compiler/rustc_builtin_macros/src/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     is_const: bool,
  20 ) {
  21     let krate = sym::rustc_serialize;
  22     let typaram = sym::__D;
  23
  24     let trait_def = TraitDef {
  25         span,
  26         path: Path::new_(vec![krate, sym::Decodable], vec![], PathKind::Global),
  27         skip_path_as_bound: false,
  28         needs_copy_as_bound_if_packed: true,
  29         additional_bounds: Vec::new(),
  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], vec![], PathKind::Global)],
  37                 )],
  38             },
  39             explicit_self: false,
  40             nonself_args: vec![(
  41                 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
  42                 sym::d,
  43             )],
  44             ret_ty: Path(Path::new_(
  45                 pathvec_std!(result::Result),
  46                 vec![
  47                     Box::new(Self_),
  48                     Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
  49                 ],
  50                 PathKind::Std,
  51             )),
  52             attributes: ast::AttrVec::new(),
  53             fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
  54             combine_substructure: combine_substructure(Box::new(|a, b, c| {
  55                 decodable_substructure(a, b, c, krate)
  56             })),
  57         }],
  58         associated_types: Vec::new(),
  59         is_const,
  60     };
  61
  62     trait_def.expand(cx, mitem, item, push)
  63 }
  64
  65 fn decodable_substructure(
  66     cx: &mut ExtCtxt<'_>,
  67     trait_span: Span,
  68     substr: &Substructure<'_>,
  69     krate: Symbol,
  70 ) -> BlockOrExpr {
  71     let decoder = substr.nonselflike_args[0].clone();
  72     let recurse = vec![
  73         Ident::new(krate, trait_span),
  74         Ident::new(sym::Decodable, trait_span),
  75         Ident::new(sym::decode, trait_span),
  76     ];
  77     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  78     // throw an underscore in front to suppress unused variable warnings
  79     let blkarg = Ident::new(sym::_d, trait_span);
  80     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  81
  82     let expr = match substr.fields {
  83         StaticStruct(_, summary) => {
  84             let nfields = match summary {
  85                 Unnamed(fields, _) => fields.len(),
  86                 Named(fields) => fields.len(),
  87             };
  88             let fn_read_struct_field_path: Vec<_> =
  89                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct_field]);
  90
  91             let path = cx.path_ident(trait_span, substr.type_ident);
  92             let result =
  93                 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
  94                     cx.expr_try(
  95                         span,
  96                         cx.expr_call_global(
  97                             span,
  98                             fn_read_struct_field_path.clone(),
  99                             vec![
 100                                 blkdecoder.clone(),
 101                                 cx.expr_str(span, name),
 102                                 cx.expr_usize(span, field),
 103                                 exprdecode.clone(),
 104                             ],
 105                         ),
 106                     )
 107                 });
 108             let result = cx.expr_ok(trait_span, result);
 109             let fn_read_struct_path: Vec<_> =
 110                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct]);
 111
 112             cx.expr_call_global(
 113                 trait_span,
 114                 fn_read_struct_path,
 115                 vec![
 116                     decoder,
 117                     cx.expr_str(trait_span, substr.type_ident.name),
 118                     cx.expr_usize(trait_span, nfields),
 119                     cx.lambda1(trait_span, result, blkarg),
 120                 ],
 121             )
 122         }
 123         StaticEnum(_, fields) => {
 124             let variant = Ident::new(sym::i, trait_span);
 125
 126             let mut arms = Vec::with_capacity(fields.len() + 1);
 127             let mut variants = Vec::with_capacity(fields.len());
 128
 129             let fn_read_enum_variant_arg_path: Vec<_> =
 130                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
 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_call_global(
 142                                 span,
 143                                 fn_read_enum_variant_arg_path.clone(),
 144                                 vec![blkdecoder.clone(), idx, exprdecode.clone()],
 145                             ),
 146                         )
 147                     });
 148
 149                 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
 150             }
 151
 152             arms.push(cx.arm_unreachable(trait_span));
 153
 154             let result = cx.expr_ok(
 155                 trait_span,
 156                 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
 157             );
 158             let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
 159             let variant_array_ref = cx.expr_array_ref(trait_span, variants);
 160             let fn_read_enum_variant_path: Vec<_> =
 161                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant]);
 162             let result = cx.expr_call_global(
 163                 trait_span,
 164                 fn_read_enum_variant_path,
 165                 vec![blkdecoder, variant_array_ref, lambda],
 166             );
 167             let fn_read_enum_path: Vec<_> =
 168                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
 169
 170             cx.expr_call_global(
 171                 trait_span,
 172                 fn_read_enum_path,
 173                 vec![
 174                     decoder,
 175                     cx.expr_str(trait_span, substr.type_ident.name),
 176                     cx.lambda1(trait_span, result, blkarg),
 177                 ],
 178             )
 179         }
 180         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
 181     };
 182     BlockOrExpr::new_expr(expr)
 183 }
 184
 185 /// Creates a decoder for a single enum variant/struct:
 186 /// - `outer_pat_path` is the path to this enum variant/struct
 187 /// - `getarg` should retrieve the `usize`-th field with name `@str`.
 188 fn decode_static_fields<F>(
 189     cx: &mut ExtCtxt<'_>,
 190     trait_span: Span,
 191     outer_pat_path: ast::Path,
 192     fields: &StaticFields,
 193     mut getarg: F,
 194 ) -> P<Expr>
 195 where
 196     F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
 197 {
 198     match fields {
 199         Unnamed(fields, is_tuple) => {
 200             let path_expr = cx.expr_path(outer_pat_path);
 201             if !*is_tuple {
 202                 path_expr
 203             } else {
 204                 let fields = fields
 205                     .iter()
 206                     .enumerate()
 207                     .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
 208                     .collect();
 209
 210                 cx.expr_call(trait_span, path_expr, fields)
 211             }
 212         }
 213         Named(fields) => {
 214             // use the field's span to get nicer error messages.
 215             let fields = fields
 216                 .iter()
 217                 .enumerate()
 218                 .map(|(i, &(ident, span))| {
 219                     let arg = getarg(cx, span, ident.name, i);
 220                     cx.field_imm(span, ident, arg)
 221                 })
 222                 .collect();
 223             cx.expr_struct(trait_span, outer_pat_path, fields)
 224         }
 225     }
 226 }