diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/lib.rs | 301 |
1 files changed, 301 insertions, 0 deletions
diff --git a/src/lib.rs b/src/lib.rs new file mode 100644 index 0000000..082f734 --- /dev/null +++ b/src/lib.rs @@ -0,0 +1,301 @@ +use proc_macro::TokenStream; +use proc_macro2::{Group, TokenStream as TokenStream2, TokenTree}; +use quote::quote; +use syn::parse::{Parse, ParseStream, Parser, Result}; +use syn::visit_mut::VisitMut; + +struct Scrub<'a> { + /// Whether the stream is a try stream. + is_try: bool, + /// The unit expression, `()`. + unit: Box<syn::Expr>, + has_yielded: bool, + crate_path: &'a TokenStream2, +} + +fn parse_input(input: TokenStream) -> syn::Result<(TokenStream2, Vec<syn::Stmt>)> { + let mut input = TokenStream2::from(input).into_iter(); + let crate_path = match input.next().unwrap() { + TokenTree::Group(group) => group.stream(), + _ => panic!(), + }; + let stmts = syn::Block::parse_within.parse2(replace_for_await(input))?; + Ok((crate_path, stmts)) +} + +impl<'a> Scrub<'a> { + fn new(is_try: bool, crate_path: &'a TokenStream2) -> Self { + Self { + is_try, + unit: syn::parse_quote!(()), + has_yielded: false, + crate_path, + } + } +} + +struct Partial<T>(T, TokenStream2); + +impl<T: Parse> Parse for Partial<T> { + fn parse(input: ParseStream) -> Result<Self> { + Ok(Partial(input.parse()?, input.parse()?)) + } +} + +fn visit_token_stream_impl( + visitor: &mut Scrub<'_>, + tokens: TokenStream2, + modified: &mut bool, + out: &mut TokenStream2, +) { + use quote::ToTokens; + use quote::TokenStreamExt; + + let mut tokens = tokens.into_iter().peekable(); + while let Some(tt) = tokens.next() { + match tt { + TokenTree::Ident(i) if i == "yield" => { + let stream = std::iter::once(TokenTree::Ident(i)).chain(tokens).collect(); + match syn::parse2(stream) { + Ok(Partial(yield_expr, rest)) => { + let mut expr = syn::Expr::Yield(yield_expr); + visitor.visit_expr_mut(&mut expr); + expr.to_tokens(out); + *modified = true; + tokens = rest.into_iter().peekable(); + } + Err(e) => { + out.append_all(&mut e.to_compile_error().into_iter()); + *modified = true; + return; + } + } + } + TokenTree::Ident(i) if i == "stream" || i == "try_stream" => { + out.append(TokenTree::Ident(i)); + match tokens.peek() { + Some(TokenTree::Punct(p)) if p.as_char() == '!' => { + out.extend(tokens.next()); // ! + if let Some(TokenTree::Group(_)) = tokens.peek() { + out.extend(tokens.next()); // { .. } or [ .. ] or ( .. ) + } + } + _ => {} + } + } + TokenTree::Group(group) => { + let mut content = group.stream(); + *modified |= visitor.visit_token_stream(&mut content); + let mut new = Group::new(group.delimiter(), content); + new.set_span(group.span()); + out.append(new); + } + other => out.append(other), + } + } +} + +impl Scrub<'_> { + fn visit_token_stream(&mut self, tokens: &mut TokenStream2) -> bool { + let (mut out, mut modified) = (TokenStream2::new(), false); + visit_token_stream_impl(self, tokens.clone(), &mut modified, &mut out); + + if modified { + *tokens = out; + } + + modified + } +} + +impl VisitMut for Scrub<'_> { + fn visit_expr_mut(&mut self, i: &mut syn::Expr) { + match i { + syn::Expr::Yield(yield_expr) => { + self.has_yielded = true; + + syn::visit_mut::visit_expr_yield_mut(self, yield_expr); + + let value_expr = yield_expr.expr.as_ref().unwrap_or(&self.unit); + + // let ident = &self.yielder; + + *i = if self.is_try { + syn::parse_quote! { __yield_tx.send(::core::result::Result::Ok(#value_expr)).await } + } else { + syn::parse_quote! { __yield_tx.send(#value_expr).await } + }; + } + syn::Expr::Try(try_expr) => { + syn::visit_mut::visit_expr_try_mut(self, try_expr); + // let ident = &self.yielder; + let e = &try_expr.expr; + + *i = syn::parse_quote! { + match #e { + ::core::result::Result::Ok(v) => v, + ::core::result::Result::Err(e) => { + __yield_tx.send(::core::result::Result::Err(e.into())).await; + return; + } + } + }; + } + syn::Expr::Closure(_) | syn::Expr::Async(_) => { + // Don't