| Issue |
128840
|
| Summary |
clangd false positive redefinition error of type traits template when #include <print> after import with type_traits include
|
| Labels |
false-positive
|
| Assignees |
|
| Reporter |
FalcoGer
|
So when I define such a module
```cpp
// Math.cppm
module;
#include <cmath>
#include <type_traits>
#include <utility>
export module Math;
export template <typename T>
requires std::is_arithmetic_v<T>
auto add(const T& lhs, const T& rhs)
{
return lhs + rhs;
}
```
and try to use it
```cpp
#include <print>
import Math;
auto main() -> int
{
std::println("{}", add(2.0F, 1.0F));
}
```
it works fine.
When I switch `#include <print>` and `import Math;`, it still compiles fine and gives the same results. But clangd explodes in my face telling me that it's not fine with
```text
Too many errors emitted, stopping now (clang fatal_too_many_errors)
In included file: type alias template redefinition with different types ('__is_one_of<[6 * ...], (no argument)>' vs '__is_one_of<[6 * ...], __int128>')
Related information:
* type_traits#808,11: Error occurred here
* type_traits#808,11: Previous definition is here
(clang redefinition_different_typedef)
```
Compiled against libstdc++ from gcc 15.0.1.
```text
$ clang --version
Ubuntu clang version 21.0.0 (++20250224081945+0770afb88ec1-1~exp1~20250224082103.749)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-21/bin
```
`.clangd`:
```yaml
CompileFlags:
Add:
- -fprebuilt-module-path=build/CMakeFiles/MathModule.dir
```
Built with cmake
`CMakeLists.txt`:
```cmake
cmake_minimum_required(VERSION 3.28)
project(TemplateModulesTest)
# REF: selecting-a-specific-libstdc-version-with-clang
# https://stackoverflow.com/a/50964601/10263660
set(GCC_TOOLCHAIN_PATH "/usr/local/gcc/15.0.1")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --gcc-toolchain=${GCC_TOOLCHAIN_PATH}")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} --gcc-toolchain=${GCC_TOOLCHAIN_PATH}")
set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED YES)
add_library(MathModule)
target_sources(MathModule
PUBLIC
FILE_SET cxx_modules TYPE CXX_MODULES FILES
Math.cppm
)
set_target_properties(MathModule PROPERTIES CXX_SCAN_FOR_MODULES YES)
add_executable(main main.cpp)
target_link_libraries(main PRIVATE MathModule)
```
Building first is required for clangd to find the module and not freak out about it not existing.
```bash
mkdir build
cmake -DCMAKE_C_COMPILER=/usr/bin/clang -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -G Ninja ..
ninja
```
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