Expose AIContent constructor (#6346)

Author: stephentoub

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/AIContent.cs

@@ -5,7 +5,7 @@
 
 namespace Microsoft.Extensions.AI;
 
-/// <summary>Provides a base class for all content used with AI services.</summary>
+/// <summary>Represents content used by AI services.</summary>
 [JsonPolymorphic(TypeDiscriminatorPropertyName = "$type")]
 [JsonDerivedType(typeof(DataContent), typeDiscriminator: "data")]
 [JsonDerivedType(typeof(ErrorContent), typeDiscriminator: "error")]
@@ -20,15 +20,15 @@ public class AIContent
     /// <summary>
     /// Initializes a new instance of the <see cref="AIContent"/> class.
     /// </summary>
-    protected AIContent()
+    public AIContent()
     {
     }
 
     /// <summary>Gets or sets the raw representation of the content from an underlying implementation.</summary>
     /// <remarks>
     /// If an <see cref="AIContent"/> is created to represent some underlying object from another object
     /// model, this property can be used to store that original object. This can be useful for debugging or
-    /// for enabling a consumer to access the underlying object model if needed.
+    /// for enabling a consumer to access the underlying object model, if needed.
     /// </remarks>
     [JsonIgnore]
     public object? RawRepresentation { get; set; }

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/AIContentTests.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Text.Json;
 using Xunit;
 
 namespace Microsoft.Extensions.AI;
@@ -10,15 +11,15 @@ public class AIContentTests
     [Fact]
     public void Constructor_PropsDefault()
     {
-        DerivedAIContent c = new();
+        AIContent c = new();
         Assert.Null(c.RawRepresentation);
         Assert.Null(c.AdditionalProperties);
     }
 
     [Fact]
     public void Constructor_PropsRoundtrip()
     {
-        DerivedAIContent c = new();
+        AIContent c = new();
 
         Assert.Null(c.RawRepresentation);
         object raw = new();
@@ -31,5 +32,25 @@ public void Constructor_PropsRoundtrip()
         Assert.Same(props, c.AdditionalProperties);
     }
 
-    private sealed class DerivedAIContent : AIContent;
+    [Fact]
+    public void Serialization_Roundtrips()
+    {
+        AIContent original = new()
+        {
+            RawRepresentation = new object(),
+            AdditionalProperties = new AdditionalPropertiesDictionary { { "key", "value" } }
+        };
+
+        Assert.NotNull(original.RawRepresentation);
+        Assert.Single(original.AdditionalProperties);
+
+        string json = JsonSerializer.Serialize(original, AIJsonUtilities.DefaultOptions.GetTypeInfo(typeof(AIContent)));
+        Assert.NotNull(json);
+
+        AIContent? deserialized = (AIContent?)JsonSerializer.Deserialize(json, AIJsonUtilities.DefaultOptions.GetTypeInfo(typeof(AIContent)));
+        Assert.NotNull(deserialized);
+        Assert.Null(deserialized.RawRepresentation);
+        Assert.NotNull(deserialized.AdditionalProperties);
+        Assert.Single(deserialized.AdditionalProperties);
+    }
 }