See the build log: https://gitlab.com/emmeline/bexp/-/jobs/222647788
The error is:
[ERROR] /builds/emmeline/bexp/.opam exists, but does not appear to be a valid opam root. Please remove it and use `opam init', or specify a different `--root' argument
Reading the source code, it looks like this error occurs when .opam/config does not exist:
- https://github.com/ocaml/opam/blob/7a8c05ad74d7abf69a3f66857fa59bec530b5df5/src/state/opamGlobalState.ml#L29
- https://github.com/ocaml/opam/blob/7a8c05ad74d7abf69a3f66857fa59bec530b5df5/src/state/opamStateConfig.ml#L141
- https://github.com/ocaml/opam/blob/7a8c05ad74d7abf69a3f66857fa59bec530b5df5/src/format/opamPath.ml#L20
Indeed, when I rename .opam/config to something else on my own computer, I am able to cause the error message.
However, judging from the CI build output, .opam/config clearly exists. What gives?