Spread operator for list literals (#11006)

crates/nu-protocol/src/ast/expr.rs

@@ -45,6 +45,7 @@ pub enum Expr {
     Signature(Box<Signature>),
     StringInterpolation(Vec<Expression>),
     MatchPattern(Box<MatchPattern>),
+    Spread(Box<Expression>),
     Nothing,
     Garbage,
 }

crates/nu-protocol/src/ast/expression.rs

@@ -289,6 +289,7 @@ impl Expression {
             Expr::ValueWithUnit(expr, _) => expr.has_in_variable(working_set),
             Expr::Var(var_id) => *var_id == IN_VARIABLE_ID,
             Expr::VarDecl(_) => false,
+            Expr::Spread(expr) => expr.has_in_variable(working_set),
         }
     }
 
@@ -480,6 +481,7 @@ impl Expression {
                 }
             }
             Expr::VarDecl(_) => {}
+            Expr::Spread(expr) => expr.replace_in_variable(working_set, new_var_id),
         }
     }
 
@@ -618,6 +620,7 @@ impl Expression {
             Expr::ValueWithUnit(expr, _) => expr.replace_span(working_set, replaced, new_span),
             Expr::Var(_) => {}
             Expr::VarDecl(_) => {}
+            Expr::Spread(expr) => expr.replace_span(working_set, replaced, new_span),
         }
     }
 }

crates/nu-protocol/src/eval_const.rs

@@ -278,7 +278,13 @@ pub fn eval_constant(
         Expr::List(x) => {
             let mut output = vec![];
             for expr in x {
-                output.push(eval_constant(working_set, expr)?);
+                match &expr.expr {
+                    Expr::Spread(expr) => match eval_constant(working_set, expr)? {
+                        Value::List { mut vals, .. } => output.append(&mut vals),
+                        _ => return Err(ShellError::CannotSpreadAsList { span: expr.span }),
+                    },
+                    _ => output.push(eval_constant(working_set, expr)?),
+                }
             }
             Ok(Value::list(output, expr.span))
         }

crates/nu-protocol/src/parse_error.rs

@@ -483,6 +483,10 @@ pub enum ParseError {
         #[label("Not allowed here")] Span,
         #[label("...and here")] Option<Span>,
     ),
+
+    #[error("Unexpected spread operator outside list")]
+    #[diagnostic(code(nu::parser::unexpected_spread_operator))]
+    UnexpectedSpread(#[label("Spread operator not allowed here")] Span),
 }
 
 impl ParseError {
@@ -569,6 +573,7 @@ impl ParseError {
             ParseError::InvalidLiteral(_, _, s) => *s,
             ParseError::LabeledErrorWithHelp { span: s, .. } => *s,
             ParseError::RedirectionInLetMut(s, _) => *s,
+            ParseError::UnexpectedSpread(s) => *s,
         }
     }
 }

crates/nu-protocol/src/shell_error.rs

@@ -1170,6 +1170,21 @@ This is an internal Nushell error, please file an issue https://github.com/nushe
     )]
     //todo: add error detail
     ErrorExpandingGlob(String, #[label = "{0}"] Span),
+
+    /// Tried spreading a non-list inside a list.
+    ///
+    /// ## Resolution
+    ///
+    /// Only lists can be spread inside lists. Try converting the value to a list before spreading.
+    #[error("Not a list")]
+    #[diagnostic(
+        code(nu::shell::cannot_spread),
+        help("Only lists can be spread inside lists. Try converting the value to a list before spreading")
+    )]
+    CannotSpreadAsList {
+        #[label = "cannot spread value"]
+        span: Span,
+    },
 }
 
 // TODO: Implement as From trait