Error: exception Dune_rules__coq_config.Vars.E(_)
Raised at file "src/dune_rules/coq/coq_config.ml", line 37, characters 21-49
Called from file "src/dune_rules/coq/coq_config.ml", line 194, characters
  10-53
Called from file "otherlibs/fiber/src/core.ml", line 250, characters 36-41
Called from file "otherlibs/fiber/src/scheduler.ml", line 73, characters 8-11
-> required by ("<unnamed>", ())
-> required by ("<unnamed>", ())
-> required by ("<unnamed>", ())
-> required by ("<unnamed>", ())
-> required by ("gen-rules", In_build_dir "default/tests")
-> required by ("load-dir", In_build_dir "default/tests")
-> required by ("<unnamed>", ())
-> required by
   ("build-alias", { dir = In_build_dir "default"; name = "default" })
-> required by ("top-level", ())

I must not crash.  Uncertainty is the mind-killer. Exceptions are the
little-death that brings total obliteration.  I will fully express my cases. 
Execution will pass over me and through me.  And when it has gone past, I
will unwind the stack along its path.  Where the cases are handled there will
be nothing.  Only I will remain.