False positive for used_underscore_binding

[bluss]

Using variable names like let mut _x will also suppress unused_mut warnings. I've used this in a macro, so I thought I should report this here, since it's a kind of a false positive (following clippy's suggestions leads to new warnings for the use cases of the macro where the mut is unused).

[bluss]

I'm just reporting what I see, I don't know what you want to do, of course. Found in relation to PR bluss/maplit/pull/3.

[llogiq]

So we could

• limit the lint to immutable values
• somehow check if the unused_mut lint would fire and avoid minting those matches

[oli-obk]

We should probably just ensure that the lint doesn't trigger inside macros

[phansch]

This was fixed at some point and should be covered by the tests added in #4011.