odoc does not compile

[patrick-nicodemus]

Using the with-extensions OCaml compiler, odoc failed to compile

#=== ERROR while compiling odoc.2.4.2 =========================================#
# context     2.1.6 | linux/x86_64 | ocaml-variants.5.2.0+flambda2 | https://opam.ocaml.org#a414aa7ca13f5669ba7345e31a62c2017f810a21
# path        ~/.opam/5.2.0+flambda2/.opam-switch/build/odoc.2.4.2
# command     ~/.opam/opam-init/hooks/sandbox.sh build dune build -p odoc -j 15 @install
# exit-code   1
# env-file    ~/.opam/log/odoc-497338-55724a.env
# output-file ~/.opam/log/odoc-497338-55724a.out
### output ###
# [...]
# (cd _build/default && /home/patrick/.opam/5.2.0+flambda2/bin/ocamlc.opt -w -40 -g -w -18-53 -g -bin-annot -bin-annot-occurrences -I src/loader/.odoc_loader.objs/byte -I /home/patrick/.opam/5.2.0+flambda2/lib/astring -I /home/patrick/.opam/5.2.0+flambda2/lib/camlp-streams -I /home/patrick/.opam/5.2.0+flambda2/lib/fpath -I /home/patrick/.opam/5.2.0+flambda2/lib/ocaml/compiler-libs -I /home/patr[...]
# File "src/loader/cmt.ml", line 39, characters 6-25:
# Error: The constructor "Tpat_var" expects 4 argument(s),
#        but is applied here to 3 argument(s)
# (cd _build/default && /home/patrick/.opam/5.2.0+flambda2/bin/ocamlc.opt -w -40 -g -w -18-53 -g -bin-annot -bin-annot-occurrences -I src/loader/.odoc_loader.objs/byte -I /home/patrick/.opam/5.2.0+flambda2/lib/astring -I /home/patrick/.opam/5.2.0+flambda2/lib/camlp-streams -I /home/patrick/.opam/5.2.0+flambda2/lib/fpath -I /home/patrick/.opam/5.2.0+flambda2/lib/ocaml/compiler-libs -I /home/patr[...]
# File "src/loader/odoc_loader.ml", line 115, characters 61-65:
# Error: This expression has type "Compilation_unit.t"
#        but an expression was expected of type "string"
# (cd _build/default && /home/patrick/.opam/5.2.0+flambda2/bin/ocamlopt.opt -w -40 -g -w -18-53 -g -I src/loader/.odoc_loader.objs/byte -I src/loader/.odoc_loader.objs/native -I /home/patrick/.opam/5.2.0+flambda2/lib/astring -I /home/patrick/.opam/5.2.0+flambda2/lib/camlp-streams -I /home/patrick/.opam/5.2.0+flambda2/lib/fpath -I /home/patrick/.opam/5.2.0+flambda2/lib/ocaml/compiler-libs -I /ho[...]
# File "src/loader/ident_env.cppo.ml", line 230, characters 16-33:
# Error: The constructor "Tsig_include" expects 2 argument(s),
#        but is applied here to 1 argument(s)