Merge pull request swiftlang#2300 from ikesyo/address-warnings

[gardening] Address some warnings

Author: ikesyo

Diff for: Foundation/HTTPCookieStorage.swift

@@ -89,7 +89,7 @@ open class HTTPCookieStorage: NSObject {
     private func loadPersistedCookies() {
         guard let cookieFilePath = self.cookieFilePath, let cookiesData = try? Data(contentsOf: URL(fileURLWithPath: cookieFilePath)) else { return }
         guard let cookies = try? PropertyListSerialization.propertyList(from: cookiesData, format: nil) else { return }
-        var cookies0 = cookies as? [String: [String: Any]] ?? [:]
+        let cookies0 = cookies as? [String: [String: Any]] ?? [:]
         self.syncQ.sync {
             for key in cookies0.keys {
                 if let cookie = createCookie(cookies0[key]!) {

Diff for: Foundation/JSONEncoder.swift

@@ -1078,7 +1078,7 @@ open class JSONDecoder {
             let leadingUnderscoreRange = stringKey.startIndex..<firstNonUnderscore
             let trailingUnderscoreRange = stringKey.index(after: lastNonUnderscore)..<stringKey.endIndex
 
-            var components = stringKey[keyRange].split(separator: "_")
+            let components = stringKey[keyRange].split(separator: "_")
             let joinedString : String
             if components.count == 1 {
                 // No underscores in key, leave the word as is - maybe already camel cased

Diff for: Foundation/NSData.swift

@@ -425,7 +425,7 @@ open class NSData : NSObject, NSCopying, NSMutableCopying, NSSecureCoding {
         let permissions = (try? fm._permissionsOfItem(atPath: path)) ?? 0o600
 
         if writeOptionsMask.contains(.atomic) {
-            var (newFD, auxFilePath) = try _NSCreateTemporaryFile(path)
+            let (newFD, auxFilePath) = try _NSCreateTemporaryFile(path)
             let fh = FileHandle(fileDescriptor: newFD, closeOnDealloc: true)
             do {
                 try doWrite(fh)

Diff for: TestFoundation/FTPServer.swift

@@ -202,7 +202,7 @@ class _FTPServer {
             try respondWithRawData(with: "150 Ok to send data.\r\n")
             // Read data from the data socket and respond with completion header after the transfer
             do {
-                let readData = try readDataOnDataSocket()
+                _ = try readDataOnDataSocket()
                 try respondWithRawData(with: "226 Transfer complete.\r\n")
             } catch {
                 NSLog("Transfer failed.")