swc_ecma_parser 0.6.0

//! Parser for unary operations and binary operations.
use super::{util::ExprExt, *};
use swc_common::Spanned;

#[parser]
impl<'a, I: Input> Parser<'a, I> {
    /// Name from spec: 'LogicalORExpression'
    pub(super) fn parse_bin_expr(&mut self) -> PResult<'a, (Box<Expr>)> {
        let left = self.parse_unary_expr()?;

        return_if_arrow!(left);
        self.parse_bin_op_recursively(left, 0)
    }

    /// Parse binary operators with the operator precedence parsing
    /// algorithm. `left` is the left-hand side of the operator.
    /// `minPrec` provides context that allows the function to stop and
    /// defer further parser to one of its callers when it encounters an
    /// operator that has a lower precedence than the set it is parsing.
    fn parse_bin_op_recursively(
        &mut self,
        left: Box<Expr>,
        min_prec: u8,
    ) -> PResult<'a, (Box<Expr>)> {
        let op = match {
            // Return left on eof
            match cur!(false) {
                Ok(cur) => cur,
                Err(..) => return Ok(left),
            }
        } {
            &Word(Keyword(In)) if self.ctx().include_in_expr => op!("in"),
            &Word(Keyword(InstanceOf)) => op!("instanceof"),
            &BinOp(op) => op.into(),
            _ => {
                return Ok(left);
            }
        };

        if op.precedence() <= min_prec {
            trace!(
                "returning {:?} without parsing {:?} because min_prec={}, prec={}",
                left,
                op,
                min_prec,
                op.precedence()
            );

            return Ok(left);
        }
        bump!();
        trace!(
            "parsing binary op {:?} min_prec={}, prec={}",
            op,
            min_prec,
            op.precedence()
        );

        match *left {
            // This is invalid syntax.
            Expr::Unary { .. } if op == op!("**") => {
                // Correct implementation would be returning Ok(left) and
                // returning "unexpected token '**'" on next.
                // But it's not useful error message.

                syntax_error!(SyntaxError::UnaryInExp {
                    // FIXME: Use display
                    left: format!("{:?}", left),
                    left_span: left.span(),
                })
            }
            _ => {}
        }

        let right = {
            let left_of_right = self.parse_unary_expr()?;
            self.parse_bin_op_recursively(
                left_of_right,
                if op == op!("**") {
                    // exponential operator is right associative
                    op.precedence() - 1
                } else {
                    op.precedence()
                },
            )?
        };

        let node = box Expr::Bin(BinExpr {
            span: span!(left.span().lo()),
            op,
            left,
            right,
        });

        let expr = self.parse_bin_op_recursively(node, min_prec)?;
        Ok(expr)
    }

    /// Parse unary expression and update expression.
    ///
    /// spec: 'UnaryExpression'
    fn parse_unary_expr(&mut self) -> PResult<'a, (Box<Expr>)> {
        let start = cur_pos!();

        // Parse update expression
        if is!("++") || is!("--") {
            let op = if bump!() == PlusPlus {
                op!("++")
            } else {
                op!("--")
            };

            let arg = self.parse_unary_expr()?;
            if !arg.is_valid_simple_assignment_target(self.ctx().strict) {
                // This is early ReferenceError
                syntax_error!(arg.span(), SyntaxError::NotSimpleAssign)
            }
            return Ok(box Expr::Update(UpdateExpr {
                span: span!(start),
                prefix: true,
                op,
                arg,
            }));
        }

        // Parse unary expression
        if is_one_of!("delete", "void", "typeof", '+', '-', '~', '!') {
            let op = match bump!() {
                Word(Keyword(Delete)) => op!("delete"),
                Word(Keyword(Void)) => op!("void"),
                Word(Keyword(TypeOf)) => op!("typeof"),
                BinOp(Add) => op!(unary, "+"),
                BinOp(Sub) => op!(unary, "-"),
                Tilde => op!("~"),
                Bang => op!("!"),
                _ => unreachable!(),
            };
            let arg = self.parse_unary_expr()?;
            return Ok(box Expr::Unary(UnaryExpr {
                span: span!(start),
                op,
                arg,
            }));
        }

        if self.ctx().in_async && is!("await") {
            return self.parse_await_expr();
        }

        // UpdateExpression
        let expr = self.parse_lhs_expr()?;
        return_if_arrow!(expr);

        // Line terminator isn't allowed here.
        if self.input.had_line_break_before_cur() {
            return Ok(expr);
        }

        if is_one_of!("++", "--") {
            if !expr.is_valid_simple_assignment_target(self.ctx().strict) {
                // This is eary ReferenceError
                syntax_error!(expr.span(), SyntaxError::NotSimpleAssign)
            }

            let start = cur_pos!();
            let op = if bump!() == PlusPlus {
                op!("++")
            } else {
                op!("--")
            };

            return Ok(box Expr::Update(UpdateExpr {
                span: span!(start),
                prefix: false,
                op,
                arg: expr,
            }));
        }
        Ok(expr)
    }

    fn parse_await_expr(&mut self) -> PResult<'a, (Box<Expr>)> {
        let start = cur_pos!();

        assert_and_bump!("await");
        assert!(self.ctx().in_async);

        if is!('*') {
            syntax_error!(SyntaxError::AwaitStar);
        }

        let arg = self.parse_unary_expr()?;
        Ok(box Expr::Await(AwaitExpr {
            span: span!(start),
            arg,
        }))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use swc_common::DUMMY_SP;

    fn bin(s: &'static str) -> Box<Expr> {
        test_parser(s, |p| {
            p.parse_bin_expr()
                .unwrap_or_else(|()| panic!("failed to parse '{}' as a binary expression", s))
        })
    }

    #[allow(non_upper_case_globals)]
    const span: Span = DUMMY_SP;

    #[test]
    fn simple() {
        assert_eq_ignore_span!(
            bin("5 + 4 * 7"),
            box Expr::Bin(BinExpr {
                span,
                op: op!(bin, "+"),
                left: bin("5"),
                right: bin("4 * 7"),
            })
        );
    }

    #[test]
    fn same_prec() {
        assert_eq_ignore_span!(
            bin("5 + 4 + 7"),
            box Expr::Bin(BinExpr {
                span,
                op: op!(bin, "+"),
                left: bin("5 + 4"),
                right: bin("7"),
            })
        );
    }

}