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From:   Andreas Hindborg <nmi@metaspace.dk>
To:     y86-dev@protonmail.com
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Alice Ryhl <alice@ryhl.io>, rust-for-linux@vger.kernel.org,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
Subject: Re: [PATCH v3 01/13] rust: macros: add `quote!` macro
Date:   Thu, 30 Mar 2023 13:42:29 +0200
In-reply-to: <20230329223239.138757-2-y86-dev@protonmail.com>
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y86-dev@protonmail.com writes:

> From: Gary Guo <gary@garyguo.net>
>
> Add the `quote!` macro for creating `TokenStream`s directly via the
> given Rust tokens. It also supports repetitions using iterators.
>
> It will be used by the pin-init API proc-macros to generate code.
>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
> ---
>  rust/macros/lib.rs   |   2 +
>  rust/macros/quote.rs | 145 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 147 insertions(+)
>  create mode 100644 rust/macros/quote.rs
>
> diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
> index c1d385e345b9..82b520f024dd 100644
> --- a/rust/macros/lib.rs
> +++ b/rust/macros/lib.rs
> @@ -2,6 +2,8 @@
>
>  //! Crate for all kernel procedural macros.
>
> +#[macro_use]
> +mod quote;
>  mod concat_idents;
>  mod helpers;
>  mod module;
> diff --git a/rust/macros/quote.rs b/rust/macros/quote.rs
> new file mode 100644
> index 000000000000..7efb009c25a9
> --- /dev/null
> +++ b/rust/macros/quote.rs
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: Apache-2.0 OR MIT
> +
> +use proc_macro::{TokenStream, TokenTree};
> +
> +pub(crate) trait ToTokens {
> +    fn to_tokens(&self, tokens: &mut TokenStream);
> +}
> +
> +impl<T: ToTokens> ToTokens for Option<T> {
> +    fn to_tokens(&self, tokens: &mut TokenStream) {
> +        if let Some(v) = self {
> +            v.to_tokens(tokens);
> +        }
> +    }
> +}
> +
> +impl ToTokens for proc_macro::Group {
> +    fn to_tokens(&self, tokens: &mut TokenStream) {
> +        tokens.extend([TokenTree::from(self.clone())]);
> +    }
> +}
> +
> +impl ToTokens for TokenTree {
> +    fn to_tokens(&self, tokens: &mut TokenStream) {
> +        tokens.extend([self.clone()]);
> +    }
> +}
> +
> +impl ToTokens for TokenStream {
> +    fn to_tokens(&self, tokens: &mut TokenStream) {
> +        tokens.extend(self.clone());
> +    }
> +}
> +
> +/// Converts tokens into [`proc_macro::TokenStream`] and performs variable interpolations with
> +/// the given span.
> +///
> +/// This is a similar to the
> +/// [`quote_spanned!`](https://docs.rs/quote/latest/quote/macro.quote_spanned.html) macro from the
> +/// `quote` crate but provides only just enough functionality needed by the current `macros` crate.
> +#[allow(unused_macros)]
> +macro_rules! quote_spanned {
> +    ($span:expr => $($tt:tt)*) => {
> +    #[allow(clippy::vec_init_then_push)]
> +    {
> +        let mut tokens = Vec::new();
> +        let span = $span;
> +        quote_spanned!(@proc tokens span $($tt)*);
> +        proc_macro::TokenStream::from_iter(tokens)

Should this be `::alloc::vec::Vec` and
`::proc_macro::TokenStream::from_iter` ?

Best regards,
Andreas

> +    }};
> +    (@proc $v:ident $span:ident) => {};
> +    (@proc $v:ident $span:ident #$id:ident $($tt:tt)*) => {
> +        let mut ts = proc_macro::TokenStream::new();
> +        crate::quote::ToTokens::to_tokens(&$id, &mut ts);
> +        $v.extend(ts.into_iter());
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident #(#$id:ident)* $($tt:tt)*) => {
> +        for token in $id {
> +            let mut ts = proc_macro::TokenStream::new();
> +            crate::quote::ToTokens::to_tokens(&token, &mut ts);
> +            $v.extend(ts.into_iter());
> +        }
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident ( $($inner:tt)* ) $($tt:tt)*) => {
> +        let mut tokens = Vec::new();
> +        quote_spanned!(@proc tokens $span $($inner)*);
> +        $v.push(proc_macro::TokenTree::Group(proc_macro::Group::new(
> +            proc_macro::Delimiter::Parenthesis,
> +            proc_macro::TokenStream::from_iter(tokens)
> +        )));
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident [ $($inner:tt)* ] $($tt:tt)*) => {
> +        let mut tokens = Vec::new();
> +        quote_spanned!(@proc tokens $span $($inner)*);
> +        $v.push(proc_macro::TokenTree::Group(proc_macro::Group::new(
> +            proc_macro::Delimiter::Bracket,
> +            proc_macro::TokenStream::from_iter(tokens)
> +        )));
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident { $($inner:tt)* } $($tt:tt)*) => {
> +        let mut tokens = Vec::new();
> +        quote_spanned!(@proc tokens $span $($inner)*);
> +        $v.push(proc_macro::TokenTree::Group(proc_macro::Group::new(
> +            proc_macro::Delimiter::Brace,
> +            proc_macro::TokenStream::from_iter(tokens)
> +        )));
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident :: $($tt:tt)*) => {
> +        $v.push(
> +            proc_macro::TokenTree::Punct(proc_macro::Punct::new(':', proc_macro::Spacing::Joint))
> +        );
> +        $v.push(
> +            proc_macro::TokenTree::Punct(proc_macro::Punct::new(':', proc_macro::Spacing::Alone))
> +        );
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident : $($tt:tt)*) => {
> +        $v.push(
> +            proc_macro::TokenTree::Punct(proc_macro::Punct::new(':', proc_macro::Spacing::Alone))
> +        );
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident , $($tt:tt)*) => {
> +        $v.push(
> +            proc_macro::TokenTree::Punct(proc_macro::Punct::new(',', proc_macro::Spacing::Alone))
> +        );
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident @ $($tt:tt)*) => {
> +        $v.push(
> +            proc_macro::TokenTree::Punct(proc_macro::Punct::new('@', proc_macro::Spacing::Alone))
> +        );
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident ! $($tt:tt)*) => {
> +        $v.push(
> +            proc_macro::TokenTree::Punct(proc_macro::Punct::new('!', proc_macro::Spacing::Alone))
> +        );
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +    (@proc $v:ident $span:ident $id:ident $($tt:tt)*) => {
> +        $v.push(proc_macro::TokenTree::Ident(proc_macro::Ident::new(stringify!($id), $span)));
> +        quote_spanned!(@proc $v $span $($tt)*);
> +    };
> +}
> +
> +/// Converts tokens into [`proc_macro::TokenStream`] and performs variable interpolations with
> +/// mixed site span ([`Span::mixed_site()`]).
> +///
> +/// This is a similar to the [`quote!`](https://docs.rs/quote/latest/quote/macro.quote.html) macro
> +/// from the `quote` crate but provides only just enough functionality needed by the current
> +/// `macros` crate.
> +///
> +/// [`Span::mixed_site()`]: https://doc.rust-lang.org/proc_macro/struct.Span.html#method.mixed_site
> +#[allow(unused_macros)]
> +macro_rules! quote {
> +    ($($tt:tt)*) => {
> +        quote_spanned!(proc_macro::Span::mixed_site() => $($tt)*)
> +    }
> +}