1 use proc_macro2::TokenStream;
2 use quote::quote;
3 use syn::{
4 parse::{Parse, ParseStream},
5 Attribute, Result, Token, Visibility,
6 };
7
8 use super::PIN;
9 use crate::utils::SliceExt;
10
11 // To generate the correct `Unpin` implementation and the projection methods,
12 // we need to collect the types of the pinned fields.
13 // However, since proc-macro-attribute is applied before `cfg` and `cfg_attr`
14 // on fields, we cannot be collecting field types properly at this timing.
15 // So instead of generating the `Unpin` implementation and the projection
16 // methods here, delegate their processing to proc-macro-derive.
17 //
18 // At this stage, only attributes are parsed and the following attributes are
19 // added to the attributes of the item.
20 // - `#[derive(InternalDerive)]` - An internal helper macro that does the above
21 // processing.
22 // - `#[pin(__private(#args))]` - Pass the argument of `#[pin_project]` to
23 // proc-macro-derive (`InternalDerive`).
24
parse_attribute(args: &TokenStream, input: TokenStream) -> Result<TokenStream>25 pub(super) fn parse_attribute(args: &TokenStream, input: TokenStream) -> Result<TokenStream> {
26 let Input { attrs, body } = syn::parse2(input)?;
27
28 Ok(quote! {
29 #(#attrs)*
30 #[derive(::pin_project::__private::__PinProjectInternalDerive)]
31 // Use `__private` to prevent users from trying to control `InternalDerive`
32 // manually. `__private` does not guarantee compatibility between patch
33 // versions, so it should be sufficient for this purpose in most cases.
34 #[pin(__private(#args))]
35 #body
36 })
37 }
38
39 #[allow(dead_code)] // false positive that fixed in Rust 1.39
40 struct Input {
41 attrs: Vec<Attribute>,
42 body: TokenStream,
43 }
44
45 impl Parse for Input {
parse(input: ParseStream<'_>) -> Result<Self>46 fn parse(input: ParseStream<'_>) -> Result<Self> {
47 let attrs = input.call(Attribute::parse_outer)?;
48
49 let ahead = input.fork();
50 let _: Visibility = ahead.parse()?;
51 if !ahead.peek(Token![struct]) && !ahead.peek(Token![enum]) {
52 // If we check this only on proc-macro-derive, it may generate unhelpful error
53 // messages. So it is preferable to be able to detect it here.
54 bail!(
55 input.parse::<TokenStream>()?,
56 "#[pin_project] attribute may only be used on structs or enums"
57 );
58 } else if let Some(attr) = attrs.find(PIN) {
59 bail!(attr, "#[pin] attribute may only be used on fields of structs or variants");
60 } else if let Some(attr) = attrs.find("pin_project") {
61 bail!(attr, "duplicate #[pin_project] attribute");
62 }
63 Ok(Self { attrs, body: input.parse()? })
64 }
65 }
66