Add custom UseHardBreaks extension (#342)

* Add custom DisableHtmlWithExceptions extension

* format

* Move property position back

* Add comment

* Remove `DisableHtmlWithExceptions` and implement `UseHardBreaks`.

The `DisableHtmlWithExceptions` logic was removed and replaced with a simpler `UseHardBreaks` implementation for handling `<br>` tags. This refactor simplifies the markdown pipeline and improves maintainability while retaining support for hard breaks.

* remove folder from Tests csproj

* Rename file

---------

Co-authored-by: Martijn Laarman <[email protected]>

Author: reakaleek

src/Elastic.Markdown/Myst/InlineParsers/HardBreakParser.cs

@@ -0,0 +1,65 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using Markdig;
+using Markdig.Helpers;
+using Markdig.Parsers;
+using Markdig.Parsers.Inlines;
+using Markdig.Renderers;
+using Markdig.Renderers.Html;
+using Markdig.Renderers.Html.Inlines;
+using Markdig.Syntax.Inlines;
+
+namespace Elastic.Markdown.Myst.InlineParsers;
+
+public static class HardBreakBuilderExtensions
+{
+	public static MarkdownPipelineBuilder UseHardBreaks(this MarkdownPipelineBuilder pipeline)
+	{
+		pipeline.Extensions.AddIfNotAlready<HardBreakBuilderExtension>();
+		return pipeline;
+	}
+}
+
+public class HardBreakBuilderExtension : IMarkdownExtension
+{
+	public void Setup(MarkdownPipelineBuilder pipeline) =>
+		pipeline.InlineParsers.InsertBefore<EmphasisInlineParser>(new HardBreakParser());
+
+	public void Setup(MarkdownPipeline pipeline, IMarkdownRenderer renderer) =>
+		renderer.ObjectRenderers.InsertAfter<EmphasisInlineRenderer>(new HardBreakRenderer());
+}
+
+public class HardBreakParser : InlineParser
+{
+	public HardBreakParser() => OpeningCharacters = ['<'];
+
+	public override bool Match(InlineProcessor processor, ref StringSlice slice)
+	{
+		var span = slice.AsSpan();
+		if (!span.StartsWith("<br"))
+			return false;
+
+		var closingStart = span[3..].IndexOf('>');
+		// we allow
+		if (closingStart != 0)
+			return false;
+
+		processor.Inline = new HardBreak();
+
+		var sliceEnd = slice.Start + 4; //<br + >
+		while (slice.Start != sliceEnd)
+			slice.SkipChar();
+
+		return true;
+	}
+}
+
+public class HardBreak : LeafInline;
+
+public class HardBreakRenderer : HtmlObjectRenderer<HardBreak>
+{
+	protected override void Write(HtmlRenderer renderer, HardBreak obj) =>
+		renderer.Write("<br>");
+}

src/Elastic.Markdown/Myst/MarkdownParser.cs

@@ -53,6 +53,7 @@ public class MarkdownParser(
 			.UseDirectives()
 			.UseEnhancedCodeBlocks()
 			.DisableHtml()
+			.UseHardBreaks()
 			.Build();
 
 	public ConfigurationFile Configuration { get; } = configuration;
@@ -107,6 +108,4 @@ public MarkdownDocument Parse(string yaml, IFileInfo parent, YamlFrontMatter? ma
 		var markdownDocument = Markdig.Markdown.Parse(yaml, Pipeline, context);
 		return markdownDocument;
 	}
-
-
 }

tests/Elastic.Markdown.Tests/Inline/HardBreakTests.cs

@@ -0,0 +1,42 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using FluentAssertions;
+using Xunit.Abstractions;
+
+namespace Elastic.Markdown.Tests.Inline;
+
+public class AllowBrTagTest(ITestOutputHelper output)
+	: InlineTest(output,
+		"Hello,<br>World!")
+{
+	[Fact]
+	public void GeneratesHtml() =>
+		Html.Should().Contain(
+			"<p>Hello,<br>World!</p>"
+		);
+}
+
+public class BrTagNeedsToBeExact(ITestOutputHelper output)
+	: InlineTest(output,
+		"Hello,<br >World<br />!")
+{
+	[Fact]
+	public void GeneratesHtml() =>
+		Html.Should().Contain(
+			"<p>Hello,&lt;br &gt;World&lt;br /&gt;!</p>"
+		);
+}
+
+public class DisallowSpanTag(ITestOutputHelper output)
+	: InlineTest(output,
+		"Hello,<span>World!</span>")
+{
+	[Fact]
+	// span tag is rendered as text
+	public void GeneratesHtml() =>
+		Html.Should().Contain(
+			"<p>Hello,&lt;span&gt;World!&lt;/span&gt;</p>"
+		);
+}