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