Add a JsonConverter for LevelValue

src/Seq.Syntax/Expressions/Runtime/LevelValue.cs

@@ -1,4 +1,4 @@
-// Copyright © Serilog Contributors
+// Copyright © Datalust and Contributors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -12,16 +12,22 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+using System.Text.Json.Serialization;
+
 namespace Seq.Syntax.Expressions.Runtime;
 
 /// <summary>
 /// The typed value of the <c>@Level</c> keyword property: the level name exactly as spelled in
 /// the document's <c>@l</c> (<c>Information</c> when absent). Distinguishes levels from plain
 /// strings so that fixed-width moniker formats apply.
 /// </summary>
+/// <remarks>Serializes as its name, so that a level handed to a caller through
+/// <see cref="EvaluationResult"/> degrades to a JSON string when cloned or written, rather than
+/// to an object carrying the wrapper's own fields.</remarks>
+[JsonConverter(typeof(LevelValueJsonConverter))]
 sealed class LevelValue(string name)
 {
     public string Name { get; } = name;
 
     public override string ToString() => Name;
-}
+}

src/Seq.Syntax/Expressions/Runtime/LevelValueJsonConverter.cs

@@ -0,0 +1,31 @@
+// Copyright © Datalust and Contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Seq.Syntax.Expressions.Runtime;
+
+sealed class LevelValueJsonConverter : JsonConverter<LevelValue>
+{
+    public override LevelValue Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        return LevelMapping.ToLevelValue(reader.GetString());
+    }
+
+    public override void Write(Utf8JsonWriter writer, LevelValue value, JsonSerializerOptions options)
+    {
+        writer.WriteStringValue(value.Name);
+    }
+}

src/Seq.Syntax/Expressions/Runtime/Values.cs

@@ -40,9 +40,9 @@ static class Values
         {
             switch (Underlying(value))
             {
-                // Typed scalars degrade to their JSON string forms on insertion; `DeepClone()` does
-                // this for the serializer-supported ones, but a `LevelValue` would clone as a
-                // `{"Name": ...}` object.
+                // Typed scalars degrade to their JSON string forms on insertion. `DeepClone()` does
+                // this too, via each type's serializer support, but for a `LevelValue` the direct
+                // conversion avoids a serializer round-trip.
                 case LevelValue level:
                     return JsonValue.Create(level.Name);
                 // `unsafe()` output has no JSON form to degrade to: `DeepClone()` would serialize

test/Seq.Syntax.Tests/Expressions/ValueMechanicsTests.cs

@@ -48,6 +48,21 @@ public void ClrBackedValuesRoundTrip()
         Assert.Equal(TimeSpan.FromMinutes(90), tsBack);
     }
 
+    [Fact]
+    public void LevelValuesHandedToCallersCloneAsStrings()
+    {
+        // A caller re-parenting a `@Level` result, e.g. `seqcli search --column @Level`, sees a
+        // JSON string rather than the wrapper's fields.
+        var evt = new JsonObject { ["@l"] = "Warning" };
+        var expr = SeqExpression.Compile("@Level");
+
+        Assert.True(expr(evt).TryGetValue(out var level));
+        var enriched = new JsonObject { ["Column"] = level!.DeepClone() };
+
+        Assert.Equal("Warning", (string)enriched["Column"]!);
+        Assert.Equal("""{"Column":"Warning"}""", enriched.ToJsonString());
+    }
+
     [Fact]
     public void CallablesCanBeWrappedAndRecovered()
     {