Use span-based dictionary lookup in System.Console (dotnet#103742)

* Use span-based dictionary lookup in System.Console

* Fix ctor

Author: stephentoub

src/libraries/System.Console/src/System/IO/KeyParser.cs

@@ -62,14 +62,15 @@ private static bool TryParseTerminalInputSequence(char[] buffer, TerminalFormatS
             return false;
         }
 
-        Dictionary<ReadOnlyMemory<char>, ConsoleKeyInfo> terminfoDb = terminalFormatStrings.KeyFormatToConsoleKey; // the most important source of truth
+        Dictionary<string, ConsoleKeyInfo>.AlternateLookup<ReadOnlySpan<char>> terminfoDb = // the most important source of truth
+            terminalFormatStrings.KeyFormatToConsoleKey.GetAlternateLookup<string, ConsoleKeyInfo, ReadOnlySpan<char>>();
         ConsoleModifiers modifiers = ConsoleModifiers.None;
         ConsoleKey key;
 
         // Is it a three character sequence? (examples: '^[[H' (Home), '^[OP' (F1))
         if (input[1] == 'O' || char.IsAsciiLetter(input[2]) || input.Length == MinimalSequenceLength)
         {
-            if (!terminfoDb.TryGetValue(buffer.AsMemory(startIndex, MinimalSequenceLength), out parsed))
+            if (!terminfoDb.TryGetValue(buffer.AsSpan(startIndex, MinimalSequenceLength), out parsed))
             {
                 // All terminals which use "^[O{letter}" escape sequences don't define conflicting mappings.
                 // Example: ^[OH either means Home or simply is not used by given terminal.
@@ -103,7 +104,7 @@ private static bool TryParseTerminalInputSequence(char[] buffer, TerminalFormatS
         // Is it a four character sequence used by Linux Console or PuTTy configured to emulate it? (examples: '^[[[A' (F1), '^[[[B' (F2))
         if (input[1] == '[' && input[2] == '[' && char.IsBetween(input[3], 'A', 'E'))
         {
-            if (!terminfoDb.TryGetValue(buffer.AsMemory(startIndex, 4), out parsed))
+            if (!terminfoDb.TryGetValue(buffer.AsSpan(startIndex, 4), out parsed))
             {
                 parsed = new ConsoleKeyInfo(default, ConsoleKey.F1 + input[3] - 'A', false, false, false);
             }
@@ -128,7 +129,7 @@ private static bool TryParseTerminalInputSequence(char[] buffer, TerminalFormatS
         {
             // it's a VT Sequence like ^[[11~ or rxvt like ^[[11^
             int sequenceLength = SequencePrefixLength + digitCount + 1;
-            if (!terminfoDb.TryGetValue(buffer.AsMemory(startIndex, sequenceLength), out parsed))
+            if (!terminfoDb.TryGetValue(buffer.AsSpan(startIndex, sequenceLength), out parsed))
             {
                 key = MapEscapeSequenceNumber(byte.Parse(input.Slice(SequencePrefixLength, digitCount)));
                 if (key == default)

src/libraries/System.Console/src/System/TerminalFormatStrings.cs

@@ -51,8 +51,7 @@ internal sealed class TerminalFormatStrings
     /// The dictionary of keystring to ConsoleKeyInfo.
     /// Only some members of the ConsoleKeyInfo are used; in particular, the actual char is ignored.
     /// </summary>
-    public readonly Dictionary<ReadOnlyMemory<char>, ConsoleKeyInfo> KeyFormatToConsoleKey =
-        new Dictionary<ReadOnlyMemory<char>, ConsoleKeyInfo>(new ReadOnlyMemoryContentComparer());
+    public readonly Dictionary<string, ConsoleKeyInfo> KeyFormatToConsoleKey = new(StringComparer.Ordinal);
 
     /// <summary> Max key length </summary>
     public readonly int MaxKeyFormatLength;
@@ -164,7 +163,7 @@ public TerminalFormatStrings(TermInfo.Database? db)
             MaxKeyFormatLength = int.MinValue;
             MinKeyFormatLength = int.MaxValue;
 
-            foreach (KeyValuePair<ReadOnlyMemory<char>, ConsoleKeyInfo> entry in KeyFormatToConsoleKey)
+            foreach (KeyValuePair<string, ConsoleKeyInfo> entry in KeyFormatToConsoleKey)
             {
                 if (entry.Key.Length > MaxKeyFormatLength)
                 {
@@ -229,8 +228,8 @@ private void AddKey(TermInfo.Database db, TermInfo.WellKnownStrings keyId, Conso
 
     private void AddKey(TermInfo.Database db, TermInfo.WellKnownStrings keyId, ConsoleKey key, bool shift, bool alt, bool control)
     {
-        ReadOnlyMemory<char> keyFormat = db.GetString(keyId).AsMemory();
-        if (!keyFormat.IsEmpty)
+        string? keyFormat = db.GetString(keyId);
+        if (!string.IsNullOrEmpty(keyFormat))
             KeyFormatToConsoleKey[keyFormat] = new ConsoleKeyInfo(key == ConsoleKey.Enter ? '\r' : '\0', key, shift, alt, control);
     }
 
@@ -248,17 +247,8 @@ private void AddPrefixKey(TermInfo.Database db, string extendedNamePrefix, Conso
 
     private void AddKey(TermInfo.Database db, string extendedName, ConsoleKey key, bool shift, bool alt, bool control)
     {
-        ReadOnlyMemory<char> keyFormat = db.GetExtendedString(extendedName).AsMemory();
-        if (!keyFormat.IsEmpty)
+        string? keyFormat = db.GetExtendedString(extendedName);
+        if (!string.IsNullOrEmpty(keyFormat))
             KeyFormatToConsoleKey[keyFormat] = new ConsoleKeyInfo('\0', key, shift, alt, control);
     }
-
-    private sealed class ReadOnlyMemoryContentComparer : IEqualityComparer<ReadOnlyMemory<char>>
-    {
-        public bool Equals(ReadOnlyMemory<char> x, ReadOnlyMemory<char> y) =>
-            x.Span.SequenceEqual(y.Span);
-
-        public int GetHashCode(ReadOnlyMemory<char> obj) =>
-            string.GetHashCode(obj.Span);
-    }
 }