Fetches unused dependencies

[bluss]

Each crater run fetches many dependencies that are unused:

• Optional dependencies — not needed for cargo build
• All dev-dependencies — not needed for cargo build

[brson]

How do I make cargo not fetch them?

[bluss]

I thought it was possible, but it seems it is not?

[bluss]

Cargo has learned to download deps lazily, nice rust-lang/cargo#2406