-std=c2x support for C++-style attributes in C-code.

[Iipal]

Bug type: Language Service

• OS and Version: Ubuntu 20.04
• VS Code Version: 1.56
• C/C++ Extension Version: 1.3.1

Expected behavior

No errors?
inside union allocator_t->data appears as an unknown data type (2nd screenshot)

Code sample and logs

• Code sample && Configurations in c_cpp_properties.json: on the screenshot below
• Logs from running C/C++: Log Diagnostics from the VS Code command palette: shows nothing

Theme: Darcula with JetBrains Mono font.

[Iipal]

even __auto_type behavior is strange for linux-clang-x64 mode even if __is_identifier says it's valid;

if I change the mode to linux-gcc-x64 as well as a compiler to gcc - then everything works fine. But why in clang-mode it's said that it's a valid identifier but then I see errors?

[sean-mcmanus]

Can you provide a code sample that compiles with C but gives an error with our extension? I'm seeing gcc and clang both fail to compile

typedef union {
    int i;
} allocator_t [[gnu::transparent_union]];

int main()
{
    return 0;
}

error: expected expression
} allocator_t [[gnu::transparent_union]];

[sean-mcmanus]

Oh -- I got it to compile with -std=c2x -- we don't support that std version yet. We can use this issue to track adding that.

[sean-mcmanus]

I've filed a bug against our shared VS parser at https://developercommunity.visualstudio.com/t/C-standard-2x-isnt-supported-by-Intelli/1416530 . After they enable that we can add support on our side.