lmdb depext on nixos

[RyanGibb]

No description provided.

[jmid]

Thanks! The change LGTM 👍

I had missed this hidden conf-lmdb in lmdb 😅

While we have our fingers in lmdb, I really hope you are up for fixing a couple of other things for the greater good of the package 🤞

For one, I think this is missing a lower bound on "bigstringaf":
https://opam.ci.ocaml.org/github/ocaml/opam-repository/commit/42572bec27fac3424f6dd5330fa72d5c4d17b92d/variant/compilers,4.08,lmdb.1.0,lower-bounds

#=== ERROR while compiling lmdb.1.0 ===========================================#
# context              2.5.0~beta1 | linux/x86_64 | ocaml-base-compiler.4.08.1 | pinned(https://github.com/Drup/ocaml-lmdb/archive/1.0.tar.gz)
# path                 ~/.opam/4.08/.opam-switch/build/lmdb.1.0
# command              ~/.opam/opam-init/hooks/sandbox.sh build dune build -p lmdb -j 255
# exit-code            1
# env-file             ~/.opam/log/lmdb-7-f64fc6.env
# output-file          ~/.opam/log/lmdb-7-f64fc6.out
### output ###
# File "/home/opam/.opam/4.08/lib/bigstringaf/bigstringaf.dune", line 1, characters 0-0:
# Warning: .dune files are ignored since 2.0. Reinstall the library with dune
# >= 2.0 to get rid of this warning and enable support for the subsystem this
# library provides.
#       ocamlc src/.lmdb.objs/byte/lmdb.{cmo,cmt} (exit 2)
# (cd _build/default && /home/opam/.opam/4.08/bin/ocamlc.opt -w -40 -safe-string -thread -g -bin-annot -I src/.lmdb.objs/byte -I /home/opam/.opam/4.08/lib/bigstringaf -intf-suffix .ml -no-alias-deps -open Lmdb__ -o src/.lmdb.objs/byte/lmdb.cmo -c -impl src/lmdb.ml)
# File "src/lmdb.ml", line 267, characters 8-34:
# 267 |         Bigstring.blit_from_string s ~src_off:0 a ~dst_off:0 ~len;
#               ^^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: Unbound value Bigstring.blit_from_string
#     ocamlopt src/.lmdb.objs/native/lmdb.{cmx,o} (exit 2)
# (cd _build/default && /home/opam/.opam/4.08/bin/ocamlopt.opt -w -40 -safe-string -thread -g -I src/.lmdb.objs/byte -I src/.lmdb.objs/native -I /home/opam/.opam/4.08/lib/bigstringaf -intf-suffix .ml -no-alias-deps -open Lmdb__ -o src/.lmdb.objs/native/lmdb.cmx -c -impl src/lmdb.ml)
# File "src/lmdb.ml", line 267, characters 8-34:
# 267 |         Bigstring.blit_from_string s ~src_off:0 a ~dst_off:0 ~len;
#               ^^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: Unbound value Bigstring.blit_from_string

Second, the conf- part is missing Centos support (I can see this is now fixed upstream).

Third, as a user of an Ubuntu family distribution and past fixer of several of these cases, could you expand
["liblmdb-dev"] {os-family = "debian"} to
["liblmdb-dev"] {os-family = "debian" | os-family = "ubuntu"}

(the GitHub UI will not let me make an inline suggestion 🤷)

Fourth, I see a number of runtest failures on "margin platforms" (arm32, 4.14-afl, ppc64, x86_32). What do you make of these? Should we consider disabling the test suite there?

[jmid]

I've now opened #28986 with my last suggestion to help unblock this PR.