oxc_css_parser/parser/

sass.rs

use super::{
    Parser,
    state::{ParserState, SASS_CTX_ALLOW_DIV, SASS_CTX_IN_PARENS},
};
use crate::{
    Parse,
    ast::*,
    config::Syntax,
    error::{Error, ErrorKind, PResult},
    pos::Span,
    tokenizer::{Token, TokenWithSpan},
    util,
};

const PRECEDENCE_MULTIPLY: u8 = 6;
const PRECEDENCE_PLUS: u8 = 5;
const PRECEDENCE_RELATIONAL: u8 = 4;
const PRECEDENCE_EQUALITY: u8 = 3;
const PRECEDENCE_AND: u8 = 2;
const PRECEDENCE_OR: u8 = 1;

type SassParams<'a> = (
    oxc_allocator::Vec<'a, SassParameter<'a>>,
    Option<SassArbitraryParameter<'a>>,
    oxc_allocator::Vec<'a, Span>, // comma spans
    usize,                        // end pos
);

impl<'a> Parser<'a> {
    /// In the indented syntax a statement may continue onto following lines
    /// at points where the grammar still requires more input (`@for $i`
    /// newline `from ...`, `$a:` newline `b`, a dangling binary operator).
    /// Skip the line-structure tokens there. A deeper line's `Indent` is
    /// remembered in [`Parser::sass_pending_indents`]: the statement's own
    /// block then starts "virtually" at that depth (see [`SimpleBlock`]), and
    /// leftovers are drained against `Dedent`s after the statement.
    pub(super) fn eat_sass_line_continuation(&mut self) -> PResult<()> {
        if self.syntax != Syntax::Sass {
            return Ok(());
        }
        loop {
            match &self.cursor.peek()?.token {
                Token::Indent(..) => {
                    self.cursor.bump()?;
                    self.sass_pending_indents += 1;
                }
                Token::Linebreak(..) => {
                    self.cursor.bump()?;
                }
                _ => break,
            }
        }
        Ok(())
    }

    /// Cancel pending continuation indents against incoming `Dedent`s (their
    /// mirror tokens). Returns whether any were drained.
    pub(super) fn drain_sass_pending_dedents(&mut self) -> PResult<bool> {
        let mut drained = false;
        while self.sass_pending_indents > 0
            && matches!(self.cursor.peek()?.token, Token::Dedent(..))
        {
            self.cursor.bump()?;
            self.sass_pending_indents -= 1;
            drained = true;
        }
        Ok(drained)
    }

    // A SassScript list: space- or comma-separated <expression>s (comma binds
    // looser than space). https://sass-lang.com/documentation/values/lists
    pub(super) fn parse_maybe_sass_list(
        &mut self,
        allow_comma: bool,
    ) -> PResult<ComponentValue<'a>> {
        use util::ListSeparatorKind;

        let single_value = if allow_comma {
            self.parse_maybe_sass_list(false)?
        } else if let Token::Exclamation(..) = self.cursor.peek()?.token {
            self.parse().map(ComponentValue::ImportantAnnotation)?
        } else {
            self.parse_sass_bin_expr(/* allow_comparison */ true)?
        };

        let mut elements = self.vec();
        let mut comma_spans: Option<oxc_allocator::Vec<'a, Span>> = None;
        let mut separator = ListSeparatorKind::Unknown;
        let mut end = single_value.span().end;
        loop {
            match self.cursor.peek()?.token {
                Token::LBrace(..)
                | Token::RBrace(..)
                | Token::RParen(..)
                | Token::Semicolon(..)
                | Token::Colon(..)
                | Token::DotDotDot(..)
                | Token::Eof(..) => break,
                Token::Indent(..) | Token::Dedent(..) | Token::Linebreak(..) => {
                    if comma_spans.as_ref().is_none_or(|spans| spans.is_empty())
                        || self.state.sass_ctx & SASS_CTX_IN_PARENS == 0
                    {
                        break;
                    } else {
                        self.cursor.bump()?;
                    }
                }
                Token::Comma(..) => {
                    if !allow_comma {
                        break;
                    }
                    if separator == ListSeparatorKind::Space {
                        break;
                    } else {
                        if separator == ListSeparatorKind::Unknown {
                            separator = ListSeparatorKind::Comma;
                        }
                        let TokenWithSpan { span, .. } = self.cursor.bump()?;
                        end = span.end;
                        if let Some(spans) = &mut comma_spans {
                            spans.push(span);
                        } else {
                            comma_spans = Some(self.vec1(span));
                        }
                    }
                }
                Token::Exclamation(..) => {
                    if let Ok(important_annotation) = self.try_parse(ImportantAnnotation::parse) {
                        if end < important_annotation.span.start
                            && matches!(separator, ListSeparatorKind::Unknown)
                        {
                            separator = ListSeparatorKind::Space;
                        }
                        end = important_annotation.span.end;
                        elements.push(ComponentValue::ImportantAnnotation(important_annotation));
                    } else {
                        break;
                    }
                }
                _ => {
                    if separator == ListSeparatorKind::Unknown {
                        separator = ListSeparatorKind::Space;
                    }
                    let item = if separator == ListSeparatorKind::Comma {
                        self.parse_maybe_sass_list(false)?
                    } else {
                        self.parse_sass_bin_expr(/* allow_comparison */ true)?
                    };
                    end = item.span().end;
                    elements.push(item);
                }
            }
        }

        if elements.is_empty() && separator != ListSeparatorKind::Comma {
            // If there is a trailing comma it can be a Sass list,
            // though there is only one element.
            Ok(single_value)
        } else {
            debug_assert_ne!(separator, ListSeparatorKind::Unknown);

            let span = Span { start: single_value.span().start, end };
            elements.insert(0, single_value);
            Ok(ComponentValue::SassList(SassList { elements, comma_spans, span }))
        }
    }

    // A SassScript binary-operator expression, loosest tier first:
    //   or → and → not → ==/!= → </>/<=/>= → +/- → */%// → <unary-expression>
    // https://sass-lang.com/documentation/operators
    pub(super) fn parse_sass_bin_expr(
        &mut self,
        allow_comparison: bool,
    ) -> PResult<ComponentValue<'a>> {
        debug_assert!(matches!(self.syntax, Syntax::Scss | Syntax::Sass));
        self.parse_sass_bin_expr_with_min_precedence(PRECEDENCE_OR, allow_comparison)
    }

    // Precedence-climbing worker for `parse_sass_bin_expr`.
    fn parse_sass_bin_expr_with_min_precedence(
        &mut self,
        min_precedence: u8,
        allow_comparison: bool,
    ) -> PResult<ComponentValue<'a>> {
        let mut left = self.parse_sass_unary_expression()?;

