VecDeque<T> should implement PartialEq with &[T]

[Mark-Simulacrum]

I believe this is definitely possible (comparing the iterators of each), and I suspect that there's a more efficient method as well.

See this documentation PR where it simplifies the code: https://github.com/rust-lang/rust/pull/38581/files#diff-266e22074e3b36596081857cbf5b1513R1256.

[frewsxcv]

I'm working on this.

[frewsxcv]

I ran into an issue.

rust/src/libcollections/vec_deque.rs

Lines 2530 to 2531 in a9ab778

	assert!(tester.tail < tester.cap());
	assert!(tester.head < tester.cap());

These now become errors:

error[E0282]: unable to infer enough type information about `_`
    --> src/libcollections/vec_deque.rs:2497:17
     |
2497 |             let expected = (0..).take(len).collect();
     |                 ^^^^^^^^ cannot infer type for `_`
     |
     = note: type annotations or generic parameter binding required

error: aborting due to previous error

[frewsxcv]

Is this inference issue allowed breakage?

[bluss]

It's definitely allowed, but not every allowed type inference breakage is a good idea. So it still has to be decided carefully.

[Mark-Simulacrum]

@frewsxcv Mind posting a PR? Perhaps we can find a way to fix the inference breakage.

[frewsxcv]

Opened a PR: #38661.

[bombless]

I think that inference failure was there long before Rust 1.0
https://is.gd/j8KMA1

[frewsxcv]

It occurs because prior to this PR, the only thing you could compare VecDeque with was another VecDeque, so the compiler knew to collect into a VecDeque. Now that it can compare VecDeque with VecDeque or Vec, it doesn't know which one to choose.