Repository: rust
Issue: Tracking Issue for `#[global_registration]`
Labels: T-lang,C-tracking-issue,F-global_registration

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This is a tracking issue for the global registration experiment.
The feature gate for the issue is `#![feature(global_registration)]`.

Global registration has previously been discussed on [internals.rust-lang.org](https://internals.rust-lang.org/t/global-registration-a-kind-of-pre-rfc/20813/26) and a [proposal was made on the testing devex team](https://github.com/rust-lang/testing-devex-team/issues/3) with @epage . Specific syntax has not been discussed yet, which is part of what this experiment is going to figure out. Likely, a first implementation will use built-in attribute macros.

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### Steps
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- [ ] Get lang experiment approved. (@scottmcm is liaisoning me)
- [ ] Land the experimental implementation in nightly.
    - [x] Experimental feature flag: #125314 (now available on nightly)
    - [x] Update core/std with a new `global_registration` module (implemented on forked branch)
    - [x] Add new built-in macros to rust to create and add to global registries (implemented on forked branch)
    - [x] Propagate global registries through the AST and HIR, also performing name resolution (implemented on forked branch)
    - [ ] Write docs for `core::global_registration`
    - [ ] Check whether `#[global_registry]` defenitions have the right wrapper type (`Registry<T>`)
    - [ ] Actually create nice errors instead of panicking in unexpected cases
    - [ ] tests for
        - [ ] errors generated
        - [ ] `doc(alias)` (not entirely sure about my current implementation, so test that)
        - [ ] the right `has_codegen_attrs`, I'm not sure I did that right
        - [ ] privacy of global registries
    - [ ] Add global registries to RustDoc
    - [ ] Check if my `sym::anon` in `definition.rs` is correct
- [ ] Accept an RFC
- [ ] Adjust documentation ([see instructions on rustc-dev-guide][doc-guide])
- [ ] Formatting for new syntax has been added to the [Style Guide] ([nightly-style-procedure])
- [ ] Stabilization PR ([see instructions on rustc-dev-guide][stabilization-guide])

[stabilization-guide]: https://rustc-dev-guide.rust-lang.org/stabilization_guide.html#stabilization-pr
[doc-guide]: https://rustc-dev-guide.rust-lang.org/stabilization_guide.html#documentation-prs
[nightly-style-procedure]: https://github.com/rust-lang/style-team/blob/master/nightly-style-procedure.md 
[Style Guide]: https://github.com/rust-lang/rust/tree/master/src/doc/style-guide

### Unresolved Questions

TODO

### Implementation history

TODO

### Current proposed syntax

```rust
use core::global_registration::{global_registry, register, Registry};

#[global_registry]
static ERROR_MSGS: Registry<&str>;

register!(ERROR_MSGS, "a");
register!(ERROR_MSGS, "b", "c");

fn main() {
    for msg in ERROR_MSGS {
        println!("{}", msg);
    }
}
```