        // delimiter can't be calculated
        if matches!(left, ComponentValue::Delimiter(..)) {
            return Ok(left);
        }

        loop {
            if PRECEDENCE_PLUS >= min_precedence {
                match self.cursor.peek()? {
                    TokenWithSpan { token: Token::Number(token), span }
                        if token.raw.starts_with('+')
                            || token.raw.starts_with('-') && span.start == left.span().end =>
                    {
                        let (number, number_span) = self.cursor.expect_number()?;
                        let op = SassBinaryOperator {
                            kind: if number.raw.starts_with('+') {
                                SassBinaryOperatorKind::Plus
                            } else {
                                SassBinaryOperatorKind::Minus
                            },
                            span: Span { start: number_span.start, end: number_span.start + 1 },
                        };
                        let span = Span { start: left.span().start, end: number_span.end };
                        let right = {
                            let span = Span { start: number_span.start + 1, end: number_span.end };
                            let raw = unsafe { number.raw.get_unchecked(1..number.raw.len()) };
                            raw.parse()
                                .map_err(|_| Error {
                                    kind: ErrorKind::InvalidNumber,
                                    span: span.clone(),
                                })
                                .map(|value| ComponentValue::Number(Number { value, raw, span }))?
                        };
                        left = ComponentValue::SassBinaryExpression(SassBinaryExpression {
                            left: self.alloc(left),
                            op,
                            right: self.alloc(right),
                            span,
                        });
                        continue;
                    }
                    TokenWithSpan { token: Token::Dimension(token), span }
                        if token.value.raw.starts_with('+')
                            || token.value.raw.starts_with('-')
                                && span.start == left.span().end =>
                    {
                        let (dimension, dimension_span) = self.cursor.expect_dimension()?;
                        let op = SassBinaryOperator {
                            kind: if dimension.value.raw.starts_with('+') {
                                SassBinaryOperatorKind::Plus
                            } else {
                                SassBinaryOperatorKind::Minus
                            },
                            span: Span {
                                start: dimension_span.start,
                                end: dimension_span.start + 1,
                            },
                        };
                        let span = Span { start: left.span().start, end: dimension_span.end };
                        let right = {
                            self.dimension(
                                crate::token::Dimension {
                                    value: crate::token::Number {
                                        raw: unsafe {
                                            dimension
                                                .value
                                                .raw
                                                .get_unchecked(1..dimension.value.raw.len())
                                        },
                                    },
                                    unit: dimension.unit,
                                },
                                Span { start: dimension_span.start + 1, end: dimension_span.end },
                            )
                            .map(ComponentValue::Dimension)?
                        };
                        left = ComponentValue::SassBinaryExpression(SassBinaryExpression {
                            left: self.alloc(left),
                            op,
                            right: self.alloc(right),
                            span,
                        });
                        continue;
                    }
                    _ => {}
                }
            }

            let (operator, precedence) = match self.cursor.peek()? {
                TokenWithSpan { token: Token::Asterisk(..), .. }
                    if PRECEDENCE_MULTIPLY >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::Multiply,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_MULTIPLY,
                    )
                }
                TokenWithSpan { token: Token::Solidus(..), .. }
                    if PRECEDENCE_MULTIPLY >= min_precedence
                        && (self.state.sass_ctx & SASS_CTX_ALLOW_DIV != 0
                            || matches!(
                                left,
                                ComponentValue::SassParenthesizedExpression(..)
                                    | ComponentValue::SassBinaryExpression(..)
                                    | ComponentValue::SassUnaryExpression(..)
                                    | ComponentValue::SassVariable(..)
                                    | ComponentValue::Function(..)
                                    | ComponentValue::SassQualifiedName(..)
                            )) =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::Division,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_MULTIPLY,
                    )
                }
                TokenWithSpan { token: Token::Percent(..), .. }
                    if PRECEDENCE_MULTIPLY >= min_precedence =>
                {
                    // `b: c %` — a bare `%` is a plain value token in Sass, so
                    // only take it as the modulo operator when a right operand
                    // actually follows.
                    let modulo = self.try_parse(|p| {
                        let op_span = p.cursor.bump()?.span;
                        p.eat_sass_line_continuation()?;
                        let right = p.parse_sass_bin_expr_with_min_precedence(
                            PRECEDENCE_MULTIPLY + 1,
                            allow_comparison,
                        )?;
                        Ok((op_span, right))
                    });
                    match modulo {
                        Ok((op_span, right)) => {
                            let span = Span { start: left.span().start, end: right.span().end };
                            left = ComponentValue::SassBinaryExpression(SassBinaryExpression {
                                left: self.alloc(left),
                                op: SassBinaryOperator {
                                    kind: SassBinaryOperatorKind::Modulo,
                                    span: op_span,
                                },
                                right: self.alloc(right),
                                span,
                            });
                            continue;
                        }
                        Err(_) => break,
                    }
                }
                TokenWithSpan { token: Token::Plus(..), .. }
                    if PRECEDENCE_PLUS >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::Plus,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_PLUS,
                    )
                }
                TokenWithSpan { token: Token::Minus(..), .. }
                    if PRECEDENCE_PLUS >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::Minus,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_PLUS,
                    )
                }
                TokenWithSpan { token: Token::GreaterThan(..), .. }
                    if allow_comparison && PRECEDENCE_RELATIONAL >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::GreaterThan,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_RELATIONAL,
                    )
                }
                TokenWithSpan { token: Token::GreaterThanEqual(..), .. }
                    if allow_comparison && PRECEDENCE_RELATIONAL >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::GreaterThanOrEqual,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_RELATIONAL,
                    )
                }
                TokenWithSpan { token: Token::LessThan(..), .. }
                    if allow_comparison && PRECEDENCE_RELATIONAL >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::LessThan,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_RELATIONAL,
                    )
                }
                TokenWithSpan { token: Token::LessThanEqual(..), .. }
                    if allow_comparison && PRECEDENCE_RELATIONAL >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::LessThanOrEqual,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_RELATIONAL,
                    )
                }
                TokenWithSpan { token: Token::EqualEqual(..), .. }
                    if PRECEDENCE_EQUALITY >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::EqualsEquals,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_EQUALITY,
                    )
                }
                TokenWithSpan { token: Token::ExclamationEqual(..), .. }
                    if PRECEDENCE_EQUALITY >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::ExclamationEquals,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_EQUALITY,
                    )
                }
                TokenWithSpan { token: Token::Ident(token), .. }
                    if token.raw == "and" && PRECEDENCE_AND >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::And,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_AND,
                    )
                }
                TokenWithSpan { token: Token::Ident(token), .. }
                    if token.raw == "or" && PRECEDENCE_OR >= min_precedence =>
                {
                    (
                        SassBinaryOperator {
                            kind: SassBinaryOperatorKind::Or,
                            span: self.cursor.bump()?.span,
                        },
                        PRECEDENCE_OR,
                    )
                }
                _ => break,
            };

            // `$a == b and` may continue on the next line
            self.eat_sass_line_continuation()?;
            let right =
                self.parse_sass_bin_expr_with_min_precedence(precedence + 1, allow_comparison)?;
            // delimiter can't be calculated
            if let ComponentValue::Delimiter(Delimiter { span, .. }) = right {
                return Err(Error { kind: ErrorKind::ExpectSassExpression, span });
            }

            let span = Span { start: left.span().start, end: right.span().end };
            left = ComponentValue::SassBinaryExpression(SassBinaryExpression {
                left: self.alloc(left),
                op: operator,
                right: self.alloc(right),
                span,
            });
        }

