Split AIFunction into a base class

Enable a representation that doesn't support invocation separate from one that does.

Author: stephentoub

src/Libraries/Microsoft.Extensions.AI.Abstractions/CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release History
 
+## NOT YET RELEASED
+
+- Added non-invocable `AIFunctionDeclaration` (base class for `AIFunction`), `AIFunctionFactory.CreateDeclaration`, and `AIFunction.AsDeclarationOnly`.
+
 ## 9.8.0
 
 - Added `AIAnnotation` and related types to represent citations and other annotations in chat messages.

src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatToolMode.cs

@@ -55,8 +55,7 @@ private protected ChatToolMode()
 
     /// <summary>
     /// Instantiates a <see cref="ChatToolMode"/> indicating that tool usage is required,
-    /// and that the specified <see cref="AIFunction"/> must be selected. The function name
-    /// must match an entry in <see cref="ChatOptions.Tools"/>.
+    /// and that the specified function name must be selected.
     /// </summary>
     /// <param name="functionName">The name of the required function.</param>
     /// <returns>An instance of <see cref="RequiredChatToolMode"/> for the specified function name.</returns>

src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/RequiredChatToolMode.cs

@@ -15,17 +15,17 @@ namespace Microsoft.Extensions.AI;
 public sealed class RequiredChatToolMode : ChatToolMode
 {
     /// <summary>
-    /// Gets the name of a specific <see cref="AIFunction"/> that must be called.
+    /// Gets the name of a specific tool that must be called.
     /// </summary>
     /// <remarks>
-    /// If the value is <see langword="null"/>, any available function can be selected (but at least one must be).
+    /// If the value is <see langword="null"/>, any available tool can be selected (but at least one must be).
     /// </remarks>
     public string? RequiredFunctionName { get; }
 
     /// <summary>
-    /// Initializes a new instance of the <see cref="RequiredChatToolMode"/> class that requires a specific function to be called.
+    /// Initializes a new instance of the <see cref="RequiredChatToolMode"/> class that requires a specific tool to be called.
     /// </summary>
-    /// <param name="requiredFunctionName">The name of the function that must be called.</param>
+    /// <param name="requiredFunctionName">The name of the tool that must be called.</param>
     /// <exception cref="ArgumentException"><paramref name="requiredFunctionName"/> is empty or composed entirely of whitespace.</exception>
     /// <remarks>
     /// <paramref name="requiredFunctionName"/> can be <see langword="null"/>. However, it's preferable to use

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

@@ -6,44 +6,17 @@
 using System.Threading;
 using System.Threading.Tasks;
 
+#pragma warning disable SA1202 // Elements should be ordered by access
+
 namespace Microsoft.Extensions.AI;
 
 /// <summary>Represents a function that can be described to an AI service and invoked.</summary>
-public abstract class AIFunction : AITool
+public abstract class AIFunction : AIFunctionDeclaration
 {
-    /// <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.
-    /// </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 virtual JsonElement JsonSchema => AIJsonUtilities.DefaultJsonSchema;
-
-    /// <summary>Gets a JSON Schema describing the function's return value.</summary>
-    /// <remarks>
-    /// A <see langword="null"/> typically reflects a function that doesn't specify a return schema
-    /// or a function that returns <see cref="void"/>, <see cref="Task"/>, or <see cref="ValueTask"/>.
-    /// </remarks>
-    public virtual JsonElement? ReturnJsonSchema => null;
+    /// <summary>Initializes a new instance of the <see cref="AIFunction"/> class.</summary>
+    protected AIFunction()
+    {
+    }
 
     /// <summary>
     /// Gets the underlying <see cref="MethodInfo"/> that this <see cref="AIFunction"/> might be wrapping.
@@ -72,4 +45,14 @@ public abstract class AIFunction : AITool
     protected abstract ValueTask<object?> InvokeCoreAsync(
         AIFunctionArguments arguments,
         CancellationToken cancellationToken);
+
+    /// <summary>Creates a <see cref="AIFunctionDeclaration"/> representation of this <see cref="AIFunction"/> that can't be invoked.</summary>
+    /// <returns>The created instance.</returns>
+    /// <remarks>
+    /// <see cref="AIFunction"/> derives from <see cref="AIFunctionDeclaration"/>, layering on the ability to invoke the function in addition
+    /// to describing it. <see cref="AsDeclarationOnly"/> creates a new object that describes the function but that can't be invoked.
+    /// </remarks>
+    public AIFunctionDeclaration AsDeclarationOnly() => new NonInvocableAIFunction(this);
+
+    private sealed class NonInvocableAIFunction(AIFunction function) : DelegatingAIFunctionDeclaration(function);
 }

