1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3use proc_macro2::{Span, TokenStream};
4use quote::{ToTokens as _, format_ident, quote};
5use syn::{
6 Error, FnArg, GenericArgument, Ident, ImplItem, ItemImpl, Pat, PatIdent, PatType, Path,
7 PathArguments, Result, ReturnType, Signature, Token, Type, TypePath, TypeReference,
8 parse_quote, spanned::Spanned as _, token::Colon, visit_mut::VisitMut as _,
9};
10
11use crate::utils::{ReplaceReceiver, SliceExt as _};
12
13pub(crate) fn attribute(args: &TokenStream, mut input: ItemImpl) -> TokenStream {
14 let res = (|| -> Result<()> {
15 if !args.is_empty() {
16 bail!(args, "unexpected argument: `{}`", args)
17 }
18 validate_impl(&input)?;
19 expand_impl(&mut input);
20 Ok(())
21 })();
22
23 if let Err(e) = res {
24 let mut tokens = e.to_compile_error();
25 if let Type::Path(self_ty) = &*input.self_ty {
26 let (impl_generics, _, where_clause) = input.generics.split_for_impl();
27
28 // Generate a dummy impl of `PinnedDrop`.
29 // In many cases, `#[pinned_drop] impl` is declared after `#[pin_project]`.
30 // Therefore, if `pinned_drop` compile fails, you will also get an error
31 // about `PinnedDrop` not being implemented.
32 // This can be prevented to some extent by generating a dummy
33 // `PinnedDrop` implementation.
34 // We already know that we will get a compile error, so this won't
35 // accidentally compile successfully.
36 //
37 // However, if `input.self_ty` is not Type::Path, there is a high possibility that
38 // the type does not exist (since #[pin_project] can only be used on struct/enum
39 // definitions), so do not generate a dummy impl.
40 tokens.extend(quote! {
41 impl #impl_generics ::pin_project::__private::PinnedDrop for #self_ty
42 #where_clause
43 {
44 unsafe fn drop(self: ::pin_project::__private::Pin<&mut Self>) {}
45 }
46 });
47 }
48 tokens
49 } else {
50 input.into_token_stream()
51 }
52}
53
54/// Validates the signature of given `PinnedDrop` impl.
55fn validate_impl(item: &ItemImpl) -> Result<()> {
56 const INVALID_ITEM: &str =
57 "#[pinned_drop] may only be used on implementation for the `PinnedDrop` trait";
58
59 if let Some(attr) = item.attrs.find("pinned_drop") {
60 bail!(attr, "duplicate #[pinned_drop] attribute");
61 }
62
63 if let Some((_, path, _)) = &item.trait_ {
64 if !path.is_ident("PinnedDrop") {
65 bail!(path, INVALID_ITEM);
66 }
67 } else {
68 bail!(item.self_ty, INVALID_ITEM);
69 }
70
71 if item.unsafety.is_some() {
72 bail!(item.unsafety, "implementing the trait `PinnedDrop` is not unsafe");
73 }
74 if item.items.is_empty() {
75 bail!(item, "not all trait items implemented, missing: `drop`");
76 }
77
78 match &*item.self_ty {
79 Type::Path(_) => {}
80 ty => {
81 bail!(ty, "implementing the trait `PinnedDrop` on this type is unsupported");
82 }
83 }
84
85 item.items.iter().enumerate().try_for_each(|(i, item)| match item {
86 ImplItem::Const(item) => {
87 bail!(item, "const `{}` is not a member of trait `PinnedDrop`", item.ident)
88 }
89 ImplItem::Type(item) => {
90 bail!(item, "type `{}` is not a member of trait `PinnedDrop`", item.ident)
91 }
92 ImplItem::Fn(method) => {
93 validate_sig(&method.sig)?;
94 if i == 0 { Ok(()) } else { bail!(method, "duplicate definitions with name `drop`") }
95 }
96 _ => unreachable!("unexpected ImplItem"),
97 })
98}
99
100/// Validates the signature of given `PinnedDrop::drop` method.
