Provide a Gradualizer diagnostic

[erszcz]

This implements a basic Gradualizer diagnostic for Erlang LS we, i.e. @garazdawi, Ferenc Pesti and I, built during an Erlang Solutions internal hackathon early this year. Some example screenshots of this integration in action can be seen here - josefs/Gradualizer#344 (comment).

I'm creating this as a draft, since I'm not sure what's the best way to express the dependency on Gradualizer - currently even the newly added test won't pass, since I haven't added Gradualizer to Rebar3 deps. What's the best approach for adding dependencies for optional diagnostics?

Important: Gradualizer, while being continuously improved, is still a work in progress and doesn't successfully self-gradualize yet. It's already useful, but it might also be misleading at times. That being said, I think having the integration in place is worth the effort, as it makes trying out the project and contributing easier.

[robertoaloi]

Thanks for this, amazing stuff! I asked in our Slack channel what's the Community view on this. I will also take it with the other core maintainers and come back to you shortly :)

[robertoaloi]

For visibility, copying from Slack:

We briefly discussed this internally. The current take would be to keep it simple as much as we can (e.g. just include gradualizer and have it disabled by default), until we decide on an eventual plugin-based structure

[robertoaloi]

Also, I briefly tried the Gradualizer on the Erlang LS project itself and I noticed a couple of things:

• A number of warnings appear from Gradualizer about "undefined functions"
• Some messages seem truncated. For example:

{
      "source": "Gradualizer",
      "severity": 2,
      "range": {
        "start": {
          "line": 145,
          "character": 0
        },
        "end": {
          "line": 146,
          "character": 0
        }
      },
      "message": "The pattern #{config := #{entries := Entries, task := Task} = Config,"
    },

[erszcz]

Thanks for the feedback!

• A number of warnings appear from Gradualizer about "undefined functions"

I haven't seen this happening, but I'm not saying it's not - could you provide an example?

• Some messages seem truncated. For example:

Good catch! Fixed now.

I've added the dependency on Gradualizer, but maybe it's worth waiting for josefs/Gradualizer#358 before merging this one.

[erszcz]

The warnings cleanup in Gradualizer is merged, so I'm clicking "Ready for review" :)

[robertoaloi]

Looks great, just a couple of questions and nits that can eventually be addressed as follow ups.

[robertoaloi]

In principle this could fail if, for example, gradualizer had an additional dependency which was not started. Maybe relax the matching to an {ok, _} or similar?

[robertoaloi]

Also, I wonder if we shouldn't execute this only once during the negotiation phase between client and server.

[erszcz]

Gradualizer is written with no runtime dependencies other than OTP libs. This check, together with the second clause {ok, []}, effectively makes this code run only the first time start_and_load is called.

[robertoaloi]

Can't the column be used for the diagnostic?

[erszcz]

We had some trouble making this work reliably, but I don't remember the details. I think this is something worth working out in the future, but is not critical for getting the warnings - they're just reported at line granularity for now.

[erszcz]

Having applied the fixes and added Gradualizer as a Rebar3 dependency, I'm getting an unexpected warning that

can't find include lib "gradualizer/include/gradualizer.hrl"

for -include_lib("gradualizer/include/gradualizer.hrl"). in files open in the editor. This header file contains macros for manually adding type annotations to bits of code.

Please wait with the merge until I resolve that. EDIT: resolved, please see the comment below.

[erszcz]

Ok, problem solved. This was an Erlang LS config mistake on my side. It should be:

include_dirs:
  - "_build/default/lib/"

NOT:

include_dirs:
  - "_build/default/lib/*/include"

And if Gradualizer is also added as a project dependency, then -include_lib("gradualizer/include/gradualizer.hrl"). works as expected.

[robertoaloi]

Thanks!