Auto merge of rust-lang#105587 - tgross35:once-cell-min, r=m-ou-se

Partial stabilization of `once_cell`

This PR aims to stabilize a portion of the `once_cell` feature:

- `core::cell::OnceCell`
- `std::cell::OnceCell` (re-export of the above)
- `std::sync::OnceLock`

This will leave `LazyCell` and `LazyLock` unstabilized, which have been moved to the `lazy_cell` feature flag.

Tracking issue: rust-lang#74465 (does not fully close, but it may make sense to move to a new issue)

Future steps for separate PRs:
- ~~Add `#[inline]` to many methods~~ rust-lang#105651
- Update cranelift usage of the `once_cell` crate
- Update rust-analyzer usage of the `once_cell` crate
- Update error messages discussing once_cell

## To be stabilized API summary

```rust
// core::cell (in core/cell/once.rs)

pub struct OnceCell<T> { .. }

impl<T> OnceCell<T> {
    pub const fn new() -> OnceCell<T>;
    pub fn get(&self) -> Option<&T>;
    pub fn get_mut(&mut self) -> Option<&mut T>;
    pub fn set(&self, value: T) -> Result<(), T>;
    pub fn get_or_init<F>(&self, f: F) -> &T where F: FnOnce() -> T;
    pub fn into_inner(self) -> Option<T>;
    pub fn take(&mut self) -> Option<T>;
}

impl<T: Clone> Clone for OnceCell<T>;
impl<T: Debug> Debug for OnceCell<T>
impl<T> Default for OnceCell<T>;
impl<T> From<T> for OnceCell<T>;
impl<T: PartialEq> PartialEq for OnceCell<T>;
impl<T: Eq> Eq for OnceCell<T>;
```

```rust
// std::sync (in std/sync/once_lock.rs)

impl<T> OnceLock<T> {
    pub const fn new() -> OnceLock<T>;
    pub fn get(&self) -> Option<&T>;
    pub fn get_mut(&mut self) -> Option<&mut T>;
    pub fn set(&self, value: T) -> Result<(), T>;
    pub fn get_or_init<F>(&self, f: F) -> &T where F: FnOnce() -> T;
    pub fn into_inner(self) -> Option<T>;
    pub fn take(&mut self) -> Option<T>;
}

impl<T: Clone> Clone for OnceLock<T>;
impl<T: Debug> Debug for OnceLock<T>;
impl<T> Default for OnceLock<T>;
impl<#[may_dangle] T> Drop for OnceLock<T>;
impl<T> From<T> for OnceLock<T>;
impl<T: PartialEq> PartialEq for OnceLock<T>
impl<T: Eq> Eq for OnceLock<T>;
impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceLock<T>;
unsafe impl<T: Send> Send for OnceLock<T>;
unsafe impl<T: Sync + Send> Sync for OnceLock<T>;
impl<T: UnwindSafe> UnwindSafe for OnceLock<T>;
```

No longer planned as part of this PR, and moved to the `rust_cell_try` feature gate:

```rust
impl<T> OnceCell<T> {
    pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where F: FnOnce() -> Result<T, E>;
}

impl<T> OnceLock<T> {
    pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where F: FnOnce() -> Result<T, E>;
}
```

I am new to this process so would appreciate mentorship wherever needed.

Author: bors

compiler/rustc_borrowck/src/lib.rs

@@ -5,7 +5,7 @@
 #![feature(let_chains)]
 #![feature(min_specialization)]
 #![feature(never_type)]
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![feature(rustc_attrs)]
 #![feature(stmt_expr_attributes)]
 #![feature(trusted_step)]

compiler/rustc_codegen_llvm/src/lib.rs

@@ -10,7 +10,6 @@
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(never_type)]
-#![feature(once_cell)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]

compiler/rustc_codegen_ssa/src/lib.rs

@@ -5,7 +5,6 @@
 #![feature(int_roundings)]
 #![feature(let_chains)]
 #![feature(never_type)]
-#![feature(once_cell)]
 #![feature(strict_provenance)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]

compiler/rustc_data_structures/src/lib.rs

@@ -20,7 +20,7 @@
 #![feature(never_type)]
 #![feature(type_alias_impl_trait)]
 #![feature(new_uninit)]
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![feature(rustc_attrs)]
 #![feature(negative_impls)]
 #![feature(test)]

compiler/rustc_driver_impl/src/lib.rs

@@ -6,7 +6,7 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(is_terminal)]
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![feature(decl_macro)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]

compiler/rustc_error_messages/src/lib.rs

@@ -1,5 +1,5 @@
 #![feature(let_chains)]
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![feature(rustc_attrs)]
 #![feature(type_alias_impl_trait)]
 #![deny(rustc::untranslatable_diagnostic)]

compiler/rustc_feature/src/lib.rs

@@ -11,7 +11,7 @@
 //! even if it is stabilized or removed, *do not remove it*. Instead, move the
 //! symbol to the `accepted` or `removed` modules respectively.
 
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 

compiler/rustc_hir_analysis/src/lib.rs

@@ -67,7 +67,7 @@ This API is completely unstable and subject to change.
 #![feature(let_chains)]
 #![feature(min_specialization)]
 #![feature(never_type)]
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![feature(slice_partition_dedup)]
 #![feature(try_blocks)]
 #![feature(is_some_and)]

compiler/rustc_interface/src/lib.rs

@@ -2,7 +2,7 @@
 #![feature(decl_macro)]
 #![feature(internal_output_capture)]
 #![feature(thread_spawn_unchecked)]
-#![feature(once_cell)]
+#![feature(lazy_cell)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
 #![allow(rustc::potential_query_instability)]

compiler/rustc_metadata/src/lib.rs

@@ -4,7 +4,6 @@
 #![feature(generators)]
 #![feature(iter_from_generator)]
 #![feature(let_chains)]
-#![feature(once_cell)]
 #![feature(proc_macro_internals)]
 #![feature(macro_metavar_expr)]
 #![feature(min_specialization)]