dear cfe-dev list,
Visiting the clang AST after the semantic analysis the designated
initialisers often keep classes of this type.
What is his meaning? Is it just a filler that means `zero in this place, but
the user omitted it' or there is some other meaning?
Yes, exactly. It means that the subobject in that place will be initialized with all 0s, but since the user didn't actually write a '0' there we have a different AST node for it.
The documentation is a bit weak, unfortunately: