Re: [PATCH v8 7/8] rust: add utility procedural macro crate

[Manos Pitsidianakis]

Hello Junjie,

On Mon, 26 Aug 2024 08:15, Junjie Mao <junjie.mao@intel.com> wrote:
> On 8/23/2024 4:11 PM, Manos Pitsidianakis wrote:
> > This commit adds a helper crate library, qemu-api-macros for derive (and
> > other procedural) macros to be used along qemu-api.
> >
> > It needs to be a separate library because in Rust, procedural macros, or
> > macros that can generate arbitrary code, need to be special separate
> > compilation units.
> >
> > Only one macro is introduced in this patch, #[derive(Object)]. It
> > generates a constructor to register a QOM TypeInfo on init and it must
> > be used on types that implement qemu_api::definitions::ObjectImpl trait.
> >
> > Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
> > ---
> >   MAINTAINERS                            |   1 +
> >   rust/meson.build                       |   1 +
> >   rust/qemu-api-macros/Cargo.lock        |  47 +++++++
> >   rust/qemu-api-macros/Cargo.toml        |  25 ++++
> >   rust/qemu-api-macros/README.md         |   1 +
> >   rust/qemu-api-macros/meson.build       |  25 ++++
> >   rust/qemu-api-macros/src/cstr/mod.rs   |  55 ++++++++
> >   rust/qemu-api-macros/src/cstr/parse.rs | 225 +++++++++++++++++++++++++++++++++
>
> Since Rust 1.77.0 C-string literals are stabilized [1]. I don't think we need to 
> include this cstr crate as we require Rust >= 1.80.0.


Many thanks! I got the qemu-api-macros from my git stash, I tried to 
bundle cstr in a previous version before we had proper meson 
dependencies and I hadn't raised the Rust version. So I just forgot to 
remove these files (they are not even declared in lib.rs). Oops 🤦.

> [1] https://crates.io/crates/cstr
>
> >   rust/qemu-api-macros/src/lib.rs        |  43 +++++++
> >   rust/qemu-api/meson.build              |   3 +
> >   10 files changed, 426 insertions(+)
> [snip]
> > diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build
> > index 85838d31b4..a0802ad858 100644
> > --- a/rust/qemu-api/meson.build
> > +++ b/rust/qemu-api/meson.build
> > @@ -13,6 +13,9 @@ _qemu_api_rs = static_library(
> >     rust_args: [
> >       '--cfg', 'MESON',
> >     ],
> > +  dependencies: [
> > +    qemu_api_macros,
> > +  ],
> >   )
> >   
> >   qemu_api = declare_dependency(
>
> qemu-api does not use macros provided by qemu-api-macros, but the later 
> generates code that uses types defined by the former. So to me qemu-api-macros 
> should depend on qemu-api, not vice versa.

It does generate code but it does not use those types, serde_derive for 
example does not depend on serde but serde depends on serde_derive 
(because it re-exports the macros in its API):

https://crates.io/crates/serde_derive/1.0.209/dependencies
https://crates.io/crates/serde/1.0.209/dependencies

Manos