match_in/out_struct for finding a predeclared list of types.

[i509VCB]

I was looking at something similar to match_out_struct/match_in_struct, but it returns a tuple of Option values if some type of structure was found.

The idea is largely inspired by the vk_find_struct(_const) macros in Mesa.

I'd think the macro could look like this:

fn do_something(info: &mut DeviceCreateInfo<'_>)
    // Returns Option<&mut PhysicalDeviceVulkan11Features>
    let vulkan_1_1 = ash::find_in_struct::<&mut PhysicalDeviceVulkan11Features>(info); 

    if let Some(vulkan_1_1) = vulkan_1_1 {
        ...
    }
}

Although there are a few questions worth asking:

• Accessing multiple extension types: you would have to declare all things you want to access at the same time otherwise you would have borrow checking issues.
• If multiple instances of extensions can be accessed, we need to forbid accessing the same extension type twice. I believe this would have to be done at compile time to make sense to do. Foe example you would need to forbid (&mut T, &T) and (&mut T, &mut T). (&T, &T) would technically be valid under borrowing rules but it is definitely not optimal.
• Should find_in/out_struct even support multiple elements? While this is a valid option, I find that finding a struct can be neater: https://gitlab.freedesktop.org/asahi/mesa/-/blob/c5d9a3a5a9ab57b22ae5f17d911a3b00935a4437/src/asahi/vulkan/agxv_device_memory.c#L38-39