src/libsyntax/ext/deriving/decodable.rs

   1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! The compiler code necessary for `#[derive(Decodable)]`. See encodable.rs for more.
  12
  13 use ast;
  14 use ast::{MetaItem, Item, Expr, MutMutable};
  15 use codemap::Span;
  16 use ext::base::ExtCtxt;
  17 use ext::build::AstBuilder;
  18 use ext::deriving::generic::*;
  19 use ext::deriving::generic::ty::*;
  20 use parse::token::InternedString;
  21 use parse::token;
  22 use ptr::P;
  23
  24 pub fn expand_deriving_rustc_decodable<F>(cx: &mut ExtCtxt,
  25                                           span: Span,
  26                                           mitem: &MetaItem,
  27                                           item: &Item,
  28                                           push: F) where
  29     F: FnOnce(P<Item>),
  30 {
  31     expand_deriving_decodable_imp(cx, span, mitem, item, push, "rustc_serialize")
  32 }
  33
  34 pub fn expand_deriving_decodable<F>(cx: &mut ExtCtxt,
  35                                     span: Span,
  36                                     mitem: &MetaItem,
  37                                     item: &Item,
  38                                     push: F) where
  39     F: FnOnce(P<Item>),
  40 {
  41     expand_deriving_decodable_imp(cx, span, mitem, item, push, "serialize")
  42 }
  43
  44 fn expand_deriving_decodable_imp<F>(cx: &mut ExtCtxt,
  45                                     span: Span,
  46                                     mitem: &MetaItem,
  47                                     item: &Item,
  48                                     push: F,
  49                                     krate: &'static str) where
  50     F: FnOnce(P<Item>),
  51 {
  52     let trait_def = TraitDef {
  53         span: span,
  54         attributes: Vec::new(),
  55         path: Path::new_(vec!(krate, "Decodable"), None, vec!(), true),
  56         additional_bounds: Vec::new(),
  57         generics: LifetimeBounds::empty(),
  58         methods: vec!(
  59             MethodDef {
  60                 name: "decode",
  61                 generics: LifetimeBounds {
  62                     lifetimes: Vec::new(),
  63                     bounds: vec!(("__D", vec!(Path::new_(
  64                                     vec!(krate, "Decoder"), None,
  65                                     vec!(), true))))
  66                 },
  67                 explicit_self: None,
  68                 args: vec!(Ptr(box Literal(Path::new_local("__D")),
  69                             Borrowed(None, MutMutable))),
  70                 ret_ty: Literal(Path::new_(
  71                     pathvec!(std::result::Result),
  72                     None,
  73                     vec!(box Self, box Literal(Path::new_(
  74                         vec!["__D", "Error"], None, vec![], false
  75                     ))),
  76                     true
  77                 )),
  78                 attributes: Vec::new(),
  79                 combine_substructure: combine_substructure(box |a, b, c| {
  80                     decodable_substructure(a, b, c, krate)
  81                 }),
  82             }
  83         ),
  84         associated_types: Vec::new(),
  85     };
  86
  87     trait_def.expand(cx, mitem, item, push)
  88 }
  89
  90 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  91                           substr: &Substructure,
  92                           krate: &str) -> P<Expr> {
  93     let decoder = substr.nonself_args[0].clone();
  94     let recurse = vec!(cx.ident_of(krate),
  95                     cx.ident_of("Decodable"),
  96                     cx.ident_of("decode"));
  97     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  98     // throw an underscore in front to suppress unused variable warnings
  99     let blkarg = cx.ident_of("_d");
 100     let blkdecoder = cx.expr_ident(trait_span, blkarg);
 101
 102     return match *substr.fields {
 103         StaticStruct(_, ref summary) => {
 104             let nfields = match *summary {
 105                 Unnamed(ref fields) => fields.len(),
 106                 Named(ref fields) => fields.len()
 107             };
 108             let read_struct_field = cx.ident_of("read_struct_field");
 109
 110             let path = cx.path_ident(trait_span, substr.type_ident);
 111             let result = decode_static_fields(cx,
 112                                               trait_span,
 113                                               path,
 114                                               summary,
 115                                               |cx, span, name, field| {
 116                 cx.expr_try(span,
 117                     cx.expr_method_call(span, blkdecoder.clone(), read_struct_field,
