Re: [RFC PATCH v1 0/8] qapi: add generator for Golang interface

[Daniel P . Berrangé]

On Tue, May 10, 2022 at 10:18:15AM +0100, Daniel P. Berrangé wrote:
> On Tue, May 10, 2022 at 11:06:39AM +0200, Victor Toso wrote:
> > Hi,
> > 
> > On Tue, May 10, 2022 at 09:53:05AM +0100, Daniel P. Berrangé wrote:
> > > > > * License
> > > > >
> > > > > While the generator (golang.py in this series) is GPL v2, the
> > > > 
> > > > I'd make it v2+, just to express my displeasure with the decision to
> > > > make the initial QAPI generator v2 only for no good reason at all.
> > > 
> > > Our policy is that all new code should be v2+ anyway, unless it
> > > was clearly derived from some pre-existing v2-only code. Upto
> > > Victor to say whether the golang.py is considered clean, or was
> > > copy+paste in any parts from existin v2-only code
> > 
> > Should be fine to consider it v2+, the generator.
> > 
> > > > > generated code needs to be compatible with other Golang projects,
> > > > > such as the ones mentioned above. My intention is to keep a Go
> > > > > module with a MIT license.
> > > >
> > > > Meh.  Can't be helped, I guess.
> > > 
> > > This does make me wonder though whether the license of the QAPI
> > > input files has a bearing on the Go (or other $LANGUAGE) ouput
> > > files. eg is the Go code to be considered a derived work of the
> > > QAPI JSON files.
> > 
> > GPL does not enforce that the generated code to be GPL [0] unless
> > the generator copies GPL code to the output. My only concern has
> > been the fact that I am copying the documentation of QAPI
> > specification to the Go package in order to have data structures,
> > commands, etc. with the information provided by the
> > specification.
> > 
> > [0] https://www.gnu.org/licenses/old-licenses/gpl-2.0-faq.html#GPLOutput
> >
> > > I'm not finding a clearly articulated POV on this question so
> > > far.
> > 
> > I don't find it trivial either but I've accepted that the Go data
> > structures are fine based on [0] and the documentation can be
> > split from the Go module (sadly!) if someone finds it to be a
> > legal issue.
> 
> Ah well that link above is actually reasonably clear:
> 
>   "More generally, when a program translates its input into 
>    some other form, the copyright status of the output inherits
>    that of the input it was generated from. "
> 
> In our case the input is the QAPI JSON, and we're translating that
> into  Golang. That could be read as meaning our Golang code has to
> be GPLv2+ licensed just as with the QAPI, not merely the docs.

Oh but I'm forgetting that QAPI JSON can be said to be our public API
interface, and so while the docs text would be GPLv2+, we can claim
fair use for the interface definition in the generator and pick an
arbitrary output license.

We could likely deal with the docs problem by not copying the docs
directly into the generated code, instead link to the published
docs on qemu.org. This would require us to improve our current docs
generated anchor generation. ie currently docs link for say the
struct 'NumaNodeOptions' potentially changes every time we generate
it

https://www.qemu.org/docs/master/interop/qemu-qmp-ref.html#qapidoc-2416

we would need to that be something stable, ie

https://www.qemu.org/docs/master/interop/qemu-qmp-ref.html#struct-NumaNodeOptions

Then the generated Go can just do

   // See QAPI docs at 
https://www.qemu.org/docs/master/interop/qemu-qmp-ref.html#struct-NumaNodeOptions

thus avoiding any copyright complication

With regards,
Daniel
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