compiler/rustc_builtin_macros/src/deriving/encodable.rs

   1 //! The compiler code necessary to implement the `#[derive(RustcEncodable)]`
   2 //! (and `RustcDecodable`, in `decodable.rs`) extension. The idea here is that
   3 //! type-defining items may be tagged with
   4 //! `#[derive(RustcEncodable, RustcDecodable)]`.
   5 //!
   6 //! For example, a type like:
   7 //!
   8 //! ```ignore (old code)
   9 //! #[derive(RustcEncodable, RustcDecodable)]
  10 //! struct Node { id: usize }
  11 //! ```
  12 //!
  13 //! would generate two implementations like:
  14 //!
  15 //! ```ignore (old code)
  16 //! # struct Node { id: usize }
  17 //! impl<S: Encoder<E>, E> Encodable<S, E> for Node {
  18 //!     fn encode(&self, s: &mut S) -> Result<(), E> {
  19 //!         s.emit_struct("Node", 1, |this| {
  20 //!             this.emit_struct_field("id", 0, |this| {
  21 //!                 Encodable::encode(&self.id, this)
  22 //!                 /* this.emit_usize(self.id) can also be used */
  23 //!             })
  24 //!         })
  25 //!     }
  26 //! }
  27 //!
  28 //! impl<D: Decoder<E>, E> Decodable<D, E> for Node {
  29 //!     fn decode(d: &mut D) -> Result<Node, E> {
  30 //!         d.read_struct("Node", 1, |this| {
  31 //!             match this.read_struct_field("id", 0, |this| Decodable::decode(this)) {
  32 //!                 Ok(id) => Ok(Node { id: id }),
  33 //!                 Err(e) => Err(e),
  34 //!             }
  35 //!         })
  36 //!     }
  37 //! }
  38 //! ```
  39 //!
  40 //! Other interesting scenarios are when the item has type parameters or
  41 //! references other non-built-in types. A type definition like:
  42 //!
  43 //! ```ignore (old code)
  44 //! # #[derive(RustcEncodable, RustcDecodable)]
  45 //! # struct Span;
  46 //! #[derive(RustcEncodable, RustcDecodable)]
  47 //! struct Spanned<T> { node: T, span: Span }
  48 //! ```
  49 //!
  50 //! would yield functions like:
  51 //!
  52 //! ```ignore (old code)
  53 //! # #[derive(RustcEncodable, RustcDecodable)]
  54 //! # struct Span;
  55 //! # struct Spanned<T> { node: T, span: Span }
  56 //! impl<
  57 //!     S: Encoder<E>,
  58 //!     E,
  59 //!     T: Encodable<S, E>
  60 //! > Encodable<S, E> for Spanned<T> {
  61 //!     fn encode(&self, s: &mut S) -> Result<(), E> {
  62 //!         s.emit_struct("Spanned", 2, |this| {
  63 //!             this.emit_struct_field("node", 0, |this| self.node.encode(this))
  64 //!                 .unwrap();
  65 //!             this.emit_struct_field("span", 1, |this| self.span.encode(this))
  66 //!         })
  67 //!     }
  68 //! }
  69 //!
  70 //! impl<
  71 //!     D: Decoder<E>,
  72 //!     E,
  73 //!     T: Decodable<D, E>
  74 //! > Decodable<D, E> for Spanned<T> {
  75 //!     fn decode(d: &mut D) -> Result<Spanned<T>, E> {
  76 //!         d.read_struct("Spanned", 2, |this| {
  77 //!             Ok(Spanned {
  78 //!                 node: this.read_struct_field("node", 0, |this| Decodable::decode(this))
  79 //!                     .unwrap(),
  80 //!                 span: this.read_struct_field("span", 1, |this| Decodable::decode(this))
  81 //!                     .unwrap(),
  82 //!             })
  83 //!         })
  84 //!     }
  85 //! }
  86 //! ```
  87
  88 use crate::deriving::generic::ty::*;
  89 use crate::deriving::generic::*;
  90 use crate::deriving::pathvec_std;
  91
  92 use rustc_ast::{AttrVec, ExprKind, MetaItem, Mutability};
  93 use rustc_expand::base::{Annotatable, ExtCtxt};
  94 use rustc_span::symbol::{sym, Ident, Symbol};
  95 use rustc_span::Span;
  96
  97 pub fn expand_deriving_rustc_encodable(
  98     cx: &mut ExtCtxt<'_>,
  99     span: Span,
 100     mitem: &MetaItem,
 101     item: &Annotatable,
 102     push: &mut dyn FnMut(Annotatable),
 103     is_const: bool,
 104 ) {
 105     let krate = sym::rustc_serialize;
 106     let typaram = sym::__S;
 107
 108     let trait_def = TraitDef {
 109         span,
 110         path: Path::new_(vec![krate, sym::Encodable], vec![], PathKind::Global),
 111         skip_path_as_bound: false,
 112         additional_bounds: Vec::new(),
 113         supports_unions: false,
 114         methods: vec![MethodDef {
 115             name: sym::encode,
 116             generics: Bounds {
 117                 bounds: vec![(
 118                     typaram,
 119                     vec![Path::new_(vec![krate, sym::Encoder], vec![], PathKind::Global)],
 120                 )],
 121             },
 122             explicit_self: true,
 123             nonself_args: vec![(
 124                 Ref(Box::new(Path(Path::new_local(typaram))), Mutability::Mut),
 125                 sym::s,
 126             )],
 127             ret_ty: Path(Path::new_(
 128                 pathvec_std!(result::Result),
 129                 vec![
