extensions: Don't check extension names for interior nuls at runtime (#522)

This name is emitted by the generator and already known to not contain
any null-characters: replace the runtime iteration+comparison (hidden
behind `from_bytes_with_nul`) and `.expect()` panic with an `unsafe`
"cast" through `from_bytes_with_nul_unchecked`, just like the
function-pointer loaders.

Changelog.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Extension names from `fn name()` will not be checked for interior nuls anymore at runtime (#522)
 - examples: Use `c_char` for pointer to raw string (#521)
 - Device extension `khr::PipelineExecutableProperties` and `khr::TimelineSemaphore` now expose `fn device()` instead of `fn instance()` (#499)
 - Changed `khr::PipelineExecutableProperties::new()` and `khr::TimelineSemaphore::new()` to take `instance` and `device` as arguments (#499)

generator/src/lib.rs

@@ -1203,7 +1203,6 @@ pub fn generate_extension_commands<'a>(
         extension_name.to_camel_case().strip_prefix("Vk").unwrap()
     );
     let fp = generate_function_pointers(ident.clone(), &commands, &aliases, fn_cache);
-    let byte_name = format!("{}\0", extension_name);
 
     let spec_version = items
         .iter()
@@ -1227,11 +1226,11 @@ pub fn generate_extension_commands<'a>(
             }
         });
 
-    let byte_name_ident = syn::LitByteStr::new(byte_name.as_bytes(), Span::call_site());
+    let byte_name_ident = Literal::byte_string(format!("{}\0", extension_name).as_bytes());
     let extension_cstr = quote! {
         impl #ident {
             pub fn name() -> &'static ::std::ffi::CStr {
-                ::std::ffi::CStr::from_bytes_with_nul(#byte_name_ident).expect("Wrong extension string")
+                unsafe { ::std::ffi::CStr::from_bytes_with_nul_unchecked(#byte_name_ident) }
             }
             #spec_version
         }