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