track span_before when parsing values

this allows us to remove many panics on invalid input

src/args.rs

@@ -109,7 +109,10 @@ impl CallArgs {
         super_selector: &Selector,
     ) -> Option<SassResult<Spanned<Value>>> {
         match self.0.remove(&CallArg::Named(val.into())) {
-            Some(v) => Some(Value::from_vec(v, scope, super_selector)),
+            Some(v) => {
+                let span_before = v[0].pos;
+                Some(Value::from_vec(v, scope, super_selector, span_before))
+            }
             None => None,
         }
     }
@@ -124,7 +127,10 @@ impl CallArgs {
         super_selector: &Selector,
     ) -> Option<SassResult<Spanned<Value>>> {
         match self.0.remove(&CallArg::Positional(val)) {
-            Some(v) => Some(Value::from_vec(v, scope, super_selector)),
+            Some(v) => {
+                let span_before = v[0].pos;
+                Some(Value::from_vec(v, scope, super_selector, span_before))
+            }
             None => None,
         }
     }
@@ -159,7 +165,8 @@ impl CallArgs {
         };
         args.sort_by(|(a1, _), (a2, _)| a1.cmp(a2));
         for arg in args {
-            vals.push(Value::from_vec(arg.1, scope, super_selector)?);
+            let span_before = arg.1[0].pos;
+            vals.push(Value::from_vec(arg.1, scope, super_selector, span_before)?);
         }
         Ok(vals)
     }

src/atrule/each_rule.rs

@@ -119,7 +119,12 @@ pub(crate) fn parse_each<I: Iterator<Item = Token>>(
         return Err(("Expected \"in\".", i.span).into());
     }
     devour_whitespace(toks);
-    let iter_val = Value::from_vec(read_until_open_curly_brace(toks)?, scope, super_selector)?;
+    let iter_val = Value::from_vec(
+        read_until_open_curly_brace(toks)?,
+        scope,
+        super_selector,
+        i.span,
+    )?;
     let iter = match iter_val.node.eval(iter_val.span)?.node {
         Value::List(v, ..) => v,
         Value::Map(m) => m

src/atrule/for_rule.rs

@@ -133,7 +133,7 @@ pub(crate) fn parse_for<I: Iterator<Item = Token>>(
         }
     }
     devour_whitespace(toks);
-    let from_val = Value::from_vec(from_toks, scope, super_selector)?;
+    let from_val = Value::from_vec(from_toks, scope, super_selector, span_before)?;
     let from = match from_val.node.eval(from_val.span)?.node {
         Value::Dimension(n, _) => match n.to_integer().to_isize() {
             Some(v) => v,
@@ -150,7 +150,7 @@ pub(crate) fn parse_for<I: Iterator<Item = Token>>(
 
     let to_toks = read_until_open_curly_brace(toks)?;
     toks.next();
-    let to_val = Value::from_vec(to_toks, scope, super_selector)?;
+    let to_val = Value::from_vec(to_toks, scope, super_selector, from_val.span)?;
     let to = match to_val.node.eval(to_val.span)?.node {
         Value::Dimension(n, _) => match n.to_integer().to_isize() {
             Some(v) => v,

