more robust handling of empty input after resolving interpolation

src/ast/media.rs

@@ -54,7 +54,7 @@ impl MediaQuery {
     }
 
     pub fn parse_list(list: &str, span: Span) -> SassResult<Vec<Self>> {
-        let toks = Lexer::new(list.chars().map(|x| Token::new(span, x)).collect());
+        let toks = Lexer::new(list.chars().map(|x| Token::new(span, x)).collect(), span);
 
         MediaQueryParser::new(toks).parse()
     }

src/ast/stmt.rs

@@ -204,7 +204,7 @@ pub(crate) struct AstExtendRule {
 #[derive(Debug, Clone)]
 pub(crate) struct AstAtRootRule {
     pub children: Vec<AstStmt>,
-    pub query: Option<Interpolation>,
+    pub query: Option<Spanned<Interpolation>>,
     #[allow(unused)]
     pub span: Span,
 }

src/evaluate/visitor.rs

@@ -969,14 +969,14 @@ impl<'a> Visitor<'a> {
 
     fn visit_at_root_rule(&mut self, mut at_root_rule: AstAtRootRule) -> SassResult<Option<Value>> {
         let query = match at_root_rule.query.clone() {
-            Some(val) => {
-                let resolved = self.perform_interpolation(val, true)?;
+            Some(query) => {
+                let resolved = self.perform_interpolation(query.node, true)?;
+
+                let span = query.span;
 
                 let query_toks = Lexer::new(
-                    resolved
-                        .chars()
-                        .map(|x| Token::new(self.span_before, x))
-                        .collect(),
+                    resolved.chars().map(|x| Token::new(span, x)).collect(),
+                    span,
                 );
 
                 AtRootQueryParser::new(query_toks).parse()?
@@ -1137,7 +1137,10 @@ impl<'a> Visitor<'a> {
         allows_placeholder: bool,
         span: Span,
     ) -> SassResult<SelectorList> {
-        let sel_toks = Lexer::new(selector_text.chars().map(|x| Token::new(span, x)).collect());
+        let sel_toks = Lexer::new(
+            selector_text.chars().map(|x| Token::new(span, x)).collect(),
+            span,
+        );
 
         SelectorParser::new(sel_toks, allows_parent, allows_placeholder, span).parse()
     }
@@ -2742,11 +2745,10 @@ impl<'a> Visitor<'a> {
         let selector_text = self.interpolation_to_value(ruleset_selector, true, true)?;
 
         if self.flags.in_keyframes() {
+            let span = ruleset.selector_span;
             let sel_toks = Lexer::new(
-                selector_text
-                    .chars()
-                    .map(|x| Token::new(self.span_before, x))
-                    .collect(),
+                selector_text.chars().map(|x| Token::new(span, x)).collect(),
+                span,
             );
             let parsed_selector =
                 KeyframesSelectorParser::new(sel_toks).parse_keyframes_selector()?;

src/lexer.rs

@@ -7,8 +7,11 @@ use crate::Token;
 const FORM_FEED: char = '\x0C';
 
 #[derive(Debug, Clone)]
+// todo: remove lifetime as Cow is now superfluous
 pub(crate) struct Lexer<'a> {
     buf: Cow<'a, [Token]>,
+    /// The span to be used in the case that `buf` is empty
+    empty_span: Span,
     cursor: usize,
 }
 
@@ -37,19 +40,23 @@ impl<'a> Lexer<'a> {
     }
 
     pub fn prev_span(&self) -> Span {
-        self.buf
-            .get(self.cursor.saturating_sub(1))
-            .copied()
-            .unwrap_or_else(|| self.buf.last().copied().unwrap())
-            .pos
+        match self.buf.get(self.cursor.saturating_sub(1)) {
+            Some(tok) => tok.pos,
+            None => match self.buf.last() {
+                Some(tok) => tok.pos,
+                None => self.empty_span,
+            },
+        }
     }
 
     pub fn current_span(&self) -> Span {
-        self.buf
-            .get(self.cursor)
-            .copied()
-            .unwrap_or_else(|| self.buf.last().copied().unwrap())
-            .pos
+        match self.buf.get(self.cursor) {
+            Some(tok) => tok.pos,
+            None => match self.buf.last() {
+                Some(tok) => tok.pos,
+                None => self.empty_span,
+            },
+        }
     }
 
     pub fn peek(&self) -> Option<Token> {
@@ -131,13 +138,14 @@ impl<'a> Lexer<'a> {
         }
         .collect();
 
-        Self::new(buf)
+        Self::new(buf, file.span.subspan(0, 0))
     }
 
-    pub fn new(buf: Vec<Token>) -> Self {
+    pub fn new(buf: Vec<Token>, empty_span: Span) -> Self {
         Lexer {
             buf: Cow::Owned(buf),
             cursor: 0,
+            empty_span,
         }
     }
 }

src/parse/stylesheet.rs

@@ -325,12 +325,17 @@ pub(crate) trait StylesheetParser<'a>: BaseParser<'a> + Sized {
 
     fn parse_at_root_rule(&mut self, start: usize) -> SassResult<AstStmt> {
         Ok(AstStmt::AtRootRule(if self.toks_mut().next_char_is('(') {
+            let query_start = self.toks().cursor();
             let query = self.parse_at_root_query()?;
+            let query_span = self.toks_mut().span_from(query_start);
             self.whitespace()?;
             let children = self.with_children(Self::parse_statement)?.node;
 
             AstAtRootRule {
-                query: Some(query),
+                query: Some(Spanned {
+                    node: query,
+                    span: query_span,
+                }),
                 children,
                 span: self.toks_mut().span_from(start),
             }
@@ -1521,6 +1526,7 @@ pub(crate) trait StylesheetParser<'a>: BaseParser<'a> + Sized {
                 .chars()
                 .map(|x| Token::new(self.span_before(), x))
                 .collect(),
+            self.span_before(),
         );
 
         // if namespace is empty, avoid attempting to parse an identifier from

tests/at-root.rs

@@ -279,3 +279,12 @@ error!(
     }",
     "Error: @extend may only be used within style rules."
 );
+error!(
+    selector_is_empty_after_interpolation_is_resolved,
+    "@at-root #{null} {}", "Error: expected selector."
+);
+error!(
+    // todo: dart-sass gives error r#"Error: Expected "with" or "without"."#
+    query_is_empty_parens_after_interpolation_is_resolved,
+    "@at-root (#{null}) {}", r#"Error: Expected "without"."#
+);

tests/keyframes.rs

@@ -327,6 +327,13 @@ error!(
     }",
     r#"Error: Expected digit."#
 );
+error!(
+    selector_is_empty_after_interpolation_is_resolved,
+    "@keyframes foo {
+        #{null} {}
+    }",
+    r#"Error: Expected number."#
+);
 
 // todo: span for this
 // @keyframes foo {

tests/media.rs

@@ -570,3 +570,8 @@ error!(
     }"#,
     "Error: expected no more input."
 );
+error!(
+    empty_query_after_resolving_interpolation,
+    "@media #{null} {}",
+    "Error: expected no more input."
+);