cp: context_for() should quote long paths

Change the behavior of the `context_for()` helper function so that it
adds quotes around long paths but not short paths.

src/uu/cp/src/cp.rs

@@ -1344,8 +1344,34 @@ fn symlink_file(
     Ok(())
 }
 
+/// Join the source and destination paths with an arrow in between.
+///
+/// If the paths are sufficiently long, then they will be surrounded
+/// by quotes.
+///
+/// # Examples
+///
+/// Short paths:
+///
+/// ```rust,ignore
+/// let src = Path::new("/a/b");
+/// let dest = Path::new("/c/d");
+/// assert_eq!(context_for(src, dest), "/a/b -> /c/d".to_string());
+/// ```
+///
+/// Long paths:
+///
+/// ```rust,ignore
+/// let src = Path::new("/a/b/c");
+/// let dest = Path::new("/d/e/f");
+/// assert_eq!(context_for(src, dest), "'/a/b/c' -> '/d/e/f'".to_string());
+/// ```
 fn context_for(src: &Path, dest: &Path) -> String {
-    format!("{} -> {}", src.quote(), dest.quote())
+    if src.components().count() < 3 {
+        format!("{} -> {}", src.display(), dest.display())
+    } else {
+        format!("{} -> {}", src.quote(), dest.quote())
+    }
 }
 
 /// Implements a simple backup copy for the destination file.

tests/by-util/test_cp.rs

@@ -1410,12 +1410,16 @@ fn test_cp_reflink_insufficient_permission() {
         .set_permissions(PermissionsExt::from_mode(0o000))
         .unwrap();
 
+    // FIXME On GNU cp v8.30, the error message is:
+    //
+    //     cp: cannot open 'unreadable' for reading: Permission denied
+    //
     ucmd.arg("-r")
         .arg("--reflink=auto")
         .arg("unreadable")
         .arg(TEST_EXISTING_FILE)
         .fails()
-        .stderr_only("cp: 'unreadable' -> 'existing_file.txt': Permission denied (os error 13)");
+        .stderr_only("cp: unreadable -> existing_file.txt: Permission denied (os error 13)");
 }
 
 #[cfg(any(target_os = "linux", target_os = "android"))]