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 deriving::generic::*;
  14 use deriving::generic::ty::*;
  15
  16 use syntax::ast;
  17 use syntax::ast::{MetaItem, Expr, MutMutable};
  18 use syntax::codemap::Span;
  19 use syntax::ext::base::{ExtCtxt, Annotatable};
  20 use syntax::ext::build::AstBuilder;
  21 use syntax::parse::token::InternedString;
  22 use syntax::parse::token;
  23 use syntax::ptr::P;
  24
  25 pub fn expand_deriving_rustc_decodable(cx: &mut ExtCtxt,
  26                                        span: Span,
  27                                        mitem: &MetaItem,
  28                                        item: &Annotatable,
  29                                        push: &mut FnMut(Annotatable))
  30 {
  31     expand_deriving_decodable_imp(cx, span, mitem, item, push, "rustc_serialize")
  32 }
  33
  34 pub fn expand_deriving_decodable(cx: &mut ExtCtxt,
  35                                  span: Span,
  36                                  mitem: &MetaItem,
  37                                  item: &Annotatable,
  38                                  push: &mut FnMut(Annotatable))
  39 {
  40     expand_deriving_decodable_imp(cx, span, mitem, item, push, "serialize")
  41 }
  42
  43 fn expand_deriving_decodable_imp(cx: &mut ExtCtxt,
  44                                  span: Span,
  45                                  mitem: &MetaItem,
  46                                  item: &Annotatable,
  47                                  push: &mut FnMut(Annotatable),
  48                                  krate: &'static str)
  49 {
  50     if cx.crate_root != Some("std") {
  51         // FIXME(#21880): lift this requirement.
  52         cx.span_err(span, "this trait cannot be derived with #![no_std] \
  53                            or #![no_core]");
  54         return
  55     }
  56
  57     let trait_def = TraitDef {
  58         span: span,
  59         attributes: Vec::new(),
  60         path: Path::new_(vec!(krate, "Decodable"), None, vec!(), true),
  61         additional_bounds: Vec::new(),
  62         generics: LifetimeBounds::empty(),
  63         is_unsafe: false,
  64         methods: vec!(
  65             MethodDef {
  66                 name: "decode",
  67                 generics: LifetimeBounds {
  68                     lifetimes: Vec::new(),
  69                     bounds: vec!(("__D", vec!(Path::new_(
  70                                     vec!(krate, "Decoder"), None,
  71                                     vec!(), true))))
  72                 },
  73                 explicit_self: None,
  74                 args: vec!(Ptr(Box::new(Literal(Path::new_local("__D"))),
  75                             Borrowed(None, MutMutable))),
  76                 ret_ty: Literal(Path::new_(
  77                     pathvec_std!(cx, core::result::Result),
  78                     None,
  79                     vec!(Box::new(Self_), Box::new(Literal(Path::new_(
  80                         vec!["__D", "Error"], None, vec![], false
  81                     )))),
  82                     true
  83                 )),
  84                 attributes: Vec::new(),
  85                 is_unsafe: false,
  86                 combine_substructure: combine_substructure(Box::new(|a, b, c| {
  87                     decodable_substructure(a, b, c, krate)
  88                 })),
  89             }
  90         ),
  91         associated_types: Vec::new(),
  92     };
  93
  94     trait_def.expand(cx, mitem, item, push)
  95 }
  96
  97 fn decodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
  98                           substr: &Substructure,
  99                           krate: &str) -> P<Expr> {
 100     let decoder = substr.nonself_args[0].clone();
 101     let recurse = vec!(cx.ident_of(krate),
 102                     cx.ident_of("Decodable"),
 103                     cx.ident_of("decode"));
 104     let exprdecode = cx.expr_path(cx.path_global(trait_span, recurse));
 105     // throw an underscore in front to suppress unused variable warnings
 106     let blkarg = cx.ident_of("_d");
 107     let blkdecoder = cx.expr_ident(trait_span, blkarg);
 108
 109     return match *substr.fields {
 110         StaticStruct(_, ref summary) => {
 111             let nfields = match *summary {
 112                 Unnamed(ref fields) => fields.len(),
 113                 Named(ref fields) => fields.len()
 114             };
 115             let read_struct_field = cx.ident_of("read_struct_field");
 116
 117             let path = cx.path_ident(trait_span, substr.type_ident);
 118             let result = decode_static_fields(cx,
 119                                               trait_span,
 120                                               path,
 121                                               summary,
 122                                               |cx, span, name, field| {
 123                 cx.expr_try(span,
 124                     cx.expr_method_call(span, blkdecoder.clone(), read_struct_field,
