This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 114b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-05-06


2667. Named module imports do not import macros

Section: 15.5  [cpp.import]     Status: C++23     Submitter: Richard Smith     Date: 2022-12-16

[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 ]