Make bridged empty NSDictionary and NSSet instances bridge to the empty singletons

Author: Catfish-Man

stdlib/public/core/NativeDictionary.swift

@@ -52,13 +52,17 @@ internal struct _NativeDictionary<Key: Hashable, Value> {
 
   @inlinable
   internal init(_ cocoa: __owned __CocoaDictionary, capacity: Int) {
-    _internalInvariant(cocoa.count <= capacity)
-    self._storage =
-      _DictionaryStorage<Key, Value>.convert(cocoa, capacity: capacity)
-    for (key, value) in cocoa {
-      insertNew(
-        key: _forceBridgeFromObjectiveC(key, Key.self),
-        value: _forceBridgeFromObjectiveC(value, Value.self))
+    if capacity == 0 {
+      self._storage = __RawDictionaryStorage.empty
+    } else {
+      _internalInvariant(cocoa.count <= capacity)
+      self._storage =
+        _DictionaryStorage<Key, Value>.convert(cocoa, capacity: capacity)
+      for (key, value) in cocoa {
+        insertNew(
+          key: _forceBridgeFromObjectiveC(key, Key.self),
+          value: _forceBridgeFromObjectiveC(value, Value.self))
+      }
     }
   }
 #endif

stdlib/public/core/NativeSet.swift

@@ -51,11 +51,15 @@ internal struct _NativeSet<Element: Hashable> {
 
   @inlinable
   internal init(_ cocoa: __owned __CocoaSet, capacity: Int) {
-    _internalInvariant(cocoa.count <= capacity)
-    self._storage = _SetStorage<Element>.convert(cocoa, capacity: capacity)
-    for element in cocoa {
-      let nativeElement = _forceBridgeFromObjectiveC(element, Element.self)
-      insertNew(nativeElement, isUnique: true)
+    if capacity == 0 {
+      self._storage = __RawSetStorage.empty
+    } else {
+      _internalInvariant(cocoa.count <= capacity)
+      self._storage = _SetStorage<Element>.convert(cocoa, capacity: capacity)
+      for element in cocoa {
+        let nativeElement = _forceBridgeFromObjectiveC(element, Element.self)
+        insertNew(nativeElement, isUnique: true)
+      }
     }
   }
 #endif