        Ok(left)
    }

    // Trailing declaration flags: [ '!' [ default | global ] ]*
    fn parse_sass_flags(
        &mut self,
    ) -> PResult<(oxc_allocator::Vec<'a, SassFlag<'a>>, Option<usize>)> {
        let mut flags: oxc_allocator::Vec<'a, SassFlag<'a>> = self.vec_with_capacity(1);
        let mut end = None;
        while let Some((_, exclamation_span)) = self.cursor.eat_exclamation()? {
            let keyword = self.parse::<Ident>()?;
            let keyword_span = keyword.span.clone();
            util::assert_no_ws_or_comment(&exclamation_span, &keyword_span)?;
            end = Some(keyword_span.end);

            // duplicated flags (`!default !default`) are accepted, as in dart-sass
            if !matches!(keyword.name, "default" | "global") {
                self.recoverable_errors.push(Error {
                    kind: ErrorKind::InvalidSassFlagName(keyword.name.to_string()),
                    span: keyword.span.clone(),
                });
            }

            flags.push(SassFlag {
                keyword,
                span: Span { start: exclamation_span.start, end: keyword_span.end },
            });
        }

        Ok((flags, end))
    }

    // An identifier interleaving static parts with `#{ <expression> }` interpolation.
    // https://sass-lang.com/documentation/interpolation
    pub(super) fn parse_sass_interpolated_ident(&mut self) -> PResult<InterpolableIdent<'a>> {
        debug_assert!(matches!(self.syntax, Syntax::Scss | Syntax::Sass));

        let (first, Span { start, mut end }) = match self.cursor.peek()? {
            TokenWithSpan { token: Token::Ident(..), .. } => {
                let (ident, ident_span) = self.cursor.expect_ident()?;
                (
                    SassInterpolatedIdentElement::Static(
                        self.interpolable_ident_static_part(ident, ident_span.clone()),
                    ),
                    ident_span,
                )
            }
            TokenWithSpan { token: Token::HashLBrace(..), .. } => {
                self.parse_sass_interpolated_ident_expr()?
            }
            TokenWithSpan { token, span } => {
                return Err(Error {
                    kind: ErrorKind::ExpectOneOf(vec!["<ident>", "#{"], token.symbol()),
                    span: span.clone(),
                });
            }
        };

        let mut elements = self.parse_sass_interpolated_ident_rest(&mut end)?;
        if elements.is_empty()
            && let SassInterpolatedIdentElement::Static(ident) = first
        {
            return Ok(InterpolableIdent::Literal(Ident {
                name: ident.value,
                raw: ident.raw,
                span: ident.span,
            }));
        }

        elements.insert(0, first);
        Ok(InterpolableIdent::SassInterpolated(SassInterpolatedIdent {
            elements,
            span: Span { start, end },
        }))
    }

    // The static/`#{…}` element sequence after an interpolated ident's first part.
    pub(super) fn parse_sass_interpolated_ident_rest(
        &mut self,
        end: &mut usize,
    ) -> PResult<oxc_allocator::Vec<'a, SassInterpolatedIdentElement<'a>>> {
        let mut elements = self.vec();
        loop {
            if let Some((token, span)) = self.cursor.tokenizer.scan_ident_template()? {
                *end = span.end;
                elements.push(SassInterpolatedIdentElement::Static(
                    self.interpolable_ident_static_part(token, span),
                ));
            } else if matches!(
                self.cursor.peek()?,
                TokenWithSpan { token: Token::HashLBrace(..), span } if *end == span.start
            ) {
                let (element, span) = self.parse_sass_interpolated_ident_expr()?;
                *end = span.end;
                elements.push(element);
            } else {
                return Ok(elements);
            }
        }
    }

    // One `#{ <expression> }` element of an interpolated ident.
    fn parse_sass_interpolated_ident_expr(
        &mut self,
    ) -> PResult<(SassInterpolatedIdentElement<'a>, Span)> {
        debug_assert!(matches!(self.syntax, Syntax::Scss | Syntax::Sass));

        let start = self.cursor.expect_hash_l_brace()?.1.start;
        let expr = self.parse_maybe_sass_list(/* allow_comma */ true)?;
        let end = self.cursor.expect_r_brace()?.1.end;
        Ok((SassInterpolatedIdentElement::Expression(expr), Span { start, end }))
    }

    // Call arguments for @include / function calls:
    //   [ <expression> | $<name> : <expression> | <expression>... ]#
    // https://sass-lang.com/documentation/at-rules/mixin#passing-arguments
    pub(super) fn parse_sass_invocation_args(
        &mut self,
    ) -> PResult<(oxc_allocator::Vec<'a, ComponentValue<'a>>, oxc_allocator::Vec<'a, Span>)> {
        debug_assert!(matches!(self.syntax, Syntax::Scss | Syntax::Sass));

        let mut values = self.vec_with_capacity(4);
        let mut comma_spans = self.vec();
        while !matches!(self.cursor.peek()?.token, Token::RParen(..) | Token::Eof(..)) {
            match self.cursor.peek()?.token {
                Token::Comma(..) => {
                    let TokenWithSpan { span, .. } = self.cursor.bump()?;
                    self.recoverable_errors
                        .push(Error { kind: ErrorKind::ExpectComponentValue, span });
                    continue;
                }
                _ => {
                    let value = self.parse_maybe_sass_list(/* allow_comma */ false)?;
                    if let Some((_, span)) = self.cursor.eat_dot_dot_dot()? {
                        let span = Span { start: value.span().start, end: span.end };
                        values.push(ComponentValue::SassArbitraryArgument(SassArbitraryArgument {
                            value: self.alloc(value),
                            span,
                        }));
                    } else if let ComponentValue::SassVariable(sass_var) = value {
                        if let Some((_, colon_span)) = self.cursor.eat_colon()? {
                            let value = self.parse_maybe_sass_list(/* allow_comma */ false)?;
                            let span = Span { start: sass_var.span.start, end: value.span().end };
                            values.push(ComponentValue::SassKeywordArgument(SassKeywordArgument {
                                name: sass_var,
                                colon_span,
                                value: self.alloc(value),
                                span,
                            }));
                        } else {
                            values.push(ComponentValue::SassVariable(sass_var));
                        }
                    } else {
                        values.push(value);
                    }
                }
            }
            if !matches!(self.cursor.peek()?.token, Token::RParen(..) | Token::Eof(..)) {
                comma_spans.push(self.cursor.expect_comma()?.1);
            }
        }
        debug_assert!(values.len() - comma_spans.len() <= 1);
        Ok((values, comma_spans))
    }

    // Module configuration for @use / @forward:
    //   with ( <config-item> [ , <config-item> ]* )
    // https://sass-lang.com/documentation/at-rules/use#configuration
    fn parse_sass_module_config(
        &mut self,
        allow_overridable: bool,
    ) -> PResult<Option<SassModuleConfig<'a>>> {
        match &self.cursor.peek()?.token {
            Token::Ident(ident) if ident.name().eq_ignore_ascii_case("with") => {
                let TokenWithSpan { span: with_span, .. } = self.cursor.bump()?;
                let start = with_span.start;
                let end;
                self.eat_sass_line_continuation()?;
                let (_, lparen_span) = self.cursor.expect_l_paren()?;

                let item = self.parse_sass_module_config_item(allow_overridable)?;
                let mut items = self.vec1(item);
                let mut comma_spans = self.vec();
                if let Some((_, span)) = self.cursor.eat_r_paren()? {
                    end = span.end;
                } else {
                    comma_spans.push(self.cursor.expect_comma()?.1);
                    loop {
                        if let Some((_, span)) = self.cursor.eat_r_paren()? {
                            end = span.end;
                            break;
                        }

