Replace features libfuse2,libfuse3 with a dedicated build cfg value

build.rs

@@ -1,46 +1,51 @@
 fn main() {
+    // Register rustc cfg for switching between mount implementations.
+    // When fuser MSRV is updated to v1.77 or above, we should switch from 'cargo:' to 'cargo::' syntax.
+    println!("cargo:rustc-check-cfg=cfg(fuser_mount_impl, values(\"pure-rust\", \"libfuse2\", \"libfuse3\"))");
+
     #[cfg(all(not(feature = "libfuse"), not(target_os = "linux")))]
     unimplemented!("Building without libfuse is only supported on Linux");
 
+    #[cfg(not(feature = "libfuse"))]
+    {
+        println!("cargo:rustc-cfg=fuser_mount_impl=\"pure-rust\"");
+    }
     #[cfg(feature = "libfuse")]
     {
-        #[cfg(target_os = "macos")]
-        {
+        if cfg!(target_os = "macos") {
             if pkg_config::Config::new()
                 .atleast_version("2.6.0")
                 .probe("fuse") // for macFUSE 4.x
                 .map_err(|e| eprintln!("{}", e))
                 .is_ok()
             {
-                println!("cargo:rustc-cfg=feature=\"libfuse2\"");
+                println!("cargo:rustc-cfg=fuser_mount_impl=\"libfuse2\"");
                 println!("cargo:rustc-cfg=feature=\"macfuse-4-compat\"");
             } else {
                 pkg_config::Config::new()
                     .atleast_version("2.6.0")
                     .probe("osxfuse") // for osxfuse 3.x
                     .map_err(|e| eprintln!("{}", e))
                     .unwrap();
-                println!("cargo:rustc-cfg=feature=\"libfuse2\"");
+                println!("cargo:rustc-cfg=fuser_mount_impl=\"libfuse2\"");
             }
-        }
-        #[cfg(not(target_os = "macos"))]
-        {
+        } else {
             // First try to link with libfuse3
             if pkg_config::Config::new()
                 .atleast_version("3.0.0")
                 .probe("fuse3")
                 .map_err(|e| eprintln!("{e}"))
                 .is_ok()
             {
-                println!("cargo:rustc-cfg=feature=\"libfuse3\"");
+                println!("cargo:rustc-cfg=fuser_mount_impl=\"libfuse3\"");
             } else {
                 // Fallback to libfuse
                 pkg_config::Config::new()
                     .atleast_version("2.6.0")
                     .probe("fuse")
                     .map_err(|e| eprintln!("{e}"))
                     .unwrap();
-                println!("cargo:rustc-cfg=feature=\"libfuse2\"");
+                println!("cargo:rustc-cfg=fuser_mount_impl=\"libfuse2\"");
             }
         }
     }

src/mnt/fuse2_sys.rs

@@ -16,7 +16,7 @@ pub struct fuse_args {
     pub allocated: c_int,
 }
 
-#[cfg(feature = "libfuse2")]
+#[cfg(fuser_mount_impl = "libfuse2")]
 extern "C" {
     // *_compat25 functions were introduced in FUSE 2.6 when function signatures changed.
     // Therefore, the minimum version requirement for *_compat25 functions is libfuse-2.6.0.

src/mnt/mod.rs

@@ -2,24 +2,24 @@
 //!
 //! Raw communication channel to the FUSE kernel driver.
 
-#[cfg(feature = "libfuse2")]
+#[cfg(fuser_mount_impl = "libfuse2")]
 mod fuse2;
 #[cfg(any(feature = "libfuse", test))]
 mod fuse2_sys;
-#[cfg(feature = "libfuse3")]
+#[cfg(fuser_mount_impl = "libfuse3")]
 mod fuse3;
-#[cfg(feature = "libfuse3")]
+#[cfg(fuser_mount_impl = "libfuse3")]
 mod fuse3_sys;
 
-#[cfg(not(feature = "libfuse"))]
+#[cfg(fuser_mount_impl = "pure-rust")]
 mod fuse_pure;
 pub mod mount_options;
 
-#[cfg(any(feature = "libfuse", test))]
+#[cfg(any(test, feature = "libfuse"))]
 use fuse2_sys::fuse_args;
 #[cfg(any(test, not(feature = "libfuse")))]
 use std::fs::File;
-#[cfg(any(test, not(feature = "libfuse"), not(feature = "libfuse3")))]
+#[cfg(any(test, fuser_mount_impl = "pure-rust", fuser_mount_impl = "libfuse2"))]
 use std::io;
 
 #[cfg(any(feature = "libfuse", test))]
@@ -47,16 +47,16 @@ fn with_fuse_args<T, F: FnOnce(&fuse_args) -> T>(options: &[MountOption], f: F)
     })
 }
 
-#[cfg(feature = "libfuse2")]
+#[cfg(fuser_mount_impl = "libfuse2")]
 pub use fuse2::Mount;
-#[cfg(feature = "libfuse3")]
+#[cfg(fuser_mount_impl = "libfuse3")]
 pub use fuse3::Mount;
-#[cfg(not(feature = "libfuse"))]
+#[cfg(fuser_mount_impl = "pure-rust")]
 pub use fuse_pure::Mount;
-#[cfg(not(feature = "libfuse3"))]
+#[cfg(not(fuser_mount_impl = "libfuse3"))]
 use std::ffi::CStr;
 
-#[cfg(not(feature = "libfuse3"))]
+#[cfg(not(fuser_mount_impl = "libfuse3"))]
 #[inline]
 fn libc_umount(mnt: &CStr) -> io::Result<()> {
     #[cfg(any(
@@ -87,7 +87,7 @@ fn libc_umount(mnt: &CStr) -> io::Result<()> {
 
 /// Warning: This will return true if the filesystem has been detached (lazy unmounted), but not
 /// yet destroyed by the kernel.
-#[cfg(any(test, not(feature = "libfuse")))]
+#[cfg(any(test, fuser_mount_impl = "pure-rust"))]
 fn is_mounted(fuse_device: &File) -> bool {
     use libc::{poll, pollfd};
     use std::os::unix::prelude::AsRawFd;