Remove unsafe, add MSRV policy

.github/workflows/rust.yml

@@ -31,3 +31,15 @@ jobs:
       run: cargo build --features macro --verbose
     - name: Run tests
       run: cargo test --features macro --verbose
+  msrv:
+    name: MSRV
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install MSRV
+        uses: dtolnay/rust-toolchain@master
+        with:
+            toolchain: "1.69"
+            components: rustfmt, clippy
+      - name: Check MSRV compatibility
+        run: cargo check --verbose --all-features

README.md

@@ -75,3 +75,10 @@ You can also use `#[pollster::test]` for tests.
 ## Comparison with `futures::executor::block_on`
 
 `pollster` does approximately the same thing as the `block_on` function from the `futures` crate. If you already have `futures` in your dependency tree, you might as well use it instead. `pollster` is primarily for applications that don't care to pull all of `futures` or another runtime like `tokio` into their dependency tree for the sake of evaluating simple futures.
+
+## Minimum Supported Rust Version (MSRV) Policy
+
+Current MSRV: `1.69.0`
+
+`pollster` has a policy of supporting compiler versions that are at least 18 months old. The crate *may* compile with
+older compilers, but this is not guaranteed.

src/lib.rs

@@ -109,13 +109,7 @@ impl Wake for Signal {
 /// let result = pollster::block_on(my_fut);
 /// ```
 pub fn block_on<F: IntoFuture>(fut: F) -> F::Output {
-    let mut fut = fut.into_future();
-
-    // Pin the future so that it can be polled.
-    // SAFETY: We shadow `fut` so that it cannot be used again. The future is now pinned to the stack and will not be
-    // moved until the end of this scope. This is, incidentally, exactly what the `pin_mut!` macro from `pin_utils`
-    // does.
-    let mut fut = unsafe { std::pin::Pin::new_unchecked(&mut fut) };
+    let mut fut = core::pin::pin!(fut.into_future());
 
     // Signal used to wake up the thread for polling as the future moves to completion. We need to use an `Arc`
     // because, although the lifetime of `fut` is limited to this function, the underlying IO abstraction might keep