https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112318
S. Davis Herring <herring at lanl dot gov> changed:
What |Removed |Added
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CC| |herring at lanl dot gov
--- Comment #4 from S. Davis Herring <herring at lanl dot gov> ---
The issue is really broader than just "declaration or use is not in -isystem";
since it's standard practice to use -isystem for third-party headers (to avoid
"personal" warnings like -Wparentheses taking effect in code not written to
them), this still fails to issue a warning if `foo` comes from such a header.
(But the warning works when foo's author checks for it in their own unit
tests...)
It's a very hard problem in general. A colleague pointed me at Perl's carp,
which attempts to identify whose "fault" a diagnostic is
<https://perldoc.perl.org/Carp#DESCRIPTION>. The package rule there could even
be applied to C++20 modules, or perhaps to top-level namespaces in a pinch.
Beyond that, it might be worthwhile to presume that any warning triggered by a
type- or value-dependent expression should be associated (for -Wsystem-headers
purposes) with the point of instantiation, although I'm sure there would be
some false positives from that. (There needs to be a better-than-#pragma way
to suppress individual deprecation warnings for such cases.)
