Auto merge of rust-lang#134786 - ChrisDenton:fix-rename-symlink, r=tgross35

Fix renaming symlinks on Windows

Previously we only detected mount points and not other types of links when determining reparse point behaviour.

Also added some tests to avoid this regressing again in the future.

Author: bors

library/std/src/fs/tests.rs

@@ -1953,3 +1953,32 @@ fn test_rename_directory_to_non_empty_directory() {
 
     error!(fs::rename(source_path, target_path), 145); // ERROR_DIR_NOT_EMPTY
 }
+
+#[test]
+fn test_rename_symlink() {
+    let tmpdir = tmpdir();
+    let original = tmpdir.join("original");
+    let dest = tmpdir.join("dest");
+    let not_exist = Path::new("does not exist");
+
+    symlink_file(not_exist, &original).unwrap();
+    fs::rename(&original, &dest).unwrap();
+    // Make sure that renaming `original` to `dest` preserves the symlink.
+    assert_eq!(fs::read_link(&dest).unwrap().as_path(), not_exist);
+}
+
+#[test]
+#[cfg(windows)]
+fn test_rename_junction() {
+    let tmpdir = tmpdir();
+    let original = tmpdir.join("original");
+    let dest = tmpdir.join("dest");
+    let not_exist = Path::new("does not exist");
+
+    junction_point(&not_exist, &original).unwrap();
+    fs::rename(&original, &dest).unwrap();
+
+    // Make sure that renaming `original` to `dest` preserves the junction point.
+    // Junction links are always absolute so we just check the file name is correct.
+    assert_eq!(fs::read_link(&dest).unwrap().file_name(), Some(not_exist.as_os_str()));
+}

library/std/src/sys/pal/windows/fs.rs

@@ -1295,15 +1295,18 @@ pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
             } else {
                 // SAFETY: The struct has been initialized by GetFileInformationByHandleEx
                 let file_attribute_tag_info = unsafe { file_attribute_tag_info.assume_init() };
+                let file_type = FileType::new(
+                    file_attribute_tag_info.FileAttributes,
+                    file_attribute_tag_info.ReparseTag,
+                );
 
-                if file_attribute_tag_info.FileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0
-                    && file_attribute_tag_info.ReparseTag != c::IO_REPARSE_TAG_MOUNT_POINT
-                {
-                    // The file is not a mount point: Reopen the file without inhibiting reparse point behavior.
-                    None
-                } else {
-                    // The file is a mount point: Don't reopen the file so that the mount point gets renamed.
+                if file_type.is_symlink() {
+                    // The file is a mount point, junction point or symlink so
+                    // don't reopen the file so that the link gets renamed.
                     Some(Ok(handle))
+                } else {
+                    // Otherwise reopen the file without inhibiting reparse point behavior.
+                    None
                 }
             }
         }