implement builtin sass:math variables

src/builtin/modules/math.rs

@@ -7,7 +7,8 @@ use crate::{
     },
     error::SassResult,
     parse::Parser,
-    value::Value,
+    unit::Unit,
+    value::{Number, Value},
 };
 
 #[cfg(feature = "random")]
@@ -85,4 +86,13 @@ pub(crate) fn declare(f: &mut Module) {
     f.insert_builtin("percentage", percentage);
     #[cfg(feature = "random")]
     f.insert_builtin("random", random);
+
+    f.insert_builtin_var(
+        "pi",
+        Value::Dimension(Number::from(std::f64::consts::PI), Unit::None, true),
+    );
+    f.insert_builtin_var(
+        "e",
+        Value::Dimension(Number::from(std::f64::consts::E), Unit::None, true),
+    );
 }

src/builtin/modules/mod.rs

@@ -37,6 +37,10 @@ impl Module {
         }
     }
 
+    pub fn insert_builtin_var(&mut self, name: &'static str, value: Value) {
+        self.vars.insert(name.into(), value);
+    }
+
     pub fn get_fn(&self, name: Identifier) -> Option<SassFunction> {
         self.functions.get(&name).cloned()
     }

src/parse/value/parse.rs

@@ -214,6 +214,7 @@ impl<'a> Parser<'a> {
     ) -> SassResult<Spanned<IntermediateValue>> {
         Ok(IntermediateValue::Value(
             if matches!(self.toks.peek(), Some(Token { kind: '$', .. })) {
+                self.toks.next();
                 let var = self
                     .parse_identifier_no_interpolation(false)?
                     .map_node(|i| i.into());