1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
#![recursion_limit = "128"]
extern crate proc_macro;

use quote::quote;
use syn::spanned::Spanned;
use syn::visit_mut::visit_type_mut;
use syn::{
    parse_macro_input, parse_quote, FnArg, Ident, ItemTrait, Lifetime, ReturnType, TraitItem,
    TraitItemMethod, Type,
};

type Error = syn::parse::Error;

#[proc_macro_attribute]
pub fn shadow(
    _args: proc_macro::TokenStream,
    item_tokens: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
    let item_tokens_clone = item_tokens.clone();
    let item_tokens = proc_macro2::TokenStream::from(item_tokens);
    let shadow = parse_macro_input!(item_tokens_clone as ItemTrait);

    let shadow_tokens = match generate_shadow(shadow) {
        Err(err) => err.to_compile_error().into(),
        Ok(tokens) => tokens,
    };

    let output = quote! {
      #item_tokens

      #shadow_tokens
    };
    output.into()
}

fn generate_shadow(mut shadow_trait: ItemTrait) -> Result<proc_macro2::TokenStream, Error> {
    let target_ident = shadow_trait.ident.clone();
    let shadow_ident = Ident::new(&format!("{}Shadow", target_ident), target_ident.span());
    let details_ident = Ident::new(&format!("{}ShadowInfo", target_ident), target_ident.span());
    let bind_box_ident = Ident::new(&format!("bind_{}_box", target_ident), target_ident.span());
    let visibility = shadow_trait.vis.clone();

    shadow_trait.ident = shadow_ident.clone();

    // Mark as unsafe! our "shadows" are sketchy and only work for limited cases.
    shadow_trait.unsafety = Some(syn::token::Unsafe {
        span: shadow_trait.ident.span(),
    });

    if !shadow_trait.supertraits.is_empty() {
        return Err(Error::new(
            shadow_trait.supertraits.span(),
            "supertraits are not supported yet!",
        ));
    }

    let mut funcs = Vec::new();
    for item in &mut shadow_trait.items {
        if let TraitItem::Method(ref mut method) = item {
            let (lifetime, mutability) = self_lifetime(method)?.clone();
            // Replace the first argument
            let first_mut = method.sig.decl.inputs.iter_mut().next().unwrap();

            *first_mut = parse_quote! { data: &#lifetime #mutability Self::Data };

            // Collect function arguments we care about
            let mut arg_types = Vec::new();
            for arg in &method.sig.decl.inputs {
                if let FnArg::Captured(arg) = arg {
                    let mut ty = arg.ty.clone();
                    visit_type_mut(&mut EraseLifetimes {}, &mut ty);
                    arg_types.push(ty);
                } else {
                    return Err(Error::new(arg.span(), "argument not supported"));
                }
            }

            // Generate layout info for the function
            let mut ret_type: Type = match method.sig.decl.output {
                ReturnType::Default => parse_quote! { () },
                ReturnType::Type(_, ref ty) => ty.as_ref().clone(),
            };
            visit_type_mut(&mut EraseLifetimes {}, &mut ret_type);

            let func_ident = &method.sig.ident;
            funcs.push(quote! {
              traitor::details::ShadowLayout {
                ret_slots: ret_slots::<#ret_type>(),
                arg_slots: #(slots::<#arg_types>())+*,
                func_ptr: <S as #shadow_ident>::#func_ident as *const u8,
              }
            });

            // Append &Self as a last argument -- this is our extended metadata. Use the same lifetime as
            // the original `&self` parameter, so we can borrow from the metadata (we guarantee that
            // metadata lives longer than any borrow of the data itself).
            method
                .sig
                .decl
                .inputs
                .push(parse_quote! { meta: &#lifetime Self });
        }
    }

