src/librustc_builtin_macros/deriving/decodable.rs

   1 //! The compiler code necessary for `#[derive(RustcDecodable)]`. See encodable.rs for more.
   2
   3 use crate::deriving::generic::ty::*;
   4 use crate::deriving::generic::*;
   5 use crate::deriving::pathvec_std;
   6
   7 use rustc_ast::ast;
   8 use rustc_ast::ast::{Expr, MetaItem, Mutability};
   9 use rustc_ast::ptr::P;
  10 use rustc_expand::base::{Annotatable, ExtCtxt};
  11 use rustc_span::symbol::{sym, Ident, Symbol};
  12 use rustc_span::Span;
  13
  14 pub fn expand_deriving_rustc_decodable(
  15     cx: &mut ExtCtxt<'_>,
  16     span: Span,
  17     mitem: &MetaItem,
  18     item: &Annotatable,
  19     push: &mut dyn FnMut(Annotatable),
  20 ) {
  21     let krate = sym::rustc_serialize;
  22     let typaram = sym::__D;
  23
  24     let trait_def = TraitDef {
  25         span,
  26         attributes: Vec::new(),
  27         path: Path::new_(vec![krate, sym::Decodable], None, vec![], PathKind::Global),
  28         additional_bounds: Vec::new(),
  29         generics: Bounds::empty(),
  30         is_unsafe: false,
  31         supports_unions: false,
  32         methods: vec![MethodDef {
  33             name: sym::decode,
  34             generics: Bounds {
  35                 bounds: vec![(
  36                     typaram,
  37                     vec![Path::new_(vec![krate, sym::Decoder], None, vec![], PathKind::Global)],
  38                 )],
  39             },
  40             explicit_self: None,
  41             args: vec![(
  42                 Ptr(Box::new(Literal(Path::new_local(typaram))), Borrowed(None, Mutability::Mut)),
  43                 sym::d,
  44             )],
  45             ret_ty: Literal(Path::new_(
  46                 pathvec_std!(result::Result),
  47                 None,
  48                 vec![
  49                     Box::new(Self_),
  50                     Box::new(Literal(Path::new_(
  51                         vec![typaram, sym::Error],
  52                         None,
  53                         vec![],
  54                         PathKind::Local,
  55                     ))),
  56                 ],
  57                 PathKind::Std,
  58             )),
  59             attributes: Vec::new(),
  60             is_unsafe: false,
  61             unify_fieldless_variants: false,
  62             combine_substructure: combine_substructure(Box::new(|a, b, c| {
  63                 decodable_substructure(a, b, c, krate)
  64             })),
  65         }],
  66         associated_types: Vec::new(),
  67     };
  68
  69     trait_def.expand(cx, mitem, item, push)
  70 }
  71
  72 fn decodable_substructure(
  73     cx: &mut ExtCtxt<'_>,
  74     trait_span: Span,
  75     substr: &Substructure<'_>,
  76     krate: Symbol,
  77 ) -> P<Expr> {
  78     let decoder = substr.nonself_args[0].clone();
  79     let recurse = vec![
  80         Ident::new(krate, trait_span),
  81         Ident::new(sym::Decodable, trait_span),
  82         Ident::new(sym::decode, trait_span),
  83     ];
  84     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  85     // throw an underscore in front to suppress unused variable warnings
  86     let blkarg = Ident::new(sym::_d, trait_span);
  87     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  88
  89     match *substr.fields {
  90         StaticStruct(_, ref summary) => {
  91             let nfields = match *summary {
  92                 Unnamed(ref fields, _) => fields.len(),
  93                 Named(ref fields) => fields.len(),
  94             };
  95             let read_struct_field = Ident::new(sym::read_struct_field, trait_span);
  96
  97             let path = cx.path_ident(trait_span, substr.type_ident);
  98             let result =
  99                 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
 100                     cx.expr_try(
 101                         span,
 102                         cx.expr_method_call(
 103                             span,
 104                             blkdecoder.clone(),
 105                             read_struct_field,
 106                             vec![
 107                                 cx.expr_str(span, name),
 108                                 cx.expr_usize(span, field),
 109                                 exprdecode.clone(),
 110                             ],
 111                         ),
 112                     )
 113                 });
 114             let result = cx.expr_ok(trait_span, result);
