Add needless_if lint

[Centri3]

first off: Sorry about the large diff. Seems a ton of tests do this (understandably so).

this is basically everything I wanted in #10868, while it doesn't lint all unnecessary empty blocks, it lints needless if statements; which are basically the crux of the issue (for me) anyway. I've committed code that includes this far too many times 😅 hopefully clippy can help me out soon

closes #10868

changelog: New lint [needless_if]

[rustbot]

r? @Manishearth

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[Manishearth]

@blyxyas want to take a crack at reviewing this?

(cc @xFrednet )

[blyxyas]

Yep, Will review it!

[blyxyas]

Just a minor nitpick and I think this is done. Thanks! ❤️

cc @xFrednet

[Alexendoo]

Some cases to check:

if true {
    #[cfg(any())]
    foo;
}

macro_rules! m {
    ($($t:tt)*) => {
        if true {
            $($t)*
        }
    }
}

m!();

[Manishearth]

@bors r=blyxyas,Manishearth

looks great, you can ignore the comment i left or make a followup PR if you agree with me

[bors]

📌 Commit 108c04a has been approved by blyxyas,Manishearth

It is now in the queue for this repository.

[bors]

⌛ Testing commit 108c04a with merge 21e6235...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: blyxyas,Manishearth
Pushing 21e6235 to master...

[Centri3]

Some cases to check:

if true {
    #[cfg(any())]
    foo;
}

macro_rules! m {
    ($($t:tt)*) => {
        if true {
            $($t)*
        }
    }
}

m!();

Sorry I didn't get to this 😅 I'll do this as a followup, though I'm pretty sure it'll lint on both currently.

[Alexendoo]

Opened #10935 for that + a few other cases I thought of/ran into