Boa 0.10.0

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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//! Exponentiation operator parsing.
//!
//! More information:
//!  - [MDN documentation][mdn]
//!  - [ECMAScript specification][spec]
//!
//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Exponentiation
//! [spec]: https://tc39.es/ecma262/#sec-exp-operator

use super::ParseError;
use crate::syntax::lexer::TokenKind;
use crate::{
    syntax::{
        ast::{
            node::{BinOp, Node},
            op::NumOp,
            Keyword, Punctuator,
        },
        parser::{
            expression::{unary::UnaryExpression, update::UpdateExpression},
            AllowAwait, AllowYield, Cursor, ParseResult, TokenParser,
        },
    },
    BoaProfiler,
};

use std::io::Read;

/// Parses an exponentiation expression.
///
/// More information:
///  - [MDN documentation][mdn]
///  - [ECMAScript specification][spec]
///
/// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Exponentiation
/// [spec]: https://tc39.es/ecma262/#prod-ExponentiationExpression
#[derive(Debug, Clone, Copy)]
pub(in crate::syntax::parser::expression) struct ExponentiationExpression {
    allow_yield: AllowYield,
    allow_await: AllowAwait,
}

impl ExponentiationExpression {
    /// Creates a new `ExponentiationExpression` parser.
    pub(in crate::syntax::parser::expression) fn new<Y, A>(allow_yield: Y, allow_await: A) -> Self
    where
        Y: Into<AllowYield>,
        A: Into<AllowAwait>,
    {
        Self {
            allow_yield: allow_yield.into(),
            allow_await: allow_await.into(),
        }
    }
}

/// Checks by looking at the next token to see whether it's a unary operator or not.
fn is_unary_expression<R>(cursor: &mut Cursor<R>) -> Result<bool, ParseError>
where
    R: Read,
{
    Ok(if let Some(tok) = cursor.peek(0)? {
        matches!(
            tok.kind(),
            TokenKind::Keyword(Keyword::Delete)
                | TokenKind::Keyword(Keyword::Void)
                | TokenKind::Keyword(Keyword::TypeOf)
                | TokenKind::Punctuator(Punctuator::Add)
                | TokenKind::Punctuator(Punctuator::Sub)
                | TokenKind::Punctuator(Punctuator::Not)
                | TokenKind::Punctuator(Punctuator::Neg)
        )
    } else {
        false
    })
}

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

    fn parse(self, cursor: &mut Cursor<R>) -> ParseResult {
        let _timer = BoaProfiler::global().start_event("ExponentiationExpression", "Parsing");

        if is_unary_expression(cursor)? {
            return UnaryExpression::new(self.allow_yield, self.allow_await).parse(cursor);
        }

        let lhs = UpdateExpression::new(self.allow_yield, self.allow_await).parse(cursor)?;
        if let Some(tok) = cursor.peek(0)? {
            if let TokenKind::Punctuator(Punctuator::Exp) = tok.kind() {
                cursor.next()?.expect("** token vanished"); // Consume the token.
                return Ok(BinOp::new(NumOp::Exp, lhs, self.parse(cursor)?).into());
            }
        }
        Ok(lhs)
    }
}