src/atrule/function.rs

@@ -88,11 +88,7 @@ impl Function {
             let val = match args.get(idx, arg.name.clone(), &scope, super_selector) {
                 Some(v) => v?,
                 None => match arg.default.as_mut() {
-                    Some(v) => Value::from_tokens(
-                        &mut mem::take(v).into_iter().peekmore(),
-                        &scope,
-                        super_selector,
-                    )?,
+                    Some(v) => Value::from_vec(mem::take(v), &scope, super_selector, args.span())?,
                     None => {
                         return Err(
                             (format!("Missing argument ${}.", &arg.name), args.span()).into()
@@ -137,7 +133,7 @@ impl Function {
             match stmt.node {
                 Stmt::AtRule(AtRule::Return(toks)) => {
                     return Ok(Some(
-                        Value::from_vec(toks, &self.scope, super_selector)?.node,
+                        Value::from_vec(toks, &self.scope, super_selector, stmt.span)?.node,
                     ));
                 }
                 Stmt::AtRule(AtRule::For(f)) => {
@@ -169,7 +165,8 @@ impl Function {
                 }
                 Stmt::AtRule(AtRule::While(w)) => {
                     let scope = &mut self.scope.clone();
-                    let mut val = Value::from_vec(w.cond.clone(), scope, super_selector)?;
+                    let mut val =
+                        Value::from_vec(w.cond.clone(), scope, super_selector, stmt.span)?;
                     while val.node.is_true(val.span)? {
                         let while_stmts = eat_stmts(
                             &mut w.body.clone().into_iter().peekmore(),
@@ -181,7 +178,7 @@ impl Function {
                         if let Some(v) = self.call(super_selector, while_stmts)? {
                             return Ok(Some(v));
                         }
-                        val = Value::from_vec(w.cond.clone(), scope, super_selector)?;
+                        val = Value::from_vec(w.cond.clone(), scope, super_selector, val.span)?;
                     }
                 }
                 Stmt::AtRule(AtRule::Each(..)) => todo!("@each in @function"),

src/atrule/if_rule.rs

@@ -42,10 +42,19 @@ impl If {
         devour_whitespace_or_comment(toks)?;
         let mut branches = Vec::new();
         let init_cond_toks = read_until_open_curly_brace(toks)?;
-        if init_cond_toks.is_empty() || toks.next().is_none() {
+        if init_cond_toks.is_empty() {
             return Err(("Expected expression.", span_before).into());
         }
-        let init_cond = Value::from_vec(init_cond_toks, scope, super_selector)?;
+        let span_before = match toks.next() {
+            Some(t) => t.pos,
+            None => return Err(("Expected expression.", span_before).into()),
+        };
+        let init_cond = Value::from_vec(
+            init_cond_toks,
+            scope,
+            super_selector,
+            span_before,
+        )?;
         devour_whitespace_or_comment(toks)?;
         let mut init_toks = read_until_closing_curly_brace(toks)?;
         if let Some(tok) = toks.next() {
@@ -78,11 +87,12 @@ impl If {
                 devour_whitespace(toks);
                 match tok.kind.to_ascii_lowercase() {
                     'i' if toks.next().unwrap().kind.to_ascii_lowercase() == 'f' => {
-                        toks.next();
+                        let pos = toks.next().unwrap().pos;
                         let cond = Value::from_vec(
                             read_until_open_curly_brace(toks)?,
                             scope,
                             super_selector,
+                            pos,
                         )?;
                         toks.next();
                         devour_whitespace(toks);

src/atrule/media.rs

@@ -29,9 +29,9 @@ impl Media {
             match tok.kind {
                 '{' => break,
                 '#' => {
-                    if toks.peek().unwrap().kind == '{' {
+                    if let Some(Token { kind: '{', pos }) = toks.peek().cloned() {
                         toks.next();
-                        let interpolation = parse_interpolation(toks, scope, super_selector)?;
+                        let interpolation = parse_interpolation(toks, scope, super_selector, pos)?;
                         params.push_str(&interpolation.node.to_css_string(interpolation.span)?);
                         continue;
                     } else {

src/atrule/mixin.rs

@@ -79,11 +79,7 @@ impl Mixin {
             let val = match args.get(idx, arg.name.clone(), scope, super_selector) {
                 Some(v) => v?,
                 None => match arg.default.as_mut() {
-                    Some(v) => Value::from_tokens(
-                        &mut std::mem::take(v).into_iter().peekmore(),
-                        scope,
-                        super_selector,
-                    )?,
+                    Some(v) => Value::from_vec(mem::take(v), scope, super_selector, args.span())?,
                     None => {
                         return Err(
                             (format!("Missing argument ${}.", &arg.name), args.span()).into()

src/atrule/mod.rs

@@ -72,6 +72,7 @@ impl AtRule {
                     read_until_semicolon_or_closing_curly_brace(toks)?,
                     scope,
                     super_selector,
+                    kind_span,
                 )?;
 
