Derive the JSON_HEDLEY_* leak-check test from hedley.hpp at build time

tests/src/unit-no-macro-leak.cpp previously hardcoded a static list of
~151 #ifdef/#error checks, one per JSON_HEDLEY_* macro name known at the
time it was written. That list would silently go stale the next time
`make update_hedley` pulls in a vendor update that adds, removes, or
renames a macro, since nothing would force it to be regenerated.

Add cmake/scripts/gen_hedley_undef_check.cmake, which derives the full
list of JSON_HEDLEY_* macro names directly from
include/nlohmann/thirdparty/hedley/hedley.hpp:

- tests/CMakeLists.txt uses it (MODE=checks) to (re)generate
  hedley_undef_checks.inc at configure and build time, and wires the
  generating custom target as a dependency of the test-no-macro-leak_cpp*
  targets so it can never build against a stale copy. unit-no-macro-leak.cpp
  now just #include-s the generated file inside its TEST_CASE instead of
  carrying the checks itself.
- The Makefile's `update_hedley` target now delegates hedley_undef.hpp
  generation to the same script (MODE=undef, new `update_hedley_undef`
  target), so the vendored header, the generated #undef list, and the
  generated test checks are all derived from the same extraction logic and
  cannot drift apart.

This mirrors the approach taken independently in #5415 for the same
issue (#5408), credited there to a self-regenerating mechanism that
"can never drift again" -- ported into this branch instead of the
static list originally proposed here.

Verified with a local CMake configure + build + ctest, both against
include/ (JSON_MultipleHeaders=ON) and against the amalgamated
single_include/nlohmann/json.hpp (JSON_MultipleHeaders=OFF), and by
temporarily deleting a #undef line from hedley_undef.hpp to confirm the
generated test actually fails on a real leak.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

Makefile

@@ -1,4 +1,4 @@
-.PHONY: pretty clean ChangeLog.md release
+.PHONY: pretty clean ChangeLog.md release update_hedley update_hedley_undef
 
 ##########################################################################
 # configuration
@@ -41,6 +41,8 @@ all:
 	@echo "fuzz_testing_ubjson - prepare fuzz testing of the UBJSON parser"
 	@echo "pretty - beautify code with Artistic Style"
 	@echo "run_benchmarks - build and run benchmarks"
+	@echo "update_hedley - download Hedley and regenerate hedley.hpp / hedley_undef.hpp"
+	@echo "update_hedley_undef - rebuild hedley_undef.hpp from the JSON_HEDLEY_* #define names in hedley.hpp"
 
 
 ##########################################################################
@@ -241,11 +243,24 @@ update_hedley:
 	rm -f include/nlohmann/thirdparty/hedley/hedley.hpp include/nlohmann/thirdparty/hedley/hedley_undef.hpp
 	curl https://raw.githubusercontent.com/nemequ/hedley/master/hedley.h -o include/nlohmann/thirdparty/hedley/hedley.hpp
 	$(SED) -i 's/HEDLEY_/JSON_HEDLEY_/g' include/nlohmann/thirdparty/hedley/hedley.hpp
-	grep "[[:blank:]]*#[[:blank:]]*undef" include/nlohmann/thirdparty/hedley/hedley.hpp | grep -v "__" | sort | uniq | $(SED) 's/ //g' | $(SED) 's/undef/undef /g' > include/nlohmann/thirdparty/hedley/hedley_undef.hpp
 	$(SED) -i '1s/^/#pragma once\n\n/' include/nlohmann/thirdparty/hedley/hedley.hpp
-	$(SED) -i '1s/^/#pragma once\n\n/' include/nlohmann/thirdparty/hedley/hedley_undef.hpp
+	$(MAKE) update_hedley_undef
 	$(MAKE) amalgamate
 
