On Thu, Dec 18, 2014 at 2:19 PM, Nico Weber <[email protected]> wrote: > > On Thu, Dec 18, 2014 at 2:01 PM, Richard Smith <[email protected]> > wrote: > >> On Wed, Dec 17, 2014 at 7:58 PM, Nico Weber <[email protected]> wrote: >>> >>> On Wed, Dec 17, 2014 at 7:05 PM, Richard Smith <[email protected]> >>> wrote: >>>> >>>> On Tue, Dec 16, 2014 at 1:17 PM, Nico Weber <[email protected]> >>>> wrote: >>>>> >>>>> Ok, I moved -Wkeyword-macro into -pedantic in r224371. I also removed >>>>> -Wreserved-id-macro in the same revision, as it's not covered by the >>>>> standards bit you cited >>>>> >>>> >>>> This seems backwards? >>>> >>>> -Wreserved-id-macro is (was) warning on code that is ill-formed. >>>> -Wkeyword-macro is warning on code that has undefined behavior (only) if a >>>> standard library header is #included. >>>> >>>> C++ [lex.name]p3 (introduced by DR, so applying retroactively to all >>>> C++ standards) says: >>>> >>>> "[S]ome identifiers are reserved for use by C ++ implementations and >>>> shall not be used otherwise; no diagnostic is required. >>>> — Each identifier that contains a double underscore __ or begins with >>>> an underscore followed by an uppercase letter is reserved to the >>>> implementation for any use. >>>> — Each identifier that begins with an underscore is reserved to the >>>> implementation for use as a name in the global namespace." >>>> >>>> Aaron's quote of [macro.names]p2 applies only to "C++ programs that use >>>> the facilities of the C ++ standard library." (per >>>> [constraints.overview]p1), and "If a program declares or defines a name in >>>> a context where it is reserved, other than as explicitly allowed by >>>> this Clause, its behavior is undefined." (per [reserved.names]p1). >>>> >>> >>> I'm not sure I understand the point here – do you mean the warning >>> should only fire if a standard library has been included? In pedantic mode, >>> I would expect that people would want to know about stuff that's undefined >>> behavior even if they don't happen to include a standard library header at >>> the moment. >>> >> >> The point is that -Wreserved-id-macro is *more* breaking-the-rules than >> -Wkeyword-macro, so I disagree with your argument for removing >> -Wreserved-id-macro and keeping -Wkeyword-macro. >> > > The bit you quoted says "some identifiers are reserved for use by C ++ > implementations and shall not be used otherwise", but a C++ implementation > can choose that is going to use a __identifier as part of it's public > interface, no? Something like "Define __no_exceptions if you want a > standard library without exceptions" or similar – in this case, user code > needs to define this macro and it'll be standards-compliant since it's > using the __identifier as intended by the C++ implementation it uses. Due > to this, it's difficult to predict which __identifiers are ok to define and > which aren't. The bit you quoted at least doesn't say "don't define > __idents", it just says "use __idents only as intended by your C++ > implementation" as far as I can tell. >
Right. But Clang is not the implementation; the implementation also includes the standard library, which we don't control, so we can't know which __names the implementation allows or disallows, in general. Did you see my other mail proposing a way to fix this (allow user code to define or use each reserved macro name -- but not both)? That may be imperfect, but seems like it might be a good heuristic to reduce the noise. > The other paragraph explicitly says "shall not #define or #undef names > lexically identical to keywords […]" (, in "C++ programs that use the > facilities of the C ++ standard library."). I agree that the warning would > be More Correct if it checked for that too, but it seems like a minor > detail in practice, as most programs use the C++ standard library – minor > enough to not revert the warning over it, at least. > Well, it's a Warning not an ExtWarn, so it doesn't matter if it warns on conforming code, so long as it warns on questionable and very-likely-wrong code. > (But this is discussion is somewhat pointless now that r224512 > added-Wkeyword-macro back :-) ) > > >> >> >>> In your commit message for r224371 (which hasn't yet hit the mailing >>>> list), you say: >>>> >>>> "-Wreserved-id-macro warns on >>>> >>>> #define __need_size_t >>>> >>>> which is more or less public api for glibc headers." >>>> >>>> I don't agree with your example; these __need_* macros exist only to >>>> allow communication between the /usr/include headers and the >>>> compiler-provided <stddef.h>, because /usr/include needs to include a >>>> subset of <stddef.h> depending on which of its headers is included. They're >>>> not for end-users, and these warnings should be suppressed in system >>>> headers. >>>> >>> >>> Some end user code uses them, for example to work around bugs in >>> /usr/include headers. I know of one example in Chromium ( >>> https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/ui/libgtk2ui/gtk2_ui.cc&q=__need_Null&sq=package:chromium&type=cs&l=72 >>> ) and I found >>> https://github.com/asfernandes/firebird/blob/35b06c7892e2440c4f4528b9ecc99969927728e0/src/common/utils.cpp#L35 >>> (there might be more, but github's search is somewhat hard to operate.) >>> >>> Having said that, I'm happy with the warning coming back in an improved >>> form. >>> >>> >>>> That said, there are a bunch of reserved macro names that *is* part of >>>> the glibc public API, such as the _*_SOURCE macro family. If we reinstate >>>> this warning, we should whitelist those ones at least. >>>> >>>> On Mon, Dec 15, 2014 at 10:39 AM, Joerg Sonnenberger < >>>>> [email protected]> wrote: >>>>>> >>>>>> On Mon, Dec 15, 2014 at 10:24:22AM -0800, Nico Weber wrote: >>>>>> > For the "final(a,b,c)" define: should we warn on that? It doesn't >>>>>> change >>>>>> > the meaning of the keyword "final" since that doesn't have >>>>>> parameters. >>>>>> >>>>>> For C++11 and newer: IMO yes. Otherwise, no. >>>>>> >>>>>> Joerg >>>>>> _______________________________________________ >>>>>> cfe-commits mailing list >>>>>> [email protected] >>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >>>>>> >>>>> >>>>> _______________________________________________ >>>>> cfe-commits mailing list >>>>> [email protected] >>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits >>>>> >>>>> >
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