C++
clang HEAD 12.0.0 (https://github.com/llvm/llvm-project.git 9087209314caafed4b232d4a66287f2d16054ad3)
$ clang++ prog.cc -Wall -Wextra -I/opt/wandbox/boost-1.73.0/clang-head/include -std=c++2a prog.cc:5:16: error: static data member 'i' not allowed in anonymous struct
static int i; // ill-formed
^
prog.cc:2:15: warning: anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here [-Wnon-c-typedef-for-linkage]
typedef struct : Base // inheriting from 'Base'; ill-formed
^
S
prog.cc:2:18: note: type is not C-compatible due to this base class
typedef struct : Base // inheriting from 'Base'; ill-formed
^~~~
prog.cc:10:3: note: type is given name 'S' for linkage purposes by this typedef declaration
} S;
^
1 warning and 1 error generated.