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 deriving;
  92 use deriving::generic::*;
  93 use deriving::generic::ty::*;
  94
  95 use syntax::ast::{MetaItem, Expr, ExprKind, Mutability};
  96 use syntax::ext::base::{ExtCtxt,Annotatable};
  97 use syntax::ext::build::AstBuilder;
  98 use syntax::parse::token;
  99 use syntax::ptr::P;
 100 use syntax_pos::Span;
 101
 102 pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt,
 103                                        span: Span,
 104                                        mitem: &MetaItem,
 105                                        item: &Annotatable,
 106                                        push: &mut FnMut(Annotatable))
 107 {
 108     expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
 109 }
 110
 111 pub fn expand_deriving_encodable(cx: &mut ExtCtxt,
 112                                  span: Span,
 113                                  mitem: &MetaItem,
 114                                  item: &Annotatable,
 115                                  push: &mut FnMut(Annotatable))
 116 {
 117     expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
 118 }
 119
 120 fn expand_deriving_encodable_imp(cx: &mut ExtCtxt,
 121                                  span: Span,
 122                                  mitem: &MetaItem,
 123                                  item: &Annotatable,
 124                                  push: &mut FnMut(Annotatable),
 125                                  krate: &'static str)
 126 {
 127     if cx.crate_root != Some("std") {
 128         // FIXME(#21880): lift this requirement.
 129         cx.span_err(span, "this trait cannot be derived with #![no_std] \
 130                            or #![no_core]");
 131         return;
 132     }
 133
 134     let typaram = &*deriving::hygienic_type_parameter(item, "__S");
 135
 136     let trait_def = TraitDef {
 137         span: span,
 138         attributes: Vec::new(),
 139         path: Path::new_(vec!(krate, "Encodable"), None, vec!(), true),
 140         additional_bounds: Vec::new(),
 141         generics: LifetimeBounds::empty(),
 142         is_unsafe: false,
 143         methods: vec!(
 144             MethodDef {
 145                 name: "encode",
 146                 generics: LifetimeBounds {
 147                     lifetimes: Vec::new(),
 148                     bounds: vec![(typaram,
 149                                   vec![Path::new_(vec![krate, "Encoder"], None, vec!(), true)])]
 150                 },
 151                 explicit_self: borrowed_explicit_self(),
 152                 args: vec!(Ptr(Box::new(Literal(Path::new_local(typaram))),
 153                            Borrowed(None, Mutability::Mutable))),
 154                 ret_ty: Literal(Path::new_(
 155                     pathvec_std!(cx, core::result::Result),
 156                     None,
 157                     vec!(Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
 158                         vec![typaram, "Error"], None, vec![], false
 159                     )))),
 160                     true
 161                 )),
 162                 attributes: Vec::new(),
 163                 is_unsafe: false,
 164                 unify_fieldless_variants: false,
 165                 combine_substructure: combine_substructure(Box::new(|a, b, c| {
 166                     encodable_substructure(a, b, c, krate)
 167                 })),
 168             }
 169         ),
 170         associated_types: Vec::new(),
 171     };
 172
 173     trait_def.expand(cx, mitem, item, push)
 174 }
 175
 176 fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
 177                           substr: &Substructure, krate: &'static str) -> P<Expr> {
 178     let encoder = substr.nonself_args[0].clone();
 179     // throw an underscore in front to suppress unused variable warnings
 180     let blkarg = cx.ident_of("_e");
 181     let blkencoder = cx.expr_ident(trait_span, blkarg);
 182     let fn_path = cx.expr_path(cx.path_global(trait_span, vec![cx.ident_of(krate),
 183                                                                cx.ident_of("Encodable"),
 184                                                                cx.ident_of("encode")]));
 185
 186     return match *substr.fields {
 187         Struct(_, ref fields) => {
 188             let emit_struct_field = cx.ident_of("emit_struct_field");
 189             let mut stmts = Vec::new();
 190             for (i, &FieldInfo {
 191                     name,
 192                     ref self_,
 193                     span,
 194                     ..
 195                 }) in fields.iter().enumerate() {
 196                 let name = match name {
 197                     Some(id) => id.name.as_str(),
 198                     None => {
 199                         token::intern_and_get_ident(&format!("_field{}", i))
 200                     }
 201                 };
 202                 let self_ref = cx.expr_addr_of(span, self_.clone());
 203                 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
 204                 let lambda = cx.lambda_expr_1(span, enc, blkarg);
 205                 let call = cx.expr_method_call(span, blkencoder.clone(),
 206                                                emit_struct_field,
 207                                                vec!(cx.expr_str(span, name),
 208                                                  cx.expr_usize(span, i),
 209                                                  lambda));
 210
 211                 // last call doesn't need a try!
 212                 let last = fields.len() - 1;
 213                 let call = if i != last {
 214                     cx.expr_try(span, call)
 215                 } else {
 216                     cx.expr(span, ExprKind::Ret(Some(call)))
 217                 };
 218                 stmts.push(cx.stmt_expr(call));
 219             }
 220
 221             // unit structs have no fields and need to return Ok()
 222             if stmts.is_empty() {
 223                 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
 224                 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
 225                 stmts.push(cx.stmt_expr(ret_ok));
 226             }
 227
 228             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 229             cx.expr_method_call(trait_span,
 230                                 encoder,
 231                                 cx.ident_of("emit_struct"),
 232                                 vec!(
 233                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
 234                 cx.expr_usize(trait_span, fields.len()),
 235                 blk
 236             ))
 237         }
 238
 239         EnumMatching(idx, variant, ref fields) => {
 240             // We're not generating an AST that the borrow checker is expecting,
 241             // so we need to generate a unique local variable to take the
 242             // mutable loan out on, otherwise we get conflicts which don't
 243             // actually exist.
 244             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 245             let encoder = cx.expr_ident(trait_span, blkarg);
 246             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
 247             let mut stmts = Vec::new();
 248             if !fields.is_empty() {
 249                 let last = fields.len() - 1;
 250                 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
 251                 let self_ref = cx.expr_addr_of(span, self_.clone());
 252                     let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref,
 253                                                                        blkencoder.clone()]);
 254                     let lambda = cx.lambda_expr_1(span, enc, blkarg);
 255                     let call = cx.expr_method_call(span, blkencoder.clone(),
 256                                                    emit_variant_arg,
 257                                                    vec!(cx.expr_usize(span, i),
 258                                                         lambda));
 259                     let call = if i != last {
 260                         cx.expr_try(span, call)
 261                     } else {
 262                         cx.expr(span, ExprKind::Ret(Some(call)))
 263                     };
 264                     stmts.push(cx.stmt_expr(call));
 265                 }
 266             } else {
 267                 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
 268                 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
 269                 stmts.push(cx.stmt_expr(ret_ok));
 270             }
 271
 272             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 273             let name = cx.expr_str(trait_span, variant.node.name.name.as_str());
 274             let call = cx.expr_method_call(trait_span, blkencoder,
 275                                            cx.ident_of("emit_enum_variant"),
 276                                            vec!(name,
 277                                              cx.expr_usize(trait_span, idx),
 278                                              cx.expr_usize(trait_span, fields.len()),
 279                                              blk));
 280             let blk = cx.lambda_expr_1(trait_span, call, blkarg);
 281             let ret = cx.expr_method_call(trait_span,
 282                                           encoder,
 283                                           cx.ident_of("emit_enum"),
 284                                           vec!(
 285                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
 286                 blk
 287             ));
 288             cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
 289         }
 290
 291         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)")
 292     };
 293 }