Bug: Unexported `extern "C"` block in `base.h` makes `WINRT_IMPL_*` declarations invisible to downstream modules

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Depuis le 4/11/2026.

  • #1644 par @YexuanXiao — ouverte

Évaluation

Difficulté
4/5
Temps estimé
3-5 jours
Accessibilité débutants
48/100
Type d'issue
Bug
Clarté
Plutôt claire
Activité
Active
Stack technique
cpp
Domaine
build-system

Piste de recherche

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.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Description

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.

Langage dominant
C++
Étoiles
1.9k
Forks
288
Merge moyen
18 h 15 min
PR mergées (30 j)
2

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