1// SPDX-License-Identifier: GPL-2.0
 2
 3use crate::helpers::{parse_generics, Generics};
 4use proc_macro::{TokenStream, TokenTree};
 5
 6pub(crate) fn derive(input: TokenStream) -> TokenStream {
 7    let (
 8        Generics {
 9            impl_generics,
10            ty_generics,
11        },
12        mut rest,
13    ) = parse_generics(input);
14    // This should be the body of the struct `{...}`.
15    let last = rest.pop();
16    // Now we insert `Zeroable` as a bound for every generic parameter in `impl_generics`.
17    let mut new_impl_generics = Vec::with_capacity(impl_generics.len());
18    // Are we inside of a generic where we want to add `Zeroable`?
19    let mut in_generic = !impl_generics.is_empty();
20    // Have we already inserted `Zeroable`?
21    let mut inserted = false;
22    // Level of `<>` nestings.
23    let mut nested = 0;
24    for tt in impl_generics {
25        match &tt {
26            // If we find a `,`, then we have finished a generic/constant/lifetime parameter.
27            TokenTree::Punct(p) if nested == 0 && p.as_char() == ',' => {
28                if in_generic && !inserted {
29                    new_impl_generics.extend(quote! { : ::kernel::init::Zeroable });
30                }
31                in_generic = true;
32                inserted = false;
33                new_impl_generics.push(tt);
34            }
35            // If we find `'`, then we are entering a lifetime.
36            TokenTree::Punct(p) if nested == 0 && p.as_char() == '\'' => {
37                in_generic = false;
38                new_impl_generics.push(tt);
39            }
40            TokenTree::Punct(p) if nested == 0 && p.as_char() == ':' => {
41                new_impl_generics.push(tt);
42                if in_generic {
43                    new_impl_generics.extend(quote! { ::kernel::init::Zeroable + });
44                    inserted = true;
45                }
46            }
47            TokenTree::Punct(p) if p.as_char() == '<' => {
48                nested += 1;
49                new_impl_generics.push(tt);
50            }
51            TokenTree::Punct(p) if p.as_char() == '>' => {
52                assert!(nested > 0);
53                nested -= 1;
54                new_impl_generics.push(tt);
55            }
56            _ => new_impl_generics.push(tt),
57        }
58    }
59    assert_eq!(nested, 0);
60    if in_generic && !inserted {
61        new_impl_generics.extend(quote! { : ::kernel::init::Zeroable });
62    }
63    quote! {
64        ::kernel::__derive_zeroable!(
65            parse_input:
66                @sig(#(#rest)*),
67                @impl_generics(#(#new_impl_generics)*),
68                @ty_generics(#(#ty_generics)*),
69                @body(#last),
70        );
71    }
72}