From 61208b944bf23e6c857f732e021b1910f0d1462b Mon Sep 17 00:00:00 2001
From: Simon Cropp <simon.cropp@gmail.com>
Date: Mon, 3 Aug 2026 22:05:58 +1000
Subject: [PATCH] Fragment no longer opens on a blank line
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

A fragment is parsed against a context element, and PrettyMarkupFormatter breaks
the line before every node that sits inside an element. That context element is
never itself written, so the first node took the break with nothing in front of
it and the markup opened on the second line. A document has no such context, and
a fragment leading with text is not broken before either, so the ones affected
were those leading with an element or a comment. The break is now dropped from
the front of the formatted output.

The seven fragment snapshots recorded the blank line rather than failing on it.
The registered html comparer diffs the two DOMs, where a blank line before the
first node is whitespace between nodes and no difference at all, so nothing here
could see it — only a consumer comparing the snapshot as text. The new test
compares as text for that reason, and is the only one in the fixture that fails
when the trim is taken back out.
---
 src/Directory.Build.props                     |  2 +-
 ...entDoesNotOpenWithABlankLine.verified.html |  1 +
 ...agmentIsNotWrappedInDocument.verified.html |  3 +-
 ...ts.PreservesPreformattedText.verified.html |  3 +-
 ...s.PreservesTextareaAndScript.verified.html |  3 +-
 ...tHtmlTests.TableCellFragment.verified.html |  3 +-
 ....TableFragmentBehindAComment.verified.html |  3 +-
 ...ntHtmlTests.TableRowFragment.verified.html |  3 +-
 ...mlTests.TableSectionFragment.verified.html |  3 +-
 src/Tests/PrettyPrintHtmlTests.cs             | 30 +++++++++++++++++++
 src/Verify.AngleSharp/HtmlPrettyPrint.cs      | 18 +++++++++++
 11 files changed, 57 insertions(+), 15 deletions(-)
 create mode 100644 src/Tests/PrettyPrintHtmlTests.FragmentDoesNotOpenWithABlankLine.verified.html

