From 3a7dad24b1470dee2bad556d69990fd3e8d328f4 Mon Sep 17 00:00:00 2001 From: Faisal Vali Date: Sun, 15 Oct 2017 01:26:26 +0000 Subject: [c++2a] Implement P0306 __VA_OPT__ (Comma omission and comma deletion) This patch implements an extension to the preprocessor: __VA_OPT__(contents) --> which expands into its contents if variadic arguments are supplied to the parent macro, or behaves as an empty token if none. - Currently this feature is only enabled for C++2a (this could be enabled, with some careful tweaks, for other dialects with the appropriate extension or compatibility warnings) - The patch was reviewed here: https://reviews.llvm.org/D35782 and asides from the above (and moving some of the definition and expansion recognition logic into the corresponding state machines), I believe I incorporated all of Richard's suggestions. A few technicalities (most of which were clarified through private correspondence between rsmith, hubert and thomas) are worth mentioning. Given: #define F(a,...) a #__VA_OPT__(a ## a) a ## __VA_OPT__(__VA_ARGS__) - The call F(,) Does not supply any tokens for the variadic arguments and hence VA_OPT behaves as a placeholder. - When expanding VA_OPT (for e.g. F(,1) token pasting occurs eagerly within its contents if the contents need to be stringified. - A hash or a hashhash prior to VA_OPT does not inhibit expansion of arguments if they are the first token within VA_OPT. - When a variadic argument is supplied, argument substitution occurs within the contents as does stringification - and these resulting tokens are inserted back into the macro expansions token stream just prior to the entire stream being rescanned and concatenated. See wg21.link/P0306 for further details on the feature. Acknowledgment: This patch would have been poorer if not for Richard Smith's usual thoughtful analysis and feedback. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@315840 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/clang/Basic/DiagnosticLexKinds.td | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/clang/Basic/DiagnosticLexKinds.td') diff --git a/include/clang/Basic/DiagnosticLexKinds.td b/include/clang/Basic/DiagnosticLexKinds.td index ec95dca6ac..6c35bab88a 100644 --- a/include/clang/Basic/DiagnosticLexKinds.td +++ b/include/clang/Basic/DiagnosticLexKinds.td @@ -346,6 +346,20 @@ def ext_pp_extra_tokens_at_eol : ExtWarn< def ext_pp_comma_expr : Extension<"comma operator in operand of #if">; def ext_pp_bad_vaargs_use : Extension< "__VA_ARGS__ can only appear in the expansion of a C99 variadic macro">; + +def ext_pp_bad_vaopt_use : Extension< + "__VA_OPT__ can only appear in the expansion of a variadic macro">; +def err_pp_missing_lparen_in_vaopt_use : Error< + "missing '(' following __VA_OPT__">; +def err_pp_vaopt_nested_use : Error< + "__VA_OPT__ cannot be nested within its own replacement tokens">; + +def err_vaopt_paste_at_start : Error< + "'##' cannot appear at start of __VA_OPT__ argument">; + +def err_vaopt_paste_at_end + : Error<"'##' cannot appear at end of __VA_OPT__ argument">; + def ext_pp_macro_redef : ExtWarn<"%0 macro redefined">, InGroup; def ext_variadic_macro : Extension<"variadic macros are a C99 feature">, InGroup; -- cgit v1.2.3