SelfClosing Tags have incorrect html, generated unclosed tags.

Bug Report

Prerequisites

• [/] Can you reproduce the problem in a MWE?
• [/] Are you running the latest version of AngleSharp?
• [/] Did you check the FAQs to see if that helps you?
• [/] Are you reporting to the correct repository? (there are multiple AngleSharp libraries, e.g., AngleSharp.Css for CSS support)
• [/] Did you perform a search in the issues?

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Description

Given a self-closing tag such as <input type='text' />, doing a ToHtml() on it, or using the OuterHtml property both return an unclosed tag.

Steps to Reproduce

var config = Configuration.Default;
var context= BrowsingContext.New(config);
var source = "<input type='text' />";
var document = await context.OpenAsync(req => req.Content(source));
var input = document.QuerySelector("input");
input.OuterHtml.Dump();
input.ToHtml().Dump();

Expected behavior: returns <input type='text' />

Actual behavior: returns <input type='text'>

Environment details: Windows, .NET 6.0.14

Possible Solution

https://github.com/AngleSharp/AngleSharp/blob/3a21e4c65b53dbd53d35dee4b1f692659a7f535e/src/AngleSharp/Html/HtmlMarkupFormatter.cs#L69

I believe the above line needs to have a code path that adds /> when selfClosing is true.

[FlorianRappl]

We also have an XHTML formatter - so the parsed DOM could be represented in XHTML (here, we place the solidus; see https://github.com/AngleSharp/AngleSharp/blob/devel/src/AngleSharp/Xhtml/XhtmlMarkupFormatter.cs#L103).

[jbrayfaithlife]

Learn something new every day. For anyone’s future reference, this came out of a project where we are manipulating XHTML. Apparently I misunderstood the relationship between the various specs.