Warn about using bool::then_some followed by unwrap_or, suggest if/else instead

[joshtriplett]

What it does

Detects the combination of then_some followed by unwrap_or in place of a more clear if/else.

Lint Name

bool_if_else

Category

style

Advantage

• Clarity at a glance

Drawbacks

No response

Example

let mode = executable.then_some(IsExecutable).unwrap_or(IsNotExecutable);

Could be written as:

let mode = if executable { IsExecutable } else { IsNotExecutable };

[joshtriplett]

This should also apply with any combination of then/then_some and unwrap_or/unwrap_or_else.

[arieluy]

@rustbot claim

[arieluy]

My commit adds the lint for then_some/unwrap_or, more commits needed to address other cases. I'll get to them at some point, but anyone can feel free to take them before me.