qcow2-rs: support 1.75.0 'async fn' in trait

Conditionally support for 'async fn' in trait if toolchain is >= 1.75.0,
otherwise still #[async_trait] is used.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>

Cargo.toml

@@ -39,6 +39,7 @@ miniz_oxide = { version = "0.6.2", features = ["std"] }
 futures = "0.3.29"
 log = {version = "0.4", features = ["release_max_level_off"]}
 env_logger = "0.9"
+rustversion = "1.0.14"
 
 [dev-dependencies]
 tempfile = "3.6.0"

src/dev.rs

@@ -8,6 +8,7 @@ use crate::meta::{
 };
 use crate::zero_buf;
 use async_recursion::async_recursion;
+#[rustversion::before(1.75)]
 use async_trait::async_trait;
 use futures_locks::{RwLock as AsyncRwLock, RwLockWriteGuard as LockWriteGuard};
 use miniz_oxide::inflate::core::{decompress as inflate, DecompressorOxide};
@@ -24,7 +25,8 @@ use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 ///
 /// these methods are called for reading data from image, writing data
 /// to image, and discarding range.
-#[async_trait(?Send)]
+#[rustversion::attr(before(1.75), async_trait(?Send))]
+#[rustversion::attr(since(1.75), allow(async_fn_in_trait))]
 pub trait Qcow2IoOps {
     async fn read_to(&self, offset: u64, buf: &mut [u8]) -> Qcow2Result<usize>;
     async fn write_from(&self, offset: u64, buf: &[u8]) -> Qcow2Result<()>;

src/sync_io.rs

@@ -1,5 +1,6 @@
 use crate::dev::Qcow2IoOps;
 use crate::error::Qcow2Result;
+#[rustversion::before(1.75)]
 use async_trait::async_trait;
 use nix::fcntl::{fallocate, FallocateFlags};
 use std::cell::RefCell;
@@ -35,7 +36,7 @@ impl Qcow2IoSync {
     }
 }
 
-#[async_trait(?Send)]
+#[rustversion::attr(before(1.75), async_trait(?Send))]
 impl Qcow2IoOps for Qcow2IoSync {
     async fn read_to(&self, offset: u64, buf: &mut [u8]) -> Qcow2Result<usize> {
         let res = unsafe {

src/uring.rs

@@ -1,6 +1,7 @@
 use crate::dev::Qcow2IoOps;
 use crate::error::Qcow2Result;
 use crate::helpers::slice_to_vec;
+#[rustversion::before(1.75)]
 use async_trait::async_trait;
 use nix::fcntl::{fallocate, FallocateFlags};
 use std::os::unix::io::AsRawFd;
@@ -30,7 +31,7 @@ impl Qcow2IoUring {
     }
 }
 
-#[async_trait(?Send)]
+#[rustversion::attr(before(1.75), async_trait(?Send))]
 impl Qcow2IoOps for Qcow2IoUring {
     async fn read_to(&self, offset: u64, buf: &mut [u8]) -> Qcow2Result<usize> {
         let ubuf = slice_to_vec::<u8>(buf);