Add custom global variables

crates/compiler/src/evaluate/visitor.rs

@@ -2566,7 +2566,7 @@ impl<'a> Visitor<'a> {
             AstExpr::Paren(expr) => self.visit_expr((*expr).clone())?,
             AstExpr::ParentSelector => self.visit_parent_selector(),
             AstExpr::UnaryOp(op, expr, span) => self.visit_unary_op(op, (*expr).clone(), span)?,
-            AstExpr::Variable { name, namespace } => self.env.get_var(name, namespace)?,
+            AstExpr::Variable { name, namespace } => self.visit_variable(name, namespace)?,
             AstExpr::Supports(condition) => Value::String(
                 self.visit_supports_condition((*condition).clone())?,
                 QuoteKind::None,
@@ -3079,4 +3079,22 @@ impl<'a> Visitor<'a> {
 
         Ok(None)
     }
+
+    fn visit_variable(
+        &mut self,
+        name: Spanned<Identifier>,
+        namespace: Option<Spanned<Identifier>>,
+    ) -> SassResult<Value> {
+        self.env.get_var(name, namespace).or_else(|e| {
+            if namespace.is_none() {
+                if let Some(v) = self.options.custom_vars.get(name.as_str()) {
+                    Ok(v.clone())
+                } else {
+                    Err(e)
+                }
+            } else {
+                Err(e)
+            }
+        })
+    }
 }

crates/compiler/src/options.rs

@@ -3,7 +3,7 @@ use std::{
     path::{Path, PathBuf},
 };
 
-use crate::{builtin::Builtin, Fs, Logger, StdFs, StdLogger};
+use crate::{builtin::Builtin, value::Value, Fs, Logger, StdFs, StdLogger};
 
 /// Configuration for Sass compilation
 ///
@@ -20,6 +20,7 @@ pub struct Options<'a> {
     pub(crate) quiet: bool,
     pub(crate) input_syntax: Option<InputSyntax>,
     pub(crate) custom_fns: HashMap<String, Builtin>,
+    pub(crate) custom_vars: HashMap<String, Value>,
 }
 
 impl Default for Options<'_> {
@@ -35,6 +36,7 @@ impl Default for Options<'_> {
             quiet: false,
             input_syntax: None,
             custom_fns: HashMap::new(),
+            custom_vars: HashMap::new(),
         }
     }
 }
@@ -177,6 +179,13 @@ impl<'a> Options<'a> {
         self
     }
 
+    #[must_use]
+    #[inline]
+    pub fn add_custom_var<S: Into<String>>(mut self, name: S, value: Value) -> Self {
+        self.custom_vars.insert(name.into(), value);
+        self
+    }
+
     pub(crate) fn is_compressed(&self) -> bool {
         matches!(self.style, OutputStyle::Compressed)
     }

crates/lib/tests/custom-global-variable.rs

@@ -0,0 +1,20 @@
+use grass::{from_string, Options};
+use grass_compiler::sass_value::{QuoteKind, Value};
+
+#[test]
+fn lookup_custom_global_variable() {
+    let opts = Options::default().add_custom_var("x", Value::String("foo".into(), QuoteKind::None));
+    assert_eq!(
+        from_string("a {\n  test: $x;\n}\n", &opts).ok(),
+        Some("a {\n  test: foo;\n}\n".to_owned())
+    );
+}
+
+#[test]
+fn user_defined_takes_precedence_over_global_variable() {
+    let opts = Options::default().add_custom_var("x", Value::String("foo".into(), QuoteKind::None));
+    assert_eq!(
+        from_string("$x: bar;\na {\n  test: $x;\n}\n", &opts).ok(),
+        Some("a {\n  test: bar;\n}\n".to_owned())
+    );
+}