assert.h

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#pragma once
// SPDX-FileCopyrightText: 2025 Nessan Fitzmaurice <nzznfitz+gh@icloud.com>
// SPDX-License-Identifier: MIT

 
#include <format>
#include <print>
#include <string>
#include <source_location>
 
// Avoid conflicts with other assert macros -- in particular, the ones defined in the standard library.
#ifdef assert
    #undef assert
#endif
#ifdef assert_eq
    #undef assert_eq
#endif
#ifdef debug_assert
    #undef debug_assert
#endif
#ifdef debug_assert_eq
    #undef debug_assert_eq
#endif
#ifdef always_assert
    #undef always_assert
#endif
#ifdef always_assert_eq
    #undef always_assert_eq
#endif

#define always_assert(cond, ...) \
    if (!(cond)) [[unlikely]] { failed(#cond, std::source_location::current() __VA_OPT__(, __VA_ARGS__)); }

#define always_assert_eq(lhs, rhs, ...)                                                                 \
    if (!((lhs) == (rhs))) [[unlikely]] {                                                               \
        failed_eq(#lhs, #rhs, (lhs), (rhs), std::source_location::current() __VA_OPT__(, __VA_ARGS__)); \
    }

#ifdef DEBUG
    #define debug_assert(cond, ...) always_assert(cond __VA_OPT__(, __VA_ARGS__))
#else
    #define debug_assert(cond, ...) void(0)
#endif

#ifdef DEBUG
    #define debug_assert_eq(lhs, rhs, ...) always_assert_eq(lhs, rhs __VA_OPT__(, __VA_ARGS__))
#else
    #define debug_assert_eq(a, b, ...) void(0)
#endif

#ifdef NDEBUG
    #define assert(cond, ...) void(0)
#else
    #define assert(cond, ...) always_assert(cond __VA_OPT__(, __VA_ARGS__))
#endif

#ifdef NDEBUG
    #define assert_eq(lhs, rhs, ...) void(0)
#else
    #define assert_eq(lhs, rhs, ...) always_assert_eq(lhs, rhs __VA_OPT__(, __VA_ARGS__))
#endif
 
// ---------------------------------------------------------------------------------------------------------------------
// Functions to handle assertion failures in an anonymous namespace
// ---------------------------------------------------------------------------------------------------------------------
namespace {
 
// Given a path like `/home/jj/dev/project/src/foo.cpp` this returns its "basename" `foo.cpp`
constexpr std::string
basename(std::string_view path)
{
    const auto pos = path.find_last_of("/\\\\");
    if (pos == std::string_view::npos) { return std::string(path); }
    return std::string(path.substr(pos + 1));
}
 
// Prints an error message with source code location information and optionally exits the program.
// This handles simple boolean assert `assert(cond, ...)` failures.
void
failed(std::string_view cond_str, std::source_location loc, std::string_view msg_fmt = "", auto... msg_args)
{
    std::println(stderr);
    std::println(stderr, "FAILED `assert({})` [{}:{}]", cond_str, basename(loc.file_name()), loc.line());
    if (!msg_fmt.empty()) {
        std::vprint_nonunicode(stderr, msg_fmt, std::make_format_args(msg_args...));
        std::println(stderr);
    }
    std::println(stderr);
    ::exit(1);
}

void
failed_eq(std::string_view lhs_str, std::string_view rhs_str, auto lhs, auto rhs, std::source_location loc,
          std::string_view msg_fmt = "", auto... msg_args)
{
    std::println(stderr);
    std::println(stderr, "FAILED `assert_eq({}, {})` [{}:{}]", lhs_str, rhs_str, basename(loc.file_name()), loc.line());
    if (!msg_fmt.empty()) {
        std::vprint_nonunicode(stderr, msg_fmt, std::make_format_args(msg_args...));
        std::println(stderr);
    }
    std::println(stderr, "lhs = {}", lhs);
    std::println(stderr, "rhs = {}", rhs);
    std::println(stderr);
    ::exit(1);
}
 
} // namespace