Some way to support an a handler for `BOOST_ASSERT(_MSG)` that takes a `std::source_location`

まず、既存の BOOST_ASSERT handler API と BOOST_ASSERT(_MSG) がどのように展開されるかを確認します。提案されている std::source_location を使った handler オプションを、カスタマイズ可能な BOOST_ASSERT_FAILURE_HANDLER() マクロおよび BOOST_ASSERT_MSG_FAILURE_HANDLER() マクロと比較します。メンテナーが承認した API 設計と、それに対応する実装範囲が決まれば完了です。

Problem: Using std::source_location is more efficient than passing separate file/line/column/func info because the location is a single pointer to static storage, rather than 2 pointer + 2 const ints. That can result in codegen bloat, especially on platforms like Aarch64 where it takes multiple instructions to load a global pointer. Given the usecase of assertions, this is often used for very cold (hopefully never executed!) code that sits in the same function as hot code, so you often want to make it as small as possible to maximize icache and iTLB. Note that it is important to use source_location from std:: rather than boost:: because the std:: flavor uses implementation techniques that are not available to userspace C++ to make it a single pointer to static storage.

Possible solution 1: Add a new macro like BOOST_ENABLE_ASSERT_HANDLER_WITH_STD_SOURCE_LOCATION to opt into a different handler API that takes std::source_location.

Possible solution 2: Give the user full control over the handler expression by just making the failure case be a macro call like BOOST_ASSERT_FAILURE_HANDLER() and BOOST_ASSERT_MSG_FAILURE_HANDLER(msg). The only tricky issue is that you would likely need some way to inject declarations and #includes into global scope, but it may be reasonable to say that anyone who can use this facility correctly can probably also use -include "my_boost_assert_prefix_header.h". This option also has the advantage for anyone who wants to use __builtin_trap() to get the ultimate code size reduction, while still checking asserts.