On Tue, Nov 15, 2016 at 5:44 PM, Hal Finkel <hfin...@anl.gov> wrote: > ----- Original Message ----- >> From: "Aaron Ballman" <aa...@aaronballman.com> >> To: "Hal Finkel" <hfin...@anl.gov> >> Cc: "cfe-commits" <cfe-commits@lists.llvm.org>, "Joshua Hurwitz" >> <hurwi...@google.com> >> Sent: Tuesday, November 15, 2016 4:42:05 PM >> Subject: Re: [PATCH] Warning for main returning a bool. >> >> On Tue, Nov 15, 2016 at 5:22 PM, Hal Finkel <hfin...@anl.gov> wrote: >> > ----- Original Message ----- >> >> From: "Aaron Ballman via cfe-commits" <cfe-commits@lists.llvm.org> >> >> To: "Joshua Hurwitz" <hurwi...@google.com> >> >> Cc: "cfe-commits" <cfe-commits@lists.llvm.org> >> >> Sent: Tuesday, November 15, 2016 12:17:28 PM >> >> Subject: Re: [PATCH] Warning for main returning a bool. >> >> >> >> On Fri, Oct 14, 2016 at 1:17 PM, Joshua Hurwitz via cfe-commits >> >> <cfe-commits@lists.llvm.org> wrote: >> >> > See attached. >> >> > >> >> > Returning a bool from main is a special case of return type >> >> > mismatch. The >> >> > common convention when returning a bool is that 'true' (== 1) >> >> > indicates >> >> > success and 'false' (== 0) failure. But since main expects a >> >> > return >> >> > value of >> >> > 0 on success, returning a bool is usually unintended. >> >> >> >> I am not convinced that this is a high-value diagnostic. Returning >> >> a >> >> Boolean from main() may or may not be a bug (the returned value is >> >> generally a convention more than anything else). Also, why Boolean >> >> and >> >> not, say, long long or float? >> > >> > I've seen this error often enough, but I think we need to be >> > careful about false positives here. I recommend that we check only >> > for explicit uses of boolean immediates (i.e. return true; or >> > return false;) -- these are often bugs. >> >> I could get behind that. >> >> > Aaron, I disagree that the return value is just some kind of >> > convention. It has a clear meaning. >> >> For many hosted environments, certainly. Freestanding >> implementations? >> Much less so, but I suppose this behavior is still reasonable enough >> for them (not to mention, there may not even *be* a main() for a >> freestanding implementation). >> >> > Furthermore, the behavior of the system can be quite different for >> > a non-zero exit code than otherwise, and users who don't >> > understand what's going on can find it very difficult to >> > understand what's going wrong. >> >> That's a fair point, but my question still stands -- why only Boolean >> values, and not "return 0x1234567800000000ULL;" or "return 1.2;"? >> >> Combining with your idea above, if the check flagged instances where >> a >> literal of non-integral type (other than Boolean) is returned from >> main(), that seems like good value. > > Agreed. > > FWIW, if we have a function that returns 'int' and the user tries to return > '1.2' we should probably warn for any function.
Good point, we already have -Wliteral-conversion (which catches 1.2) and -Wconstant-conversion (which catches 0x1234567800000000ULL), and -Wint-conversion for C programs returning awful things like string literals, all of which are enabled by default. Perhaps Boolean values really are the only case we don't explicitly warn about. ~Aaron > > -Hal > >> >> ~Aaron >> >> > >> > Thanks again, >> > Hal >> > >> >> >> >> ~Aaron >> >> >> >> > >> >> > _______________________________________________ >> >> > cfe-commits mailing list >> >> > cfe-commits@lists.llvm.org >> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> >> > >> >> _______________________________________________ >> >> cfe-commits mailing list >> >> cfe-commits@lists.llvm.org >> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> >> >> > >> > -- >> > Hal Finkel >> > Lead, Compiler Technology and Programming Languages >> > Leadership Computing Facility >> > Argonne National Laboratory >> > > -- > Hal Finkel > Lead, Compiler Technology and Programming Languages > Leadership Computing Facility > Argonne National Laboratory _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
