In 20a3bf5e71d6 I introduced a temporary bugfix to align Rust code with a new
behavior from C/Python and forgot about a few Results (cargo's compiler cache
does not re-emit warnings on cached modules). This fixes it.
For the record, I am still unsure that this behavior change is a good idea.
Note: I was already quite unhappy with the setters and getters for the
DirstateMap and, indirectly, Dirs, and this only further reinforces my
feelings. I hope we can one day fix that situation at the type level; Georges
Racinet and I were just talking about devising a POC for using the builder
pattern in the context of FFI with Python, we'll see what comes out of it.