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,
  56                          vec!(box Literal(Path::new_local("__D")),
  57                               box Literal(Path::new_local("__E"))), true),
  58         additional_bounds: Vec::new(),
  59         generics: LifetimeBounds {
  60             lifetimes: Vec::new(),
  61             bounds: vec!(("__D", vec!(Path::new_(
  62                             vec!(krate, "Decoder"), None,
  63                             vec!(box Literal(Path::new_local("__E"))), true))),
  64                          ("__E", vec!()))
  65         },
  66         methods: vec!(
  67             MethodDef {
  68                 name: "decode",
  69                 generics: LifetimeBounds::empty(),
  70                 explicit_self: None,
  71                 args: vec!(Ptr(box Literal(Path::new_local("__D")),
  72                             Borrowed(None, MutMutable))),
  73                 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"), None,
  74                                           vec!(box Self,
  75                                                box Literal(Path::new_local("__E"))), true)),
  76                 attributes: Vec::new(),
  77                 combine_substructure: combine_substructure(|a, b, c| {
  78                     decodable_substructure(a, b, c, krate)
  79                 }),
  80             })
  81     };
  82
  83     trait_def.expand(cx, mitem, item, push)
  84 }
  85
  86 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  87                           substr: &Substructure,
  88                           krate: &str) -> P<Expr> {
  89     let decoder = substr.nonself_args[0].clone();
  90     let recurse = vec!(cx.ident_of(krate),
  91                     cx.ident_of("Decodable"),
  92                     cx.ident_of("decode"));
  93     // throw an underscore in front to suppress unused variable warnings
  94     let blkarg = cx.ident_of("_d");
  95     let blkdecoder = cx.expr_ident(trait_span, blkarg);
  96     let calldecode = cx.expr_call_global(trait_span, recurse, vec!(blkdecoder.clone()));
  97     let lambdadecode = cx.lambda_expr_1(trait_span, calldecode, blkarg);
  98
  99     return match *substr.fields {
 100         StaticStruct(_, ref summary) => {
 101             let nfields = match *summary {
 102                 Unnamed(ref fields) => fields.len(),
 103                 Named(ref fields) => fields.len()
 104             };
 105             let read_struct_field = cx.ident_of("read_struct_field");
 106
 107             let path = cx.path_ident(trait_span, substr.type_ident);
 108             let result = decode_static_fields(cx,
 109                                               trait_span,
 110                                               path,
 111                                               summary,
 112                                               |cx, span, name, field| {
 113                 cx.expr_try(span,
 114                     cx.expr_method_call(span, blkdecoder.clone(), read_struct_field,
 115                                         vec!(cx.expr_str(span, name),
 116                                           cx.expr_uint(span, field),
 117                                           lambdadecode.clone())))
 118             });
 119             let result = cx.expr_ok(trait_span, result);
 120             cx.expr_method_call(trait_span,
 121                                 decoder,
 122                                 cx.ident_of("read_struct"),
 123                                 vec!(
 124                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 125                 cx.expr_uint(trait_span, nfields),
 126                 cx.lambda_expr_1(trait_span, result, blkarg)
 127             ))
 128         }
 129         StaticEnum(_, ref fields) => {
 130             let variant = cx.ident_of("i");
 131
 132             let mut arms = Vec::new();
 133             let mut variants = Vec::new();
 134             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 135
 136             for (i, &(name, v_span, ref parts)) in fields.iter().enumerate() {
 137                 variants.push(cx.expr_str(v_span, token::get_ident(name)));
 138
 139                 let path = cx.path(trait_span, vec![substr.type_ident, name]);
 140                 let decoded = decode_static_fields(cx,
 141                                                    v_span,
 142                                                    path,
 143                                                    parts,
 144                                                    |cx, span, _, field| {
 145                     let idx = cx.expr_uint(span, field);
 146                     cx.expr_try(span,
 147                         cx.expr_method_call(span, blkdecoder.clone(), rvariant_arg,
 148                                             vec!(idx, lambdadecode.clone())))
 149                 });
 150
 151                 arms.push(cx.arm(v_span,
 152                                  vec!(cx.pat_lit(v_span, cx.expr_uint(v_span, i))),
 153                                  decoded));
 154             }
 155
 156             arms.push(cx.arm_unreachable(trait_span));
 157
 158             let result = cx.expr_ok(trait_span,
 159                                     cx.expr_match(trait_span,
 160                                                   cx.expr_ident(trait_span, variant), arms));
 161             let lambda = cx.lambda_expr(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(trait_span, blkdecoder,
 165                                              cx.ident_of("read_enum_variant"),
 166                                              vec!(variant_vec, lambda));
 167             cx.expr_method_call(trait_span,
 168                                 decoder,
 169                                 cx.ident_of("read_enum"),
 170                                 vec!(
 171                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 172                 cx.lambda_expr_1(trait_span, result, blkarg)
 173             ))
 174         }
 175         _ => cx.bug("expected StaticEnum or StaticStruct in deriving(Decodable)")
 176     };
 177 }
 178
 179 /// Create a decoder for a single enum variant/struct:
 180 /// - `outer_pat_path` is the path to this enum variant/struct
 181 /// - `getarg` should retrieve the `uint`-th field with name `@str`.
 182 fn decode_static_fields<F>(cx: &mut ExtCtxt,
 183                            trait_span: Span,
 184                            outer_pat_path: ast::Path,
 185                            fields: &StaticFields,
 186                            mut getarg: F)
 187                            -> P<Expr> where
 188     F: FnMut(&mut ExtCtxt, Span, InternedString, uint) -> P<Expr>,
 189 {
 190     match *fields {
 191         Unnamed(ref fields) => {
 192             let path_expr = cx.expr_path(outer_pat_path);
 193             if fields.is_empty() {
 194                 path_expr
 195             } else {
 196                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 197                     getarg(cx, span,
 198                            token::intern_and_get_ident(format!("_field{}",
 199                                                                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 }