Dongle.GuidRVAGen 1.0.2

GuidRVAGen

A source generator that generates RVAs for GUIDs using a GuidAttribute equivalent.

Jump to usage

Purpose

Typically, static GUIDs are defined using static readonly fields, like below:

static readonly Guid IID_IUnknown = new Guid(0x00000000, 0x0000, 0x0000, 0xc000, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46);

While this is a fine solution, it can be a bit more cumbersome to use in case of doing lower-level COM interop (which is required if you want to use CsWin32 with Native AOT). Under CsWin32's "disable-marshalling" mode (which must be used for AOT compilation), it generates a QueryInterface method which takes a Guid*:

HRESULT QueryInterface(Guid* riid, void** ppv);

This means to use it with static readonly Guid, you would have to copy it to another variable:

IUnknown* comObject;
IUnknown* queriedObject;
Guid guid = IID_IUnknown;
Marshal.ThrowExceptionForHR(comObject->QueryInterface(&guid, (void**)(&queriedObject)));

Or pin it yourself:

IUnknown* comObject;
IUnknown* queriedObject;

fixed (Guid* pGuid = IID_IUnknown)
{
  Marshal.ThrowExceptionForHR(comObject->QueryInterface(pGuid, (void**)(&queriedObject)));
}

Or use Marshal.QueryInterface, which even though gives an idiomatic way to pass in the field using ref, requires a lot of casting:

IUnknown* comObject;
IUnknown* queriedObject;

Marshal.ThrowExceptionForHR(Marshal.QueryInterface((nint)comObject, ref IUnknown, out nint pQueriedObject);
queriedObject = (IUnknown*)pQueriedObject;

This is not to mention that having lots of static readonly fields can impact performance, due to the fact that they have to be initialized all at once.

GuidRVAGen helps resolve those problems for you!

Usage

To start with, you will need the following:

• .NET 9 SDK Preview 6 or newer

[!NOTE]

You don't need to use the .NET 9 target framework itself. You only need to have the SDK installed.

• Visual Studio 2022, version 17.12 or newer (or another IDE with .NET 9 Preview 6 support or newer)
• The C# version to be set to 13.0 or newer
  • You don't need to change it in .NET 9 or newer unless you have explicitly changed the <LangVersion> MSBuild property. For older targets, add the following line to one of your <PropertyGroup>:

    <LangVersion>13.0</LangVersion>
    

Then, install the NuGet package and add a class, like the following:

namespace YourNamespace;

public static unsafe partial class IID
{
  [GuidRVAGen.Guid("00000000-0000-0000-c000-000000000046")]
  public static partial Guid* IID_IUnknown { get; }
}

[!WARNING]

The partial keyword is critical. Make sure you set it to the property, as long with any types that the property resides in (in this case, the IID class).

[!CAUTION]

Do NOT change the value of the Guid* that the property returns! Doing so can cause crashes, memory corruption, etc.

As you can see, we now have a Guid* property that we can now use:

IUnknown* comObject;
IUnknown* queriedObject;

Marshal.ThrowExceptionForHR(comObject->QueryInterface(IID.IID_IUnknown, (void**)(&queriedObject)));

If you need a ref or ref readonly return value instead, you can also do that!

namespace YourNamespace;

public static unsafe partial class IID
{
  [GuidRVAGen.Guid("00000000-0000-0000-c000-000000000046")]
  public static partial ref readonly Guid IID_IUnknown { get; }
}

namespace YourNamespace;

public static unsafe partial class IID
{
  [GuidRVAGen.Guid("00000000-0000-0000-c000-000000000046")]
  public static partial ref Guid IID_IUnknown { get; }
}

[!CAUTION]

Similar to the Guid* return type, do NOT change the value of the ref returned!