transform inner closures or async blocks. + } + syn::Expr::ForLoop(expr) => { + syn::visit_mut::visit_expr_for_loop_mut(self, expr); + // TODO: Should we allow other attributes? + if expr.attrs.len() != 1 || !expr.attrs[0].path.is_ident("await") { + return; + } + let syn::ExprForLoop { + attrs, + label, + pat, + expr, + body, + .. + } = expr; + + let attr = attrs.pop().unwrap(); + if let Err(e) = syn::parse2::<syn::parse::Nothing>(attr.tokens) { + *i = syn::parse2(e.to_compile_error()).unwrap(); + return; + } + + let crate_path = self.crate_path; + *i = syn::parse_quote! {{ + let mut __pinned = #expr; + let mut __pinned = unsafe { + ::core::pin::Pin::new_unchecked(&mut __pinned) + }; + #label + loop { + let #pat = match #crate_path::__private::next(&mut __pinned).await { + ::core::option::Option::Some(e) => e, + ::core::option::Option::None => break, + }; + #body + } + }} + } + _ => syn::visit_mut::visit_expr_mut(self, i), + } + } + + fn visit_macro_mut(&mut self, mac: &mut syn::Macro) { + let mac_ident = mac.path.segments.last().map(|p| &p.ident); + if mac_ident.map_or(false, |i| i == "stream" || i == "try_stream") { + return; + } + + self.visit_token_stream(&mut mac.tokens); + } + + fn visit_item_mut(&mut self, i: &mut syn::Item) { + // Recurse into macros but otherwise don't transform inner items. + if let syn::Item::Macro(i) = i { + self.visit_macro_mut(&mut i.mac); + } + } +} + +/// The first token tree in the stream must be a group containing the path to the `async-stream` +/// crate. +#[proc_macro] +#[doc(hidden)] +pub fn stream_inner(input: TokenStream) -> TokenStream { + let (crate_path, mut stmts) = match parse_input(input) { + Ok(x) => x, + Err(e) => return e.to_compile_error().into(), + }; + + let mut scrub = Scrub::new(false, &crate_path); + + for stmt in &mut stmts { + scrub.visit_stmt_mut(stmt); + } + + let dummy_yield = if scrub.has_yielded { + None + } else { + Some(quote!(if false { + __yield_tx.send(()).await; + })) + }; + + quote!({ + let (mut __yield_tx, __yield_rx) = unsafe { #crate_path::__private::yielder::pair() }; + #crate_path::__private::AsyncStream::new(__yield_rx, async move { + #dummy_yield + #(#stmts)* + }) + }) + .into() +} + +/// The first token tree in the stream must be a group containing the path to the `async-stream` +/// crate. +#[proc_macro] +#[doc(hidden)] +pub fn try_stream_inner(input: TokenStream) -> TokenStream { + let (crate_path, mut stmts) = match parse_input(input) { + Ok(x) => x, + Err(e) => return e.to_compile_error().into(), + }; + + let mut scrub = Scrub::new(true, &crate_path); + + for stmt in &mut stmts { + scrub.visit_stmt_mut(stmt); + } + + let dummy_yield = if scrub.has_yielded { + None + } else { + Some(quote!(if false { + __yield_tx.send(()).await; + })) + }; + + quote!({ + let (mut __yield_tx, __yield_rx) = unsafe { #crate_path::__private::yielder::pair() }; + #crate_path::__private::AsyncStream::new(__yield_rx, async move { + #dummy_yield + #(#stmts)* + }) + }) + .into() +} + +/// Replace `for await` with `#[await] for`, which will be later transformed into a `next` loop. +fn replace_for_await(input: impl IntoIterator<Item = TokenTree>) -> TokenStream2 { + let mut input = input.into_iter().peekable(); + let mut tokens = Vec::new(); + + while let Some(token) = input.next() { + match token { + TokenTree::Ident(ident) => { + match input.peek() { + Some(TokenTree::Ident(next)) if ident == "for" && next == "await" => { + tokens.extend(quote!(#[#next])); + let _ = input.next(); + } + _ => {} + } + tokens.push(ident.into()); + } + TokenTree::Group(group) => { + let stream = replace_for_await(group.stream()); + let mut new_group = Group::new(group.delimiter(), stream); + new_group.set_span(group.span()); + tokens.push(new_group.into()); + } + _ => tokens.push(token), + } + } + + tokens.into_iter().collect() +} |