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use proc_macro2::TokenStream;
use quote::{format_ident, quote, ToTokens};
use syn::{
parse_quote, spanned::Spanned, token::Colon, visit_mut::VisitMut, Error, FnArg,
GenericArgument, Ident, ImplItem, ItemImpl, Pat, PatIdent, PatType, Path, PathArguments,
Result, ReturnType, Signature, Token, Type, TypePath, TypeReference,
};
use crate::utils::{ReplaceReceiver, SliceExt};
pub(crate) fn attribute(args: &TokenStream, mut input: ItemImpl) -> TokenStream {
let res = (|| -> Result<()> {
if !args.is_empty() {
bail!(args, "unexpected argument: `{}`", args)
}
validate_impl(&input)?;
expand_impl(&mut input);
Ok(())
})();
if let Err(e) = res {
let mut tokens = e.to_compile_error();
if let Type::Path(self_ty) = &*input.self_ty {
let (impl_generics, _, where_clause) = input.generics.split_for_impl();
// Generate a dummy impl of `PinnedDrop`.
// In many cases, `#[pinned_drop] impl` is declared after `#[pin_project]`.
// Therefore, if `pinned_drop` compile fails, you will also get an error
// about `PinnedDrop` not being implemented.
// This can be prevented to some extent by generating a dummy
// `PinnedDrop` implementation.
// We already know that we will get a compile error, so this won't
// accidentally compile successfully.
//
// However, if `input.self_ty` is not Type::Path, there is a high possibility that
// the type does not exist (since #[pin_project] can only be used on struct/enum
// definitions), so do not generate a dummy impl.
tokens.extend(quote! {
impl #impl_generics ::pin_project::__private::PinnedDrop for #self_ty
#where_clause
{
unsafe fn drop(self: ::pin_project::__private::Pin<&mut Self>) {}
}
});
}
tokens
} else {
input.into_token_stream()
}
}
/// Validates the signature of given `PinnedDrop` impl.
fn validate_impl(item: &ItemImpl) -> Result<()> {
const INVALID_ITEM: &str =
"#[pinned_drop] may only be used on implementation for the `PinnedDrop` trait";
if let Some(attr) = item.attrs.find("pinned_drop") {
bail!(attr, "duplicate #[pinned_drop] attribute");
}
if let Some((_, path, _)) = &item.trait_ {
if !path.is_ident("PinnedDrop") {
bail!(path, INVALID_ITEM);
}
} else {
bail!(item.self_ty, INVALID_ITEM);
}
if item.unsafety.is_some() {
bail!(item.unsafety, "implementing the trait `PinnedDrop` is not unsafe");
}
if item.items.is_empty() {
bail!(item, "not all trait items implemented, missing: `drop`");
}
match &*item.self_ty {
Type::Path(_) => {}
ty => {
bail!(ty, "implementing the trait `PinnedDrop` on this type is unsupported");
}
}
item.items.iter().enumerate().try_for_each(|(i, item)| match item {
ImplItem::Const(item) => {
bail!(item, "const `{}` is not a member of trait `PinnedDrop`", item.ident)
}
ImplItem::Type(item) => {
bail!(item, "type `{}` is not a member of trait `PinnedDrop`", item.ident)
}
ImplItem::Fn(method) => {
validate_sig(&method.sig)?;
if i == 0 {
Ok(())
} else {
bail!(method, "duplicate definitions with name `drop`")
}
}
_ => unreachable!("unexpected ImplItem"),
})
}
/// Validates the signature of given `PinnedDrop::drop` method.
