implement unary ops + and -

src/value/mod.rs

@@ -20,6 +20,7 @@ pub(crate) enum Value {
     Dimension(Number, Unit),
     List(Vec<Value>, ListSeparator),
     Color(Color),
+    UnaryOp(Op, Box<Value>),
     BinaryOp(Box<Value>, Op, Box<Value>),
     Paren(Box<Value>),
     Ident(String, QuoteKind),
@@ -45,7 +46,7 @@ impl Display for Value {
                     .join(sep.as_str())
             ),
             Self::Color(c) => write!(f, "{}", c),
-            Self::BinaryOp(..) => write!(
+            Self::UnaryOp(..) | Self::BinaryOp(..) => write!(
                 f,
                 "{}",
                 match self.clone().eval() {
@@ -148,6 +149,13 @@ impl Value {
         })
     }
 
+    pub fn unary_op_plus(self) -> SassResult<Self> {
+        Ok(match self.eval()? {
+            v @ Value::Dimension(..) => v,
+            v => Value::Ident(format!("+{}", v), QuoteKind::None),
+        })
+    }
+
     pub fn eval(self) -> SassResult<Self> {
         match self {
             Self::BinaryOp(lhs, op, rhs) => match op {
@@ -161,6 +169,11 @@ impl Value {
                 _ => Ok(Self::BinaryOp(lhs, op, rhs)),
             },
             Self::Paren(v) => v.eval(),
+            Self::UnaryOp(op, val) => match op {
+                Op::Plus => val.unary_op_plus(),
+                Op::Minus => -*val,
+                _ => unreachable!(),
+            },
             _ => Ok(self),
         }
     }

src/value/ops.rs

@@ -1,4 +1,4 @@
-use std::ops::{Add, Div, Mul, Rem, Sub};
+use std::ops::{Add, Div, Mul, Neg, Rem, Sub};
 
 use crate::common::QuoteKind;
 use crate::error::SassResult;
@@ -70,7 +70,7 @@ impl Add for Value {
                 Self::List(..) => Value::Ident(format!("{}{}", c, other), QuoteKind::None),
                 _ => return Err(format!("Undefined operation \"{} + {}\".", c, other).into()),
             },
-            Self::BinaryOp(..) | Self::Paren(..) => (self.eval()? + other)?,
+            Self::UnaryOp(..) | Self::BinaryOp(..) | Self::Paren(..) => (self.eval()? + other)?,
             Self::Ident(s1, quotes1) => match other {
                 Self::Ident(s2, quotes2) => {
                     let quotes = match (quotes1, quotes2) {
@@ -104,7 +104,7 @@ impl Add for Value {
                     Value::Ident(format!("{}{}", s1, c), quotes)
                 }
                 Self::List(..) => Value::Ident(format!("{}{}", s1, other), quotes1),
-                Self::BinaryOp(..) | Self::Paren(..) => todo!(),
+                Self::UnaryOp(..) | Self::BinaryOp(..) | Self::Paren(..) => todo!(),
             },
             Self::List(..) => match other {
                 Self::Ident(s, q) => {
@@ -417,3 +417,14 @@ impl Rem for Value {
         })
     }
 }
+
+impl Neg for Value {
+    type Output = SassResult<Self>;
+
+    fn neg(self) -> Self::Output {
+        Ok(match self.eval()? {
+            Value::Dimension(n, u) => Value::Dimension(-n, u),
+            v => Value::Ident(format!("-{}", v), QuoteKind::None),
+        })
+    }
+}

src/value/parse.rs

@@ -292,7 +292,17 @@ impl Value {
             TokenKind::Keyword(Keyword::From(s)) => Ok(Value::Ident(s, QuoteKind::None)),
             TokenKind::Keyword(Keyword::Through(s)) => Ok(Value::Ident(s, QuoteKind::None)),
             TokenKind::Keyword(Keyword::To(s)) => Ok(Value::Ident(s, QuoteKind::None)),
-            TokenKind::AtRule(_) => return Err("expected \";\".".into()),
+            TokenKind::AtRule(_) => Err("expected \";\".".into()),
+            TokenKind::Op(Op::Plus) | TokenKind::Symbol(Symbol::Plus) => {
+                devour_whitespace_or_comment(toks);
+                let v = Self::_from_tokens(toks, scope, super_selector)?;
+                Ok(Value::UnaryOp(Op::Plus, Box::new(v)))
+            }
+            TokenKind::Op(Op::Minus) | TokenKind::Symbol(Symbol::Minus) => {
+                devour_whitespace_or_comment(toks);
+                let v = Self::_from_tokens(toks, scope, super_selector)?;
+                Ok(Value::UnaryOp(Op::Minus, Box::new(v)))
+            }
             v => {
                 dbg!(v);
                 panic!("Unexpected token in value parsing")

tests/unary.rs

@@ -0,0 +1,47 @@
+#![cfg(test)]
+
+#[macro_use]
+mod macros;
+
+test!(unary_pos_unquoted_ident, "a {\n  color: +foo;\n}\n");
+test!(
+    unary_pos_whitespace,
+    "a {\n  color: +     foo;\n}\n",
+    "a {\n  color: +foo;\n}\n"
+);
+test!(unary_pos_dblquoted_ident, "a {\n  color: +\"foo\";\n}\n");
+test!(
+    unary_pos_sglquoted_ident,
+    "a {\n  color: +'foo';\n}\n",
+    "a {\n  color: +\"foo\";\n}\n"
+);
+test!(unary_pos_color, "a {\n  color: +\"foo\";\n}\n");
+test!(
+    unary_pos_number,
+    "a {\n  color: +1px;\n}\n",
+    "a {\n  color: 1px;\n}\n"
+);
+test!(
+    unary_pos_in_list,
+    "a {\n  color: bar,+ \"bar\" - foo;\n}\n",
+    "a {\n  color: bar, +\"bar\"-foo;\n}\n"
+);
+test!(unary_neg_unquoted_ident, "a {\n  color: -foo;\n}\n");
+test!(unary_neg_dblquoted_ident, "a {\n  color: -\"foo\";\n}\n");
+test!(
+    unary_neg_sglquoted_ident,
+    "a {\n  color: -'foo';\n}\n",
+    "a {\n  color: -\"foo\";\n}\n"
+);
+test!(unary_neg_color, "a {\n  color: -\"foo\";\n}\n");
+test!(unary_neg_number, "a {\n  color: -1px;\n}\n");
+test!(
+    unary_neg_whitespace,
+    "a {\n  color: - 1px;\n}\n",
+    "a {\n  color: -1px;\n}\n"
+);
+test!(
+    unary_neg_number_type,
+    "a {\n  color: type-of(- 1px);\n}\n",
+    "a {\n  color: number;\n}\n"
+);