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         additional_bounds: Vec::new(),
  27         generics: Bounds::empty(),
  28         supports_unions: false,
  29         methods: vec![MethodDef {
  30             name: sym::decode,
  31             generics: Bounds {
  32                 bounds: vec![(
  33                     typaram,
  34                     vec![Path::new_(vec![krate, sym::Decoder], vec![], PathKind::Global)],
  35                 )],
  36             },
  37             explicit_self: false,
  38             nonself_args: vec![(
  39                 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
  40                 sym::d,
  41             )],
  42             ret_ty: Path(Path::new_(
  43                 pathvec_std!(result::Result),
  44                 vec![
  45                     Box::new(Self_),
  46                     Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
  47                 ],
  48                 PathKind::Std,
  49             )),
  50             attributes: ast::AttrVec::new(),
  51             unify_fieldless_variants: false,
  52             combine_substructure: combine_substructure(Box::new(|a, b, c| {
  53                 decodable_substructure(a, b, c, krate)
  54             })),
  55         }],
  56         associated_types: Vec::new(),
  57     };
  58
  59     trait_def.expand(cx, mitem, item, push)
  60 }
  61
  62 fn decodable_substructure(
  63     cx: &mut ExtCtxt<'_>,
  64     trait_span: Span,
  65     substr: &Substructure<'_>,
  66     krate: Symbol,
  67 ) -> BlockOrExpr {
  68     let decoder = substr.nonselflike_args[0].clone();
  69     let recurse = vec![
  70         Ident::new(krate, trait_span),
  71         Ident::new(sym::Decodable, trait_span),
  72         Ident::new(sym::decode, trait_span),
  73     ];
  74     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  75     // throw an underscore in front to suppress unused variable warnings
  76     let blkarg = Ident::new(sym::_d, trait_span);
  77     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  78
  79     let expr = match *substr.fields {
  80         StaticStruct(_, ref summary) => {
  81             let nfields = match *summary {
  82                 Unnamed(ref fields, _) => fields.len(),
  83                 Named(ref fields) => fields.len(),
  84             };
  85             let fn_read_struct_field_path: Vec<_> =
  86                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct_field]);
  87
  88             let path = cx.path_ident(trait_span, substr.type_ident);
  89             let result =
  90                 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
  91                     cx.expr_try(
  92                         span,
  93                         cx.expr_call_global(
  94                             span,
  95                             fn_read_struct_field_path.clone(),
  96                             vec![
  97                                 blkdecoder.clone(),
  98                                 cx.expr_str(span, name),
  99                                 cx.expr_usize(span, field),
 100                                 exprdecode.clone(),
 101                             ],
 102                         ),
 103                     )
 104                 });
 105             let result = cx.expr_ok(trait_span, result);
 106             let fn_read_struct_path: Vec<_> =
 107                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct]);
 108
 109             cx.expr_call_global(
 110                 trait_span,
 111                 fn_read_struct_path,
 112                 vec![
 113                     decoder,
 114                     cx.expr_str(trait_span, substr.type_ident.name),
 115                     cx.expr_usize(trait_span, nfields),
 116                     cx.lambda1(trait_span, result, blkarg),
 117                 ],
 118             )
 119         }
 120         StaticEnum(_, ref fields) => {
 121             let variant = Ident::new(sym::i, trait_span);
 122
 123             let mut arms = Vec::with_capacity(fields.len() + 1);
 124             let mut variants = Vec::with_capacity(fields.len());
 125
 126             let fn_read_enum_variant_arg_path: Vec<_> =
 127                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
 128
 129             for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
 130                 variants.push(cx.expr_str(v_span, ident.name));
 131
 132                 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
 133                 let decoded =
 134                     decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
 135                         let idx = cx.expr_usize(span, field);
 136                         cx.expr_try(
 137                             span,
 138                             cx.expr_call_global(
 139                                 span,
 140                                 fn_read_enum_variant_arg_path.clone(),
 141                                 vec![blkdecoder.clone(), idx, exprdecode.clone()],
 142                             ),
 143                         )
 144                     });
 145
 146                 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
 147             }
 148
 149             arms.push(cx.arm_unreachable(trait_span));
 150
 151             let result = cx.expr_ok(
 152                 trait_span,
 153                 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
 154             );
 155             let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
 156             let variant_array_ref = cx.expr_array_ref(trait_span, variants);
 157             let fn_read_enum_variant_path: Vec<_> =
 158                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant]);
 159             let result = cx.expr_call_global(
 160                 trait_span,
 161                 fn_read_enum_variant_path,
 162                 vec![blkdecoder, variant_array_ref, lambda],
 163             );
 164             let fn_read_enum_path: Vec<_> =
 165                 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
 166
 167             cx.expr_call_global(
 168                 trait_span,
 169                 fn_read_enum_path,
 170                 vec![
 171                     decoder,
 172                     cx.expr_str(trait_span, substr.type_ident.name),
 173                     cx.lambda1(trait_span, result, blkarg),
 174                 ],
 175             )
 176         }
 177         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
 178     };
 179     BlockOrExpr::new_expr(expr)
 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 }