Incorrect dependency filtering for completions

[scohen]

I was working on a project, telemetry_metrics_statsd, and completions for its struct modules failed. This is because in server/code_intelligence/completion.ex, the function displayable? checks to see if the emitted completion is one of lexical's dependencies, and if it is, says that it's not displayable. There are two bugs here.

The first is that it just does a prefix check, and thinks TelemetryMetricsStatsd.UDP... is a module in Telemetry. This is wrong, there should be a more rigorous module prefix check rather than a substring check.

The second bug is that we're pulling all of the project's dependencies, and expert might depend on a module that your project depends on, and you definitely want to see that show up in completions.

I think we should get a list of the project under test's dependencies and do a check to see if the module is included in them in order to see if it's displayable.

[lukaszsamson]

Do you think we should get the deps from mix or apps from the application controller? Elixir compiler is quite lazy with application controller state updates. There’s also an option of reading app manifests manually.

[scohen]

I don't have an opinion on where we get the dependencies. I was thinking of using mix, since remote control has tooling for that. How lazy is mix?