…as-schievink

Rollup of 13 pull requests

Successful merges:

 - rust-lang#77802 (Allow making `RUSTC_BOOTSTRAP` conditional on the crate name)
 - rust-lang#79004 (Add `--color` support to bootstrap)
 - rust-lang#79005 (cleanup: Remove `ParseSess::injected_crate_name`)
 - rust-lang#79016 (Make `_` an expression, to discard values in destructuring assignments)
 - rust-lang#79019 (astconv: extract closures into a separate trait)
 - rust-lang#79026 (Implement BTreeMap::retain and BTreeSet::retain)
 - rust-lang#79031 (Validate that locals have a corresponding `LocalDecl`)
 - rust-lang#79034 (rustc_resolve: Make `macro_rules` scope chain compression lazy)
 - rust-lang#79036 (Move Steal to rustc_data_structures.)
 - rust-lang#79041 (Rename clean::{ItemEnum -> ItemKind}, clean::Item::{inner -> kind})
 - rust-lang#79058 (Move likely/unlikely argument outside of invisible unsafe block)
 - rust-lang#79059 (Print 'checking cranelift artifacts' to easily separate it from other artifacts)
 - rust-lang#79063 (Update rustfmt to v1.4.26)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Test drop order for (destructuring) assignments

Add a test that checks whether the drop order of `let` bindings is consistent with the drop order of the corresponding destructuring assignments.

Thanks to `@RalfJung` for the suggesting this test ([here](rust-lang#79016 (comment))) and an implementation!

r? `@RalfJung`

Test drop order for (destructuring) assignments

Add a test that checks whether the drop order of `let` bindings is consistent with the drop order of the corresponding destructuring assignments.

Thanks to ``@RalfJung`` for the suggesting this test ([here](rust-lang#79016 (comment))) and an implementation!

r? ``@RalfJung``

Test drop order for (destructuring) assignments

Add a test that checks whether the drop order of `let` bindings is consistent with the drop order of the corresponding destructuring assignments.

Thanks to ```@RalfJung``` for the suggesting this test ([here](rust-lang#79016 (comment))) and an implementation!

r? ```@RalfJung```

…etrochenkov

Make `_` an expression, to discard values in destructuring assignments

This is the third and final step towards implementing destructuring assignment (RFC: rust-lang/rfcs#2909, tracking issue: rust-lang#71126). This PR is the third and final part of rust-lang#71156, which was split up to allow for easier review.

With this PR, an underscore `_` is parsed as an expression but is allowed *only* on the left-hand side of a destructuring assignment. There it simply discards a value, similarly to the wildcard `_` in patterns. For instance,
```rust
(a, _) = (1, 2)
```
will simply assign 1 to `a` and discard the 2. Note that for consistency,
```
_ = foo
```
is also allowed and equivalent to just `foo`.

Thanks to ````@varkor```` who helped with the implementation, particularly around pre-expansion gating.

r? ````@petrochenkov````