generator: Replace Extends{Root} with StructExtends<Root> generic

Instead of emitting a new `trait` for every `Root` struct that is being
implemented by one or more "child" structs (those that have `Root` in
their `structextends`), create one trait that takes the root struct as a
generic parameter, and implement that directly instead.

This not only saves on having to define the `trait` for every
`Root` struct but also paves the way towards providing default trait
implementations for any pair of root and child struct, such as the
`p_next` builder methods.

Changelog.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     - `get_pipeline_executable_statistics()`.
   The expected length of this array can be queried with the respective `*_len()` variant of these functions.
 - `push_next()` has been renamed to `extend()` and marked as `unsafe`. Users are encouraged to call `push()` for singular structs instead. (#909)
+- All `Extends{Root}` traits have been replaced with a single `Extends<Root>` trait using generics. (#971)
 
 ### Removed
 

ash/Cargo.toml

@@ -24,6 +24,9 @@ rust-version = "1.69.0"
 [dependencies]
 libloading = { version = "0.8", optional = true }
 
+[dev-dependencies]
+trybuild = "1.0"
+
 [features]
 default = ["loaded", "debug", "std"]
 # Link the Vulkan loader at compile time.

ash/src/extensions/khr/acceleration_structure.rs

@@ -263,7 +263,10 @@ impl crate::khr::acceleration_structure::Device {
         max_primitive_counts: &[u32],
         size_info: &mut vk::AccelerationStructureBuildSizesInfoKHR<'_>,
     ) {
-        assert_eq!(max_primitive_counts.len(), build_info.geometry_count as _);
+        assert_eq!(
+            max_primitive_counts.len(),
+            build_info.geometry_count as usize
+        );
 
         (self.fp.get_acceleration_structure_build_sizes_khr)(
             self.handle,

ash/src/lib.rs

@@ -255,3 +255,9 @@ where
         }
     }
 }
+
+#[test]
+fn trybuild() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/fail/long_lived_root_struct_borrow.rs");
+}

ash/src/vk.rs

@@ -56,6 +56,15 @@ pub unsafe trait TaggedStructure {
     const STRUCTURE_TYPE: StructureType;
 }
 
+/// Implemented for every structure that extends base structure `B`. Concretely that means struct
+/// `B` is listed in its array of [`structextends` in the Vulkan registry][1].
+///
+/// Similar to [`TaggedStructure`] , all `unsafe` implementers of this trait must guarantee that
+/// their structure is layout-compatible [`vk::BaseInStructure`] and [`vk::BaseOutStructure`].
+///
+/// [1]: https://registry.khronos.org/vulkan/specs/latest/styleguide.html#extensions-interactions
+pub unsafe trait Extends<B> {}
+
 /// Iterates through the pointer chain. Includes the item that is passed into the function.
 /// Stops at the last [`BaseOutStructure`] that has a null [`BaseOutStructure::p_next`] field.
 pub(crate) unsafe fn ptr_chain_iter<T: ?Sized>(
@@ -222,6 +231,62 @@ mod tests {
         assert_eq!(chain, chain2);
     }
 
+    #[test]
+    #[should_panic]
+    fn disallow_nested_ptr_chains() {
+        let mut generated_commands =
+            vk::PhysicalDeviceDeviceGeneratedCommandsFeaturesEXT::default();
+        let mut private_data = vk::PhysicalDevicePrivateDataFeatures {
+            p_next: <*mut _>::cast(&mut generated_commands),
+            ..Default::default()
+        };
+        let _device_create_info = vk::DeviceCreateInfo::default().push(&mut private_data);
+    }
+
+    #[test]
+    fn test_nested_ptr_chains() {
+        let mut generated_commands =
+            vk::PhysicalDeviceDeviceGeneratedCommandsFeaturesEXT::default();
+        let mut private_data = vk::PhysicalDevicePrivateDataFeatures {
+            p_next: <*mut _>::cast(&mut generated_commands),
+            ..Default::default()
+        };
+        let mut variable_pointers = vk::PhysicalDeviceVariablePointerFeatures::default();
+        let mut corner = vk::PhysicalDeviceCornerSampledImageFeaturesNV::default();
+        let chain = alloc::vec![
+            <*mut _>::cast(&mut private_data),
+            <*mut _>::cast(&mut generated_commands),
+            <*mut _>::cast(&mut variable_pointers),
+            <*mut _>::cast(&mut corner),
+        ];
+        let mut device_create_info = vk::DeviceCreateInfo::default()
+            .push(&mut corner)
+            .push(&mut variable_pointers);
+        // Insert private_data->generated_commands into the chain, such that generate_commands->variable_pointers->corner:
+        device_create_info = unsafe { device_create_info.extend(&mut private_data) };
+        let chain2: Vec<*mut vk::BaseOutStructure<'_>> = unsafe {
+            vk::ptr_chain_iter(&mut device_create_info)
+                .skip(1)
+                .collect()
+        };
+        assert_eq!(chain, chain2);
+    }
+
+    #[test]
+    fn test_dynamic_add_to_ptr_chain() {
+        let mut variable_pointers = vk::PhysicalDeviceVariablePointerFeatures::default();
+        let variable_pointers: &mut dyn vk::Extends<vk::DeviceCreateInfo<'_>> =
+            &mut variable_pointers;
+        let chain = alloc::vec![<*mut _>::cast(variable_pointers)];
+        let mut device_create_info = vk::DeviceCreateInfo::default().push(variable_pointers);
+        let chain2: Vec<*mut vk::BaseOutStructure<'_>> = unsafe {
+            vk::ptr_chain_iter(&mut device_create_info)
+                .skip(1)
+                .collect()
+        };
+        assert_eq!(chain, chain2);
+    }
+
     #[test]
     fn test_debug_flags() {
         assert_eq!(