Re: [RFC PATCH v2 0/8] qapi: add generator for Golang interface

[Victor Toso <victortoso@redhat.com>]

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Hi,

On Mon, Aug 29, 2022 at 01:53:51PM +0200, Markus Armbruster wrote:
> Victor Toso <victortoso@redhat.com> writes:
>
> > Hi,
> >
> > On Tue, Jul 05, 2022 at 08:46:34AM -0700, Andrea Bolognani wrote:
> >> I've commented in detail to the single patches, just a couple of
> >> additional points.
> >>
> >> On Fri, Jun 17, 2022 at 02:19:24PM +0200, Victor Toso wrote:
> >> > * 7) Flat structs by removing embed types. Discussion with Andrea
> >> >      Thread: https://lists.gnu.org/archive/html/qemu-devel/2022-05/msg01590.html
> >> >
> >> >      No one required it but I decided to give it a try. Major issue that
> >> >      I see with this approach is to have generated a few 'Base' structs
> >> >      that are now useless. Overall, less nested structs seems better to
> >> >      me. Opnions?
> >> >
> >> >      Example:
> >> >       | /* This is now useless, should be removed? */
> >> >       | type InetSocketAddressBase struct {
> >> >       |     Host string `json:"host"`
> >> >       |     Port string `json:"port"`
> >> >       | }
> >>
> >> Can we somehow keep track, in the generator, of types that are
> >> only used as building blocks for other types, and prevent them
> >> from showing up in the generated code?
> >
> > I'm not 100% sure it is good to remove them from generated code
> > because technically it is a valid qapi type. If all @base types
> > are embed types and they don't show in other way or form, sure we
> > can remove them from generated code... I'm not sure if it is
> > possible to guarantee this.
> >
> > But yes, if possible, I'd like to remove what seems useless type
> > definitions.
>
> The existing C generators have to generate all the types, because the
> generated code is for QEMU's own use, where we need all the types.
>
> The existing introspection generator generates only the types visible in
> QAPI/QMP introspection.
>
> The former generate for internal use (where we want all the types), and
> the latter for external use (where only the types visible in the
> external interface are actually useful).

My doubt are on types that might be okay to be hidden because
they are embed in other types, like InetSocketAddressBase.

Note that what I mean with the struct being embed is that the
actual fields of InetSocketAddressBase being added to the type
which uses it, like InetSocketAddress.

  | type InetSocketAddressBase struct {
  |     Host string `json:"host"`
  |     Port string `json:"port"`
  | }
  |
  | type InetSocketAddress struct {
  |     // Base fields
  |     Host string `json:"host"`
  |     Port string `json:"port"`
  |
  |     Numeric   *bool   `json:"numeric,omitempty"`
  |     To        *uint16 `json:"to,omitempty"`
  |     Ipv4      *bool   `json:"ipv4,omitempty"`
  |     Ipv6      *bool   `json:"ipv6,omitempty"`
  |     KeepAlive *bool   `json:"keep-alive,omitempty"`
  |     Mptcp     *bool   `json:"mptcp,omitempty"`
  | }

Andrea's suggestions is to have the generator to track if a given
type is always embed in which case we can skip generating it in
the Go module.

I think that could work indeed. In the hypothetical case that
hiddens structs like InetSocketAddressBase becomes a parameter on
command in the future, the generator would know and start
generating this type from that point onwards.

> >> Finally, looking at the repository containing the generated
> >> code I see that the generated type are sorted by kind, e.g. all
> >> unions are in a file, all events in another one and so on. I
> >> believe the structure should match more closely that of the
> >> QAPI schema, so e.g.  block-related types should all go in one
> >> file, net-related types in another one and so on.
> >
> > That's something I don't mind adding but some hardcoded mapping
> > is needed. If you look into git history of qapi/ folder, .json
> > files can come and go, types be moved around, etc. So, we need to
> > proper map types in a way that the generated code would be kept
> > stable even if qapi files would have been rearranged. What I
> > proposed was only the simplest solution.
> >
> > Also, the generator takes a qapi-schema.json as input. We are
> > more focused in qemu/qapi/qapi-schema.json generated coded but
> > would not hurt to think we could even use it for qemu-guest-agent
> > from qemu/qga/qapi-schema.json -- this to say that the hardcoded
> > mapping needs to take into account non qemu qapi schemas too.
>
> In the beginning, the QAPI schema was monolithic.
> qga/qapi-schema.json still is.
>
> When keeping everything in a single qapi-schema.json became
> unwieldy, we split it into "modules" tied together with a
> simple include directive.  Generated code remained monolithic.

> When monolithic generated code became too annoying (touch
> schema, recompile everything), we made it match the module
> structure: code for FOO.json goes into *-FOO.c and *-FOO.h,
> where the *-FOO.h #include the generated headers for the .json
> modules FOO.json includes.
>
> Schema code motion hasn't been much of a problem.  Moving from
> FOO.json to one of the modules it includes is transparent.
> Non-transparent moves are relatively rare as long as the split
> into modules actually makes sense.

To be honest, splitting it into different files based on their
module names should not be a problem if we keep them in a single
Go module as do intend to for this generated go code.

So I'll go ahead and split it.

Cheers,
Victor

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