Lints table allows both `-` and `_` separators, including allowing redundant entries.

[epage]

Today, you can do:

[lints.rust]
unexpected_cfgs = "warn"
unexpected-cfgs = "allow"

and the behavior is unspecified.

After #13913, you can also do

[lints.rust]
unexpected-cfgs = { level = "warn", check-cfg = ['cfg(foo, values("bar"))'] }

and you'll get an "unused manifest key" warning for check-cfg.

[epage]

We talked about this in today's Cargo team meeting.

On the command-line, rustc accepts lint names with both _ and - and it normalizes them to _ which is considered the canonical name.

For lints.cargo, we had previously decided to only support rustc's canonical format of _ (#13837).

I propose that we deprecate the use of - in lints and in a future edition (2027? we don't want to rush this for 2024), we remove support for - in lint names.