Possibly wrong declaration visibility with C++ module imports

[rohanlean]

The following is accepted by clang version 20.1.6:

//--- A.cppm
export module A;
export using T = int;

//--- M.cppm
export module M;
import A;

//--- M.cpp
module M;

T x;

This is rejected:

//--- A.cppm
export module A;
export using T = int;

//--- P.cppm
export module M:P;
import A;

//--- M.cppm
export module M;
export import :P;

//--- M.cpp
module M;

T x;

But this is again accepted:

//--- A.cppm
export module A;
export using T = int;

//--- P.cppm
module M:P;
import A;

//--- M.cppm
export module M;
import :P;

//--- M.cpp
module M;

T x;

I think the relevant paragraphs are [basic.lookup.general]//p2,3 and that the correct behaviour is to reject in all cases. Because of [basic.lookup.general]//p2,3 in combination with [module.import]//p7 the correct behaviour is probably to accept in all cases.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: None (rohanlean)

The following is accepted by clang version 20.1.6: ``` //--- A.cppm export module A; export using T = int;

//--- M.cppm
export module M;
import A;

//--- M.cpp
module M;

T x;

This is rejected:

//--- A.cppm
export module A;
export using T = int;

//--- P.cppm
export module M:P;
import A;

//--- M.cppm
export module M;
export import :P;

//--- M.cpp
module M;

T x;

But this is again accepted:

//--- A.cppm
export module A;
export using T = int;

//--- P.cppm
module M:P;
import A;

//--- M.cppm
export module M;
import :P;

//--- M.cpp
module M;

T x;

~~I think the relevant paragraphs are [basic.lookup.general]//p2,3 and that the correct behaviour is to reject in all cases.~~ Because of [basic.lookup.general]//p2,3 in combination with [module.import]//p7 the correct behaviour is probably to accept in all cases.
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