Generator can create duplicate RegisterSchema functions

[Hoops]

After the change for #479, if you have multiple capnp files in a package, e.g.

$ cat book.capnp
using Go = import "/go.capnp";
@0x85d3acc39d94e0f8;
$Go.package("books");
$Go.import("foo/books");

struct Book {
    title @0 :Text;
    # Title of the book.

    pageCount @1 :Int32;
    # Number of pages in the book.
}

and

$ cat book2.capnp
using Go = import "/go.capnp";
@0x86115605f6b5e399;
$Go.package("books");
$Go.import("foo/books");

struct Book2 {
    title @0 :Text;
    # Title of the book.

    pageCount @1 :Int32;
    # Number of pages in the book.
}

then

$ capnp compile -I$HOME/go/pkg/mod/capnproto.org/go/capnp/v3@v3.0.0-alpha.24/std -ogo:. *.capnp 
$ go mod init books; go mod tidy
go: creating new go.mod: module books
go: to add module requirements and sums:
	go mod tidy
go: finding module for package capnproto.org/go/capnp/v3/schemas
go: finding module for package capnproto.org/go/capnp/v3/encoding/text
go: finding module for package capnproto.org/go/capnp/v3
go: found capnproto.org/go/capnp/v3 in capnproto.org/go/capnp/v3 v3.0.0-alpha.25
go: found capnproto.org/go/capnp/v3/encoding/text in capnproto.org/go/capnp/v3 v3.0.0-alpha.25
go: found capnproto.org/go/capnp/v3/schemas in capnproto.org/go/capnp/v3 v3.0.0-alpha.25
$ go build ./...
# books
./book2.capnp.go:113:6: RegisterSchema redeclared in this block
	./book.capnp.go:113:6: other declaration of RegisterSchema

There will be duplicate functions in the same package. Maybe the register function needs to be generated in a separate file per-package with one RegisterSchema for all?

[zenhack]

Thanks for the report. This one's on me -- I never put more than one schema in a package so I always forget this use case. We should add some tests that do this. The solution you propose sounds reasonable.

[hspaay]

Is there a recommended workaround for the interim? Downgrade to alpha.24?

[lthibault]

@hspaay I think the workaround would be to merge your files into one. Note that you can still import types from separate packages; I do this quite a bit, and it has prevented me from ever requiring mutli-file packages.

[hspaay]

@lthibault thanks for the very quick reply :)

merge your files into one

Not sure if I follow. I've got 13 capnp files, one per micro-service and they go into the 'api' package. Are you recommending to put all of these into a single file? I love how compact capnp files are but putting all in a single file might be a bit too much.

[hspaay]

[zenhack]

I tend to put each .capnp file in its own package (which is basically why this hasn't come up); I agree dumping everything into the same file could get unwieldly, and furthermore, you'd have to make the interface IDs explicit to avoid changing them, since those are a function of the parent namespace's ID (the root of which is the file ID) and the name of the type/interface.

See e.g. https://github.com/zenhack/go.sandstorm/tree/master/capnp

[hspaay]

@zenhack thanks for that.
The primary reason I like the single folder is that to use an api it is a simple import "hubapi".
But yeah, I understand the problem now and possible workarounds. Maybe I'll come around and switch to use the package folders. For a large project that makes a lot of sense.

For now I think I'll wait a bit using alpha.24 and hope for a fix. Its all still alpha (including my stuff) so no rush.

Again, I much appreciate the awesome support you guys are giving.

[lthibault]

@hspaay I use the same approach as @zenhack. Correspondingly, here is my typical application structure. The cluster.capnp package/file imports from all the others (the Host interface is basically the top-level capability in my system).

Hope this helps.

Again, I much appreciate the awesome support you guys are giving.

It's truly our pleasure! 😃

[alexforster]

Just chiming in to say that this is affecting us at Cloudflare too. We're pinning to alpha.24 in the meantime.

[lthibault]

@alexforster Any chance you might be able to submit a PR? @zenhack recently passed away and we're spread very thin right now. Realistically, I don't think I'll be getting to this one for a while.

If you are able to contribute, I am more than happy to lend my support.

P.S.: thank you for your feedback, btw!

[hspaay]

@lthibault wrt "zenhack recently passed away".
OMG! That is terrible news. My condolences to those who knew him. He was such a friendly and helpful person. 😢

[lthibault]

@hspaay OMG, I'm so sorry to drop the news on you so suddenly. For some reason I thought you already knew! Yes, Ian was truly an exceptional guy, and it was all very sudden. Go-capnp will be fine, but Ian's presence is truly missed :(

[hspaay]

Well I've been away for a bit so my own fault for not keeping up to date.
Sigh I'm going to have a stiff drink later and a good toast to Ian.
Hope you are all okay. He will indeed be truly missed.
All the best Ian, and thank you so much for the help. You won't be forgotten.