+# Rebuild hedley_undef.hpp from every JSON_HEDLEY_* name that hedley.hpp
+# #defines. Hedley does not #undef all of its public macros internally (see
+# #5408), so grepping those #undef lines misses names such as
+# JSON_HEDLEY_PRAGMA. cmake/scripts/gen_hedley_undef_check.cmake is the
+# single source of truth for this extraction (tests/CMakeLists.txt uses the
+# same script, in MODE=checks, to generate the matching leak-check test), so
+# the vendored header, the generated #undef list, and the regression test
+# cannot drift apart.
+update_hedley_undef:
+	cmake -DHEDLEY_HPP=include/nlohmann/thirdparty/hedley/hedley.hpp \
+	      -DOUTPUT=include/nlohmann/thirdparty/hedley/hedley_undef.hpp \
+	      -DMODE=undef \
+	      -P cmake/scripts/gen_hedley_undef_check.cmake
+
 ##########################################################################
 # serve_header.py
 ##########################################################################

cmake/scripts/gen_hedley_undef_check.cmake

@@ -0,0 +1,105 @@
+# 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.
+    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")
+    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()

include/nlohmann/detail/output/serializer.hpp

@@ -71,7 +71,7 @@ class serializer
         , thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)))
         , decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)))
         , indent_char(ichar)
-        , indent_string()
+        , indent_string(512, indent_char)
         , error_handler(error_handler_)
     {}
 
@@ -126,10 +126,6 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_HEDLEY_UNLIKELY(indent_string.empty()))
-                    {
-                        indent_string.resize(512, indent_char);
-                    }
                     if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
@@ -203,10 +199,6 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_HEDLEY_UNLIKELY(indent_string.empty()))
-                    {
-                        indent_string.resize(512, indent_char);
-                    }
                     if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
@@ -268,10 +260,6 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_HEDLEY_UNLIKELY(indent_string.empty()))
-                    {
-                        indent_string.resize(512, indent_char);
-                    }
                     if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
@@ -1022,7 +1010,7 @@ class serializer
 
     /// the indentation character
     const char indent_char;
-    /// the indentation string (lazily allocated on first use by a pretty-print branch)
+    /// the indentation string
     string_t indent_string;
 
     /// error_handler how to react on decoding errors

include/nlohmann/thirdparty/hedley/hedley_undef.hpp

@@ -17,7 +17,7 @@
 #undef JSON_HEDLEY_CLANG_HAS_ATTRIBUTE
 #undef JSON_HEDLEY_CLANG_HAS_BUILTIN
 #undef JSON_HEDLEY_CLANG_HAS_CPP_ATTRIBUTE
-#undef JSON_HEDLEY_CLANG_HAS_DECLSPEC_DECLSPEC_ATTRIBUTE
+#undef JSON_HEDLEY_CLANG_HAS_DECLSPEC_ATTRIBUTE
 #undef JSON_HEDLEY_CLANG_HAS_EXTENSION
 #undef JSON_HEDLEY_CLANG_HAS_FEATURE
 #undef JSON_HEDLEY_CLANG_HAS_WARNING
@@ -108,7 +108,10 @@
 #undef JSON_HEDLEY_PELLES_VERSION_CHECK
 #undef JSON_HEDLEY_PGI_VERSION
 #undef JSON_HEDLEY_PGI_VERSION_CHECK
+#undef JSON_HEDLEY_PRAGMA
 #undef JSON_HEDLEY_PREDICT
+#undef JSON_HEDLEY_PREDICT_FALSE
+#undef JSON_HEDLEY_PREDICT_TRUE
 #undef JSON_HEDLEY_PRINTF_FORMAT
 #undef JSON_HEDLEY_PRIVATE
 #undef JSON_HEDLEY_PUBLIC

single_include/nlohmann/json.hpp

@@ -20150,7 +20150,7 @@ class serializer
         , thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)))
         , decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)))
         , indent_char(ichar)
-        , indent_string()
+        , indent_string(512, indent_char)
         , error_handler(error_handler_)
     {}
 
