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 `#[derive(Encodable)]`
  12 //! (and `Decodable`, in decodable.rs) extension.  The idea here is that
  13 //! type-defining items may be tagged with `#[derive(Encodable, Decodable)]`.
  14 //!
  15 //! For example, a type like:
  16 //!
  17 //! ```ignore
  18 //! #[derive(Encodable, Decodable)]
  19 //! struct Node { id: usize }
  20 //! ```
  21 //!
  22 //! would generate two implementations like:
  23 //!
  24 //! ```ignore
  25 //! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
  26 //!     fn encode(&self, s: &mut S) -> Result<(), E> {
  27 //!         s.emit_struct("Node", 1, |this| {
  28 //!             this.emit_struct_field("id", 0, |this| {
  29 //!                 Encodable::encode(&self.id, this)
  30 //!                 /* this.emit_usize(self.id) can also be used */
  31 //!             })
  32 //!         })
  33 //!     }
  34 //! }
  35 //!
  36 //! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
  37 //!     fn decode(d: &mut D) -> Result<Node, E> {
  38 //!         d.read_struct("Node", 1, |this| {
  39 //!             match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
  40 //!                 Ok(id) => Ok(Node { id: id }),
  41 //!                 Err(e) => Err(e),
  42 //!             }
  43 //!         })
  44 //!     }
  45 //! }
  46 //! ```
  47 //!
  48 //! Other interesting scenarios are when the item has type parameters or
  49 //! references other non-built-in types.  A type definition like:
  50 //!
  51 //! ```ignore
  52 //! #[derive(Encodable, Decodable)]
  53 //! struct Spanned<T> { node: T, span: Span }
  54 //! ```
  55 //!
  56 //! would yield functions like:
  57 //!
  58 //! ```ignore
  59 //! impl<
  60 //!     S: Encoder<E>,
  61 //!     E,
  62 //!     T: Encodable<S, E>
  63 //! > Encodable<S, E> for Spanned<T> {
  64 //!     fn encode(&self, s: &mut S) -> Result<(), E> {
  65 //!         s.emit_struct("Spanned", 2, |this| {
  66 //!             this.emit_struct_field("node", 0, |this| self.node.encode(this))
  67 //!                 .unwrap();
  68 //!             this.emit_struct_field("span", 1, |this| self.span.encode(this))
  69 //!         })
  70 //!     }
  71 //! }
  72 //!
  73 //! impl<
  74 //!     D: Decoder<E>,
  75 //!     E,
  76 //!     T: Decodable<D, E>
  77 //! > Decodable<D, E> for Spanned<T> {
  78 //!     fn decode(d: &mut D) -> Result<Spanned<T>, E> {
  79 //!         d.read_struct("Spanned", 2, |this| {
  80 //!             Ok(Spanned {
  81 //!                 node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
  82 //!                     .unwrap(),
  83 //!                 span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
  84 //!                     .unwrap(),
  85 //!             })
  86 //!         })
  87 //!     }
  88 //! }
  89 //! ```
  90
  91 use ast::{MetaItem, Expr, ExprRet, MutMutable};
  92 use codemap::Span;
  93 use ext::base::{ExtCtxt,Annotatable};
  94 use ext::build::AstBuilder;
  95 use ext::deriving::generic::*;
  96 use ext::deriving::generic::ty::*;
  97 use parse::token;
  98 use ptr::P;
  99
 100 pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt,
 101                                        span: Span,
 102                                        mitem: &MetaItem,
 103                                        item: Annotatable,
 104                                        push: &mut FnMut(Annotatable))
 105 {
 106     expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
 107 }
 108
 109 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
 110                                  span: Span,
 111                                  mitem: &MetaItem,
 112                                  item: Annotatable,
 113                                  push: &mut FnMut(Annotatable))
 114 {
 115     expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
 116 }
 117
 118 fn expand_deriving_encodable_imp(cx: &mut ExtCtxt,
 119                                  span: Span,
 120                                  mitem: &MetaItem,
 121                                  item: Annotatable,
 122                                  push: &mut FnMut(Annotatable),
 123                                  krate: &'static str)
 124 {
 125     if !cx.use_std {
 126         // FIXME(#21880): lift this requirement.
