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 ) {
  20     let krate = sym::rustc_serialize;
  21     let typaram = sym::__D;
  22
  23     let trait_def = TraitDef {
  24         span,
  25         path: Path::new_(vec![krate, sym::Decodable], vec![], PathKind::Global),
  26         skip_path_as_bound: false,
  27         additional_bounds: Vec::new(),
  28         generics: Bounds::empty(),
  29         supports_unions: false,
  30         methods: vec![MethodDef {
  31             name: sym::decode,
  32             generics: Bounds {
  33                 bounds: vec![(
  34                     typaram,
  35                     vec![Path::new_(vec![krate, sym::Decoder], vec![], PathKind::Global)],
  36                 )],
  37             },
  38             explicit_self: false,
  39             nonself_args: vec![(
  40                 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
  41                 sym::d,
  42             )],
  43             ret_ty: Path(Path::new_(
  44                 pathvec_std!(result::Result),
  45                 vec![
  46                     Box::new(Self_),
  47                     Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
  48                 ],
  49                 PathKind::Std,
  50             )),
  51             attributes: ast::AttrVec::new(),
  52             unify_fieldless_variants: false,
  53             combine_substructure: combine_substructure(Box::new(|a, b, c| {
  54                 decodable_substructure(a, b, c, krate)
  55             })),
  56         }],
  57         associated_types: Vec::new(),
  58     };
  59
  60     trait_def.expand(cx, mitem, item, push)
  61 }
  62
  63 fn decodable_substructure(
  64     cx: &mut ExtCtxt<'_>,
  65     trait_span: Span,
  66     substr: &Substructure<'_>,
  67     krate: Symbol,
  68 ) -> BlockOrExpr {
  69     let decoder = substr.nonselflike_args[0].clone();
  70     let recurse = vec![
  71         Ident::new(krate, trait_span),
  72         Ident::new(sym::Decodable, trait_span),
  73         Ident::new(sym::decode, trait_span),
  74     ];
  75     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  76     // throw an underscore in front to suppress unused variable warnings
  77     let blkarg = Ident::new(sym::_d, trait_span);
  78     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  79
  80     let expr = match *substr.fields {
  81         StaticStruct(_, ref summary) => {
  82             let nfields = match *summary {
  83                 Unnamed(ref fields, _) => fields.len(),
  84                 Named(ref fields) => fields.len(),
  85             };
  86             let fn_read_struct_field_path: Vec<_> =
  87                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct_field]);
  88
  89             let path = cx.path_ident(trait_span, substr.type_ident);
  90             let result =
  91                 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
  92                     cx.expr_try(
  93                         span,
  94                         cx.expr_call_global(
  95                             span,
  96                             fn_read_struct_field_path.clone(),
  97                             vec![
  98                                 blkdecoder.clone(),
  99                                 cx.expr_str(span, name),
 100                                 cx.expr_usize(span, field),
 101                                 exprdecode.clone(),
 102                             ],
 103                         ),
 104                     )
 105                 });
 106             let result = cx.expr_ok(trait_span, result);
 107             let fn_read_struct_path: Vec<_> =
 108                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct]);
 109
 110             cx.expr_call_global(
 111                 trait_span,
 112                 fn_read_struct_path,
 113                 vec![
 114                     decoder,
 115                     cx.expr_str(trait_span, substr.type_ident.name),
 116                     cx.expr_usize(trait_span, nfields),
 117                     cx.lambda1(trait_span, result, blkarg),
 118                 ],
 119             )
 120         }
 121         StaticEnum(_, ref fields) => {
 122             let variant = Ident::new(sym::i, trait_span);
 123
 124             let mut arms = Vec::with_capacity(fields.len() + 1);
 125             let mut variants = Vec::with_capacity(fields.len());
 126
 127             let fn_read_enum_variant_arg_path: Vec<_> =
 128                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
 129
 130             for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
 131                 variants.push(cx.expr_str(v_span, ident.name));
 132
 133                 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
 134                 let decoded =
 135                     decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
 136                         let idx = cx.expr_usize(span, field);
 137                         cx.expr_try(
 138                             span,
 139                             cx.expr_call_global(
 140                                 span,
 141                                 fn_read_enum_variant_arg_path.clone(),
 142                                 vec![blkdecoder.clone(), idx, exprdecode.clone()],
 143                             ),
 144                         )
 145                     });
 146
 147                 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
 148             }
 149
 150             arms.push(cx.arm_unreachable(trait_span));
 151
 152             let result = cx.expr_ok(
 153                 trait_span,
 154                 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
 155             );
 156             let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
 157             let variant_array_ref = cx.expr_array_ref(trait_span, variants);
 158             let fn_read_enum_variant_path: Vec<_> =
 159                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant]);
 160             let result = cx.expr_call_global(
 161                 trait_span,
 162                 fn_read_enum_variant_path,
 163                 vec![blkdecoder, variant_array_ref, lambda],
 164             );
 165             let fn_read_enum_path: Vec<_> =
 166                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
 167
 168             cx.expr_call_global(
 169                 trait_span,
 170                 fn_read_enum_path,
 171                 vec![
 172                     decoder,
 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     BlockOrExpr::new_expr(expr)
 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 }