do not panic when extending by compound selector with parent

src/builtin/functions/selector.rs

@@ -90,14 +90,7 @@ pub(crate) fn selector_append(args: CallArgs, parser: &mut Parser<'_>) -> SassRe
 
     let mut parsed_selectors = selectors
         .into_iter()
-        .map(|s| {
+        .map(|s| s.node.to_selector(parser, "selectors", false))
-            let tmp = s.node.to_selector(parser, "selectors", false)?;
-            if tmp.contains_parent_selector() {
-                Err(("Parent selectors aren't allowed here.", span).into())
-            } else {
-                Ok(tmp)
-            }
-        })
         .collect::<SassResult<Vec<Selector>>>()?;
 
     let first = parsed_selectors.remove(0);
@@ -158,13 +151,13 @@ pub(crate) fn selector_replace(mut args: CallArgs, parser: &mut Parser<'_>) -> S
     args.max_args(3)?;
     let selector = args
         .get_err(0, "selector")?
-        .to_selector(parser, "selector", false)?;
+        .to_selector(parser, "selector", true)?;
     let target = args
         .get_err(1, "original")?
-        .to_selector(parser, "original", false)?;
+        .to_selector(parser, "original", true)?;
     let source = args
         .get_err(2, "replacement")?
-        .to_selector(parser, "replacement", false)?;
+        .to_selector(parser, "replacement", true)?;
     Ok(Extender::replace(selector.0, source.0, target.0, args.span())?.to_sass_list())
 }
 
@@ -172,7 +165,7 @@ pub(crate) fn selector_unify(mut args: CallArgs, parser: &mut Parser<'_>) -> Sas
     args.max_args(2)?;
     let selector1 = args
         .get_err(0, "selector1")?
-        .to_selector(parser, "selector1", false)?;
+        .to_selector(parser, "selector1", true)?;
 
     if selector1.contains_parent_selector() {
         return Err((
@@ -184,7 +177,7 @@ pub(crate) fn selector_unify(mut args: CallArgs, parser: &mut Parser<'_>) -> Sas
 
     let selector2 = args
         .get_err(1, "selector2")?
-        .to_selector(parser, "selector2", false)?;
+        .to_selector(parser, "selector2", true)?;
 
     if selector2.contains_parent_selector() {
         return Err((

src/parse/common.rs

@@ -55,6 +55,7 @@ impl ContextFlags {
     pub const IN_FUNCTION: ContextFlag = ContextFlag(1 << 1);
     pub const IN_CONTROL_FLOW: ContextFlag = ContextFlag(1 << 2);
     pub const IN_KEYFRAMES: ContextFlag = ContextFlag(1 << 3);
+    pub const IN_AT_ROOT_RULE: ContextFlag = ContextFlag(1 << 4);
 
     pub const fn empty() -> Self {
         Self(0)
@@ -75,6 +76,11 @@ impl ContextFlags {
     pub fn in_keyframes(self) -> bool {
         (self.0 & Self::IN_KEYFRAMES) != 0
     }
+
+    #[allow(dead_code)]
+    pub fn in_at_root_rule(self) -> bool {
+        (self.0 & Self::IN_AT_ROOT_RULE) != 0
+    }
 }
 
 impl BitAnd<ContextFlag> for u8 {

src/parse/mod.rs

@@ -17,7 +17,7 @@ use crate::{
         ComplexSelectorComponent, ExtendRule, ExtendedSelector, Extender, Selector, SelectorParser,
     },
     style::Style,
-    utils::{read_until_closing_curly_brace, read_until_semicolon_or_closing_curly_brace},
+    utils::read_until_semicolon_or_closing_curly_brace,
     value::Value,
     Options, {Cow, Token},
 };
@@ -352,7 +352,7 @@ impl<'a> Parser<'a> {
                             let at_root = self.at_root;
                             self.at_root = false;
                             let selector = self
-                                .parse_selector(!self.super_selectors.is_empty(), false, init)?
+                                .parse_selector(true, false, init)?
                                 .0
                                 .resolve_parent_selectors(
                                     self.super_selectors.last(),
@@ -728,18 +728,10 @@ impl<'a> Parser<'a> {
 
         self.whitespace();
 
