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, Expr, MutMutable};
  15 use codemap::Span;
  16 use ext::base::{ExtCtxt, Annotatable};
  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(cx: &mut ExtCtxt,
  25                                        span: Span,
  26                                        mitem: &MetaItem,
  27                                        item: &Annotatable,
  28                                        push: &mut FnMut(Annotatable))
  29 {
  30     expand_deriving_decodable_imp(cx, span, mitem, item, push, "rustc_serialize")
  31 }
  32
  33 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
  34                                  span: Span,
  35                                  mitem: &MetaItem,
  36                                  item: &Annotatable,
  37                                  push: &mut FnMut(Annotatable))
  38 {
  39     expand_deriving_decodable_imp(cx, span, mitem, item, push, "serialize")
  40 }
  41
  42 fn expand_deriving_decodable_imp(cx: &mut ExtCtxt,
  43                                  span: Span,
  44                                  mitem: &MetaItem,
  45                                  item: &Annotatable,
  46                                  push: &mut FnMut(Annotatable),
  47                                  krate: &'static str)
  48 {
  49     if !cx.use_std {
  50         // FIXME(#21880): lift this requirement.
  51         cx.span_err(span, "this trait cannot be derived with #![no_std]");
  52         return;
  53     }
  54
  55     let trait_def = TraitDef {
  56         span: span,
  57         attributes: Vec::new(),
  58         path: Path::new_(vec!(krate, "Decodable"), None, vec!(), true),
  59         additional_bounds: Vec::new(),
  60         generics: LifetimeBounds::empty(),
  61         methods: vec!(
  62             MethodDef {
  63                 name: "decode",
  64                 generics: LifetimeBounds {
  65                     lifetimes: Vec::new(),
  66                     bounds: vec!(("__D", vec!(Path::new_(
  67                                     vec!(krate, "Decoder"), None,
  68                                     vec!(), true))))
  69                 },
  70                 explicit_self: None,
  71                 args: vec!(Ptr(Box::new(Literal(Path::new_local("__D"))),
  72                             Borrowed(None, MutMutable))),
  73                 ret_ty: Literal(Path::new_(
  74                     pathvec_std!(cx, core::result::Result),
  75                     None,
  76                     vec!(Box::new(Self_), Box::new(Literal(Path::new_(
  77                         vec!["__D", "Error"], None, vec![], false
  78                     )))),
  79                     true
  80                 )),
  81                 attributes: Vec::new(),
  82                 is_unsafe: false,
  83                 combine_substructure: combine_substructure(Box::new(|a, b, c| {
  84                     decodable_substructure(a, b, c, krate)
  85                 })),
  86             }
  87         ),
  88         associated_types: Vec::new(),
  89     };
  90
  91     trait_def.expand(cx, mitem, item, push)
  92 }
  93
  94 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  95                           substr: &Substructure,
  96                           krate: &str) -> P<Expr> {
  97     let decoder = substr.nonself_args[0].clone();
  98     let recurse = vec!(cx.ident_of(krate),
  99                     cx.ident_of("Decodable"),
 100                     cx.ident_of("decode"));
 101     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
 102     // throw an underscore in front to suppress unused variable warnings
 103     let blkarg = cx.ident_of("_d");
 104     let blkdecoder = cx.expr_ident(trait_span, blkarg);
 105
 106     return match *substr.fields {
 107         StaticStruct(_, ref summary) => {
 108             let nfields = match *summary {
 109                 Unnamed(ref fields) => fields.len(),
 110                 Named(ref fields) => fields.len()
 111             };
 112             let read_struct_field = cx.ident_of("read_struct_field");
 113
 114             let path = cx.path_ident(trait_span, substr.type_ident);
 115             let result = decode_static_fields(cx,
 116                                               trait_span,
 117                                               path,
 118                                               summary,
 119                                               |cx, span, name, field| {
 120                 cx.expr_try(span,
 121                     cx.expr_method_call(span, blkdecoder.clone(), read_struct_field,
 122                                         vec!(cx.expr_str(span, name),
 123                                           cx.expr_usize(span, field),