///
/// The correct signature is: `(mut) self: (<path>::)Pin<&mut Self>`
fn validate_sig(sig: &Signature) -> Result<()> {
fn get_ty_path(ty: &Type) -> Option<&Path> {
if let Type::Path(TypePath { qself: None, path }) = ty {
Some(path)
} else {
None
}
}
const INVALID_ARGUMENT: &str = "method `drop` must take an argument `self: Pin<&mut Self>`";
if sig.ident != "drop" {
bail!(sig.ident, "method `{}` is not a member of trait `PinnedDrop", sig.ident,);
}
if let ReturnType::Type(_, ty) = &sig.output {
match &**ty {
Type::Tuple(ty) if ty.elems.is_empty() => {}
_ => bail!(ty, "method `drop` must return the unit type"),
}
}
match sig.inputs.len() {
1 => {}
0 => return Err(Error::new(sig.paren_token.span.join(), INVALID_ARGUMENT)),
_ => bail!(sig.inputs, INVALID_ARGUMENT),
}
if let Some(arg) = sig.receiver() {
// (mut) self: <path>
if let Some(path) = get_ty_path(&arg.ty) {
let ty =
path.segments.last().expect("Type paths should always have at least one segment");
if let PathArguments::AngleBracketed(args) = &ty.arguments {
// (mut) self: (<path>::)<ty><&mut <elem>..>
if let Some(GenericArgument::Type(Type::Reference(TypeReference {
mutability: Some(_),
elem,
..
}))) = args.args.first()
{
// (mut) self: (<path>::)Pin<&mut Self>
if args.args.len() == 1
&& ty.ident == "Pin"
&& get_ty_path(elem).map_or(false, |path| path.is_ident("Self"))
{
if sig.unsafety.is_some() {
bail!(sig.unsafety, "implementing the method `drop` is not unsafe");
}
return Ok(());
}
}
}
}
}
bail!(sig.inputs[0], INVALID_ARGUMENT)
}
// from:
//
// fn drop(self: Pin<&mut Self>) {
// // ...
// }
//
// into:
//
// unsafe fn drop(self: Pin<&mut Self>) {
// fn __drop_inner<T>(__self: Pin<&mut Foo<'_, T>>) {
// fn __drop_inner() {}
// // ...
// }
// __drop_inner(self);
// }
//
fn expand_impl(item: &mut ItemImpl) {
// `PinnedDrop` is a private trait and should not appear in docs.
item.attrs.push(parse_quote!(#[doc(hidden)]));
let path = &mut item.trait_.as_mut().expect("unexpected inherent impl").1;
*path = parse_quote_spanned! { path.span() =>
::pin_project::__private::PinnedDrop
};
let method =
if let ImplItem::Fn(method) = &mut item.items[0] { method } else { unreachable!() };
// `fn drop(mut self: Pin<&mut Self>)` -> `fn __drop_inner<T>(mut __self: Pin<&mut Receiver>)`
let drop_inner = {
let mut drop_inner = method.clone();
let ident = format_ident!("__drop_inner");
// Add a dummy `__drop_inner` function to prevent users call outer `__drop_inner`.
drop_inner.block.stmts.insert(0, parse_quote!(fn #ident() {}));
drop_inner.sig.ident = ident;
drop_inner.sig.generics = item.generics.clone();
let receiver = drop_inner.sig.receiver().expect("drop() should have a receiver").clone();
let pat = Box::new(Pat::Ident(PatIdent {
attrs: Vec::new(),
by_ref: None,
mutability: receiver.mutability,
ident: Ident::new("__self", receiver.self_token.span()),
subpat: None,
}));
drop_inner.sig.inputs[0] = FnArg::Typed(PatType {
attrs: receiver.attrs,
pat,
colon_token: Colon::default(),
ty: receiver.ty,
});
let self_ty = if let Type::Path(ty) = &*item.self_ty { ty } else { unreachable!() };
let mut visitor = ReplaceReceiver(self_ty);
visitor.visit_signature_mut(&mut drop_inner.sig);
visitor.visit_block_mut(&mut drop_inner.block);
drop_inner
};
// `fn drop(mut self: Pin<&mut Self>)` -> `unsafe fn drop(self: Pin<&mut Self>)`
method.sig.unsafety = Some(<Token![unsafe]>::default());
let self_token = if let FnArg::Receiver(ref mut rec) = method.sig.inputs[0] {
rec.mutability = None;
&rec.self_token
} else {
panic!("drop() should have a receiver")
};
method.block.stmts = parse_quote! {
#[allow(clippy::needless_pass_by_value)] // This lint does not warn the receiver.
#drop_inner
__drop_inner(#self_token);
};
}