rust dependency hell with features

I've encountered my first bit of rust dependency hell. I'm trying to use a combination of nom v3.2.1 (a parsing combinator framework) plus nom_pem v1.0.3 (which uses nom to parse the PEM file format) plus der-parser v0.4.4 (which uses nom to parse DER data). This would almost work EXCEPT der-parser has the following line in it's Cargo.toml:

nom = {version = "^3.1", features = ["verbose-errors"]}

I haven't used feature toggling at all yet, and my initial reaction is OMG whose ideas was this and how did they think this would ever work?. In this case, the feature verbose-errors enables a totally different and incompatible Error API in nom, so it's very likely this only works if all of your nom-based deps agree on whether to use or not use this feature. One out of line and it's a hung jury: your code doesn't compile.

So at the moment my thought is: only top-level application projects should use cargo feature toggles and library crates should never use them. But as I read more maybe it'll get refined to something like "feature toggles are OK only within the bounds defined by the semver version, but if a feature toggle changes the semver API conventions, it's verboten."

Off to read a bit more on this topic.