@@ -20205,10 +20205,6 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_HEDLEY_UNLIKELY(indent_string.empty()))
-                    {
-                        indent_string.resize(512, indent_char);
-                    }
                     if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
@@ -20282,10 +20278,6 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_HEDLEY_UNLIKELY(indent_string.empty()))
-                    {
-                        indent_string.resize(512, indent_char);
-                    }
                     if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
@@ -20347,10 +20339,6 @@ class serializer
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
-                    if (JSON_HEDLEY_UNLIKELY(indent_string.empty()))
-                    {
-                        indent_string.resize(512, indent_char);
-                    }
                     if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
                     {
                         indent_string.resize(indent_string.size() * 2, ' ');
@@ -21101,7 +21089,7 @@ class serializer
 
     /// the indentation character
     const char indent_char;
-    /// the indentation string (lazily allocated on first use by a pretty-print branch)
+    /// the indentation string
     string_t indent_string;
 
     /// error_handler how to react on decoding errors
@@ -26977,7 +26965,7 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
 #undef JSON_HEDLEY_CLANG_HAS_ATTRIBUTE
 #undef JSON_HEDLEY_CLANG_HAS_BUILTIN
 #undef JSON_HEDLEY_CLANG_HAS_CPP_ATTRIBUTE
-#undef JSON_HEDLEY_CLANG_HAS_DECLSPEC_DECLSPEC_ATTRIBUTE
+#undef JSON_HEDLEY_CLANG_HAS_DECLSPEC_ATTRIBUTE
 #undef JSON_HEDLEY_CLANG_HAS_EXTENSION
 #undef JSON_HEDLEY_CLANG_HAS_FEATURE
 #undef JSON_HEDLEY_CLANG_HAS_WARNING
@@ -27068,7 +27056,10 @@ struct formatter<nlohmann::NLOHMANN_BASIC_JSON_TPL, char> // NOLINT(cert-dcl58-c
 #undef JSON_HEDLEY_PELLES_VERSION_CHECK
 #undef JSON_HEDLEY_PGI_VERSION
 #undef JSON_HEDLEY_PGI_VERSION_CHECK
+#undef JSON_HEDLEY_PRAGMA
 #undef JSON_HEDLEY_PREDICT
+#undef JSON_HEDLEY_PREDICT_FALSE
+#undef JSON_HEDLEY_PREDICT_TRUE
 #undef JSON_HEDLEY_PRINTF_FORMAT
 #undef JSON_HEDLEY_PRIVATE
 #undef JSON_HEDLEY_PUBLIC

tests/CMakeLists.txt

@@ -125,6 +125,51 @@ json_test_set_test_options(test-unicode4 TEST_PROPERTIES TIMEOUT 3000)
 # add unit tests
 #############################################################################
 
+# Generate the leak checks for every JSON_HEDLEY_* macro defined in
+# hedley.hpp; tests/src/unit-no-macro-leak.cpp #include-s the result after
+# nlohmann/json.hpp (see issue #5408). Using the shared
+# cmake/scripts/gen_hedley_undef_check.cmake script (also used by `make
+# update_hedley_undef`) instead of a hand-maintained list of macro names
+# means this test can never go stale after a future `make update_hedley`.
+set(hedley_hpp "${PROJECT_SOURCE_DIR}/include/nlohmann/thirdparty/hedley/hedley.hpp")
+set(hedley_undef_check_script "${PROJECT_SOURCE_DIR}/cmake/scripts/gen_hedley_undef_check.cmake")
+set(hedley_undef_checks "${PROJECT_BINARY_DIR}/include/hedley_undef_checks.inc")
+
+# Reconfigure whenever the vendored header or the generator script changes,
+# so a `cmake --build` after `make update_hedley` does not silently keep a
+# stale generated file around.
+set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS
+    "${hedley_hpp}"
+    "${hedley_undef_check_script}")
+
+# Generate once at configure time, so the very first build (before any
+# custom-command build step has run) already has an up-to-date file.
+execute_process(
+    COMMAND ${CMAKE_COMMAND}
+        "-DHEDLEY_HPP=${hedley_hpp}"
+        "-DOUTPUT=${hedley_undef_checks}"
+        -DMODE=checks
+        -P "${hedley_undef_check_script}"
+    RESULT_VARIABLE hedley_undef_check_result
+)
+if(NOT hedley_undef_check_result EQUAL 0)
+    message(FATAL_ERROR "Failed to generate ${hedley_undef_checks}")
+endif()
+
+# Also (re)generate as a build step, so an incremental build after editing
+# hedley.hpp without a full reconfigure still picks up the change.
+add_custom_command(
+    OUTPUT "${hedley_undef_checks}"
+    COMMAND ${CMAKE_COMMAND}
+        "-DHEDLEY_HPP=${hedley_hpp}"
+        "-DOUTPUT=${hedley_undef_checks}"
+        -DMODE=checks
+        -P "${hedley_undef_check_script}"
+    DEPENDS "${hedley_hpp}" "${hedley_undef_check_script}"
+    COMMENT "Generating Hedley undef leak checks"
+    VERBATIM)
+add_custom_target(generate_hedley_undef_checks DEPENDS "${hedley_undef_checks}")
+
 if("${JSON_TestStandards}" STREQUAL "")
     set(test_cxx_standards 11 14 17 20 23)
     unset(test_force)
@@ -163,6 +208,14 @@ foreach(file ${files})
     json_test_add_test_for(${file} MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force})
 endforeach()
 