 115             cx.expr_method_call(
 116                 trait_span,
 117                 decoder,
 118                 Ident::new(sym::read_struct, trait_span),
 119                 vec![
 120                     cx.expr_str(trait_span, substr.type_ident.name),
 121                     cx.expr_usize(trait_span, nfields),
 122                     cx.lambda1(trait_span, result, blkarg),
 123                 ],
 124             )
 125         }
 126         StaticEnum(_, ref fields) => {
 127             let variant = Ident::new(sym::i, trait_span);
 128
 129             let mut arms = Vec::with_capacity(fields.len() + 1);
 130             let mut variants = Vec::with_capacity(fields.len());
 131             let rvariant_arg = Ident::new(sym::read_enum_variant_arg, trait_span);
 132
 133             for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
 134                 variants.push(cx.expr_str(v_span, ident.name));
 135
 136                 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
 137                 let decoded =
 138                     decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
 139                         let idx = cx.expr_usize(span, field);
 140                         cx.expr_try(
 141                             span,
 142                             cx.expr_method_call(
 143                                 span,
 144                                 blkdecoder.clone(),
 145                                 rvariant_arg,
 146                                 vec![idx, exprdecode.clone()],
 147                             ),
 148                         )
 149                     });
 150
 151                 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
 152             }
 153
 154             arms.push(cx.arm_unreachable(trait_span));
 155
 156             let result = cx.expr_ok(
 157                 trait_span,
 158                 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
 159             );
 160             let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
 161             let variant_vec = cx.expr_vec(trait_span, variants);
 162             let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
 163             let result = cx.expr_method_call(
 164                 trait_span,
 165                 blkdecoder,
 166                 Ident::new(sym::read_enum_variant, trait_span),
 167                 vec![variant_vec, lambda],
 168             );
 169             cx.expr_method_call(
 170                 trait_span,
 171                 decoder,
 172                 Ident::new(sym::read_enum, trait_span),
 173                 vec![
 174                     cx.expr_str(trait_span, substr.type_ident.name),
 175                     cx.lambda1(trait_span, result, blkarg),
 176                 ],
 177             )
 178         }
 179         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
 180     }
 181 }
 182
 183 /// Creates a decoder for a single enum variant/struct:
 184 /// - `outer_pat_path` is the path to this enum variant/struct
 185 /// - `getarg` should retrieve the `usize`-th field with name `@str`.
 186 fn decode_static_fields<F>(
 187     cx: &mut ExtCtxt<'_>,
 188     trait_span: Span,
 189     outer_pat_path: ast::Path,
 190     fields: &StaticFields,
 191     mut getarg: F,
 192 ) -> P<Expr>
 193 where
 194     F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
 195 {
 196     match *fields {
 197         Unnamed(ref fields, is_tuple) => {
 198             let path_expr = cx.expr_path(outer_pat_path);
 199             if !is_tuple {
 200                 path_expr
 201             } else {
 202                 let fields = fields
 203                     .iter()
 204                     .enumerate()
 205                     .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
 206                     .collect();
 207
 208                 cx.expr_call(trait_span, path_expr, fields)
 209             }
 210         }
 211         Named(ref fields) => {
 212             // use the field's span to get nicer error messages.
 213             let fields = fields
 214                 .iter()
 215                 .enumerate()
 216                 .map(|(i, &(ident, span))| {
 217                     let arg = getarg(cx, span, ident.name, i);
 218                     cx.field_imm(span, ident, arg)
 219                 })
 220                 .collect();
 221             cx.expr_struct(trait_span, outer_pat_path, fields)
 222         }
 223     }
 224 }