`sstables::write()` has multiple overloads, which are defined in
`sstables/writer.hh`. two of these overloads are template functions,
which have a template parameter named `W`, which has a type constraint
requiring it to fulfill the `Writer` concept. but in `types.hh`, when
the compiler tries to instantiate the template function with signature
of `write(sstable_version_types v, W& out, const T& t)` with
`file_writer` as the template parameter of `w`, `file_writer` is only
forward-declared using `class file_writer` in the same header file, so
this type is still an incomplete type at that moment. that's why the
compiler is not able to determine if `file_writer` fulfills the
constraint or not. actually, the declaration of `file_writer` is located
in `sstables/writer.hh`, which in turn includes `types.hh`. so they
form a cyclic dependency.
in this change, in order to break this cycle, we extract file_writer out
into a separate header file, so that both `sstables/writer.hh` and
`sstables/types.hh` can include it. this address the build failure.
Fixesscylladb/scylladb#19667
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#19669
06ba523818