Re: [PATCH v2 2/5] rust: macros: support additional tokens in quote!

Tamir Duberstein
2025-02-28T15:26:20Z

On Fri, Feb 28, 2025 at 7:42 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> This gives the quote! macro support for the following additional tokens:
>
> * The = token.
> * The _ token.
> * Using #my_var with variables of type Ident.
>
> Additionally, some type annotations are added to allow cases where
> groups are empty. For example, quote! does support () in the input, but
> only when it is *not* empty. When it is empty, the compiler cannot infer
> the item type of `tokens`.
>
> These additional quote! features are used by a new proc macro that
> generates code looking like this:
>
> const _: () = {
> if true {
> ::kernel::bindings::#name
> } else {
> #name
> };
> };
>
> where #name has type Ident.
>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> rust/macros/quote.rs | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/rust/macros/quote.rs b/rust/macros/quote.rs
> index 33a199e4f176..c18960a91082 100644
> --- a/rust/macros/quote.rs
> +++ b/rust/macros/quote.rs
> @@ -20,6 +20,12 @@ fn to_tokens(&self, tokens: &mut TokenStream) {
> }
> }
>
> +impl ToTokens for proc_macro::Ident {
> + 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()]);
> @@ -40,7 +46,7 @@ fn to_tokens(&self, tokens: &mut TokenStream) {
> /// `quote` crate but provides only just enough functionality needed by the current `macros` crate.
> macro_rules! quote_spanned {
> ($span:expr => $($tt:tt)*) => {{
> - let mut tokens;
> + let mut tokens: ::std::vec::Vec<::proc_macro::TokenTree>;
> #[allow(clippy::vec_init_then_push)]
> {
> tokens = ::std::vec::Vec::new();
> @@ -65,7 +71,8 @@ macro_rules! quote_spanned {
> quote_spanned!(@proc $v $span $($tt)*);
> };
> (@proc $v:ident $span:ident ( $($inner:tt)* ) $($tt:tt)*) => {
> - let mut tokens = ::std::vec::Vec::new();
> + #[allow(unused_mut)]

It'd be nice to mention the need for this attribute in the commit
message along with the added type annotations.

> + let mut tokens = ::std::vec::Vec::<::proc_macro::TokenTree>::new();
> quote_spanned!(@proc tokens $span $($inner)*);
> $v.push(::proc_macro::TokenTree::Group(::proc_macro::Group::new(
> ::proc_macro::Delimiter::Parenthesis,
> @@ -136,6 +143,16 @@ macro_rules! quote_spanned {
> ));
> 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::Ident(::proc_macro::Ident::new("_", $span)));
> + 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)*);
>
> --
> 2.48.1.711.g2feabab25a-goog

Reviewed-by: Tamir Duberstein <tamird@gmail.com>