cp: reduce memory usage for cp -al by skipping unnecessary tracking (#9805)

Co-authored-by: Sylvestre Ledru <sylvestre@debian.org>

src/uu/cp/src/copydir.rs

@@ -27,7 +27,8 @@ use uucore::uio_error;
 use walkdir::{DirEntry, WalkDir};
 
 use crate::{
-    CopyResult, CpError, Options, aligned_ancestors, context_for, copy_attributes, copy_file,
+    CopyMode, CopyResult, CpError, Options, aligned_ancestors, context_for, copy_attributes,
+    copy_file,
 };
 
 /// Ensure a Windows path starts with a `\\?`.
@@ -468,6 +469,15 @@ pub(crate) fn copy_directory(
                 let is_dir_for_permissions =
                     entry_is_dir_no_follow || (options.dereference && direntry_path.is_dir());
                 if is_dir_for_permissions {
+                    // For --link mode, copy attributes immediately to avoid O(n) memory
+                    if options.copy_mode == CopyMode::Link {
+                        copy_attributes(
+                            &entry.source_absolute,
+                            &entry.local_to_target,
+                            &options.attributes,
+                        )?;
+                        continue;
+                    }
                     // Add this directory to our list for permission fixing later
                     dirs_needing_permissions
                         .push((entry.source_absolute.clone(), entry.local_to_target.clone()));

src/uu/cp/src/cp.rs

@@ -2448,7 +2448,9 @@ fn copy_file(
         return Err(translate!("cp-error-cannot-change-attribute", "dest" => dest.quote()).into());
     }
 
-    if options.preserve_hard_links() {
+    // When using --link mode, hard link structure is automatically preserved
+    // because we link to source files (which share inodes).
+    if options.preserve_hard_links() && options.copy_mode != CopyMode::Link {
         // if we encounter a matching device/inode pair in the source tree
         // we can arrange to create a hard link between the corresponding names
         // in the destination tree.
@@ -2565,10 +2567,14 @@ fn copy_file(
         }
     }
 
-    copied_files.insert(
-        FileInformation::from_path(source, options.dereference(source_in_command_line))?,
-        dest.to_path_buf(),
-    );
+    // Skip tracking copied files when using --link mode since hard link
+    // structure is automatically preserved
+    if options.copy_mode != CopyMode::Link {
+        copied_files.insert(
+            FileInformation::from_path(source, options.dereference(source_in_command_line))?,
+            dest.to_path_buf(),
+        );
+    }
 
     if let Some(progress_bar) = progress_bar {
         progress_bar.inc(source_metadata.len());