This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2024-10-26
Consider:
using module = int; module i; int foo() { return i; }
Is this a valid translation unit?
It is not a valid module-file, because the translation unit does not start with module or export module (15.4 [cpp.module]). It is also not a valid traditional preprocessing-file (15.1 [cpp.pre]), because module i is considered a preprocessing directive (15.1 [cpp.pre] bullet 1.3, which is never a text-line (15.1 [cpp.pre] paragraph 2):
A sequence of preprocessing tokens is only a text-line if it does not begin with a directive-introducing token. ...
A clarifying note would be appreciated.
Possible resolution (August, 2024):
Change in 15.1 [cpp.pre] paragraph 2 as follows:
A sequence of preprocessing tokens is only a text-line if it does not begin with a directive-introducing token. [ Note: A source line starting with module identifier is always interpreted as a preprocessing directive, not as a text-line, even if parsing the source file as a preprocessing-file subsequently fails. -- end note ]
A sequence of preprocessing tokens is only a conditionally-supported-directive if ...
CWG 2024-09-13
A source line starting with module identifier appearing in a macro argument may or may not be interpreted as a preprocessing directive (15.6.2 [cpp.subst] paragraph 13), thus the note as written is incorrect.
Proposed resolution (approved by CWG 2024-09-27):
Change in 15.1 [cpp.pre] paragraph 2 as follows:
A sequence of preprocessing tokens is only a text-line if it does not begin with a directive-introducing token. [ Example:
using module = int; module i; // not a text-line and not a control-line int foo() { return i; }
The example is not a valid preprocessing-file. -- end example]