hide unused exports on other platforms

library/std/src/io/mod.rs

@@ -283,10 +283,8 @@ pub use self::stdio::{set_panic, set_print};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::util::{empty, repeat, sink, Empty, Repeat, Sink};
 
-pub(crate) use self::copy::generic_copy;
-
 mod buffered;
-mod copy;
+pub(crate) mod copy;
 mod cursor;
 mod error;
 mod impls;

library/std/src/io/stdio.rs

@@ -409,6 +409,8 @@ impl Read for Stdin {
     }
 }
 
+// only used by platform-dependent io::copy specializations, i.e. unused on some platforms
+#[cfg(any(target_os = "linux", target_os = "android"))]
 impl StdinLock<'_> {
     pub(crate) fn as_mut_buf(&mut self) -> &mut BufReader<impl Read> {
         &mut self.inner

library/std/src/sys/unix/fs.rs

@@ -1276,7 +1276,7 @@ pub(crate) fn copy_regular_files(
                         // - copy_file_range is disallowed, for example by seccomp (EPERM)
                         // - copy_file_range cannot be used with pipes or device nodes (EINVAL)
                         assert_eq!(written, 0);
-                        return io::generic_copy(reader, writer);
+                        return io::copy::generic_copy(reader, writer);
                     }
                     _ => return Err(err),
                 }
@@ -1328,7 +1328,7 @@ pub(crate) fn sendfile_splice(
                         // Try fallback io::copy if splice/sendfile do not support this particular
                         // file descritor (EINVAL)
                         assert_eq!(written, 0);
-                        return io::generic_copy(reader, writer);
+                        return io::copy::generic_copy(reader, writer);
                     }
                     _ => return Err(err),
                 }