https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113129
Bug ID: 113129
Summary: "using declaration" not detected as "exported" in
exported namespace
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: admin at hexadigm dot com
Target Milestone: ---
Hi there,
See https://godbolt.org/z/MdToP8nP8 for a demo (self-explanatory and very
short). GCC version fails in top window (see error there), while Clang succeeds
in bottom window (also succeeds in MSVC - haven't test any others).
Issue is that the "using" declaration seen in "Consts.cppm" compiles
successfully but the variable being declared ("Test_v") isn't being exported
even though its "Const" namespace is exported. "Test_v" is therefore
inaccessible to any client that imports the "Consts" module (resulting in the
GCC compiler error seen in the top window).
I don't see any obvious reason why it shouldn't compile however unless it's a
GCC bug (but like so many I'm new to modules and this particular construct is a
fuzzy area - maybe Clang and MSVC got it wrong but read on).
Please note that this technique is very useful since it allows existing C++
headers to be easily used in C++ modules without any changes to the headers
themselves (so correcting it would be highly desirable to many). Users
therefore have the choice to either #include the existing header ("Consts.h" in
this example) or import the module instead ("Consts" in this example). The
module just defers to the header itself by applying "using" declarations as
seen in this example (to export whatever it needs from the header, in this case
"Test_v").
