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Deferred macros are needed for C++ modules. Header units may export macro definitions and undefinitions. These are resolved lazily at the point of (potential) use. (The language specifies that, it's not just a useful optimization.) Thus, identifier nodes grow a 'deferred' field, which fortunately doesn't expand the structure on 64-bit systems as there was padding there. This is non-zero on NT_MACRO nodes, if the macro is deferred. When such an identifier is lexed, it is resolved via a callback that I added recently. That will either provide the macro definition, or discover it there was an overriding undef. Either way the identifier is no longer a deferred macro. Notice it is now possible for NT_MACRO nodes to have a NULL macro expansion. libcpp/ * include/cpplib.h (struct cpp_hashnode): Add deferred field. (cpp_set_deferred_macro): Define. (cpp_get_deferred_macro): Declare. (cpp_macro_definition): Reformat, add overload. (cpp_macro_definition_location): Deal with deferred macro. (cpp_alloc_token_string, cpp_compare_macro): Declare. * internal.h (_cpp_notify_macro_use): Return bool (_cpp_maybe_notify_macro_use): Likewise. * directives.c (do_undef): Check macro is not undef before warning. (do_ifdef, do_ifndef): Deal with deferred macro. * expr.c (parse_defined): Likewise. * lex.c (cpp_allocate_token_string): Break out of ... (create_literal): ... here. Call it. (cpp_maybe_module_directive): Deal with deferred macro. * macro.c (cpp_get_token_1): Deal with deferred macro. (warn_of_redefinition): Deal with deferred macro. (compare_macros): Rename to ... (cpp_compare_macro): ... here. Make extern. (cpp_get_deferred_macro): New. (_cpp_notify_macro_use): Deal with deferred macro, return bool indicating definedness. (cpp_macro_definition): Deal with deferred macro.
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