Merge pull request #3647 from philgebhardt/backup-protect-source

cp: make `--b=simple` protective of source

src/uu/cp/src/cp.rs

@@ -1256,7 +1256,16 @@ fn handle_existing_dest(source: &Path, dest: &Path, options: &Options) -> CopyRe
 
     let backup_path = backup_control::get_backup_path(options.backup, dest, &options.backup_suffix);
     if let Some(backup_path) = backup_path {
-        backup_dest(dest, &backup_path)?;
+        if paths_refer_to_same_file(source, &backup_path)? {
+            return Err(format!(
+                "backing up {} might destroy source;  {} not copied",
+                dest.quote(),
+                source.quote()
+            )
+            .into());
+        } else {
+            backup_dest(dest, &backup_path)?;
+        }
     }
 
     match options.overwrite {

tests/by-util/test_cp.rs

@@ -558,6 +558,24 @@ fn test_cp_backup_simple() {
     );
 }
 
+#[test]
+fn test_cp_backup_simple_protect_source() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    let source = format!("{}~", TEST_HELLO_WORLD_SOURCE);
+    at.touch(&source);
+    ucmd.arg("--backup=simple")
+        .arg(&source)
+        .arg(TEST_HELLO_WORLD_SOURCE)
+        .fails()
+        .stderr_only(format!(
+            "cp: backing up '{}' might destroy source;  '{}' not copied",
+            TEST_HELLO_WORLD_SOURCE, source,
+        ));
+
+    assert_eq!(at.read(TEST_HELLO_WORLD_SOURCE), "Hello, World!\n");
+    assert_eq!(at.read(&source), "");
+}
+
 #[test]
 fn test_cp_backup_never() {
     let (at, mut ucmd) = at_and_ucmd!();