1 // SPDX-License-Identifier: Apache-2.0 OR MIT
2
3 use proc_macro2::TokenStream;
4 use quote::quote;
5 use syn::{
6 parse::{Parse, ParseStream},
7 Attribute, Result, Token, Visibility,
8 };
9
10 use super::PIN;
11 use crate::utils::SliceExt;
12
13 // To generate the correct `Unpin` implementation and the projection methods,
14 // we need to collect the types of the pinned fields.
15 // However, since proc-macro-attribute is applied before `cfg` and `cfg_attr`
16 // on fields, we cannot be collecting field types properly at this timing.
17 // So instead of generating the `Unpin` implementation and the projection
18 // methods here, delegate their processing to proc-macro-derive.
19 //
20 // At this stage, only attributes are parsed and the following attributes are
21 // added to the attributes of the item.
22 // - `#[derive(InternalDerive)]` - An internal helper macro that does the above
23 // processing.
24 // - `#[pin(__private(#args))]` - Pass the argument of `#[pin_project]` to
25 // proc-macro-derive (`InternalDerive`).
26
parse_attribute(args: &TokenStream, input: TokenStream) -> Result<TokenStream>27 pub(super) fn parse_attribute(args: &TokenStream, input: TokenStream) -> Result<TokenStream> {
28 let Input { attrs, body } = syn::parse2(input)?;
29
30 Ok(quote! {
31 #(#attrs)*
32 #[derive(::pin_project::__private::__PinProjectInternalDerive)]
33 // Use `__private` to prevent users from trying to control `InternalDerive`
34 // manually. `__private` does not guarantee compatibility between patch
35 // versions, so it should be sufficient for this purpose in most cases.
36 #[pin(__private(#args))]
37 #body
38 })
39 }
40
41 struct Input {
42 attrs: Vec<Attribute>,
43 body: TokenStream,
44 }
45
46 impl Parse for Input {
parse(input: ParseStream<'_>) -> Result<Self>47 fn parse(input: ParseStream<'_>) -> Result<Self> {
48 let attrs = input.call(Attribute::parse_outer)?;
49
50 let ahead = input.fork();
51 let _vis: Visibility = ahead.parse()?;
52 if !ahead.peek(Token![struct]) && !ahead.peek(Token![enum]) {
53 // If we check this only on proc-macro-derive, it may generate unhelpful error
54 // messages. So it is preferable to be able to detect it here.
55 bail!(
56 input.parse::<TokenStream>()?,
57 "#[pin_project] attribute may only be used on structs or enums"
58 );
59 } else if let Some(attr) = attrs.find(PIN) {
60 bail!(attr, "#[pin] attribute may only be used on fields of structs or variants");
61 } else if let Some(attr) = attrs.find("pin_project") {
62 bail!(attr, "duplicate #[pin_project] attribute");
63 }
64 Ok(Self { attrs, body: input.parse()? })
65 }
66 }
67