[WIP] Add recipe to show Nav2 to Nav3 migration plan

[dturner]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @dturner, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new recipe to guide developers through the migration process from Android's Navigation 2 to Navigation 3. It sets up a foundational Navigation 2 example and then demonstrates the initial step of integrating Navigation 3 components while retaining the existing Navigation 2 structure.

Highlights

• New Migration Recipe: Introduced a new 'recipe' to the project specifically designed to illustrate the migration path from Android's Navigation 2 to Navigation 3.
• Incremental Migration Steps: Added two distinct MainActivity implementations (start and step1) to represent different stages of the migration. The start activity provides a basic Navigation 2 setup, while the step1 activity shows how to begin integrating Navigation 3's NavDisplay by bridging it with the existing Navigation 2 NavHost.
• Dependency Management: Updated various Kotlin and serialization dependencies and explicitly added the Navigation 2 library to support the migration example.

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[gemini-code-assist]

Code Review

This pull request introduces a new recipe to demonstrate a migration path from Navigation 2 to Navigation 3. It adds a 'start' state using Nav2 and a 'step1' state showing how to embed a Nav2 NavHost within a Nav3 NavDisplay.

The code is a good starting point, but I've identified a few areas for improvement:

• There is a critical memory leak due to improper CoroutineScope usage in Nav3NavigatorSimple. I've provided suggestions to fix this using a lifecycle-aware scope from rememberCoroutineScope.
• I've also suggested replacing a println call with standard Android logging and improving a brittle check on a class name for better maintainability.

[gemini-code-assist]

To ensure proper lifecycle management and prevent memory leaks, a CoroutineScope should be created using rememberCoroutineScope() and passed to Nav3NavigatorSimple. This scope is lifecycle-aware and will be cancelled when the composable leaves the composition. This declaration should precede the nav3Navigator initialization. Don't forget to add import androidx.compose.runtime.rememberCoroutineScope.

Suggested change

	val navController = rememberNavController()
	val coroutineScope = rememberCoroutineScope()

[gemini-code-assist]

The Nav3NavigatorSimple should receive a lifecycle-aware CoroutineScope from its constructor to prevent memory leaks. This ensures that any coroutines launched within Nav3NavigatorSimple are properly cancelled when the MainActivity composable is disposed. This change is paired with the declaration of coroutineScope.

Suggested change

	val nav3Navigator = remember { Nav3NavigatorSimple(navController) }
	val nav3Navigator = remember { Nav3NavigatorSimple(navController, coroutineScope) }

[gemini-code-assist]

Using CoroutineScope(Job()) creates a scope that is not tied to any lifecycle, which causes memory leaks. The coroutine launched in init will never be cancelled. This class should receive a lifecycle-aware CoroutineScope from its creator (the MainActivity composable in this case) via its constructor. This change is paired with another one in MainActivity where the scope is created and passed.

Suggested change

	class Nav3NavigatorSimple(val navController: NavHostController){
	val coroutineScope = CoroutineScope(Job())
	class Nav3NavigatorSimple(
	val navController: NavHostController,
	private val coroutineScope: CoroutineScope
	) {

[gemini-code-assist]

Using println for logging is generally discouraged in Android applications. It's better to use the Log class (e.g., Log.d(TAG, ...)), which allows for filtering by tag and log level. While this might be acceptable for a simple recipe, using Log is a better practice to demonstrate.

Suggested change

	println("Key $key not handled by entryProvider, using fallback")
	android.util.Log.d("Nav3Migration", "Key $key not handled by entryProvider, using fallback")

[gemini-code-assist]

Checking the qualified name of the destination class is brittle and can break with library updates. A more robust way to identify and ignore the root navigation graph entry is to check if its parent is null.

                            if (entry.destination.parent == null) {
                                // Ignore nav graph root entries
                                null
                            } else {
                                entry
                            }