ps: keep a column for a field that has no value yet

src/uu/ps/src/picker.rs

@@ -50,7 +50,8 @@ pub(crate) fn collect_pickers(
             "time" | "cputime" => pickers.push(helper(time)),
             "ucmd" | "comm" => pickers.push(helper(ucmd)),
             "cmd" | "command" | "args" => pickers.push(helper(cmd)),
-            _ => {}
+            // Not implemented yet: keep the column so later values stay under their headers
+            _ => pickers.push(helper(|_| "-".to_string())),
         }
     }
 

tests/by-util/test_ps.rs

@@ -417,3 +417,23 @@ fn test_combined_selection_criteria() {
     assert!(pids.contains(&1));
     assert!(pids.len() > 1);
 }
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_unimplemented_field_keeps_columns_aligned() {
+    // wchan has no value yet; pid must still be printed in its own column
+    let out = new_ucmd!()
+        .args(&["-p", "1", "--no-headers", "-o", "wchan,pid"])
+        .succeeds()
+        .stdout_move_str();
+    assert_eq!(out.split_whitespace().collect::<Vec<_>>(), ["-", "1"]);
+
+    let out = new_ucmd!()
+        .args(&["-p", "1", "-l"])
+        .succeeds()
+        .stdout_move_str();
+    let mut lines = out.lines();
+    let headers = lines.next().unwrap().split_whitespace().count();
+    let values = lines.next().unwrap().split_whitespace().count();
+    assert_eq!(headers, values);
+}