Move AIFunction parameter schematization from parameter level to function level.

src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionMetadata.cs

@@ -17,19 +17,22 @@ namespace Microsoft.Extensions.AI;
 public sealed class AIFunctionMetadata
 {
     /// <summary>The name of the function.</summary>
-    private string _name = string.Empty;
+    private readonly string _name = string.Empty;
 
     /// <summary>The description of the function.</summary>
-    private string _description = string.Empty;
+    private readonly string _description = string.Empty;
+
+    /// <summary>The JSON schema describing the function and its input parameters.</summary>
+    private readonly JsonElement _schema = AIJsonUtilities.DefaultJsonSchema;
 
     /// <summary>The function's parameters.</summary>
-    private IReadOnlyList<AIFunctionParameterMetadata> _parameters = [];
+    private readonly IReadOnlyList<AIFunctionParameterMetadata> _parameters = [];
 
     /// <summary>The function's return parameter.</summary>
-    private AIFunctionReturnParameterMetadata _returnParameter = AIFunctionReturnParameterMetadata.Empty;
+    private readonly AIFunctionReturnParameterMetadata _returnParameter = AIFunctionReturnParameterMetadata.Empty;
 
     /// <summary>Optional additional properties in addition to the named properties already available on this class.</summary>
-    private IReadOnlyDictionary<string, object?> _additionalProperties = EmptyReadOnlyDictionary<string, object?>.Instance;
+    private readonly IReadOnlyDictionary<string, object?> _additionalProperties = EmptyReadOnlyDictionary<string, object?>.Instance;
 
     /// <summary><see cref="_parameters"/> indexed by name, lazily initialized.</summary>
     private Dictionary<string, AIFunctionParameterMetadata>? _parametersByName;
@@ -55,6 +58,7 @@ public AIFunctionMetadata(AIFunctionMetadata metadata)
         Parameters = metadata.Parameters;
         ReturnParameter = metadata.ReturnParameter;
         AdditionalProperties = metadata.AdditionalProperties;
+        Schema = metadata.Schema;
     }
 
     /// <summary>Gets the name of the function.</summary>
@@ -100,6 +104,43 @@ public AIFunctionReturnParameterMetadata ReturnParameter
         init => _returnParameter = Throw.IfNull(value);
     }
 
+    /// <summary>Gets a JSON Schema describing the function and its input parameters.</summary>
+    /// <remarks>
+    /// <para>
+    /// When specified, declares a self-contained JSON schema document that describes the function and its input parameters.
+    /// A simple example of a JSON schema for a function that adds two numbers together is shown below:
+    /// </para>
+    /// <code>
+    /// {
+    ///   "title" : "addNumbers",
+    ///   "description": "A simple function that adds two numbers together.",
+    ///   "type": "object",
+    ///   "properties": {
+    ///     "a" : { "type": "number" },
+    ///     "b" : { "type": "number", "default": 1 }
+    ///   }, 
+    ///   "required" : ["a"]
+    /// }
+    /// </code>
+    /// <para>
+    /// The metadata present in the schema document plays an important role in guiding AI function invocation.
+    /// Functions should incorporate as much detail as possible. The arity of the "properties" keyword should
+    /// also match the length of the <see cref="Parameters"/> list.
+    /// </para>
+    /// <para>
+    /// When no schema is specified, consuming chat clients should assume the "{}" or "true" schema, indicating that any JSON input is admissible.
+    /// </para>
+    /// </remarks>
+    public JsonElement Schema
+    {
+        get => _schema;
+        init
+        {
+            AIJsonUtilities.ValidateSchemaDocument(value);
+            _schema = value;
+        }
+    }
+
     /// <summary>Gets any additional properties associated with the function.</summary>
     public IReadOnlyDictionary<string, object?> AdditionalProperties
     {

src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionParameterMetadata.cs

@@ -11,7 +11,7 @@ namespace Microsoft.Extensions.AI;
 /// </summary>
 public sealed class AIFunctionParameterMetadata
 {
-    private string _name;
+    private readonly string _name;
 
     /// <summary>Initializes a new instance of the <see cref="AIFunctionParameterMetadata"/> class for a parameter with the specified name.</summary>
     /// <param name="name">The name of the parameter.</param>
@@ -37,7 +37,6 @@ public AIFunctionParameterMetadata(AIFunctionParameterMetadata metadata)
         DefaultValue = metadata.DefaultValue;
         IsRequired = metadata.IsRequired;
         ParameterType = metadata.ParameterType;
-        Schema = metadata.Schema;
     }
 
     /// <summary>Gets the name of the parameter.</summary>
@@ -61,7 +60,4 @@ public string Name
 
     /// <summary>Gets the .NET type of the parameter.</summary>
     public Type? ParameterType { get; init; }
-
-    /// <summary>Gets a JSON Schema describing the parameter's type.</summary>
-    public object? Schema { get; init; }
 }

src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionReturnParameterMetadata.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Text.Json;
 using Microsoft.Shared.Diagnostics;
 
 namespace Microsoft.Extensions.AI;
@@ -14,6 +15,9 @@ public sealed class AIFunctionReturnParameterMetadata
     /// <summary>Gets an empty return parameter metadata instance.</summary>
     public static AIFunctionReturnParameterMetadata Empty { get; } = new();
 
+    /// <summary>The JSON schema describing the function and its input parameters.</summary>
+    private readonly JsonElement _schema = AIJsonUtilities.DefaultJsonSchema;
+
     /// <summary>Initializes a new instance of the <see cref="AIFunctionReturnParameterMetadata"/> class.</summary>
     public AIFunctionReturnParameterMetadata()
     {
@@ -34,5 +38,13 @@ public AIFunctionReturnParameterMetadata(AIFunctionReturnParameterMetadata metad
     public Type? ParameterType { get; init; }
 
     /// <summary>Gets a JSON Schema describing the type of the return parameter.</summary>
-    public object? Schema { get; init; }
+    public JsonElement Schema
+    {
+        get => _schema;
+        init
+        {
+            AIJsonUtilities.ValidateSchemaDocument(value);
+            _schema = value;
+        }
+    }
 }