make sure no duplicate records exists during eval and merge (#5633)

crates/nu-command/src/filters/merge.rs

@@ -59,6 +59,14 @@ impl Command for Merge {
                     vec![Value::test_int(1), Value::test_int(2), Value::test_int(3)],
                 )),
             },
+            Example {
+                example: "{a: 1, b: 3} | merge { {b: 2, c: 4} }",
+                description: "Merge two records with overlap key",
+                result: Some(Value::test_record(
+                    vec!["a", "b", "c"],
+                    vec![Value::test_int(1), Value::test_int(2), Value::test_int(4)],
+                )),
+            },
         ]
     }
 
@@ -106,8 +114,10 @@ impl Command for Merge {
                             (Ok((inp_cols, inp_vals)), Some(to_merge)) => {
                                 match to_merge.as_record() {
                                     Ok((to_merge_cols, to_merge_vals)) => {
-                                        let cols = [inp_cols, to_merge_cols].concat();
-                                        let vals = [inp_vals, to_merge_vals].concat();
+                                        let (cols, vals) = do_merge(
+                                            (inp_cols.to_vec(), inp_vals.to_vec()),
+                                            (to_merge_cols.to_vec(), to_merge_vals.to_vec()),
+                                        );
                                         Value::Record {
                                             cols,
                                             vals,
@@ -146,12 +156,10 @@ impl Command for Merge {
                     ..,
                 ),
             ) => {
-                let mut cols = inp_cols.to_vec();
-                cols.extend(to_merge_cols.to_vec());
-
-                let mut vals = inp_vals.to_vec();
-                vals.extend(to_merge_vals.to_vec());
-
+                let (cols, vals) = do_merge(
+                    (inp_cols.to_vec(), inp_vals.to_vec()),
+                    (to_merge_cols.to_vec(), to_merge_vals.to_vec()),
+                );
                 Ok(Value::Record {
                     cols,
                     vals,
@@ -181,6 +189,29 @@ impl Command for Merge {
     }
 }
 
+fn do_merge(
+    input_record: (Vec<String>, Vec<Value>),
+    to_merge_record: (Vec<String>, Vec<Value>),
+) -> (Vec<String>, Vec<Value>) {
+    let (mut result_cols, mut result_vals) = input_record;
+    let (to_merge_cols, to_merge_vals) = to_merge_record;
+
+    for (col, val) in to_merge_cols.into_iter().zip(to_merge_vals) {
+        let pos = result_cols.iter().position(|c| c == &col);
+        // if find, replace existing data, else, push new data.
+        match pos {
+            Some(index) => {
+                result_vals[index] = val;
+            }
+            None => {
+                result_cols.push(col);
+                result_vals.push(val);
+            }
+        }
+    }
+    (result_cols, result_vals)
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

crates/nu-command/tests/commands/reject.rs

@@ -81,3 +81,29 @@ fn ignores_duplicate_columns_rejected() {
 
     assert_eq!(actual.out, "last name");
 }
+
+#[test]
+fn reject_record_from_raw_eval() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+            r#"
+            {"a": 3, "a": 4} | reject a | describe
+            "#
+        )
+    );
+
+    assert!(actual.out.contains("record<>"));
+}
+
+#[test]
+fn reject_table_from_raw_eval() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+            r#"
+            [{"a": 3, "a": 4}] | reject a
+            "#
+        )
+    );
+
+    assert!(actual.out.contains("record 0 fields"));
+}

crates/nu-engine/src/eval.rs

@@ -472,8 +472,18 @@ pub fn eval_expression(
             let mut cols = vec![];
             let mut vals = vec![];
             for (col, val) in fields {
-                cols.push(eval_expression(engine_state, stack, col)?.as_string()?);
-                vals.push(eval_expression(engine_state, stack, val)?);
+                // avoid duplicate cols.
+                let col_name = eval_expression(engine_state, stack, col)?.as_string()?;
+                let pos = cols.iter().position(|c| c == &col_name);
+                match pos {
+                    Some(index) => {
+                        vals[index] = eval_expression(engine_state, stack, val)?;
+                    }
+                    None => {
+                        cols.push(col_name);
+                        vals.push(eval_expression(engine_state, stack, val)?);
+                    }
+                }
             }
 
             Ok(Value::Record {