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                     vec!("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
  85     trait_def.expand(cx, mitem, item, push)
  86 }
  87
  88 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  89                           substr: &Substructure,
  90                           krate: &str) -> P<Expr> {
  91     let decoder = substr.nonself_args[0].clone();
  92     let recurse = vec!(cx.ident_of(krate),
  93                     cx.ident_of("Decodable"),
  94                     cx.ident_of("decode"));
  95     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
  96     // throw an underscore in front to suppress unused variable warnings
  97     let blkarg = cx.ident_of("_d");
  98     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  99
 100     return match *substr.fields {
 101         StaticStruct(_, ref summary) => {
 102             let nfields = match *summary {
 103                 Unnamed(ref fields) => fields.len(),
 104                 Named(ref fields) => fields.len()
 105             };
 106             let read_struct_field = cx.ident_of("read_struct_field");
 107
 108             let path = cx.path_ident(trait_span, substr.type_ident);
 109             let result = decode_static_fields(cx,
 110                                               trait_span,
 111                                               path,
 112                                               summary,
 113                                               |cx, span, name, field| {
 114                 cx.expr_try(span,
 115                     cx.expr_method_call(span, blkdecoder.clone(), read_struct_field,
 116                                         vec!(cx.expr_str(span, name),
 117                                           cx.expr_usize(span, field),
 118                                           exprdecode.clone())))
 119             });
 120             let result = cx.expr_ok(trait_span, result);
 121             cx.expr_method_call(trait_span,
 122                                 decoder,
 123                                 cx.ident_of("read_struct"),
 124                                 vec!(
 125                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 126                 cx.expr_usize(trait_span, nfields),
 127                 cx.lambda_expr_1(trait_span, result, blkarg)
 128             ))
 129         }
 130         StaticEnum(_, ref fields) => {
 131             let variant = cx.ident_of("i");
 132
 133             let mut arms = Vec::new();
 134             let mut variants = Vec::new();
 135             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 136
 137             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 138                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 139
 140                 let path = cx.path(trait_span, vec![substr.type_ident, name]);
 141                 let decoded = decode_static_fields(cx,
 142                                                    v_span,
 143                                                    path,
 144                                                    parts,
 145                                                    |cx, span, _, field| {
 146                     let idx = cx.expr_usize(span, field);
 147                     cx.expr_try(span,
 148                         cx.expr_method_call(span, blkdecoder.clone(), rvariant_arg,
 149                                             vec!(idx, exprdecode.clone())))
 150                 });
 151
 152                 arms.push(cx.arm(v_span,
 153                                  vec!(cx.pat_lit(v_span, cx.expr_usize(v_span, i))),
 154                                  decoded));
 155             }
 156
 157             arms.push(cx.arm_unreachable(trait_span));
 158
 159             let result = cx.expr_ok(trait_span,
 160                                     cx.expr_match(trait_span,
 161                                                   cx.expr_ident(trait_span, variant), arms));
 162             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 163             let variant_vec = cx.expr_vec(trait_span, variants);
 164             let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
 165             let result = cx.expr_method_call(trait_span, blkdecoder,
 166                                              cx.ident_of("read_enum_variant"),
 167                                              vec!(variant_vec, lambda));
 168             cx.expr_method_call(trait_span,
 169                                 decoder,
 170                                 cx.ident_of("read_enum"),
 171                                 vec!(
 172                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 173                 cx.lambda_expr_1(trait_span, result, blkarg)
 174             ))
 175         }
 176         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)")
 177     };
 178 }
 179
 180 /// Create a decoder for a single enum variant/struct:
 181 /// - `outer_pat_path` is the path to this enum variant/struct
 182 /// - `getarg` should retrieve the `usize`-th field with name `@str`.
 183 fn decode_static_fields<F>(cx: &mut ExtCtxt,
 184                            trait_span: Span,
 185                            outer_pat_path: ast::Path,
 186                            fields: &StaticFields,
 187                            mut getarg: F)
 188                            -> P<Expr> where
 189     F: FnMut(&mut ExtCtxt, Span, InternedString, usize) -> P<Expr>,
 190 {
 191     match *fields {
 192         Unnamed(ref fields) => {
 193             let path_expr = cx.expr_path(outer_pat_path);
 194             if fields.is_empty() {
 195                 path_expr
 196             } else {
 197                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 198                     getarg(cx, span,
 199                            token::intern_and_get_ident(&format!("_field{}", i)[]),
 200                            i)
 201                 }).collect();
 202
 203                 cx.expr_call(trait_span, path_expr, fields)
 204             }
 205         }
 206         Named(ref fields) => {
 207             // use the field's span to get nicer error messages.
 208             let fields = fields.iter().enumerate().map(|(i, &(name, span))| {
 209                 let arg = getarg(cx, span, token::get_ident(name), i);
 210                 cx.field_imm(span, name, arg)
 211             }).collect();
 212             cx.expr_struct(trait_span, outer_pat_path, fields)
 213         }
 214     }
 215 }