Module code_elimination 

Maximizing Code Elimination

If you were to use cargo expand on the proto_message or proto_oneof, you’ll realize that the ProtoValidation, ValidatedMessage and ValidatedOneof traits use associated constants to check if oneofs and messages have validators in them or not.

This is done with the intent of maximizing code elimination, so that the .validate() method will be completely eliminated by the compiler if a oneof/message has no validators, and any call to it will also be eliminated.

This is very important because it allows us to implement these traits freely without hurting performance or binary size, and it also means that we can make blanket calls to .validate() for all incoming messages, because if some of those messages do not have validators, that call will be a no-op and it will be eliminated by the compiler entirely, rather than needlessly setting up stack frames.

The crate has a dedicated test to guard against regressions in this area.

use std::collections::HashMap;

use protify::*;

proto_package!(TESTING_PKG, name = "testing", no_cel_test);

define_proto_file!(TESTING, name = "testing.proto", package = TESTING_PKG);

#[allow(clippy::use_self)]
#[proto_message]
#[proto(skip_checks(all))]
struct MsgWithNoValidator {
	id: i32,
	#[proto(oneof(tags(1, 2, 3)))]
	oneof: Option<OneofWithNoValidator>,
	#[proto(message)]
	recursive: Option<Box<MsgWithNoValidator>>,
	#[proto(repeated(message))]
	vec: Vec<MsgWithNoValidator>,
	#[proto(map(int32, message))]
	map: HashMap<i32, MsgWithNoValidator>,
	#[proto(message)]
	second_degree_recursion: Option<SecondDegreeRecursion>,
}

#[proto_message]
#[proto(skip_checks(all))]
struct SecondDegreeRecursion {
	#[proto(message)]
	recursive: Option<Box<MsgWithNoValidator>>,
	#[proto(oneof(tags(1, 2, 3)))]
	third_degree_recursion: Option<OneofWithNoValidator>,
}

#[proto_oneof]
#[proto(skip_checks(all))]
enum OneofWithNoValidator {
	#[proto(tag = 1)]
	A(i32),
	#[proto(tag = 2)]
	B(i32),
	#[proto(tag = 3, message)]
	Recursive(Box<MsgWithNoValidator>),
}

// You can clone the repo and run `just check-asm-output` to view the asm output of this function.
//
// If the validator is being correctly detected as empty, the assembly output should be just an empty return:
//
// .section .text.trigger_validation,"ax",@progbits
// .globl  trigger_validation
// .p2align        4
// .type   trigger_validation,@function
// trigger_validation:
// .cfi_startproc
// ret
#[unsafe(no_mangle)]
#[inline(never)]
fn trigger_validation(msg: &MsgWithNoValidator) {
	let _ = msg.validate();
}

// Dummy fn that should crash the test if there is a regression
// about code elimination
unsafe extern "C" {
	fn __this_code_should_have_been_eliminated();
}

#[test]
fn code_elimination_test() {
	if MsgWithNoValidator::HAS_DEFAULT_VALIDATOR
	  // The check above actually implies these two,
		// but we add them manually out of caution
    || OneofWithNoValidator::HAS_DEFAULT_VALIDATOR
    || SecondDegreeRecursion::HAS_DEFAULT_VALIDATOR
	{
		unsafe { __this_code_should_have_been_eliminated() }
	}
}