Graph verification feature

[Nek-12]

One of the main complaints I see about kodein vs koin is that there is no way to verify the validity of the dependency graph.

On the surface a simple unit test doesnt't look like a particularly hard to implement feature to me.
We will need to investigate what actual blockers there are to such a feature, but in general this seems to be important to large teams - ensuring safety of the graph.

I don't think we need verification codegeneration or something like that, or compile-time safety. a simple unit test hooked up to CI will be enough to verify no crashes will slip into production.

[romainbsl]

We had some plans about it back in 2021/22, but we needed context parameters at some point, so we've put this on hold and still waiting... I'll try to think of something else. Do you have some thought about this?

[Nek-12]

Well, the context parameters are out! So nothing's stopping us now. But I still wonder what you needed them for.

I do have some thoughts:

It doesn't have to be perfect, but it can work, especially since Kodein's architecture is much better than Koin's regarding parameters.

Essentially the work we need to do is use the existing scaffolding of showing the entire graph when a dependency is not found, but trigger it proactively.

I envison an API like:

fun DI.verifyGraph(
   externallyProvided: List<KClass>,
)

Usage:

@Test
fun testGraph() = DI.global.verifyGraph(


)

1. We take a di, and go and instantiate each included module recursively until we reach the end.
2. We collect all usages of all dependencies into a map.
3. If there's binding for a type declared by given KClass, we mark it as present. If there isn't we mark it as missing and note who requested it.
4. When we traversed the entire graph, we go and check that all usages we marked have a corresponding bindings declared.
5. If not all usages have a binding at the end, we throw and print the graph and missing deps.
6. We can also easily ignore the parameters (arguments) types since they are their own thing (factories). This will not verify that parameters are passed, but oh well, can't have a cake and eat it too.

I can take a stab at it if you'd like me to, but I'll need your help with possible caveats and limitations