implement builtin function global-var-exists

src/builtin/meta.rs

@@ -2,6 +2,7 @@ use std::collections::HashMap;
 
 use super::{Builtin, GLOBAL_FUNCTIONS};
 use crate::common::QuoteKind;
+use crate::scope::global_var_exists;
 use crate::unit::Unit;
 use crate::value::Value;
 
@@ -89,6 +90,16 @@ pub(crate) fn register(f: &mut HashMap<String, Builtin>) {
             }
         }),
     );
+    f.insert(
+        "global-variable-exists".to_owned(),
+        Box::new(|args, _| {
+            max_args!(args, 1);
+            match arg!(args, 0, "name") {
+                Value::Ident(s, _) => Ok(Value::bool(global_var_exists(&s))),
+                v => Err(format!("$name: {} is not a string.", v).into()),
+            }
+        }),
+    );
     f.insert(
         "mixin-exists".to_owned(),
         Box::new(|args, scope| {

src/scope.rs

@@ -14,6 +14,10 @@ pub(crate) fn get_global_var(s: &str) -> SassResult<Value> {
     })
 }
 
+pub fn global_var_exists(v: &str) -> bool {
+    GLOBAL_SCOPE.with(|scope| scope.borrow().var_exists(v))
+}
+
 pub(crate) fn get_global_fn(s: &str) -> SassResult<Function> {
     GLOBAL_SCOPE.with(|scope| match scope.borrow().functions().get(s) {
         Some(v) => Ok(v.clone()),