CFFI 1.16.0 fails to recognize nested structs properly for purposes of partial notation #36

ffi = FFI()

ffi.set_source("buggy",
"""
struct a {
    int b;
    struct {
        int c;
    } d;
};
""")

ffi.cdef("""
struct a {
    struct {
        ...;
    } d;
    ...;
};
""")```

The following is the error message:

```Traceback (most recent call last):
  File "~/code/cffi/bug_report_1/bug.py", line 15, in <module>
    ffi.cdef("""
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/api.py", line 112, in cdef
    self._cdef(csource, override=override, packed=packed, pack=pack)
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/api.py", line 126, in _cdef
    self._parser.parse(csource, override=override, **options)
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 389, in parse
    self._internal_parse(csource)
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 412, in _internal_parse
    self._parse_decl(decl)
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 508, in _parse_decl
    self._get_struct_union_enum_type('struct', node)
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 839, in _get_struct_union_enum_type
    type, fqual = self._get_type_and_quals(decl.type,
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 674, in _get_type_and_quals
    tp = self._get_struct_union_enum_type('struct', type, name)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 832, in _get_struct_union_enum_type
    self._make_partial(tp, nested)
  File "~/code/cffi/bug_report_1/ve/lib/python3.11/site-packages/cffi/cparser.py", line 867, in _make_partial
    raise NotImplementedError("%s is partial but has no C name" %(tp,))
NotImplementedError: <struct $1> is partial but has no C name```

Looking at the code in and around cparser.py:867 it looks as if there's supposed to be some sort of support for marking the struct as nested, but it never gets called with a parameter for that argument, so it defaults to false.

I don't see a workaround, so in my application I'm just removing the inner struct and hoping I don't need it later, but this does seem as if it would be quite a nasty problem. It gets past the first checks if I put a name on the inner struct, but then fails when it tries to match with the "real" C code, so it definitely seems to be the inner struct and not have a simple workaround.