Support unique callouts for enhanced code blocks

src/Elastic.Markdown/Myst/CodeBlocks/EnhancedCodeBlock.cs

@@ -22,6 +22,8 @@ public class EnhancedCodeBlock(BlockParser parser, ParserContext context)
 
 	public List<CallOut>? CallOuts { get; set; }
 
+	public IReadOnlyCollection<CallOut> UniqueCallOuts => CallOuts?.DistinctBy(c => c.Index).ToList() ?? [];
+
 	public bool InlineAnnotations { get; set; }
 
 	public string Language { get; set; } = "unknown";

src/Elastic.Markdown/Myst/CodeBlocks/EnhancedCodeBlockHtmlRenderer.cs

@@ -25,7 +25,7 @@ private static void RenderRazorSlice<T>(RazorSlice<T> slice, HtmlRenderer render
 	}
 	protected override void Write(HtmlRenderer renderer, EnhancedCodeBlock block)
 	{
-		var callOuts = block.CallOuts ?? [];
+		var callOuts = block.UniqueCallOuts;
 
 		var slice = Code.Create(new CodeViewModel
 		{
@@ -46,7 +46,7 @@ protected override void Write(HtmlRenderer renderer, EnhancedCodeBlock block)
 				var siblingBlock = block.Parent[index + 1];
 				if (siblingBlock is not ListBlock)
 					block.EmitError("Code block with annotations is not followed by a list");
-				if (siblingBlock is ListBlock l && l.Count != callOuts.Count)
+				if (siblingBlock is ListBlock l && l.Count < callOuts.Count)
 				{
 					block.EmitError(
 						$"Code block has {callOuts.Count} callouts but the following list only has {l.Count}");
@@ -84,7 +84,7 @@ protected override void Write(HtmlRenderer renderer, EnhancedCodeBlock block)
 		else if (block.InlineAnnotations)
 		{
 			renderer.WriteLine("<ol class=\"code-callouts\">");
-			foreach (var c in block.CallOuts ?? [])
+			foreach (var c in block.UniqueCallOuts)
 			{
 				renderer.WriteLine("<li>");
 				renderer.WriteLine(c.Text);

src/Elastic.Markdown/Myst/CodeBlocks/EnhancedCodeBlockParser.cs

@@ -172,9 +172,14 @@ public override bool Close(BlockProcessor processor, Block block)
 
 			callOutIndex++;
 			var callout = span.Slice(match.Index + startIndex, match.Length - startIndex);
+			var index = callOutIndex;
+			if (!inlineCodeAnnotation && int.TryParse(callout.Trim(['<', '>']), out index))
+			{
+
+			}
 			return new CallOut
 			{
-				Index = callOutIndex,
+				Index = index,
 				Text = callout.TrimStart('/').TrimStart('#').TrimStart().ToString(),
 				InlineCodeAnnotation = inlineCodeAnnotation,
 				SliceStart = startIndex,

tests/Elastic.Markdown.Tests/CodeBlocks/CallOutTests.cs

@@ -117,6 +117,35 @@ public void RequiresContentToFollow() => Collector.Diagnostics.Should().HaveCoun
 		.And.OnlyContain(c => c.Message.StartsWith("Code block has 2 callouts but the following list only has 1"));
 }
 
+public class ClassicCallOutsReuseHighlights(ITestOutputHelper output) : CodeBlockCallOutTests(output, "csharp",
+"""
+var x = 1; <1>
+var y = x - 2; <2>
+var z = y - 2; <2>
+""",
+"""
+1. The first
+2. The second appears twice
+"""
+
+	)
+{
+	[Fact]
+	public void SeesTwoUniqueCallouts() => Block!.UniqueCallOuts
+		.Should().NotBeNullOrEmpty()
+		.And.HaveCount(2)
+		.And.OnlyContain(c => c.Text.StartsWith("<"));
+
+	[Fact]
+	public void ParsesAllForLineInformation() => Block!.CallOuts
+		.Should().NotBeNullOrEmpty()
+		.And.HaveCount(3)
+		.And.OnlyContain(c => c.Text.StartsWith("<"));
+
+	[Fact]
+	public void RequiresContentToFollow() => Collector.Diagnostics.Should().BeEmpty();
+}
+
 public class ClassicCallOutWithTheRightListItems(ITestOutputHelper output) : CodeBlockCallOutTests(output, "csharp",
 """
 var x = 1; <1>