edlin expansion takes ~15s for erl_syntax

[robertoaloi]

Describe the bug
In the context of #WhatsApp/erlang-language-platform/issues/70, I started playing around with edlin auto-completion and noticed it can be very slow for certain functions.

To Reproduce

1> timer:tc(fun() -> edlin_expand:expand(lists:reverse("erl_syntax:concrete("),[]) end).

This takes almost 15s for me the first time. Then, the result is cached.

Expected behavior
Completions are provided much faster.

Affected versions
OTP 27

[garazdawi]

There is a reason why there is a cache :) We could add a way to heat up the cache in advance, but it could be rather memory hungry on large system.

[josevalim]

@garazdawi do you know what is expensive in this case? Trying to resolve the types?

[garazdawi]

I haven't looked into this specific case, but in general when we do completions we follow all the types until their end, so the first completion request can en up touching a lot of files that are parsed for their type information.

@frazze-jobb probably has a better idea around what is slow.