Ex_aws lambda invoke is undefined

i have an app app1 which uses ExAws.Lambda.invoke/4. All is well and no compile warnings.

Another app say app2 uses app1 as a dependency. For some reason I get a compile warning: ExAws.Lambda.invoke/4 is undefined (module ExAws.Lambda is not available or is yet to be defined) lib/app2/client.ex:40: App2.Client.get_page/2.

Now in App1, i have aliased
alias ExAws.Lambda and calling the function as such:

    |> Lambda.invoke(
      invocation_type: :request_response
    |> ex_aws.request()

The warning comes from app2 on a fresh compile but not on subsequent compiles even when forced using the --force option. I also have to remove _build and deps for the warning to show.

What’s happening in lib/app2/client.ex:40: App2.Client.get_page/2? If app2 wants to use ExAws directly, it needs to add it to it’s own dependencies.

It feels like forcing the “parent” app (app2 in this example) to specify this as a dependency is giving the parent too much knowledge about an implementation detail. Or is it expected that when an app depends on other smaller apps, the parent may need to explicitly list the dependencies of its dependencies?

The “parent” app needs to add the library as a dependency only if it explicitly calls it. Looking at the error, it seems that this is the case here.

Thanks for the reply. i realized the app1 and app2 might be a bit confusing so lets call one app fetch (the child app in this case) which uses ex_aws_lambda and “parent” app called worker.

Worker has ex_aws_lambda already inside of the mix.exs.

fetch also has ex_aws_lambda inside of mix.exs also.

Worker is also not calling ex_aws_lambda directly inside of the code. We have ex_aws_lambda inside of Worker because inside of fetch we describe ex_aws_lambda as an optional dep which gives the “parent” app (worker) in this case to define the dep

I realized in my example i may have crossed the wires and confused myself.

The cause can be if the “child” app has any options in its mix.exs that qualify the dependency, e.g.

{:ex_aws_lambda, "~> 2.0.2", optional: true}

might need to be just:

{:ex_aws_lambda, "~> 2.0.2"}

The optional parameter is one of those weird gotchas that in effect makes the child app say “hey parent – your call on what to do here.” In effect, it requires the parent app to be aware of what the child app is doing EVEN IF the parent isn’t directly calling that dependency.

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yep! the solution was to remove the optional: true and all was fine. The warning was gone from the parent app.