Improve performance of JSONDecoder and JSONEncoder for large apps (swiftlang#1481)

* Improve performance of JSONDecoder and JSONEncoder for large apps

* use switch instead of casting to protocol

* replace as with specializingCast

* fix styling and remove extra diff

* make extensions fileprivate

Author: ChrisBenua

Sources/FoundationEssentials/JSON/JSONDecoder.swift

@@ -610,7 +610,7 @@ extension JSONDecoderImpl: Decoder {
         if type == Decimal.self {
             return try self.unwrapDecimal(from: mapValue, for: codingPathNode, additionalKey) as! T
         }
-        if T.self is _JSONStringDictionaryDecodableMarker.Type {
+        if !options.keyDecodingStrategy.isDefault, T.self is _JSONStringDictionaryDecodableMarker.Type {
             return try self.unwrapDictionary(from: mapValue, as: type, for: codingPathNode, additionalKey)
         }
 
@@ -1857,5 +1857,14 @@ extension EncodingError {
      }
  }
 
+fileprivate extension JSONDecoder.KeyDecodingStrategy {
+    var isDefault: Bool {
+        switch self {
+        case .useDefaultKeys: true
+        default: false
+        }
+    }
+}
+
 @available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
 extension JSONDecoder : @unchecked Sendable {}

Sources/FoundationEssentials/JSON/JSONEncoder.swift

@@ -1214,9 +1214,9 @@ private extension __JSONEncoder {
             return self.wrap(url.absoluteString)
         } else if let decimal = value as? Decimal {
             return .number(decimal.description)
-        } else if let encodable = value as? _JSONStringDictionaryEncodableMarker {
+        } else if !options.keyEncodingStrategy.isDefault, let encodable = value as? _JSONStringDictionaryEncodableMarker {
             return try self.wrap(encodable as! [String:Encodable], for: additionalKey)
-        } else if let array = value as? _JSONDirectArrayEncodable {
+        } else if let array = _asDirectArrayEncodable(value, for: additionalKey) {
             if options.outputFormatting.contains(.prettyPrinted) {
                 let (bytes, lengths) = try array.individualElementRepresentation(encoder: self, additionalKey)
                 return .directArray(bytes, lengths: lengths)
@@ -1246,6 +1246,42 @@ private extension __JSONEncoder {
         return encoder.takeValue()
     }
 
+    func _asDirectArrayEncodable<T: Encodable>(_ value: T, for additionalKey: (some CodingKey)? = _CodingKey?.none) -> _JSONDirectArrayEncodable? {
+        return if let array = _specializingCast(array, to: [Int8].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Int16].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Int32].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Int64].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Int128].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Int].self) {
+            array
+        } else if let array = _specializingCast(array, to: [UInt8].self) {
+            array
+        } else if let array = _specializingCast(array, to: [UInt16].self) {
+            array
+        } else if let array = _specializingCast(array, to: [UInt32].self) {
+            array
+        } else if let array = _specializingCast(array, to: [UInt64].self) {
+            array
+        } else if let array = _specializingCast(array, to: [UInt128].self) {
+            array
+        } else if let array = _specializingCast(array, to: [UInt].self) {
+            array
+        } else if let array = _specializingCast(array, to: [String].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Float].self) {
+            array
+        } else if let array = _specializingCast(array, to: [Double].self) {
+            array
+        } else {
+            nil
+        }
+    }
+
     @inline(__always)
     func getEncoder(for additionalKey: CodingKey?) -> __JSONEncoder {
         if let additionalKey {
@@ -1466,3 +1502,14 @@ extension Array : _JSONDirectArrayEncodable where Element: _JSONSimpleValueArray
         return (writer.bytes, lengths: byteLengths)
     }
 }
+
+fileprivate extension JSONEncoder.KeyEncodingStrategy {
+    var isDefault: Bool {
+        switch self {
+        case .useDefaultKeys:
+            return true
+        case .custom, .convertToSnakeCase:
+            return false
+        }
+    }
+}