Spread operator in record literals (nushell#11144)

Goes towards implementing nushell#10598, which asks for a spread operator in
lists, in records, and when calling commands (continuation of nushell#11006,
which only implements it in lists)

# Description
This PR is for adding a spread operator that can be used when building
records. Additional functionality can be added later.

Changes:

- Previously, the `Expr::Record` variant held `(Expression, Expression)`
pairs. It now holds instances of an enum `RecordItem` (the name isn't
amazing) that allows either a key-value mapping or a spread operator.
- `...` will be treated as the spread operator when it appears before
`$`, `{`, or `(` inside records (no whitespace allowed in between) (not
implemented yet)
- The error message for duplicate columns now includes the column name
itself, because if two spread records are involved in such an error, you
can't tell which field was duplicated from the spans alone

`...` will still be treated as a normal string outside records, and even
in records, it is not treated as a spread operator when not followed
immediately by a `$`, `{`, or `(`.

# User-Facing Changes
Users will be able to use `...` when building records.

```
> let rec = { x: 1, ...{ a: 2 } }
> $rec
╭───┬───╮
│ x │ 1 │
│ a │ 2 │
╰───┴───╯
> { foo: bar, ...$rec, baz: blah }
╭─────┬──────╮
│ foo │ bar  │
│ x   │ 1    │
│ a   │ 2    │
│ baz │ blah │
╰─────┴──────╯
```
If you want to update a field of a record, you'll have to use `merge`
instead:
```
> { ...$rec, x: 5 }
Error: nu::shell::column_defined_twice

  × Record field or table column used twice: x
   ╭─[entry nushell#2:1:1]
 1 │  { ...$rec, x: 5 }
   ·       ──┬─  ┬
   ·         │   ╰── field redefined here
   ·         ╰── field first defined here
   ╰────
> $rec | merge { x: 5 }
╭───┬───╮
│ x │ 5 │
│ a │ 2 │
╰───┴───╯
```

# Tests + Formatting

# After Submitting

crates/nu-cli/src/syntax_highlight.rs

@@ -2,7 +2,7 @@ use log::trace;
 use nu_ansi_term::Style;
 use nu_color_config::{get_matching_brackets_style, get_shape_color};
 use nu_parser::{flatten_block, parse, FlatShape};
-use nu_protocol::ast::{Argument, Block, Expr, Expression, PipelineElement};
+use nu_protocol::ast::{Argument, Block, Expr, Expression, PipelineElement, RecordItem};
 use nu_protocol::engine::{EngineState, StateWorkingSet};
 use nu_protocol::{Config, Span};
 use reedline::{Highlighter, StyledText};
@@ -365,9 +365,16 @@ fn find_matching_block_end_in_expr(
                     Some(expr_last)
                 } else {
                     // cursor is inside record
-                    for (k, v) in exprs {
-                        find_in_expr_or_continue!(k);
-                        find_in_expr_or_continue!(v);
+                    for expr in exprs {
+                        match expr {
+                            RecordItem::Pair(k, v) => {
+                                find_in_expr_or_continue!(k);
+                                find_in_expr_or_continue!(v);
+                            }
+                            RecordItem::Spread(_, record) => {
+                                find_in_expr_or_continue!(record);
+                            }
+                        }
                     }
                     None
                 }

crates/nu-command/src/formats/from/nuon.rs

@@ -1,4 +1,4 @@
-use nu_protocol::ast::{Call, Expr, Expression, PipelineElement};
+use nu_protocol::ast::{Call, Expr, Expression, PipelineElement, RecordItem};
 use nu_protocol::engine::{Command, EngineState, Stack, StateWorkingSet};
 use nu_protocol::{
     record, Category, Example, IntoPipelineData, PipelineData, Range, Record, ShellError,
@@ -316,22 +316,34 @@ fn convert_to_value(
         Expr::Record(key_vals) => {
             let mut record = Record::new();
 
