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use darling::export::NestedMeta;
use darling::FromMeta;
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote};
use syn::visit::Visit;
use syn::{Expr, ExprLit, Lit, LitInt, ReturnType, Type};
use crate::util::*;
#[derive(Debug, FromMeta, Default)]
struct Args {
#[darling(default)]
pool_size: Option<syn::Expr>,
}
pub fn run(args: TokenStream, item: TokenStream) -> TokenStream {
let mut errors = TokenStream::new();
// If any of the steps for this macro fail, we still want to expand to an item that is as close
// to the expected output as possible. This helps out IDEs such that completions and other
// related features keep working.
let f: ItemFn = match syn::parse2(item.clone()) {
Ok(x) => x,
Err(e) => return token_stream_with_error(item, e),
};
let args = match NestedMeta::parse_meta_list(args) {
Ok(x) => x,
Err(e) => return token_stream_with_error(item, e),
};
let args = match Args::from_list(&args) {
Ok(x) => x,
Err(e) => {
errors.extend(e.write_errors());
Args::default()
}
};
let pool_size = args.pool_size.unwrap_or(Expr::Lit(ExprLit {
attrs: vec![],
lit: Lit::Int(LitInt::new("1", Span::call_site())),
}));
if f.sig.asyncness.is_none() {
error(&mut errors, &f.sig, "task functions must be async");
}
if !f.sig.generics.params.is_empty() {
error(&mut errors, &f.sig, "task functions must not be generic");
}
if !f.sig.generics.where_clause.is_none() {
error(&mut errors, &f.sig, "task functions must not have `where` clauses");
}
if !f.sig.abi.is_none() {
error(&mut errors, &f.sig, "task functions must not have an ABI qualifier");
}
if !f.sig.variadic.is_none() {
error(&mut errors, &f.sig, "task functions must not be variadic");
}
match &f.sig.output {
ReturnType::Default => {}
ReturnType::Type(_, ty) => match &**ty {
Type::Tuple(tuple) if tuple.elems.is_empty() => {}
Type::Never(_) => {}
_ => error(
&mut errors,
&f.sig,
"task functions must either not return a value, return `()` or return `!`",
),
},
}
let mut args = Vec::new();
let mut fargs = f.sig.inputs.clone();
for arg in fargs.iter_mut() {
match arg {
syn::FnArg::Receiver(_) => {
error(&mut errors, arg, "task functions must not have receiver arguments");
}
syn::FnArg::Typed(t) => {
check_arg_ty(&mut errors, &t.ty);
match t.pat.as_mut() {
syn::Pat::Ident(id) => {
id.mutability = None;
args.push((id.clone(), t.attrs.clone()));
}
_ => {
error(
&mut errors,
arg,
"pattern matching in task arguments is not yet supported",
);
}
}
}
}
}
let task_ident = f.sig.ident.clone();
let task_inner_ident = format_ident!("__{}_task", task_ident);
let mut task_inner = f.clone();
let visibility = task_inner.vis.clone();
task_inner.vis = syn::Visibility::Inherited;
task_inner.sig.ident = task_inner_ident.clone();
// assemble the original input arguments,
// including any attributes that may have
// been applied previously
let mut full_args = Vec::new();
for (arg, cfgs) in args {
full_args.push(quote!(
#(#cfgs)*
#arg
));
}
#[cfg(feature = "nightly")]
let mut task_outer_body = quote! {
trait _EmbassyInternalTaskTrait {
type Fut: ::core::future::Future + 'static;
fn construct(#fargs) -> Self::Fut;
}
impl _EmbassyInternalTaskTrait for () {
type Fut = impl core::future::Future + 'static;
fn construct(#fargs) -> Self::Fut {
#task_inner_ident(#(#full_args,)*)
}
}
const POOL_SIZE: usize = #pool_size;
static POOL: ::embassy_executor::raw::TaskPool<<() as _EmbassyInternalTaskTrait>::Fut, POOL_SIZE> = ::embassy_executor::raw::TaskPool::new();
unsafe { POOL._spawn_async_fn(move || <() as _EmbassyInternalTaskTrait>::construct(#(#full_args,)*)) }
};
#[cfg(not(feature = "nightly"))]
let mut task_outer_body = quote! {
const POOL_SIZE: usize = #pool_size;
static POOL: ::embassy_executor::_export::TaskPoolRef = ::embassy_executor::_export::TaskPoolRef::new();
unsafe { POOL.get::<_, POOL_SIZE>()._spawn_async_fn(move || #task_inner_ident(#(#full_args,)*)) }
};
let task_outer_attrs = task_inner.attrs.clone();
if !errors.is_empty() {
task_outer_body = quote! {
#![allow(unused_variables, unreachable_code)]
let _x: ::embassy_executor::SpawnToken<()> = ::core::todo!();
_x
};
}
// Copy the generics + where clause to avoid more spurious errors.
let generics = &f.sig.generics;
let where_clause = &f.sig.generics.where_clause;
let result = quote! {
// This is the user's task function, renamed.
// We put it outside the #task_ident fn below, because otherwise
// the items defined there (such as POOL) would be in scope
// in the user's code.
#[doc(hidden)]
#task_inner
#(#task_outer_attrs)*
#visibility fn #task_ident #generics (#fargs) -> ::embassy_executor::SpawnToken<impl Sized> #where_clause{
#task_outer_body
}
#errors
};
result
}
fn check_arg_ty(errors: &mut TokenStream, ty: &Type) {
struct Visitor<'a> {
errors: &'a mut TokenStream,
}
impl<'a, 'ast> Visit<'ast> for Visitor<'a> {
fn visit_type_impl_trait(&mut self, i: &'ast syn::TypeImplTrait) {
error(self.errors, i, "`impl Trait` is not allowed in task arguments. It is syntax sugar for generics, and tasks can't be generic.");
}
}
Visit::visit_type(&mut Visitor { errors }, ty);
}
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