`syntax_expand` -> `rustc_expand`
`syntax_pos` -> `rustc_span`
`syntax_ext` -> `rustc_builtin_macros`

Resolve long compile times when evaluating always valid constants

This extends the existing logic which skips validating every integer or
floating point number type to also skip validating empty structs because
they are also trivially valid.

Fixes #67539

r? @oli-obk
cc @RalfJung @spastorino

Avoid memory copy logic for zsts

r? @oli-obk

One of the included commits is work done by @HeroicKatora in #62655

Rollup of 10 pull requests

Successful merges:

 - #64273 (Stabilize attribute macros on inline modules)
 - #67287 (typeck: note other end-point when checking range pats)
 - #67564 (docs: Iterator adapters have unspecified results after a panic)
 - #67622 (Some keyword documentation.)
 - #67657 (Clean up const-hack PRs now that const if / match exist.)
 - #67677 (resolve: Minor cleanup of duplicate macro reexports)
 - #67687 (Do not ICE on lifetime error involving closures)
 - #67698 (Move reachable_set and diagnostic_items to librustc_passes.)
 - #67701 (tidy: Enforce formatting rather than just check it if `--bless` is specified)
 - #67715 (Typo fix)

Failed merges:

r? @ghost

Typo fix

tidy: Enforce formatting rather than just check it if `--bless` is specified

Ensuring the "tidy"-ness currently requires running `rustfmt` twice:
```sh
./x.py fmt && ./x.py test tidy
```
, once to actually format code and the second time as a part of tidy to check that the code is formatted.

Running `rustfmt` is slow, so we don't want to run it twice.

With this PR tidy enforces the formatting rather than just checks it if `--bless` was passed to it:
```sh
./x.py test tidy --bless
```

r? @Mark-Simulacrum

Move reachable_set and diagnostic_items to librustc_passes.

Split out of #67688

r? @Zoxc

Do not ICE on lifetime error involving closures

Fix #67634.

resolve: Minor cleanup of duplicate macro reexports

Enabled by https://github.com/rust-lang/rust/pull/65785 which changed `duplicate_macro_exports` from a lint to a hard error.

Clean up const-hack PRs now that const if / match exist.

Closes #67627.

Cleans up these merged PRs tagged with `const-hack`:

- #63810
- #63786
- #61635
- #58044

reverting their contents to have the match or if expressions they originally contained.

r? @oli-obk

There's one more PR in those tagged with `const-hack` that originally wasn't merged (#65107). Reading the thread, it looks like it was originally closed because the `const-hack` for the checked arithmetic non-negligibly hurt performance, and because there was no way to manipulate the returned Option at compile time anyway (with neither const if nor const match). Would you like me to add these changes to the changes from this PR here too, now that we have the necessary features?

Some keyword documentation.

I thought about going into detail, but I'd much rather route them to the async book asap.

docs: Iterator adapters have unspecified results after a panic

Fixes #58170.

That issue also has rough consensus from 3 members of the library team for this being the behavior we would like to specify.

typeck: note other end-point when checking range pats

Fixes #57389, alternative to #67214 that should be less invasive to type checking logic.

r? @estebank

Stabilize attribute macros on inline modules

While still gating non-inline modules in proc macro input.

Split from https://github.com/rust-lang/rust/pull/63931
cc https://github.com/rust-lang/rust/issues/54727

Work around a resolve bug in const prop

r? @wesleywiser @anp

This isn't exposed right now, but further changes to rustc may start causing bugs without this.

Allocate HIR on an arena 3/4 -- Ty

This is the third PR in the series started by #66931 and #66936

Once again, commits don't really make sense on their own.
They are mostly split by type of compile error.

The additional diff is here: https://github.com/cjgillot/rust/compare/hirene-expr...hirene-ty

This extends the existing logic which skips validating every integer or
floating point number type to also skip validating empty structs because
they are also trivially valid.

Fixes #67539

Refactor expression parsing thoroughly

Based on https://github.com/rust-lang/rust/pull/66994 together with which this has refactored basically the entirety of `expr.rs`.

r? @estebank

Update Clippy and cargo

includes latest rustup and resolves dependency conflicts with cargo
Closes #67541

r? @oli-obk @Manishearth

Rollup of 3 pull requests

Successful merges:

 - #67482 (Fix outdated comment)
 - #67673 (Update .mailmap)
 - #67679 (Change "be returning" to "return")

Failed merges:

r? @ghost

Change "be returning" to "return"

Update .mailmap

r? @Mark-Simulacrum

Fix outdated comment

Logics in `libsyntax/ext/expand.rs:MacroExpander::expand()` have been moved to `libsyntax_expand/expand.rs:MacroExpander::fully_expand_fragment()`
This pull request fixs the dangling file path.

#### Old

https://github.com/rust-lang/rust/blob/35176867f62f76b9bc27267878f2d74d9c776221/src/libsyntax/ext/expand.rs#L285-L301

#### New

https://github.com/rust-lang/rust/blob/9ff30a7810c586819a78188c173a7b74adbb9730/src/libsyntax_expand/expand.rs#L421-L439

https://github.com/rust-lang/rust/blob/9ff30a7810c586819a78188c173a7b74adbb9730/src/libsyntax_expand/base.rs#L224-L234