support variation selectors, ZWJ sequences and surrogate pairs in length calculation

src/Spectre.Console.Tests/Expectations/Widgets/Table/Render_Wide_Emoji_Hearts.Output.verified.txt

@@ -0,0 +1,6 @@
+┌──────────┬────────┬──────────────────────┐
+│ hearts   │ length │ LengthInTextElements │
+├──────────┼────────┼──────────────────────┤
+│ wide ❤️  │ 2      │ 1                    │
+│ normal ♥ │ 1      │ 1                    │
+└──────────┴────────┴──────────────────────┘

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

@@ -0,0 +1,20 @@
+namespace Spectre.Console.Tests.Unit;
+
+public sealed class CellTests
+{
+    [Theory]
+    [InlineData("A", 1)]               // ASCII
+    [InlineData("中", 2)]              // CJK wide
+    [InlineData("♥", 1)]              // U+2665 text heart, no variation selector
+    [InlineData("❤️", 2)]             // U+2764 + U+FE0F emoji variation selector
+    [InlineData("👨‍👩‍👧", 2)]       // ZWJ family sequence
+    [InlineData("❤️‍🔥", 2)]          // U+2764 + FE0F + ZWJ + U+1F525 (heart on fire)
+    [InlineData("🇩🇪", 2)]           // Regional Indicator pair (flag)
+    [InlineData("", 0)]               // empty string
+    [InlineData("Hello World", 11)]
+    public void GetCellLength_Returns_Correct_Display_Width(string text, int expectedWidth)
+    {
+        Cell.GetCellLength(text).ShouldBe(expectedWidth);
+    }
+
+}

src/Spectre.Console.Tests/Unit/Widgets/Table/TableTests.cs

@@ -1034,4 +1034,23 @@ public void Should_Not_Throw_When_Rendering_Multiple_Long_CJK_Headers_In_Narrow_
         // Then
         result.ShouldBeNull();
     }
+
+    [Fact]
+    [Expectation("Render_Wide_Emoji_Hearts")]
+    [GitHubIssue("https://github.com/spectreconsole/spectre.console/issues/1847")]
+    public Task Should_Render_Table_With_Wide_Emoji_Correctly()
+    {
+        // Given
+        var console = new TestConsole();
+        var table = new Table();
+        table.AddColumns("hearts", "length", "LengthInTextElements");
+        table.AddRow("wide ❤️", "2", "1");
+        table.AddRow("normal ♥", "1", "1");
+
+        // When
+        console.Write(table);
+
+        // Then
+        return Verifier.Verify(console.Output);
+    }
 }

src/Spectre.Console/Internal/Cell.cs

@@ -23,19 +23,24 @@ static Cell()
 #endif
     }
 
-    public static int GetCellLength(string text) => GetCellLength(text.AsSpan());
-
-    public static int GetCellLength(ReadOnlySpan<char> text)
+    public static int GetCellLength(string text)
     {
+#if !NETSTANDARD2_0
+        return UnicodeCalculator.GetWidth(text);
+#else
         var sum = 0;
         foreach (var rune in text)
         {
             sum += GetCellLength(rune);
         }
 
         return sum;
+#endif
     }
 
+    public static int GetCellLength(ReadOnlySpan<char> text)
+        => GetCellLength(text.ToString());
+
     public static int GetCellLength(char rune)
     {
         // TODO: We need to figure out why Segment.SplitLines fails

src/Spectre.Console/Rendering/Segment.cs

@@ -109,6 +109,11 @@ public int CellCount()
             return 0;
         }
 
+        if (Text == "\n") 
+        {
+            return 1;
+        }
+
         return Cell.GetCellLength(Text);
     }
 
@@ -160,10 +165,12 @@ public Segment StripLineEndings()
         if (offset > 0)
         {
             var accumulated = 0;
-            foreach (var character in Text)
+            var enumerator = StringInfo.GetTextElementEnumerator(Text);
+            while (enumerator.MoveNext())
             {
-                index++;
-                accumulated += Cell.GetCellLength(character);
+                var cluster = enumerator.GetTextElement();
+                accumulated += Cell.GetCellLength(cluster);
+                index += cluster.Length;
                 if (accumulated >= offset)
                 {
                     break;
@@ -429,16 +436,18 @@ public static List<Segment> Truncate(IEnumerable<Segment> segments, int maxWidth
 
         var builder = new StringBuilder();
         var accumulatedCellWidth = 0;
-        foreach (var character in segment.Text)
+        var truncateEnumerator = StringInfo.GetTextElementEnumerator(segment.Text);
+        while (truncateEnumerator.MoveNext())
         {
-            var characterWidth = UnicodeCalculator.GetWidth(character);
-            if (accumulatedCellWidth + characterWidth > maxWidth)
+            var cluster = truncateEnumerator.GetTextElement();
+            var clusterWidth = Cell.GetCellLength(cluster);
+            if (accumulatedCellWidth + clusterWidth > maxWidth)
             {
                 break;
             }
 
-            builder.Append(character);
-            accumulatedCellWidth += characterWidth;
+            builder.Append(cluster);
+            accumulatedCellWidth += clusterWidth;
         }
 
         if (builder.Length == 0)
@@ -571,17 +580,20 @@ internal static List<string> SplitSegment(string text, int maxCellLength)
 
         var length = 0;
         var sb = new StringBuilder();
-        foreach (var ch in text)
+        var splitEnumerator = StringInfo.GetTextElementEnumerator(text);
+        while (splitEnumerator.MoveNext())
         {
-            if (length + UnicodeCalculator.GetWidth(ch) > maxCellLength)
+            var cluster = splitEnumerator.GetTextElement();
+            var clusterWidth = Cell.GetCellLength(cluster);
+            if (length + clusterWidth > maxCellLength)
             {
                 list.Add(sb.ToString());
                 sb.Clear();
                 length = 0;
             }
 
-            length += UnicodeCalculator.GetWidth(ch);
-            sb.Append(ch);
+            length += clusterWidth;
+            sb.Append(cluster);
         }
 
         list.Add(sb.ToString());