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use std::rc::Rc;
use super::*;
use crate::syntax::visit::*;
/// A visitor that captures variable slots.
#[derive(Debug)]
pub struct CapturesVisitor<'a> {
external: &'a Scopes<'a>,
internal: Scopes<'a>,
captures: Scope,
}
impl<'a> CapturesVisitor<'a> {
/// Create a new visitor for the given external scopes.
pub fn new(external: &'a Scopes) -> Self {
Self {
external,
internal: Scopes::default(),
captures: Scope::new(),
}
}
/// Return the scope of capture variables.
pub fn finish(self) -> Scope {
self.captures
}
/// Define an internal variable.
fn define(&mut self, ident: &Ident) {
self.internal.def_mut(ident.as_str(), Value::None);
}
}
impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
fn visit_expr(&mut self, item: &'ast Expr) {
match item {
Expr::Ident(ident) => {
// Find out whether the identifier is not locally defined, but
// captured, and if so, replace it with its value.
if self.internal.get(ident).is_none() {
if let Some(slot) = self.external.get(ident) {
self.captures.def_slot(ident.as_str(), Rc::clone(slot));
}
}
}
expr => visit_expr(self, expr),
}
}
fn visit_block(&mut self, item: &'ast ExprBlock) {
// Blocks create a scope except if directly in a template.
if item.scopes {
self.internal.push();
}
visit_block(self, item);
if item.scopes {
self.internal.pop();
}
}
fn visit_template(&mut self, item: &'ast ExprTemplate) {
// Templates always create a scope.
self.internal.push();
visit_template(self, item);
self.internal.pop();
}
fn visit_let(&mut self, item: &'ast ExprLet) {
self.define(&item.pat.v);
visit_let(self, item);
}
fn visit_for(&mut self, item: &'ast ExprFor) {
match &item.pat.v {
ForPattern::Value(value) => self.define(value),
ForPattern::KeyValue(key, value) => {
self.define(key);
self.define(value);
}
}
visit_for(self, item);
}
}
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