                        items.push(self.parse_sass_module_config_item(allow_overridable)?);
                        if let Some((_, span)) = self.cursor.eat_r_paren()? {
                            end = span.end;
                            break;
                        } else {
                            comma_spans.push(self.cursor.expect_comma()?.1);
                        }
                    }
                }
                debug_assert!(items.len() - comma_spans.len() <= 1);

                Ok(Some(SassModuleConfig {
                    with_span,
                    lparen_span,
                    items,
                    comma_spans,
                    span: Span { start, end },
                }))
            }
            _ => Ok(None),
        }
    }

    // <config-item> = $<name> : <expression> [ !default ]?
    fn parse_sass_module_config_item(
        &mut self,
        allow_overridable: bool,
    ) -> PResult<SassModuleConfigItem<'a>> {
        let variable = self.parse::<SassVariable>()?;
        let (_, colon_span) = self.cursor.expect_colon()?;
        let value = self.parse_maybe_sass_list(/* allow_comma */ false)?;

        let (flags, end) = if allow_overridable {
            self.parse_sass_flags()
                .map(|(flags, end)| (flags, end.unwrap_or_else(|| value.span().end)))?
        } else {
            (self.vec(), value.span().end)
        };

        let span = Span { start: variable.span.start, end };
        Ok(SassModuleConfigItem { variable, colon_span, value, flags, span })
    }

    /// This method will consume `)` token.
    // Declared @mixin / @function parameters:
    //   [ $<name> [ : <default-expression> ]? ]#  with an optional trailing
    //   `$<name>...` (arbitrary/rest argument).
    fn parse_sass_params(&mut self) -> PResult<SassParams<'a>> {
        let mut parameters = self.vec();
        let mut arbitrary_parameter = None;
        let mut comma_spans = self.vec();
        let end;
        loop {
            if let Some((_, span)) = self.cursor.eat_r_paren()? {
                end = span.end;
                break;
            }

            let name = self.parse::<SassVariable>()?;
            let token_with_span = self.cursor.bump()?;
            match token_with_span.token {
                Token::Comma(..) => {
                    let span = name.span.clone();
                    parameters.push(SassParameter { name, default_value: None, span });
                    comma_spans.push(token_with_span.span);
                    continue;
                }
                Token::Colon(..) => {
                    let value = self.parse_maybe_sass_list(/* allow_comma */ false)?;
                    let end = value.span().end;
                    let default_value_span = Span { start: token_with_span.span.start, end };
                    let span = Span { start: name.span.start, end };
                    parameters.push(SassParameter {
                        name,
                        default_value: Some(SassParameterDefaultValue {
                            colon_span: token_with_span.span,
                            value,
                            span: default_value_span,
                        }),
                        span,
                    });
                }
                Token::DotDotDot(..) => {
                    let span = Span { start: name.span().start, end: token_with_span.span.end };
                    arbitrary_parameter = Some(SassArbitraryParameter { name, span });
                    if let Some((_, comma_span)) = self.cursor.eat_comma()? {
                        comma_spans.push(comma_span);
                    }
                    end = self.cursor.expect_r_paren()?.1.end;
                    break;
                }
                Token::RParen(..) => {
                    let span = name.span.clone();
                    parameters.push(SassParameter { name, default_value: None, span });
                    end = token_with_span.span.end;
                    break;
                }
                token => {
                    return Err(Error {
                        kind: ErrorKind::Unexpected(")", token.symbol()),
                        span: token_with_span.span,
                    });
                }
            }
            if let Some((_, span)) = self.cursor.eat_r_paren()? {
                end = span.end;
                break;
            } else {
                comma_spans.push(self.cursor.expect_comma()?.1);
            }
        }

        debug_assert!(
            parameters.len() + arbitrary_parameter.iter().count() - comma_spans.len() <= 1
        );
        Ok((parameters, arbitrary_parameter, comma_spans, end))
    }

    // A namespaced module member: <module-ident> '.' <member>
    pub(super) fn parse_sass_qualified_name(
        &mut self,
        module: Ident<'a>,
    ) -> PResult<SassQualifiedName<'a>> {
        debug_assert!(matches!(self.syntax, Syntax::Scss | Syntax::Sass));

        let (_, dot_span) = self.cursor.expect_dot()?;
        let member = if let Token::DollarVar(..) = self.cursor.peek()?.token {
            self.parse().map(SassModuleMemberName::Variable)?
        } else {
            self.parse().map(SassModuleMemberName::Ident)?
        };

        let expr_span = member.span();
        util::assert_no_ws_or_comment(&dot_span, expr_span)?;

        let span = Span { start: module.span.start, end: expr_span.end };
        Ok(SassQualifiedName { module, member, span })
    }

    // <unary-expression> = [ '+' | '-' | not ]? <value>
    fn parse_sass_unary_expression(&mut self) -> PResult<ComponentValue<'a>> {
        // dart-sass accepts a bare `%` in declaration values (`b: %`,
        // `b: % c`, `b: c %`) as a plain token. Calculations bypass this
        // (they parse atoms directly), so `calc(1px % 2px)` stays invalid.
        if let Token::Percent(..) = &self.cursor.peek()?.token {
            return Ok(ComponentValue::TokenWithSpan(self.cursor.bump()?));
        }
        let op = match &self.cursor.peek()?.token {
            Token::Plus(..) => SassUnaryOperator {
                kind: SassUnaryOperatorKind::Plus,
                span: self.cursor.bump()?.span,
            },
            Token::Minus(..) => SassUnaryOperator {
                kind: SassUnaryOperatorKind::Minus,
                span: self.cursor.bump()?.span,
            },
            Token::Ident(token) if token.raw == "not" => SassUnaryOperator {
                kind: SassUnaryOperatorKind::Not,
                span: self.cursor.bump()?.span,
            },
            _ => return self.parse_component_value_atom(),
        };

        // `$a: not` may continue on the next line
        self.eat_sass_line_continuation()?;
        let expr = self.parse_sass_unary_expression()?;
        let span = Span { start: op.span.start, end: expr.span().end };
        Ok(ComponentValue::SassUnaryExpression(SassUnaryExpression {
            expr: self.alloc(expr),
            op,
            span,
        }))
    }
}

