Set the MSRV to 1.65 and test this in CI

Currently this crate has no clear MSRV. Pick a common ecosystem point of
1.65 (let-else!) and start testing that in CI.

We could easily bump this further if needed, but there isn't much active
development and it is unlikely to be a point of contributor friction. We
can't easily be much below this because of `cc`.

Author: tgross35

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
           rustup component add clippy
       - uses: Swatinem/rust-cache@v2
       - run: cargo clippy --all-features --all-targets -- -D warnings
-  
+
   test:
     name: Test
     runs-on: ${{ matrix.os }}
@@ -133,10 +133,29 @@ jobs:
       - uses: actions/checkout@v4
       - run: |
           rustup update nightly --no-self-update
-          rustup default nightly 
+          rustup default nightly
       - uses: Swatinem/rust-cache@v2
       - run: cargo doc
 
+  msrv:
+    name: MSRV check
+    runs-on: ubuntu-24.04
+    timeout-minutes: 10
+    env:
+      RUSTFLAGS: # No need to check warnings on old MSRV, unset `-Dwarnings`
+    steps:
+    - uses: actions/checkout@master
+    - name: Install Rust
+      run: |
+        msrv="$(
+          cargo metadata --format-version=1 |
+          jq -r '.packages[] | select(.name == "cmake") | .rust_version'
+        )"
+        echo "MSRV: $msrv"
+        rustup update "$msrv" --no-self-update && rustup default "$msrv"
+    - uses: Swatinem/rust-cache@v2
+    - run: cargo check
+
   success:
     needs:
       - clippy
@@ -145,6 +164,7 @@ jobs:
       - ios_cross_compile_test
       - rustfmt
       - doc
+      - msrv
     runs-on: ubuntu-latest
     # GitHub branch protection is exceedingly silly and treats "jobs skipped because a dependency
     # failed" as success. So we have to do some contortions to ensure the job fails if any of its

Cargo.toml

@@ -13,6 +13,7 @@ A build dependency for running `cmake` to build a native library
 """
 categories = ["development-tools::build-utils"]
 edition = "2021"
+rust-version = "1.65"
 
 [dependencies]
 cc = "1.1.0"