Builds on ocaml 4.07.0

[ismith]

Solves #4 without a lock file, and allows for compatibility with ocaml 4.07.0.

Does require

opam pin -y nocrypto git+https://github.com/gasche/ocaml-nocrypto.git#master-ocamlbuild-pack
opam pin -y jwt git+https://github.com/ismith/ocaml-jwt.git#rsa256-verification

[ismith]

Test build on ocaml 4.07.0 using Docker:

FROM ubuntu:xenial

ENV ocaml_version 4.07.0

RUN apt update; \
    apt install -y apt ocaml-nox zlib1g-dev git curl \
      make m4 unzip libgmp-dev pkg-config vim libssl-dev \
      software-properties-common; \
    apt-add-repository ppa:avsm/ppa; \
    apt update; \
    apt install -y opam

RUN opam init -a --disable-sandboxing; \
    opam switch create $ocaml_version ocaml-base-compiler.$ocaml_version; \
    eval $(opam env); \
    opam install dune

RUN opam pin -y nocrypto git+https://github.com/gasche/ocaml-nocrypto.git#master-ocamlbuild-pack
RUN opam pin -y jwt git+https://github.com/ismith/ocaml-jwt.git#rsa256-verification # rsa256-verification
RUN opam pin -y gcloud git+https://github.com/ismith/ocaml-gcloud.git#builds-on-ocaml-4.07.0

[actionshrimp]

Interesting, thanks for taking a look! I had a bit of a read of the various nocrypto issue threads, and saw this:

ocaml/opam-repository#12062

So it looks like the other approach for nocrypto+ppx_sexp_conv from this PR is on opam at the minute, although the patches are applied to an older version of nocrypto without the function Nocrypto.Rsa.PKCS1.sign that the jwt fork needs.

I tried your Dockerfile with the PR version of @diml's branch that should be on the more up to date version of nocrypto, but got a built error, so happy to merge this unless you can think of another solution!

[ERROR] The compilation of nocrypto failed at "/root/.opam/4.07.0/bin/ocaml pkg/pkg.ml build --pinned true --tests false --with-lwt false --xen false --mirage false --freestanding false".

#=== ERROR while compiling nocrypto.0.5.4-1 ===================================#
# context              2.0.2 | linux/x86_64 | ocaml-base-compiler.4.07.0 | pinned(git+https://github.com/diml/ocaml-nocrypto.git#detect-ppx_sexp_conv-runtime#6252cc6e)
# path                 ~/.opam/4.07.0/.opam-switch/build/nocrypto.0.5.4-1
# command              ~/.opam/4.07.0/bin/ocaml pkg/pkg.ml build --pinned true --tests false --with-lwt false --xen false --mirage false --freestanding false
# exit-code            1
# env-file             ~/.opam/log/nocrypto-6-a75bcf.env
# output-file          ~/.opam/log/nocrypto-6-a75bcf.out
### output ###
# Error: The implementation (obtained by packing)
# [...]
# Command exited with code 2.
# pkg.ml: [ERROR] cmd ['ocamlbuild' '-use-ocamlfind' '-classic-display' '-j' '4' '-tag' 'debug'
#      '-build-dir' '_build' '-plugin-tag' 'package(ocb-stubblr)' '-tag'
#      'accelerate' 'opam' 'pkg/META' 'CHANGES.md' 'LICENSE.md' 'README.md'
#      'src/dllnocrypto_stubs.so' 'src/libnocrypto_stubs.a' 'src/nocrypto.a'
#      'src/nocrypto.cmxs' 'src/nocrypto.cmxa' 'src/nocrypto.cma'
#      'src/nocrypto.cmx' 'src/nocrypto.cmi' 'src/nocrypto.mli'
#      'unix/nocrypto_unix.a' 'unix/nocrypto_unix.cmxs'
#      'unix/nocrypto_unix.cmxa' 'unix/nocrypto_unix.cma'
#      'unix/nocrypto_entropy_unix.cmx' 'unix/nocrypto_entropy_unix.cmi'
#      'unix/nocrypto_entropy_unix.mli']: exited with 10