rust: macros: add `quote!` macro

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 <benno.lossin@proton.me>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-3-y86-dev@protonmail.comSigned-off-by: Miguel Ojeda <ojeda@kernel.org>

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;

rust/macros/quote.rs

+// 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 = ::std::vec::Vec::new();
+        let span = $span;
+        quote_spanned!(@proc tokens span $($tt)*);
+        ::proc_macro::TokenStream::from_iter(tokens)
+    }};
+    (@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);
+        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);
+        }
+        quote_spanned!(@proc $v $span $($tt)*);
+    };
+    (@proc $v:ident $span:ident ( $($inner:tt)* ) $($tt:tt)*) => {
+        let mut tokens = ::std::vec::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 = ::std::vec::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 = ::std::vec::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)*)
+    }
+}