Nonsense rust-version values have a non-ideal error message

[shepmaster]

Problem

Using a rust-version of x produces the error

thread 'main' panicked at crates/cargo-util-schemas/src/core/partial_version.rs:99:17:
assertion `left == right` failed: guaranteed by is_req
  left: 0
 right: 1

Steps

Create a new package with the following Cargo.toml:

[package]
name = "x"
version = "0.1.0"
edition = "2021"
rust-version = "x"

Run cargo build

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.77.1 (e52e36006 2024-03-26)
release: 1.77.1
commit-hash: e52e360061cacbbeac79f7f1215a7a90b6f08442
commit-date: 2024-03-26
host: aarch64-apple-darwin
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.4.0 (sys:0.4.70+curl-8.5.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Mac OS 14.4.1 [64-bit]

cargo 1.79.0-nightly (a59aba136 2024-03-28)
release: 1.79.0-nightly
commit-hash: a59aba136aab5510c16b0750a36cbd9916f91796
commit-date: 2024-03-28
host: aarch64-apple-darwin
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.4.0 (sys:0.4.72+curl-8.6.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Mac OS 14.4.1 [64-bit]

[epage]

... x is a valid semver::VersionReq wildcard?

https://github.com/dtolnay/semver/blob/master/src/parse.rs#L191-L201

• Added to semver in Parse x and X as wildcard dtolnay/semver#247 but it looks like it was supported before the 1.0 rewrite
• This dates back to the beginning, steveklabnik/semver-parser@1bfa9b3