defmt is still evolving and making breaking changes, and it currently doesn't allow supporting multiple versions of it (https://github.com/knurling-rs/defmt/issues/426). By making it opt-in and leaving its version unspecified, it should not stand in the way of bxcan 1.0 anymore.
jonas-schievink
commented
3 years ago 
bors[bot]
defmtis still evolving and making breaking changes, and it currently doesn't allow supporting multiple versions of it (https://github.com/knurling-rs/defmt/issues/426). By making it opt-in and leaving its version unspecified, it should not stand in the way of bxcan 1.0 anymore.