src/libsyntax_ext/deriving/encodable.rs

   1 //! The compiler code necessary to implement the `#[derive(Encodable)]`
   2 //! (and `Decodable`, in `decodable.rs`) extension. The idea here is that
   3 //! type-defining items may be tagged with `#[derive(Encodable, Decodable)]`.
   4 //!
   5 //! For example, a type like:
   6 //!
   7 //! ```
   8 //! #[derive(Encodable, Decodable)]
   9 //! struct Node { id: usize }
  10 //! ```
  11 //!
  12 //! would generate two implementations like:
  13 //!
  14 //! ```
  15 //! # struct Node { id: usize }
  16 //! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
  17 //!     fn encode(&self, s: &mut S) -> Result<(), E> {
  18 //!         s.emit_struct("Node", 1, |this| {
  19 //!             this.emit_struct_field("id", 0, |this| {
  20 //!                 Encodable::encode(&self.id, this)
  21 //!                 /* this.emit_usize(self.id) can also be used */
  22 //!             })
  23 //!         })
  24 //!     }
  25 //! }
  26 //!
  27 //! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
  28 //!     fn decode(d: &mut D) -> Result<Node, E> {
  29 //!         d.read_struct("Node", 1, |this| {
  30 //!             match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
  31 //!                 Ok(id) => Ok(Node { id: id }),
  32 //!                 Err(e) => Err(e),
  33 //!             }
  34 //!         })
  35 //!     }
  36 //! }
  37 //! ```
  38 //!
  39 //! Other interesting scenarios are when the item has type parameters or
  40 //! references other non-built-in types. A type definition like:
  41 //!
  42 //! ```
  43 //! # #[derive(Encodable, Decodable)] struct Span;
  44 //! #[derive(Encodable, Decodable)]
  45 //! struct Spanned<T> { node: T, span: Span }
  46 //! ```
  47 //!
  48 //! would yield functions like:
  49 //!
  50 //! ```
  51 //! # #[derive(Encodable, Decodable)] struct Span;
  52 //! # struct Spanned<T> { node: T, span: Span }
  53 //! impl<
  54 //!     S: Encoder<E>,
  55 //!     E,
  56 //!     T: Encodable<S, E>
  57 //! > Encodable<S, E> for Spanned<T> {
  58 //!     fn encode(&self, s: &mut S) -> Result<(), E> {
  59 //!         s.emit_struct("Spanned", 2, |this| {
  60 //!             this.emit_struct_field("node", 0, |this| self.node.encode(this))
  61 //!                 .unwrap();
  62 //!             this.emit_struct_field("span", 1, |this| self.span.encode(this))
  63 //!         })
  64 //!     }
  65 //! }
  66 //!
  67 //! impl<
  68 //!     D: Decoder<E>,
  69 //!     E,
  70 //!     T: Decodable<D, E>
  71 //! > Decodable<D, E> for Spanned<T> {
  72 //!     fn decode(d: &mut D) -> Result<Spanned<T>, E> {
  73 //!         d.read_struct("Spanned", 2, |this| {
  74 //!             Ok(Spanned {
  75 //!                 node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
  76 //!                     .unwrap(),
  77 //!                 span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
  78 //!                     .unwrap(),
  79 //!             })
  80 //!         })
  81 //!     }
  82 //! }
  83 //! ```
  84
  85 use crate::deriving::{self, pathvec_std};
  86 use crate::deriving::generic::*;
  87 use crate::deriving::generic::ty::*;
  88
  89 use syntax::ast::{Expr, ExprKind, MetaItem, Mutability};
  90 use syntax::ext::base::{Annotatable, ExtCtxt};
  91 use syntax::ptr::P;
  92 use syntax::symbol::Symbol;
  93 use syntax_pos::Span;
  94
  95 pub fn expand_deriving_rustc_encodable(cx: &mut ExtCtxt<'_>,
  96                                        span: Span,
  97                                        mitem: &MetaItem,
  98                                        item: &Annotatable,
  99                                        push: &mut dyn FnMut(Annotatable)) {
 100     expand_deriving_encodable_imp(cx, span, mitem, item, push, "rustc_serialize")
 101 }
 102
 103 pub fn expand_deriving_encodable(cx: &mut ExtCtxt<'_>,
 104                                  span: Span,
 105                                  mitem: &MetaItem,
 106                                  item: &Annotatable,
 107                                  push: &mut dyn FnMut(Annotatable)) {
 108     expand_deriving_encodable_imp(cx, span, mitem, item, push, "serialize")
 109 }
 110
 111 fn expand_deriving_encodable_imp(cx: &mut ExtCtxt<'_>,
 112                                  span: Span,
 113                                  mitem: &MetaItem,
 114                                  item: &Annotatable,
 115                                  push: &mut dyn FnMut(Annotatable),
 116                                  krate: &'static str) {
 117     let typaram = &*deriving::hygienic_type_parameter(item, "__S");
 118
 119     let trait_def = TraitDef {
 120         span,
 121         attributes: Vec::new(),
 122         path: Path::new_(vec![krate, "Encodable"], None, vec![], PathKind::Global),
 123         additional_bounds: Vec::new(),
 124         generics: LifetimeBounds::empty(),
 125         is_unsafe: false,
 126         supports_unions: false,
 127         methods: vec![
 128             MethodDef {
 129                 name: "encode",
 130                 generics: LifetimeBounds {
 131                     lifetimes: Vec::new(),
 132                     bounds: vec![
 133                         (typaram,
 134                          vec![Path::new_(vec![krate, "Encoder"], None, vec![], PathKind::Global)])
 135                     ],
 136                 },
 137                 explicit_self: borrowed_explicit_self(),
 138                 args: vec![(Ptr(Box::new(Literal(Path::new_local(typaram))),
 139                            Borrowed(None, Mutability::Mutable)), "s")],
 140                 ret_ty: Literal(Path::new_(
 141                     pathvec_std!(cx, result::Result),
 142                     None,
 143                     vec![Box::new(Tuple(Vec::new())), Box::new(Literal(Path::new_(
 144                         vec![typaram, "Error"], None, vec![], PathKind::Local
 145                     )))],
 146                     PathKind::Std
 147                 )),
 148                 attributes: Vec::new(),
 149                 is_unsafe: false,
 150                 unify_fieldless_variants: false,
 151                 combine_substructure: combine_substructure(Box::new(|a, b, c| {
 152                     encodable_substructure(a, b, c, krate)
 153                 })),
 154             }
