src/libsyntax/ext/deriving/encodable.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 to implement the `#[deriving(Encodable)]`
  12 //! (and `Decodable`, in decodable.rs) extension.  The idea here is that
  13 //! type-defining items may be tagged with `#[deriving(Encodable, Decodable)]`.
  14 //!
  15 //! For example, a type like:
  16 //!
  17 //! ```ignore
  18 //! #[deriving(Encodable, Decodable)]
  19 //! struct Node { id: uint }
  20 //! ```
  21 //!
  22 //! would generate two implementations like:
  23 //!
  24 //! ```ignore
  25 //! impl<S:serialize::Encoder> Encodable<S> for Node {
  26 //!     fn encode(&self, s: &S) {
  27 //!         s.emit_struct("Node", 1, || {
  28 //!             s.emit_field("id", 0, || s.emit_uint(self.id))
  29 //!         })
  30 //!     }
  31 //! }
  32 //!
  33 //! impl<D:Decoder> Decodable for node_id {
  34 //!     fn decode(d: &D) -> Node {
  35 //!         d.read_struct("Node", 1, || {
  36 //!             Node {
  37 //!                 id: d.read_field("x".to_string(), 0, || decode(d))
  38 //!             }
  39 //!         })
  40 //!     }
  41 //! }
  42 //! ```
  43 //!
  44 //! Other interesting scenarios are when the item has type parameters or
  45 //! references other non-built-in types.  A type definition like:
  46 //!
  47 //! ```ignore
  48 //! #[deriving(Encodable, Decodable)]
  49 //! struct spanned<T> { node: T, span: Span }
  50 //! ```
  51 //!
  52 //! would yield functions like:
  53 //!
  54 //! ```ignore
  55 //!     impl<
  56 //!         S: Encoder,
  57 //!         T: Encodable<S>
  58 //!     > spanned<T>: Encodable<S> {
  59 //!         fn encode<S:Encoder>(s: &S) {
  60 //!             s.emit_rec(|| {
  61 //!                 s.emit_field("node", 0, || self.node.encode(s));
  62 //!                 s.emit_field("span", 1, || self.span.encode(s));
  63 //!             })
  64 //!         }
  65 //!     }
  66 //!
  67 //!     impl<
  68 //!         D: Decoder,
  69 //!         T: Decodable<D>
  70 //!     > spanned<T>: Decodable<D> {
  71 //!         fn decode(d: &D) -> spanned<T> {
  72 //!             d.read_rec(|| {
  73 //!                 {
  74 //!                     node: d.read_field("node".to_string(), 0, || decode(d)),
  75 //!                     span: d.read_field("span".to_string(), 1, || decode(d)),
  76 //!                 }
  77 //!             })
  78 //!         }
  79 //!     }
  80 //! ```
  81
  82 use ast::{MetaItem, Item, Expr, ExprRet, MutMutable, LitNil};
  83 use codemap::Span;
  84 use ext::base::ExtCtxt;
  85 use ext::build::AstBuilder;
  86 use ext::deriving::generic::*;
  87 use ext::deriving::generic::ty::*;
  88 use parse::token;
  89 use ptr::P;
  90
  91 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
  92                                  span: Span,
  93                                  mitem: &MetaItem,
  94                                  item: &Item,
  95                                  push: |P<Item>|) {
  96     let trait_def = TraitDef {
  97         span: span,
  98         attributes: Vec::new(),
  99         path: Path::new_(vec!("serialize", "Encodable"), None,
 100                          vec!(box Literal(Path::new_local("__S")),
 101                               box Literal(Path::new_local("__E"))), true),
 102         additional_bounds: Vec::new(),
 103         generics: LifetimeBounds {
 104             lifetimes: Vec::new(),
 105             bounds: vec!(("__S", None, vec!(Path::new_(
 106                             vec!("serialize", "Encoder"), None,
 107                             vec!(box Literal(Path::new_local("__E"))), true))),
 108                          ("__E", None, vec!()))
 109         },
 110         methods: vec!(
 111             MethodDef {
 112                 name: "encode",
 113                 generics: LifetimeBounds::empty(),
 114                 explicit_self: borrowed_explicit_self(),
 115                 args: vec!(Ptr(box Literal(Path::new_local("__S")),
 116                             Borrowed(None, MutMutable))),
 117                 ret_ty: Literal(Path::new_(vec!("std", "result", "Result"),
 118                                            None,
 119                                            vec!(box Tuple(Vec::new()),
 120                                                 box Literal(Path::new_local("__E"))),
 121                                            true)),
 122                 attributes: Vec::new(),
 123                 combine_substructure: combine_substructure(|a, b, c| {
 124                     encodable_substructure(a, b, c)
 125                 }),
 126             })
 127     };
 128
 129     trait_def.expand(cx, mitem, item, push)
 130 }
 131
 132 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
 133                           substr: &Substructure) -> P<Expr> {
 134     let encoder = substr.nonself_args[0].clone();
 135     // throw an underscore in front to suppress unused variable warnings
 136     let blkarg = cx.ident_of("_e");
 137     let blkencoder = cx.expr_ident(trait_span, blkarg);
 138     let encode = cx.ident_of("encode");
 139
 140     return match *substr.fields {
 141         Struct(ref fields) => {
 142             let emit_struct_field = cx.ident_of("emit_struct_field");
 143             let mut stmts = Vec::new();
 144             let last = fields.len() - 1;
 145             for (i, &FieldInfo {
 146                     name,
 147                     ref self_,
 148                     span,
 149                     ..