// https://sass-lang.com/documentation/at-rules/at-root
//
// @at-root [ ( <at-root-query> ) | <selector> ] { <block> }
impl<'a> Parse<'a> for SassAtRoot<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let kind = if matches!(input.cursor.peek()?.token, Token::LParen(..)) {
            SassAtRootKind::Query(input.parse()?)
        } else {
            SassAtRootKind::Selector(input.parse()?)
        };

        let span = kind.span().clone();
        Ok(SassAtRoot { kind, span })
    }
}

// <at-root-query> = ( [ with | without ] : [ <ident> | <string> ]+ )
impl<'a> Parse<'a> for SassAtRootQuery<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let start = input.cursor.expect_l_paren()?.1.start;

        let modifier = {
            let (token, span) = input.cursor.expect_ident()?;
            let ident_name = token.name();
            if ident_name.eq_ignore_ascii_case("with") {
                SassAtRootQueryModifier { kind: SassAtRootQueryModifierKind::With, span }
            } else if ident_name.eq_ignore_ascii_case("without") {
                SassAtRootQueryModifier { kind: SassAtRootQueryModifierKind::Without, span }
            } else {
                return Err(Error { kind: ErrorKind::ExpectSassAtRootWithOrWithout, span });
            }
        };
        let colon_span = input.cursor.expect_colon()?.1;

        let mut rules = input.vec_with_capacity(1);
        loop {
            match &input.cursor.peek()?.token {
                Token::Ident(..) | Token::HashLBrace(..) => {
                    rules.push(SassAtRootQueryRule::Ident(input.parse()?));
                }
                Token::Str(..) | Token::StrTemplate(..) => {
                    rules.push(SassAtRootQueryRule::Str(input.parse()?));
                }
                _ => break,
            }
        }
        let end = input.cursor.expect_r_paren()?.1.end;

        Ok(SassAtRootQuery { modifier, colon_span, rules, span: Span { start, end } })
    }
}

// A conditional clause: <expression> { <block> }  (body of @if / @else if / @while)
impl<'a> Parse<'a> for SassConditionalClause<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        input.eat_sass_line_continuation()?;
        let condition = input.parse::<ComponentValue>()?;
        let block = input.parse::<SimpleBlock>()?;
        let span = Span { start: condition.span().start, end: block.span.end };
        Ok(SassConditionalClause { condition, block, span })
    }
}

// https://sass-lang.com/documentation/at-rules/mixin#content-blocks
//
// @content [ ( <invocation-args> ) ]?
impl<'a> Parse<'a> for SassContent<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let (_, Span { start, .. }) = input.cursor.expect_l_paren()?;
        let (args, comma_spans) = input.parse_sass_invocation_args()?;
        let (_, Span { end, .. }) = input.cursor.expect_r_paren()?;
        Ok(SassContent { args, comma_spans, span: Span { start, end } })
    }
}

// https://sass-lang.com/documentation/at-rules/control/each
//
// @each <variable> [ , <variable> ]* in <expression>
impl<'a> Parse<'a> for SassEach<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        input.eat_sass_line_continuation()?;
        let first_binding = input.parse::<SassVariable>()?;
        let start = first_binding.span().start;

        let mut bindings = input.vec1(first_binding);
        let mut comma_spans = input.vec();
        loop {
            // the comma may sit on a continuation line (`@each $a\n  , $b in ...`)
            input.eat_sass_line_continuation()?;
            let Some((_, comma_span)) = input.cursor.eat_comma()? else { break };
            comma_spans.push(comma_span);
            input.eat_sass_line_continuation()?;
            bindings.push(input.parse()?);
        }
        debug_assert_eq!(comma_spans.len() + 1, bindings.len());

        input.eat_sass_line_continuation()?;
        let (keyword_in, keyword_in_span) = input.cursor.expect_ident()?;
        if keyword_in.name() != "in" {
            return Err(Error { kind: ErrorKind::ExpectSassKeyword("in"), span: keyword_in_span });
        }

        input.eat_sass_line_continuation()?;
        let expr = input.parse_maybe_sass_list(/* allow_comma */ true)?;
        let span = Span { start, end: expr.span().end };
        Ok(SassEach { bindings, comma_spans, in_span: keyword_in_span, expr, span })
    }
}

// https://sass-lang.com/documentation/at-rules/extend
//
// @extend <compound-selector-list> [ !optional ]?
impl<'a> Parse<'a> for SassExtend<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        input.eat_sass_line_continuation()?;
        let selectors = input.parse::<CompoundSelectorList>()?;
        let start = selectors.span.start;
        let mut end = selectors.span.end;

        let optional = if let Some((_, exclamation_span)) = input.cursor.eat_exclamation()? {
            let (keyword, keyword_span) =
                input.cursor.expect_ident_without_ws_or_comments(false)?;
            if keyword.name().eq_ignore_ascii_case("optional") {
                end = keyword_span.end;
                let span = Span { start: exclamation_span.start, end: keyword_span.end };
                Some(SassFlag { keyword: input.ident(keyword, keyword_span), span })
            } else {
                input.recoverable_errors.push(Error {
                    kind: ErrorKind::ExpectSassKeyword("optional"),
                    span: keyword_span,
                });
                None
            }
        } else {
            None
        };

        Ok(SassExtend { selectors, optional, span: Span { start, end } })
    }
}

// https://sass-lang.com/documentation/at-rules/control/for
//
// @for <variable> from <expression> [ to | through ] <expression>
impl<'a> Parse<'a> for SassFor<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        input.eat_sass_line_continuation()?;
        let binding = input.parse::<SassVariable>()?;

        input.eat_sass_line_continuation()?;
        let (keyword_from, keyword_from_span) = input.cursor.expect_ident()?;
        if keyword_from.name() != "from" {
            return Err(Error {
                kind: ErrorKind::ExpectSassKeyword("from"),
                span: keyword_from_span,
            });
        }

        input.eat_sass_line_continuation()?;
        let start = input.parse()?;
        input.eat_sass_line_continuation()?;
        let boundary = input.parse()?;
        input.eat_sass_line_continuation()?;
        let end = input.parse::<ComponentValue>()?;

        let span = Span { start: binding.span.start, end: end.span().end };
        Ok(SassFor { binding, from_span: keyword_from_span, start, end, boundary, span })
    }
}

// to | through   (exclusive | inclusive upper bound of @for)
impl<'a> Parse<'a> for SassForBoundary {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let (keyword, span) = input.cursor.expect_ident()?;
        match &*keyword.name() {
            "to" => Ok(SassForBoundary { kind: SassForBoundaryKind::Exclusive, span }),
            "through" => Ok(SassForBoundary { kind: SassForBoundaryKind::Inclusive, span }),
            _ => Err(Error { kind: ErrorKind::ExpectSassKeyword("to"), span }),
        }
    }
}

