V14 Bugfix ensures correct line endings for partial view snippets (#15906)

* Created extension class so we can ensure native line endings

* Added usage of extension method for ensuring native line endings

* Added tests, to see if the snippets return the correct content

* Removed space

src/Umbraco.Core/Extensions/LineEndingsExtensions.cs

@@ -0,0 +1,50 @@
+using System.Runtime.InteropServices;
+
+namespace Umbraco.Cms.Core.Extensions;
+
+public static class LineEndingsExtensions
+{
+    /// <summary>
+    ///     Ensures Lf only everywhere.
+    /// </summary>
+    /// <param name="text">The text to filter.</param>
+    /// <returns>The filtered text.</returns>
+    private static string Lf(string text)
+    {
+        if (string.IsNullOrEmpty(text))
+        {
+            return text;
+        }
+
+        text = text.Replace("\r", string.Empty); // remove CR
+        return text;
+    }
+
+    /// <summary>
+    ///     Ensures CrLf everywhere.
+    /// </summary>
+    /// <param name="text">The text to filter.</param>
+    /// <returns>The filtered text.</returns>
+    private static string CrLf(string text)
+    {
+        if (string.IsNullOrEmpty(text))
+        {
+            return text;
+        }
+
+        text = text.Replace("\r", string.Empty); // remove CR
+        text = text.Replace("\n", "\r\n"); // add CRLF everywhere
+        return text;
+    }
+
+    /// <summary>
+    /// Ensures native line endings.
+    /// </summary>
+    /// <param name="text">the text to ensure native line endings for.</param>
+    /// <returns>the text with native line endings.</returns>
+    public static string EnsureNativeLineEndings(this string text)
+    {
+        var useCrLf = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+        return useCrLf ? CrLf(text) : Lf(text);
+    }
+}

src/Umbraco.Core/Snippets/PartialViewSnippetCollectionBuilder.cs

@@ -2,6 +2,7 @@ using System.Text.RegularExpressions;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
 using Umbraco.Cms.Core.Composing;
+using Umbraco.Cms.Core.Extensions;
 using Umbraco.Cms.Core.Strings;
 using Umbraco.Extensions;
 
@@ -38,6 +39,7 @@ public partial class PartialViewSnippetCollectionBuilder : LazyCollectionBuilder
     private string CleanUpSnippetContent(string content)
     {
         const string partialViewHeader = "@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage";
+        content = content.EnsureNativeLineEndings();
 
         // Strip the @inherits if it's there
         Regex headerMatch = HeaderRegex();