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::Symbol;
14 pub fn expand_deriving_rustc_decodable(
19 push: &mut dyn FnMut(Annotatable),
21 let krate = "rustc_serialize";
24 let trait_def = TraitDef {
26 attributes: Vec::new(),
27 path: Path::new_(vec![krate, "Decodable"], None, vec![], PathKind::Global),
28 additional_bounds: Vec::new(),
29 generics: LifetimeBounds::empty(),
31 supports_unions: false,
32 methods: vec![MethodDef {
34 generics: LifetimeBounds {
35 lifetimes: Vec::new(),
38 vec![Path::new_(vec![krate, "Decoder"], None, vec![], PathKind::Global)],
43 Ptr(Box::new(Literal(Path::new_local(typaram))), Borrowed(None, Mutability::Mut)),
46 ret_ty: Literal(Path::new_(
47 pathvec_std!(cx, result::Result),
51 Box::new(Literal(Path::new_(
52 vec![typaram, "Error"],
60 attributes: Vec::new(),
62 unify_fieldless_variants: false,
63 combine_substructure: combine_substructure(Box::new(|a, b, c| {
64 decodable_substructure(a, b, c, krate)
67 associated_types: Vec::new(),
70 trait_def.expand(cx, mitem, item, push)
73 fn decodable_substructure(
76 substr: &Substructure<'_>,
79 let decoder = substr.nonself_args[0].clone();
81 cx.ident_of(krate, trait_span),
82 cx.ident_of("Decodable", trait_span),
83 cx.ident_of("decode", trait_span),
85 let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
86 // throw an underscore in front to suppress unused variable warnings
87 let blkarg = cx.ident_of("_d", trait_span);
88 let blkdecoder = cx.expr_ident(trait_span, blkarg);
90 match *substr.fields {
91 StaticStruct(_, ref summary) => {
92 let nfields = match *summary {
93 Unnamed(ref fields, _) => fields.len(),
94 Named(ref fields) => fields.len(),
96 let read_struct_field = cx.ident_of("read_struct_field", trait_span);
98 let path = cx.path_ident(trait_span, substr.type_ident);
100 decode_static_fields(cx, trait_span, path, summary, |cx, span, name, field| {
108 cx.expr_str(span, name),
109 cx.expr_usize(span, field),
115 let result = cx.expr_ok(trait_span, result);
119 cx.ident_of("read_struct", trait_span),
121 cx.expr_str(trait_span, substr.type_ident.name),
122 cx.expr_usize(trait_span, nfields),
123 cx.lambda1(trait_span, result, blkarg),
127 StaticEnum(_, ref fields) => {
128 let variant = cx.ident_of("i", trait_span);
130 let mut arms = Vec::with_capacity(fields.len() + 1);
131 let mut variants = Vec::with_capacity(fields.len());
132 let rvariant_arg = cx.ident_of("read_enum_variant_arg", trait_span);
134 for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
135 variants.push(cx.expr_str(v_span, ident.name));
137 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
139 decode_static_fields(cx, v_span, path, parts, |cx, span, _, field| {
140 let idx = cx.expr_usize(span, field);
147 vec![idx, exprdecode.clone()],
152 arms.push(cx.arm(v_span, cx.pat_lit(v_span, cx.expr_usize(v_span, i)), decoded));
155 arms.push(cx.arm_unreachable(trait_span));
157 let result = cx.expr_ok(
159 cx.expr_match(trait_span, cx.expr_ident(trait_span, variant), arms),
161 let lambda = cx.lambda(trait_span, vec![blkarg, variant], result);
162 let variant_vec = cx.expr_vec(trait_span, variants);
163 let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
164 let result = cx.expr_method_call(
167 cx.ident_of("read_enum_variant", trait_span),
168 vec![variant_vec, lambda],
173 cx.ident_of("read_enum", trait_span),
175 cx.expr_str(trait_span, substr.type_ident.name),
176 cx.lambda1(trait_span, result, blkarg),
180 _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)"),
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)