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

[Manos Pitsidianakis <manos.pitsidianakis@linaro.org>]

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