In the case that a trait is not implemented for an ADT with type errors, cancel the error.

This commit improves the way build-manifest calculates the checksums
included in the manifest, speeding it up:

* Instead of calculating all the hashes beforehand and then using the
  ones we need, the manifest is first generated with placeholder hashes,
  and then a function walks through the manifest and calculates only the
  needed checksums.

* Calculating the checksums is now done in parallel with rayon, to
  better utilize all the available disk bandwidth.

* Calculating the checksums now uses the sha2 crate instead of the
  sha256sum CLI tool: this avoids the overhead of calling another
  process, but more importantly uses hardware acceleration whenever
  available (the CLI tool doesn't support it at all).

This avoids overloading the old server, and disrupting the other
programs running on it.

These appear along the cleanup path inside functions with
`#[unwind(aborts)]`. We don't const-check the cleanup path anyways,
since const-eval already has "abort-on-panic" semantics and there's
often drops that would otherwise be forbidden, so the check wasn't
really preventing anything anyways.

Now that we have by-value array iterators...

Co-authored-by: Ralf Jung <post@ralfj.de>

…r=jyn514

Use more intra-doc-links in `core::fmt`

This is a follow-up to rust-lang#75819, which encountered some broken links due to rust-lang#75176, so this PR contains the links that are blocked on rust-lang#75176.

r? @jyn514

Remove trait_selection error message in specific case

In the case that a trait is not implemented for an ADT with type errors, cancel the error.

Fixes rust-lang#75627

…l, r=matthewjasper

Add check for doc alias attribute at crate level

Fixes rust-lang#76298, rust-lang#64734, rust-lang#69365.

r? @ollie27

core::global_allocator docs link to std::alloc::GlobalAlloc

Closes rust-lang#77100

…mments, r=Mark-Simulacrum

BTreeMap: admit the existence of leaf edges in comments

The btree code is ambiguous about leaf edges (i.e., edges within leaf nodes). Iteration relies on them heavily, but some of the comments suggest there are no leaf edges (extracted from rust-lang#77025)

r? @Mark-Simulacrum

…=Mark-Simulacrum

Improve build-manifest to work with the improved promote-release

This PR makes some changes to build-manifest to have it work better with the other improvements I'm making to [promote-release](https://github.com/rust-lang/promote-release).

A new way to invoke the tool was added: `./x.py run src/tools/build-manifest`. The new invocation disables the generation of `.sha256` files and the generation of GPG signatures, as those steps are not tied to the Rust version we're building the manifest of: handling them in `promote-release` will improve the maintenability of our release process. Invocations through the old command (`./x.py dist hash-and-sign`) are referred inside the source code as "legacy". The new invocation also enables internal parallelism, disabled on legacy to avoid overloading our old server.

Improvements were also made on how the checksums included in the manifest are generated:

* The manifest is first generated with placeholder checksums, and then a function walks through the manifes and calculates only the needed hashes. Before this PR, all the hashes were calculated beforehand, including the hashes of unused files.
* Calculating the hashes is now done in parallel with rayon, to better utilize all the available disk bandwidth.
* The `sha2` crate is now used instead of the `sha256sum` CLI tool: this avoids the overhead of calling another process, but more importantly enables hardware acceleration whenever available (the `sha256sum` CLI tool doesn't support it at all).

r? @Mark-Simulacrum
This PR is best reviewed commit-by-commit.

Include scope id in SocketAddrV6::Display

r? @tmandry

I couldn't find any unit tests for these functions.

cc @ghanan94 @brunowonka

…lcnr,estebank

Fix missing diagnostic span for `impl Trait` with const generics, and add various tests for `min_const_generics` and `const_generics`

Closes rust-lang#61410.

Adds `min_const_generics` tests for:
- rust-lang#73727
- rust-lang#72293
- rust-lang#67375
- rust-lang#75153
- rust-lang#71922
- rust-lang#69913
- rust-lang#67945
- rust-lang#69239

Adds `const_generics` tests for:
- rust-lang#67375
- rust-lang#75153
- rust-lang#71922
- rust-lang#69913
- rust-lang#67945
- rust-lang#69239

(I only added separate `min_const_generics` and `const_generics` tests if they were handled differently by the two features.)

We need to figure out how to deduplicate when `const_generics` is stabilised, but we can discuss that later. For now, we should be checking neither feature breaks, so require regression tests for both. I've given them identical names when I've added both, which should make it easier to spot them later.

r? @lcnr

…ulacrum

BTreeMap: refactoring around edges, missed spots

Tweaks from rust-lang#77244 (and more) that are really inconsistencies in rust-lang#77005.

r? @Mark-Simulacrum

…-abort, r=RalfJung

Allow `Abort` terminators in all const-contexts

We never unwind during const-eval, so we basically have these semantics already. Also I just figured out that these only appear along the cleanup path, which doesn't get const-checked. In other words, this doesn't actually change behavior: the `check-pass` test I added compiles just fine on nightly.

r? @RalfJung
cc @rust-lang/wg-const-eval

…tebank

Replace some once(x).chain(once(y)) with [x, y] IntoIter

Now that we have by-value array iterators that are [already used](https://github.com/rust-lang/rust/blob/25c8c53dd994acb3f4f7c02fe6bb46076393f8b0/compiler/rustc_hir/src/def.rs#L305-L307)...

For example,
```diff
-        once(self.type_ns).chain(once(self.value_ns)).chain(once(self.macro_ns)).filter_map(|it| it)
+        IntoIter::new([self.type_ns, self.value_ns, self.macro_ns]).filter_map(|it| it)
```