Feature: Expert should detect a changed elixir version for the project node

[Terbium-135]

On changing the elixir version of a project I sometimes see strange behaviours of expert (like red or yellow curly line - in VSCode)
To solve this I have to delete the experts's _build folder.
I'm not sure if this is the real problem though

Expert should detect a changed elixir version for the project node and do the proper actions needed

[mhanberg]

I'm not sure how we can do this other than polling elixir --version, which doesn't sound correct. I think restarting your editor should be enough.

Is your intent to not have to restart your editor?

[mkaput]

are we able to detect that caches in _build suddenly happen to have been changed? as far as I see elixirc leaves traces of its own version there

iex(3)> file2 = File.read!("_build/dev/lib/<pkg>/.mix/compile.elixir_scm")
<<131, 104, 3, 97, 1, 104, 2, 109, 0, 0, 0, 6, 49, 46, 49, 57, 46, 52, 107, 0,
  2, 50, 56, 119, 14, 69, 108, 105, 120, 105, 114, 46, 72, 101, 120, 46, 83, 67,                                                                                                                                                                                                                                                                                  
  77>>                                                                                                                                                                                                                                                                                                                                                            
iex(4)> :erlang.binary_to_term(file2)
{1, {"1.19.4", ~c"28"}, Hex.SCM}

---

Is your intent to not have to restart your editor?

I guess yes. DX-wise, I think a milder thing but still pretty good would be to send a notification prompting to do the restart. But this looks to me like just Expert's Engine needs to be restarted, right?

[mkaput]

Another trick is to employ didChangeWatchedFiles and watch for mix.exs, .tool-versions file changes and restart the engine in reaction to this.

[mhanberg]

are we able to detect that caches in _build suddenly happen to have been changed? as far as I see elixirc leaves traces of its own version there

iex(3)> file2 = File.read!("_build/dev/lib/<pkg>/.mix/compile.elixir_scm")
<<131, 104, 3, 97, 1, 104, 2, 109, 0, 0, 0, 6, 49, 46, 49, 57, 46, 52, 107, 0,
  2, 50, 56, 119, 14, 69, 108, 105, 120, 105, 114, 46, 72, 101, 120, 46, 83, 67,                                                                                                                                                                                                                                                                                  
  77>>                                                                                                                                                                                                                                                                                                                                                            
iex(4)> :erlang.binary_to_term(file2)
{1, {"1.19.4", ~c"28"}, Hex.SCM}

---

Is your intent to not have to restart your editor?

I guess yes. DX-wise, I think a milder thing but still pretty good would be to send a notification prompting to do the restart. But this looks to me like just Expert's Engine needs to be restarted, right?

The elixir version is dependent on what we find in the path. The version stored in this data won't change as the LSP will still be using the same elixir version as it was started with.

[mhanberg]

Another trick is to employ didChangeWatchedFiles and watch for mix.exs, .tool-versions file changes and restart the engine in reaction to this.

Mix.exs doesn't declare what elixir or Erlang version is being used and tool versions is not reliable.

[mkaput]

The elixir version is dependent on what we find in the path. The version stored in this data won't change as the LSP will still be using the same elixir version as it was started with.

If the user didn't compile the code manually, then it's questionable whether we can state that the Elixir version has even been changed, isn't it? I understand this issue is about this scanario:

$ asdf set -u elixir 1.18.4
# User opens the project
$ asdf set -u elixir 1.19.5
$ mix compile
# Expert goes crazy

[mkaput]

Mix.exs doesn't declare what elixir or Erlang version is being used

True. I just generalized here. Isn't a similar story happening when user changes dependencies?

and tool versions is not reliable.

Yes, it is not - but that's at least something we can easily observe and is relatively popular in this ecosystem.

[mhanberg]

Isn't a similar story happening when user changes dependencies?

Yes, but that we are alerted to directly by getting compiler errors. Also we don't do this yet, Next LS did it but we haven't ported it over yet.

We can continue to explore this feature, but its not a current priority

[Terbium-135]

It is NOT about restarting the editor.
Don't call me lazy please

A restart does not help. After changing the elixir version only thing which helps to get rid of these false positive error messages is to remove the build folder within elixir.

Perhaps the true reason lies somewhere else.
Let me know if I can help

[mhanberg]

Don't call me lazy please

I didn't call you lazy, I asked a basic question.