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

@@ -0,0 +1,58 @@
+// 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 System.Threading.Tasks;
+
+#pragma warning disable S1694 // An abstract class should have both abstract and concrete methods
+
+namespace Microsoft.Extensions.AI;
+
+/// <summary>Represents a function that can be described to an AI service.</summary>
+/// <remarks>
+/// <see cref="AIFunctionDeclaration"/> is the base class for <see cref="AIFunction"/>, which
+/// adds the ability to invoke the function. Components may type test <see cref="AITool"/> instances
+/// for <see cref="AIFunctionDeclaration"/> to determine whether they can be described as functions,
+/// and may type test for <see cref="AIFunction"/> to determine whether they can be invoked.
+/// </remarks>
+public abstract class AIFunctionDeclaration : AITool
+{
+    /// <summary>Initializes a new instance of the <see cref="AIFunctionDeclaration"/> class.</summary>
+    protected AIFunctionDeclaration()
+    {
+    }
+
+    /// <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.
+    /// </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 virtual JsonElement JsonSchema => AIJsonUtilities.DefaultJsonSchema;
+
+    /// <summary>Gets a JSON Schema describing the function's return value.</summary>
+    /// <remarks>
+    /// A <see langword="null"/> typically reflects a function that doesn't specify a return schema
+    /// or a function that returns <see cref="void"/>, <see cref="Task"/>, or <see cref="ValueTask"/>.
+    /// </remarks>
+    public virtual JsonElement? ReturnJsonSchema => null;
+}

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

@@ -49,7 +49,7 @@ public static partial class AIFunctionFactory
     /// <para>
     /// By default, any parameters to <paramref name="method"/> are sourced from the <see cref="AIFunctionArguments"/>'s dictionary
     /// of key/value pairs and are represented in the JSON schema for the function, as exposed in the returned <see cref="AIFunction"/>'s
-    /// <see cref="AIFunction.JsonSchema"/>. There are a few exceptions to this:
+    /// <see cref="AIFunctionDeclaration.JsonSchema"/>. There are a few exceptions to this:
     /// <list type="bullet">
     ///   <item>
     ///     <description>
@@ -131,7 +131,7 @@ public static AIFunction Create(Delegate method, AIFunctionFactoryOptions? optio
     /// <para>
     /// Any parameters to <paramref name="method"/> are sourced from the <see cref="AIFunctionArguments"/>'s dictionary
     /// of key/value pairs and are represented in the JSON schema for the function, as exposed in the returned <see cref="AIFunction"/>'s
-    /// <see cref="AIFunction.JsonSchema"/>. There are a few exceptions to this:
+    /// <see cref="AIFunctionDeclaration.JsonSchema"/>. There are a few exceptions to this:
     /// <list type="bullet">
     ///   <item>
     ///     <description>
@@ -212,7 +212,7 @@ public static AIFunction Create(Delegate method, string? name = null, string? de
     /// <para>
     /// By default, any parameters to <paramref name="method"/> are sourced from the <see cref="AIFunctionArguments"/>'s dictionary
     /// of key/value pairs and are represented in the JSON schema for the function, as exposed in the returned <see cref="AIFunction"/>'s
-    /// <see cref="AIFunction.JsonSchema"/>. There are a few exceptions to this:
+    /// <see cref="AIFunctionDeclaration.JsonSchema"/>. There are a few exceptions to this:
     /// <list type="bullet">
     ///   <item>
     ///     <description>
@@ -304,7 +304,7 @@ public static AIFunction Create(MethodInfo method, object? target, AIFunctionFac
     /// <para>
     /// Any parameters to <paramref name="method"/> are sourced from the <see cref="AIFunctionArguments"/>'s dictionary
     /// of key/value pairs and are represented in the JSON schema for the function, as exposed in the returned <see cref="AIFunction"/>'s
-    /// <see cref="AIFunction.JsonSchema"/>. There are a few exceptions to this:
+    /// <see cref="AIFunctionDeclaration.JsonSchema"/>. There are a few exceptions to this:
     /// <list type="bullet">
     ///   <item>
     ///     <description>
@@ -398,7 +398,7 @@ public static AIFunction Create(MethodInfo method, object? target, string? name
     /// <para>
     /// By default, any parameters to <paramref name="method"/> are sourced from the <see cref="AIFunctionArguments"/>'s dictionary
     /// of key/value pairs and are represented in the JSON schema for the function, as exposed in the returned <see cref="AIFunction"/>'s
-    /// <see cref="AIFunction.JsonSchema"/>. There are a few exceptions to this:
+    /// <see cref="AIFunctionDeclaration.JsonSchema"/>. There are a few exceptions to this:
     /// <list type="bullet">
     ///   <item>
     ///     <description>
@@ -467,6 +467,39 @@ public static AIFunction Create(
         AIFunctionFactoryOptions? options = null) =>
         ReflectionAIFunction.Build(method, createInstanceFunc, options ?? _defaultOptions);
 
