feat(runtime): Add "default" tables

drake-runtime/src/lib.rs

@@ -103,9 +103,10 @@ impl<L: Clone> Environment<L> {
  &mut self,
  kind: TableHeaderKind,
  pattern: Pattern<L>,
- default: Table<L>,
+ mut default: Table<L>,
  errors: &mut Vec<Error<L>>,
  ) {
+ default.make_default();
  if let Some(mut cur) = core::mem::take(&mut self.current) {
  if cur.is_movable(kind, &pattern) {
  cur.next_array(default, errors);
@@ -260,7 +261,7 @@ fn table_insert<L: Clone>(
  &mut table.local
  };
 
- if table.contains_key(&name) {
+ if table.contains_key(&name) && !table[&name].default {
  errors.push(Error::DuplicateKey {
  existing: table[&name].defined.clone(),
  found: span,
@@ -272,6 +273,7 @@ fn table_insert<L: Clone>(
  value,
  defined: span,
  used: global,
+ default: false,
  },
  );
  }

drake-types/src/runtime.rs

@@ -28,6 +28,8 @@ pub struct Element<L> {
  pub value: Value<L>,
  /// A position where the element is defined
  pub defined: Range<L>,
+ /// A flag marks as the element is overridable.
+ pub default: bool,
  /// A flag checks if the element is used, or not
  pub used: bool,
 }
@@ -55,4 +57,12 @@ impl<L> Table<L> {
  pub fn new() -> Self {
  Self::default()
  }
+
+ /// Marks the table as a default table.
+ pub fn make_default(&mut self) {
+ self.global
+ .values_mut()
+ .for_each(|elem| elem.default = true);
+ self.local.values_mut().for_each(|elem| elem.default = true);
+ }
 }