 150                 }) in fields.iter().enumerate() {
 151                 let name = match name {
 152                     Some(id) => token::get_ident(id),
 153                     None => {
 154                         token::intern_and_get_ident(format!("_field{}",
 155                                                             i).as_slice())
 156                     }
 157                 };
 158                 let enc = cx.expr_method_call(span, self_.clone(),
 159                                               encode, vec!(blkencoder.clone()));
 160                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 161                 let call = cx.expr_method_call(span, blkencoder.clone(),
 162                                                emit_struct_field,
 163                                                vec!(cx.expr_str(span, name),
 164                                                  cx.expr_uint(span, i),
 165                                                  lambda));
 166
 167                 // last call doesn't need a try!
 168                 let call = if i != last {
 169                     cx.expr_try(span, call)
 170                 } else {
 171                     cx.expr(span, ExprRet(Some(call)))
 172                 };
 173                 stmts.push(cx.stmt_expr(call));
 174             }
 175
 176             // unit structs have no fields and need to return Ok()
 177             if stmts.is_empty() {
 178                 let ret_ok = cx.expr(trait_span,
 179                                      ExprRet(Some(cx.expr_ok(trait_span,
 180                                                              cx.expr_lit(trait_span, LitNil)))));
 181                 stmts.push(cx.stmt_expr(ret_ok));
 182             }
 183
 184             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 185             cx.expr_method_call(trait_span,
 186                                 encoder,
 187                                 cx.ident_of("emit_struct"),
 188                                 vec!(
 189                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 190                 cx.expr_uint(trait_span, fields.len()),
 191                 blk
 192             ))
 193         }
 194
 195         EnumMatching(idx, variant, ref fields) => {
 196             // We're not generating an AST that the borrow checker is expecting,
 197             // so we need to generate a unique local variable to take the
 198             // mutable loan out on, otherwise we get conflicts which don't
 199             // actually exist.
 200             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 201             let encoder = cx.expr_ident(trait_span, blkarg);
 202             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
 203             let mut stmts = Vec::new();
 204             let last = fields.len() - 1;
 205             for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
 206                 let enc = cx.expr_method_call(span, self_.clone(),
 207                                               encode, vec!(blkencoder.clone()));
 208                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 209                 let call = cx.expr_method_call(span, blkencoder.clone(),
 210                                                emit_variant_arg,
 211                                                vec!(cx.expr_uint(span, i),
 212                                                  lambda));
 213                 let call = if i != last {
 214                     cx.expr_try(span, call)
 215                 } else {
 216                     cx.expr(span, ExprRet(Some(call)))
 217                 };
 218                 stmts.push(cx.stmt_expr(call));
 219             }
 220
 221             // enums with no fields need to return Ok()
 222             if stmts.len() == 0 {
 223                 let ret_ok = cx.expr(trait_span,
 224                                      ExprRet(Some(cx.expr_ok(trait_span,
 225                                                              cx.expr_lit(trait_span, LitNil)))));
 226                 stmts.push(cx.stmt_expr(ret_ok));
 227             }
 228
 229             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 230             let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
 231             let call = cx.expr_method_call(trait_span, blkencoder,
 232                                            cx.ident_of("emit_enum_variant"),
 233                                            vec!(name,
 234                                              cx.expr_uint(trait_span, idx),
 235                                              cx.expr_uint(trait_span, fields.len()),
 236                                              blk));
 237             let blk = cx.lambda_expr_1(trait_span, call, blkarg);
 238             let ret = cx.expr_method_call(trait_span,
 239                                           encoder,
 240                                           cx.ident_of("emit_enum"),
 241                                           vec!(
 242                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 243                 blk
 244             ));
 245             cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
 246         }
 247
 248         _ => cx.bug("expected Struct or EnumMatching in deriving(Encodable)")
 249     };
 250 }