previously this would cause an infinite loop due to it being
unable to read `n` bytes.

It's very rare for developers to need to modify LLVM,
so "if-unchanged" isn't a good default since it fetches
the LLVM submodule to track changes.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Signed-off-by: onur-ozkan <work@onurozkan.dev>

…=Amanieu

properly handle EOF in BufReader::peek

previously this would cause an infinite loop due to it being unable to read `n` bytes.

…kSimulacrum,workingjubilee

Add `NonNull` convenience methods to `Box` and `Vec`

Implements the ACP: rust-lang/libs-team#418.

The docs for the added methods are mostly copied from the existing methods that use raw pointers instead of `NonNull`.

I'm new to this "contributing to rustc" thing, so I'm sorry if I did something wrong. In particular, I don't know what the process is for creating a new unstable feature. Please advise me if I should do something. Thank you.

…t-profiles, r=Mark-Simulacrum

set `download-ci-llvm = true` by default on "library" and "tools" profiles

It's very rare for developers to need to modify LLVM, so "if-unchanged" isn't a good default for "tools" and "library" profiles since it fetches the LLVM submodule to track changes.

MaybeUninit::zeroed: mention that padding is not zeroed

That should clarify cases like [this](rust-lang#129778 (comment)).

Make some lint doctests compatible with `--stage=0`

Currently, running `x test compiler --stage=0` (with `rust.parallel-compiler=false` to avoid other problems) results in two failures, because these lint doctests aren't compatible with the current stage0 compiler.

In theory, the more “correct” solution would be to wrap the opening triple-backtick line in  `#[cfg_attr(not(bootstrap), doc = "..."]`. However, that causes a few practical problems:
- `tidy` doesn't understand that syntax, and miscounts the number of backticks in the comment block.
- `lint-docs` doesn't understand that syntax, and thinks it's trying to declare the lint name.
- Working around the above problems would cause more work and more confusion for whoever does the next bootstrap beta bump.

So instead this PR adds some bootstrap gates inside the individual doctests, which end up producing the desired behaviour, and are straightforward to remove.

unstable-book: `trait_upcasting` example should not have `#![allow(incomplete_features)]`

Tracking issue: rust-lang#65991

`trait_upcasting` is not currently an incomplete feature; therefore examples of its use do not require `#![allow(incomplete_features)]`.