…r=Mark-Simulacrum

Update provider API docs

NVPTX does not support cycles in static initializers (see rust-lang#146787). LLVM produces an error when attempting to generate code for such constructs, like self-referential structs.

To avoid LLVM UB, we emit a post-monomorphization error on the Rust side before reaching codegen.

This is achieved by analyzing a subgraph of the "mono item graph" that only contains statics.
1. Calculate the strongly connected components (SCCs) of the graph.
2. Check for cycles (more than one node in an SCC or one node that references itself).

…imulacrum

Update provider API docs

related: rust-lang#145899 (comment)

print error from EnzymeWrapper::get_or_init(sysroot) as a note

r? @ZuseZ4

e.g.

1. when libEnzyme not found

```shell
$ rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: autodiff backend not found in the sysroot: failed to find a `libEnzyme-21` folder in the sysroot candidates:
       * /Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib
  |
  = note: it will be distributed via rustup in the future
```

2. when could not load libEnzyme successfully

```shell
rustc +stage1 -Z autodiff=Enable -C lto=fat src/main.rs
error: failed to load our autodiff backend: DlOpen { source: "dlopen(/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib, 0x0005): tried: \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file), \'/System/Volumes/Preboot/Cryptexes/OS/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (no such file), \'/Volumes/WD_BLACK_SN850X_HS_1TB/rust-lang/rust/build/aarch64-apple-darwin/stage1/lib/rustlib/aarch64-apple-darwin/lib/libEnzyme-21.dylib\' (slice is not valid mach-o file)" }
```

Update provider API docs

tracking issue: rust-lang#44930

Provide our own implementations in order to guarantee the behavior of `va_arg`. We will only be able to stabilize `c_variadic` on targets where we know and guarantee the properties of `va_arg`.

r? workingjubilee

Update provider API docs

Tracking issue: rust-lang#132980

Fixes rust-lang#133965
Fixes rust-lang#150613

r? @BoxyUwU

…crum

Update provider API docs

Adds guidance on a specific provider API implementation anti pattern that implementers of the error trait should avoid.

resolves rust-lang#99301 (comment)

…crum

Update provider API docs

Adds guidance on a specific provider API implementation anti pattern that implementers of the error trait should avoid.

resolves rust-lang#99301 (comment)

…crum

Update provider API docs

Adds guidance on a specific provider API implementation anti pattern that implementers of the error trait should avoid.

resolves rust-lang#99301 (comment)

Rollup of 11 pull requests

Successful merges:

 - #149976 (Add waker_fn and local_waker_fn to std::task)
 - #150074 (Update provider API docs)
 - #150094 (`c_variadic`: provide our own `va_arg` implementation for more targets)
 - #150164 (rustc: Fix `-Zexport-executable-symbols` on wasm)
 - #150569 (Ensure that static initializers are acyclic for NVPTX)
 - #150607 (Add amdgpu_dispatch_ptr intrinsic)
 - #150694 (./x check miri: enable check_only feature)
 - #150717 (Thread `--jobs` from `bootstrap` -> `compiletest` -> `run-make-support`)
 - #150736 (Add AtomicPtr::null)
 - #150787 (Add myself as co-maintainer for s390x-unknown-linux-musl)
 - #150789 (Fix copy-n-paste error in `vtable_for` docs)

r? @ghost

Rollup of 10 pull requests

Successful merges:

 - #149976 (Add waker_fn and local_waker_fn to std::task)
 - #150074 (Update provider API docs)
 - #150094 (`c_variadic`: provide our own `va_arg` implementation for more targets)
 - #150164 (rustc: Fix `-Zexport-executable-symbols` on wasm)
 - #150569 (Ensure that static initializers are acyclic for NVPTX)
 - #150694 (./x check miri: enable check_only feature)
 - #150717 (Thread `--jobs` from `bootstrap` -> `compiletest` -> `run-make-support`)
 - #150736 (Add AtomicPtr::null)
 - #150787 (Add myself as co-maintainer for s390x-unknown-linux-musl)
 - #150789 (Fix copy-n-paste error in `vtable_for` docs)

r? @ghost

Rollup merge of #150074 - provider-doc-update, r=Mark-Simulacrum

Update provider API docs

Adds guidance on a specific provider API implementation anti pattern that implementers of the error trait should avoid.

resolves #99301 (comment)