This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-09-25

2667. Named module imports do not import macros

[Accepted as a DR at the February, 2023 meeting.]

It should be clarified via an example or a note that named module imports do not make macros available.

Proposed resolution (approved by CWG 2023-01-06):

1. Change in 10.3 [module.import] paragraph 7 as follows:

   ... These rules can in turn lead to the importation of yet more translation units. [ Note: Such indirect importation does not make macros available, because a translation unit is a sequence of tokens in translation phase 7 (5.2 [lex.phases]). Macros can be made available by directly importing header units as described in 15.5 [cpp.import]. -- end note ]

2. Add to the example in 15.5 [cpp.import] paragraph 8 as follows:

     import "a.h";  // point of definition of #1, #2, and #3, point of undefinition of #1 in "e.h"
     import "d.h";  // point of definition of #4 and #5 in "e.h"
     int a = Y;     // OK, active macro definitions #2 and #4 are valid redefinitions
     int c = Z;     // error: active macro definitions #3 and #5 are not valid redefinitions of Z
   

   Module unit f:

   export module f;
   export import "a.h";
   
   int a = Y;    // OK
   

   Translation unit #1:

   import f;
   int x = Y;   // error: Y is neither a defined macro nor a declared name
   

   -- end example ]