Element ids: string keys read from the members MessagePack writes; AllowPrivate, inherited-formatter and unwritten-string-key pins; README states the whole-value exception

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/GameCult.Caching/CultElementIds.cs

@@ -617,12 +617,12 @@ namespace GameCult.Caching
 
         // A type MessagePack writes as one value the walk cannot look into: its own formatter ([MessagePackFormatter] on the type,
         // inherited), [DataContract] on a type that is not [MessagePackObject] (the object resolver writes its members), or string
-        // keys (KeyAsPropertyName, or any [Key] with a string key). Such a type is Leaf, even when it is also enumerable.
+        // keys (KeyAsPropertyName, or a [Key] with a string key on a member MessagePack writes: a private or [IgnoreMember] one is not written). Such a type is Leaf, even when it is also enumerable.
         private static bool IsWrittenWhole(Type type) =>
             type.IsDefined(typeof(MessagePackFormatterAttribute), true) ||
             (type.IsDefined(typeof(DataContractAttribute), true) && !type.IsDefined(typeof(MessagePackObjectAttribute), true)) ||
             type.GetCustomAttribute<MessagePackObjectAttribute>(true)?.KeyAsPropertyName == true ||
-            AllInstanceMembers(type).Any(member => member.GetCustomAttribute<KeyAttribute>(true)?.StringKey != null);
+            MembersOf(type).Any(member => member.GetCustomAttribute<KeyAttribute>(true)?.StringKey != null);
 
         // A type MessagePack serializes by key: [MessagePackObject] or [Union].
         private static bool IsKeyed(Type type) =>

src/GameCult.Caching/README.md

@@ -195,6 +195,15 @@ A document type that holds a list of objects gives every object type in that lis
 `[Key]`. The id is what lets a variant override one list element instead of the
 whole list. Lists of strings, numbers and other non-object values need none.
 
