Autocomplete for other file

Let's say I have a file called foo.c:
    typedef struct {
        int value;
    } Foo;

and another file called main.c:
    #include "foo.c"   
    int main {
        Foo foo = {};
    };

when I now start typing `foo.` I see no autocomplete options, while `foo.value = 3;` does indeed compile just fine. It does suggest `value` when I place the struct in the same  file though.

Any reason/solution for this?