fixup! Hackish workaround for ocurrent/obuilder#77

lib/opam_build.ml

@@ -41,12 +41,13 @@ let opam_install ~variant ~opam_version ~pin ~lower_bounds ~with_tests ~pkg =
  (if with_tests then [
  (* TODO: Remove this hack when https://github.com/ocurrent/obuilder/issues/77 is fixed *)
  (* NOTE: This hack will fail for packages that have src: "git+https://..." *)
- run ~cache ~network "(%sopam reinstall --with-test %s) || true"
+ run ~network "(%sopam reinstall --with-test %s) || true"
  (match opam_version with `V2_1 | `Dev -> "" | `V2_0 -> fmt "opam depext%s %s && " with_tests_opt pkg) pkg
  ] else []) @ [
  (* TODO: Replace by two calls to opam install + opam install -t using the OPAMDROPINSTALLEDPACKAGES feature *)
  (* NOTE: See above for the ~network:(if with_tests ...) hack *)
- run ~cache ~network:(if with_tests then [] else network)
+ (* NOTE: We cannot use the cache as concurrent access to the cache might overwrite it and the required archives might not be available anymore at this point *)
+ run ~cache:(if with_tests then [] else cache) ~network:(if with_tests then [] else network)
  {|%sopam reinstall%s%s %s;
  res=$?;
  test "$res" != 31 && exit "$res";