fix: deno_resolver crate without 'sync' feature (#27403)

resolvers/deno/sync.rs

@@ -13,21 +13,35 @@ mod inner {
 
 #[cfg(not(feature = "sync"))]
 mod inner {
+  use std::cell::Ref;
+  use std::cell::RefCell;
+  use std::collections::HashMap;
+  use std::hash::BuildHasher;
+  use std::hash::Hash;
   use std::hash::RandomState;
   pub use std::rc::Rc as MaybeArc;
 
   // Wrapper struct that exposes a subset of `DashMap` API.
-  #[derive(Default)]
-  struct MaybeDashMap<K, V, S = RandomState>(RefCell<HashMap<K, V, S>>);
+  #[derive(Debug)]
+  pub struct MaybeDashMap<K, V, S = RandomState>(RefCell<HashMap<K, V, S>>);
+
+  impl<K, V, S> Default for MaybeDashMap<K, V, S>
+  where
+    K: Eq + Hash,
+    S: Default + BuildHasher + Clone,
+  {
+    fn default() -> Self {
+      Self(RefCell::new(Default::default()))
+    }
+  }
 
-  impl MaybeDashMap<K, V, S> {
-    pub fn get(&'a self, key: &K) -> Option<&'a V> {
-      let inner = self.0.borrow();
-      inner.get(key)
+  impl<K: Eq + Hash, V, S: BuildHasher> MaybeDashMap<K, V, S> {
+    pub fn get<'a>(&'a self, key: &K) -> Option<Ref<'a, V>> {
+      Ref::filter_map(self.0.borrow(), |map| map.get(key)).ok()
     }
 
     pub fn insert(&self, key: K, value: V) -> Option<V> {
-      let inner = self.0.borrow_mut();
+      let mut inner = self.0.borrow_mut();
       inner.insert(key, value)
     }
   }