).

Gotchas Discovered

1. K2 Compiler Plugin signature collision: Multiple @Single providers with identical JVM signatures in the same @Module cause ClassCastException. Fix: split into separate @Module classes.
2. Circular dependencies: Lazy<T> injection can still StackOverflowError if Lazy is accessed too early (e.g., in init coroutine). Fix: pass dependencies as function parameters instead.
3. Robolectric KoinApplicationAlreadyStartedException: Call stopKoin() in onTerminate.

Consequences

• Hilt completely removed
• All 23 KMP modules can contain Koin-annotated definitions
• Desktop bootstraps its own DesktopKoinModule with stubs + real implementations
• 11 passthrough Android ViewModel wrappers eliminated