I suspect this is not possible, as I discussed in the commit message of 0f7cb660801f90fe055e9359058023f607afecec
Also, inlined records, that type of the form
type u = U of { foo : bar }
are still not supported, and might never be supported due to the
restriction of OCaml regarding these types (embodied by the error
message “This form is not allowed as the type of the inlined record
could escape”).
I suspect this is not possible, as I discussed in the commit message of 0f7cb660801f90fe055e9359058023f607afecec