Make optional cell paths work with reject (#8697)

This PR makes `?` work with `reject`. For example:

```bash
> {} | reject foo
Error: nu:🐚:column_not_found

  × Cannot find column
   ╭─[entry #2:1:1]
 1 │ {} | reject foo
   ·      ───┬── ─┬─
   ·         │    ╰── cannot find column 'foo'
   ·         ╰── value originates here
   ╰────

> {} | reject foo?
╭──────────────╮
│ empty record │
╰──────────────╯
```

This was prompted by [a user
question](https://discord.com/channels/601130461678272522/614593951969574961/1091466428546306078).
I would like to get this in for 0.78, I think it's low-risk and I want
the `?` feature to be as polished as possible for its debut.

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

@@ -147,3 +147,24 @@ fn reject_large_vec_with_two_identical_elements() {
     assert!(actual.out.contains("100"));
     assert!(actual.out.contains('2'));
 }
+
+#[test]
+fn reject_optional_column() {
+    let actual = nu!("{} | reject foo? | to nuon");
+    assert_eq!(actual.out, "{}");
+
+    let actual = nu!("[{}] | reject foo? | to nuon");
+    assert_eq!(actual.out, "[{}]");
+
+    let actual = nu!("[{} {foo: 2}] | reject foo? | to nuon");
+    assert_eq!(actual.out, "[{}, {}]");
+
+    let actual = nu!("[{foo: 1} {foo: 2}] | reject foo? | to nuon");
+    assert_eq!(actual.out, "[{}, {}]");
+}
+
+#[test]
+fn reject_optional_row() {
+    let actual = nu!("[{foo: 'bar'}] | reject 3? | to nuon");
+    assert_eq!(actual.out, "[[foo]; [bar]]");
+}

crates/nu-protocol/src/value/mod.rs

@@ -1208,7 +1208,7 @@ impl Value {
                     PathMember::String {
                         val: col_name,
                         span,
-                        ..
+                        optional,
                     } => match self {
                         Value::List { vals, .. } => {
                             for val in vals.iter_mut() {
@@ -1230,7 +1230,7 @@ impl Value {
                                                 true
                                             }
                                         });
-                                        if !found {
+                                        if !found && !optional {
                                             return Err(ShellError::CantFindColumn {
                                                 col_name: col_name.to_string(),
                                                 span: *span,
@@ -1262,7 +1262,7 @@ impl Value {
                                     found = true;
                                 }
                             }
-                            if !found {
+                            if !found && !optional {
                                 return Err(ShellError::CantFindColumn {
                                     col_name: col_name.to_string(),
                                     span: *span,
@@ -1278,12 +1278,16 @@ impl Value {
                         }),
                     },
                     PathMember::Int {
-                        val: row_num, span, ..
+                        val: row_num,
+                        span,
+                        optional,
                     } => match self {
                         Value::List { vals, .. } => {
                             if vals.get_mut(*row_num).is_some() {
                                 vals.remove(*row_num);
                                 Ok(())
+                            } else if *optional {
+                                Ok(())
                             } else if vals.is_empty() {
                                 Err(ShellError::AccessEmptyContent { span: *span })
                             } else {
@@ -1306,7 +1310,7 @@ impl Value {
                     PathMember::String {
                         val: col_name,
                         span,
-                        ..
+                        optional,
                     } => match self {
                         Value::List { vals, .. } => {
                             for val in vals.iter_mut() {
@@ -1323,7 +1327,7 @@ impl Value {
                                                 col.1.remove_data_at_cell_path(&cell_path[1..])?
                                             }
                                         }
-                                        if !found {
+                                        if !found && !optional {
                                             return Err(ShellError::CantFindColumn {
                                                 col_name: col_name.to_string(),
                                                 span: *span,
@@ -1356,7 +1360,7 @@ impl Value {
                                     col.1.remove_data_at_cell_path(&cell_path[1..])?
                                 }
                             }
-                            if !found {
+                            if !found && !optional {
                                 return Err(ShellError::CantFindColumn {
                                     col_name: col_name.to_string(),
                                     span: *span,
@@ -1372,11 +1376,15 @@ impl Value {
                         }),
                     },
                     PathMember::Int {
-                        val: row_num, span, ..
+                        val: row_num,
+                        span,
+                        optional,
                     } => match self {
                         Value::List { vals, .. } => {
                             if let Some(v) = vals.get_mut(*row_num) {
                                 v.remove_data_at_cell_path(&cell_path[1..])
+                            } else if *optional {
+                                Ok(())
                             } else if vals.is_empty() {
                                 Err(ShellError::AccessEmptyContent { span: *span })
                             } else {