support OCaml 5.3

[anmonteiro]

the expect tests still have some failures like this if ran on 5.3. Any advice on how to make them conditional?

File "test/bin/mdx-test/expect/simple-mli/test-case.mli", line 1, characters 0-0:
diff --git a/_build/default/test/bin/mdx-test/expect/simple-mli/test-case.mli b/_build/default/test/bin/mdx-test/expect/simple-mli.actual
index ad197127..ad54569e 100644
--- a/_build/default/test/bin/mdx-test/expect/simple-mli/test-case.mli
+++ b/_build/default/test/bin/mdx-test/expect/simple-mli.actual
@@ -56,7 +56,7 @@ val baz : string
 ][
 {err@mdx-error[
 Line 1, characters 15-18:
-Error: This expression has type string but an expression was expected of type
+Error: This constant has type string but an expression was expected of type
          int
 ]err}]}
 *)

[samoht]

@voodoos is this the right way to fix this? What about using ~current_unit:None instead?

[samoht]

I've rebased on top of main to fix the tests

[voodoos]

To answer @samoht question I would say that this is the closest way to get the same "current_unit" information as before in the uid since Uid.make will use the modname part of the Unit_info which is "Mdx".

As to whether this information is important to have, I guess it's not (and therefore None would probably work too), unless there is tooling that expect this information to be "correct". (AFAIK it's only important for tooling.)

For reference, (I don't know if it would make sense here), in the compiler this information is retrieved from the environment: Uid.mk ~current_unit:(Env.get_current_unit ())

[samoht]

Thanks! I've simplified the support as I don't think the tooling needs anything complicated here.