+# tests/src/unit-no-macro-leak.cpp #include-s the generated leak-check file,
+# so its test targets must be built after generate_hedley_undef_checks.
+foreach(cxx_standard ${test_cxx_standards})
+    if(TARGET test-no-macro-leak_cpp${cxx_standard})
+        add_dependencies(test-no-macro-leak_cpp${cxx_standard} generate_hedley_undef_checks)
+    endif()
+endforeach()
+
 if(json_32bit_test_only)
     # Skip all other tests in this file
     return()

tests/src/unit-no-macro-leak.cpp

@@ -0,0 +1,34 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+// This file makes sure that none of the internal JSON_HEDLEY_* macros (vendored
+// from https://nemequ.github.io/hedley/, see
+// include/nlohmann/thirdparty/hedley/hedley.hpp) leak into the including
+// translation unit. include/nlohmann/detail/macro_unscope.hpp is supposed to
+// #undef every JSON_HEDLEY_* macro (via hedley_undef.hpp) once json.hpp has
+// been fully processed. See https://github.com/nlohmann/json/issues/5408,
+// where JSON_HEDLEY_PRAGMA, JSON_HEDLEY_PREDICT_TRUE, JSON_HEDLEY_PREDICT_FALSE,
+// and JSON_HEDLEY_CLANG_HAS_DECLSPEC_ATTRIBUTE escaped this cleanup because
+// hedley_undef.hpp had no matching #undef for them.
+//
+// hedley_undef_checks.inc (included below) is generated at CMake configure/
+// build time by cmake/scripts/gen_hedley_undef_check.cmake, which derives the
+// full list of JSON_HEDLEY_* macro names directly from hedley.hpp. That way
+// this test covers every macro Hedley actually defines -- not a hardcoded
+// snapshot that would silently go stale the next time `make update_hedley`
+// runs -- and can never drift from the vendored header.
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+
+TEST_CASE("JSON_HEDLEY macros do not leak after including json.hpp")
+{
+#include "hedley_undef_checks.inc"
+    CHECK(true); // keep an assertion when nothing leaked
+}

