$ opam pin add ocamlformat_reason https://github.com/ocaml-ppx/ocamlformat.git
Package ocamlformat_reason does not exist, create as a NEW package? [Y/n] y
[ocamlformat_reason.~dev] synchronised from git+https://github.com/ocaml-ppx/ocamlformat.git
ocamlformat_reason is now pinned to git+https://github.com/ocaml-ppx/ocamlformat.git (version ~dev)

The following actions will be performed:
  ∗ install ocamlformat_reason ~dev*
Do you want to continue? [Y/n] y
[ocamlformat_reason.~dev] synchronised from git+https://github.com/ocaml-ppx/ocamlformat.git

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
[ERROR] The compilation of ocamlformat_reason failed at "/home/rt/.opam/opam-init/hooks/sandbox.sh build
        dune build -p ocamlformat_reason -j 1".

#=== ERROR while compiling ocamlformat_reason.~dev ============================#
# context     2.0.5 | linux/x86_64 | ocaml-base-compiler.4.07.1 | pinned(git+https://github.com/ocaml-ppx/ocamlformat.git#ce9e5393)
# path        ~/.opam/4.07.1/.opam-switch/build/ocamlformat_reason.~dev
# command     ~/.opam/opam-init/hooks/sandbox.sh build dune build -p ocamlformat_reason -j 1
# exit-code   1
# env-file    ~/.opam/log/ocamlformat_reason-10335-d6d332.env
# output-file ~/.opam/log/ocamlformat_reason-10335-d6d332.out
### output ###
#        ocaml (internal) (exit 2)
# (cd test/passing && /home/rt/.opam/4.07.1/bin/ocaml -I +compiler-libs /home/rt/.opam/4.07.1/.opam-switch/build/ocamlformat_reason.~dev/_build/.dune/default/test/passing/dune.ml)
# File "test/passing/dune", line 54, characters 23-35:
# Error: Unbound module Option


<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
┌─ The following actions failed
│ λ build ocamlformat_reason ~dev
└─ 
╶─ No changes have been performed
[NOTE] Pinning command successful, but your installed packages may be out of sync.

┌─ The following changes have been performed
│ ∗ install menhir        20190924
│ ∗ install merlin-extend 0.5
│ ∗ install reason        3.5.0
└─