Emit if_let_mutex in presence of other mutexes

[y21]

Currently (master, not nightly nor stable) if_let_mutex does not emit a warning here:

let m1 = Mutex::new(10);
let m2 = Mutex::new(());

if let 100..=200 = *m1.lock().unwrap() {
  m2.lock();
} else {
  m1.lock();
}

It currently looks for the first call to .lock() on any mutex receiver inside of the if/else body, and only later (outside of the visitor) checks that the receiver matches the mutex in the scrutinee. That means that in cases like the above, it finds the m2.lock() expression, stops the visitor, fails the check that it's the same mutex (m2 != m1) and then does not look for any other .lock() calls.

So, just make the receiver check also part of the visitor so that we only stop the visitor when we also find the right receiver.

The first commit has the actual changes described here. The sceond one just unnests all the if lets

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changelog: none

[rustbot]

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[llogiq]

Looks good to me. Thank you!

@bors r+

[bors]

📌 Commit 61dcf6c has been approved by llogiq

It is now in the queue for this repository.

[bors]

⌛ Testing commit 61dcf6c with merge 834b691...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: llogiq
Pushing 834b691 to master...