                 return Err((message.inspect(span)?.to_string(), span.merge(kind_span)).into());
@@ -84,6 +85,7 @@ impl AtRule {
                     read_until_semicolon_or_closing_curly_brace(toks)?,
                     scope,
                     super_selector,
+                    kind_span,
                 )?;
                 span.merge(kind_span);
                 if toks.peek().unwrap().kind == ';' {
@@ -106,6 +108,7 @@ impl AtRule {
                     read_until_semicolon_or_closing_curly_brace(toks)?,
                     scope,
                     super_selector,
+                    kind_span,
                 )?;
                 span.merge(kind_span);
                 if toks.peek().unwrap().kind == ';' {

src/atrule/unknown.rs

@@ -41,9 +41,9 @@ impl UnknownAtRule {
             match tok.kind {
                 '{' => break,
                 '#' => {
-                    if let Some(Token { kind: '{', .. }) = toks.peek() {
+                    if let Some(Token { kind: '{', pos }) = toks.peek().cloned() {
                         toks.next();
-                        let interpolation = parse_interpolation(toks, scope, super_selector)?;
+                        let interpolation = parse_interpolation(toks, scope, super_selector, pos)?;
                         params.push_str(&interpolation.node.to_css_string(interpolation.span)?);
                     } else {
                         params.push(tok.kind);

src/atrule/while_rule.rs

@@ -28,7 +28,7 @@ impl While {
         content: Option<&[Spanned<Stmt>]>,
     ) -> SassResult<Vec<Spanned<Stmt>>> {
         let mut stmts = Vec::new();
-        let mut val = Value::from_vec(self.cond.clone(), scope, super_selector)?;
+        let mut val = Value::from_vec(self.cond.clone(), scope, super_selector, self.cond[0].pos)?;
         let scope = &mut scope.clone();
         while val.node.is_true(val.span)? {
             ruleset_eval(
@@ -39,7 +39,7 @@ impl While {
                 content,
                 &mut stmts,
             )?;
-            val = Value::from_vec(self.cond.clone(), scope, super_selector)?;
+            val = Value::from_vec(self.cond.clone(), scope, super_selector, self.cond[0].pos)?;
         }
         Ok(stmts)
     }

src/lib.rs

@@ -232,7 +232,7 @@ pub(crate) fn eat_expr<I: Iterator<Item = Token>>(
                     String::new(),
                     span_before,
                 )?;
-                let value = Style::parse_value(&mut v, scope, super_selector)?;
+                let value = Style::parse_value(&mut v, scope, super_selector, span_before)?;
                 return Ok(Some(Spanned {
                     node: Expr::Style(Box::new(Style { property, value })),
                     span,
@@ -259,7 +259,7 @@ pub(crate) fn eat_expr<I: Iterator<Item = Token>>(
                         String::new(),
                         tok.pos,
                     )?;
-                    let value = Style::parse_value(&mut v, scope, super_selector)?;
+                    let value = Style::parse_value(&mut v, scope, super_selector, tok.pos)?;
                     return Ok(Some(Spanned {
                         node: Expr::Style(Box::new(Style { property, value })),
                         span,
@@ -298,7 +298,7 @@ pub(crate) fn eat_expr<I: Iterator<Item = Token>>(
                         val,
                         default,
                         global,
-                    } = eat_variable_value(toks, scope, super_selector)?;
+                    } = eat_variable_value(toks, scope, super_selector, name.span)?;
                     if global {
                         insert_global_var(&name.node, val.clone())?;
                     }

src/selector/mod.rs

@@ -233,10 +233,10 @@ impl Selector {
             span = span.merge(tok.pos());
             match tok.kind {
                 '#' => {
-                    if toks.peek().is_some() && toks.peek().unwrap().kind == '{' {
+                    if let Some(Token { kind: '{', pos }) = toks.peek().cloned() {
                         toks.next();
                         string.push_str(
-                            &parse_interpolation(toks, scope, super_selector)?
+                            &parse_interpolation(toks, scope, super_selector, pos)?
                                 .to_css_string(span)?,
                         );
                     } else {

src/style.rs

@@ -49,8 +49,9 @@ impl Style {
         toks: &mut PeekMoreIterator<I>,
         scope: &Scope,
         super_selector: &Selector,
+        span_before: Span,
     ) -> SassResult<Spanned<Value>> {
-        StyleParser::new(scope, super_selector).parse_style_value(toks, scope)
+        StyleParser::new(scope, super_selector).parse_style_value(toks, scope, span_before)
     }
 
