remove superfluous allocations when resolving idents

src/builtin/list.rs

@@ -142,7 +142,7 @@ fn append(mut args: CallArgs, scope: &Scope, super_selector: &Selector) -> SassR
         2,
         "separator" = Value::Ident(InternedString::get_or_intern("auto"), QuoteKind::None)
     ) {
-        Value::Ident(s, ..) => match s.resolve().as_str() {
+        Value::Ident(s, ..) => match s.resolve_ref() {
             "auto" => sep,
             "comma" => ListSeparator::Comma,
             "space" => ListSeparator::Space,
@@ -190,7 +190,7 @@ fn join(mut args: CallArgs, scope: &Scope, super_selector: &Selector) -> SassRes
         2,
         "separator" = Value::Ident(InternedString::get_or_intern("auto"), QuoteKind::None)
     ) {
-        Value::Ident(s, ..) => match s.resolve().as_str() {
+        Value::Ident(s, ..) => match s.resolve_ref() {
             "auto" => {
                 if list1.is_empty() || (list1.len() == 1 && sep1 == ListSeparator::Space) {
                     sep2
@@ -227,7 +227,7 @@ fn join(mut args: CallArgs, scope: &Scope, super_selector: &Selector) -> SassRes
         3,
         "bracketed" = Value::Ident(InternedString::get_or_intern("auto"), QuoteKind::None)
     ) {
-        Value::Ident(s, ..) => match s.resolve().as_str() {
+        Value::Ident(s, ..) => match s.resolve_ref() {
             "auto" => brackets,
             _ => Brackets::Bracketed,
         },

src/builtin/meta.rs

@@ -28,7 +28,7 @@ fn feature_exists(
 ) -> SassResult<Value> {
     args.max_args(1)?;
     match arg!(args, scope, super_selector, 0, "feature") {
-        Value::Ident(s, _) => Ok(match s.resolve().as_str() {
+        Value::Ident(s, _) => Ok(match s.resolve_ref() {
             // A local variable will shadow a global variable unless
             // `!global` is used.
             "global-variable-shadowing" => Value::True,
@@ -207,7 +207,7 @@ fn get_function(mut args: CallArgs, scope: &Scope, super_selector: &Selector) ->
         span: args.span(),
     }) {
         Ok(f) => SassFunction::UserDefined(Box::new(f), name.into()),
-        Err(..) => match GLOBAL_FUNCTIONS.get(&name.resolve().as_str()) {
+        Err(..) => match GLOBAL_FUNCTIONS.get(&name.resolve_ref()) {
             Some(f) => SassFunction::Builtin(f.clone(), name.into()),
             None => return Err((format!("Function not found: {}", name), args.span()).into()),
         },

src/common.rs

@@ -127,7 +127,7 @@ pub(crate) struct Identifier(InternedString);
 impl Into<Identifier> for InternedString {
     fn into(self) -> Identifier {
         Identifier(InternedString::get_or_intern(
-            self.resolve().replace('_', "-"),
+            self.resolve_ref().replace('_', "-"),
         ))
     }
 }

src/interner.rs

@@ -39,13 +39,19 @@ impl InternedString {
         Self(STRINGS.with(|interner| interner.borrow_mut().get_or_intern(s)))
     }
 
-    pub fn resolve(&self) -> String {
+    pub fn resolve(self) -> String {
         STRINGS.with(|interner| interner.borrow().resolve(&self.0).to_string())
     }
 
     pub fn is_empty(self) -> bool {
         EMPTY_STRING.with(|f| self == **f)
     }
+
+    pub fn resolve_ref<'a>(self) -> &'a str {
+        unsafe {
+            STRINGS.with(|interner| &(*(interner.as_ptr()).as_ref().unwrap().resolve(&self.0)))
+        }
+    }
 }
 
 impl Display for InternedString {

src/value/mod.rs

@@ -252,7 +252,7 @@ impl Value {
 
     pub fn is_special_function(&self) -> bool {
         match self {
-            Self::Ident(s, QuoteKind::None) => is_special_function(&s.resolve()),
+            Self::Ident(s, QuoteKind::None) => is_special_function(s.resolve_ref()),
             _ => false,
         }
     }

src/value/ops.rs

@@ -395,7 +395,7 @@ impl Value {
             Self::UnaryOp(..) | Self::Paren(..) => self.eval(span)?.node.add(other, span)?,
             Self::Ident(text, quotes) => match other {
                 Self::Ident(text2, ..) => Self::Ident(
-                    InternedString::get_or_intern(text.resolve() + &text2.resolve()),
+                    InternedString::get_or_intern(text.resolve() + text2.resolve_ref()),
                     quotes,
                 ),
                 _ => Value::Ident(