chore: add and guard MSRV

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-24.04, macos-14, windows-2022 ]
-        rust-version: [ "stable", "nightly" ]
+        rust-version: [ "1.85.0", "stable", "nightly" ]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v6

Cargo.toml

@@ -22,6 +22,7 @@ homepage = "https://github.com/fast/exn"
 license = "Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/fast/exn"
+rust-version = "1.85.0"
 
 [workspace.dependencies]
 # Workspace dependencies
@@ -34,8 +35,8 @@ insta = { version = "1.45.1" }
 which = { version = "8.0.0" }
 
 [workspace.lints.rust]
-unexpected_cfgs = { level = "deny", check-cfg = ['cfg(windows_test)'] }
 unknown_lints = "deny"
+unused_must_use = "deny"
 
 [workspace.lints.clippy]
 dbg_macro = "deny"

README.md

@@ -2,13 +2,15 @@
 
 [![Crates.io][crates-badge]][crates-url]
 [![Documentation][docs-badge]][docs-url]
+[![MSRV 1.85][msrv-badge]](https://www.whatrustisit.com)
 [![Apache 2.0 licensed][license-badge]][license-url]
 [![Build Status][actions-badge]][actions-url]
 
 [crates-badge]: https://img.shields.io/crates/v/exn.svg
 [crates-url]: https://crates.io/crates/exn
 [docs-badge]: https://docs.rs/exn/badge.svg
 [docs-url]: https://docs.rs/exn
+[msrv-badge]: https://img.shields.io/badge/MSRV-1.85-green?logo=rust
 [license-badge]: https://img.shields.io/crates/l/exn
 [license-url]: LICENSE
 [actions-badge]: https://github.com/fast/exn/workflows/CI/badge.svg
@@ -30,6 +32,12 @@ This crate is `no_std` compatible, while the `alloc` crate is still required for
 
 It is worth noting that `no_std` support is a nice-to-have feature, and can be dropped if it blocks other important features in the future. Before 1.0, once `exn` APIs settle down, the decision on whether to keep `no_std` as a promise will be finalized.
 
+## Minimum Rust version policy
+
+This crate is built against the latest stable release, and its minimum supported rustc version is 1.85.0.
+
+The policy is that the minimum Rust version required to use this crate can be increased in minor version updates. For example, if version 1.0 requires Rust 1.60.0, then version 1.0.z for all values of z will also require Rust 1.60.0 or newer. However, version 1.y for y > 0 may require a newer minimum version of Rust.
+
 ## License
 
 This project is licensed under [Apache License, Version 2.0](LICENSE).

rust-toolchain.toml

@@ -13,5 +13,5 @@
 # limitations under the License.
 
 [toolchain]
-channel = "stable"
+channel = "1.85.0"
 components = ["cargo", "rustfmt", "clippy", "rust-analyzer"]