-            for (key, val) in key_vals {
-                let key_str = match key.expr {
-                    Expr::String(key_str) => key_str,
-                    _ => {
+            for key_val in key_vals {
+                match key_val {
+                    RecordItem::Pair(key, val) => {
+                        let key_str = match key.expr {
+                            Expr::String(key_str) => key_str,
+                            _ => {
+                                return Err(ShellError::OutsideSpannedLabeledError(
+                                    original_text.to_string(),
+                                    "Error when loading".into(),
+                                    "only strings can be keys".into(),
+                                    key.span,
+                                ))
+                            }
+                        };
+
+                        let value = convert_to_value(val, span, original_text)?;
+
+                        record.push(key_str, value);
+                    }
+                    RecordItem::Spread(_, inner) => {
                         return Err(ShellError::OutsideSpannedLabeledError(
                             original_text.to_string(),
                             "Error when loading".into(),
-                            "only strings can be keys".into(),
-                            key.span,
-                        ))
+                            "spread operator not supported in nuon".into(),
+                            inner.span,
+                        ));
                     }
-                };
-
-                let value = convert_to_value(val, span, original_text)?;
-
-                record.push(key_str, value);
+                }
             }
 
             Ok(Value::record(record, span))
@@ -387,6 +399,7 @@ fn convert_to_value(
 
                 if let Some(idx) = cols.iter().position(|existing| existing == key_str) {
                     return Err(ShellError::ColumnDefinedTwice {
+                        col_name: key_str.clone(),
                         second_use: key.span,
                         first_use: headers[idx].span,
                     });

crates/nu-engine/src/documentation.rs

@@ -1,4 +1,4 @@
-use nu_protocol::ast::{Argument, Expr, Expression};
+use nu_protocol::ast::{Argument, Expr, Expression, RecordItem};
 use nu_protocol::{
     ast::Call,
     engine::{EngineState, Stack},
@@ -378,10 +378,10 @@ fn get_argument_for_color_value(
 ) -> Option<Argument> {
     match color {
         Value::Record { val, .. } => {
-            let record_exp: Vec<(Expression, Expression)> = val
+            let record_exp: Vec<RecordItem> = val
                 .into_iter()
                 .map(|(k, v)| {
-                    (
+                    RecordItem::Pair(
                         Expression {
                             expr: Expr::String(k.clone()),
                             span,

crates/nu-engine/src/eval.rs

@@ -3,7 +3,7 @@ use nu_path::expand_path_with;
 use nu_protocol::{
     ast::{
         eval_operator, Argument, Assignment, Bits, Block, Boolean, Call, Comparison, Expr,
-        Expression, Math, Operator, PathMember, PipelineElement, Redirection,
+        Expression, Math, Operator, PathMember, PipelineElement, RecordItem, Redirection,
     },
     engine::{Closure, EngineState, Stack},
     DeclId, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, Range, Record,
@@ -549,22 +549,45 @@ pub fn eval_expression(
             }
             Ok(Value::list(output, expr.span))
         }
-        Expr::Record(fields) => {
+        Expr::Record(items) => {
             let mut record = Record::new();
 
