learn-ocaml is broken on stock Centos 7 virtual machines

[gasche]

I deployed a learn-ocaml server for my OCaml source, on a Centos 7 virtual machine. I learned the hard way that learn-ocaml does not function properly in this environment: only the teacher token works (creating student tokens fails) and then the grader fails.

The problem, as I could reconstruct from error messages (which I haven't kept around, sorry), is that Centos 7 provides a fairly old version of git (1.8.3), which does not support some options that the learn-ocaml codebase uses. More precisely, the problems appears to come from the git -C invocation in https://github.com/ocaml-sf/learn-ocaml/blob/ccfedd4/src/state/learnocaml_store.ml#L54 . (There may be other incompatibilies, but this is the one I found in error messages.)

I fixed the problem by compiling git from source in my Centos 7 machine and installing the result in /usr/local. But I'm afraid that Centos 7 virtual machines are going to remain used for a while in various deployment environments, so I think that it would be useful for other users in the future to ensure that learn-ocaml works properly with its older version of git.