Implement 1581 (FusedIterator)
* [ ] Implement on patterns. See https://github.com/rust-lang/rust/issues/27721#issuecomment-239638642.
* [ ] Handle OS Iterators. A bunch of iterators (`Args`, `Env`, etc.) in libstd wrap platform specific iterators. The current ones all appear to be well-behaved but can we assume that future ones will be?
* [ ] Does someone want to audit this? On first glance, all of the iterators on which I implemented `FusedIterator` appear to be well-behaved but there are a *lot* of them so a second pair of eyes would be nice.
* I haven't touched rustc internal iterators (or the internal rand) because rustc doesn't actually call `fuse()`.
* `FusedIterator` can't be implemented on `std::io::{Bytes, Chars}`.
Closes: #35602 (Tracking Issue)
Implements: rust-lang/rfcs#1581
Implement `CoerceUnsized` for `{Cell, RefCell, UnsafeCell}`
These impls are analogous to the one for `NonZero`. It's occasionally useful to be able to coerce the cell types when they're being used inside another abstraction. See Manishearth/rust-gc#17 for an example.
r? @eddyb
cstring: avoid excessive growth just to 0-terminate
Based on following what happens in CString::new("string literal"):
1. Using `Into<Vec<u8>>`, a Vec is allocated with capacity exactly equal
to the string's input length.
2. By `v.push(0)`, the Vec is grown to twice capacity, since it was full.
3. By `v.into_boxed_slice()`, the Vec capacity is shrunk to fit the length again.
If we use `.reserve_exact(1)` just before the push, then we avoid the
capacity doubling that we're going to have to shrink anyway.
Growing by just 1 byte means that the step (2) is less likely to have to
move the memory to a larger allocation chunk, and that the step (3) does
not have to reallocate.
Addresses part of #35838
Check that executable file is in-tree before failing tidy check
I silenced stdout and stderr for ls-files, not sure if that's appropriate (is `make tidy` intended to give debugging information)? Otherwise it prints each file it find to stdout/stderr, which currently prints nothing (only executable files are checked).
I have not done major testing regarding the behavior of ls-files when the file is ignored, but judging by the man page everything should be fine.
I've duplicated the code which makes the path git-friendly from the `Cargo.lock` checking code; I can extract that into a common helper if wanted (it's only two lines).
Fixes#35689.
Carrier trait (third attempt)
This adds a `Carrier` trait to operate with `?`. The only public implementation is for `Result`, so effectively the trait does not exist, however, it ensures future compatibility for the `?` operator. This is not intended to be used, nor is it intended to be a long-term solution.
Although this exact PR has not been through Crater, I do not expect it to be a breaking change based on putting numerous similar PRs though Crater in the past.
cc:
* [? tracking issue](https://github.com/rust-lang/rust/issues/31436)
* [previous PR](https://github.com/rust-lang/rust/pull/35056)
* [RFC issue](https://github.com/rust-lang/rfcs/issues/1718) for discussion of long-term Carrier trait solutions.
r? @nikomatsakis
