Replaces emoji regex with ReadOnlySpan implementation

The RegEx runtime perf was never anything noticeable - it was the startup time that was eating over a third of time during initialization.

This shaves 200ms off the startup time.

src/Spectre.Console.Tests/Unit/EmojiTests.cs

@@ -41,5 +41,56 @@ namespace Spectre.Console.Tests.Unit
                 result.ShouldBe("Hello 🌍!");
             }
         }
+
+        public sealed class Parsing
+        {
+            [Theory]
+            [InlineData(":", ":")]
+            [InlineData("::", "::")]
+            [InlineData(":::", ":::")]
+            [InlineData("::::", "::::")]
+            [InlineData("::i:", "::i:")]
+            [InlineData(":i:i:", ":i:i:")]
+            [InlineData("::globe_showing_europe_africa::", ":🌍:")]
+            [InlineData(":globe_showing_europe_africa::globe_showing_europe_africa:", "🌍🌍")]
+            [InlineData("::globe_showing_europe_africa:::test:::globe_showing_europe_africa:::", ":🌍::test::🌍::")]
+            public void Can_Handle_Different_Combinations(string markup, string expected)
+            {
+                // Given
+                var console = new FakeAnsiConsole(ColorSystem.Standard, AnsiSupport.Yes);
+
+                // When
+                console.Markup(markup);
+
+                // Then
+                console.Output.ShouldBe(expected);
+            }
+
+            [Fact]
+            public void Should_Leave_Single_Colons()
+            {
+                // Given
+                var console = new FakeAnsiConsole(ColorSystem.Standard, AnsiSupport.Yes);
+
+                // When
+                console.Markup("Hello :globe_showing_europe_africa:! Output: good");
+
+                // Then
+                console.Output.ShouldBe("Hello 🌍! Output: good");
+            }
+
+            [Fact]
+            public void Unknown_emojis_should_remain()
+            {
+                // Given
+                var console = new FakeAnsiConsole(ColorSystem.Standard, AnsiSupport.Yes);
+
+                // When
+                console.Markup("Hello :globe_showing_flat_earth:!");
+
+                // Then
+                console.Output.ShouldBe("Hello :globe_showing_flat_earth:!");
+            }
+        }
     }
 }

src/Spectre.Console/Emoji.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel.Design;
+using System.Text;
 using System.Text.RegularExpressions;
 
 namespace Spectre.Console
@@ -9,7 +11,6 @@ namespace Spectre.Console
     /// </summary>
     public static partial class Emoji
     {
-        private static readonly Regex _emojiCode = new Regex(@"(:(\S*?):)", RegexOptions.Compiled);
         private static readonly Dictionary<string, string> _remappings;
 
         static Emoji()
@@ -40,6 +41,7 @@ namespace Spectre.Console
             _remappings[tag] = emoji;
         }
 
+#if NETSTANDARD2_0
         /// <summary>
         /// Replaces emoji markup with corresponding unicode characters.
         /// </summary>
@@ -47,24 +49,86 @@ namespace Spectre.Console
         /// <returns>A string with emoji codes replaced with actual emoji.</returns>
         public static string Replace(string value)
         {
-            static string ReplaceEmoji(Match match)
+            return Replace(value.AsSpan());
+        }
+#endif
+
+        /// <summary>
+        /// Replaces emoji markup with corresponding unicode characters.
+        /// </summary>
+        /// <param name="value">A string with emojis codes, e.g. "Hello :smiley:!".</param>
+        /// <returns>A string with emoji codes replaced with actual emoji.</returns>
+        public static string Replace(ReadOnlySpan<char> value)
+        {
+            var output = new StringBuilder();
+            var colonPos = value.IndexOf(':');
+            if (colonPos == -1)
             {
-                var key = match.Groups[2].Value;
-
-                if (_remappings.Count > 0 && _remappings.TryGetValue(key, out var remappedEmoji))
-                {
-                    return remappedEmoji;
-                }
-
-                if (_emojis.TryGetValue(key, out var emoji))
-                {
-                    return emoji;
-                }
-
-                return match.Value;
+                // No colons, no emoji. return what was passed in with no changes.
+                return value.ToString();
             }
 
-            return _emojiCode.Replace(value, ReplaceEmoji);
+            while ((colonPos = value.IndexOf(':')) != -1)
+            {
+                // Append text up to colon
+                output.AppendSpan(value.Slice(0, colonPos));
+
+                // Set value equal to that colon and the rest of the string
+                value = value.Slice(colonPos);
+
+                // Find colon after that. if no colon, break out
+                var nextColonPos = value.IndexOf(':', 1);
+                if (nextColonPos == -1)
+                {
+                    break;
+                }
+
+                // Get the emoji text minus the colons
+                var emojiKey = value.Slice(1, nextColonPos - 1).ToString();
+                if (TryGetEmoji(emojiKey, out var emojiValue))
+                {
+                    output.Append(emojiValue);
+                    value = value.Slice(nextColonPos + 1);
+                }
+                else
+                {
+                    output.Append(':');
+                    value = value.Slice(1);
+                }
+            }
+
+            output.AppendSpan(value);
+            return output.ToString();
+        }
+
+        private static bool TryGetEmoji(string emoji, out string value)
+        {
+            if (_remappings.TryGetValue(emoji, out var remappedEmojiValue))
+            {
+                value = remappedEmojiValue;
+                return true;
+            }
+
+            if (_emojis.TryGetValue(emoji, out var emojiValue))
+            {
+                value = emojiValue;
+                return true;
+            }
+
+            value = string.Empty;
+            return false;
+        }
+
+        private static int IndexOf(this ReadOnlySpan<char> span, char value, int startIndex)
+        {
+            var indexInSlice = span.Slice(startIndex).IndexOf(value);
+
+            if (indexInSlice == -1)
+            {
+                return -1;
+            }
+
+            return startIndex + indexInSlice;
         }
     }
-}
+}

src/Spectre.Console/Extensions/StringBuilderExtensions.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Globalization;
 using System.Text;
 
@@ -25,5 +26,16 @@ namespace Spectre.Console
 
             return builder.Append(value);
         }
+
+        public static void AppendSpan(this StringBuilder builder, ReadOnlySpan<char> span)
+        {
+            // NetStandard 2 lacks the override for StringBuilder to add the span. We'll need to convert the span
+            // to a string for it, but for .NET 5.0 we'll use the override.
+#if NETSTANDARD2_0
+            builder.Append(span.ToString());
+#else
+            builder.Append(span);
+#endif
+        }
     }
 }

src/Spectre.Console/Spectre.Console.csproj

@@ -8,6 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="Wcwidth" Version="0.2.0" />
+    <PackageReference Include="System.Memory" Version="4.5.0" Condition="'$(TargetFramework)' == 'netstandard2.0'" />
   </ItemGroup>
 
   <ItemGroup>