     pub fn from_tokens<I: Iterator<Item = Token>>(
@@ -80,9 +81,10 @@ impl<'a> StyleParser<'a> {
         &self,
         toks: &mut PeekMoreIterator<I>,
         scope: &Scope,
+        span_before: Span,
     ) -> SassResult<Spanned<Value>> {
         devour_whitespace(toks);
-        Value::from_tokens(toks, scope, self.super_selector)
+        Value::from_tokens(toks, scope, self.super_selector, span_before)
     }
 
     pub(crate) fn eat_style_group<I: Iterator<Item = Token>>(
@@ -93,7 +95,7 @@ impl<'a> StyleParser<'a> {
     ) -> SassResult<Expr> {
         let mut styles = Vec::new();
         devour_whitespace(toks);
-        while let Some(tok) = toks.peek() {
+        while let Some(tok) = toks.peek().cloned() {
             match tok.kind {
                 '{' => {
                     let span_before = toks.next().unwrap().pos;
@@ -121,7 +123,7 @@ impl<'a> StyleParser<'a> {
                                 continue;
                             }
                         }
-                        let value = self.parse_style_value(toks, scope)?;
+                        let value = self.parse_style_value(toks, scope, span_before)?;
                         match toks.peek().unwrap().kind {
                             '}' => {
                                 styles.push(Style { property, value });
@@ -160,7 +162,7 @@ impl<'a> StyleParser<'a> {
                     }
                 }
                 _ => {
-                    let value = self.parse_style_value(toks, scope)?;
+                    let value = self.parse_style_value(toks, scope, tok.pos)?;
                     let t = toks.peek().ok_or(("expected more input.", value.span))?;
                     match t.kind {
                         '}' => {}

src/stylesheet.rs

@@ -195,14 +195,15 @@ impl<'a> StyleSheetParser<'a> {
                     let whitespace = peek_whitespace(self.lexer);
 
                     match self.lexer.peek() {
-                        Some(Token { kind: ':', .. }) => {
+                        Some(Token { kind: ':', pos }) => {
+                            let pos = *pos;
                             self.lexer
                                 .take(name.node.chars().count() + whitespace + 1)
                                 .for_each(drop);
                             devour_whitespace(self.lexer);
 
                             let VariableDecl { val, default, .. } =
-                                eat_variable_value(self.lexer, &Scope::new(), &Selector::new())?;
+                                eat_variable_value(self.lexer, &Scope::new(), &Selector::new(), pos)?;
 
                             if !(default && global_var_exists(&name.node)) {
                                 insert_global_var(&name.node, val)?;

src/utils/comment_whitespace.rs

@@ -100,16 +100,20 @@ pub(crate) fn eat_comment<I: Iterator<Item = Token>>(
     };
     while let Some(tok) = toks.next() {
         span = span.merge(tok.pos());
-        if tok.kind == '*' && toks.peek().unwrap().kind == '/' {
-            toks.next();
-            break;
-        } else if tok.kind == '#' && toks.peek().unwrap().kind == '{' {
-            toks.next();
-            comment
-                .push_str(&parse_interpolation(toks, scope, super_selector)?.to_css_string(span)?);
-            continue;
+        match (tok.kind, toks.peek()) {
+            ('*', Some(Token { kind: '/', .. })) => {
+                toks.next();
+                break;
+            }
+            ('#', Some(Token { kind: '{', .. })) => {
+                toks.next();
+                comment.push_str(
+                    &parse_interpolation(toks, scope, super_selector, span)?.to_css_string(span)?,
+                );
+                continue;
+            }
+            (..) => comment.push(tok.kind),
         }
-        comment.push(tok.kind);
     }
     devour_whitespace(toks);
     Ok(Spanned {

src/utils/interpolation.rs

@@ -1,6 +1,6 @@
 use std::iter::Iterator;
 
-use codemap::Spanned;
+use codemap::{Span, Spanned};
 
 use peekmore::PeekMoreIterator;
 
