chore(lint): satisfy Rust 1.96 GCD diagnostics

Author: presempathy-awb

src/vfs/gcd/file.rs

@@ -1,7 +1,7 @@
 //! `GcdFile`: per-file I/O against a `DispatchIO` channel.
 //!
 //! The channel is created in `DISPATCH_IO_RANDOM` mode and owns a duplicated
-//! file descriptor (so dispatch_io can asynchronously close its own copy when
+//! file descriptor (so `dispatch_io` can asynchronously close its own copy when
 //! the channel is released, independently of the `std::fs::File` we hold).
 //! Reads and writes call `dispatch_io_read` / `dispatch_io_write` with block
 //! handlers; the handlers accumulate chunks and, on `done`, send the result
@@ -14,7 +14,7 @@ use std::sync::Arc;
 
 use parking_lot::Mutex;
 
-use block2::{Block, DynBlock, RcBlock};
+use block2::{DynBlock, RcBlock};
 use dispatch2::{DispatchData, DispatchIO, DispatchIOCloseFlags, DispatchQueue, DispatchRetained};
 
 use crate::Result;
@@ -135,16 +135,10 @@ fn submit_read(
             }
         });
 
-    // SAFETY: transmute is from the stand-in block signature to the typedef
-    // declared by dispatch2 — the ABI is identical because `bool` and `u8`
-    // share the same one-byte ABI, and a `*mut DispatchData` is bit-identical
-    // to a `*mut c_void`.
-    let handler_ptr: *mut DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)> = unsafe {
-        std::mem::transmute::<
-            *mut Block<dyn Fn(u8, *mut c_void, libc::c_int)>,
-            *mut DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)>,
-        >(RcBlock::as_ptr(&handler))
-    };
+    // SAFETY: ABI-compatible pointer cast to the typedef declared by dispatch2.
+    // `bool` and `u8` are one byte, while both data arguments are pointers.
+    let handler_ptr: *mut DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)> =
+        RcBlock::as_ptr(&handler).cast::<DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)>>();
 
     // SAFETY: channel and queue are valid (owned by the caller's `GcdFile`);
     // the handler block is retained by libdispatch on submission.
@@ -185,13 +179,9 @@ fn submit_write(
         },
     );
 
-    // SAFETY: ABI-compatible transmute; see `submit_read`.
-    let handler_ptr: *mut DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)> = unsafe {
-        std::mem::transmute::<
-            *mut Block<dyn Fn(u8, *mut c_void, libc::c_int)>,
-            *mut DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)>,
-        >(RcBlock::as_ptr(&handler))
-    };
+    // SAFETY: ABI-compatible pointer cast; see `submit_read`.
+    let handler_ptr: *mut DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)> =
+        RcBlock::as_ptr(&handler).cast::<DynBlock<dyn Fn(bool, *mut DispatchData, libc::c_int)>>();
 
     // SAFETY: channel/queue/data all valid; libdispatch retains both the data
     // object and the handler block for the operation's duration.