Re: [PATCH 11/19] rust/qobject: add from/to JSON bindings for QObject

Il ven 5 dic 2025, 13:16 Markus Armbruster <[email protected]> ha scritto:

> > Note however that there is no support for push parsing, therefore this
> > would not replace the balanced-parentheses machinery in
> > qobject/json-streamer.c, and therefore QMP would still need a minimal
> lexer.
>
> That push parser...  I never liked it.  First, it's half-assed: it's a
> push lexer wed to a pull parser with parenthesis counting.  Second, why
> complicated & half-assed when you can do simple & quarter-assed instead?
> We could've required "exactly one complete JSON value per line", or some
> expression separator such as an empty line.
>

Hmm not sure I agree, actually I think I disagree. It seems simpler but it
is also different.

Push parsing is not rocket science. It would be easy to write a proper one,
it's just that there is no real reason other than cleanliness.

> Grr... I just remembered about interpolation :/ so no, we still need a
> > parser for libqmp.c.
>
> Right.
>
> Interpolation lets us build QObjects from literal templates with
> variable scalars or QObjects interpolated.  More concise and much easier
> to read than the equivalend nest of constructor calls.  Drawback: chains
> us to our own, bespoke JSON parser.
>

And also, for similar reasons of practicality, single quotes (which IIRC
also became valid QMP, and that's less excusable).

But while it's a pity, we still get a lot from serde, namely making the
automatic generation of visitor code for structs someone else's problem.

Out of curiosity: how would we do better than "nest of constructor
> calls" in Rust?
>

You'd do that with a quoting macro, i.e.

qobject!({"command": cmd})

where the macro compiles to the nest of constructor calls, like
QObject::from_iter([(c"command", to_qobject(cmd))]).

Paolo

>