From #1529 I suggested the following

[...] but I'd like a way to have the docs generated for all of my direct dependencies, but not their dependencies. In fact I'd argue this should be the default behavior.

If I add a crate "bar" as a dependency of the crate I'm working on "foo", then I'd love to see both "foo" and "bar"s documentation. However, if "bar" needs "baz" I frankly couldn't care less, as that's the decision of "bar" and I shouldn't need to look up anything in "baz".

All this is to say, generate docs for dependencies in Cargo.toml, but not Cargo.lock.