Make MSRV explicit & check accidental bump in the CI

.github/workflows/build.yml

@@ -345,6 +345,9 @@ jobs:
   testcfail:
     name: testcfail
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: -D warnings
+      MSRV: 1.87.0
     defaults:
       run:
         working-directory: cfail
@@ -374,7 +377,9 @@ jobs:
             ${{ runner.OS }}-build-
 
       - name: Install Rust
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ env.MSRV }}
 
       - name: Run cargo
         run: cargo run

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- Make MSRV of 1.87.0 explicit.
+
 ## [v0.9.1] - 2025-08-19
 
 ### Added
@@ -701,7 +703,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Initial release
 
 [Unreleased]: https://github.com/rust-embedded/heapless/compare/v0.9.1...HEAD
-[v0.9.0]: https://github.com/rust-embedded/heapless/compare/v0.9.0...v0.9.1
+[v0.9.1]: https://github.com/rust-embedded/heapless/compare/v0.9.0...v0.9.1
 [v0.9.0]: https://github.com/rust-embedded/heapless/compare/v0.8.0...v0.9.0
 [v0.8.0]: https://github.com/rust-embedded/heapless/compare/v0.7.16...v0.8.0
 [v0.7.16]: https://github.com/rust-embedded/heapless/compare/v0.7.15...v0.7.16

Cargo.toml

@@ -1,13 +1,14 @@
 [package]
 authors = [
-  "Jorge Aparicio <jorge@japaric.io>",
-  "Per Lindgren <per.lindgren@ltu.se>",
-  "Emil Fresk <emil.fresk@gmail.com>",
+    "Jorge Aparicio <jorge@japaric.io>",
+    "Per Lindgren <per.lindgren@ltu.se>",
+    "Emil Fresk <emil.fresk@gmail.com>",
 ]
 categories = ["data-structures", "no-std"]
 description = "`static` friendly data structures that don't require dynamic memory allocation"
 documentation = "https://docs.rs/heapless"
 edition = "2021"
+rust-version = "1.87"
 keywords = ["static", "no-heap"]
 license = "MIT OR Apache-2.0"
 name = "heapless"
@@ -23,11 +24,19 @@ bytes = ["dep:bytes"]
 portable-atomic = ["dep:portable-atomic"]
 
 # Enable polyfilling of atomics via portable-atomic, using critical section for locking
-portable-atomic-critical-section = ["dep:portable-atomic", "portable-atomic", "portable-atomic?/critical-section"]
+portable-atomic-critical-section = [
+    "dep:portable-atomic",
+    "portable-atomic",
+    "portable-atomic?/critical-section",
+]
 
 # Enable polyfilling of atomics via portable-atomic, using disabling interrupts for locking.
 # WARNING: this is only sound for single-core bare-metal privileged-mode targets!
-portable-atomic-unsafe-assume-single-core = ["dep:portable-atomic", "portable-atomic", "portable-atomic?/unsafe-assume-single-core"]
+portable-atomic-unsafe-assume-single-core = [
+    "dep:portable-atomic",
+    "portable-atomic",
+    "portable-atomic?/unsafe-assume-single-core",
+]
 
 # implement serde traits.
 serde = ["dep:serde"]
@@ -65,13 +74,13 @@ static_assertions = "1.1.0"
 
 [package.metadata.docs.rs]
 features = [
-  "bytes",
-  "ufmt",
-  "serde",
-  "defmt",
-  "mpmc_large",
-  "portable-atomic-critical-section",
-  "alloc",
+    "bytes",
+    "ufmt",
+    "serde",
+    "defmt",
+    "mpmc_large",
+    "portable-atomic-critical-section",
+    "alloc",
 ]
 # for the pool module
 targets = ["i686-unknown-linux-gnu"]

README.md

@@ -32,6 +32,11 @@ Licensed under either of
 
 at your option.
 
+## MSRV Policy
+
+This crate is guaranteed to compile with the latest two stable releases of Rust. For example, if the
+latest stable Rust release is 1.70, then this crate is guaranteed to compile with Rust 1.69 and 1.70.
+
 ## Contribution
 
 Unless you explicitly state otherwise, any contribution intentionally submitted