Currently the verbosity settings are:
- 2: RUSTC-SHIM envvars get spammed on every invocation, O(30) lines
     cargo is passed -v which outputs CLI invocations, O(5) lines
- 3: cargo is passed -vv which outputs build script output, O(0-10) lines

This commit changes it to:

- 1: cargo is passed -v, O(5) lines
- 2: cargo is passed -vv, O(10) lines
- 3: RUSTC-SHIM envvars get spammed, O(30) lines

The equivalent for `Symbol`s was renamed some time ago (`kw::Invalid` -> `kw::Empty`), and it makes sense to do the same thing for `Ident`s.

Closes rust-lang#85526.

rust-lang/backtrace-rs#446 allows binaries built
with Nix on macOS to be symbolized.

bootstrap: tweak verbosity settings

Currently the verbosity settings are:
- 2: RUSTC-SHIM envvars get spammed on every invocation, O(30) lines
     cargo is passed -v which outputs CLI invocations, O(5) lines
- 3: cargo is passed -vv which outputs build script output, O(0-10) lines

This commit changes it to:

- 1: cargo is passed -v, O(5) lines
- 2: cargo is passed -vv, O(10) lines
- 3: RUSTC-SHIM envvars get spammed, O(30) lines

…-mut, r=petrochenkov

Fix ICE with `let...else` and `ref mut`

Fixes rust-lang#89960, opened for review.
I'm not satisfied with the current diagnostics, any ideas?

Nicer error message if the user attempts to do let...else if

Gives a nice "conditional `else if` is not supported for `let...else`" error when encountering a `let...else if` pattern, as suggested in the [let...else tracking issue](rust-lang#87335 (comment)).

…c, r=GuillaumeGomez

Check implementing type for `#[doc(hidden)]`

Closes rust-lang#85526.

rustdoc: Add static size assertion for `clean::Type`

r? `@jyn514`

rustc_span: `Ident::invalid` -> `Ident::empty`

The equivalent for `Symbol`s was renamed some time ago (`kw::Invalid` -> `kw::Empty`), and it makes sense to do the same thing for `Ident`s as well.

Remove dead code from `compiletest::json`

Currently getting a dead code warning on master. Might make sense to remove.

…ulacrum

Bump backtrace

rust-lang/backtrace-rs#446 allows binaries built with Nix on macOS to be symbolized.