…uwer

Rollup of 8 pull requests

Successful merges:

 - #159425 (Windows: add context when opening NUL for child stdio fails)
 - #159467 (Add explicit `Iterator::count` impl for `str::EncodeUtf16`)
 - #157860 (Move rustdoc run-make tests into new `tests/run-make/rustdoc/`)
 - #158545 (Move `std::io::read_to_string` to `alloc::io`)
 - #159328 (tests/assembly-llvm: pin frame pointer in issue-141649 aarch64 test)
 - #159459 (Detect when trait bound requires closure to return itself)
 - #159470 (Fix string indexing in diagnostic format strings)
 - #159500 (Move compiletest CLI parsing to `cli.rs`)

Rollup merge of #159459 - estebank:closure-ret-self, r=mu001999

Detect when trait bound requires closure to return itself

A trait bound `T: Fn() -> T` is non-sensical code, point that out:

```
error[E0271]: expected `{[email protected]:8:25}` to return `{[email protected]:8:25}`, but it returns `{integer}`
  --> $DIR/trait-bound-expects-closure-returns-itself.rs:8:28
   |
LL |     closure_ret_closure(|| 4);
   |                         -- ^ expected closure, found integer
   |                         |
   |                         the expected closure
   |
note: a bound in `closure_ret_closure` requires that a closure return itself, which is not possible
  --> $DIR/trait-bound-expects-closure-returns-itself.rs:1:39
   |
LL | fn closure_ret_closure<T: FnOnce() -> T>(f: T) -> T {
   |                                       ^ this requires the closure to return itself
...
LL |     closure_ret_closure(|| 4);
   |                         ---- this closure would have to return itself
   = note: expected closure `{closure@$DIR/trait-bound-expects-closure-returns-itself.rs:8:25: 8:27}`
                 found type `{integer}`
```

This was highlighted in #80638. We'd since improved the output enough to close the ticket, but I wanted to ensure we had something even clearer.

…uwer

Rollup of 8 pull requests

Successful merges:

 - rust-lang/rust#159425 (Windows: add context when opening NUL for child stdio fails)
 - rust-lang/rust#159467 (Add explicit `Iterator::count` impl for `str::EncodeUtf16`)
 - rust-lang/rust#157860 (Move rustdoc run-make tests into new `tests/run-make/rustdoc/`)
 - rust-lang/rust#158545 (Move `std::io::read_to_string` to `alloc::io`)
 - rust-lang/rust#159328 (tests/assembly-llvm: pin frame pointer in issue-141649 aarch64 test)
 - rust-lang/rust#159459 (Detect when trait bound requires closure to return itself)
 - rust-lang/rust#159470 (Fix string indexing in diagnostic format strings)
 - rust-lang/rust#159500 (Move compiletest CLI parsing to `cli.rs`)