Bug: Unexported `extern "C"` block in `base.h` makes `WINRT_IMPL_*` declarations invisible to downstream modules
維護者通常 1 天內回覆
評估
- 難度
- 4/5
- 預估耗時
- 3-5 天
- 新手友好度
- 48/100
- Issue 類型
- 缺陷
- 描述清晰度
- 基本清楚
- 活躍度
- 活躍
- 技術堆疊
- cpp
- 領域
- build-system
研究方向
Start with the first extern "C" block in base.h and the references in Windows.Foundation.h from wait_for_completed and when_any; the issue identifies winrt.Windows.Foundation.ixx as a place where Clang reports the visibility error. Check how winrt_base exports declarations used by downstream modules, then build the module with Clang to confirm the reported failure is resolved.
由索引模型根據 Issue 內容生成。
描述
Version
3.0.260818.1
Summary
In module builds, base.h is included in the module purview of winrt_base, and winrt.Windows.Foundation gets its base.h declarations via export import winrt_base;.
The first extern "C" block in base.h (declaring WINRT_IMPL_* functions) is not marked export. When Windows.Foundation.h calls WINRT_IMPL_CreateEventW, WINRT_IMPL_SetEvent, and WINRT_IMPL_WaitForSingleObject (in wait_for_completed and when_any), these functions are not visible to name lookup in winrt.Windows.Foundation.
extern "C" in a module purview only specifies C language linkage and global module ownership; it does not export the declarations. MSVC currently masks this bug by exposing unexported extern "C" declarations to importing modules, whereas Clang rejects winrt.Windows.Foundation.ixx with an undeclared/invisible identifier error.
Expected behavior
All declarations in winrt_base that are referenced by downstream namespace modules or generated component files (module.g.cpp) should either be explicitly exported (WINRT_EXPORT / export extern "C") or placed in a shared header included in the global module fragment.
Actual behavior
No response
Additional comments
A few related module-visibility mismatches stem from the same pattern in module builds:
1. Missing <intrin.h> in winrt.Windows.Foundation.ixx: <intrin.h> is only included in the global module fragments of winrt_base.ixx and winrt_numerics.ixx, but strings/base_coroutine_foundation.h (winrt::when_any) directly calls _InterlockedCompareExchangePointer inside winrt.Windows.Foundation.
2. Inconsistent linkage/export specifiers on namespace std specializations:
- strings/base_std_hash.h, strings/base_coroutine_threadpool.h, and strings/base_coroutine_foundation.h use WINRT_IMPL_STD_EXPORT namespace std (extern "C++" without export).
- strings/base_collections_map.h uses WINRT_EXPORT namespace std (export extern "C++").
- strings/base_string.h, strings/base_stringable_format.h, strings/base_stringable_format_1.h, and wrap_std_namespace in cppwinrt/code_writers.h declare std::hash and std::formatter specializations inside the module purview without extern "C++" or export, attaching std specializations to named modules.
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