Re: [PATCH] c++: Fix location for -Wunused-macros [PR66290]

[Jeff Law <jeffreyalaw@gmail.com>]

On 7/28/2022 8:01 AM, Lewis Hyatt via Gcc-patches wrote:
> In C++, since all tokens are lexed from libcpp up front, diagnostics generated
> by libcpp after lexing has completed do not get a valid location from libcpp
> (rather, libcpp thinks they all pertain to the end of the file.) This has long
> been addressed using the global variable "done_lexing", which the C++ frontend
> sets at the appropriate time; when done_lexing is true, then c_cpp_diagnostic(),
> which outputs libcpp's diagnostics, uses input_location instead of the wrong
> libcpp location. The C++ frontend arranges that input_location will point to the
> token it is currently processing, so this generally works fine. However, there
> is one exception currently, which is -Wunused-macros. This gets generated at the
> end of processing in cpp_finish (), since we need to wait until then to
> determine whether a macro was eventually used or not. But the locations it
> passes to c_cpp_diagnostic () were remembered from the original lexing and hence
> they should not be overridden with input_location, which is now the one
> incorrectly pointing to the end of the file.
>
> Fixed by setting done_lexing=false again just prior to calling cpp_finish (). I
> also renamed the variable from done_lexing to "override_libcpp_locations", since
> it's now not strictly about lexing anymore.
>
> There is no new testcase with this patch, since we already had an xfailed
> testcase which is now fixed.
>
> gcc/c-family/ChangeLog:
>
> 	PR c++/66290
> 	* c-common.h: Rename global done_lexing to
> 	override_libcpp_locations.
> 	* c-common.cc (c_cpp_diagnostic): Likewise.
> 	* c-opts.cc (c_common_finish): Set override_libcpp_locations
> 	(formerly done_lexing) immediately prior to calling cpp_finish ().
>
> gcc/cp/ChangeLog:
>
> 	PR c++/66290
> 	* parser.cc (cp_lexer_new_main): Rename global done_lexing to
> 	override_libcpp_locations.
>
> gcc/testsuite/ChangeLog:
>
> 	PR c++/66290
> 	* c-c++-common/pragma-diag-15.c: Remove xfail for C++.
Ewww.  But OK.
Jeff