`cargo-extern-fn` Proc-macro code review | Rust Programming Language Community | Page 1

broken socket Dec 22, 2022, 2:59 PM

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Hey, I've been hacking around proc-macro for a few days due to some need would like some guidance on how to best combines syn and quote: https://github.com/kraktus/cargo-extern-fn/tree/aab6bfc414c0f15ef85f1a1037162402fb3b4930 (code only living at src/main.rs)

I'm especially unpleased by call_function_from_sig and union internal functions, but more generally how to combine TokenStream together. For now I'm mostly using String back and forth, something re-quoteing, sometimes parsing, this does not feel very organised.

Thank you for looking into it, I know this type of code can be rather dense, and in my case has not been polished.

pallid depot Dec 22, 2022, 3:15 PM

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I only see a suboptimal format! over here: https://github.com/kraktus/cargo-extern-fn/blob/aab6bfc414c0f15ef85f1a1037162402fb3b4930/src/main.rs#L233-L240

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I think you should be able to do something along the lines of:

let fn_ident = {
    let Sig { ident, .. } = &sig;
    let ty =
        self.current_impl_ty.as_ref()
            // trick to make the `Option` be `#( … )*`-interpolable
            .map_or(&[][..], ::core::slice_from_ref)
    ;
    quote!(
        #( < #ty > ::)* 
        #ident
    )
};

broken socket Dec 22, 2022, 3:24 PM

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That's some quote! magic! 😄 Nice thanks

broken socket Dec 22, 2022, 5:06 PM

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An annoying issue is that syn removes comment and transform doc comments /// doc into doc comment attribute #[doc = "doc"]

pallid depot Dec 22, 2022, 6:22 PM

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Yeah, comments are not part of Rustc tokens ferrisPensive

broken socket Dec 22, 2022, 7:13 PM

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When parsing back is it possible to tell syn/quote to remap doc comments to use the /// doc syntax? Or need to be post-processed manually

pallid depot Dec 23, 2022, 12:27 PM

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?eval "/// test".parse::<::proc_macro2::TokenStream>().unwrap().to_string()

timid juniperBOT Dec 23, 2022, 12:27 PM

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     Running `target/debug/playground`

"# [doc = \" test\"]"

pallid depot Dec 23, 2022, 12:28 PM

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Yeah, it looks like TokenStream's own .to_string() logic use #[doc = "…"], so you'd need to preprocess manually

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?fmt #[doc = "test"] extern {}

timid juniperBOT Dec 23, 2022, 12:28 PM

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#[doc = "test"]
extern "C" {}

pallid depot Dec 23, 2022, 12:29 PM

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Hmm, I could have hoped that a formatter would do this, but it doesn't seem to be the case ferrisPensive

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Ah, wait, maybe prettyplease does

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https://www.rustexplorer.com/b#%2F* [dependencies] prettyplease.version %3D "0.1.22" syn.version %3D "1.0.106" syn.features %3D ["full"] *%2F fn main() { println!("{}"%2C %3A%3Aprettyplease%3A%3Aunparse(%26%3A%3Asyn%3A%3Aparse_quote!( %23[doc %3D " Test"] extern {} )))%3B }

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This would be a programmatic usage of it, otherwise you can always post-process from the command-line using prettyplease-cli: https://github.com/danielhenrymantilla/prettyplease-cli

#`cargo-extern-fn` Proc-macro code review