aaron.ballman added a comment. In D122895#3512314 <https://reviews.llvm.org/D122895#3512314>, @aaron.ballman wrote:
> In D122895#3511682 <https://reviews.llvm.org/D122895#3511682>, @aaron.ballman > wrote: > >> In D122895#3511632 <https://reviews.llvm.org/D122895#3511632>, @jyknight >> wrote: >> >>> The warnings for this case aren't great: >>> >>> int foo(); >>> >>> int >>> foo(int arg) { >>> return 5; >>> } >> >> Yeah, that's not ideal, I'm looking into it to see if I can improve that >> scenario or not. > > There's not much to be done about the strict prototype warning for the > declaration; the issue is that we need to give the strict prototypes warning > when forming the function *type* for the declaration, which is long before we > have any idea there's a subsequent definition (also, because this is for > forming the type, we don't know what declarations, if any, may be related, so > there's no real way to improve the fix-it behavior). However, I think the > second warning is just bad wording -- we know we have a function definition > with a prototype for this particular diagnostic. However, there's the > redeclaration case to consider at the same time. So here's the full test and > the best behavior that I can come up with so far: > > void foo(); > void foo(int arg); > > void bar(); > void bar(int arg) {} > > With `-Wstrict-prototypes` enabled: > > F:\source\llvm-project>llvm\out\build\x64-Debug\bin\clang.exe -fsyntax-only > -Wstrict-prototypes "C:\Users\aballman\OneDrive - Intel > Corporation\Desktop\test.c" > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:1:9: warning: > a function declaration without a prototype > is deprecated in all versions of C [-Wstrict-prototypes] > void foo(); > ^ > void > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:2:6: warning: > this function declaration with a prototype > will change behavior in C2x because of a previous declaration with no > prototype [-Wdeprecated-non-prototype] > void foo(int arg); > ^ > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:4:9: warning: > a function declaration without a prototype > is deprecated in all versions of C [-Wstrict-prototypes] > void bar(); > ^ > void > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:5:6: warning: > this function definition with a prototype > will change behavior in C2x because of a previous declaration with no > prototype [-Wdeprecated-non-prototype] > void bar(int arg) {} > ^ > 4 warnings generated. > > With `-Wstrict-prototypes` disabled: > > F:\source\llvm-project>llvm\out\build\x64-Debug\bin\clang.exe -fsyntax-only > "C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c" > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:1:6: warning: > a function declaration without a prototype > is deprecated in all versions of C and is not supported in C2x > [-Wdeprecated-non-prototype] > void foo(); > ^ > void > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:2:6: warning: > this function declaration with a prototype > will change behavior in C2x because of a previous declaration with no > prototype [-Wdeprecated-non-prototype] > void foo(int arg); > ^ > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:4:6: warning: > a function declaration without a prototype > is deprecated in all versions of C and is not supported in C2x > [-Wdeprecated-non-prototype] > void bar(); > ^ > void > C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:5:6: warning: > this function definition with a prototype > will change behavior in C2x because of a previous declaration with no > prototype [-Wdeprecated-non-prototype] > void bar(int arg) {} > ^ > 4 warnings generated. > > It's not ideal, but it's about the most workable solution I can come up with > that doesn't regress far more important cases. It'd be nice if we had a note > instead of leaning on the previous warning like we're doing, but I still > claim this is defensible given how rare the situation is that you'd declare > without a prototype and later redeclare (perhaps through a definition) with a > non-`void` prototype. Note (it's easy to miss with the wall of text), the > difference between the two runs is that when strict prototypes are enabled, > we issue the strict prototype warning on the first declaration and when > strict prototypes are disabled, we issue the "is not supported in C2x" > diagnostic on the first declaration -- but in either case the intention is to > alert the user to which previous declaration has no prototype for the > subsequent declaration/definition that caused the issue. > > `this function declaration|definition with a prototype will change behavior > in C2x because of a previous declaration with no prototype` is the new > diagnostic wording I've got so far, and I'm not strongly tied to it, if you > have suggestions to improve it. I would also be happy with `this function > declaration|definition with a prototype is not supported in C2x because of a > previous declaration with no prototype` or something along those lines. I put up a review at https://reviews.llvm.org/D125814 going in this direction and added you both as reviewers. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D122895/new/ https://reviews.llvm.org/D122895 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
