cmake/scripts/gen_hedley_undef_check.cmake

# Shared extractor for the JSON_HEDLEY_* macro names defined in hedley.hpp.
#
# Every macro that hedley.hpp #defines must be #undef-ed again once json.hpp
# has been fully processed (see include/nlohmann/detail/macro_unscope.hpp
# and https://github.com/nlohmann/json/issues/5408). Deriving the macro list
# straight from hedley.hpp here -- instead of hand-maintaining it in two
# places -- means hedley_undef.hpp and the regression test that checks for
# leaked macros can never drift apart, even after a future `make
# update_hedley` pulls in new macros from upstream Hedley.
#
#   MODE=undef  (default): write hedley_undef.hpp (SPDX header, #pragma once,
#               one #undef per macro name) -- used by `make update_hedley_undef`
#   MODE=checks:            write one #ifdef/FAIL_CHECK/#endif per macro name,
#               meant to be #include-d inside a TEST_CASE -- used by
#               tests/CMakeLists.txt to (re)generate the include for
#               tests/src/unit-no-macro-leak.cpp
#
# Required variables:
#   HEDLEY_HPP  path to include/nlohmann/thirdparty/hedley/hedley.hpp
#   OUTPUT      path of the file to (over)write
# Optional:
#   MODE        "undef" (default) or "checks"

if(NOT DEFINED HEDLEY_HPP OR NOT DEFINED OUTPUT)
    message(FATAL_ERROR "HEDLEY_HPP and OUTPUT must be set")
endif()

if(NOT EXISTS "${HEDLEY_HPP}")
    message(FATAL_ERROR "Hedley header not found: ${HEDLEY_HPP}")
endif()

if(NOT DEFINED MODE)
    set(MODE undef)
endif()

if(NOT MODE STREQUAL "undef" AND NOT MODE STREQUAL "checks")
    message(FATAL_ERROR "MODE must be undef or checks, got: ${MODE}")
endif()

# Line-anchored, like `grep -oE "^[[:blank:]]*#[[:blank:]]*define[[:blank:]]+JSON_HEDLEY_[A-Za-z0-9_]+"`.
# Unanchored matching would also pick up JSON_HEDLEY_* mentions inside
# comments or string literals elsewhere in the file, which must not turn
# into #undef lines.
file(STRINGS "${HEDLEY_HPP}" hedley_lines)
set(macro_names)
foreach(line IN LISTS hedley_lines)
    if("${line}" MATCHES "^[ \t]*#[ \t]*define[ \t]+(JSON_HEDLEY_[A-Za-z0-9_]+)")
        list(APPEND macro_names "${CMAKE_MATCH_1}")
    endif()
endforeach()

if(NOT macro_names)
    message(FATAL_ERROR "No JSON_HEDLEY_* macros found in ${HEDLEY_HPP}")
endif()

list(REMOVE_DUPLICATES macro_names)
# Lexicographic, locale-independent (ASCII-only names) -- matches `LC_ALL=C sort`.
list(SORT macro_names COMPARE STRING)
list(LENGTH macro_names macro_count)

set(generated "")
if(MODE STREQUAL "undef")
    # Same banner `make update_hedley_undef` would stamp by hand, so the
    # recipe is self-contained and its output is byte-stable across reruns.
    # The embedded SPDX tags below are part of the *generated* file's
    # content, not a REUSE header for this .cmake script itself (which is
    # already covered by the blanket path = "**" rule in REUSE.toml) -- keep
    # them wrapped in REUSE-IgnoreStart/End so `reuse lint` does not try to
    # parse "MIT\n")" as this file's own SPDX-License-Identifier value.
    # REUSE-IgnoreStart
    string(APPEND generated "//     __ _____ _____ _____\n")
    string(APPEND generated "//  __|  |   __|     |   | |  JSON for Modern C++\n")
    string(APPEND generated "// |  |  |__   |  |  | | | |  version 3.12.0\n")
    string(APPEND generated "// |_____|_____|_____|_|___|  https://github.com/nlohmann/json\n")
    string(APPEND generated "//\n")
    string(APPEND generated "// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>\n")
    string(APPEND generated "// SPDX-License-Identifier: MIT\n")
    # REUSE-IgnoreEnd
    string(APPEND generated "\n")
    string(APPEND generated "#pragma once\n")
    string(APPEND generated "\n")
    foreach(name IN LISTS macro_names)
        string(APPEND generated "#undef ${name}\n")
    endforeach()
else()
    string(APPEND generated "// This file is generated by cmake/scripts/gen_hedley_undef_check.cmake\n")
    string(APPEND generated "// from include/nlohmann/thirdparty/hedley/hedley.hpp. Do not edit it by\n")
    string(APPEND generated "// hand -- it is regenerated on every build. ${macro_count} macros checked.\n\n")
    foreach(name IN LISTS macro_names)
        string(APPEND generated "#ifdef ${name}\n")
        string(APPEND generated "    FAIL_CHECK(\"${name} leaked after including nlohmann/json.hpp\");\n")
        string(APPEND generated "#endif\n")
    endforeach()
endif()

get_filename_component(output_dir "${OUTPUT}" DIRECTORY)
if(output_dir)
    file(MAKE_DIRECTORY "${output_dir}")
endif()

# Avoid rewriting the file (and busting downstream incremental rebuilds)
# when the content has not actually changed.
set(write_output TRUE)
if(EXISTS "${OUTPUT}")
    file(READ "${OUTPUT}" existing_content)
    if(existing_content STREQUAL generated)
        set(write_output FALSE)
    endif()
endif()
if(write_output)
    file(WRITE "${OUTPUT}" "${generated}")
endif()