Limit number of structs in iex autocomplete

[v0idpwn]

Getting structs for iex autocomplete is expensive: modules need to be loaded and checked to see if they define structs. This means that autocompleting for an empty struct name or a short one can be very slow in codebases with many modules and dependencies. In my work codebase, it might take several seconds for the autocomplete to return something and iex get stuck meanwhile.

This PR limits the number of structs, so that if a query that would return too many results is made, iex returns the completion quickly enough.

Sample:

v0idpwn ~/oss/elixir [feat/limit-number-of-structs-in-autocomplete] $ ./bin/iex
Erlang/OTP 25 [erts-13.1.4] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]

Interactive Elixir (1.16.0-dev) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> %<TAB>
Config.Provider            Date
Date.Range                 DateTime
DynamicSupervisor          File.Stat
File.Stream                GenEvent.Stream
HashDict                   HashSet
IEx.History                IEx.Server
IO.Stream                  Inspect.Opts
Logger.Backends.Console    Logger.Formatter
Macro.Env                  MapSet
NaiveDateTime              Range
•••

[v0idpwn]

Will add tests, opening for early denial if you disagree with the solution. The limit is also up to discussion.

[josevalim]

I wonder if we could try to optimize this first. We could use Code.ensure_all_loaded for example to load modules (which will be done in parallel IIRC).

[v0idpwn]

Made a branch where I load the modules in advance, leveraging concurrency/parallelism: v0idpwn@276f2f8. No tests broken, everything behaves the same. Didn't bench, will need to setup a project for benching, probably will do it in the weekend.

[josevalim]

Ping. :)

[josevalim]

I pushed a commit that uses Code.ensure_all_loaded. I think with the code path cache from Erlang/OTP 26 and Elixir v1.15 with the Code.ensure_all_loaded, this is probably quite fast now :)

[v0idpwn]

Thanks, @josevalim. I didn't manage to prioritise benching the solutions.