 155         ],
 156         associated_types: Vec::new(),
 157     };
 158
 159     trait_def.expand(cx, mitem, item, push)
 160 }
 161
 162 fn encodable_substructure(cx: &mut ExtCtxt<'_>,
 163                           trait_span: Span,
 164                           substr: &Substructure<'_>,
 165                           krate: &'static str)
 166                           -> P<Expr> {
 167     let encoder = substr.nonself_args[0].clone();
 168     // throw an underscore in front to suppress unused variable warnings
 169     let blkarg = cx.ident_of("_e");
 170     let blkencoder = cx.expr_ident(trait_span, blkarg);
 171     let fn_path = cx.expr_path(cx.path_global(trait_span,
 172                                               vec![cx.ident_of(krate),
 173                                                    cx.ident_of("Encodable"),
 174                                                    cx.ident_of("encode")]));
 175
 176     return match *substr.fields {
 177         Struct(_, ref fields) => {
 178             let emit_struct_field = cx.ident_of("emit_struct_field");
 179             let mut stmts = Vec::new();
 180             for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
 181                 let name = match name {
 182                     Some(id) => id.name,
 183                     None => Symbol::intern(&format!("_field{}", i)),
 184                 };
 185                 let self_ref = cx.expr_addr_of(span, self_.clone());
 186                 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
 187                 let lambda = cx.lambda1(span, enc, blkarg);
 188                 let call = cx.expr_method_call(span,
 189                                                blkencoder.clone(),
 190                                                emit_struct_field,
 191                                                vec![cx.expr_str(span, name),
 192                                                     cx.expr_usize(span, i),
 193                                                     lambda]);
 194
 195                 // last call doesn't need a try!
 196                 let last = fields.len() - 1;
 197                 let call = if i != last {
 198                     cx.expr_try(span, call)
 199                 } else {
 200                     cx.expr(span, ExprKind::Ret(Some(call)))
 201                 };
 202
 203                 let stmt = cx.stmt_expr(call);
 204                 stmts.push(stmt);
 205             }
 206
 207             // unit structs have no fields and need to return Ok()
 208             let blk = if stmts.is_empty() {
 209                 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
 210                 cx.lambda1(trait_span, ok, blkarg)
 211             } else {
 212                 cx.lambda_stmts_1(trait_span, stmts, blkarg)
 213             };
 214
 215             cx.expr_method_call(trait_span,
 216                                 encoder,
 217                                 cx.ident_of("emit_struct"),
 218                                 vec![cx.expr_str(trait_span, substr.type_ident.name),
 219                                      cx.expr_usize(trait_span, fields.len()),
 220                                      blk])
 221         }
 222
 223         EnumMatching(idx, _, variant, ref fields) => {
 224             // We're not generating an AST that the borrow checker is expecting,
 225             // so we need to generate a unique local variable to take the
 226             // mutable loan out on, otherwise we get conflicts which don't
 227             // actually exist.
 228             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 229             let encoder = cx.expr_ident(trait_span, blkarg);
 230             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
 231             let mut stmts = Vec::new();
 232             if !fields.is_empty() {
 233                 let last = fields.len() - 1;
 234                 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
 235                     let self_ref = cx.expr_addr_of(span, self_.clone());
 236                     let enc =
 237                         cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
 238                     let lambda = cx.lambda1(span, enc, blkarg);
 239                     let call = cx.expr_method_call(span,
 240                                                    blkencoder.clone(),
 241                                                    emit_variant_arg,
 242                                                    vec![cx.expr_usize(span, i), lambda]);
 243                     let call = if i != last {
 244                         cx.expr_try(span, call)
 245                     } else {
 246                         cx.expr(span, ExprKind::Ret(Some(call)))
 247                     };
 248                     stmts.push(cx.stmt_expr(call));
 249                 }
 250             } else {
 251                 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
 252                 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
 253                 stmts.push(cx.stmt_expr(ret_ok));
 254             }
 255
 256             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 257             let name = cx.expr_str(trait_span, variant.node.ident.name);
 258             let call = cx.expr_method_call(trait_span,
 259                                            blkencoder,
 260                                            cx.ident_of("emit_enum_variant"),
 261                                            vec![name,
 262                                                 cx.expr_usize(trait_span, idx),
 263                                                 cx.expr_usize(trait_span, fields.len()),
 264                                                 blk]);
 265             let blk = cx.lambda1(trait_span, call, blkarg);
 266             let ret = cx.expr_method_call(trait_span,
 267                                           encoder,
 268                                           cx.ident_of("emit_enum"),
 269                                           vec![cx.expr_str(trait_span ,substr.type_ident.name),
 270                                                blk]);
 271             cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
 272         }
 273
 274         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
 275     };
 276 }