False positive 'option-map-unit-fn' for std::process::exit

[jyn514]

warning: called `map(f)` on an Option value where `f` is a unit function
   --> src/bin/rcc.rs:124:9
    |
124 |         unsafe { rccjit.run_main() }.map(std::process::exit);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
    |         |
    |         help: try this: `if let Some(_) = unsafe { rccjit.run_main() } { std::process::exit(_) }`

This suggestion makes no sense: you can't pass _ to a function. Furthermore, exit() is not a unit function, it takes i32.

cargo clippy -V: clippy 0.0.212 (e8642c7 2020-01-06) (but also happens in stable)

[flip1995]

Furthermore, exit() is not a unit function, it takes i32.

The unit functions refers to the return value, not the param. ! is treated like the unit type in this lint apparently. The suggestion uses _ as a placeholder. Maybe we could use a or something similar as a placeholder instead.

[jyn514]

The unit functions refers to the return value, not the param.

I see, that makes more sense. That wasn't very clear from the suggestion, maybe it could say 'f is a function returning unit type' instead?

[jyn514]

That PR (#5292) didn't address my main concern, which is that 'unit function' is not very clear. Can this be reopened?

[flip1995]

#5290 addressed this comment #5180 (comment)

With #5292, this issue should be resolved completely, right?

[jyn514]

Oops, I didn't notice that #5290 had been merged. In that case I'm happy with the fix :)