[stdlib] Change the signature of Dictionary’s bulk initializer (swiftlang#23758)

The initializer was originally introduced without proper availability; in swiftlang#23643, we fixed this by applying the `@_alwaysEmitIntoClient` attribute. However, this had the unfortunate side-effect that the symbol disappeared from `libswiftCore.dylib`, which somehow confuses some simulator builds.

Try to figure out what’s happening by replacing the third closure argument with an integer return value. This changes the mangled name of the bulk initializer, which should make it more obvious how/why these builds fail.

rdar://problem/49479386

Author: lorentey

stdlib/public/Darwin/Foundation/NSDictionary.swift

@@ -238,7 +238,7 @@ extension Dictionary : _ObjectiveCBridgeable {
       let handleDuplicates = (Key.self == String.self)
 
       result = Dictionary(_unsafeUninitializedCapacity: numElems,
-        allowingDuplicates: handleDuplicates) { (keys, vals, outCount) in
+        allowingDuplicates: handleDuplicates) { keys, vals in
 
         let objectKeys = UnsafeMutableRawPointer(mutating:
           keys.baseAddress!).assumingMemoryBound(to: AnyObject.self)
@@ -253,7 +253,7 @@ extension Dictionary : _ObjectiveCBridgeable {
         _forceBridge(objectKeys, count: numElems, to: Key.self)
         _forceBridge(objectVals, count: numElems, to: Value.self)
 
-        outCount = numElems
+        return numElems
       }
     }
   }
@@ -293,7 +293,7 @@ extension Dictionary : _ObjectiveCBridgeable {
     let handleDuplicates = (Key.self == String.self)
 
     let tmpResult = Dictionary(_unsafeUninitializedCapacity: numElems,
-      allowingDuplicates: handleDuplicates) { (keys, vals, outCount) in
+      allowingDuplicates: handleDuplicates) { keys, vals in
 
       let objectKeys = UnsafeMutableRawPointer(mutating:
         keys.baseAddress!).assumingMemoryBound(to: AnyObject.self)
@@ -314,7 +314,7 @@ extension Dictionary : _ObjectiveCBridgeable {
             Key.self)).deinitialize(count: numElems)
         }
       }
-      outCount = success ? numElems : 0
+      return success ? numElems : 0
     }
 
     result = success ? tmpResult : nil

stdlib/public/core/DictionaryBuilder.swift

@@ -72,16 +72,14 @@ extension Dictionary {
   ///     closure must return the count of the initialized elements, starting at
   ///     the beginning of the buffer.
   @_alwaysEmitIntoClient // Introduced in 5.1
-  @inlinable
   public // SPI(Foundation)
   init(
     _unsafeUninitializedCapacity capacity: Int,
     allowingDuplicates: Bool,
     initializingWith initializer: (
       _ keys: UnsafeMutableBufferPointer<Key>,
-      _ values: UnsafeMutableBufferPointer<Value>,
-      _ initializedCount: inout Int
-    ) -> Void
+      _ values: UnsafeMutableBufferPointer<Value>
+    ) -> Int
   ) {
     self.init(_native: _NativeDictionary(
         _unsafeUninitializedCapacity: capacity,
@@ -92,23 +90,19 @@ extension Dictionary {
 
 extension _NativeDictionary {
   @_alwaysEmitIntoClient // Introduced in 5.1
-  @inlinable
   internal init(
     _unsafeUninitializedCapacity capacity: Int,
     allowingDuplicates: Bool,
     initializingWith initializer: (
       _ keys: UnsafeMutableBufferPointer<Key>,
-      _ values: UnsafeMutableBufferPointer<Value>,
-      _ initializedCount: inout Int
-    ) -> Void
+      _ values: UnsafeMutableBufferPointer<Value>
+    ) -> Int
   ) {
     self.init(capacity: capacity)
-    var initializedCount = 0
-    initializer(
+    let initializedCount = initializer(
       UnsafeMutableBufferPointer(start: _keys, count: capacity),
-      UnsafeMutableBufferPointer(start: _values, count: capacity),
-      &initializedCount)
-    _precondition(count >= 0 && count <= capacity)
+      UnsafeMutableBufferPointer(start: _values, count: capacity))
+    _precondition(initializedCount >= 0 && initializedCount <= capacity)
     _storage._count = initializedCount
 
     // Hash initialized elements and move each of them into their correct

validation-test/stdlib/Dictionary.swift

@@ -5700,14 +5700,14 @@ DictionaryTestSuite.test("BulkLoadingInitializer.Unique") {
     let d1 = Dictionary<TestKeyTy, TestEquatableValueTy>(
       _unsafeUninitializedCapacity: c,
       allowingDuplicates: false
-    ) { keys, values, count in
+    ) { keys, values in
       let k = keys.baseAddress!
       let v = values.baseAddress!
       for i in 0 ..< c {
         (k + i).initialize(to: TestKeyTy(i))
         (v + i).initialize(to: TestEquatableValueTy(i))
-        count += 1
       }
+      return c
     }
 
     let d2 = Dictionary(
@@ -5727,14 +5727,14 @@ DictionaryTestSuite.test("BulkLoadingInitializer.Nonunique") {
     let d1 = Dictionary<TestKeyTy, TestEquatableValueTy>(
       _unsafeUninitializedCapacity: c,
       allowingDuplicates: true
-    ) { keys, values, count in
+    ) { keys, values in
       let k = keys.baseAddress!
       let v = values.baseAddress!
       for i in 0 ..< c {
         (k + i).initialize(to: TestKeyTy(i / 2))
         (v + i).initialize(to: TestEquatableValueTy(i / 2))
-        count += 1
       }
+      return c
     }
 
     let d2 = Dictionary(