rsass 0.29.2

Sass implementation in pure rust (not complete yet)
Documentation 
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use super::{
    BodyItem, Comment, CustomProperty, Import, Item, MediaRule, Property,
    Rule, Value,
};
use crate::output::CssBuf;
use std::io::{self, Write};

/// An `@something` rule in css.
///
/// Note that some well-known at rules (`@media`, `@keyframes`, ...)
/// probably should have their own types.
#[derive(Clone, Debug)]
pub struct AtRule {
    name: String,
    args: Value,
    // Some<[]> outputs "{}", None outputs ";".
    body: Option<Vec<AtRuleBodyItem>>,
}

impl AtRule {
    pub(crate) fn new(
        name: String,
        args: Value,
        body: Option<Vec<AtRuleBodyItem>>,
    ) -> Self {
        Self { name, args, body }
    }
    pub(crate) fn no_body(&self) -> bool {
        self.body.is_none()
    }
    pub(crate) fn write(&self, buf: &mut CssBuf) -> io::Result<()> {
        buf.do_indent_no_nl();
        write!(buf, "@{}", self.name)?;
        if !self.args.is_null() {
            write!(buf, " {}", self.args.format(buf.format()))?;
        }
        if let Some(body) = &self.body {
            if let [AtRuleBodyItem::Comment(c)] = &body[..] {
                buf.add_one(" { ", "{");
                c.write(buf);
                buf.pop_nl();
                buf.add_one(" }\n", "}");
            } else {
                buf.start_block();
                for item in body {
                    item.write(buf)?;
                }
                buf.end_block();
            }
        } else {
            buf.add_one(";\n", ";");
        }
        Ok(())
    }
}

/// Something that may exist in the body of an [`AtRule`].
#[derive(Clone, Debug)]
pub enum AtRuleBodyItem {
    /// An `@import` statement.
    Import(Import),
    /// A comment
    Comment(Comment),
    /// A rule
    Rule(Rule),
    /// A raw property.
    Property(Property),
    /// A custom property declaration with a name and a value.
    CustomProperty(CustomProperty),
    /// An `@media` rule.
    MediaRule(MediaRule),
    /// An `@` rule.
    AtRule(AtRule),
}

impl AtRuleBodyItem {
    pub(crate) fn write(&self, buf: &mut CssBuf) -> io::Result<()> {
        match self {
            Self::Import(import) => import.write(buf)?,
            Self::Comment(comment) => comment.write(buf),
            Self::Rule(rule) => rule.write(buf)?,
            Self::Property(property) => property.write(buf),
            Self::CustomProperty(cp) => cp.write(buf),
            Self::MediaRule(rule) => rule.write(buf)?,
            Self::AtRule(rule) => rule.write(buf)?,
        }
        Ok(())
    }
}
impl From<Rule> for AtRuleBodyItem {
    fn from(rule: Rule) -> Self {
        Self::Rule(rule)
    }
}
impl From<Comment> for AtRuleBodyItem {
    fn from(rule: Comment) -> Self {
        Self::Comment(rule)
    }
}
impl From<Import> for AtRuleBodyItem {
    fn from(rule: Import) -> Self {
        Self::Import(rule)
    }
}
impl From<Property> for AtRuleBodyItem {
    fn from(rule: Property) -> Self {
        Self::Property(rule)
    }
}
impl From<AtRule> for AtRuleBodyItem {
    fn from(rule: AtRule) -> Self {
        Self::AtRule(rule)
    }
}
impl From<MediaRule> for AtRuleBodyItem {
    fn from(rule: MediaRule) -> Self {
        Self::MediaRule(rule)
    }
}
impl From<BodyItem> for AtRuleBodyItem {
    fn from(value: BodyItem) -> Self {
        match value {
            BodyItem::Import(i) => Self::Import(i),
            BodyItem::Property(p) => Self::Property(p),
            BodyItem::CustomProperty(p) => Self::CustomProperty(p),
            BodyItem::Comment(c) => Self::Comment(c),
            BodyItem::ARule(r) => Self::AtRule(r),
        }
    }
}

impl TryFrom<Item> for AtRuleBodyItem {
    type Error = &'static str;

    fn try_from(value: Item) -> Result<Self, Self::Error> {
        match value {
            Item::Comment(x) => Ok(x.into()),
            Item::Import(x) => Ok(x.into()),
            Item::Rule(x) => Ok(x.into()),
            Item::MediaRule(x) => Ok(x.into()),
            Item::AtRule(x) => Ok(x.into()),
            Item::Separator => Err("separator not supported here"),
        }
    }
}