@@ -15,8 +15,14 @@ pub(crate) fn parse_interpolation<I: Iterator<Item = Token>>(
     toks: &mut PeekMoreIterator<I>,
     scope: &Scope,
     super_selector: &Selector,
+    span_before: Span,
 ) -> SassResult<Spanned<Value>> {
-    let val = Value::from_vec(read_until_closing_curly_brace(toks)?, scope, super_selector)?;
+    let val = Value::from_vec(
+        read_until_closing_curly_brace(toks)?,
+        scope,
+        super_selector,
+        span_before,
+    )?;
     toks.next();
     Ok(Spanned {
         node: val.node.eval(val.span)?.node.unquote(),

src/utils/strings.rs

@@ -97,11 +97,11 @@ fn interpolated_ident_body<I: Iterator<Item = Token>>(
                 buf.push_str(&escape(toks, false)?);
             }
             '#' => {
-                if let Some(Token { kind: '{', .. }) = toks.peek_forward(1) {
+                if let Some(Token { kind: '{', pos }) = toks.peek_forward(1).cloned() {
                     toks.next();
                     toks.next();
                     // TODO: if ident, interpolate literally
-                    let interpolation = parse_interpolation(toks, scope, super_selector)?;
+                    let interpolation = parse_interpolation(toks, scope, super_selector, pos)?;
                     buf.push_str(&interpolation.node.to_css_string(interpolation.span)?);
                 } else {
                     toks.reset_view();
@@ -207,20 +207,21 @@ pub(crate) fn eat_ident<I: Iterator<Item = Token>>(
     // (first == '#' && scanner.peekChar(1) == $lbrace)
     } else if first == '#' {
         toks.next();
-        if toks.peek().is_none() {
+        let Token { kind, pos } = if let Some(tok) = toks.peek() {
+            *tok
+        } else {
             return Err(("Expected identifier.", pos).into());
-        }
-        let Token { kind, pos } = toks.peek().unwrap();
-        if kind == &'{' {
+        };
+        if kind == '{' {
             toks.next();
             text.push_str(
-                &match parse_interpolation(toks, scope, super_selector)?.node {
+                &match parse_interpolation(toks, scope, super_selector, pos)?.node {
                     Value::String(s, ..) => s,
                     v => v.to_css_string(span)?.into(),
                 },
             );
         } else {
-            return Err(("Expected identifier.", *pos).into());
+            return Err(("Expected identifier.", pos).into());
         }
     } else {
         return Err(("Expected identifier.", pos).into());
@@ -293,9 +294,9 @@ pub(crate) fn parse_quoted_string<I: Iterator<Item = Token>>(
             '"' if q == '"' => break,
             '\'' if q == '\'' => break,
             '#' => {
-                if toks.peek().unwrap().kind == '{' {
+                if let Some(Token { kind: '{', pos }) = toks.peek().cloned() {
                     toks.next();
-                    let interpolation = parse_interpolation(toks, scope, super_selector)?;
+                    let interpolation = parse_interpolation(toks, scope, super_selector, pos)?;
                     s.push_str(&match interpolation.node {
                         Value::String(s, ..) => s,
                         v => v.to_css_string(interpolation.span)?.into(),

src/utils/variables.rs

@@ -1,6 +1,6 @@
 use std::iter::Iterator;
 
-use codemap::Spanned;
+use codemap::{Span, Spanned};
 
 use peekmore::PeekMoreIterator;
 
@@ -34,6 +34,7 @@ pub(crate) fn eat_variable_value<I: Iterator<Item = Token>>(
     toks: &mut PeekMoreIterator<I>,
     scope: &Scope,
     super_selector: &Selector,
+    span_before: Span,
 ) -> SassResult<VariableDecl> {
     devour_whitespace(toks);
     let mut default = false;
@@ -126,6 +127,6 @@ pub(crate) fn eat_variable_value<I: Iterator<Item = Token>>(
         }
     }
     devour_whitespace(toks);
-    let val = Value::from_vec(val_toks, scope, super_selector)?;
+    let val = Value::from_vec(val_toks, scope, super_selector, span_before)?;
     Ok(VariableDecl::new(val, default, global))
 }