 125                                         vec!(cx.expr_str(span, name),
 126                                           cx.expr_usize(span, field),
 127                                           exprdecode.clone())))
 128             });
 129             let result = cx.expr_ok(trait_span, result);
 130             cx.expr_method_call(trait_span,
 131                                 decoder,
 132                                 cx.ident_of("read_struct"),
 133                                 vec!(
 134                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
 135                 cx.expr_usize(trait_span, nfields),
 136                 cx.lambda_expr_1(trait_span, result, blkarg)
 137             ))
 138         }
 139         StaticEnum(_, ref fields) => {
 140             let variant = cx.ident_of("i");
 141
 142             let mut arms = Vec::new();
 143             let mut variants = Vec::new();
 144             let rvariant_arg = cx.ident_of("read_enum_variant_arg");
 145
 146             for (i, &(ident, v_span, ref parts)) in fields.iter().enumerate() {
 147                 variants.push(cx.expr_str(v_span, ident.name.as_str()));
 148
 149                 let path = cx.path(trait_span, vec![substr.type_ident, ident]);
 150                 let decoded = decode_static_fields(cx,
 151                                                    v_span,
 152                                                    path,
 153                                                    parts,
 154                                                    |cx, span, _, field| {
 155                     let idx = cx.expr_usize(span, field);
 156                     cx.expr_try(span,
 157                         cx.expr_method_call(span, blkdecoder.clone(), rvariant_arg,
 158                                             vec!(idx, exprdecode.clone())))
 159                 });
 160
 161                 arms.push(cx.arm(v_span,
 162                                  vec!(cx.pat_lit(v_span, cx.expr_usize(v_span, i))),
 163                                  decoded));
 164             }
 165
 166             arms.push(cx.arm_unreachable(trait_span));
 167
 168             let result = cx.expr_ok(trait_span,
 169                                     cx.expr_match(trait_span,
 170                                                   cx.expr_ident(trait_span, variant), arms));
 171             let lambda = cx.lambda_expr(trait_span, vec!(blkarg, variant), result);
 172             let variant_vec = cx.expr_vec(trait_span, variants);
 173             let variant_vec = cx.expr_addr_of(trait_span, variant_vec);
 174             let result = cx.expr_method_call(trait_span, blkdecoder,
 175                                              cx.ident_of("read_enum_variant"),
 176                                              vec!(variant_vec, lambda));
 177             cx.expr_method_call(trait_span,
 178                                 decoder,
 179                                 cx.ident_of("read_enum"),
 180                                 vec!(
 181                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
 182                 cx.lambda_expr_1(trait_span, result, blkarg)
 183             ))
 184         }
 185         _ => cx.bug("expected StaticEnum or StaticStruct in derive(Decodable)")
 186     };
 187 }
 188
 189 /// Create a decoder for a single enum variant/struct:
 190 /// - `outer_pat_path` is the path to this enum variant/struct
 191 /// - `getarg` should retrieve the `usize`-th field with name `@str`.
 192 fn decode_static_fields<F>(cx: &mut ExtCtxt,
 193                            trait_span: Span,
 194                            outer_pat_path: ast::Path,
 195                            fields: &StaticFields,
 196                            mut getarg: F)
 197                            -> P<Expr> where
 198     F: FnMut(&mut ExtCtxt, Span, InternedString, usize) -> P<Expr>,
 199 {
 200     match *fields {
 201         Unnamed(ref fields) => {
 202             let path_expr = cx.expr_path(outer_pat_path);
 203             if fields.is_empty() {
 204                 path_expr
 205             } else {
 206                 let fields = fields.iter().enumerate().map(|(i, &span)| {
 207                     getarg(cx, span,
 208                            token::intern_and_get_ident(&format!("_field{}", i)),
 209                            i)
 210                 }).collect();
 211
 212                 cx.expr_call(trait_span, path_expr, fields)
 213             }
 214         }
 215         Named(ref fields) => {
 216             // use the field's span to get nicer error messages.
 217             let fields = fields.iter().enumerate().map(|(i, &(ident, span))| {
 218                 let arg = getarg(cx, span, ident.name.as_str(), i);
 219                 cx.field_imm(span, ident, arg)
 220             }).collect();
 221             cx.expr_struct(trait_span, outer_pat_path, fields)
 222         }
 223     }
 224 }