// https://sass-lang.com/documentation/at-rules/forward
//
// @forward <string> [ as <ident> '*' ]? [ [ show | hide ] <member># ]? [ with ( <config> ) ]?
impl<'a> Parse<'a> for SassForward<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        input.eat_sass_line_continuation()?;
        let path = input.parse::<InterpolableStr>()?;
        let mut span = path.span().clone();

        let prefix = match &input.cursor.peek()?.token {
            Token::Ident(ident) if ident.name().eq_ignore_ascii_case("as") => {
                let TokenWithSpan { span: as_span, .. } = input.cursor.bump()?;
                input.eat_sass_line_continuation()?;
                let name = input.parse()?;
                let (_, Span { end, .. }) =
                    input.cursor.expect_asterisk_without_ws_or_comments()?;
                let span = Span { start: as_span.start, end };
                Some(SassForwardPrefix { as_span, name, span })
            }
            _ => None,
        };

        let visibility = if let TokenWithSpan { token: Token::Ident(keyword), span: keyword_span } =
            input.cursor.peek()?
        {
            let start = keyword_span.start;
            let name = keyword.name();
            if name.eq_ignore_ascii_case("hide") {
                let keyword_span = input.cursor.bump()?.span;
                let mut members = input.vec();
                let mut comma_spans = input.vec();
                loop {
                    input.eat_sass_line_continuation()?;
                    match &input.cursor.peek()?.token {
                        Token::Ident(..) => {
                            members.push(input.parse().map(SassForwardMember::Ident)?)
                        }
                        _ => members.push(input.parse().map(SassForwardMember::Variable)?),
                    }
                    if let Some((_, span)) = input.cursor.eat_comma()? {
                        comma_spans.push(span);
                    } else {
                        break;
                    }
                }
                Some(SassForwardVisibility {
                    modifier: SassForwardVisibilityModifier {
                        kind: SassForwardVisibilityModifierKind::Hide,
                        span: keyword_span,
                    },
                    members,
                    comma_spans,
                    span: Span { start, end: input.cursor.tokenizer.current_offset() },
                })
            } else if name.eq_ignore_ascii_case("show") {
                let keyword_span = input.cursor.bump()?.span;
                let mut members = input.vec();
                let mut comma_spans = input.vec();
                loop {
                    input.eat_sass_line_continuation()?;
                    match &input.cursor.peek()?.token {
                        Token::Ident(..) => {
                            members.push(input.parse().map(SassForwardMember::Ident)?)
                        }
                        _ => members.push(input.parse().map(SassForwardMember::Variable)?),
                    }
                    if let Some((_, span)) = input.cursor.eat_comma()? {
                        comma_spans.push(span);
                    } else {
                        break;
                    }
                }
                Some(SassForwardVisibility {
                    modifier: SassForwardVisibilityModifier {
                        kind: SassForwardVisibilityModifierKind::Show,
                        span: keyword_span,
                    },
                    members,
                    comma_spans,
                    span: Span { start, end: input.cursor.tokenizer.current_offset() },
                })
            } else {
                None
            }
        } else {
            None
        };

        let config = input.parse_sass_module_config(/* allow_overridable */ true)?;
        if let Some(config) = &config {
            span.end = config.span.end;
        }

        Ok(SassForward { path, prefix, visibility, config, span })
    }
}

// https://sass-lang.com/documentation/at-rules/function
//
// @function <ident> <parameters> { <block> }
impl<'a> Parse<'a> for SassFunction<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        input.eat_sass_line_continuation()?;
        let name = input.parse::<Ident>()?;
        let start = name.span.start;

        input.eat_sass_line_continuation()?;
        let parameters = input.parse::<SassParameters>()?;

        let span = Span { start, end: parameters.span.end };
        Ok(SassFunction { name, parameters, span })
    }
}

// https://sass-lang.com/documentation/at-rules/control/if
//
// @if <clause> [ @else if <clause> ]* [ @else { <block> } ]?
impl<'a> Parse<'a> for SassIfAtRule<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        let start = input.cursor.expect_at_keyword()?.1.start;

        let if_clause = input.parse::<SassConditionalClause>()?;
        let mut else_if_clauses: oxc_allocator::Vec<'a, SassConditionalClause<'a>> = input.vec();
        let mut else_clause: Option<SimpleBlock> = None;
        let mut else_spans = input.vec();

        loop {
            // In the indented syntax `@else` sits on the line after the
            // previous clause's block, so a Linebreak may precede it; only
            // consume that separator when an else/elseif actually follows.
            // (Linebreak tokens exist only in the indented syntax, so the
            // rollback snapshot is needed only when one is present.)
            fn else_keyword<'a>(p: &mut Parser<'a>) -> PResult<(Span, bool)> {
                while p.cursor.eat_linebreak()?.is_some() {}
                let is_else = match &p.cursor.peek()?.token {
                    Token::AtKeyword(at_keyword) => match &*at_keyword.ident.name() {
                        "else" => true,
                        // `elseif` is deprecated by Sass
                        "elseif" => false,
                        _ => {
                            let span = p.cursor.peek()?.span.clone();
                            return Err(Error { kind: ErrorKind::TryParseError, span });
                        }
                    },
                    _ => {
                        let span = p.cursor.peek()?.span.clone();
                        return Err(Error { kind: ErrorKind::TryParseError, span });
                    }
                };
                Ok((p.cursor.bump()?.span, is_else))
            }
            let else_keyword = if matches!(input.cursor.peek()?.token, Token::Linebreak(..)) {
                input.try_parse(else_keyword)
            } else {
                else_keyword(input)
            };
            let Ok((else_span, is_else)) = else_keyword else { break };
            else_spans.push(else_span);
            if is_else {
                input.eat_sass_line_continuation()?;
                match &input.cursor.peek()?.token {
                    Token::Ident(ident) if ident.name() == "if" => {
                        input.cursor.bump()?;
                        else_if_clauses.push(input.parse()?);
                    }
                    _ => {
                        else_clause = Some(input.parse()?);
                        break;
                    }
                }
            } else {
                else_if_clauses.push(input.parse()?);
            }
        }

        debug_assert_eq!(else_spans.len(), else_if_clauses.len() + else_clause.iter().count());
        let span = Span {
            start,
            end: else_clause
                .as_ref()
                .map(|else_clause| else_clause.span.end)
                .or_else(|| else_if_clauses.last().map(|else_if_clause| else_if_clause.span.end))
                .unwrap_or(if_clause.span.end),
        };
        Ok(SassIfAtRule { if_clause, else_if_clauses, else_clause, else_spans, span })
    }
}

// https://sass-lang.com/documentation/at-rules/import
//
// @import <string> [ , <string> ]*   (Sass multi-path import of literal strings)
impl<'a> Parse<'a> for SassImportPrelude<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let first = input.parse::<Str>()?;
        let mut span = first.span.clone();

        let mut paths = input.vec1(first);
        let mut comma_spans = input.vec();
        while let Some((_, comma_span)) = input.cursor.eat_comma()? {
            comma_spans.push(comma_span);
            paths.push(input.parse()?);
        }
        debug_assert_eq!(comma_spans.len() + 1, paths.len());

        if let Some(Str { span: Span { end, .. }, .. }) = paths.last() {
            span.end = *end;
        }
        Ok(SassImportPrelude { paths, comma_spans, span })
    }
}

// https://sass-lang.com/documentation/at-rules/mixin
//
// @include <name> [ ( <invocation-args> ) ]? [ using ( <parameters> ) ]?
impl<'a> Parse<'a> for SassInclude<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        input.eat_sass_line_continuation()?;
        let name = input.parse::<FunctionName>()?;
        let mut span = name.span().clone();

        let arguments = if matches!(input.cursor.peek()?.token, Token::LParen(..)) {
            let arguments = input.parse::<SassIncludeArgs>()?;
            span.end = arguments.span.end;
            Some(arguments)
        } else {
            None
        };

        let content_block_params = match &input.cursor.peek()?.token {
            Token::Ident(ident) if ident.name().eq_ignore_ascii_case("using") => {
                let content_block_params = input.parse::<SassIncludeContentBlockParams>()?;
                span.end = content_block_params.span.end;
                Some(content_block_params)
            }
            _ => None,
        };

