inclyc added inline comments.
================ Comment at: clang/test/Sema/offsetof.c:79 + int a; + struct B // no-error, struct B is not defined within __builtin_offsetof directly + { ---------------- aaron.ballman wrote: > inclyc wrote: > > inclyc wrote: > > > aaron.ballman wrote: > > > > inclyc wrote: > > > > > aaron.ballman wrote: > > > > > > I think this is defensible. The wording in the standard is "If the > > > > > > specified type defines a new type or if the specified member is a > > > > > > bit-field, the behavior is undefined." and the specified type in > > > > > > this case is `struct A`; that `struct A` happens to also define > > > > > > `struct B` is immaterial. > > > > > > > > > > > > However, the intent behind the change to the rule is to support > > > > > > older implementations of `offsetof` to protect them from having to > > > > > > deal with a case like: `offsetof(struct S { int a, b }, b);` where > > > > > > `offsetof` is a macro and thus the comma between `a` and `b` is > > > > > > treated as a separator. So there's a part of me that wonders if we > > > > > > want to also support diagnosing this case. But then we'd have to > > > > > > look at the declarator context more recursively to see whether any > > > > > > of the contexts on the stack are an `offsetof` context and that > > > > > > might be tricky. > > > > > > > > > > > > Thoughts? > > > > > FWIW, gcc seems just rejects all definitions in this context. > > > > > (Perhaps during Parsing the statements). If we add a bool state to > > > > > the Parser (just using RAII object as before) struct B will trigger > > > > > diagnostic error because the state "ParsingOffsetof" is passed into > > > > > inner declaration. > > > > GCC accepts currently: https://godbolt.org/z/oEvzjW6Ee but you're > > > > correct regarding switching back to an RAII object being an easier way > > > > to address the nested declarations. > > > > > > > > Let me think on this situation a bit.... > > > > GCC accepts currently > > > > > > C++: https://godbolt.org/z/fon8e7dzf > > ``` > > <source>: In function 'int main()': > > <source>:3:3: error: types may not be defined within '__builtin_offsetof' > > 3 | { > > | ^ > > <source>:6:5: error: types may not be defined within '__builtin_offsetof' > > 6 | { > > | ^ > > Compiler returned: 1 > > ``` > C++ is a different language in this case though. In C, you can generally > define types anywhere you can spell a type, and in C++ you cannot. e.g., > `void func(struct S { int x, y; } s);` is valid in C and invalid in C++. GCC explicitly reject type definitions since GCC 8 (in C++ mode). I guess the logic here in GCC may also add a boolean state parameter to parser. Interestingly, in C++ we treat the first parameter of `__builtin_offsetof` as a type specifier, rejecting the definition of `struct A`, but not rejecting nested definition `struct B` https://godbolt.org/z/PqWjzqqYn Emm, so, how about switch back to RAIIObject to support diagnosing nested definitions? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D133574/new/ https://reviews.llvm.org/D133574 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits