Re: [PATCH v1 0/9] qapi-go: add generator for Golang interface

[Daniel P . Berrangé]

On Thu, Sep 28, 2023 at 02:40:27PM +0100, Daniel P. Berrangé wrote:
> On Wed, Sep 27, 2023 at 01:25:35PM +0200, Victor Toso wrote:
> > Hi, long time no see!
> > 
> > This patch series intent is to introduce a generator that produces a Go
> > module for Go applications to interact over QMP with QEMU.
> 
> snip
>  
> > Victor Toso (9):
> >   qapi: golang: Generate qapi's enum types in Go
> >   qapi: golang: Generate qapi's alternate types in Go
> >   qapi: golang: Generate qapi's struct types in Go
> >   qapi: golang: structs: Address 'null' members
> >   qapi: golang: Generate qapi's union types in Go
> >   qapi: golang: Generate qapi's event types in Go
> >   qapi: golang: Generate qapi's command types in Go
> >   qapi: golang: Add CommandResult type to Go
> >   docs: add notes on Golang code generator
> > 
> >  docs/devel/qapi-golang-code-gen.rst |  341 +++++++++
> >  scripts/qapi/golang.py              | 1047 +++++++++++++++++++++++++++
> >  scripts/qapi/main.py                |    2 +
> >  3 files changed, 1390 insertions(+)
> >  create mode 100644 docs/devel/qapi-golang-code-gen.rst
> >  create mode 100644 scripts/qapi/golang.py
> 
> So the formatting of the code is kinda all over the place eg
> 
> func (s *StrOrNull) ToAnyOrAbsent() (any, bool) {
>     if s != nil {
>         if s.IsNull {
>             return nil, false
>     } else if s.S != nil {
>         return *s.S, false
>         }
>     }
> 
>     return nil, true
> }
> 
> 
> ought to be
> 
> func (s *StrOrNull) ToAnyOrAbsent() (any, bool) {
>         if s != nil {
>                 if s.IsNull {
>                         return nil, false
>                 } else if s.S != nil {
>                         return *s.S, false
>                 }
>         }
> 
>         return nil, true
> }
> 
> I'd say we should add a 'make check-go' target, wired into 'make check'
> that runs 'go fmt' on the generated code to validate that we generated
> correct code. Then fix the generator to actually emit the reqired
> format.
> 
> 
> Having said that, this brings up the question of how we expect apps to
> consume the Go code. Generally an app would expect to just add the
> module to their go.mod file, and have the toolchain download it on
> the fly during build.
> 
> If we assume a go namespace under qemu.org, we'll want one or more
> modules. Either we have one module, containing APIs for all of QEMU,
> QGA, and QSD, or we have separate go modules for each. I'd probably
> tend towards the latter, since it means we can version them separately
> which might be useful if we're willing to break API in one of them,
> but not the others.
> 
> IOW, integrating this directly into qemu.git as a build time output
> is not desirable in this conext though, as 'go build' can't consume
> that.
> 
> IOW, it would push towards
> 
>    go-qemu.git
>    go-qga.git
>    go-qsd.git
> 
> and at time of each QEMU release, we would need to invoke the code
> generator, and store its output in the respective git modules.
> 
> This would also need the generator application to be a standalone
> tool, separate from the C QAPI generator.

Oh, and we need to assume that all CONFIG conditionals in the QAPI
files are true, as we want the Go API to be feature complete such
that it can be used with any QEMU build, regardless of which CONFIG
conditions are turned on/off. We also don't want applications to
suddenly fail to compile because some API was stopped being generated
by a disabled CONFIG condition - it needs to be a runtime error
that apps can catch and handle as they desire.

> 
> Finally Go apps would want to do
> 
>    import (
>        qemu.org/go/qemu
>        qemu.org/go/qga
>        qemu.org/go/gsd
>    )
> 
> and would need us to create the "https://qemu.org/go/qemu"; page
> containing dummy HTML content with 
> 
>     <meta name="go-import" content="qemu.org/go/qemu git 
> https://gitlab.com/qemu-project/go-qemu.git@/>
> 
> and likewise for the other modules.
> 
> Regards,
> Daniel
> -- 
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> 
> 

With regards,
Daniel
-- 
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