        Ok(SassInclude { name, arguments, content_block_params, span })
    }
}

// ( <invocation-args> )
impl<'a> Parse<'a> for SassIncludeArgs<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let (_, Span { start, .. }) = input.cursor.expect_l_paren()?;
        let (args, comma_spans) = input.parse_sass_invocation_args()?;
        let (_, Span { end, .. }) = input.cursor.expect_r_paren()?;
        Ok(SassIncludeArgs { args, comma_spans, span: Span { start, end } })
    }
}

// using ( <parameters> )   (parameters the mixin passes to its @content block)
impl<'a> Parse<'a> for SassIncludeContentBlockParams<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        match input.cursor.bump()? {
            TokenWithSpan { token: Token::Ident(ident), span: using_span }
                if ident.name().eq_ignore_ascii_case("using") =>
            {
                input.eat_sass_line_continuation()?;
                let params = input.parse::<SassParameters>()?;
                let span = Span { start: using_span.start, end: params.span.end };
                Ok(SassIncludeContentBlockParams { using_span, params, span })
            }
            TokenWithSpan { span, .. } => {
                Err(Error { kind: ErrorKind::ExpectSassKeyword("using"), span })
            }
        }
    }
}

// A quoted string containing `#{ <expression> }` interpolation.
// https://sass-lang.com/documentation/interpolation
impl<'a> Parse<'a> for SassInterpolatedStr<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let (first, first_span) = input.cursor.expect_str_template()?;
        let quote = first.raw.chars().next().unwrap();
        debug_assert!(quote == '\'' || quote == '"');
        let mut span = first_span.clone();
        let first = input.interpolable_str_static_part(first, first_span);
        let mut elements = input.vec1(SassInterpolatedStrElement::Static(first));

        let mut is_parsing_static_part = false;
        loop {
            if is_parsing_static_part {
                let (token, str_tpl_span) = input.cursor.tokenizer.scan_string_template(quote)?;
                let tail = token.tail;
                let end = str_tpl_span.end;
                elements.push(SassInterpolatedStrElement::Static(
                    input.interpolable_str_static_part(token, str_tpl_span),
                ));
                if tail {
                    span.end = end;
                    break;
                }
            } else {
                // '#' is consumed, so '{' left only
                input.cursor.expect_l_brace()?;
                elements.push(SassInterpolatedStrElement::Expression(
                    input.parse_maybe_sass_list(/* allow_comma */ true)?,
                ));
                input.cursor.expect_r_brace()?;
            }
            is_parsing_static_part = !is_parsing_static_part;
        }

        Ok(SassInterpolatedStr { elements, span })
    }
}

// A `url()` body containing `#{ <expression> }` interpolation.
impl<'a> Parse<'a> for SassInterpolatedUrl<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        let (first, first_span) = match input.cursor.tokenizer.scan_url_raw_or_template()? {
            TokenWithSpan { token: Token::UrlTemplate(template), span } => (template, span),
            TokenWithSpan { token, span } => {
                return Err(Error {
                    kind: ErrorKind::Unexpected("<url template>", token.symbol()),
                    span,
                });
            }
        };
        let mut span = first_span.clone();
        let first = input.interpolable_url_static_part(first, first_span);
        let mut elements = input.vec1(SassInterpolatedUrlElement::Static(first));

        let mut is_parsing_static_part = false;
        loop {
            if is_parsing_static_part {
                let (token, url_tpl_span @ Span { end, .. }) =
                    input.cursor.tokenizer.scan_url_template()?;
                let tail = token.tail;
                elements.push(SassInterpolatedUrlElement::Static(
                    input.interpolable_url_static_part(token, url_tpl_span),
                ));
                if tail {
                    span.end = end;
                    break;
                }
            } else {
                // '#' is consumed, so '{' left only
                input.cursor.expect_l_brace()?;
                elements.push(SassInterpolatedUrlElement::Expression(
                    input.parse_maybe_sass_list(/* allow_comma */ true)?,
                ));
                input.cursor.expect_r_brace()?;
            }
            is_parsing_static_part = !is_parsing_static_part;
        }

        Ok(SassInterpolatedUrl { elements, span })
    }
}

// https://sass-lang.com/documentation/values/lists
//
// <sass-list> = <expression> [ <separator> <expression> ]*   (separator: ' ' or ',')
impl<'a> Parse<'a> for SassList<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        if let ComponentValue::SassList(list) =
            input.parse_maybe_sass_list(/* allow_comma */ true)?
        {
            Ok(list)
        } else {
            let TokenWithSpan { token, span } = input.cursor.bump()?;
            Err(Error { kind: ErrorKind::Unexpected(",", token.symbol()), span })
        }
    }
}

// https://sass-lang.com/documentation/values/maps
//
// <sass-map> = ( [ <map-item> [ , <map-item> ]* ]? )
impl<'a> Parse<'a> for SassMap<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let start = input.cursor.expect_l_paren()?.1.start;

        let mut items = input.vec();
        let mut comma_spans = input.vec();
        loop {
            match input.cursor.peek()?.token {
                Token::RParen(..) => break,
                Token::Indent(..) | Token::Dedent(..) | Token::Linebreak(..) => {
                    input.cursor.bump()?;
                }
                _ => {
                    items.push(input.parse()?);
                    if matches!(
                        input.cursor.peek()?.token,
                        Token::Indent(..) | Token::Dedent(..) | Token::Linebreak(..)
                    ) {
                        input.cursor.bump()?;
                    }
                    if !matches!(&input.cursor.peek()?.token, Token::RParen(..)) {
                        comma_spans.push(input.cursor.expect_comma()?.1);
                    }
                }
            }
        }
        debug_assert!(items.len() - comma_spans.len() <= 1);

        let end = input.cursor.expect_r_paren()?.1.end;
        Ok(SassMap { items, comma_spans, span: Span { start, end } })
    }
}

// <map-item> = <expression> : <expression>
impl<'a> Parse<'a> for SassMapItem<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let key = input.parse_maybe_sass_list(/* allow_comma */ false)?;
        let (_, colon_span) = input.cursor.expect_colon()?;
        let value = input.parse_maybe_sass_list(/* allow_comma */ false)?;
        let span = Span { start: key.span().start, end: value.span().end };
        Ok(SassMapItem { key, colon_span, value, span })
    }
}

// https://sass-lang.com/documentation/at-rules/mixin
//
// @mixin <ident> [ <parameters> ]? { <block> }
impl<'a> Parse<'a> for SassMixin<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        input.eat_sass_line_continuation()?;
        let name = input.parse::<Ident>()?;
        let start = name.span.start;
        let mut end = name.span.end;

        let parameters = if matches!(input.cursor.peek()?.token, Token::LParen(..)) {
            let parameters = input.parse::<SassParameters>()?;
            end = parameters.span.end;
            Some(parameters)
        } else {
            None
        };