+The rule covers the shapes the id walk owns: arrays, `IEnumerable<T>` classes and
+interfaces, dictionary values, and integer-keyed `[MessagePackObject]` and `[Union]`
+types. Any other holder is one whole value: `ImmutableArray<T>`, `ArraySegment<T>`,
+`Memory<T>`, `KeyValuePair`, tuples, `Lazy<T>`, a class without `[MessagePackObject]`,
+a `[DataContract]` or string-keyed type, and a type or member declaring
+`[MessagePackFormatter]`. Its elements carry no element ids: a `[CultElementId]`
+member inside it is a plain string, never minted or checked, and a variant can only
+replace the holder whole.
+
 ```csharp
 [MessagePackObject]
 public sealed class Line

tests/GameCult.Caching.Tests/ElementIdEngineTests.cs

@@ -357,6 +357,8 @@ namespace GameCult.Caching.Tests
         {
             Assert.That(Problems(typeof(HOverFormattedId)).Single(), Does.Contain("Id").And.Contain("[MessagePackFormatter]"));
             Assert.That(Problems(typeof(OwnerOverFormatted)), Is.Empty, "the override inherits its base's formatter, so the member is a whole value");
+            Assert.That(CultElementIds.Inspect(typeof(OwnerOverFormatted)).IdPath, Is.Empty, "a walked override would put its list on the id path");
+            Assert.That(Assign(new OwnerOverFormatted { Items = { new EIded() } }, "r", deterministic: false), Is.EqualTo(0), "and mint into a list its formatter may drop ids from");
 
             Assert.That(Problems(typeof(HIdOverride)), Is.Empty, "a base [CultElementId] is the override's id");
             var root = new HIdOverride { Items = { new IdOverride() } };
@@ -544,7 +546,7 @@ namespace GameCult.Caching.Tests
             Assert.That(Problems(typeof(ApIgn)), Is.Empty, "an ignored private member is not written");
             Assert.That(Problems(typeof(PgHold)), Is.Empty, "a list behind a private getter is not written without AllowPrivate");
 
-            foreach (var type in new[] { typeof(EIded), typeof(HHiddenLeaf), typeof(PubIgn), typeof(ApIgn), typeof(PgHold), typeof(MemberMix), typeof(HOptHidden), typeof(ApDerived), typeof(NoApDerived), typeof(ApInheritor) })
+            foreach (var type in new[] { typeof(EIded), typeof(HHiddenLeaf), typeof(PubIgn), typeof(ApIgn), typeof(PgHold), typeof(MemberMix), typeof(HOptHidden), typeof(ApDerived), typeof(NoApDerived), typeof(ApInheritor), typeof(ApIgnAp), typeof(PSkH), typeof(ISkH) })
             {
                 var allowPrivate = type.GetCustomAttribute<MessagePackObjectAttribute>(true)!.AllowPrivate;
                 Assert.That(CultElementIds.WrittenKeyedMembers(type).Select(member => member.Name),
@@ -661,6 +663,33 @@ namespace GameCult.Caching.Tests
             RefusesBare(typeof(Whole<List<EBare>>));
         }
 
+        // A string key counts only on a member MessagePack writes: a private or [IgnoreMember] one leaves the type integer-keyed and owned.
+        [Test]
+        public void AStringKeyOnAMemberMessagePackDoesNotWriteLeavesTheTypeOwned()
+        {
+            foreach (var holder in new object[] { new PSkH { Items = { new EIded(), new EIded() } }, new ISkH { Items = { new EIded(), new EIded() } } })
+            {
+                Assert.That(Problems(holder.GetType()), Is.Empty, holder.GetType().Name);
+                Assert.That(CultElementIds.Inspect(holder.GetType()).IdPath, Does.Contain(holder.GetType()), holder.GetType().Name);
+                Assert.That(Assign(holder, "r", deterministic: false), Is.EqualTo(2), holder.GetType().Name);
+                Assert.That(CultElementIds.Holds(holder.GetType(), holder), Is.True, holder.GetType().Name);
+            }
+
+            Assert.That(Problems(typeof(Whole<List<NoIdPlain>>)).Single(), Does.Contain("[CultElementId]"));
+            Assert.That(Problems(typeof(Whole<List<NoIdEl>>)).Single(), Does.Contain("[CultElementId]"), "an element whose only string key is ignored is as bare as its twin");
+        }
+
+        // The AllowPrivate edges: an [IgnoreMember] member is not written even under it, and only the element's own most derived
+        // declaration lets a private setter be read back.
+        [Test]
+        public void TheAllowPrivateEdgesFollowWhatMessagePackWrites()
+        {
+            Assert.That(CultElementIds.WrittenKeyedMembers(typeof(ApIgnAp)), Is.Empty, "an ignored member is not written under AllowPrivate");
+            Assert.That(Problems(typeof(HApIgnId)).Single(), Does.Contain("does not write").And.Contain("Id"));
+            Assert.That(Problems(typeof(HNoApPrivSet)).Single(), Does.Contain("setter is not public").And.Contain("Id"),
+                "the derived plain [MessagePackObject] decides: its private setter is not read back, whatever its base declares");
+        }
+
         // MessagePack writes an AllowPrivate type with every member up its base chain, and the most derived [MessagePackObject]
         // declaration decides whether that is so.
         [Test]
@@ -993,6 +1022,16 @@ namespace GameCult.Caching.Tests
         public class ApInheritor : ApDerived { }
         [MessagePackObject] public class SkElem { [Key("x")] public string X { get; set; } = ""; }
         [System.Runtime.Serialization.DataContract] public class DcHold { [System.Runtime.Serialization.DataMember(Order = 0)] public List<EIded> Items = new(); }
+        [MessagePackObject(AllowPrivate = true)] public class ApIgnAp { [Key(0)] [IgnoreMember] private List<EIded> l = new(); }
+        [MessagePackObject] public class PSkH { [Key(0)] public List<EIded> Items = new(); [Key("x")] private int x = 1; }
+        [MessagePackObject] public class ISkH { [Key(0)] public List<EIded> Items = new(); [IgnoreMember] [Key("x")] public int X { get; set; } }
+        [MessagePackObject] public class NoIdEl { [Key(0)] public int N { get; set; } [IgnoreMember] [Key("x")] public int X { get; set; } }
+        [MessagePackObject] public class NoIdPlain { [Key(0)] public int N { get; set; } }
+        [MessagePackObject(AllowPrivate = true)] public class EApIgnId { [Key(0)] public int N { get; set; } [Key(1)] [IgnoreMember] [CultElementId] public string Id { get; set; } = ""; }
+        [MessagePackObject] public class HApIgnId { [Key(0)] public List<EApIgnId> Items { get; set; } = new(); }
+        [MessagePackObject(AllowPrivate = true)] public class ApIdBase { [Key(0)] public int N { get; set; } }
+        [MessagePackObject] public class ENoApPrivSet : ApIdBase { [Key(1)] [CultElementId] public string? Id { get; private set; } }
+        [MessagePackObject] public class HNoApPrivSet { [Key(0)] public List<ENoApPrivSet> Items { get; set; } = new(); }
         [MessagePackObject(AllowPrivate = true)] public class EApPrivSet { [Key(0)] [CultElementId] public string? Id { get; private set; } }
         [MessagePackObject] public class HApPrivSet { [Key(0)] public List<EApPrivSet> Items { get; set; } = new(); }