Use of `num_derive::FromPrimitive` throws Clippy lint `clippy::use_self`

[Fuwn]

I've just bumped my tool-chain release up from nightly-2021-02-20 to nightly-2021-06-04 and a new warning arises for the num_derive::FromPrimitive derive macro.

The Clippy lint clippy::use_self is thrown for the following derive macro use-case:

[cuviper]

ref: https://rust-lang.github.io/rust-clippy/master/#use_self

That's currently labeled "Nursery" and is allowed by default. I find that a rather pedantic style lint, and not really relevant to macro-generated code. That said, if Self does work in that position even in MSRV 1.31, I'd be fine with a PR changing it.

[Fuwn]

While I'm at it, you mind if I fix any other Clippy lints that come up do you prefer I just patch this one instance?

[Fuwn]

Actually, this lint might not even originate from the num-derive crate, I strictly denied the clippy::use_self lint and not a single lint presented itself, I then required the crate from a local path and the lint is still present. Might be a Clippy false-positive.

[cuviper]

Ah, there are subtle differences in how "local" crates are treated for stuff like this. I know that "remote" crates are built with --cap-lints allow, but I'm not exactly sure how that affects proc-macro-generated code.

[barafael]

The same problem haunts a number of other crates. It is tracked in clippy here: rust-lang/rust-clippy#6902

[cuviper]

Clippy seems to exempt the proc-macro code now! rust-lang/rust-clippy#8694