 127         cx.span_err(span, "this trait cannot be derived with #![no_std]");
 128         return;
 129     }
 130
 131     let trait_def = TraitDef {
 132         span: span,
 133         attributes: Vec::new(),
 134         path: Path::new_(vec!(krate, "Encodable"), None, vec!(), true),
 135         additional_bounds: Vec::new(),
 136         generics: LifetimeBounds::empty(),
 137         methods: vec!(
 138             MethodDef {
 139                 name: "encode",
 140                 generics: LifetimeBounds {
 141                     lifetimes: Vec::new(),
 142                     bounds: vec!(("__S", vec!(Path::new_(
 143                                     vec!(krate, "Encoder"), None,
 144                                     vec!(), true))))
 145                 },
 146                 explicit_self: borrowed_explicit_self(),
 147                 args: vec!(Ptr(Box::new(Literal(Path::new_local("__S"))),
 148                             Borrowed(None, MutMutable))),
 149                 ret_ty: Literal(Path::new_(
 150                     pathvec_std!(cx, core::result::Result),
 151                     None,
 152                     vec!(Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
 153                         vec!["__S", "Error"], None, vec![], false
 154                     )))),
 155                     true
 156                 )),
 157                 attributes: Vec::new(),
 158                 combine_substructure: combine_substructure(Box::new(|a, b, c| {
 159                     encodable_substructure(a, b, c)
 160                 })),
 161             }
 162         ),
 163         associated_types: Vec::new(),
 164     };
 165
 166     trait_def.expand(cx, mitem, &item, push)
 167 }
 168
 169 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
 170                           substr: &Substructure) -> P<Expr> {
 171     let encoder = substr.nonself_args[0].clone();
 172     // throw an underscore in front to suppress unused variable warnings
 173     let blkarg = cx.ident_of("_e");
 174     let blkencoder = cx.expr_ident(trait_span, blkarg);
 175     let encode = cx.ident_of("encode");
 176
 177     return match *substr.fields {
 178         Struct(ref fields) => {
 179             let emit_struct_field = cx.ident_of("emit_struct_field");
 180             let mut stmts = Vec::new();
 181             for (i, &FieldInfo {
 182                     name,
 183                     ref self_,
 184                     span,
 185                     ..
 186                 }) in fields.iter().enumerate() {
 187                 let name = match name {
 188                     Some(id) => token::get_ident(id),
 189                     None => {
 190                         token::intern_and_get_ident(&format!("_field{}", i))
 191                     }
 192                 };
 193                 let enc = cx.expr_method_call(span, self_.clone(),
 194                                               encode, vec!(blkencoder.clone()));
 195                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 196                 let call = cx.expr_method_call(span, blkencoder.clone(),
 197                                                emit_struct_field,
 198                                                vec!(cx.expr_str(span, name),
 199                                                  cx.expr_usize(span, i),
 200                                                  lambda));
 201
 202                 // last call doesn't need a try!
 203                 let last = fields.len() - 1;
 204                 let call = if i != last {
 205                     cx.expr_try(span, call)
 206                 } else {
 207                     cx.expr(span, ExprRet(Some(call)))
 208                 };
 209                 stmts.push(cx.stmt_expr(call));
 210             }
 211
 212             // unit structs have no fields and need to return Ok()
 213             if stmts.is_empty() {
 214                 let ret_ok = cx.expr(trait_span,
 215                                      ExprRet(Some(cx.expr_ok(trait_span,
 216                                                              cx.expr_tuple(trait_span, vec![])))));
 217                 stmts.push(cx.stmt_expr(ret_ok));
 218             }
 219
 220             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 221             cx.expr_method_call(trait_span,
 222                                 encoder,
 223                                 cx.ident_of("emit_struct"),
 224                                 vec!(
 225                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 226                 cx.expr_usize(trait_span, fields.len()),
 227                 blk
 228             ))
 229         }
 230
 231         EnumMatching(idx, variant, ref fields) => {
 232             // We're not generating an AST that the borrow checker is expecting,
 233             // so we need to generate a unique local variable to take the
 234             // mutable loan out on, otherwise we get conflicts which don't
 235             // actually exist.
 236             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 237             let encoder = cx.expr_ident(trait_span, blkarg);
 238             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
 239             let mut stmts = Vec::new();
 240             if !fields.is_empty() {
 241                 let last = fields.len() - 1;
 242                 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
 243                     let enc = cx.expr_method_call(span, self_.clone(),
 244                                                   encode, vec!(blkencoder.clone()));
 245                     let lambda = cx.lambda_expr_1(span, enc, blkarg);
 246                     let call = cx.expr_method_call(span, blkencoder.clone(),
 247                                                    emit_variant_arg,
 248                                                    vec!(cx.expr_usize(span, i),
 249                                                         lambda));
 250                     let call = if i != last {
 251                         cx.expr_try(span, call)
 252                     } else {
 253                         cx.expr(span, ExprRet(Some(call)))
 254                     };
 255                     stmts.push(cx.stmt_expr(call));
 256                 }
 257             } else {
 258                 let ret_ok = cx.expr(trait_span,
 259                                      ExprRet(Some(cx.expr_ok(trait_span,
 260                                                              cx.expr_tuple(trait_span, vec![])))));
 261                 stmts.push(cx.stmt_expr(ret_ok));
 262             }
 263
 264             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 265             let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
 266             let call = cx.expr_method_call(trait_span, blkencoder,
 267                                            cx.ident_of("emit_enum_variant"),
 268                                            vec!(name,
 269                                              cx.expr_usize(trait_span, idx),
 270                                              cx.expr_usize(trait_span, fields.len()),
 271                                              blk));
 272             let blk = cx.lambda_expr_1(trait_span, call, blkarg);
 273             let ret = cx.expr_method_call(trait_span,
 274                                           encoder,
 275                                           cx.ident_of("emit_enum"),
 276                                           vec!(
 277                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 278                 blk
 279             ));
 280             cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
 281         }
 282
 283         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)")
 284     };
 285 }