src/value/css_function.rs

@@ -1,3 +1,5 @@
+use codemap::{Span, Spanned};
+
 use peekmore::PeekMoreIterator;
 
 use crate::error::SassResult;
@@ -7,6 +9,7 @@ use crate::utils::{
     devour_whitespace, parse_interpolation, peek_escape, peek_until_closing_curly_brace,
     peek_whitespace,
 };
+use crate::value::Value;
 use crate::Token;
 
 pub(crate) fn eat_calc_args<I: Iterator<Item = Token>>(
@@ -26,10 +29,10 @@ pub(crate) fn eat_calc_args<I: Iterator<Item = Token>>(
             }
             '#' => {
                 if toks.peek().is_some() && toks.peek().unwrap().kind == '{' {
-                    let span = toks.next().unwrap().pos();
-                    buf.push_str(
-                        &parse_interpolation(toks, scope, super_selector)?.to_css_string(span)?,
-                    );
+                    let span_before = toks.next().unwrap().pos();
+                    let interpolation =
+                        parse_interpolation(toks, scope, super_selector, span_before)?;
+                    buf.push_str(&interpolation.node.to_css_string(interpolation.span)?);
                 } else {
                     buf.push('#');
                 }
@@ -106,11 +109,11 @@ pub(crate) fn try_eat_url<I: Iterator<Item = Token>>(
         } else if kind == '\\' {
             buf.push_str(&peek_escape(toks)?);
         } else if kind == '#' {
-            let next = toks.peek();
-            if next.is_some() && next.unwrap().kind == '{' {
+            if let Some(Token { kind: '{', pos }) = toks.peek() {
+                let pos = *pos;
                 toks.move_forward(1);
                 peek_counter += 1;
-                let (interpolation, count) = peek_interpolation(toks, scope, super_selector)?;
+                let (interpolation, count) = peek_interpolation(toks, scope, super_selector, pos)?;
                 peek_counter += count;
                 buf.push_str(&match interpolation.node {
                     Value::String(s, ..) => s,
@@ -144,18 +147,16 @@ pub(crate) fn try_eat_url<I: Iterator<Item = Token>>(
     Ok(None)
 }
 
-use crate::value::Value;
-use codemap::Spanned;
-
 fn peek_interpolation<I: Iterator<Item = Token>>(
     toks: &mut PeekMoreIterator<I>,
     scope: &Scope,
     super_selector: &Selector,
+    span_before: Span,
 ) -> SassResult<(Spanned<Value>, usize)> {
     let vec = peek_until_closing_curly_brace(toks);
     let peek_counter = vec.len();
     toks.move_forward(1);
-    let val = Value::from_vec(vec, scope, super_selector)?;
+    let val = Value::from_vec(vec, scope, super_selector, span_before)?;
     Ok((
         Spanned {
             node: val.node.eval(val.span)?.node.unquote(),

src/value/parse.rs

@@ -189,7 +189,12 @@ fn parse_paren(
     let paren_toks = &mut t.node.into_iter().peekmore();
 
     let mut map = SassMap::new();
-    let key = Value::from_vec(read_until_char(paren_toks, ':')?, scope, super_selector)?;
+    let key = Value::from_vec(
+        read_until_char(paren_toks, ':')?,
+        scope,
+        super_selector,
+        t.span,
+    )?;
 
     if paren_toks.peek().is_none() {
         return Ok(Spanned {
@@ -198,7 +203,12 @@ fn parse_paren(
         });
     }
 
-    let val = Value::from_vec(read_until_char(paren_toks, ',')?, scope, super_selector)?;
+    let val = Value::from_vec(
+        read_until_char(paren_toks, ',')?,
+        scope,
+        super_selector,
+        key.span,
+    )?;
 
     map.insert(key.node, val.node);
 
