From e6c65d6c890a89e14e1ec18b7dbc778e6c2e0f68 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Fri, 20 Sep 2024 09:34:38 -0600
Subject: [PATCH] build: `MP_UNITS_BUILD_IMPORT_STD` CMake option removed

---
 conanfile.py                                   | 1 -
 docs/getting_started/cpp_compiler_support.md   | 2 +-
 docs/getting_started/installation_and_usage.md | 8 --------
 src/CMakeLists.txt                             | 4 +---
 src/core/CMakeLists.txt                        | 2 +-
 test_package/conanfile.py                      | 1 -
 6 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/conanfile.py b/conanfile.py
index 266a8acc..f7f3e97b 100644
--- a/conanfile.py
+++ b/conanfile.py
@@ -266,7 +266,6 @@ class MPUnitsConan(ConanFile):
             tc.cache_variables["MP_UNITS_BUILD_CXX_MODULES"] = True
         if self.options.import_std:
             tc.cache_variables["CMAKE_CXX_MODULE_STD"] = True
-            tc.cache_variables["MP_UNITS_BUILD_IMPORT_STD"] = True
             # Current experimental support according to `Help/dev/experimental.rst`
             tc.cache_variables[
                 "CMAKE_EXPERIMENTAL_CXX_IMPORT_STD"
diff --git a/docs/getting_started/cpp_compiler_support.md b/docs/getting_started/cpp_compiler_support.md
index c62e0393..d5eb5a34 100644
--- a/docs/getting_started/cpp_compiler_support.md
+++ b/docs/getting_started/cpp_compiler_support.md
@@ -84,7 +84,7 @@ C++ feature:
   `import std;` instead of the "old-style" header includes.
 - Related build options:
     - Conan: [import_std](installation_and_usage.md#import_std)
-    - CMake: [MP_UNITS_BUILD_IMPORT_STD](installation_and_usage.md#MP_UNITS_BUILD_IMPORT_STD)
+    - CMake: [CMAKE_CXX_MODULE_STD](https://cmake.org/cmake/help/latest/variable/CMAKE_CXX_MODULE_STD.html)
 
 
 ## Static `constexpr` variables in `constexpr` functions
diff --git a/docs/getting_started/installation_and_usage.md b/docs/getting_started/installation_and_usage.md
index 3a59deac..d9fcbcb6 100644
--- a/docs/getting_started/installation_and_usage.md
+++ b/docs/getting_started/installation_and_usage.md
@@ -186,14 +186,6 @@ dependencies by other means, some modifications to the library's CMake files mig
 
         [cmake build cxx modules support]: https://github.com/mpusz/mp-units/releases/tag/v2.2.0
 
-    [`MP_UNITS_BUILD_IMPORT_STD`](#MP_UNITS_BUILD_IMPORT_STD){ #MP_UNITS_BUILD_IMPORT_STD }
-
-    :   [:octicons-tag-24: 2.3.0][cmake import std support] · :octicons-milestone-24: `ON`/`OFF` (Default: `OFF`)
-
-        Enables `import std;` usage.
-
-        [cmake import std support]: https://github.com/mpusz/mp-units/releases/tag/v2.3.0
-
     [`MP_UNITS_API_STD_FORMAT`](#MP_UNITS_API_STD_FORMAT){ #MP_UNITS_API_STD_FORMAT }
 
     :   [:octicons-tag-24: 2.2.0][cmake std::format support] · :octicons-milestone-24: `ON`/`OFF` (Default: automatically determined)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index c9c1fbb8..7449d678 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -38,11 +38,9 @@ check_libcxx_in_use(${projectPrefix}LIBCXX)
 # project build options
 option(${projectPrefix}BUILD_AS_SYSTEM_HEADERS "Export library as system headers" OFF)
 option(${projectPrefix}BUILD_CXX_MODULES "Add C++ modules to the list of default targets" OFF)
-option(${projectPrefix}BUILD_IMPORT_STD "Enable `import std;` usage" OFF)
 
 message(STATUS "${projectPrefix}BUILD_AS_SYSTEM_HEADERS: ${${projectPrefix}BUILD_AS_SYSTEM_HEADERS}")
 message(STATUS "${projectPrefix}BUILD_CXX_MODULES: ${${projectPrefix}BUILD_CXX_MODULES}")
-message(STATUS "${projectPrefix}BUILD_IMPORT_STD: ${${projectPrefix}BUILD_IMPORT_STD}")
 
 if(${projectPrefix}BUILD_AS_SYSTEM_HEADERS)
     set(${projectPrefix}_AS_SYSTEM SYSTEM)
@@ -126,7 +124,7 @@ else()
     set(${projectPrefix}TARGET_SCOPE "INTERFACE")
 endif()
 
-if(${projectPrefix}BUILD_IMPORT_STD)
+if(CMAKE_CXX_MODULE_STD)
     if(CMAKE_VERSION VERSION_LESS "3.30")
         message(FATAL_ERROR "CMake versions before 3.30 do not support `import std;` properly")
     endif()
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index ce9db06b..1adba1e9 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -125,7 +125,7 @@ if(${projectPrefix}BUILD_CXX_MODULES)
     endif()
 endif()
 
-if(${projectPrefix}BUILD_IMPORT_STD)
+if(CMAKE_CXX_MODULE_STD)
     target_compile_definitions(mp-units-core ${${projectPrefix}TARGET_SCOPE} ${projectPrefix}IMPORT_STD)
     # https://github.com/llvm/llvm-project/issues/75057
     if(CMAKE_CXX_COMPILER_ID MATCHES ".*Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19)
diff --git a/test_package/conanfile.py b/test_package/conanfile.py
index 73f188e1..d0ea2369 100644
--- a/test_package/conanfile.py
+++ b/test_package/conanfile.py
@@ -45,7 +45,6 @@ class TestPackageConan(ConanFile):
             tc.cache_variables["MP_UNITS_BUILD_CXX_MODULES"] = True
         if opt.import_std:
             tc.cache_variables["CMAKE_CXX_MODULE_STD"] = True
-            tc.cache_variables["MP_UNITS_BUILD_IMPORT_STD"] = True
             # Current experimental support according to `Help/dev/experimental.rst`
             tc.cache_variables[
                 "CMAKE_EXPERIMENTAL_CXX_IMPORT_STD"