Skip alternate version links when resolving link parents

src/Jellyfin.Database/Jellyfin.Database.Implementations/DescendantQueryHelper.cs

@@ -177,9 +177,17 @@ public static class DescendantQueryHelper
     // Resolves the folders whose linked children lead, at any depth, to a matching item.
     private static List<Guid> ResolveLinkParents(JellyfinDbContext context, IQueryable<Guid> matchingItemIds, IQueryable<Guid> ancestorsOfMatches)
     {
+        // An alternate version is a second file for the item that links it, not a child of it, so that
+        // edge is not walked. It is also the one link a non-folder owns, and there is one per remuxed
+        // movie: walking it would swell this list from the BoxSet and Playlist count to the item count,
+        // and the list is bound into every statement the returned queryable is embedded in.
+        var containerLinks = context.LinkedChildren
+            .Where(e => e.ChildType != LinkedChildType.LocalAlternateVersion
+                && e.ChildType != LinkedChildType.LinkedAlternateVersion);
+
         // A link sits above the closure and above another link alike, so the hop repeats until nothing
-        // new turns up. Only link owners are collected, which bounds it by BoxSets and Playlists.
-        var resolved = context.LinkedChildren
+        // new turns up.
+        var resolved = containerLinks
             .Where(e => matchingItemIds.Contains(e.ChildId) || ancestorsOfMatches.Contains(e.ChildId))
             .Select(e => e.ParentId)
             .Distinct()
@@ -193,11 +201,11 @@ public static class DescendantQueryHelper
                 .WhereOneOrMany(frontier, e => e.ItemId)
                 .Select(e => e.ParentItemId);
 
-            var directLinkParents = context.LinkedChildren
+            var directLinkParents = containerLinks
                 .WhereOneOrMany(frontier, e => e.ChildId)
                 .Select(e => e.ParentId);
 
-            var indirectLinkParents = context.LinkedChildren
+            var indirectLinkParents = containerLinks
                 .Where(e => containingFolders.Contains(e.ChildId))
                 .Select(e => e.ParentId);
 

tests/Jellyfin.Server.Implementations.Tests/Item/DescendantQueryHelperTests.cs

@@ -363,6 +363,44 @@ public sealed class DescendantQueryHelperTests : SqliteDbTestFixture
         }
     }
 
+    [Fact]
+    public void GetFolderIdsMatching_AlternateVersionLinks_AreNotWalked()
+    {
+        var collections = Guid.NewGuid();
+        var boxSet = Guid.NewGuid();
+        var library = Guid.NewGuid();
+        var movie = Guid.NewGuid();
+        var alternateVersion = Guid.NewGuid();
+
+        using (var ctx = CreateDbContext())
+        {
+            AddFolder(ctx, collections);
+            AddItem(ctx, boxSet, BoxSetType, isFolder: true);
+            AddFolder(ctx, library);
+            AddItem(ctx, movie, MovieType);
+            AddItem(ctx, alternateVersion, MovieType);
+
+            AddAncestors(ctx, boxSet, collections);
+            AddAncestors(ctx, movie, library);
+            AddAncestors(ctx, alternateVersion, library);
+            // Only the second file carries the subtitles, and it hangs off the movie by an alternate
+            // version link. The movie is not a folder, so that link is not a parent-child edge.
+            AddLink(ctx, movie, alternateVersion, LinkedChildType.LocalAlternateVersion);
+            AddLink(ctx, boxSet, movie);
+            AddStream(ctx, alternateVersion, MediaStreamTypeEntity.Subtitle);
+            ctx.SaveChanges();
+        }
+
+        using (var ctx = CreateDbContext())
+        {
+            var folders = DescendantQueryHelper.GetFolderIdsMatching(ctx, new HasSubtitles()).ToHashSet();
+
+            // The library still matches: the alternate version carries its own closure. The box set does
+            // not, matching the descendant side, which does not follow a non-folder's links either.
+            Assert.Equal([library], folders);
+        }
+    }
+
     [Fact]
     public void GetOwnedDescendantIds_IgnoresLinkedChildren()
     {
@@ -472,7 +510,7 @@ public sealed class DescendantQueryHelperTests : SqliteDbTestFixture
     }
 
     // LinkedChildren is keyed on (ParentId, SortOrder), so every link of a parent needs its own slot.
-    private void AddLink(JellyfinDbContext context, Guid parentId, Guid childId)
+    private void AddLink(JellyfinDbContext context, Guid parentId, Guid childId, LinkedChildType childType = LinkedChildType.Manual)
     {
         _linkCounters.TryGetValue(parentId, out var sortOrder);
         _linkCounters[parentId] = sortOrder + 1;
@@ -481,7 +519,7 @@ public sealed class DescendantQueryHelperTests : SqliteDbTestFixture
         {
             ParentId = parentId,
             ChildId = childId,
-            ChildType = LinkedChildType.Manual,
+            ChildType = childType,
             SortOrder = sortOrder
         });
     }