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 /*!
  12 The compiler code necessary for `#[deriving(Decodable)]`. See
  13 encodable.rs for more.
  14 */
  15
  16 use ast;
  17 use ast::{MetaItem, Item, Expr, MutMutable, Ident};
  18 use codemap::Span;
  19 use ext::base::ExtCtxt;
  20 use ext::build::AstBuilder;
  21 use ext::deriving::generic::*;
  22 use parse::token::InternedString;
  23 use parse::token;
  24
  25 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
  26                                  span: Span,
  27                                  mitem: @MetaItem,
  28                                  item: @Item,
  29                                  push: |@Item|) {
  30     let trait_def = TraitDef {
  31         span: span,
  32         attributes: Vec::new(),
  33         path: Path::new_(vec!("serialize", "Decodable"), None,
  34                          vec!(~Literal(Path::new_local("__D")),
  35                               ~Literal(Path::new_local("__E"))), true),
  36         additional_bounds: Vec::new(),
  37         generics: LifetimeBounds {
  38             lifetimes: Vec::new(),
  39             bounds: vec!(("__D", ast::StaticSize, vec!(Path::new_(
  40                             vec!("serialize", "Decoder"), None,
  41                             vec!(~Literal(Path::new_local("__E"))), true))),
  42                          ("__E", ast::StaticSize, vec!()))
  43         },
  44         methods: vec!(
  45             MethodDef {
  46                 name: "decode",
  47                 generics: LifetimeBounds::empty(),
  48                 explicit_self: None,
  49                 args: vec!(Ptr(~Literal(Path::new_local("__D")),
  50                             Borrowed(None, MutMutable))),
  51                 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"), None,
  52                                           vec!(~Self, ~Literal(Path::new_local("__E"))), true)),
  53                 attributes: Vec::new(),
  54                 const_nonmatching: true,
  55                 combine_substructure: decodable_substructure,
  56             })
  57     };
  58
  59     trait_def.expand(cx, mitem, item, push)
  60 }
  61
  62 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  63                           substr: &Substructure) -> @Expr {
  64     let decoder = substr.nonself_args[0];
  65     let recurse = vec!(cx.ident_of("serialize"),
  66                     cx.ident_of("Decodable"),
  67                     cx.ident_of("decode"));
  68     // throw an underscore in front to suppress unused variable warnings
  69     let blkarg = cx.ident_of("_d");
  70     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  71     let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
  72     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  73
  74     return match *substr.fields {
  75         StaticStruct(_, ref summary) => {
  76             let nfields = match *summary {
  77                 Unnamed(ref fields) => fields.len(),
  78                 Named(ref fields) => fields.len()
  79             };
  80             let read_struct_field = cx.ident_of("read_struct_field");
  81
  82             let result = decode_static_fields(cx,
  83                                               trait_span,
  84                                               substr.type_ident,
  85                                               summary,
  86                                               |cx, span, name, field| {
  87                 cx.expr_try(span,
  88                     cx.expr_method_call(span, blkdecoder, read_struct_field,
  89                                         vec!(cx.expr_str(span, name),
  90                                           cx.expr_uint(span, field),
  91                                           lambdadecode)))
  92             });
  93             let result = cx.expr_ok(trait_span, result);
  94             cx.expr_method_call(trait_span,
  95                                 decoder,
  96                                 cx.ident_of("read_struct"),
  97                                 vec!(
  98                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
  99                 cx.expr_uint(trait_span, nfields),
 100                 cx.lambda_expr_1(trait_span, result, blkarg)
 101             ))
 102         }
 103         StaticEnum(_, ref fields) => {
 104             let variant = cx.ident_of("i");
 105
 106             let mut arms = Vec::new();
 107             let mut variants = Vec::new();
 108             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 109
 110             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 111                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 112
 113                 let decoded = decode_static_fields(cx,
 114                                                    v_span,
 115                                                    name,
 116                                                    parts,
 117                                                    |cx, span, _, field| {
 118                     let idx = cx.expr_uint(span, field);
 119                     cx.expr_try(span,
 120                         cx.expr_method_call(span, blkdecoder, rvariant_arg,
 121                                             vec!(idx, lambdadecode)))
 122                 });
 123
 124                 arms.push(cx.arm(v_span,
 125                                  vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
 126                                  decoded));
 127             }
 128
 129             arms.push(cx.arm_unreachable(trait_span));
 130
 131             let result = cx.expr_ok(trait_span,
 132                                     cx.expr_match(trait_span,
 133                                                   cx.expr_ident(trait_span, variant), arms));
 134             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 135             let variant_vec = cx.expr_vec(trait_span, variants);
 136             let result = cx.expr_method_call(trait_span, blkdecoder,
 137                                              cx.ident_of("read_enum_variant"),
 138                                              vec!(variant_vec, lambda));
 139             cx.expr_method_call(trait_span,
 140                                 decoder,
 141                                 cx.ident_of("read_enum"),
 142                                 vec!(
 143                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 144                 cx.lambda_expr_1(trait_span, result, blkarg)
 145             ))
 146         }
 147         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 148     };
 149 }
 150
 151 /// Create a decoder for a single enum variant/struct:
 152 /// - `outer_pat_ident` is the name of this enum variant/struct
 153 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 154 fn decode_static_fields(cx: &mut ExtCtxt,
 155                         trait_span: Span,
 156                         outer_pat_ident: Ident,
 157                         fields: &StaticFields,
 158                         getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
 159                         -> @Expr {
 160     match *fields {
 161         Unnamed(ref fields) => {
 162             if fields.is_empty() {
 163                 cx.expr_ident(trait_span, outer_pat_ident)
 164             } else {
 165                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 166                     getarg(cx, span,
 167                            token::intern_and_get_ident(format!("_field{}",
 168                                                                i)),
 169                            i)
 170                 }).collect();
 171
 172                 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
 173             }
 174         }
 175         Named(ref fields) => {
 176             // use the field's span to get nicer error messages.
 177             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 178                 let arg = getarg(cx, span, token::get_ident(name), i);
 179                 cx.field_imm(span, name, arg)
 180             }).collect();
 181             cx.expr_struct_ident(trait_span, outer_pat_ident, fields)
 182         }
 183     }
 184 }