Cleaner intf-impl mismatch error

[ulugbekna]

Example:

Here we could

• [x] have better formatting
• [ ] show path to the intf file rather than the cmi, if possible

edit:

• [ ] we should also not show the mismatch diagnostic on the first word only

[rgrinberg]

I'd say this is a dune issue rather than an LSP issue. But more concretely, we should be able to address things the following way:

1. Improve ocamlc-loc to understand this particular error better
2. Improve the RPC protocol to offer a richer diagnostic type that reflects these OCaml errors better. In particular it should tell us that the interface has a corresponding .mli in the source directory.
3. Finally, on the lsp side we should transform this richer format into something more readable for the user.

PS:

have better formatting

This should be improved across the board in 3.3.1

[ulugbekna]

Improve ocamlc-loc to understand this particular error better

But is ocamlc-loc intended to recognize merlin errors (which seem to be different from compiler ones in some cases)

For example, the compiler reports

Warning 26 [unused-var]: unused variable b.

which is reported by merlin as

Error (warning 26): unused variable b.

Am I missing something?

[rgrinberg]

Merlin reuses the compiler api for printing errors so the distinction is usually a matter of flags + version differences. So we should be able to use the same api.

For example, the compiler reports

I'm pretty sure ocamlc-loc handles both as of today.