        Ok(SassMixin { name, parameters, span: Span { start, end } })
    }
}

// Declared parameters: ( [ <parameter># ]? [ , <variable>... ]? )
impl<'a> Parse<'a> for SassParameters<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let (_, Span { start, .. }) = input.cursor.expect_l_paren()?;
        let (params, arbitrary_param, comma_spans, end) = input.parse_sass_params()?;
        Ok(SassParameters { params, arbitrary_param, comma_spans, span: Span { start, end } })
    }
}

// The nested `{ <declaration-list> }` of a Sass nested property (`font: { … }`).
// https://sass-lang.com/documentation/style-rules/declarations#nesting
impl<'a> Parse<'a> for SassNestingDeclaration<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let block = input.parse::<SimpleBlock>()?;
        let span = block.span.clone();

        Ok(SassNestingDeclaration { block, span })
    }
}

// ( <expression> )   (a parenthesized SassScript expression)
impl<'a> Parse<'a> for SassParenthesizedExpression<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let start = input.cursor.expect_l_paren()?.1.start;
        input.cursor.eat_indent()?;
        let expr = input
            .with_state(ParserState {
                sass_ctx: input.state.sass_ctx | SASS_CTX_ALLOW_DIV | SASS_CTX_IN_PARENS,
                ..input.state.clone()
            })
            .parse_maybe_sass_list(/* allow_comma */ true)?;
        let expr = input.alloc(expr);
        let end = input.cursor.expect_r_paren()?.1.end;
        Ok(SassParenthesizedExpression { expr, span: Span { start, end } })
    }
}

// https://sass-lang.com/documentation/style-rules/placeholder-selectors
//
// <placeholder-selector> = '%' <ident>
impl<'a> Parse<'a> for SassPlaceholderSelector<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let (_, percent_span) = input.cursor.expect_percent()?;
        let name = input.parse::<InterpolableIdent>()?;
        let name_span = name.span();
        util::assert_no_ws_or_comment(&percent_span, name_span)?;
        let span = Span { start: percent_span.start, end: name_span.end };
        Ok(SassPlaceholderSelector { name, span })
    }
}

// https://sass-lang.com/documentation/at-rules/use
//
// @use <string> [ as [ <ident> | '*' ] ]? [ with ( <config> ) ]?
impl<'a> Parse<'a> for SassUse<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        input.eat_sass_line_continuation()?;
        let path = input.parse::<InterpolableStr>()?;
        let mut span = path.span().clone();

        let namespace = match &input.cursor.peek()?.token {
            Token::Ident(ident) if ident.name().eq_ignore_ascii_case("as") => {
                let namespace = input.parse::<SassUseNamespace>()?;
                span.end = namespace.span.end;
                Some(namespace)
            }
            _ => None,
        };

        let config = input.parse_sass_module_config(/* allow_overridable */ false)?;
        if let Some(config) = &config {
            span.end = config.span.end;
        }

        Ok(SassUse { path, namespace, config, span })
    }
}

// as [ <ident> | '*' ]   ('*' loads members without a namespace prefix)
impl<'a> Parse<'a> for SassUseNamespace<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        let as_span = match input.cursor.peek()? {
            TokenWithSpan { token: Token::Ident(ident), .. }
                if ident.name().eq_ignore_ascii_case("as") =>
            {
                input.cursor.bump()?.span
            }
            TokenWithSpan { span, .. } => {
                return Err(Error { kind: ErrorKind::ExpectSassKeyword("as"), span: span.clone() });
            }
        };
        input.eat_sass_line_continuation()?;
        match input.cursor.bump()? {
            TokenWithSpan { token: Token::Asterisk(..), span: asterisk_span } => {
                let span = Span { start: as_span.start, end: asterisk_span.end };
                Ok(SassUseNamespace {
                    as_span,
                    kind: SassUseNamespaceKind::Unnamed(SassUnnamedNamespace {
                        span: asterisk_span,
                    }),
                    span,
                })
            }
            TokenWithSpan { token: Token::Ident(ident), span: ident_span } => {
                let span = Span { start: as_span.start, end: ident_span.end };
                Ok(SassUseNamespace {
                    as_span,
                    kind: SassUseNamespaceKind::Named(input.ident(ident, ident_span)),
                    span,
                })
            }
            TokenWithSpan { span, .. } => {
                Err(Error { kind: ErrorKind::ExpectSassUseNamespace, span })
            }
        }
    }
}

// https://sass-lang.com/documentation/variables
//
// <sass-variable> = '$' <ident>
impl<'a> Parse<'a> for SassVariable<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        let (name, span) = input.parse_dollar_var_ident()?;
        Ok(SassVariable { name, span })
    }
}

// https://sass-lang.com/documentation/variables
//
// [ <namespace> '.' ]? '$' <ident> ':' <expression> <flag>*
// <flag> = !default | !global
impl<'a> Parse<'a> for SassVariableDeclaration<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        let namespace = if let Some((ident_token, span)) = input.cursor.eat_ident()? {
            let (_, dot_span) = input.cursor.expect_dot()?;
            util::assert_no_ws_or_comment(&span, &dot_span)?;
            let TokenWithSpan { span: next_span, .. } = input.cursor.peek()?;
            util::assert_no_ws_or_comment(&dot_span, next_span)?;
            Some(input.ident(ident_token, span))
        } else {
            None
        };

        let name = input.parse::<SassVariable>()?;
        input.eat_sass_line_continuation()?;
        let (_, colon_span) = input.cursor.expect_colon()?;
        input.eat_sass_line_continuation()?;
        let value = input
            .with_state(ParserState {
                sass_ctx: input.state.sass_ctx | SASS_CTX_ALLOW_DIV,
                ..input.state.clone()
            })
            .parse_maybe_sass_list(/* allow_comma */ true)?;

        let (flags, end) = input.parse_sass_flags()?;

        let span = Span {
            start: namespace
                .as_ref()
                .map(|namespace| namespace.span.start)
                .unwrap_or(name.span.start),
            end: end.unwrap_or_else(|| value.span().end),
        };

        if namespace.is_some() && flags.iter().any(|flag| flag.keyword.name == "global") {
            input
                .recoverable_errors
                .push(Error { kind: ErrorKind::UnexpectedSassFlag("global"), span: span.clone() });
        }

        Ok(SassVariableDeclaration { namespace, name, colon_span, value, flags, span })
    }
}

// A Sass at-rule with an unrecognized (possibly interpolated) name:
// '@' <interpolated-ident> <prelude>? [ { <block> } | ; ]
impl<'a> Parse<'a> for UnknownSassAtRule<'a> {
    fn parse(input: &mut Parser<'a>) -> PResult<Self> {
        debug_assert!(matches!(input.syntax, Syntax::Scss | Syntax::Sass));

        let (_, at_span) = input.cursor.expect_at()?;
        let name = input.parse_sass_interpolated_ident()?;
        let name_span = name.span();
        util::assert_no_ws_or_comment(&at_span, name_span)?;

        let (prelude, block, end) = input.parse_unknown_at_rule()?;
        let span = Span { start: at_span.start, end: end.unwrap_or(name_span.end) };
        Ok(UnknownSassAtRule { name, prelude, block, span })
    }
}