preprocessor: C++ module-directives

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.

1 files changed, 9 insertions, 0 deletions

diff --git a/libcpp/internal.h b/libcpp/internal.h
index 3f5bafb..4c1100b 100644
--- a/libcpp/internal.h
+++ b/libcpp/internal.h
@@ -280,6 +280,9 @@ struct lexer_state
   /* Nonzero when tokenizing a deferred pragma.  */
   unsigned char in_deferred_pragma;
 
+  /* Count to token that is a header-name.  */
+  unsigned char directive_file_token;
+
   /* Nonzero if the deferred pragma being handled allows macro expansion.  */
   unsigned char pragma_allow_expansion;
 };
@@ -292,6 +295,12 @@ struct spec_nodes
   cpp_hashnode *n_false;		/* C++ keyword false */
   cpp_hashnode *n__VA_ARGS__;		/* C99 vararg macros */
   cpp_hashnode *n__VA_OPT__;		/* C++ vararg macros */
+
+  enum {M_EXPORT, M_MODULE, M_IMPORT, M__IMPORT, M_HWM};
+  
+  /* C++20 modules, only set when module_directives is in effect.
+     incoming variants [0], outgoing ones [1] */
+  cpp_hashnode *n_modules[M_HWM][2];
 };
 
 typedef struct _cpp_line_note _cpp_line_note;