# import std appears to be broken in release 4.0.2
**URL:** https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062
**Category:** Development
**Tags:** os:windows, gen:ninja
**Created:** [May 8, 2025, 4:01pm UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062 "2025-05-08T16:01:17Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@abbator](https://discourse.cmake.org/u/abbator)
#### Post date: [May 8, 2025, 4:01pm UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062/1 "2025-05-08T16:01:17Z")
I attempted to upgrade to 4.0.2 but found that my modules projects using `import std` are now unbuildable. I’m using Visual Studio Community 17.15.0 Preview 4.0 + Ninja.
After fiddling across a large-scale project with a number of C++ module deps, I went ahead and tried a minimal project to confirm, and it too was unbuildable. The CMakeLists for the minimal project looks like this:
```auto
cmake_minimum_required(VERSION 4.0.2)
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "d0edc3af-4c50-42ea-a356-e2862fe7a444")
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_MODULE_STD 1)
project(minimal LANGUAGES CXX)
add_executable(minimal)
target_sources(minimal
PUBLIC
FILE_SET cxx_modules TYPE CXX_MODULES FILES
main.ixx
)
```
I fiddled with various configurations (one call before another - i.e. `sets` before `project(...)` and after it, - different hashes for CMAKE\_EXPERIMENTAL\_CXX\_IMPORT\_STD, etc.). Regardless, the result is always this error:
```auto
CMake Error in CMakeLists.txt:
The "CXX_MODULE_STD" property on the target "minimal" requires that the
"__CMAKE::CXX23" target exist, but it was not provided by the toolchain.
Reason:
Experimental `import std` support not enabled when detecting toolchain; it must be set before `CXX` is enabled (usually a `project()` call)
```
Rolling back to 3.31.7 is the only way I could get things to build again.
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [May 8, 2025, 6:44pm UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062/2 "2025-05-08T18:44:06Z")
The UUID for 4.0.2 is different (because the set of features changed). It is `a9e1cf81-9932-4810-974b-6eccaf14e457` for 4.0.2.
---
### Author:  [@abbator](https://discourse.cmake.org/u/abbator)
#### Post date: [May 8, 2025, 8:30pm UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062/3 "2025-05-08T20:30:16Z")
That was the problem. Where is the UUID for the current version documented?
The UUID I was using was the one on this page: [CMake/Help/dev/experimental.rst at master · Kitware/CMake](https://github.com/Kitware/CMake/blob/master/Help/dev/experimental.rst)
But that one is apparently out of date.
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [May 9, 2025, 7:05am UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062/4 "2025-05-09T07:05:52Z")
> [@abbator](#):
>
> Where is the UUID for the current version documented?
In the `Help/dev/experimental.rst` file of the version you’re using (change `master` to `v4.0.1` in the URL). If you build `master`, it is correct. It was most recently bumped because CMake learned to support `clang -stdlib=libstdc++` and `import std;`. 4.0.1 lacks it, so it uses an older UUID.
---
### Author:  [@legatt](https://discourse.cmake.org/u/legatt)
#### Post date: [February 8, 2026, 3:46pm UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062/5 "2026-02-08T15:46:14Z")
I just tried both CMake 4.0.2 and 4.2.3 with correct UUIDs from needed tag tree but still have the same issue. And I set it before `project` as said in docs.
I use it like this:
```CMake
# root CMakeLists.txt
cmake_minimum_required (VERSION 4.2.3)
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "d0edc3af-4c50-42ea-a356-e2862fe7a444")
set(CMAKE_CXX_MODULE_STD ON)
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_SCAN_FOR_MODULES ON)
set(CMAKE_POSITION_INDEPENDENT_CODE OFF)
set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
project (my_project LANGUAGES CXX)
add_subdirectory(utils)
```
```CMake
# library.cmake
function(add_library_target TARGET_NAME)
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
project(${TARGET_NAME} LANGUAGES CXX)
add_library(${TARGET_NAME})
file(GLOB_RECURSE SOURCES CONFIGURE_DEPENDS
src/*.cpp
src/*.c
)
file(GLOB_RECURSE HEADERS CONFIGURE_DEPENDS
include/*.hpp
include/*.h
)
file(GLOB_RECURSE MODULES CONFIGURE_DEPENDS
modules/*.cppm
)
target_sources(${TARGET_NAME} PUBLIC FILE_SET modules TYPE CXX_MODULES BASE_DIRS ${PROJECT_SOURCE_DIR} FILES ${MODULES})
target_sources(${TARGET_NAME} PUBLIC FILE_SET headers TYPE HEADERS BASE_DIRS ${PROJECT_SOURCE_DIR} FILES ${HEADERS})
target_sources(${TARGET_NAME} PRIVATE ${SOURCES})
# Enable compiled MSVC STD module
target_compile_options(${TARGET_NAME} PRIVATE
/EHsc
"SHELL:/reference \"std=$ENV{STD_MODULE_DIR}/std.ifc\""
"SHELL:/reference \"std.compat=$ENV{STD_MODULE_DIR}/std.compat.ifc\""
)
target_link_libraries(${TARGET_NAME} PRIVATE "$ENV{STD_MODULE_DIR}/std.obj")
target_link_libraries(${TARGET_NAME} PRIVATE "$ENV{STD_MODULE_DIR}/std.compat.obj")
target_compile_options(${TARGET_NAME} PRIVATE
/wd5050
)
target_compile_features(${TARGET_NAME} PRIVATE cxx_std_23 INTERFACE cxx_std_23)
target_include_directories(${TARGET_NAME} PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)
endfunction()
```
```CMake
# utils/CMakeLists.txt
include(${CMAKE_SOURCE_DIR}/cmake/library.cmake)
set(LIB utils)
# Find dependencies
find_package(Boost REQUIRED COMPONENTS lockfree)
# Link library
add_library_target(${LIB})
target_link_libraries(${LIB} PUBLIC p7)
target_link_libraries(${LIB} PRIVATE Boost::lockfree)
```
I also tried to set it inside `library.cmake` in the function begining . Actually, it builds ok even without `CMAKE_CXX_MODULE_STD` so I’m not sure do I really need it?
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [February 9, 2026, 3:47am UTC](https://discourse.cmake.org/t/import-std-appears-to-be-broken-in-release-4-0-2/14062/6 "2026-02-09T03:47:06Z")
> [@legatt](#):
>
> ```auto
> # Enable compiled MSVC STD module
> target_compile_options(${TARGET_NAME} PRIVATE
> /EHsc
> "SHELL:/reference \"std=$ENV{STD_MODULE_DIR}/std.ifc\""
> "SHELL:/reference \"std.compat=$ENV{STD_MODULE_DIR}/std.compat.ifc\""
> )
> target_link_libraries(${TARGET_NAME} PRIVATE "$ENV{STD_MODULE_DIR}/std.obj")
>
> ```
Well, when you do this, you’re telling the compiler how to satisfy `import std` without CMake knowing about it. Not having to do this is kind of the point of the `import std` feature in CMake.