Use extern "C++" scopes for explicit specializations after P2615R1 Meaningful Exports - #6074
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extern "C++" scopes for explicit specializations after P2615R1
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Simple change, LGTM
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Stephan T. Lavavej (StephanTLavavej)
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WG21-P2615R1 Meaningful Exports forbids
extern "C++"from being directly applied to an explicit specialization. Now, every declaration is either a name-declaration or a special-declaration. An explicit-specialization is considered a special-declaration. But when directly applyingextern "C++", the grammar for linkage-specialization requires that theexternstring-literal name-declaration syntax cannot accept a special-declaration.Clang 17 implemented P2615R1 as a DR in C++20 mode, but as of Clang 20 they don't enforce this rule (yet?). Xiang Fan (@xiangfan-ms) brought this to my attention as he was implementing P2615R1 in MSVC.
The fix is simple: use
extern "C++" { ... }scopes.I am allowing the
_Codecvt_guardhelper to permanently remain in this scope, as it's not harmful, and I didn't think it was worth the effort to pull outside of the scope. (Indeed, right now the entire STL is marked withextern "C++"as a workaround.)