respect $module argument passed to function-exists

src/builtin/functions/meta.rs

@@ -173,16 +173,38 @@ pub(crate) fn mixin_exists(mut args: CallArgs, parser: &mut Parser<'_>) -> SassR
 
 pub(crate) fn function_exists(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult<Value> {
     args.max_args(2)?;
-    match args.get_err(0, "name")? {
-        Value::String(s, _) => Ok(Value::bool(
-            parser.scopes.fn_exists(s.into(), parser.global_scope),
-        )),
-        v => Err((
-            format!("$name: {} is not a string.", v.inspect(args.span())?),
-            args.span(),
-        )
-            .into()),
-    }
+
+    let name: Identifier = match args.get_err(0, "name")? {
+        Value::String(s, _) => s.into(),
+        v => {
+            return Err((
+                format!("$name: {} is not a string.", v.inspect(args.span())?),
+                args.span(),
+            )
+                .into())
+        }
+    };
+
+    let module = match args.default_arg(1, "module", Value::Null)? {
+        Value::String(s, _) => Some(s),
+        Value::Null => None,
+        v => {
+            return Err((
+                format!("$module: {} is not a string.", v.inspect(args.span())?),
+                args.span(),
+            )
+                .into())
+        }
+    };
+
+    Ok(Value::bool(if let Some(module_name) = module {
+        parser
+            .modules
+            .get(module_name.into(), args.span())?
+            .fn_exists(name)
+    } else {
+        parser.scopes.fn_exists(name, parser.global_scope)
+    }))
 }
 
 pub(crate) fn get_function(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult<Value> {

src/builtin/modules/mod.rs

@@ -191,6 +191,10 @@ impl Module {
         !name.as_str().starts_with('-') && self.scope.mixin_exists(name)
     }
 
+    pub fn fn_exists(&self, name: Identifier) -> bool {
+        !name.as_str().starts_with('-') && self.scope.fn_exists(name)
+    }
+
     pub fn insert_builtin(
         &mut self,
         name: &'static str,

src/scope.rs

@@ -67,7 +67,7 @@ impl Scope {
         self.functions.insert(s, v)
     }
 
-    fn fn_exists(&self, name: Identifier) -> bool {
+    pub fn fn_exists(&self, name: Identifier) -> bool {
         if self.functions.is_empty() {
             return false;
         }

tests/meta-module.rs

@@ -18,6 +18,16 @@ test!(
     "@use 'sass:math';\na {\n  color: global-variable-exists(pi, $module: math);\n}\n",
     "a {\n  color: true;\n}\n"
 );
+test!(
+    fn_exists_builtin,
+    "@use 'sass:math';\na {\n  color: function-exists(acos, $module: math);\n}\n",
+    "a {\n  color: true;\n}\n"
+);
+error!(
+    fn_exists_module_dne,
+    "a {\n  color: function-exists(c, d);\n}\n",
+    "Error: There is no module with the namespace \"d\"."
+);
 
 #[test]
 fn mixin_exists_module() {