Remove redundant return value from write_loop()

This function ought to match the standard write_all().

src/common.rs

@@ -1369,9 +1369,7 @@ pub fn valid_func_name(name: &wstr) -> bool {
 
 /// A rusty port of the C++ `write_loop()` function from `common.cpp`. This should be deprecated in
 /// favor of native rust read/write methods at some point.
-///
-/// Returns the number of bytes written or an IO error.
-pub fn write_loop<Fd: AsRawFd>(fd: &Fd, buf: &[u8]) -> std::io::Result<usize> {
+pub fn write_loop<Fd: AsRawFd>(fd: &Fd, buf: &[u8]) -> std::io::Result<()> {
     let fd = fd.as_raw_fd();
     let mut total = 0;
     while total < buf.len() {
@@ -1387,7 +1385,7 @@ pub fn write_loop<Fd: AsRawFd>(fd: &Fd, buf: &[u8]) -> std::io::Result<usize> {
             }
         }
     }
-    Ok(total)
+    Ok(())
 }
 
 /// A rusty port of the C++ `read_loop()` function from `common.cpp`. This should be deprecated in

src/env_universal_common.rs

@@ -522,13 +522,13 @@ impl EnvUniversal {
     }
 
     /// Writes our state to the fd. path is provided only for error reporting.
-    fn write_to_fd(&mut self, fd: impl AsFd, path: &wstr) -> std::io::Result<usize> {
+    fn write_to_fd(&mut self, fd: impl AsFd, path: &wstr) -> std::io::Result<()> {
         let fd = fd.as_fd();
         let contents = Self::serialize_with_vars(&self.vars);
 
         let res = write_loop(&fd, &contents);
         match res.as_ref() {
-            Ok(_) => {
+            Ok(()) => {
                 // Since we just wrote out this file, it matches our internal state; pretend we read from it.
                 self.last_read_file = file_id_for_fd(fd);
             }