@@ -212,9 +222,19 @@ fn parse_paren(
     let mut span = key.span;
 
     loop {
-        let key = Value::from_vec(read_until_char(paren_toks, ':')?, scope, super_selector)?;
+        let key = Value::from_vec(
+            read_until_char(paren_toks, ':')?,
+            scope,
+            super_selector,
+            span,
+        )?;
         devour_whitespace(paren_toks);
-        let val = Value::from_vec(read_until_char(paren_toks, ',')?, scope, super_selector)?;
+        let val = Value::from_vec(
+            read_until_char(paren_toks, ',')?,
+            scope,
+            super_selector,
+            key.span,
+        )?;
         span = span.merge(val.span);
         devour_whitespace(paren_toks);
         if map.insert(key.node, val.node) {
@@ -387,7 +407,7 @@ fn single_value<I: Iterator<Item = Token>>(
         IntermediateValue::Whitespace => unreachable!(),
         IntermediateValue::Comma => return Err(("Expected expression.", span).into()),
         IntermediateValue::Bracketed(t) => {
-            let v = Value::from_vec(t, scope, super_selector)?;
+            let v = Value::from_vec(t, scope, super_selector, span)?;
             match v.node {
                 Value::List(v, sep, Brackets::None) => Value::List(v, sep, Brackets::Bracketed),
                 v => Value::List(vec![v], ListSeparator::Space, Brackets::Bracketed),
@@ -416,10 +436,11 @@ impl Value {
         toks: &mut PeekMoreIterator<I>,
         scope: &Scope,
         super_selector: &Selector,
+        span_before: Span,
     ) -> SassResult<Spanned<Self>> {
         let span = match toks.peek() {
             Some(Token { pos, .. }) => *pos,
-            None => todo!("Expected expression."),
+            None => return Err(("Expected expression.", span_before).into()),
         };
         devour_whitespace(toks);
         let mut last_was_whitespace = false;
@@ -490,13 +511,15 @@ impl Value {
                         );
                         continue;
                     }
-                    space_separated.push(match Value::from_vec(t, scope, super_selector)?.node {
-                        Value::List(v, sep, Brackets::None) => {
-                            Value::List(v, sep, Brackets::Bracketed).span(val.span)
-                        }
-                        v => Value::List(vec![v], ListSeparator::Space, Brackets::Bracketed)
-                            .span(val.span),
-                    })
+                    space_separated.push(
+                        match Value::from_vec(t, scope, super_selector, val.span)?.node {
+                            Value::List(v, sep, Brackets::None) => {
+                                Value::List(v, sep, Brackets::Bracketed).span(val.span)
+                            }
+                            v => Value::List(vec![v], ListSeparator::Space, Brackets::Bracketed)
+                                .span(val.span),
+                        },
+                    )
                 }
                 IntermediateValue::Paren(t) => {
                     last_was_whitespace = false;
@@ -547,8 +570,17 @@ impl Value {
         toks: Vec<Token>,
         scope: &Scope,
         super_selector: &Selector,
+        span_before: Span,
     ) -> SassResult<Spanned<Value>> {
-        Self::from_tokens(&mut toks.into_iter().peekmore(), scope, super_selector)
+        if toks.is_empty() {
+            return Err(("Expected expression.", span_before).into());
+        }
+        Self::from_tokens(
+            &mut toks.into_iter().peekmore(),
+            scope,
+            super_selector,
+            span_before,
+        )
     }
 
     fn ident<I: Iterator<Item = Token>>(

tests/error.rs

@@ -208,3 +208,19 @@ error!(
     at_else_alone,
     "@else {}", "Error: This at-rule is not allowed here."
 );
+error!(
+    no_expression_for_variable,
+    "a {$color: {ed;}", "Error: Expected expression."
+);
+error!(
+    empty_style_value_no_semicolon,
+    "a {color:}", "Error: Expected expression."
+);
+error!(
+    empty_style_value_semicolon,
+    "a {color:;}", "Error: Expected expression."
+);
+error!(
+    ident_colon_closing_brace,
+    "r:}", "Error: Expected expression."
+);

tests/units.rs

@@ -87,7 +87,7 @@ test!(
 test!(
     non_ascii_numeric_interpreted_as_unit,
     "a {\n  color: 2߄;\n}\n",
-    "@charset \"UTF-8\";\na {\n  color: 2߄;\n}"
+    "@charset \"UTF-8\";\na {\n  color: 2߄;\n}\n"
 );
 error!(
     display_single_mul,