…rrays

The documentation for atomic integers says that they have the "same
in-memory representation" as their underlying integers. This might be
misconstrued as implying that they have the same layout. Therefore,
clarify that atomic integers' alignment is equal to their size.

The goal of this commit is to remove warnings using LLVM tip-of-tree
`wasm-ld`. In llvm/llvm-project#78658 the `wasm-ld` LLD driver no longer
looks at archive indices and instead looks at all the objects in
archives. Previously `lib.rmeta` files were simply raw rustc metadata
bytes, not wasm objects, meaning that `wasm-ld` would emit a warning
indicating so.

WebAssembly targets previously passed `--fatal-warnings` to `wasm-ld` by
default which meant that if Rust were to update to LLVM 18 then all wasm
targets would not work. This immediate blocker was resolved in
rust-lang#120278 which removed `--fatal-warnings` which enabled a
theoretical update to LLVM 18 for wasm targets. This current state is
ok-enough for now because rustc squashes all linker output by default if
it doesn't fail. This means, for example, that rustc squashes all the
linker warnings coming out of `wasm-ld` about `lib.rmeta` files with
LLVM 18. This again isn't a pressing issue because the information is
all hidden, but it runs the risk of being annoying if another linker
error were to happen and then the output would have all these unrelated
warnings that couldn't be fixed.

Thus, this PR comes into the picture. The goal of this PR is to resolve
these warnings by using the WebAssembly object file format on wasm
targets instead of using raw rustc metadata. When I first implemented
the rlib-in-objects scheme in rust-lang#84449 I remember either concluding that
`wasm-ld` would either include the metadata in the output or I thought
we didn't have to do anything there at all. I think I was wrong on both
counts as `wasm-ld` does not include the metadata in the final output
unless the object is referenced and we do actually need to do something
to resolve these warnings.

This PR updates the object file format containing rustc metadata on
WebAssembly targets to be an actual WebAssembly file. This enables the
`wasm` feature of the `object` crate to be able to read the custom
section in the same manner as other platforms, but currently `object`
doesn't support writing wasm object files so a handwritten encoder is
used instead.

The only caveat I know of with this is that if `wasm-ld` does indeed
look at the object file then the metadata will be included in the final
output. I believe the only thing that could cause that at this time is
`--whole-archive` which I don't think is passed for rlibs. I would
clarify that I'm not 100% certain about this, however.

Co-authored-by: bjorn3 <17426603+bjorn3@users.noreply.github.com>

The meaning of this assertion changed in rust-lang#120828 when the meaning of
`has_errors` changed to exclude stashed errors. Evidently the new
meaning is too restrictive.

Fixes rust-lang#120856.

…le fatal error

Implementing traits marked with `#[rustc_specialization_trait]` normally
requires (min-)specialization to be enabled for the enclosing crate.

With this change, that permission can also be granted by an
`allow_internal_unstable` attribute on the macro that generates the impl.

These crates all needed specialization for `newtype_index!`, which will no
longer be necessary when the current nightly eventually becomes the next
bootstrap compiler.

…wco,oli-obk

static mut: allow mutable reference to arbitrary types, not just slices and arrays

For historical reasons, we allow this:
```rust
static mut ARRAY: &'static mut [isize] = &mut [1];
```
However, we do not allow this:
```rust
static mut INT: &'static mut isize = &mut 1;
```

I think that's terribly inconsistent. I don't care much for `static mut`, but we have to keep it around for backwards compatibility and so we have to keep supporting it properly in the compiler. In recent refactors of how we deal with mutability of data in `static` and `const`, I almost made a fatal mistake since I tested `static mut INT: &'static mut isize = &mut 1` and concluded that we don't allow such `'static` mutable references even inside `static mut`. After all, nobody would expect this to be allowed only for arrays and slices, right?!?? So for the sake of our own sanity, and of whoever else reverse engineers these rules in the future to understand what the Rust compiler accepts or does not accept, I propose that we accept this for all types, not just arrays and slices.

…wesleywiser

wasm: Store rlib metadata in wasm object files

The goal of this commit is to remove warnings using LLVM tip-of-tree `wasm-ld`. In llvm/llvm-project#78658 the `wasm-ld` LLD driver no longer looks at archive indices and instead looks at all the objects in archives. Previously `lib.rmeta` files were simply raw rustc metadata bytes, not wasm objects, meaning that `wasm-ld` would emit a warning indicating so.

