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