aaron.ballman added a comment. In D157572#4604595 <https://reviews.llvm.org/D157572#4604595>, @philnik wrote:
> In D157572#4604482 <https://reviews.llvm.org/D157572#4604482>, @aaron.ballman > wrote: > >>> This allows standard libraries to mark symbols as extensions, so the >>> compiler can generate extension warnings when they are used. >> >> Huh, so this is basically the opposite of the `__extension__` macro (which >> is used to silence extension warnings)? > > I guess, kind-of. I never really understood the semantics of `__extension__` > though, so I'm not 100% certain. It's used in system headers to say "I'm using an extension here, don't warn about it in -pedantic mode". >> I don't think we need to introduce a new attribute to do this, we already >> have `diagnose_if`. e.g., https://godbolt.org/z/a5ae4T56o would that suffice? > > Part of the idea here is that the diagnostics should be part of > `-Wc++ab-extension`. Hmmm, okay. And I'm assuming `-Wsystem-headers -pedantic` is too chatty because it's telling the user about all use of extensions, not extensions being introduced by the library itself? (e.g., https://godbolt.org/z/Gs3YGheMM is also not what you're after) > I guess we could allow warning flags instead of just `"warning"` and > `"error"` in `diagnose_if` that specifies which warning group the diagnostic > should be part of. Something like `__attribute__((__diagnose_if__(__cplusplus > >= 201703L, "basic_string_view is a C++17 extension", > "-Wc++17-extensions")))`. I'm not sure how one could implement that, but I > guess there is some mechanism to translate "-Wwhatever" to a warning group, > since you can push and pop warnings. That would open people up to add a > diagnostic to pretty much any warning group. I don't know if that's a good > idea. I don't really see a problem with that other than people writing weird > code, but people do that all the time anyways. Maybe I'm missing something > really problematic though. That's actually a pretty interesting idea; `diagnose_if` could be given another parameter to specify a diagnostic group to associate the diagnostic with. This would let you do some really handy things like: void func(int i) __attribute__((diagnose_if(i < 0, "passing a negative value to 'func' is deprecated", "warning", "-Wdeprecated"))); But if we went this route, would we want to expose other diagnostic-related knobs like "show in system header" and "default to an error"? Also, the attribute currently can only be associated with a function; we can use this for classes by sticking it on a constructor but there's not much help for putting it on say a namespace or an enumeration. So we may need to extend the attribute in other ways. CC @cjdb as this seems of interest to you as well. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D157572/new/ https://reviews.llvm.org/D157572 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
