Add readonly modifier to some private fields (#1984)

Author: daxian-dbw

PSReadLine/CharMap.cs

@@ -63,7 +63,9 @@ public void ProcessKey(ConsoleKeyInfo key)
     // Hard-coded translator for the only VT mode Windows supports.
     internal class WindowsAnsiCharMap : ICharMap
     {
-        private List<ConsoleKeyInfo> _pendingKeys;
+        private readonly List<ConsoleKeyInfo> _pendingKeys;
+        private readonly Stopwatch _escTimeoutStopwatch = new Stopwatch();
+
         // The next index in `_pendingKeys` to write to.
         private int _addKeyIndex;
         // The next index in `_pendingKeys` to read from. This index becomes
@@ -75,8 +77,6 @@ internal class WindowsAnsiCharMap : ICharMap
         // The upper bound of `_pendingKeys` to read from, exclusive.
         private int _readKeyIndexTo;
 
-        private Stopwatch _escTimeoutStopwatch = new Stopwatch();
-
         public WindowsAnsiCharMap(long escapeTimeout = 50)
         {
             // In theory this shouldn't need to be any longer, but one time

PSReadLine/Completion.cs

@@ -40,7 +40,7 @@ public partial class PSConsoleReadLine
         private static readonly char[] EolChars = {'\r', '\n'};
 
         // String helper for directory paths
-        private static string DirectorySeparatorString = System.IO.Path.DirectorySeparatorChar.ToString();
+        private static readonly string DirectorySeparatorString = System.IO.Path.DirectorySeparatorChar.ToString();
 
         // Stub helper method so completion can be mocked
         [ExcludeFromCodeCoverage]

PSReadLine/PlatformWindows.cs

@@ -403,8 +403,8 @@ public static bool IsConsoleApiAvailable(bool input, bool output)
 
     internal class LegacyWin32Console : VirtualTerminal
     {
-        private static ConsoleColor InitialFG = Console.ForegroundColor;
-        private static ConsoleColor InitialBG = Console.BackgroundColor;
+        private static readonly ConsoleColor InitialFG = Console.ForegroundColor;
+        private static readonly ConsoleColor InitialBG = Console.BackgroundColor;
         private static int maxTop = 0;
 
         private static readonly Dictionary<int, Action> VTColorAction = new Dictionary<int, Action> {

test/MockConsole.cs

@@ -68,8 +68,8 @@ internal class TestConsole : IConsole
         private readonly int _bufferHeight;
         private readonly int _windowWidth;
         private readonly int _windowHeight;
+        private readonly dynamic _keyboardLayout;
         private bool _ignoreNextNewline;
-        private dynamic _keyboardLayout;
 
         internal TestConsole(dynamic keyboardLayout)
         {