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::{self as ast, Expr, MetaItem, Mutability};
9 use rustc_expand::base::{Annotatable, ExtCtxt};
10 use rustc_span::symbol::{sym, Ident, Symbol};
13 pub fn expand_deriving_rustc_decodable(
18 push: &mut dyn FnMut(Annotatable),
21 let krate = sym::rustc_serialize;
22 let typaram = sym::__D;
24 let trait_def = TraitDef {
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 {
35 vec![Path::new_(vec![krate, sym::Decoder], vec![], PathKind::Global)],
40 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
43 ret_ty: Path(Path::new_(
44 pathvec_std!(result::Result),
47 Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
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)
57 associated_types: Vec::new(),
61 trait_def.expand(cx, mitem, item, push)
64 fn decodable_substructure(
67 substr: &Substructure<'_>,
70 let decoder = substr.nonselflike_args[0].clone();
72 Ident::new(krate, trait_span),
73 Ident::new(sym::Decodable, trait_span),
74 Ident::new(sym::decode, trait_span),
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);
81 let expr = match *substr.fields {
82 StaticStruct(_, ref summary) => {
83 let nfields = match *summary {
84 Unnamed(ref fields, _) => fields.len(),
85 Named(ref fields) => fields.len(),
87 let fn_read_struct_field_path: Vec<_> =
88 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_struct_field]);
90 let path = cx.path_ident(trait_span, substr.type_ident);
92 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
97 fn_read_struct_field_path.clone(),
100 cx.expr_str(span, name),
101 cx.expr_usize(span, field),
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]);
116 cx.expr_str(trait_span, substr.type_ident.name),
117 cx.expr_usize(trait_span, nfields),
118 cx.lambda1(trait_span, result, blkarg),
122 StaticEnum(_, ref fields) => {
123 let variant = Ident::new(sym::i, trait_span);
125 let mut arms = Vec::with_capacity(fields.len() + 1);
126 let mut variants = Vec::with_capacity(fields.len());
128 let fn_read_enum_variant_arg_path: Vec<_> =
129 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum_variant_arg]);
131 for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
132 variants.push(cx.expr_str(v_span, ident.name));
134 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
136 decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
137 let idx = cx.expr_usize(span, field);
142 fn_read_enum_variant_arg_path.clone(),
143 vec![blkdecoder.clone(), idx, exprdecode.clone()],
148 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
151 arms.push(cx.arm_unreachable(trait_span));
153 let result = cx.expr_ok(
155 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
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(
163 fn_read_enum_variant_path,
164 vec![blkdecoder, variant_array_ref, lambda],
166 let fn_read_enum_path: Vec<_> =
167 cx.def_site_path(&[sym::rustc_serialize, sym::Decoder, sym::read_enum]);
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)"),
181 BlockOrExpr::new_expr(expr)
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<'_>,
190 outer_pat_path: ast::Path,
191 fields: &StaticFields,
195 F: FnMut(&mut ExtCtxt<'_>, Span, Symbol, usize) -> P<Expr>,
198 Unnamed(ref fields, is_tuple) => {
199 let path_expr = cx.expr_path(outer_pat_path);
206 .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
209 cx.expr_call(trait_span, path_expr, fields)
212 Named(ref fields) => {
213 // use the field's span to get nicer error messages.
217 .map(|(i, &(ident, span))| {
218 let arg = getarg(cx, span, ident.name, i);
219 cx.field_imm(span, ident, arg)
222 cx.expr_struct(trait_span, outer_pat_path, fields)