boa_engine 0.16.0

Boa is a Javascript lexer, parser and Just-in-Time compiler written in Rust. Currently, it has support for some of the language.
Documentation 
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use crate::syntax::{
    ast::{Keyword, Node, Punctuator},
    lexer::TokenKind,
    parser::{
        cursor::Cursor,
        error::ParseError,
        expression::LabelIdentifier,
        statement::{
            declaration::hoistable::FunctionDeclaration, AllowAwait, AllowReturn, Statement,
        },
        AllowYield, TokenParser,
    },
};
use boa_interner::{Interner, Sym};
use boa_profiler::Profiler;
use std::io::Read;

/// Labelled Statement Parsing
///
/// More information
/// - [MDN documentation][mdn]
/// - [ECMAScript specification][spec]
///
/// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label
/// [spec]: https://tc39.es/ecma262/#sec-labelled-statements
#[derive(Debug, Clone, Copy)]
pub(super) struct LabelledStatement {
    allow_yield: AllowYield,
    allow_await: AllowAwait,
    allow_return: AllowReturn,
}

impl LabelledStatement {
    pub(super) fn new<Y, A, R>(allow_yield: Y, allow_await: A, allow_return: R) -> Self
    where
        Y: Into<AllowYield>,
        A: Into<AllowAwait>,
        R: Into<AllowReturn>,
    {
        Self {
            allow_yield: allow_yield.into(),
            allow_await: allow_await.into(),
            allow_return: allow_return.into(),
        }
    }
}

impl<R> TokenParser<R> for LabelledStatement
where
    R: Read,
{
    type Output = Node;

    fn parse(
        self,
        cursor: &mut Cursor<R>,
        interner: &mut Interner,
    ) -> Result<Self::Output, ParseError> {
        let _timer = Profiler::global().start_event("Label", "Parsing");

        let name =
            LabelIdentifier::new(self.allow_yield, self.allow_await).parse(cursor, interner)?;

        cursor.expect(Punctuator::Colon, "Labelled Statement", interner)?;

        let strict = cursor.strict_mode();
        let next_token = cursor.peek(0, interner)?.ok_or(ParseError::AbruptEnd)?;
        let mut node = match next_token.kind() {
            // Early Error: It is a Syntax Error if any strict mode source code matches this rule.
            // https://tc39.es/ecma262/#sec-labelled-statements-static-semantics-early-errors
            // https://tc39.es/ecma262/#sec-labelled-function-declarations
            TokenKind::Keyword((Keyword::Function, _)) if strict => {
                return Err(ParseError::general(
                    "In strict mode code, functions can only be declared at top level or inside a block.",
                    next_token.span().start()
                ))
            }
            TokenKind::Keyword((Keyword::Function, _)) => {
                FunctionDeclaration::new(self.allow_yield, self.allow_await, false)
                .parse(cursor, interner)?
                .into()
            }
            _ => Statement::new(self.allow_yield, self.allow_await, self.allow_return).parse(cursor, interner)?
        };

        set_label_for_node(&mut node, name);
        Ok(node)
    }
}

fn set_label_for_node(node: &mut Node, name: Sym) {
    match node {
        Node::ForLoop(ref mut for_loop) => for_loop.set_label(name),
        Node::ForOfLoop(ref mut for_of_loop) => for_of_loop.set_label(name),
        Node::ForInLoop(ref mut for_in_loop) => for_in_loop.set_label(name),
        Node::DoWhileLoop(ref mut do_while_loop) => do_while_loop.set_label(name),
        Node::WhileLoop(ref mut while_loop) => while_loop.set_label(name),
        Node::Block(ref mut block) => block.set_label(name),
        _ => (),
    }
}