From 1721031322b7e51137796f9816b82353b3222286 Mon Sep 17 00:00:00 2001
From: Ben Deane <ben@elbeno.com>
Date: Wed, 15 Oct 2025 12:03:03 -0600
Subject: [PATCH] :art: Provide better control over freestanding

Problem:
- The `SIMULATE_FREESTANDING` macro applies to multiple repos. Sometimes we
  might want finer-grained control over which elements of which repos are
  freestanding-compatible, because toolchains differ in what they support.

Solution:
- Introduce `STDX_FREESTANDING` for this repo control.
- Defining `SIMULATE_FREESTANDING` will also control `STDX_FREESTANDING`.
---
 CMakeLists.txt                       | 1 +
 include/stdx/detail/fmt.hpp          | 8 +++++++-
 include/stdx/detail/freestanding.hpp | 5 +++++
 test/CMakeLists.txt                  | 2 +-
 test/ct_format.cpp                   | 2 +-
 usage_test/CMakeLists.txt            | 2 +-
 6 files changed, 16 insertions(+), 4 deletions(-)
 create mode 100644 include/stdx/detail/freestanding.hpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 174be64..c91fa2d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -61,6 +61,7 @@ target_sources(
               include/stdx/cx_vector.hpp
               include/stdx/detail/bitset_common.hpp
               include/stdx/detail/fmt.hpp
+              include/stdx/detail/freestanding.hpp
               include/stdx/detail/list_common.hpp
               include/stdx/env.hpp
               include/stdx/for_each_n_args.hpp
diff --git a/include/stdx/detail/fmt.hpp b/include/stdx/detail/fmt.hpp
index 3d2abe4..fd6172a 100644
--- a/include/stdx/detail/fmt.hpp
+++ b/include/stdx/detail/fmt.hpp
@@ -1,6 +1,10 @@
 #pragma once
 
-#if not STDX_FMT_FREESTANDING
+#include <stdx/detail/freestanding.hpp>
+
+// NOLINTBEGIN(cppcoreguidelines-macro-usage)
+
+#ifndef STDX_FREESTANDING
 
 #include <fmt/compile.h>
 #include <fmt/format.h>
@@ -172,3 +176,5 @@ CONSTEVAL auto format_to(It dest, auto fmtstr, auto v) -> void {
 } // namespace stdx
 
 #endif
+
+// NOLINTEND(cppcoreguidelines-macro-usage)
diff --git a/include/stdx/detail/freestanding.hpp b/include/stdx/detail/freestanding.hpp
new file mode 100644
index 0000000..d113323
--- /dev/null
+++ b/include/stdx/detail/freestanding.hpp
@@ -0,0 +1,5 @@
+#pragma once
+
+#ifdef SIMULATE_FREESTANDING
+#define STDX_FREESTANDING
+#endif
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 2bef2bf..1d888ca 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -95,7 +95,7 @@ if(${CMAKE_CXX_STANDARD} GREATER_EQUAL 20)
         warnings
         stdx)
     target_compile_definitions(ct_format_freestanding_test
-                               PRIVATE -DSTDX_FMT_FREESTANDING=1)
+                               PRIVATE STDX_FREESTANDING)
 endif()
 
 add_subdirectory(fail)
diff --git a/test/ct_format.cpp b/test/ct_format.cpp
index af34730..5876da8 100644
--- a/test/ct_format.cpp
+++ b/test/ct_format.cpp
@@ -106,7 +106,7 @@ TEST_CASE("format a compile-time argument with different base", "[ct_format]") {
                    "Hello 0x2a"_fmt_res);
 }
 
-#if not STDX_FMT_FREESTANDING
+#ifndef STDX_FREESTANDING
 TEST_CASE("format a compile-time argument with fmt spec", "[ct_format]") {
     STATIC_REQUIRE(stdx::ct_format<"Hello {:*>#6x}">(CX_VALUE(42)) ==
                    "Hello **0x2a"_fmt_res);
diff --git a/usage_test/CMakeLists.txt b/usage_test/CMakeLists.txt
index d490908..0ff84f4 100644
--- a/usage_test/CMakeLists.txt
+++ b/usage_test/CMakeLists.txt
@@ -12,6 +12,6 @@ cpmaddpackage(NAME stdx SOURCE_DIR "${CMAKE_CURRENT_LIST_DIR}/.." GIT_TAG HEAD)
 add_executable(app main.cpp)
 target_link_libraries(app PRIVATE stdx)
 if(CPP_IMPLEMENTATION STREQUAL "FREESTANDING")
-    target_compile_definitions(app PRIVATE STDX_FMT_FREESTANDING)
+    target_compile_definitions(app PRIVATE SIMULATE_FREESTANDING)
     target_compile_options(app PRIVATE -ffreestanding)
 endif()