Resource leak if allocation of `SafeHandle` fails

[carlreinke]

Actual behavior

The generated code leaks the resource if allocation of the SafeHandle instance causes OOM. E.g.

internal static unsafe winmdroot.Devices.DeviceAndDriverInstallation.CONFIGRET CM_Open_DevNode_Key(uint dnDevNode, uint samDesired, uint ulHardwareProfile, uint Disposition, out Microsoft.Win32.SafeHandles.SafeRegistryHandle phkDevice, uint ulFlags)
{
    winmdroot.System.Registry.HKEY phkDeviceLocal;
    winmdroot.Devices.DeviceAndDriverInstallation.CONFIGRET __result = PInvoke.CM_Open_DevNode_Key(dnDevNode, samDesired, ulHardwareProfile, Disposition, &phkDeviceLocal, ulFlags);
    phkDevice = new Microsoft.Win32.SafeHandles.SafeRegistryHandle(phkDeviceLocal, ownsHandle: true);  // OOM
    return __result;
}

Expected behavior

The generated code should allocate the SafeHandle instance before the P/Invoke and use Marshal.InitHandle to initialize the handle after the P/Invoke. E.g.

internal static unsafe winmdroot.Devices.DeviceAndDriverInstallation.CONFIGRET CM_Open_DevNode_Key(uint dnDevNode, uint samDesired, uint ulHardwareProfile, uint Disposition, out Microsoft.Win32.SafeHandles.SafeRegistryHandle phkDevice, uint ulFlags)
{
    phkDevice = new Microsoft.Win32.SafeHandles.SafeRegistryHandle();
    winmdroot.System.Registry.HKEY phkDeviceLocal;
    winmdroot.Devices.DeviceAndDriverInstallation.CONFIGRET __result = PInvoke.CM_Open_DevNode_Key(dnDevNode, samDesired, ulHardwareProfile, Disposition, &phkDeviceLocal, ulFlags);
    System.Runtime.InteropServices.Marshal.InitHandle(phkDevice, phkDeviceLocal);
    return __result;
}

See also the API review for Marshal.InitHandle.

Context

• CsWin32 version: 0.3.183
• Target Framework: net8.0

[colejohnson66]

If you encounter an OOM, you have other issues than a memory leak.

[jevansaks]

I'll review a PR if someone wants to make this change, but hardening cswin32 against OOM seems unnecessary.