Lint to warn on empty blocks

[Centri3]

What it does

Emits a warning on empty blocks (no statements nor an expression).

Advantage

This is always unnecessary (afaik), and even on the off chance it mutates something else (like potentially in the condition for an if), the if can be entirely removed, leaving just the condition.

Drawbacks

None

Example

if i_mutate_a_variable(&mut owo) {}
let _x = {};

Could be written as:

i_mutate_a_variable(&mut owo);
// <removed>

[Centri3]

I feel like this could be turned into more specific lints, as an example of one, needless_if similar to needless_else, but for if <expr> {} instead (suggesting to omit the if altogether, and only have <expr>).

It's worth noting though that many cases will likely require an empty block, so a catchall can't really be used (except for maybe a block on its own, not part of an if statement or anything)

@rustbot claim