[stdlib] Implement formIndex(after:) in all hashed collections

Author: lorentey

stdlib/public/core/Dictionary.swift

@@ -647,6 +647,11 @@ extension Dictionary: Collection {
     return _variant.index(after: i)
   }
 
+  @inlinable
+  public func formIndex(after i: inout Index) {
+    _variant.formIndex(after: &i)
+  }
+
   /// Returns the index for the given key.
   ///
   /// If the given key is found in the dictionary, this method returns an index
@@ -1350,6 +1355,11 @@ extension Dictionary {
       return _variant.index(after: i)
     }
 
+    @inlinable
+    public func formIndex(after i: inout Index) {
+      _variant.formIndex(after: &i)
+    }
+
     @inlinable
     public subscript(position: Index) -> Element {
       return _variant.key(at: position)
@@ -1456,6 +1466,11 @@ extension Dictionary {
       return _variant.index(after: i)
     }
 
+    @inlinable
+    public func formIndex(after i: inout Index) {
+      _variant.formIndex(after: &i)
+    }
+
     @inlinable
     public subscript(position: Index) -> Element {
       // FIXME(accessors): Provide a _read

stdlib/public/core/DictionaryVariant.swift

@@ -189,6 +189,20 @@ extension Dictionary._Variant: _DictionaryBuffer {
     }
   }
 
+  @inlinable
+  internal func formIndex(after index: inout Index) {
+    switch self {
+    case .native(let native):
+      index = native.index(after: index)
+#if _runtime(_ObjC)
+    case .cocoa(let cocoa):
+      cocoaPath()
+      let isUnique = index._isUniquelyReferenced()
+      cocoa.formIndex(after: &index._asCocoa, isUnique: isUnique)
+#endif
+    }
+  }
+
   @inlinable
   @inline(__always)
   internal func index(forKey key: Key) -> Index? {

stdlib/public/core/Set.swift

@@ -340,6 +340,11 @@ extension Set: Collection {
     return _variant.index(after: i)
   }
 
+  @inlinable
+  public func formIndex(after i: inout Index) {
+    _variant.formIndex(after: &i)
+  }
+
   // APINAMING: complexity docs are broadly missing in this file.
 
   /// Returns the index of the given element in the set, or `nil` if the

stdlib/public/core/SetVariant.swift

@@ -182,6 +182,20 @@ extension Set._Variant: _SetBuffer {
     }
   }
 
+  @inlinable
+  internal func formIndex(after index: inout Index) {
+    switch self {
+    case .native(let native):
+      index = native.index(after: index)
+#if _runtime(_ObjC)
+    case .cocoa(let cocoa):
+      cocoaPath()
+      let isUnique = index._isUniquelyReferenced()
+      cocoa.formIndex(after: &index._asCocoa, isUnique: isUnique)
+#endif
+    }
+  }
+
   @inlinable
   @inline(__always)
   internal func index(for element: Element) -> Index? {