Hover of a mutually recursive type can cause a stack overflow

[Chaarlesss]

Hi,

Merlin produces a stack overflow which causes Emacs to freeze when hovering the type b on line 1 of the following code:

type a = A | B of int * b
and b = a list

Strangely, the problem does not occur when hovering the type a on line 2.

I am using Merlin 4.14-501 with OCaml 5.1.1.

The end of the stack trace is:

[voodoos]

Thank for your report @Chaarlesss.

Are you using merlin mode or an lsp mode ?

Could it be that your "hover" query has a high verbosity by default ?

[Chaarlesss]

I am using merlin mode (with merlin-eldoc).

To clarify, I found this error in the log's buffer and does not appear when the problem occurs.

I guess the freeze may come from my own configuration of Emacs (which is roughly Doom Emacs with the OCaml module), but I think that the underlying problem may come from Merlin.

I also tried to reproduce this in VSCode (standard setup with OCamlPlatform), and I also get a strange result (but I am not sure Merlin the one in cause here):

[voodoos]

Looking into eglot, it does seems that there is a verbosity setting that can be min or max. You might want to set that on min.

Verbosity was not meant to be always set on max and it can lead to strange issues with recursive types.

While setting verbosity to min might be a workaround I agree that the behavior of Merlin is not satisfying here, it would be worth to have a look.

[Chaarlesss]

Changing the verbosity fixed indeed the freezing. Thanks for pointing me to this solution !