aaron.ballman 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
+ {
----------------
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++.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D133574/new/
https://reviews.llvm.org/D133574
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