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            decl_generics: _,
11            ty_generics,
12        },
13        mut rest,
14    ) = parse_generics(input);
15    // This should be the body of the struct `{...}`.
16    let last = rest.pop();
17    // Now we insert `Zeroable` as a bound for every generic parameter in `impl_generics`.
18    let mut new_impl_generics = Vec::with_capacity(impl_generics.len());
19    // Are we inside of a generic where we want to add `Zeroable`?
20    let mut in_generic = !impl_generics.is_empty();
21    // Have we already inserted `Zeroable`?
22    let mut inserted = false;
23    // Level of `<>` nestings.
24    let mut nested = 0;
25    for tt in impl_generics {
26        match &tt {
27            // If we find a `,`, then we have finished a generic/constant/lifetime parameter.
28            TokenTree::Punct(p) if nested == 0 && p.as_char() == ',' => {
29                if in_generic && !inserted {
30                    new_impl_generics.extend(quote! { : ::kernel::init::Zeroable });
31                }
32                in_generic = true;
33                inserted = false;
34                new_impl_generics.push(tt);
35            }
36            // If we find `'`, then we are entering a lifetime.
37            TokenTree::Punct(p) if nested == 0 && p.as_char() == '\'' => {
38                in_generic = false;
39                new_impl_generics.push(tt);
40            }
41            TokenTree::Punct(p) if nested == 0 && p.as_char() == ':' => {
42                new_impl_generics.push(tt);
43                if in_generic {
44                    new_impl_generics.extend(quote! { ::kernel::init::Zeroable + });
45                    inserted = true;
46                }
47            }
48            TokenTree::Punct(p) if p.as_char() == '<' => {
49                nested += 1;
50                new_impl_generics.push(tt);
51            }
52            TokenTree::Punct(p) if p.as_char() == '>' => {
53                assert!(nested > 0);
54                nested -= 1;
55                new_impl_generics.push(tt);
56            }
57            _ => new_impl_generics.push(tt),
58        }
59    }
60    assert_eq!(nested, 0);
61    if in_generic && !inserted {
62        new_impl_generics.extend(quote! { : ::kernel::init::Zeroable });
63    }
64    quote! {
65        ::kernel::__derive_zeroable!(
66            parse_input:
67                @sig(#(#rest)*),
68                @impl_generics(#(#new_impl_generics)*),
69                @ty_generics(#(#ty_generics)*),
70                @body(#last),
71        );
72    }
73}