+    /// <summary>Creates an <see cref="AIFunctionDeclaration"/> using the specified parameters as the implementation of its corresponding properties.</summary>
+    /// <param name="name">The name of the function.</param>
+    /// <param name="description">A description of the function, suitable for use in describing the purpose to a model.</param>
+    /// <param name="jsonSchema">A JSON schema describing the function and its input parameters.</param>
+    /// <param name="returnJsonSchema">A JSON schema describing the function's return value.</param>
+    /// <returns>The created <see cref="AIFunctionDeclaration"/> that describes a function.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="name"/> is <see langword="null"/>.</exception>
+    /// <remarks>
+    /// <see cref="CreateDeclaration"/> creates an <see cref="AIFunctionDeclaration"/> that can be used to describe a function
+    /// but not invoke it. To create an invocable <see cref="AIFunction"/>, use Create. A non-invocable <see cref="AIFunctionDeclaration"/>
+    /// may also be created from an invocable <see cref="AIFunction"/> using that function's <see cref="AIFunction.AsDeclarationOnly"/> method.
+    /// </remarks>
+    public static AIFunctionDeclaration CreateDeclaration(
+        string name,
+        string? description,
+        JsonElement jsonSchema,
+        JsonElement? returnJsonSchema = null) =>
+        new DefaultAIFunctionDeclaration(
+            Throw.IfNullOrEmpty(name),
+            description ?? string.Empty,
+            jsonSchema,
+            returnJsonSchema);
+
+    private sealed class DefaultAIFunctionDeclaration(
+        string name, string description, JsonElement jsonSchema, JsonElement? returnJsonSchema) :
+        AIFunctionDeclaration
+    {
+        public override string Name => name;
+        public override string Description => description;
+        public override JsonElement JsonSchema => jsonSchema;
+        public override JsonElement? ReturnJsonSchema => returnJsonSchema;
+    }
+
     private sealed class ReflectionAIFunction : AIFunction
     {
         public static ReflectionAIFunction Build(MethodInfo method, object? target, AIFunctionFactoryOptions options)

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

@@ -107,14 +107,14 @@ public AIFunctionFactoryOptions()
     public Func<object?, Type?, CancellationToken, ValueTask<object?>>? MarshalResult { get; set; }
 
     /// <summary>
-    /// Gets or sets a value indicating whether a schema should be created for the function's result type, if possible, and included as <see cref="AIFunction.ReturnJsonSchema" />.
+    /// Gets or sets a value indicating whether a schema should be created for the function's result type, if possible, and included as <see cref="AIFunctionDeclaration.ReturnJsonSchema" />.
     /// </summary>
     /// <remarks>
     /// <para>
     /// The default value is <see langword="false"/>.
     /// </para>
     /// <para>
-    /// When set to <see langword="true"/>, results in the produced <see cref="AIFunction.ReturnJsonSchema"/> to always be <see langword="null"/>.
+    /// When set to <see langword="true"/>, results in the produced <see cref="AIFunctionDeclaration.ReturnJsonSchema"/> to always be <see langword="null"/>.
     /// </para>
     /// </remarks>
     public bool ExcludeResultSchema { get; set; }

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

@@ -0,0 +1,48 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Text.Json;
+using Microsoft.Shared.Diagnostics;
+
+#pragma warning disable SA1202 // Elements should be ordered by access
+
+namespace Microsoft.Extensions.AI;
+
+/// <summary>
+/// Provides an optional base class for an <see cref="AIFunctionDeclaration"/> that passes through calls to another instance.
+/// </summary>
+internal class DelegatingAIFunctionDeclaration : AIFunctionDeclaration // could be made public in the future if there's demand
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DelegatingAIFunctionDeclaration"/> class as a wrapper around <paramref name="innerFunction"/>.
+    /// </summary>
+    /// <param name="innerFunction">The inner AI function to which all calls are delegated by default.</param>
+    /// <exception cref="ArgumentNullException"><paramref name="innerFunction"/> is <see langword="null"/>.</exception>
+    protected DelegatingAIFunctionDeclaration(AIFunctionDeclaration innerFunction)
+    {
+        InnerFunction = Throw.IfNull(innerFunction);
+    }
+
+    /// <summary>Gets the inner <see cref="AIFunctionDeclaration" />.</summary>
+    protected AIFunctionDeclaration InnerFunction { get; }
+
+    /// <inheritdoc />
+    public override string Name => InnerFunction.Name;
+
+    /// <inheritdoc />
+    public override string Description => InnerFunction.Description;
+
+    /// <inheritdoc />
+    public override JsonElement JsonSchema => InnerFunction.JsonSchema;
+
+    /// <inheritdoc />
+    public override JsonElement? ReturnJsonSchema => InnerFunction.ReturnJsonSchema;
+
+    /// <inheritdoc />
+    public override IReadOnlyDictionary<string, object?> AdditionalProperties => InnerFunction.AdditionalProperties;
+
+    /// <inheritdoc />
+    public override string ToString() => InnerFunction.ToString();
+}