use Identifier for SassFunction names

src/builtin/meta.rs

@@ -204,9 +204,9 @@ fn get_function(mut args: CallArgs, scope: &Scope, super_selector: &Selector) ->
         node: name.clone(),
         span: args.span(),
     }) {
-        Ok(f) => SassFunction::UserDefined(Box::new(f), name),
+        Ok(f) => SassFunction::UserDefined(Box::new(f), name.into()),
         Err(..) => match GLOBAL_FUNCTIONS.get(name.as_str()) {
-            Some(f) => SassFunction::Builtin(f.clone(), name),
+            Some(f) => SassFunction::Builtin(f.clone(), name.into()),
             None => return Err((format!("Function not found: {}", name), args.span()).into()),
         },
     };

src/value/sass_function.rs

@@ -14,6 +14,7 @@ use std::fmt;
 use crate::args::CallArgs;
 use crate::atrule::Function;
 use crate::builtin::Builtin;
+use crate::common::Identifier;
 use crate::error::SassResult;
 use crate::scope::Scope;
 use crate::selector::Selector;
@@ -27,15 +28,15 @@ use crate::value::Value;
 /// for use in the builtin function `inspect()`
 #[derive(Clone)]
 pub(crate) enum SassFunction {
-    Builtin(Builtin, String),
-    UserDefined(Box<Function>, String),
+    Builtin(Builtin, Identifier),
+    UserDefined(Box<Function>, Identifier),
 }
 
 impl SassFunction {
     /// Get the name of the function referenced
     ///
     /// Used mainly in debugging and `inspect()`
-    pub fn name(&self) -> &str {
+    pub fn name(&self) -> &Identifier {
         match self {
             Self::Builtin(_, name) => name,
             Self::UserDefined(_, name) => name,