Stabilize `str::len`, `[T]::len` and `str::as_bytes` as const fn
r? @Centril
cc @RalfJung
This also introduces a scheme for making certain feature gates legal in stabilized const fns
Delete most of `src/bootstrap/bin/rustc.rs`
This commit is an attempt at deleting as much of the `rustc.rs` shim that we have in rustbuild as possible. This shim predates `RUSTFLAGS` and is as old as rustbuild itself. While useful for quick hacks, it subverts Cargo's knowledge of `rustc`, makes it more difficult to build crates out of rustbuild, and is generally a hazard/code smell due to its architecture.
Additionally since the inception of this script we've added a number of features to Cargo such as profile overrides and `RUSTFLAGS`. This commit attempts to use these features of Cargo as much as possible to delete almost all of `src/bootstrap/bin/rustc.rs`. It's hoped that all new configuration for the Rust compiler can be codified in rustbuild rather than in this shim, allowing Cargo to have more knowledge about what's going on and making it a bit easier to reproduce builds outside of Cargo itself.
This was primarily motivated by some recent work on std-aware Cargo, and is also generally a cleanup of the script itself. This internally resulted in a number of refactorings of rustbuild itself, and the commits should be readable one-at-a-time instead of having to digest them all at once.
This is needed to ensure that the crates during a normal build are
shared with the crates during testing, otherwise they'll end up hasing
differently and we'll recompile crates like `core` during tests.
This commit changes the return type of `Builder::cargo` to return a
builder that allows dynamically adding more `RUSTFLAGS` values
after-the-fact. While not used yet, this will later be used to delete
more of `rustc.rs`
Most of `bootstrap/bin/rustc.rs` doesn't need to exist with the advent
of `RUSTFLAGS` (yes this is super old) so this starts by refactoring a
bit to make it easier locally in the `Builder::cargo` method to append
to `RUSTFLAGS` that gets down to rustc.
Refactor librustc_errors::Handler API
This should be reviewed by-commit.
The last commit moves all fields into an inner struct behind a single lock; this is done to prevent possible deadlocks in a multi-threaded compiler, as well as inconsistent state observation.
Infer consts more consistently
Moved some duplicated logic in `TypeRelation` methods into `super_combined_consts`. Before some `TypeRelation`s like `Lub` wasn't using `replace_if_possible`, meaning some inference types were staying around longer than they should be.
Fixes https://github.com/rust-lang/rust/issues/64519
r? @varkor
