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use std::sync::Arc;
use super::{Scope, Scopes, Value};
use crate::syntax::ast::{ClosureParam, Expr, Ident, Imports, TypedNode};
use crate::syntax::RedRef;
/// A visitor that captures variable slots.
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::new(None),
captures: Scope::new(),
}
}
/// Return the scope of captured variables.
pub fn finish(self) -> Scope {
self.captures
}
/// Bind a new internal variable.
pub fn bind(&mut self, ident: Ident) {
self.internal.def_mut(ident.take(), Value::None);
}
/// Capture a variable if it isn't internal.
pub fn capture(&mut self, ident: Ident) {
if self.internal.get(&ident).is_none() {
if let Some(slot) = self.external.get(&ident) {
self.captures.def_slot(ident.take(), Arc::clone(slot));
}
}
}
/// Visit any node and collect all captured variables.
pub fn visit(&mut self, node: RedRef) {
match node.cast() {
// Every identifier is a potential variable that we need to capture.
// Identifiers that shouldn't count as captures because they
// actually bind a new name are handled further below (individually
// through the expressions that contain them).
Some(Expr::Ident(ident)) => self.capture(ident),
// A closure contains parameter bindings, which are bound before the
// body is evaluated. Take must be taken so that the default values
// of named parameters cannot access previous parameter bindings.
Some(Expr::Closure(expr)) => {
for param in expr.params() {
if let ClosureParam::Named(named) = param {
self.visit(named.expr().as_red());
}
}
for param in expr.params() {
match param {
ClosureParam::Pos(ident) => self.bind(ident),
ClosureParam::Named(named) => self.bind(named.name()),
ClosureParam::Sink(ident) => self.bind(ident),
}
}
self.visit(expr.body().as_red());
}
// A let expression contains a binding, but that binding is only
// active after the body is evaluated.
Some(Expr::Let(expr)) => {
if let Some(init) = expr.init() {
self.visit(init.as_red());
}
self.bind(expr.binding());
}
// A for loop contains one or two bindings in its pattern. These are
// active after the iterable is evaluated but before the body is
// evaluated.
Some(Expr::For(expr)) => {
self.visit(expr.iter().as_red());
let pattern = expr.pattern();
if let Some(key) = pattern.key() {
self.bind(key);
}
self.bind(pattern.value());
self.visit(expr.body().as_red());
}
// An import contains items, but these are active only after the
// path is evaluated.
Some(Expr::Import(expr)) => {
self.visit(expr.path().as_red());
if let Imports::Items(items) = expr.imports() {
for item in items {
self.bind(item);
}
}
}
// Blocks and templates create a scope.
Some(Expr::Block(_) | Expr::Template(_)) => {
self.internal.enter();
for child in node.children() {
self.visit(child);
}
self.internal.exit();
}
// Everything else is traversed from left to right.
_ => {
for child in node.children() {
self.visit(child);
}
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::parse::parse;
use crate::source::SourceId;
use crate::syntax::RedNode;
#[track_caller]
fn test(src: &str, result: &[&str]) {
let green = parse(src);
let red = RedNode::from_root(green, SourceId::from_raw(0));
let mut scopes = Scopes::new(None);
scopes.def_const("x", 0);
scopes.def_const("y", 0);
scopes.def_const("z", 0);
let mut visitor = CapturesVisitor::new(&scopes);
visitor.visit(red.as_ref());
let captures = visitor.finish();
let mut names: Vec<_> = captures.iter().map(|(k, _)| k).collect();
names.sort();
assert_eq!(names, result);
}
#[test]
fn test_captures() {
// Let binding and function definition.
test("#let x = x", &["x"]);
test("#let x; {x + y}", &["y"]);
test("#let f(x, y) = x + y", &[]);
// Closure with different kinds of params.
test("{(x, y) => x + z}", &["z"]);
test("{(x: y, z) => x + z}", &["y"]);
test("{(..x) => x + y}", &["y"]);
test("{(x, y: x + z) => x + y}", &["x", "z"]);
// For loop.
test("#for x in y { x + z }", &["y", "z"]);
test("#for x, y in y { x + y }", &["y"]);
// Import.
test("#import x, y from z", &["z"]);
test("#import x, y, z from x + y", &["x", "y"]);
// Scoping.
test("{ let x = 1; { let y = 2; y }; x + y }", &["y"]);
test("[#let x = 1]#x", &["x"]);
}
}
|
