Optimize away some path lookups in the generic `fs::copy` implementation.

This also eliminates a use of a `Path` convenience function, in support
of #80741, refactoring `std::path` to focus on pure data structures and
algorithms.

1 files changed, 6 insertions, 4 deletions

diff --git a/library/std/src/sys_common/fs.rs b/library/std/src/sys_common/fs.rs
index e30e8018a31..6bdb26cd078 100644
--- a/library/std/src/sys_common/fs.rs
+++ b/library/std/src/sys_common/fs.rs
@@ -5,19 +5,21 @@ use crate::io::{self, Error, ErrorKind};
 use crate::path::Path;
 
 pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
-    if !from.is_file() {
+    let mut reader = fs::File::open(from)?;
+    let metadata = reader.metadata()?;
+
+    if !metadata.is_file() {
         return Err(Error::new(
             ErrorKind::InvalidInput,
             "the source path is not an existing regular file",
         ));
     }
 
-    let mut reader = fs::File::open(from)?;
     let mut writer = fs::File::create(to)?;
-    let perm = reader.metadata()?.permissions();
+    let perm = metadata.permissions();
 
     let ret = io::copy(&mut reader, &mut writer)?;
-    fs::set_permissions(to, perm)?;
+    writer.set_permissions(perm)?;
     Ok(ret)
 }