Add derive serde attributes to the generated message and service struct

[ZhangHanDong]

hi @adnanademovic ,

thanks very much for your contribution , rosrust is a great crate.

I recently plan to use it in production environment, but I need to return json string directly from the generated struct. But now , rosrust doesn't support this feature, so I implemented it by myself, and test available in the actual environment.

I found that someone else has submitted the PR #135 of similar feature, but his is wrong and can't be compiled.

I hope you can merge and release a new crate version so that my project can use the new version instand of relying on git.

thanks !

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usage:

rosrust = { version = "0.9.5",  features = ["derive-serde"]} 

[ZhangHanDong]

@adnanademovic

[adnanademovic]

Will this cause build failure if you try to serialize a fixed length array longer than 32?
That's the reason the feature isn't already there, due to const generics not existing yet, and thus serde has that limitation.

[ZhangHanDong]

The const generics function will be stable in version 1.51, and this defect may be improved in the future.

I still close the pr first.

[adnanademovic]

Yeah once the feature is there, and serde implements it, adding serde support will be extremely simple, and I'd likely add it directly without any feature flags.

[ZhangHanDong]

ok

[KrasnovPavel]

@adnanademovic @ZhangHanDong
Hi! It is Rust 1.54 already here. Can you add this feature or serde still doesn't support it?

[adnanademovic]

@KrasnovPavel It still doesn't

serde-rs/serde#1937

[adnanademovic]

In the meantime, I've added rosrust::Value and rosrust::MessageValue, which do support serde, and are just dynamic representations of ROS messages.

https://github.com/adnanademovic/rosrust/blob/master/rosrust/tests/dynamic_msg.rs#L100-L144

You can do .into() to convert into a Value/MessageValue, or ,try_from() to convert from an arbitrary one.