 124                                           exprdecode.clone())))
 125             });
 126             let result = cx.expr_ok(trait_span, result);
 127             cx.expr_method_call(trait_span,
 128                                 decoder,
 129                                 cx.ident_of("read_struct"),
 130                                 vec!(
 131                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
 132                 cx.expr_usize(trait_span, nfields),
 133                 cx.lambda_expr_1(trait_span, result, blkarg)
 134             ))
 135         }
 136         StaticEnum(_, ref fields) => {
 137             let variant = cx.ident_of("i");
 138
 139             let mut arms = Vec::new();
 140             let mut variants = Vec::new();
 141             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 142
 143             for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
 144                 variants.push(cx.expr_str(v_span, ident.name.as_str()));
 145
 146                 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
 147                 let decoded = decode_static_fields(cx,
 148                                                    v_span,
 149                                                    path,
 150                                                    parts,
 151                                                    |cx, span, _, field| {
 152                     let idx = cx.expr_usize(span, field);
 153                     cx.expr_try(span,
 154                         cx.expr_method_call(span, blkdecoder.clone(), rvariant_arg,
 155                                             vec!(idx, exprdecode.clone())))
 156                 });
 157
 158                 arms.push(cx.arm(v_span,
 159                                  vec!(cx.pat_lit(v_span, cx.expr_usize(v_span, i))),
 160                                  decoded));
 161             }
 162
 163             arms.push(cx.arm_unreachable(trait_span));
 164
 165             let result = cx.expr_ok(trait_span,
 166                                     cx.expr_match(trait_span,
 167                                                   cx.expr_ident(trait_span, variant), arms));
 168             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 169             let variant_vec = cx.expr_vec(trait_span, variants);
 170             let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
 171             let result = cx.expr_method_call(trait_span, blkdecoder,
 172                                              cx.ident_of("read_enum_variant"),
 173                                              vec!(variant_vec, lambda));
 174             cx.expr_method_call(trait_span,
 175                                 decoder,
 176                                 cx.ident_of("read_enum"),
 177                                 vec!(
 178                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
 179                 cx.lambda_expr_1(trait_span, result, blkarg)
 180             ))
 181         }
 182         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)")
 183     };
 184 }
 185
 186 /// Create a decoder for a single enum variant/struct:
 187 /// - `outer_pat_path` is the path to this enum variant/struct
 188 /// - `getarg` should retrieve the `usize`-th field with name `@str`.
 189 fn decode_static_fields<F>(cx: &mut ExtCtxt,
 190                            trait_span: Span,
 191                            outer_pat_path: ast::Path,
 192                            fields: &StaticFields,
 193                            mut getarg: F)
 194                            -> P<Expr> where
 195     F: FnMut(&mut ExtCtxt, Span, InternedString, usize) -> P<Expr>,
 196 {
 197     match *fields {
 198         Unnamed(ref fields) => {
 199             let path_expr = cx.expr_path(outer_pat_path);
 200             if fields.is_empty() {
 201                 path_expr
 202             } else {
 203                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 204                     getarg(cx, span,
 205                            token::intern_and_get_ident(&format!("_field{}", i)),
 206                            i)
 207                 }).collect();
 208
 209                 cx.expr_call(trait_span, path_expr, fields)
 210             }
 211         }
 212         Named(ref fields) => {
 213             // use the field's span to get nicer error messages.
 214             let fields = fields.iter().enumerate().map(|(i, &(ident, span))| {
 215                 let arg = getarg(cx, span, ident.name.as_str(), i);
 216                 cx.field_imm(span, ident, arg)
 217             }).collect();
 218             cx.expr_struct(trait_span, outer_pat_path, fields)
 219         }
 220     }
 221 }