Passing -W for an unknown lint gives an error without saying why

[jyn514]

$ rustc -W unknown_blah ~/src/test-rustdoc/test.rs 
error[E0602]: unknown lint: `unknown_blah`
  |
  = note: requested on the command line with `-W unknown_blah`

Not sure if this is actually a bug? cc @Mark-Simulacrum

[Mark-Simulacrum]

We should at least give a brief blurb about how to silence this. (Does -Wunknown-lints help?)

[jyn514]

(Does -Wunknown-lints help?)

It does not.

$ rustc -Aunknown-lints -Alegacy-derive-helpers hello.rs
error[E0602]: unknown lint: `legacy_derive_helpers`
  |
  = note: requested on the command line with `-A legacy_derive_helpers`

[tmandry]

Copying what I said in #81906:

Since the same problem that unknown-lints solves exists on the command line, I'd argue that this is a bug in the CLI.

As a corollary, it would be nice if we could do something like -Aunknown-lints -Alegacy-derive-helpers -Dunknown-lints to prevent misspellings elsewhere in the command line.

[djkoloski]

#94274 fixes the issue of -Aunknown-lints not applying to subsequent CLI arguments.

[Herschel]

I ran into this when adopting Embark's workaround for using .cargo/config.toml to allow/disable lints for an entire workspace via rustflags. I'd like to -Aunknown_lints here and then squelch certain nightly clippy lints, but subsequent -Afoobar still give me errors.

#94274 fixes the issue of -Aunknown-lints not applying to subsequent CLI arguments.

This makes it sound like the above should work correctly, but I guess I'm mistaken? rustc 1.63.0-nightly (9257f5a 2022-05-21)

[ComputerDruid]

I think #94274 only helps with unstable lints, not unknown ones, unfortunately.