US132 15.03 Macros from the command-line not exported by header units #131
Description
Header units may provide macro definitions and undefinitions to their importers. These are #define and #undefs (of imported macros) that are encountered ‘when preprocessing each translation unit’. There is ambiguity as to whether this includes: a) macros defined on the command line, b) macros defined by the implementation (including indirectly via command line option), c) macros defined in forced headers. Mailing list discussion concluded that such macros should NOT be exported.
Proposed change:
Add wording to explicitly exclude these macro definitions (as there can be no imported macros visible at the point they are defined, explicit undefinitions are irrelevant).