101///
102/// The correct signature is: `(mut) self: (<path>::)Pin<&mut Self>`
103fn validate_sig(sig: &Signature) -> Result<()> {
104 fn get_ty_path(ty: &Type) -> Option<&Path> {
105 if let Type::Path(TypePath { qself: None, path }) = ty { Some(path) } else { None }
106 }
107
108 const INVALID_ARGUMENT: &str = "method `drop` must take an argument `self: Pin<&mut Self>`";
109
110 if sig.ident != "drop" {
111 bail!(sig.ident, "method `{}` is not a member of trait `PinnedDrop`", sig.ident);
112 }
113
114 if let ReturnType::Type(_, ty) = &sig.output {
115 match &**ty {
116 Type::Tuple(ty) if ty.elems.is_empty() => {}
117 _ => bail!(ty, "method `drop` must return the unit type"),
118 }
119 }
120
121 match sig.inputs.len() {
122 1 => {}
123 0 => return Err(Error::new(sig.paren_token.span.join(), INVALID_ARGUMENT)),
124 _ => bail!(sig.inputs, INVALID_ARGUMENT),
125 }
126
127 if let Some(arg) = sig.receiver() {
128 // (mut) self: <path>
129 if let Some(path) = get_ty_path(&arg.ty) {
130 let ty =
131 path.segments.last().expect("type paths should always have at least one segment");
132 if let PathArguments::AngleBracketed(args) = &ty.arguments {
133 // (mut) self: (<path>::)<ty><&mut <elem>..>
134 if let Some(GenericArgument::Type(Type::Reference(TypeReference {
135 mutability: Some(_),
136 elem,
137 ..
138 }))) = args.args.first()
139 {
140 // (mut) self: (<path>::)Pin<&mut Self>
141 if args.args.len() == 1
142 && ty.ident == "Pin"
143 && get_ty_path(elem).map_or(false, |path| path.is_ident("Self"))
144 {
145 if sig.unsafety.is_some() {
146 bail!(sig.unsafety, "implementing the method `drop` is not unsafe");
147 }
148 return Ok(());
149 }
150 }
151 }
152 }
153 }
154
155 bail!(sig.inputs[0], INVALID_ARGUMENT)
156}
157
158// from:
159//
160// fn drop(self: Pin<&mut Self>) {
161// // ...
162// }
163//
164// into:
165//
166// unsafe fn drop(self: Pin<&mut Self>) {
167// fn __drop_inner<T>(__self: Pin<&mut Foo<'_, T>>) {
168// fn __drop_inner() {}
169// // ...
170// }
171// __drop_inner(self);
172// }
173//
174fn expand_impl(item: &mut ItemImpl) {
175 // `PinnedDrop` is a private trait and should not appear in docs.
176 item.attrs.push(parse_quote!(#[doc(hidden)]));
177
178 let path = &mut item.trait_.as_mut().expect("unexpected inherent impl").1;
179 *path = parse_quote_spanned! { Span::call_site().located_at(path.span()) =>
180 ::pin_project::__private::PinnedDrop
181 };
182
183 let method =
184 if let ImplItem::Fn(method) = &mut item.items[0] { method } else { unreachable!() };
185
186 // `fn drop(mut self: Pin<&mut Self>)` -> `fn __drop_inner<T>(mut __self: Pin<&mut Receiver>)`
187 let drop_inner = {
188 let mut drop_inner = method.clone();
189 let ident = format_ident!("__drop_inner");
190 // Add a dummy `__drop_inner` function to prevent users call outer `__drop_inner`.
191 drop_inner.block.stmts.insert(0, parse_quote!(fn #ident() {}));
192 drop_inner.sig.ident = ident;
193 drop_inner.sig.generics = item.generics.clone();
194 let receiver = drop_inner.sig.receiver().expect("drop() should have a receiver").clone();
195 let pat = Box::new(Pat::Ident(PatIdent {
196 attrs: vec![],
197 by_ref: None,
198 mutability: receiver.mutability,
199 ident: Ident::new("__self", receiver.self_token.span()),
200 subpat: None,
201 }));
202 drop_inner.sig.inputs[0] = FnArg::Typed(PatType {
203 attrs: receiver.attrs,
204 pat,
205 colon_token: Colon::default(),
206 ty: receiver.ty,
207 });
208 let self_ty = if let Type::Path(ty) = &*item.self_ty { ty } else { unreachable!() };
209 let mut visitor = ReplaceReceiver(self_ty);
210 visitor.visit_signature_mut(&mut drop_inner.sig);
211 visitor.visit_block_mut(&mut drop_inner.block);
212 drop_inner
213 };
214
215 // `fn drop(mut self: Pin<&mut Self>)` -> `unsafe fn drop(self: Pin<&mut Self>)`
216 method.sig.unsafety = Some(<Token![unsafe]>::default());
217 let self_token = if let FnArg::Receiver(ref mut rec) = method.sig.inputs[0] {
218 rec.mutability = None;
219 &rec.self_token
220 } else {
221 panic!("drop() should have a receiver")
222 };
223
224 method.block.stmts = parse_quote! {
225 #[allow(
226 clippy::missing_const_for_fn,
227 clippy::needless_pass_by_value, // This lint does not warn the receiver.
228 clippy::single_call_fn
229 )]
230 #drop_inner
231 __drop_inner(#self_token);
232 };
233}
234