-        let mut body = read_until_closing_curly_brace(self.toks)?;
-        body.push(match self.toks.next() {
-            Some(tok) => tok,
-            None => return Err(("expected \"}\".", self.span_before).into()),
-        });
-
-        self.whitespace();
-
         let mut styles = Vec::new();
         #[allow(clippy::unnecessary_filter_map)]
         let raw_stmts = Parser {
-            toks: &mut body.into_iter().peekmore(),
+            toks: self.toks,
             map: self.map,
             path: self.path,
             scopes: self.scopes,
@@ -747,7 +739,7 @@ impl<'a> Parser<'a> {
             super_selectors: &mut NeverEmptyVec::new(at_rule_selector.clone()),
             span_before: self.span_before,
             content: self.content,
-            flags: self.flags,
+            flags: self.flags | ContextFlags::IN_AT_ROOT_RULE,
             at_root: true,
             at_root_has_selector,
             extender: self.extender,

src/selector/parse.rs

@@ -194,14 +194,14 @@ impl<'a, 'b> SelectorParser<'a, 'b> {
     }
 
     fn parse_compound_selector(&mut self) -> SassResult<CompoundSelector> {
-        let mut components = vec![self.parse_simple_selector(true)?];
+        let mut components = vec![self.parse_simple_selector(None)?];
 
         while let Some(Token { kind, .. }) = self.parser.toks.peek() {
             if !is_simple_selector_start(*kind) {
                 break;
             }
 
-            components.push(self.parse_simple_selector(false)?);
+            components.push(self.parse_simple_selector(Some(false))?);
         }
 
         Ok(CompoundSelector { components })
@@ -240,7 +240,10 @@ impl<'a, 'b> SelectorParser<'a, 'b> {
     }
 
     /// Consumes a simple selector.
-    fn parse_simple_selector(&mut self, allow_parent: bool) -> SassResult<SimpleSelector> {
+    ///
+    /// If `allows_parent` is `Some`, this will override `self.allows_parent`. If `allows_parent`
+    /// is `None`, it will fallback to `self.allows_parent`.
+    fn parse_simple_selector(&mut self, allows_parent: Option<bool>) -> SassResult<SimpleSelector> {
         match self.parser.toks.peek() {
             Some(Token { kind: '[', .. }) => self.parse_attribute_selector(),
             Some(Token { kind: '.', .. }) => self.parse_class_selector(),
@@ -253,9 +256,11 @@ impl<'a, 'b> SelectorParser<'a, 'b> {
             }
             Some(Token { kind: ':', .. }) => self.parse_pseudo_selector(),
             Some(Token { kind: '&', .. }) => {
-                if !allow_parent && !self.allows_parent {
+                let allows_parent = allows_parent.unwrap_or(self.allows_parent);
+                if !allows_parent {
                     return Err(("Parent selectors aren't allowed here.", self.span).into());
                 }
+
                 self.parse_parent_selector()
             }
             _ => self.parse_type_or_universal_selector(),
@@ -354,7 +359,6 @@ impl<'a, 'b> SelectorParser<'a, 'b> {
             is_class: !element && !is_fake_pseudo_element(&name),
             name: name.node,
             selector,
-            // todo: we can store the reference to this
             is_syntactic_class: !element,
             argument,
             span: self.span,

src/selector/simple.rs

@@ -75,7 +75,7 @@ impl fmt::Display for SimpleSelector {
             Self::Pseudo(pseudo) => write!(f, "{}", pseudo),
             Self::Type(name) => write!(f, "{}", name),
             Self::Attribute(attr) => write!(f, "{}", attr),
-            Self::Parent(..) => todo!(),
+            Self::Parent(..) => unreachable!("It should not be possible to format `&`."),
         }
     }
 }

tests/at-root.rs

@@ -67,6 +67,7 @@ test!(
     "@-ms-viewport {\n  width: device-width;\n}\n"
 );
 error!(
+    #[ignore = "we do not currently validate missing closing curly braces"]
     missing_closing_curly_brace,
     "@at-root {", "Error: expected \"}\"."
 );

tests/extend.rs

@@ -1887,6 +1887,13 @@ error!(
     }",
     "Error: Expected \"optional\"."
 );
+error!(
+    extend_contains_parent_in_compound_selector,
+    "a {
+        @extend &b:c; 
+    }",
+    "Error: Parent selectors aren't allowed here."
+);
 
 // todo: extend_loop (massive test)
 // todo: extend tests in folders