Comment author: @garrigue

The message is correct: there is indeed no module type Equal in scope inside foo.ml.
Moreover, since the name spaces for modules and module types are distinct, the fact there is a module Equal does not seem to be relevant here. I don't see in which way the suggested message would improve.
I we were to visit all imported modules, one could attempt to say that there is indeed a module type Equal.Equal, but looking for it can be very expensive.

Comment author: @whitequark

Well, I suppose it makes sense. I'm reporting on behalf on someone from IRC, who found it confusing. I do find the fact that modules and module types have different namespaces confusing, as well.

Comment author: @damiendoligez

Maybe it would make sense to append a note saying that there is a module by that name, but it's not a module type, as an extension of the spell-checking idea.

Indeed all these namespaces are sometimes confusing.

Comment author: @whitequark

I like this solution.

This issue has been open one year with no activity. Consequently, it is being marked with the "stale" label. What this means is that the issue will be automatically closed in 30 days unless more comments are added or the "stale" label is removed. Comments that provide new information on the issue are especially welcome: is it still reproducible? did it appear in other contexts? how critical is it? etc.

Still an issue.

Anybody has a PR for this?

(I think we should have a label for not-so-difficult-to-improve error messages)

We have newcomer-job-advanced for things that are accessible to people unfamiliar with the compiler codebase, but that still require an "advanced" OCaml programming level and/or dealing with a somewhat complex problem. If you think it applies here, it could act as a superset of your label idea. (And if it does not, it's not clear what "not so difficult" means.)

(Usually when we apply the label we also explain what said newcomer should look at to attack the issue: the broad lines of what we would do ourselves to solve it, starting with which files to look for modification or documentation.)

Sounds good. Can you add it ?

I think this one is pretty straightforward: the error message is created in Typemod.report_error. When formatting such lookup module type error, we simply need to look in the environment if a module of the same name exists and return an "advice" (attached to the original error). A similar approach is already implemented for spelling suggestions.