Minimise amount of code behind conditional compilation (#2362)

* Minimise amount of code behind conditional compilation

* An additional case

* Copy paste derp

* Fix unreachable warnings

* Typo

* Let's hope this works...

Author: Rua

vulkano/src/device/mod.rs

@@ -965,7 +965,6 @@ impl Device {
     /// # Safety
     ///
     /// - `file` must be a handle to external memory that was created outside the Vulkan API.
-    #[cfg_attr(not(unix), allow(unused_variables))]
     #[inline]
     pub unsafe fn memory_fd_properties(
         &self,
@@ -1009,35 +1008,38 @@ impl Device {
     }
 
     #[cfg_attr(not(feature = "document_unchecked"), doc(hidden))]
-    #[cfg_attr(not(unix), allow(unused_variables))]
     pub unsafe fn memory_fd_properties_unchecked(
         &self,
         handle_type: ExternalMemoryHandleType,
         file: File,
     ) -> Result<MemoryFdProperties, VulkanError> {
-        #[cfg(not(unix))]
-        unreachable!("`khr_external_memory_fd` was somehow enabled on a non-Unix system");
+        let mut memory_fd_properties = ash::vk::MemoryFdPropertiesKHR::default();
 
         #[cfg(unix)]
-        {
-            use std::os::unix::io::IntoRawFd;
+        let fd = {
+            use std::os::fd::IntoRawFd;
+            file.into_raw_fd()
+        };
 
-            let mut memory_fd_properties = ash::vk::MemoryFdPropertiesKHR::default();
+        #[cfg(not(unix))]
+        let fd = {
+            let _ = file;
+            -1
+        };
 
-            let fns = self.fns();
-            (fns.khr_external_memory_fd.get_memory_fd_properties_khr)(
-                self.handle,
-                handle_type.into(),
-                file.into_raw_fd(),
-                &mut memory_fd_properties,
-            )
-            .result()
-            .map_err(VulkanError::from)?;
+        let fns = self.fns();
+        (fns.khr_external_memory_fd.get_memory_fd_properties_khr)(
+            self.handle,
+            handle_type.into(),
+            fd,
+            &mut memory_fd_properties,
+        )
+        .result()
+        .map_err(VulkanError::from)?;
 
-            Ok(MemoryFdProperties {
-                memory_type_bits: memory_fd_properties.memory_type_bits,
-            })
-        }
+        Ok(MemoryFdProperties {
+            memory_type_bits: memory_fd_properties.memory_type_bits,
+        })
     }
 
     /// Assigns a human-readable name to `object` for debugging purposes.