CmdPal: Make it easier to add APIs in the future (#41056)

We learned a lot about adding interfaces in WinRT this week. I figured
I'd send a PR to write it all down.

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/CommandProvider.cs

@@ -6,7 +6,7 @@ using Windows.Foundation;
 
 namespace Microsoft.CommandPalette.Extensions.Toolkit;
 
-public abstract partial class CommandProvider : ICommandProvider
+public abstract partial class CommandProvider : ICommandProvider, ICommandProvider2
 {
     public virtual string Id { get; protected set; } = string.Empty;
 
@@ -47,4 +47,26 @@ public abstract partial class CommandProvider : ICommandProvider
         {
         }
     }
+
+    /// <summary>
+    /// This is used to manually populate the WinRT type cache in CmdPal with
+    /// any interfaces that might not follow a straight linear path of requires.
+    ///
+    /// You don't need to call this as an extension author.
+    /// </summary>
+    /// <returns>an array of objects that implement all the leaf interfaces we support</returns>
+    public object[] GetApiExtensionStubs()
+    {
+        return [new SupportCommandsWithProperties()];
+    }
+
+    /// <summary>
+    /// A stub class which implements IExtendedAttributesProvider. Just marshalling this
+    /// across the ABI will be enough for CmdPal to store IExtendedAttributesProvider in
+    /// its type cache.
+    /// </summary>
+    private sealed partial class SupportCommandsWithProperties : IExtendedAttributesProvider
+    {
+        public IDictionary<string, object>? GetProperties() => null;
+    }
 }

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/FontIconData.cs

@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+using Windows.Foundation.Collections;
+
+namespace Microsoft.CommandPalette.Extensions.Toolkit;
+
+/// <summary>
+/// Represents an icon that is a font glyph.
+/// This is used for icons that are defined by a specific font face,
+/// such as Wingdings.
+///
+/// Note that Command Palette will default to using the Segoe Fluent Icons,
+/// Segoe MDL2 Assets font for glyphs in the Segoe UI Symbol range, or Segoe
+/// UI for any other glyphs. This class is only needed if you want a non-Segoe
+/// font icon.
+/// </summary>
+public partial class FontIconData : IconData, IExtendedAttributesProvider
+{
+    public string FontFamily { get; set; }
+
+    public FontIconData(string glyph, string fontFamily)
+        : base(glyph)
+    {
+        FontFamily = fontFamily;
+    }
+
+    public IDictionary<string, object>? GetProperties() => new ValueSet()
+        {
+            { "FontFamily", FontFamily },
+        };
+}

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/IconData.cs

@@ -2,6 +2,7 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics.CodeAnalysis;
 using Windows.Storage.Streams;
 
 namespace Microsoft.CommandPalette.Extensions.Toolkit;

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/IconInfo.cs

@@ -27,6 +27,12 @@ public partial class IconInfo : IIconInfo
         Dark = dark;
     }
 
+    public IconInfo(IconData icon)
+    {
+        Light = icon;
+        Dark = icon;
+    }
+
     internal IconInfo()
         : this(string.Empty)
     {

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions/Microsoft.CommandPalette.Extensions.idl

@@ -364,5 +364,17 @@ namespace Microsoft.CommandPalette.Extensions
         void InitializeWithHost(IExtensionHost host);
     };
     
+    [contract(Microsoft.CommandPalette.Extensions.ExtensionsContract, 1)]
+    interface IExtendedAttributesProvider
+    {
+        Windows.Foundation.Collections.IMap<String, Object> GetProperties();
+    };
+    
+    [contract(Microsoft.CommandPalette.Extensions.ExtensionsContract, 1)]
+    interface ICommandProvider2 requires ICommandProvider
+    {
+        Object[] GetApiExtensionStubs();
+    };
+    
 
 }