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Mateusz Pusz
96965634f5
mp-units' minimum-supported MSVC 195 (VS 2026) has solid `import std;`
support, but enabling `-o import_std=True` against the build hit two
issues that this change fixes.
(1) Module scanning was only enabled when `cxx_modules=True`.
Without `CMAKE_CXX_SCAN_FOR_MODULES=ON`, CMake doesn't link the implicit
std module BMI into non-module translation units that do `import std;`,
producing C2230 "could not find module 'std'". Enable scanning whenever
`import_std=True` as well. Same bug fixed in `test_package/conanfile.py`.
(2) The std module BMI is built with mismatched compile flags.
CMake materializes the implicit std module BMI as `__cmake_cxx_std_NN`,
a separate internal target that does not link mp-units and therefore
does not inherit mp-units' target-level options. On MSVC this caused
C5050 (`_UTF8` defined on consumer but not on module command line) and
on Clang 21 there is a parallel `-Wreserved-module-identifier` issue
already partially handled in `src/CMakeLists.txt` but in a directory
scope that did not actually reach the BMI either.
Consolidate the workarounds into one `src/cmake/import-std-setup.cmake`
snippet that applies the flags project-wide via `add_compile_options`,
self-guarded by `if(NOT CMAKE_CXX_MODULE_STD) return()`. It is included
from every entry point so all delivery paths converge:
- top-level `CMakeLists.txt` for the dev build
- bundled `mp-unitsConfig.cmake` for `find_package` consumers
- via `cmake_build_modules` in `package_info()` for Conan-generated
configs (the `cxx_modules=False` consumer path)
Other pieces:
- `test/static/unit_magnitude_test.cpp` was the only test in the repo
missing the `MP_UNITS_IMPORT_STD` gate around `#include <type_traits>`,
causing duplicate `std::integral_constant` definitions in this
configuration.
- Compiler support table announces MSVC 195+ for `import std;`.
- Installation docs gain a consumer-side setup note covering the
CMake cache variables required, what mp-units handles automatically
via the snippet, and the `add_subdirectory`-vendored caveat.
Verified: `conan build . -pr msvc195 -o '&:cxx_modules=False'
-o '&:import_std=True' -s compiler.cppstd=23 -c
user.mp-units.build:all=True` -> 40/40 tests pass.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>