We store an `ImplicitCtxt` pointer in a thread-local value (TLV). This allows
implicit access to a `GlobalCtxt` and some other things.

We also store a `GlobalCtxt` pointer in `GCX_PTR`. This is always the same
`GlobalCtxt` as the one within the `ImplicitCtxt` pointer in TLV. `GCX_PTR`
is only used in the parallel compiler's `handle_deadlock()` function.

This commit does the following.
- It removes `GCX_PTR`.
- It also adds `ImplicitCtxt::new()`, which constructs an `ImplicitCtxt` from a
  `GlobalCtxt`. `ImplicitCtxt::new()` + `tls::enter_context()` is now
  equivalent to the old `tls::enter_global()`.
- Makes `tls::get_tlv()` public for the parallel compiler, because it's
  now used in `handle_deadlock()`.

Introduce NonterminalKind for more type-safe mbe parsing

It encapsulate the (part of) the interface between the parser and
macro by example (macro_rules) parser.

The second bit is somewhat more general `parse_ast_fragment`, which is
the reason why we keep some `parse_xxx` functions as public.

Fix ICEs with `@ ..` binding

This reverts #74557 and introduces an alternative fix while ensuring that #74954 is not broken.
The diagnostics are verbose though, it fixes three related issues.
cc #74954, #74539, and #74702

Rollup of 10 pull requests

Successful merges:

 - #74686 (BTreeMap: remove into_slices and its unsafe block)
 - #74762 (BTreeMap::drain_filter should not touch the root during iteration)
 - #74781 (Clean up E0733 explanation)
 - #74874 (BTreeMap: define forget_type only when relevant)
 - #74974 (Make tests faster in Miri)
 - #75010 (Update elasticlunr-rs and ammonia transitive deps)
 - #75041 (Replaced log with tracing crate)
 - #75044 (Clean up E0744 explanation)
 - #75054 (Rename rustc_middle::cstore::DepKind to CrateDepKind)
 - #75057 (Avoid dumping rustc invocations to stdout)

Failed merges:

 - #74827 (Move bulk of BTreeMap::insert method down to new method on handle)

r? @ghost

Avoid dumping rustc invocations to stdout

These are quite long, usually, and in most cases not interesting. On smaller
terminals they can take up more than a full page of output, hiding the error
diagnostics emitted.

Rename rustc_middle::cstore::DepKind to CrateDepKind

It is ambiguous with DepGraph's own DepKind.

Clean up E0744 explanation

r? @Dylan-DPC

Replaced log with tracing crate

Issue #74747

Update elasticlunr-rs and ammonia transitive deps

This removes all dependencies on pre-1.0 proc-macro ecosystem crates
(syn, quote, and proc-macro2)

Make tests faster in Miri

Reduce some test iteration counts in Miri.

BTreeMap: define forget_type only when relevant

Similar to `forget_node_type` for handles.
No effect on generated code, apart maybe from the superfluous calls that might not have been optimized away.

r? @Mark-Simulacrum

Clean up E0733 explanation

r? @Dylan-DPC

BTreeMap::drain_filter should not touch the root during iteration

Although Miri doesn't point it out, I believe there is undefined behaviour using `drain_filter` when draining the 11th-last element from a tree that was larger. When this happens, the last remaining child nodes are merged, the root becomes empty and is popped from the tree. That last step establishes a mutable reference to the node elected root and writes a pointer in `node::Root`, while iteration continues to visit the same node.

This is mostly code from #74437, slightly adapted.

BTreeMap: remove into_slices and its unsafe block

A small tweak to make BTreeMap code shorter and less unsafe.

r? @Mark-Simulacrum

These are quite long, usually, and in most cases not interesting. On smaller
terminals they can take up more than a full page of output, hiding the error
diagnostics emitted.

Add fallible AArch64 CI builder

This adds the `aarch64-gnu` CI builder to the `auto-fallible` job, as a first step in the process of actually gating on it.

r? @Mark-Simulacrum

Deduplicate `::` -> `:` typo errors

Deduplicate errors caused by the same type ascription typo, including
ones suggested during parsing that would get reported again during
resolve. Fix #70382.

Seems to be a fallout from rustfmt transition

This is more type safe and allows us to remove a few dead branches

It encapsulate the (part of) the interface between the parser and
macro by example (macro_rules) parser.

The second bit is somewhat more general `parse_ast_fragment`, which is
the reason why we keep some `parse_xxx` functions as public.

Fix std::fs::File::metadata permission on WASI target

Previously `std::fs::File::metadata` on wasm32-wasi would call `fd_filestat_get`
to get metadata associated with fd, but that fd is opened without
RIGHTS_FD_FILESTAT_GET right, so it will failed on correctly implemented WASI
environment.

This change instead to add the missing rights when opening an fd.

bump libc version to 0.2.74

Move 'probably equal' methods to librustc_parse

This is preparation for PR #73084

report kind of deprecated item in message

This is important for fields, which are incorrectly referred to as
"items".

This removes all dependencies on pre-1.0 proc-macro ecosystem crates
(syn, quote, and proc-macro2)

This is preparation for PR #73084

Rollup of 5 pull requests

Successful merges:

 - #74602 (Clarify the doc for MaybeUninit::zeroed on incorrect use)
 - #74720 (Clean up E0728 explanation)
 - #74992 (fix rustdoc generic param order)
 - #75015 (Add Vec::spare_capacity_mut)
 - #75022 (Use a slice pattern instead of rchunks_exact(_).next())

Failed merges:

r? @ghost

Use a slice pattern instead of rchunks_exact(_).next()

This is a minor cleanup, but trying a single-use `rchunks` iterator can
be more directly matched with a slice pattern, `[.., a, b]`.

Add Vec::spare_capacity_mut

Returns the remaining spare capacity of the vector as a slice of `MaybeUninit<T>`.

As suggested by @sfackler in https://github.com/rust-lang/rust/pull/70967#issuecomment-612659006.

r? @sfackler

fix rustdoc generic param order

fixes #61292

r? @varkor cc @GuillaumeGomez

Clean up E0728 explanation

r? @Dylan-DPC

Clarify the doc for MaybeUninit::zeroed on incorrect use

Fixes #74343.

@rustbot modify labels: C-enhancement, T-doc

Stabilize Vec::leak as a method

Closes https://github.com/rust-lang/rust/issues/62195

The signature is changed to a method rather than an associated function:

```diff
-pub fn leak<'a>(vec: Vec<T>) -> &'a mut [T]
+pub fn leak<'a>(self) -> &'a mut [T]
```

The reason for `Box::leak` not to be a method (`Deref` to an arbitrary `T` which might have its own, different `leak` method) does not apply.

Move from `log` to `tracing`

The only visible change is that we now get timestamps in our logs:

```
Jul 24 18:41:01.065 TRACE rustc_mir::transform::const_prop: skipping replace of Rvalue::Use(const () because it is already a const
Jul 24 18:41:01.065 TRACE rustc_mir::transform::const_prop: propagated into _2
Jul 24 18:41:01.065 TRACE rustc_mir::transform::const_prop: visit_constant: const ()
```

This PR was explicitly designed to be as low-impact as possible. We can now move to using the name `tracing` insteads of `log` on a crate-by-crate basis and use any of the other tracing features where desirable.

As far as I can tell this will allow tools to seamlessly keep working (since they are using `rustc_driver::init_log...`).

This is the first half of step 1 of the accepted `tracing` MCP (https://github.com/rust-lang/compiler-team/issues/331)