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 //!                 .ok().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 //!                     .ok().unwrap(),
  83 //!                 span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
  84 //!                     .ok().unwrap(),
  85 //!             })
  86 //!         })
  87 //!     }
  88 //! }
  89 //! ```
  90
  91 use ast::{MetaItem, Item, Expr, ExprRet, MutMutable};
  92 use codemap::Span;
  93 use ext::base::ExtCtxt;
  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<F>(cx: &mut ExtCtxt,
 101                                           span: Span,
 102                                           mitem: &MetaItem,
 103                                           item: &Item,
 104                                           push: F) where
 105     F: FnOnce(P<Item>),
 106 {
 107     expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
 108 }
 109
 110 pub fn expand_deriving_encodable<F>(cx: &mut ExtCtxt,
 111                                     span: Span,
 112                                     mitem: &MetaItem,
 113                                     item: &Item,
 114                                     push: F) where
 115     F: FnOnce(P<Item>),
 116 {
 117     expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
 118 }
 119
 120 fn expand_deriving_encodable_imp<F>(cx: &mut ExtCtxt,
 121                                     span: Span,
 122                                     mitem: &MetaItem,
 123                                     item: &Item,
 124                                     push: F,
 125                                     krate: &'static str) where
 126     F: FnOnce(P<Item>),
 127 {
 128     let trait_def = TraitDef {
 129         span: span,
 130         attributes: Vec::new(),
 131         path: Path::new_(vec!(krate, "Encodable"), None, vec!(), true),
 132         additional_bounds: Vec::new(),
 133         generics: LifetimeBounds::empty(),
 134         methods: vec!(
 135             MethodDef {
 136                 name: "encode",
 137                 generics: LifetimeBounds {
 138                     lifetimes: Vec::new(),
 139                     bounds: vec!(("__S", vec!(Path::new_(
 140                                     vec!(krate, "Encoder"), None,
 141                                     vec!(), true))))
 142                 },
 143                 explicit_self: borrowed_explicit_self(),
 144                 args: vec!(Ptr(box Literal(Path::new_local("__S")),
 145                             Borrowed(None, MutMutable))),
 146                 ret_ty: Literal(Path::new_(
 147                     vec!("std", "result", "Result"),
 148                     None,
 149                     vec!(box Tuple(Vec::new()), box Literal(Path::new_(
 150                         vec!["__S", "Error"], None, vec![], false
 151                     ))),
 152                     true
 153                 )),
 154                 attributes: Vec::new(),
 155                 combine_substructure: combine_substructure(box |a, b, c| {
 156                     encodable_substructure(a, b, c)
 157                 }),
 158             }
 159         ),
 160         associated_types: Vec::new(),
 161     };
 162
 163     trait_def.expand(cx, mitem, item, push)
 164 }
 165
 166 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
 167                           substr: &Substructure) -> P<Expr> {
 168     let encoder = substr.nonself_args[0].clone();
 169     // throw an underscore in front to suppress unused variable warnings
 170     let blkarg = cx.ident_of("_e");
 171     let blkencoder = cx.expr_ident(trait_span, blkarg);
 172     let encode = cx.ident_of("encode");
 173
 174     return match *substr.fields {
 175         Struct(ref fields) => {
 176             let emit_struct_field = cx.ident_of("emit_struct_field");
 177             let mut stmts = Vec::new();
 178             let last = fields.len() - 1;
 179             for (i, &FieldInfo {
 180                     name,
 181                     ref self_,
 182                     span,
 183                     ..
 184                 }) in fields.iter().enumerate() {
 185                 let name = match name {
 186                     Some(id) => token::get_ident(id),
 187                     None => {
 188                         token::intern_and_get_ident(&format!("_field{}", i)[])
 189                     }
 190                 };
 191                 let enc = cx.expr_method_call(span, self_.clone(),
 192                                               encode, vec!(blkencoder.clone()));
 193                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 194                 let call = cx.expr_method_call(span, blkencoder.clone(),
 195                                                emit_struct_field,
 196                                                vec!(cx.expr_str(span, name),
 197                                                  cx.expr_usize(span, i),
 198                                                  lambda));
 199
 200                 // last call doesn't need a try!
 201                 let call = if i != last {
 202                     cx.expr_try(span, call)
 203                 } else {
 204                     cx.expr(span, ExprRet(Some(call)))
 205                 };
 206                 stmts.push(cx.stmt_expr(call));
 207             }
 208
 209             // unit structs have no fields and need to return Ok()
 210             if stmts.is_empty() {
 211                 let ret_ok = cx.expr(trait_span,
 212                                      ExprRet(Some(cx.expr_ok(trait_span,
 213                                                              cx.expr_tuple(trait_span, vec![])))));
 214                 stmts.push(cx.stmt_expr(ret_ok));
 215             }
 216
 217             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 218             cx.expr_method_call(trait_span,
 219                                 encoder,
 220                                 cx.ident_of("emit_struct"),
 221                                 vec!(
 222                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 223                 cx.expr_usize(trait_span, fields.len()),
 224                 blk
 225             ))
 226         }
 227
 228         EnumMatching(idx, variant, ref fields) => {
 229             // We're not generating an AST that the borrow checker is expecting,
 230             // so we need to generate a unique local variable to take the
 231             // mutable loan out on, otherwise we get conflicts which don't
 232             // actually exist.
 233             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 234             let encoder = cx.expr_ident(trait_span, blkarg);
 235             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
 236             let mut stmts = Vec::new();
 237             let last = fields.len() - 1;
 238             for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
 239                 let enc = cx.expr_method_call(span, self_.clone(),
 240                                               encode, vec!(blkencoder.clone()));
 241                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 242                 let call = cx.expr_method_call(span, blkencoder.clone(),
 243                                                emit_variant_arg,
 244                                                vec!(cx.expr_usize(span, i),
 245                                                  lambda));
 246                 let call = if i != last {
 247                     cx.expr_try(span, call)
 248                 } else {
 249                     cx.expr(span, ExprRet(Some(call)))
 250                 };
 251                 stmts.push(cx.stmt_expr(call));
 252             }
 253
 254             // enums with no fields need to return Ok()
 255             if stmts.len() == 0 {
 256                 let ret_ok = cx.expr(trait_span,
 257                                      ExprRet(Some(cx.expr_ok(trait_span,
 258                                                              cx.expr_tuple(trait_span, vec![])))));
 259                 stmts.push(cx.stmt_expr(ret_ok));
 260             }
 261
 262             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 263             let name = cx.expr_str(trait_span, token::get_ident(variant.node.name));
 264             let call = cx.expr_method_call(trait_span, blkencoder,
 265                                            cx.ident_of("emit_enum_variant"),
 266                                            vec!(name,
 267                                              cx.expr_usize(trait_span, idx),
 268                                              cx.expr_usize(trait_span, fields.len()),
 269                                              blk));
 270             let blk = cx.lambda_expr_1(trait_span, call, blkarg);
 271             let ret = cx.expr_method_call(trait_span,
 272                                           encoder,
 273                                           cx.ident_of("emit_enum"),
 274                                           vec!(
 275                 cx.expr_str(trait_span, token::get_ident(substr.type_ident)),
 276                 blk
 277             ));
 278             cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
 279         }
 280
 281         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)")
 282     };
 283 }