Fix compact output crash on empty received

readme.md

@@ -169,7 +169,7 @@ public Task TestLevelUsage()
     return Verify(target, settings);
 }
 ```
-<sup><a href='/src/Tests/Tests.cs#L111-L122' title='Snippet source file'>snippet source</a> | <a href='#snippet-TestLevelUsage' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/Tests/Tests.cs#L133-L144' title='Snippet source file'>snippet source</a> | <a href='#snippet-TestLevelUsage' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 Or Fluently
@@ -185,5 +185,5 @@ public Task TestLevelUsageFluent()
         .UseDiffPlex();
 }
 ```
-<sup><a href='/src/Tests/Tests.cs#L124-L134' title='Snippet source file'>snippet source</a> | <a href='#snippet-TestLevelUsageFluent' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/Tests/Tests.cs#L146-L156' title='Snippet source file'>snippet source</a> | <a href='#snippet-TestLevelUsageFluent' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU1608;NU1109</NoWarn>
-    <Version>3.3.0</Version>
+    <Version>3.3.1</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <LangVersion>preview</LangVersion>
     <PackageTags>DiffPlex, Verify</PackageTags>

src/Tests/Tests.CompactEmptyReceived.verified.txt

@@ -0,0 +1,23 @@
+{
+  Type: VerifyException,
+  Message:
+Directory: {ProjectDirectory}
+NotEqual:
+  - Received: Tests.CompactEmptyReceivedFake.received.txt
+    Verified: Tests.CompactEmptyReceivedFake.verified.txt
+
+FileContent:
+
+NotEqual:
+
+Received: Tests.CompactEmptyReceivedFake.received.txt
+Verified: Tests.CompactEmptyReceivedFake.verified.txt
+Compare Result:
+  [BOF]
+- First
+- Second
+- Third
+  [EOF]
+
+
+}

src/Tests/Tests.CompactEmptyReceivedFake.verified.txt

@@ -0,0 +1,3 @@
+First
+Second
+Third

src/Tests/Tests.cs

@@ -79,6 +79,28 @@ public Task AtTestLevelCompact()
                 settings));
     }
 
+    [Test]
+    public Task CompactEmptyReceived()
+    {
+        var settings = new VerifySettings();
+        settings.UseMethodName("CompactEmptyReceivedFake");
+        settings.DisableDiff();
+        settings.UseDiffPlex(OutputType.Compact);
+        // Scrub every line so the received content is empty. The resulting diff is all
+        // deletions (every line has a null Position), which used to throw
+        // ArgumentOutOfRangeException in the Compact formatter.
+        settings.ScrubLines(_ => true);
+
+        return ThrowsTask(() =>
+            Verify(
+                """
+                First
+                Second
+                Third
+                """,
+                settings));
+    }
+
     [Test]
     public Task AtTestLevelMinimal()
     {

src/Verify.DiffPlex/VerifyDiffPlex.cs

@@ -101,8 +101,11 @@ static StringBuilder CompactCompare(string received, string verified)
         var diff = InlineDiffBuilder.Diff(verified, received);
         var builder = new StringBuilder();
 
-        // ReSharper disable once RedundantSuppressNullableWarningExpression
-        var prefixLength = diff.Lines.Max(_ => _.Position).ToString()!.Length;
+        // Position is null for deleted lines. When the received side is empty the diff is
+        // all deletions, so Max returns null; fall back to 0 (a single-digit width) to avoid
+        // a negative spacePrefix length.
+        var maxPosition = diff.Lines.Max(_ => _.Position) ?? 0;
+        var prefixLength = maxPosition.ToString().Length;
         var spacePrefix = new string(' ', prefixLength - 1);
 
         static bool IsChanged(DiffPiece? line) => line?.Type is ChangeType.Inserted or ChangeType.Deleted;