Hello all, (Re-adding gcc-patches, since it got dropped and missed six emails)
=== CPP FEATURE SUGGESTION === Adding line directives inside of a macro expansion to differentiate between system tokens and user tokens is a valid solution. As Manuel pointed out, there would need to be many line directives. So, if "#define FOO(x) (x) + 1/0" was in a system file, and was instantiated from a user file like "FOO(2/0)", the "2/0" are user tokens (which should raise a div-by-zero warning), but the "1/0" are system tokens (and so should not raise a warning). This would need to expand as follows: # 1 "user.cpp" 3 ( # 1 "user.cpp" 2/0 # 1 "user.cpp" 3 ) + 1/0 # 2 "user.cpp" The last line directive is crucial, to specify that the rest of the file is not comprised of user tokens. Currently, compiling a user program with "FOO(2/0)" yields a single div-by-zero error. Compiling that same program with -no-integrated-cpp yields two errors: the original and correct 2/0 error, but also the 1/0 system error. So adjusting the preprocessor to emit extra line directives would be consistent with the integrated-cpp mode. === NEXT STEPS === The bugzilla report now has two independent reports, so this is an issue which is currently affecting the community. Both reports, it should be noted, stem from the use of ccache, which caches preprocessed output (since this bug is not present with integrated preprocessing). The status quo is subtle and infrequent, but confounding. The extremely specific requirements to trigger the bug mean that it is effectively undiagnosable (my initial bug report was the result of a very chance set of circumstances and a lot of elbow grease, which ended up being the reason for a years-old abnormality in our error messages). Further, when the bug does happen, it is severely detrimental, since it disables warnings in the rest of the file. Given these two circumstances, undiagnosability and high-impact, I think that a fix should be applied immediately. We currently have two possible approaches. I see the trade-offs between these two solutions as follows: Adding full line directives is not implemented, and will be more complicated than my patch. It will require someone else to implement it, but should fix the problem in its entirety. My solution is simple, battle-tested (I've had it in our production gcc for a few months now), and ready to roll. The primary downside is that it will not supress system-token errors in macro expansions (though in my experience this is not a problem). Cheers, Nicholas