-            for (col, val) in fields {
-                // avoid duplicate cols.
-                let col_name = eval_expression(engine_state, stack, col)?.as_string()?;
-                let pos = record.index_of(&col_name);
-                match pos {
-                    Some(index) => {
-                        return Err(ShellError::ColumnDefinedTwice {
-                            second_use: col.span,
-                            first_use: fields[index].0.span,
-                        })
+            let mut col_names = HashMap::new();
+
+            for item in items {
+                match item {
+                    RecordItem::Pair(col, val) => {
+                        // avoid duplicate cols
+                        let col_name = eval_expression(engine_state, stack, col)?.as_string()?;
+                        if let Some(orig_span) = col_names.get(&col_name) {
+                            return Err(ShellError::ColumnDefinedTwice {
+                                col_name,
+                                second_use: col.span,
+                                first_use: *orig_span,
+                            });
+                        } else {
+                            col_names.insert(col_name.clone(), col.span);
+                            record.push(col_name, eval_expression(engine_state, stack, val)?);
+                        }
                     }
-                    None => {
-                        record.push(col_name, eval_expression(engine_state, stack, val)?);
+                    RecordItem::Spread(_, inner) => {
+                        match eval_expression(engine_state, stack, inner)? {
+                            Value::Record { val: inner_val, .. } => {
+                                for (col_name, val) in inner_val {
+                                    if let Some(orig_span) = col_names.get(&col_name) {
+                                        return Err(ShellError::ColumnDefinedTwice {
+                                            col_name,
+                                            second_use: inner.span,
+                                            first_use: *orig_span,
+                                        });
+                                    } else {
+                                        col_names.insert(col_name.clone(), inner.span);
+                                        record.push(col_name, val);
+                                    }
+                                }
+                            }
+                            _ => return Err(ShellError::CannotSpreadAsRecord { span: inner.span }),
+                        }
                     }
                 }
             }
@@ -580,6 +603,7 @@ pub fn eval_expression(
                     .position(|existing| existing == &header)
                 {
                     return Err(ShellError::ColumnDefinedTwice {
+                        col_name: header,
                         second_use: expr.span,
                         first_use: headers[idx].span,
                     });

crates/nu-parser/src/flatten.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::{
     Block, Expr, Expression, ImportPatternMember, MatchPattern, PathMember, Pattern, Pipeline,
-    PipelineElement,
+    PipelineElement, RecordItem,
 };
 use nu_protocol::{engine::StateWorkingSet, Span};
 use nu_protocol::{DeclId, VarId};
@@ -410,29 +410,47 @@ pub fn flatten_expression(
 
             let mut output = vec![];
             for l in list {
-                let flattened_lhs = flatten_expression(working_set, &l.0);
-                let flattened_rhs = flatten_expression(working_set, &l.1);
+                match l {
+                    RecordItem::Pair(key, val) => {
+                        let flattened_lhs = flatten_expression(working_set, key);
+                        let flattened_rhs = flatten_expression(working_set, val);
+
+                        if let Some(first) = flattened_lhs.first() {
+                            if first.0.start > last_end {
+                                output
+                                    .push((Span::new(last_end, first.0.start), FlatShape::Record));
+                            }
+                        }
+                        if let Some(last) = flattened_lhs.last() {
+                            last_end = last.0.end;
+                        }
+                        output.extend(flattened_lhs);
 
-                if let Some(first) = flattened_lhs.first() {
-                    if first.0.start > last_end {
-                        output.push((Span::new(last_end, first.0.start), FlatShape::Record));
+                        if let Some(first) = flattened_rhs.first() {
+                            if first.0.start > last_end {
+                                output
+                                    .push((Span::new(last_end, first.0.start), FlatShape::Record));
+                            }
+                        }
+                        if let Some(last) = flattened_rhs.last() {
+                            last_end = last.0.end;
+                        }
+
+                        output.extend(flattened_rhs);
                     }
-                }
-                if let Some(last) = flattened_lhs.last() {
-                    last_end = last.0.end;
-                }
-                output.extend(flattened_lhs);
+                    RecordItem::Spread(op_span, record) => {
+                        if op_span.start > last_end {
+                            output.push((Span::new(last_end, op_span.start), FlatShape::Record));
+                        }
+                        output.push((*op_span, FlatShape::Operator));
 
-                if let Some(first) = flattened_rhs.first() {
-                    if first.0.start > last_end {
-                        output.push((Span::new(last_end, first.0.start), FlatShape::Record));
+                        let flattened_inner = flatten_expression(working_set, record);
+                        if let Some(last) = flattened_inner.last() {
+                            last_end = last.0.end;
+                        }
+                        output.extend(flattened_inner);
                     }
                 }
-                if let Some(last) = flattened_rhs.last() {
-                    last_end = last.0.end;
-                }
-
-                output.extend(flattened_rhs);
             }
             if last_end < outer_span.end {
                 output.push((Span::new(last_end, outer_span.end), FlatShape::Record));