From 837640bc0235533f498aace9fc5c9541638ad88f Mon Sep 17 00:00:00 2001
From: Sylvestre Ledru <sylvestre@debian.org>
Date: Sat, 23 Dec 2023 11:53:25 +0100
Subject: [PATCH] cp: manages the 'seen' file list before copying

Should help with tests/mv/childproof.sh
---
 src/uu/cp/src/cp.rs      | 46 ++++++++++++++++++++++++++++++----------
 tests/by-util/test_cp.rs | 19 +++++++++++++++++
 2 files changed, 54 insertions(+), 11 deletions(-)

diff --git a/src/uu/cp/src/cp.rs b/src/uu/cp/src/cp.rs
index de01a5ef3..d7aeea1b9 100644
--- a/src/uu/cp/src/cp.rs
+++ b/src/uu/cp/src/cp.rs
@@ -1171,6 +1171,9 @@ pub fn copy(sources: &[PathBuf], target: &Path, options: &Options) -> CopyResult
     //
     // key is the source file's information and the value is the destination filepath.
     let mut copied_files: HashMap<FileInformation, PathBuf> = HashMap::with_capacity(sources.len());
+    // remember the copied destinations for further usage.
+    // we can't use copied_files as it is because the key is the source file's information.
+    let mut copied_destinations: HashSet<PathBuf> = HashSet::with_capacity(sources.len());
 
     let progress_bar = if options.progress_bar {
         let pb = ProgressBar::new(disk_usage(sources, options.recursive)?)
@@ -1191,17 +1194,38 @@ pub fn copy(sources: &[PathBuf], target: &Path, options: &Options) -> CopyResult
         if seen_sources.contains(source) {
             // FIXME: compare sources by the actual file they point to, not their path. (e.g. dir/file == dir/../dir/file in most cases)
             show_warning!("source {} specified more than once", source.quote());
-        } else if let Err(error) = copy_source(
-            &progress_bar,
-            source,
-            target,
-            target_type,
-            options,
-            &mut symlinked_files,
-            &mut copied_files,
-        ) {
-            show_error_if_needed(&error);
-            non_fatal_errors = true;
+        } else {
+            // We need to compute the destination path
+
+            let dest = construct_dest_path(source, target, target_type, options)
+                .unwrap_or_else(|_| target.to_path_buf());
+
+            if fs::metadata(&dest).is_ok() && !fs::symlink_metadata(&dest)?.file_type().is_symlink()
+            {
+                // There is already a file and it isn't a symlink (managed in a different place)
+                if copied_destinations.contains(&dest) {
+                    // If the target file was already created in this cp call, do not overwrite
+                    return Err(Error::Error(format!(
+                        "will not overwrite just-created '{}' with '{}'",
+                        dest.display(),
+                        source.display()
+                    )));
+                }
+            }
+
+            if let Err(error) = copy_source(
+                &progress_bar,
+                source,
+                target,
+                target_type,
+                options,
+                &mut symlinked_files,
+                &mut copied_files,
+            ) {
+                show_error_if_needed(&error);
+                non_fatal_errors = true;
+            }
+            copied_destinations.insert(dest.clone());
         }
         seen_sources.insert(source);
     }
diff --git a/tests/by-util/test_cp.rs b/tests/by-util/test_cp.rs
index 37bec5222..5227f0194 100644
--- a/tests/by-util/test_cp.rs
+++ b/tests/by-util/test_cp.rs
@@ -3559,3 +3559,22 @@ fn test_cp_attributes_only() {
     assert_eq!(mode_a, at.metadata(a).mode());
     assert_eq!(mode_b, at.metadata(b).mode());
 }
+
+#[test]
+fn test_cp_seen_file() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.mkdir("a");
+    at.mkdir("b");
+    at.mkdir("c");
+    at.write("a/f", "a");
+    at.write("b/f", "b");
+
+    ucmd.arg("a/f")
+        .arg("b/f")
+        .arg("c")
+        .fails()
+        .stderr_contains("will not overwrite just-created 'c/f' with 'b/f'");
+
+    assert!(at.plus("c").join("f").exists());
+}