Fix version dropdown notice (#1381)

If there is a mapping, but was fully migrated to docs v3, say so

Author: reakaleek

src/Elastic.Documentation/Legacy/ILegacyUrlMapper.cs

@@ -11,7 +11,7 @@ public record LegacyPageMapping(string RawUrl, string Version, bool Exists)
 
 public interface ILegacyUrlMapper
 {
-	IReadOnlyCollection<LegacyPageMapping> MapLegacyUrl(IReadOnlyCollection<string>? mappedPages);
+	IReadOnlyCollection<LegacyPageMapping>? MapLegacyUrl(IReadOnlyCollection<string>? mappedPages);
 }
 
 public record NoopLegacyUrlMapper : ILegacyUrlMapper

src/Elastic.Markdown/Slices/HtmlWriter.cs

@@ -110,9 +110,9 @@ private async Task<string> RenderLayout(MarkdownFile markdown, MarkdownDocument
 			Features = DocumentationSet.Configuration.Features,
 			StaticFileContentHashProvider = StaticFileContentHashProvider,
 			ReportIssueUrl = reportUrl,
-			CurrentVersion = legacyPages.Count > 0 ? legacyPages.ElementAt(0).Version : "9.0+",
-			LegacyPages = legacyPages.Skip(1).ToArray(),
-			VersionDropdownItems = VersionDrownDownItemViewModel.FromLegacyPageMappings(legacyPages.Skip(1).ToArray()),
+			CurrentVersion = legacyPages?.Count > 0 ? legacyPages.ElementAt(0).Version : "9.0+",
+			LegacyPages = legacyPages?.Skip(1).ToArray(),
+			VersionDropdownItems = VersionDrownDownItemViewModel.FromLegacyPageMappings(legacyPages?.Skip(1).ToArray()),
 			Products = allProducts
 		});
 		return await slice.RenderAsync(cancellationToken: ctx);

src/Elastic.Markdown/Slices/IndexViewModel.cs

@@ -33,9 +33,9 @@ public class IndexViewModel
 	public required INavigationItem[] Parents { get; init; }
 
 	public required string NavigationHtml { get; init; }
-	public required string? CurrentVersion { get; init; }
-	public required LegacyPageMapping[] LegacyPages { get; init; }
-	public required VersionDrownDownItemViewModel[] VersionDropdownItems { get; init; }
+	public required string CurrentVersion { get; init; }
+	public required LegacyPageMapping[]? LegacyPages { get; init; }
+	public required VersionDrownDownItemViewModel[]? VersionDropdownItems { get; init; }
 	public required string? UrlPathPrefix { get; init; }
 	public required string? GithubEditUrl { get; init; }
 	public required string? ReportIssueUrl { get; init; }
@@ -63,8 +63,12 @@ public class VersionDrownDownItemViewModel
 	public required VersionDrownDownItemViewModel[]? Children { get; init; }
 
 	// This logic currently only handles one level of children. Although the model supports multiple levels, it is not currently used.
-	public static VersionDrownDownItemViewModel[] FromLegacyPageMappings(LegacyPageMapping[] legacyPageMappings)
+	public static VersionDrownDownItemViewModel[]? FromLegacyPageMappings(LegacyPageMapping[]? legacyPageMappings)
 	{
+		if (legacyPageMappings is null)
+		{
+			return null;
+		}
 		var groupedVersions = GroupByMajorVersion(legacyPageMappings);
 		return groupedVersions.Select(m =>
 		{

src/Elastic.Markdown/Slices/Layout/_TableOfContents.cshtml

@@ -47,7 +47,7 @@
 							}
 						</a>						
 					</li>
-					@foreach (var legacyPage in Model.LegacyPages)
+					@foreach (var legacyPage in Model.LegacyPages ?? [])
 					{
 						<li class="block">
 							@if (legacyPage.Exists)
@@ -68,13 +68,20 @@
 
 						</li>
 					}
-					@if (Model.LegacyPages.Length == 0)
+					@if (Model.LegacyPages is null) // This means there is no mapping because the page is new in v3
 					{
 						<li class="block border-t-1 border-grey-20">
 							<div class="py-1 px-4 text-sm">
 								There is no previous version of this page.
 							</div>
 						</li>
+					} else if (Model.LegacyPages.Length == 0) // This means there is a legacy page mapping with 0 entries, which means the page was fully migrated and is also redirecting to the new system.
+					{
+						<li class="block border-t-1 border-grey-20">
+							<div class="py-1 px-4 text-sm">
+								This page was fully migrated to the current version.
+							</div>
+						</li>
 					}
 				</ul>
 			</div>

src/Elastic.Markdown/Slices/MarkdownLayoutViewModel.cs

@@ -18,7 +18,7 @@ public class MarkdownLayoutViewModel : GlobalLayoutViewModel
 
 	public required string? CurrentVersion { get; init; }
 
-	public required LegacyPageMapping[] LegacyPages { get; init; }
+	public required LegacyPageMapping[]? LegacyPages { get; init; }
 
 	public required IReadOnlyCollection<PageTocItem> PageTocItems { get; init; }