WebAssembly targets previously passed `--fatal-warnings` to `wasm-ld` by default which meant that if Rust were to update to LLVM 18 then all wasm targets would not work. This immediate blocker was resolved in rust-lang#120278 which removed `--fatal-warnings` which enabled a theoretical update to LLVM 18 for wasm targets. This current state is ok-enough for now because rustc squashes all linker output by default if it doesn't fail. This means, for example, that rustc squashes all the linker warnings coming out of `wasm-ld` about `lib.rmeta` files with LLVM 18. This again isn't a pressing issue because the information is all hidden, but it runs the risk of being annoying if another linker error were to happen and then the output would have all these unrelated warnings that couldn't be fixed.

Thus, this PR comes into the picture. The goal of this PR is to resolve these warnings by using the WebAssembly object file format on wasm targets instead of using raw rustc metadata. When I first implemented the rlib-in-objects scheme in rust-lang#84449 I remember either concluding that `wasm-ld` would either include the metadata in the output or I thought we didn't have to do anything there at all. I think I was wrong on both counts as `wasm-ld` does not include the metadata in the final output unless the object is referenced and we do actually need to do something to resolve these warnings.

This PR updates the object file format containing rustc metadata on WebAssembly targets to be an actual WebAssembly file. To avoid bringing in any new dependencies I've opted to hand-code this encoding at this time. If the object gets more complicated though it'd probably be best to pull in `wasmparser` and `wasm-encoder`. For now though there's two adjacent functions reading/writing wasm.

The only caveat I know of with this is that if `wasm-ld` does indeed look at the object file then the metadata will be included in the final output. I believe the only thing that could cause that at this time is `--whole-archive` which I don't think is passed for rlibs. I would clarify that I'm not 100% certain about this, however.

Remove support for `associated_type_bound` nested in `dyn` types

These necessarily desugar to `impl Trait`, which is inconsistent with the `associated_type_bound` feature after rust-lang#120584.

This PR keeps the `is_in_dyn_type` hack, which kind of makes me sad. Ideally, we'd be validating that no object types have associated type bounds somewhere else. Unfortunately, we can't do this later during astconv (i think?), nor can we do it earlier during ast validation (i think?) because of the feature gating of ATB being a *warning* rather than an *error*. Let me know if you have thoughts about this.

r? lcnr

…gn, r=RalfJung

Clarify that atomic and regular integers can differ in alignment

The documentation for atomic integers says that they have the "same in-memory representation" as their underlying integers. This might be misconstrued as implying that they have the same layout. Therefore, clarify that atomic integers' alignment is equal to their size.

Loosen an assertion to account for stashed errors.

The meaning of this assertion changed in rust-lang#120828 when the meaning of `has_errors` changed to exclude stashed errors. Evidently the new meaning is too restrictive.

Fixes rust-lang#120856.

r? ``@oli-obk``

…rcote

Turn the "no saved object file in work product" ICE into a translatable fatal error

I don't know if it's fair to say this fixes rust-lang#120854 but it surely makes the error reporting better and should encourage people with good instincts like ``@CinchBlue.``

…rrors

Remove unnecessary `#![feature(min_specialization)]`

As of rust-lang#119963 and rust-lang#120676, we can now rely on `newtype_index!` having `#[allow_internal_unstable(min_specialization)]`, so there are a few compiler crates that no longer need to include min-spec in their own crate features.

---

Some of the expansions of `newtype_index!` still appear to require min-spec in the crate features. I think this is because `#[orderable]` causes the expansion to include an implementation of `TrustedStep`, which is flagged with `#[rustc_specialization_trait]`, and for whatever reason that isn't permitted by allow-internal-unstable. So this PR only touches the crates where that isn't the case.

Allow restricted trait impls under `#[allow_internal_unstable(min_specialization)]`

This is a follow-up to rust-lang#119963 and a companion to rust-lang#120866, though it can land independently from the latter.

---

We have several compiler crates that only enable `#[feature(min_specialization)]` because it is required by their expansions of `newtype_index!`, in order to implement traits marked with `#[rustc_specialization_trait]`.

This PR allows those traits to be implemented internally by macros with `#[allow_internal_unstable(min_specialization)]`, without needing specialization to be enabled in the enclosing crate.