```
error package `log v0.4.19` cannot be built because it requires rustc 1.60.0 or newer, while the currently active rustc version is 1.56.1
```

```
error[E0635]: unknown feature `proc_macro_span_shrink`
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.52/src/lib.rs:92:30
   |
92 |     feature(proc_macro_span, proc_macro_span_shrink)
   |                              ^^^^^^^^^^^^^^^^^^^^^^
```

- add `len`, `is_empty` methods to inspect how many messages are
  enqueued in the message queue.
- add test for `len` and `is_empty`

Co-authored-by: Jakub Horak <jakub.horak@ibawizard.net>

and `push_back` instead of `push` (which is deprecated).

…rcuit

These futures should panic if they are polled after completing.
Currently they do so but only if they complete due to exhausting the
`Stream` that they pull data from. If they complete due to
short-circuiting, they are left in a state where `fut` and `accum` are
still `Some`. This means that if they are polled again, they end up
polling the inner `fut` again. That usually causes a panic but the error
message will likely reference the internal `Future`, not `All` / `Any`.

With this commit, `All` and `Any`'s internal state will be set such that
if they are polled again after completing, they will panic without
polling `fut`.

It looks like `All` was originally implemented by copying from `TryFold`
from which it inherited its `accum` field. However, `accum` can only
ever be one of two values: `None` (if `All` has already completed) or
`Some(true)` (if it's still processing values from the inner `Stream`).
It doesn't need to keep track of an accumulator because the very fact
that it hasn't short-circuited yet means that the accumulated value
can't be `Some(false)`. Therefore, we only need two values here and we
can represent them with a `bool` indicating whether or not `All` has
already completed.

The same principle applies for `Any` but substituting `Some(false)` for
`Some(true)`.

```
   error: unused import: `self::stream_select_mod::*`
    --> futures-util/src/async_await/mod.rs:38:9
     |
  38 | pub use self::stream_select_mod::*;
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = note: `-D unused-imports` implied by `-D warnings`
     = help: to override `-D warnings` add `#[allow(unused_imports)]`
```

Fixes #2786

…omic CAS is not available