 118                                         vec!(cx.expr_str(span, name),
 119                                           cx.expr_usize(span, field),
 120                                           exprdecode.clone())))
 121             });
 122             let result = cx.expr_ok(trait_span, result);
 123             cx.expr_method_call(trait_span,
 124                                 decoder,
 125                                 cx.ident_of("read_struct"),
 126                                 vec!(
 127                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 128                 cx.expr_usize(trait_span, nfields),
 129                 cx.lambda_expr_1(trait_span, result, blkarg)
 130             ))
 131         }
 132         StaticEnum(_, ref fields) => {
 133             let variant = cx.ident_of("i");
 134
 135             let mut arms = Vec::new();
 136             let mut variants = Vec::new();
 137             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 138
 139             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 140                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 141
 142                 let path = cx.path(trait_span, vec![substr.type_ident, name]);
 143                 let decoded = decode_static_fields(cx,
 144                                                    v_span,
 145                                                    path,
 146                                                    parts,
 147                                                    |cx, span, _, field| {
 148                     let idx = cx.expr_usize(span, field);
 149                     cx.expr_try(span,
 150                         cx.expr_method_call(span, blkdecoder.clone(), rvariant_arg,
 151                                             vec!(idx, exprdecode.clone())))
 152                 });
 153
 154                 arms.push(cx.arm(v_span,
 155                                  vec!(cx.pat_lit(v_span, cx.expr_usize(v_span, i))),
 156                                  decoded));
 157             }
 158
 159             arms.push(cx.arm_unreachable(trait_span));
 160
 161             let result = cx.expr_ok(trait_span,
 162                                     cx.expr_match(trait_span,
 163                                                   cx.expr_ident(trait_span, variant), arms));
 164             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 165             let variant_vec = cx.expr_vec(trait_span, variants);
 166             let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
 167             let result = cx.expr_method_call(trait_span, blkdecoder,
 168                                              cx.ident_of("read_enum_variant"),
 169                                              vec!(variant_vec, lambda));
 170             cx.expr_method_call(trait_span,
 171                                 decoder,
 172                                 cx.ident_of("read_enum"),
 173                                 vec!(
 174                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 175                 cx.lambda_expr_1(trait_span, result, blkarg)
 176             ))
 177         }
 178         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)")
 179     };
 180 }
 181
 182 /// Create 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>(cx: &mut ExtCtxt,
 186                            trait_span: Span,
 187                            outer_pat_path: ast::Path,
 188                            fields: &StaticFields,
 189                            mut getarg: F)
 190                            -> P<Expr> where
 191     F: FnMut(&mut ExtCtxt, Span, InternedString, usize) -> P<Expr>,
 192 {
 193     match *fields {
 194         Unnamed(ref fields) => {
 195             let path_expr = cx.expr_path(outer_pat_path);
 196             if fields.is_empty() {
 197                 path_expr
 198             } else {
 199                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 200                     getarg(cx, span,
 201                            token::intern_and_get_ident(&format!("_field{}", i)[]),
 202                            i)
 203                 }).collect();
 204
 205                 cx.expr_call(trait_span, path_expr, fields)
 206             }
 207         }
 208         Named(ref fields) => {
 209             // use the field's span to get nicer error messages.
 210             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 211                 let arg = getarg(cx, span, token::get_ident(name), i);
 212                 cx.field_imm(span, name, arg)
 213             }).collect();
 214             cx.expr_struct(trait_span, outer_pat_path, fields)
 215         }
 216     }
 217 }