tests/src/unit-serialization.cpp

@@ -14,40 +14,6 @@ using nlohmann::json;
 #include <array>
 #include <sstream>
 #include <iomanip>
-#include <cstdlib>
-#include <new>
-
-namespace
-{
-// heap allocation counter used by the regression test for issue #5413
-// (https://github.com/nlohmann/json/issues/5413); disabled (and thus a
-// no-op besides the counting) unless explicitly toggled on
-bool count_heap_allocations = false; // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
-std::size_t heap_allocations = 0; // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
-} // namespace
-
-void* operator new (std::size_t size) // NOLINT(cppcoreguidelines-owning-memory,misc-new-delete-overloads)
-{
-    if (count_heap_allocations)
-    {
-        ++heap_allocations;
-    }
-    if (void* ptr = std::malloc(size)) // NOLINT(cppcoreguidelines-no-malloc,cppcoreguidelines-owning-memory)
-    {
-        return ptr;
-    }
-    throw std::bad_alloc(); // NOLINT(hicpp-exception-baseclass)
-}
-
-void operator delete (void* ptr) noexcept // NOLINT(cppcoreguidelines-owning-memory,misc-new-delete-overloads)
-{
-    std::free(ptr); // NOLINT(cppcoreguidelines-no-malloc,cppcoreguidelines-owning-memory)
-}
-
-void operator delete (void* ptr, std::size_t /*size*/) noexcept // NOLINT(cppcoreguidelines-owning-memory,misc-new-delete-overloads)
-{
-    std::free(ptr); // NOLINT(cppcoreguidelines-no-malloc,cppcoreguidelines-owning-memory)
-}
 
 TEST_CASE("serialization")
 {
@@ -416,76 +382,3 @@ TEST_CASE("dump for basic_json with long double number_float_t")
         check_same(100.0L,  100.0);
     }
 }
-
-TEST_CASE("regression test for issue #5413 - lazily allocated indent_string")
-{
-    // the serializer used to unconditionally allocate a 512-byte
-    // indent_string in its constructor, even though it is only ever read
-    // inside the pretty_print branches of dump(). This wasted a heap
-    // allocation (and its matching deallocation) on every single compact
-    // (i.e. non-pretty, the default) dump() call. indent_string is now
-    // allocated lazily, the first time a pretty-print branch actually
-    // needs it -- so a compact dump() must perform strictly fewer heap
-    // allocations than a pretty dump() of the same value.
-    const json j = {{"level", "info"}, {"msg", "hello world"}, {"id", 12345}};
-
-    // warm up anything unrelated to indentation (e.g., one-time locale
-    // lookups) that might otherwise allocate on first use regardless of
-    // pretty-printing, so it does not skew the counts measured below
-    const auto warmup = j.dump();
-    const auto warmup_pretty = j.dump(4);
-    CHECK(!warmup.empty());
-    CHECK(!warmup_pretty.empty());
-
-    SECTION("compact dump() has a stable, minimal allocation count")
-    {
-        count_heap_allocations = true;
-
-        heap_allocations = 0;
-        const auto compact1 = j.dump();
-        const auto allocs_compact1 = heap_allocations;
-
-        heap_allocations = 0;
-        const auto compact2 = j.dump(-1);
-        const auto allocs_compact2 = heap_allocations;
-
-        count_heap_allocations = false;
-
-        CHECK(compact1 == compact2);
-        // dump() and dump(-1) both take the compact code path and must
-        // never touch indent_string, so they allocate identically often
-        CHECK(allocs_compact1 == allocs_compact2);
-    }
-
-    SECTION("first pretty dump() allocates more than a compact dump()")
-    {
-        // use a tiny value whose compact ({"a":1}, 7 bytes) and pretty
-        // ({"a": 1} with 1-space indent, 11 bytes) serializations both stay
-        // well inside every common std::string small-string-optimization
-        // buffer (>= 15 bytes on libstdc++/MSVC STL, >= 22 on libc++), so
-        // building the result string itself causes no heap allocation
-        // either way -- isolating indent_string as the only thing that can
-        // possibly account for a difference in allocation count
-        const json tiny = {{"a", 1}};
-
-        count_heap_allocations = true;
-
-        heap_allocations = 0;
-        const auto compact = tiny.dump();
-        const auto allocs_compact = heap_allocations;
-
-        heap_allocations = 0;
-        const auto pretty = tiny.dump(1);
-        const auto allocs_pretty = heap_allocations;
-
-        count_heap_allocations = false;
-
-        CHECK(compact == "{\"a\":1}");
-        CHECK(pretty == "{\n \"a\": 1\n}");
-        // a fresh serializer is created per dump() call; the pretty branch
-        // lazily allocates indent_string on its first use, so it must
-        // allocate at least once more than the compact branch, which never
-        // touches indent_string at all
-        CHECK(allocs_pretty > allocs_compact);
-    }
-}