    // Append `Data` associated type
    // FIXME: bounds for supertraits: type Data: Sized + std::fmt::Debug + ...;
    shadow_trait.items.push(parse_quote! {
        type Data: Sized;
    });

    let details_struct = quote! {
        #visibility struct #details_ident<'meta, S>
            where
                S: #shadow_ident + 'meta,
        {
            inner: S,
            _phantom: std::marker::PhantomData<&'meta S>,
        }
    };

    let details_impl = quote! {
        impl<'meta, S> #details_ident<'meta, S>
        where
            S: #shadow_ident + 'meta,
        {
            pub fn new(meta: S) -> Self {
                Self {
                    inner: meta,
                    _phantom: Default::default(),
                }
            }
        }
    };

    // FIXME: we should handle floats / doubles!
    let details_binding = quote! {
        impl<'meta, S> traitor::details::InternalBindingInfo for #details_ident<'meta, S>
          where
            S: #shadow_ident + 'meta,
        {
            type Data = <S as #shadow_ident>::Data;
            type Shadow = S;
            type Target = #target_ident;

            fn layout() -> traitor::details::LayoutInfo {
                const US: usize = std::mem::size_of::<usize>();
                fn slots<T>() -> usize {
                    match (std::mem::size_of::<T>() + US - 1) / US {
                        v if v <= 2 => v,
                        // uses pointer instead which is one slot
                        _ => 1,
                    }
                }
                fn ret_slots<T>() -> usize {
                    match (std::mem::size_of::<T>() + US - 1) / US {
                        // uses pointer to return value, pointer is passed by caller
                        v if v > 2 => 1,
                        // uses registers, no slots are taken
                        _ => 0,
                    }
                }
                traitor::details::LayoutInfo {
                    shadow: vec![
                        #(#funcs),*
                    ],
                  other: vec![
                //            <traitor::details::VTableInfo as traitor::details::VTableInfoTrait<
                //              Self::Data,
                //              std::fmt::Debug,
                //            >>::VTABLE_FUNCS,
                  ],
                }
            }

            fn into_shadow(self) -> S {
                self.inner
            }
        }

    };

    let bind_box = quote! {
        pub fn #bind_box_ident<'b, D>(
            data: Box<D>,
            binder: &'b traitor::Binder<D, #target_ident>
        ) -> Box<#target_ident + 'b> {
            unsafe {
                let raw = Box::into_raw(data);
                let bound = binder.bind_mut(std::mem::transmute::<*mut D, &mut D>(raw));
                Box::from_raw(bound)
            }
        }
    };

    let result = quote! {
        #shadow_trait

        #details_struct
        #details_impl
        #details_binding
        #bind_box
    };
    Ok(result)
}

fn self_lifetime(method: &TraitItemMethod) -> Result<(Lifetime, Option<syn::token::Mut>), Error> {
    match method.sig.decl.inputs.first().as_ref().map(|v| v.value()) {
        Some(FnArg::SelfRef(self_ref)) => {
            let lifetime = self_ref.lifetime.as_ref().ok_or_else(|| {
                Error::new(
                    self_ref.self_token.span,
                    "&self argument must have an explicit lifetime!",
                )
            })?;

            Ok((lifetime.clone(), self_ref.mutability.clone()))
        }
        _ => {
            return Err(Error::new(
                method.sig.ident.span(),
                "function must be object-safe and have `&self` as a first argument!",
            ));
        }
    }
}

struct EraseLifetimes {}

impl syn::visit_mut::VisitMut for EraseLifetimes {
    fn visit_type_reference_mut(&mut self, tr: &mut syn::TypeReference) {
        tr.lifetime = None;
        syn::visit_mut::visit_type_reference_mut(self, tr)
    }

    fn visit_angle_bracketed_generic_arguments_mut(
        &mut self,
        list: &mut syn::AngleBracketedGenericArguments,
    ) {
        let old = std::mem::replace(&mut list.args, Default::default());
        for item in old {
            if let syn::GenericArgument::Lifetime(_) = item {
                // drop all lifetimes
            } else {
                list.args.push(item);
            }
        }
        syn::visit_mut::visit_angle_bracketed_generic_arguments_mut(self, list)
    }
}