1 //! The compiler code necessary for `#[derive(RustcDecodable)]`. See encodable.rs for more.
3 use crate::deriving::generic::ty::*;
4 use crate::deriving::generic::*;
5 use crate::deriving::pathvec_std;
8 use rustc_ast::ast::{Expr, MetaItem, Mutability};
10 use rustc_expand::base::{Annotatable, ExtCtxt};
11 use rustc_span::symbol::{sym, Ident, Symbol};
14 pub fn expand_deriving_rustc_decodable(
19 push: &mut dyn FnMut(Annotatable),
21 let krate = sym::rustc_serialize;
22 let typaram = sym::__D;
24 let trait_def = TraitDef {
26 attributes: Vec::new(),
27 path: Path::new_(vec![krate, sym::Decodable], None, vec![], PathKind::Global),
28 additional_bounds: Vec::new(),
29 generics: Bounds::empty(),
31 supports_unions: false,
32 methods: vec![MethodDef {
37 vec![Path::new_(vec![krate, sym::Decoder], None, vec![], PathKind::Global)],
42 Ptr(Box::new(Literal(Path::new_local(typaram))), Borrowed(None, Mutability::Mut)),
45 ret_ty: Literal(Path::new_(
46 pathvec_std!(result::Result),
50 Box::new(Literal(Path::new_(
51 vec![typaram, sym::Error],
59 attributes: Vec::new(),
61 unify_fieldless_variants: false,
62 combine_substructure: combine_substructure(Box::new(|a, b, c| {
63 decodable_substructure(a, b, c, krate)
66 associated_types: Vec::new(),
69 trait_def.expand(cx, mitem, item, push)
72 fn decodable_substructure(
75 substr: &Substructure<'_>,
78 let decoder = substr.nonself_args[0].clone();
80 Ident::new(krate, trait_span),
81 Ident::new(sym::Decodable, trait_span),
82 Ident::new(sym::decode, trait_span),
84 let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
85 // throw an underscore in front to suppress unused variable warnings
86 let blkarg = Ident::new(sym::_d, trait_span);
87 let blkdecoder = cx.expr_ident(trait_span, blkarg);
89 match *substr.fields {
90 StaticStruct(_, ref summary) => {
91 let nfields = match *summary {
92 Unnamed(ref fields, _) => fields.len(),
93 Named(ref fields) => fields.len(),
95 let read_struct_field = Ident::new(sym::read_struct_field, trait_span);
97 let path = cx.path_ident(trait_span, substr.type_ident);
99 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
107 cx.expr_str(span, name),
108 cx.expr_usize(span, field),
114 let result = cx.expr_ok(trait_span, result);
118 Ident::new(sym::read_struct, trait_span),
120 cx.expr_str(trait_span, substr.type_ident.name),
121 cx.expr_usize(trait_span, nfields),
122 cx.lambda1(trait_span, result, blkarg),
126 StaticEnum(_, ref fields) => {
127 let variant = Ident::new(sym::i, trait_span);
129 let mut arms = Vec::with_capacity(fields.len() + 1);
130 let mut variants = Vec::with_capacity(fields.len());
131 let rvariant_arg = Ident::new(sym::read_enum_variant_arg, trait_span);
133 for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
134 variants.push(cx.expr_str(v_span, ident.name));
136 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
138 decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
139 let idx = cx.expr_usize(span, field);
146 vec![idx, exprdecode.clone()],
151 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
154 arms.push(cx.arm_unreachable(trait_span));
156 let result = cx.expr_ok(
158 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
160 let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
161 let variant_vec = cx.expr_vec(trait_span, variants);
162 let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
163 let result = cx.expr_method_call(
166 Ident::new(sym::read_enum_variant, trait_span),
167 vec![variant_vec, lambda],
172 Ident::new(sym::read_enum, trait_span),
174 cx.expr_str(trait_span, substr.type_ident.name),
175 cx.lambda1(trait_span, result, blkarg),
179 _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
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<'_>,
189 outer_pat_path: ast::Path,
190 fields: &StaticFields,
194 F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
197 Unnamed(ref fields, is_tuple) => {
198 let path_expr = cx.expr_path(outer_pat_path);
205 .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
208 cx.expr_call(trait_span, path_expr, fields)
211 Named(ref fields) => {
212 // use the field's span to get nicer error messages.
216 .map(|(i, &(ident, span))| {
217 let arg = getarg(cx, span, ident.name, i);
218 cx.field_imm(span, ident, arg)
221 cx.expr_struct(trait_span, outer_pat_path, fields)