RUSTSEC-2026-0173: proc-macro-error2 is unmaintained

> proc-macro-error2 is unmaintained

| Details | |
| ------------------- | ---------------------------------------------- |
| Status | unmaintained |
| Package | `proc-macro-error2` |
| Version | `2.0.1` |
| URL | [https://github.com/GnomedDev/proc-macro-error-2/issues/17](https://github.com/GnomedDev/proc-macro-error-2/issues/17) |
| Date | 2026-06-07 |

The author of `proc-macro-error2` has [confirmed](https://github.com/GnomedDev/proc-macro-error-2/issues/17#issuecomment-4643215473) that the crate is no longer maintained and recommends that users migrate away from it.

`proc-macro-error2` was originally created as a maintained fork of [`proc-macro-error`](https://crates.io/crates/proc-macro-error) (see [RUSTSEC-2024-0370](https://rustsec.org/advisories/RUSTSEC-2024-0370)). Both the original crate and this fork are now unmaintained.

## Possible Alternative(s)

- [manyhow](https://crates.io/crates/manyhow)
- [proc-macro2-diagnostics](https://github.com/SergioBenitez/proc-macro2-diagnostics)

See [advisory page](https://rustsec.org/advisories/RUSTSEC-2026-0173.html) for additional details.

Start by locating proc-macro-error2 in the repository's dependency manifests and searching for its usage. Compare the affected APIs with manyhow or proc-macro2-diagnostics, then run the relevant Rust checks and tests. Done means the unmaintained dependency is removed and the project still builds and passes its existing tests.

索引モデルが issue の本文から書いたものです。