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         additional_bounds: Vec::new(),
  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         is_const,
  59     };
  60
  61     trait_def.expand(cx, mitem, item, push)
  62 }
  63
  64 fn decodable_substructure(
  65     cx: &mut ExtCtxt<'_>,
  66     trait_span: Span,
  67     substr: &Substructure<'_>,
  68     krate: Symbol,
  69 ) -> BlockOrExpr {
  70     let decoder = substr.nonselflike_args[0].clone();
  71     let recurse = vec![
  72         Ident::new(krate, trait_span),
  73         Ident::new(sym::Decodable, trait_span),
  74         Ident::new(sym::decode, trait_span),
  75     ];
  76     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  77     // throw an underscore in front to suppress unused variable warnings
  78     let blkarg = Ident::new(sym::_d, trait_span);
  79     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  80
  81     let expr = match substr.fields {
  82         StaticStruct(_, summary) => {
  83             let nfields = match summary {
  84                 Unnamed(fields, _) => fields.len(),
  85                 Named(fields) => fields.len(),
  86             };
  87             let fn_read_struct_field_path: Vec<_> =
  88                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct_field]);
  89
  90             let path = cx.path_ident(trait_span, substr.type_ident);
  91             let result =
  92                 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
  93                     cx.expr_try(
  94                         span,
  95                         cx.expr_call_global(
  96                             span,
  97                             fn_read_struct_field_path.clone(),
  98                             vec![
  99                                 blkdecoder.clone(),
 100                                 cx.expr_str(span, name),
 101                                 cx.expr_usize(span, field),
 102                                 exprdecode.clone(),
 103                             ],
 104                         ),
 105                     )
 106                 });
 107             let result = cx.expr_ok(trait_span, result);
 108             let fn_read_struct_path: Vec<_> =
 109                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct]);
 110
 111             cx.expr_call_global(
 112                 trait_span,
 113                 fn_read_struct_path,
 114                 vec![
 115                     decoder,
 116                     cx.expr_str(trait_span, substr.type_ident.name),
 117                     cx.expr_usize(trait_span, nfields),
 118                     cx.lambda1(trait_span, result, blkarg),
 119                 ],
 120             )
 121         }
 122         StaticEnum(_, fields) => {
 123             let variant = Ident::new(sym::i, trait_span);
 124
 125             let mut arms = Vec::with_capacity(fields.len() + 1);
 126             let mut variants = Vec::with_capacity(fields.len());
 127
 128             let fn_read_enum_variant_arg_path: Vec<_> =
 129                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
 130
 131             for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
 132                 variants.push(cx.expr_str(v_span, ident.name));
 133
 134                 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
 135                 let decoded =
 136                     decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
 137                         let idx = cx.expr_usize(span, field);
 138                         cx.expr_try(
 139                             span,
 140                             cx.expr_call_global(
 141                                 span,
 142                                 fn_read_enum_variant_arg_path.clone(),
 143                                 vec![blkdecoder.clone(), idx, exprdecode.clone()],
 144                             ),
 145                         )
 146                     });
 147
 148                 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
 149             }
 150
 151             arms.push(cx.arm_unreachable(trait_span));
 152
 153             let result = cx.expr_ok(
 154                 trait_span,
 155                 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
 156             );
 157             let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
 158             let variant_array_ref = cx.expr_array_ref(trait_span, variants);
 159             let fn_read_enum_variant_path: Vec<_> =
 160                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant]);
 161             let result = cx.expr_call_global(
 162                 trait_span,
 163                 fn_read_enum_variant_path,
 164                 vec![blkdecoder, variant_array_ref, lambda],
 165             );
 166             let fn_read_enum_path: Vec<_> =
 167                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
 168
 169             cx.expr_call_global(
 170                 trait_span,
 171                 fn_read_enum_path,
 172                 vec![
 173                     decoder,
 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     BlockOrExpr::new_expr(expr)
 182 }
 183
 184 /// Creates a decoder for a single enum variant/struct:
 185 /// - `outer_pat_path` is the path to this enum variant/struct
 186 /// - `getarg` should retrieve the `usize`-th field with name `@str`.
 187 fn decode_static_fields<F>(
 188     cx: &mut ExtCtxt<'_>,
 189     trait_span: Span,
 190     outer_pat_path: ast::Path,
 191     fields: &StaticFields,
 192     mut getarg: F,
 193 ) -> P<Expr>
 194 where
 195     F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
 196 {
 197     match fields {
 198         Unnamed(fields, is_tuple) => {
 199             let path_expr = cx.expr_path(outer_pat_path);
 200             if !*is_tuple {
 201                 path_expr
 202             } else {
 203                 let fields = fields
 204                     .iter()
 205                     .enumerate()
 206                     .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
 207                     .collect();
 208
 209                 cx.expr_call(trait_span, path_expr, fields)
 210             }
 211         }
 212         Named(fields) => {
 213             // use the field's span to get nicer error messages.
 214             let fields = fields
 215                 .iter()
 216                 .enumerate()
 217                 .map(|(i, &(ident, span))| {
 218                     let arg = getarg(cx, span, ident.name, i);
 219                     cx.field_imm(span, ident, arg)
 220                 })
 221                 .collect();
 222             cx.expr_struct(trait_span, outer_pat_path, fields)
 223         }
 224     }
 225 }