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: combine_substructure(|a, b, c| {
  56                     decodable_substructure(a, b, c)
  57                 }),
  58             })
  59     };
  60
  61     trait_def.expand(cx, mitem, item, push)
  62 }
  63
  64 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  65                           substr: &Substructure) -> @Expr {
  66     let decoder = substr.nonself_args[0];
  67     let recurse = vec!(cx.ident_of("serialize"),
  68                     cx.ident_of("Decodable"),
  69                     cx.ident_of("decode"));
  70     // throw an underscore in front to suppress unused variable warnings
  71     let blkarg = cx.ident_of("_d");
  72     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  73     let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder));
  74     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  75
  76     return match *substr.fields {
  77         StaticStruct(_, ref summary) => {
  78             let nfields = match *summary {
  79                 Unnamed(ref fields) => fields.len(),
  80                 Named(ref fields) => fields.len()
  81             };
  82             let read_struct_field = cx.ident_of("read_struct_field");
  83
  84             let result = decode_static_fields(cx,
  85                                               trait_span,
  86                                               substr.type_ident,
  87                                               summary,
  88                                               |cx, span, name, field| {
  89                 cx.expr_try(span,
  90                     cx.expr_method_call(span, blkdecoder, read_struct_field,
  91                                         vec!(cx.expr_str(span, name),
  92                                           cx.expr_uint(span, field),
  93                                           lambdadecode)))
  94             });
  95             let result = cx.expr_ok(trait_span, result);
  96             cx.expr_method_call(trait_span,
  97                                 decoder,
  98                                 cx.ident_of("read_struct"),
  99                                 vec!(
 100                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 101                 cx.expr_uint(trait_span, nfields),
 102                 cx.lambda_expr_1(trait_span, result, blkarg)
 103             ))
 104         }
 105         StaticEnum(_, ref fields) => {
 106             let variant = cx.ident_of("i");
 107
 108             let mut arms = Vec::new();
 109             let mut variants = Vec::new();
 110             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 111
 112             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 113                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 114
 115                 let decoded = decode_static_fields(cx,
 116                                                    v_span,
 117                                                    name,
 118                                                    parts,
 119                                                    |cx, span, _, field| {
 120                     let idx = cx.expr_uint(span, field);
 121                     cx.expr_try(span,
 122                         cx.expr_method_call(span, blkdecoder, rvariant_arg,
 123                                             vec!(idx, lambdadecode)))
 124                 });
 125
 126                 arms.push(cx.arm(v_span,
 127                                  vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
 128                                  decoded));
 129             }
 130
 131             arms.push(cx.arm_unreachable(trait_span));
 132
 133             let result = cx.expr_ok(trait_span,
 134                                     cx.expr_match(trait_span,
 135                                                   cx.expr_ident(trait_span, variant), arms));
 136             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 137             let variant_vec = cx.expr_vec(trait_span, variants);
 138             let result = cx.expr_method_call(trait_span, blkdecoder,
 139                                              cx.ident_of("read_enum_variant"),
 140                                              vec!(variant_vec, lambda));
 141             cx.expr_method_call(trait_span,
 142                                 decoder,
 143                                 cx.ident_of("read_enum"),
 144                                 vec!(
 145                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 146                 cx.lambda_expr_1(trait_span, result, blkarg)
 147             ))
 148         }
 149         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 150     };
 151 }
 152
 153 /// Create a decoder for a single enum variant/struct:
 154 /// - `outer_pat_ident` is the name of this enum variant/struct
 155 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 156 fn decode_static_fields(cx: &mut ExtCtxt,
 157                         trait_span: Span,
 158                         outer_pat_ident: Ident,
 159                         fields: &StaticFields,
 160                         getarg: |&mut ExtCtxt, Span, InternedString, uint| -> @Expr)
 161                         -> @Expr {
 162     match *fields {
 163         Unnamed(ref fields) => {
 164             if fields.is_empty() {
 165                 cx.expr_ident(trait_span, outer_pat_ident)
 166             } else {
 167                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 168                     getarg(cx, span,
 169                            token::intern_and_get_ident(format!("_field{}",
 170                                                                i)),
 171                            i)
 172                 }).collect();
 173
 174                 cx.expr_call_ident(trait_span, outer_pat_ident, fields)
 175             }
 176         }
 177         Named(ref fields) => {
 178             // use the field's span to get nicer error messages.
 179             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 180                 let arg = getarg(cx, span, token::get_ident(name), i);
 181                 cx.field_imm(span, name, arg)
 182             }).collect();
 183             cx.expr_struct_ident(trait_span, outer_pat_ident, fields)
 184         }
 185     }
 186 }