Fixes: https://github.com/llvm/llvm-project/issues/141659
In C23, something like [[/*possible attributes*/]]; is an attribute
declaration, not a statement. So it is not allowed by the syntax in
places where a statement is required, specifically as the secondary
block of a selection or iteration statement.
Therefore, code like the following should give a diagnostic (at least
with -std=c23 -pedantic), but Clang currently does not produce one:
```cpp
int main(void) {
if (1)
[[]];
}
```
---------
Signed-off-by: yronglin <yronglin777@gmail.com>
Signed-off-by: Wang, Yihan <yronglin777@gmail.com>
Co-authored-by: Mariya Podchishchaeva <mariya.podchishchaeva@intel.com>
The original proposal was seen in Apr 2019 and we accidentally used
that date (201904L) as the feature testing value. However, WG14 N2408
was adopted at the Oct 2019 meeting and so that's the correct date for
the feature testing macro. The committee draft for C2x shows 201910L
for this value, so this changes brings us in line with the standard.
These proposals make the same changes to both C++ and C and remove a
restriction on standard attributes appearing multiple times in the same
attribute list.
We could warn on the duplicate attributes, but do not. This is for
consistency as we do not warn on attributes duplicated within the
attribute specifier sequence. If we want to warn on duplicated
standard attributes, we should do so both for both situations:
[[foo, foo]] and [[foo]][[foo]].
Clang currently automates a fair amount of diagnostic checking for
declaration attributes based on the declarations in Attr.td. It checks
for things like subject appertainment, number of arguments, language
options, etc. This patch uses the same machinery to perform diagnostic
checking on statement attributes.
