Use Rust-1.78 #[diagnostic::on_unimplemented] to clarify push_next trait

[MarijnS95]

When a user passes an invalid type into push_next(), since Rust 1.78 we can now customize the diagnostics error to more clearly decsribe what and why they are not allowed to pass a certain type into this structure instead of having to refer to the trait definition (which contains no docs either).

This turns the following, rather obnoxious error:

error[E0277]: the trait bound `HdrMetadataEXT<'_>: ExtendsDeviceCreateInfo` is not satisfied
    --> ash-examples/src/lib.rs:336:42
     |
336  |             device_create_info.push_next(&mut vk::HdrMetadataEXT::default());
     |                                --------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `ExtendsDeviceCreateInfo` is not implemented for `HdrMetadataEXT<'_>`
     |                                |
     |                                required by a bound introduced by this call
     |
     = help: the following other types implement trait `ExtendsDeviceCreateInfo`:
               PhysicalDeviceDeviceGeneratedCommandsFeaturesNV<'_>
               PhysicalDeviceDeviceGeneratedCommandsComputeFeaturesNV<'_>
               DevicePrivateDataCreateInfo<'_>
               PhysicalDevicePrivateDataFeatures<'_>
               PhysicalDeviceFeatures2<'_>
               PhysicalDeviceVariablePointersFeatures<'_>
               PhysicalDeviceMultiviewFeatures<'_>
               DeviceGroupDeviceCreateInfo<'_>
             and 186 others
note: required by a bound in `DeviceCreateInfo::<'a>::push_next`
    --> /newdata/Code/TraverseResearch/ash/ash/src/vk/definitions.rs:1383:25
     |
1383 |     pub fn push_next<T: ExtendsDeviceCreateInfo + ?Sized>(mut self, next: &'a mut T) -> Self {
     |                         ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `DeviceCreateInfo::<'a>::push_next`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `ash-examples` (lib) due to 1 previous error

Into something more digestible:

error[E0277]: `HdrMetadataEXT<'_>` is not allowed in the `pNext` chain of `vk::DeviceCreateInfo`
    --> ash-examples/src/lib.rs:336:42
     |
336  |             device_create_info.push_next(&mut vk::HdrMetadataEXT::default());
     |                                --------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `HdrMetadataEXT<'_>` does not extend `vk::DeviceCreateInfo`
     |                                |
     |                                required by a bound introduced by this call
     |
     = help: the trait `ExtendsDeviceCreateInfo` is not implemented for `HdrMetadataEXT<'_>`
     = help: the following other types implement trait `ExtendsDeviceCreateInfo`:
               PhysicalDeviceDeviceGeneratedCommandsFeaturesNV<'_>
               PhysicalDeviceDeviceGeneratedCommandsComputeFeaturesNV<'_>
               DevicePrivateDataCreateInfo<'_>
               PhysicalDevicePrivateDataFeatures<'_>
               PhysicalDeviceFeatures2<'_>
               PhysicalDeviceVariablePointersFeatures<'_>
               PhysicalDeviceMultiviewFeatures<'_>
               DeviceGroupDeviceCreateInfo<'_>
             and 186 others
note: required by a bound in `DeviceCreateInfo::<'a>::push_next`
    --> /newdata/Code/TraverseResearch/ash/ash/src/vk/definitions.rs:1391:25
     |
1391 |     pub fn push_next<T: ExtendsDeviceCreateInfo + ?Sized>(mut self, next: &'a mut T) -> Self {
     |                         ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `DeviceCreateInfo::<'a>::push_next`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `ash-examples` (lib) due to 1 previous error

Please help me bike-shed the wording though! I was also hoping to find some upstream documentation (or a list of current extensions) based on the vk.xml structextends field, to reference in a note = attribute.

[Ralith]

Awesome idea! The wording looks good to me. Could we link to e.g. https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkDeviceCreateInfo.html#VUID-VkDeviceCreateInfo-pNext-pNext? Not sure that's much more helpful than just linking the trait rustdoc, but it's authoritative and cross-referenced.

[MarijnS95]

Awesome idea! The wording looks good to me. Could we link to e.g. https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkDeviceCreateInfo.html#VUID-VkDeviceCreateInfo-pNext-pNext? Not sure that's much more helpful than just linking the trait rustdoc, but it's authoritative and cross-referenced.

Good one, I didn't realize that the VUID was so front and center, and is easy to generate links to.

[MarijnS95]

Unsure if the link should be wrapped in <>, let me check some other diagnostics.