diff --git a/src/Directory.Build.props b/src/Directory.Build.props
index 2c31178..986736d 100644
--- a/src/Directory.Build.props
+++ b/src/Directory.Build.props
@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU1608;NU1109</NoWarn>
-    <Version>5.1.1</Version>
+    <Version>5.1.2</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <LangVersion>preview</LangVersion>
     <PackageTags>AngleSharp, Verify</PackageTags>
diff --git a/src/Tests/PrettyPrintHtmlTests.FragmentDoesNotOpenWithABlankLine.verified.html b/src/Tests/PrettyPrintHtmlTests.FragmentDoesNotOpenWithABlankLine.verified.html
new file mode 100644
index 0000000..4f11014
--- /dev/null
+++ b/src/Tests/PrettyPrintHtmlTests.FragmentDoesNotOpenWithABlankLine.verified.html
@@ -0,0 +1 @@
+<p>My first paragraph.</p>
\ No newline at end of file
diff --git a/src/Tests/PrettyPrintHtmlTests.FragmentIsNotWrappedInDocument.verified.html b/src/Tests/PrettyPrintHtmlTests.FragmentIsNotWrappedInDocument.verified.html
index 46fac00..4f11014 100644
--- a/src/Tests/PrettyPrintHtmlTests.FragmentIsNotWrappedInDocument.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.FragmentIsNotWrappedInDocument.verified.html
@@ -1,2 +1 @@
-
-<p>My first paragraph.</p>
\ No newline at end of file
+<p>My first paragraph.</p>
\ No newline at end of file
diff --git a/src/Tests/PrettyPrintHtmlTests.PreservesPreformattedText.verified.html b/src/Tests/PrettyPrintHtmlTests.PreservesPreformattedText.verified.html
index 65709a6..f9a64f7 100644
--- a/src/Tests/PrettyPrintHtmlTests.PreservesPreformattedText.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.PreservesPreformattedText.verified.html
@@ -1,5 +1,4 @@
-
-<div>
+<div>
   <pre>SELECT [e].[Name]
 FROM [Employees] AS [e]
 WHERE [e].[Active] = 1</pre>
diff --git a/src/Tests/PrettyPrintHtmlTests.PreservesTextareaAndScript.verified.html b/src/Tests/PrettyPrintHtmlTests.PreservesTextareaAndScript.verified.html
index 9e897ae..9ec22f0 100644
--- a/src/Tests/PrettyPrintHtmlTests.PreservesTextareaAndScript.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.PreservesTextareaAndScript.verified.html
@@ -1,5 +1,4 @@
-
-<div>
+<div>
   <textarea>line one
 line two</textarea>
   <script>
diff --git a/src/Tests/PrettyPrintHtmlTests.TableCellFragment.verified.html b/src/Tests/PrettyPrintHtmlTests.TableCellFragment.verified.html
index a7b8dbf..1f04f00 100644
--- a/src/Tests/PrettyPrintHtmlTests.TableCellFragment.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.TableCellFragment.verified.html
@@ -1,3 +1,2 @@
-
-<td>Aaron</td>
+<td>Aaron</td>
 <td>FullTime</td>
\ No newline at end of file
diff --git a/src/Tests/PrettyPrintHtmlTests.TableFragmentBehindAComment.verified.html b/src/Tests/PrettyPrintHtmlTests.TableFragmentBehindAComment.verified.html
index bab4b62..78a134c 100644
--- a/src/Tests/PrettyPrintHtmlTests.TableFragmentBehindAComment.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.TableFragmentBehindAComment.verified.html
@@ -1,5 +1,4 @@
-
-<!--marker-->
+<!--marker-->
 <thead>
   <tr>
     <th>Name</th>
diff --git a/src/Tests/PrettyPrintHtmlTests.TableRowFragment.verified.html b/src/Tests/PrettyPrintHtmlTests.TableRowFragment.verified.html
index b920f6b..8d275c9 100644
--- a/src/Tests/PrettyPrintHtmlTests.TableRowFragment.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.TableRowFragment.verified.html
@@ -1,5 +1,4 @@
-
-<tr>
+<tr>
   <td>Aaron</td>
   <td>FullTime</td>
 </tr>
\ No newline at end of file
diff --git a/src/Tests/PrettyPrintHtmlTests.TableSectionFragment.verified.html b/src/Tests/PrettyPrintHtmlTests.TableSectionFragment.verified.html
index c0412f8..2c5bfaf 100644
--- a/src/Tests/PrettyPrintHtmlTests.TableSectionFragment.verified.html
+++ b/src/Tests/PrettyPrintHtmlTests.TableSectionFragment.verified.html
@@ -1,5 +1,4 @@
-
-<thead>
+<thead>
   <tr>
     <th>Name</th>
   </tr>
diff --git a/src/Tests/PrettyPrintHtmlTests.cs b/src/Tests/PrettyPrintHtmlTests.cs
index 1f6c215..b92f761 100644
--- a/src/Tests/PrettyPrintHtmlTests.cs
+++ b/src/Tests/PrettyPrintHtmlTests.cs
@@ -128,4 +128,34 @@ public Task FragmentOpeningWithText()
         return Verify(html, "html")
             .PrettyPrintHtml();
     }
+
+    // A fragment is parsed against a context element that is never written, and the formatter breaks
+    // the line before every node inside an element. So the first node took a break with nothing in
+    // front of it and the markup opened on the second line.
+    //
+    // Compared as text rather than by the registered html comparer: that one diffs the two DOMs, where
+    // a blank line before the first node is whitespace between nodes and no difference at all. Every
+    // other test here is blind to the thing this one is for.
+    [Test]
+    public Task FragmentDoesNotOpenWithABlankLine()
+    {
+        var html = "<p>My first paragraph.</p>";
+        return Verify(html, "html")
+            .PrettyPrintHtml()
+            .UseStringComparer(CompareText);
+    }
+
+    static Task<VerifyTests.CompareResult> CompareText(
+        string received,
+        string verified,
+        IReadOnlyDictionary<string, object> context)
+    {
+        if (string.Equals(received, verified, StringComparison.Ordinal))
+        {
+            return Task.FromResult(VerifyTests.CompareResult.Equal);
+        }
+
+        return Task.FromResult(
+            VerifyTests.CompareResult.NotEqual($"Received:{Environment.NewLine}{received}"));
+    }
 }
diff --git a/src/Verify.AngleSharp/HtmlPrettyPrint.cs b/src/Verify.AngleSharp/HtmlPrettyPrint.cs
index 304ac01..c5f8ca8 100644
--- a/src/Verify.AngleSharp/HtmlPrettyPrint.cs
+++ b/src/Verify.AngleSharp/HtmlPrettyPrint.cs
@@ -313,12 +313,30 @@ static void CleanSource(StringBuilder builder, Action<INodeList>? action)
             document.ToHtml(writer, formatter);
         }
 
+        TrimLeadingNewLine(builder);
+
         for (var index = 0; index < preserved.Count; index++)
         {
             builder.Replace(Placeholder(index), preserved[index]);
         }
     }
 
+    /// <summary>
+    /// The formatter breaks the line before every node that sits inside an element, to part it from
+    /// whatever came before. A fragment is parsed against a context element that is never itself
+    /// written, so its first node takes that break with nothing in front of it and the markup opens on
+    /// the second line. A document has no such context, and a fragment opening with text is not broken
+    /// before either, so in those cases there is nothing here to remove.
+    /// </summary>
+    static void TrimLeadingNewLine(StringBuilder builder)
+    {
+        if (builder.Length > 0 &&
+            builder[0] == '\n')
+        {
+            builder.Remove(0, 1);
+        }
+    }
+
     /// <summary>
     /// Swaps the content of each preformatted element for a placeholder, returning the markup each
     /// stood for. The element keeps its place, so the document is laid out exactly as it would have