Allow $env to be mutated by =

crates/nu-engine/src/eval.rs

@@ -491,30 +491,39 @@ pub fn eval_expression(
  }
  Expr::FullCellPath(cell_path) => match &cell_path.head.expr {
  Expr::Var(var_id) | Expr::VarDecl(var_id) => {
- if var_id == &ENV_VARIABLE_ID {
- // let mut lhs =
- // eval_expression(engine_state, stack, &cell_path.head)?;
- //lhs.update_data_at_cell_path(&cell_path.tail, rhs)?;
- match &cell_path.tail[0] {
- PathMember::String { val, .. } => {
- stack.add_env_var(val.to_string(), rhs);
+ // The $env variable is considered "mutable" in Nushell.
+ // As such, give it special treatment here.
+ let is_env = var_id == &ENV_VARIABLE_ID;
+ if is_env || engine_state.get_var(*var_id).mutable {
+ let mut lhs =
+ eval_expression(engine_state, stack, &cell_path.head)?;
+
+ if is_env {
+ // Unlike "real" mutable vars, though, $env can be upserted by =
+ // instead of just updated. This allows external env-vars like $env.PYTHON_IO_ENCODING
+ // to be added using this syntax.
+ lhs.upsert_data_at_cell_path(&cell_path.tail, rhs)?;
+ // The special $env treatment: for something like $env.config.history.max_size = 2000,
+ // get $env.config AFTER the above mutation, and set it as the "config" environment variable.
+ let vardata = lhs.follow_cell_path(
+ &[cell_path.tail[0].clone()],
+ false,
+ )?;
+ match &cell_path.tail[0] {
+ PathMember::String { val, .. } => {
+ stack.add_env_var(val.to_string(), vardata);
+ }
+ PathMember::Int { val, .. } => {
+ stack.add_env_var(val.to_string(), vardata);
+ }
  }
- PathMember::Int { val, .. } => {
- stack.add_env_var(val.to_string(), rhs);
- }
- }
- Ok(Value::nothing(cell_path.head.span))
- } else {
- let var_info = engine_state.get_var(*var_id);
- if var_info.mutable {
- let mut lhs =
- eval_expression(engine_state, stack, &cell_path.head)?;
+ } else {
  lhs.update_data_at_cell_path(&cell_path.tail, rhs)?;
  stack.vars.insert(*var_id, lhs);
- Ok(Value::nothing(cell_path.head.span))
- } else {
- Err(ShellError::AssignmentRequiresMutableVar(lhs.span))
  }
+ Ok(Value::nothing(cell_path.head.span))
+ } else {
+ Err(ShellError::AssignmentRequiresMutableVar(lhs.span))
  }
  }
  _ => Err(ShellError::AssignmentRequiresVar(lhs.span)),