C++20 modules introduces a new kind of preprocessor directive -- a
module directive. These are directives but without the leading '#'.
We have to detect them by sniffing the start of a logical line. When
detected we replace the initial identifiers with unspellable tokens
and pass them through to the language parser the same way deferred
pragmas are. There's a PRAGMA_EOL at the logical end of line too.
One additional complication is that we have to do header-name lexing
after the initial tokens, and that requires changes in the macro-aware
piece of the preprocessor. The above sniffer sets a counter in the
lexer state, and that triggers at the appropriate point. We then do
the same header-name lexing that occurs on a #include directive or
has_include pseudo-macro. Except that the header name ends up in the
token stream.
A couple of token emitters need to deal with the new token possibility.
gcc/c-family/
* c-lex.c (c_lex_with_flags): CPP_HEADER_NAMEs can now be seen.
libcpp/
* include/cpplib.h (struct cpp_options): Add module_directives
option.
(NODE_MODULE): New node flag.
(struct cpp_hashnode): Make rid-code a bitfield, increase bits in
flags and swap with type field.
* init.c (post_options): Create module-directive identifier nodes.
* internal.h (struct lexer_state): Add directive_file_token &
n_modules fields. Add module node enumerator.
* lex.c (cpp_maybe_module_directive): New.
(_cpp_lex_token): Call it.
(cpp_output_token): Add '"' around CPP_HEADER_NAME token.
(do_peek_ident, do_peek_module): New.
(cpp_directives_only): Detect module-directive lines.
* macro.c (cpp_get_token_1): Deal with directive_file_token
triggering.
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