 130                     Box::new(Unit),
 131                     Box::new(Path(Path::new_(vec![typaram, sym::Error], vec![], PathKind::Local))),
 132                 ],
 133                 PathKind::Std,
 134             )),
 135             attributes: AttrVec::new(),
 136             fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
 137             combine_substructure: combine_substructure(Box::new(|a, b, c| {
 138                 encodable_substructure(a, b, c, krate)
 139             })),
 140         }],
 141         associated_types: Vec::new(),
 142         is_const,
 143     };
 144
 145     trait_def.expand(cx, mitem, item, push)
 146 }
 147
 148 fn encodable_substructure(
 149     cx: &mut ExtCtxt<'_>,
 150     trait_span: Span,
 151     substr: &Substructure<'_>,
 152     krate: Symbol,
 153 ) -> BlockOrExpr {
 154     let encoder = substr.nonselflike_args[0].clone();
 155     // throw an underscore in front to suppress unused variable warnings
 156     let blkarg = Ident::new(sym::_e, trait_span);
 157     let blkencoder = cx.expr_ident(trait_span, blkarg);
 158     let fn_path = cx.expr_path(cx.path_global(
 159         trait_span,
 160         vec![
 161             Ident::new(krate, trait_span),
 162             Ident::new(sym::Encodable, trait_span),
 163             Ident::new(sym::encode, trait_span),
 164         ],
 165     ));
 166
 167     match substr.fields {
 168         Struct(_, fields) => {
 169             let fn_emit_struct_field_path =
 170                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct_field]);
 171             let mut stmts = Vec::new();
 172             for (i, &FieldInfo { name, ref self_expr, span, .. }) in fields.iter().enumerate() {
 173                 let name = match name {
 174                     Some(id) => id.name,
 175                     None => Symbol::intern(&format!("_field{}", i)),
 176                 };
 177                 let self_ref = cx.expr_addr_of(span, self_expr.clone());
 178                 let enc = cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
 179                 let lambda = cx.lambda1(span, enc, blkarg);
 180                 let call = cx.expr_call_global(
 181                     span,
 182                     fn_emit_struct_field_path.clone(),
 183                     vec![
 184                         blkencoder.clone(),
 185                         cx.expr_str(span, name),
 186                         cx.expr_usize(span, i),
 187                         lambda,
 188                     ],
 189                 );
 190
 191                 // last call doesn't need a try!
 192                 let last = fields.len() - 1;
 193                 let call = if i != last {
 194                     cx.expr_try(span, call)
 195                 } else {
 196                     cx.expr(span, ExprKind::Ret(Some(call)))
 197                 };
 198
 199                 let stmt = cx.stmt_expr(call);
 200                 stmts.push(stmt);
 201             }
 202
 203             // unit structs have no fields and need to return Ok()
 204             let blk = if stmts.is_empty() {
 205                 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
 206                 cx.lambda1(trait_span, ok, blkarg)
 207             } else {
 208                 cx.lambda_stmts_1(trait_span, stmts, blkarg)
 209             };
 210
 211             let fn_emit_struct_path =
 212                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_struct]);
 213
 214             let expr = cx.expr_call_global(
 215                 trait_span,
 216                 fn_emit_struct_path,
 217                 vec![
 218                     encoder,
 219                     cx.expr_str(trait_span, substr.type_ident.name),
 220                     cx.expr_usize(trait_span, fields.len()),
 221                     blk,
 222                 ],
 223             );
 224             BlockOrExpr::new_expr(expr)
 225         }
 226
 227         EnumMatching(idx, _, variant, fields) => {
 228             // We're not generating an AST that the borrow checker is expecting,
 229             // so we need to generate a unique local variable to take the
 230             // mutable loan out on, otherwise we get conflicts which don't
 231             // actually exist.
 232             let me = cx.stmt_let(trait_span, false, blkarg, encoder);
 233             let encoder = cx.expr_ident(trait_span, blkarg);
 234
 235             let fn_emit_enum_variant_arg_path: Vec<_> =
 236                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant_arg]);
 237
 238             let mut stmts = Vec::new();
 239             if !fields.is_empty() {
 240                 let last = fields.len() - 1;
 241                 for (i, &FieldInfo { ref self_expr, span, .. }) in fields.iter().enumerate() {
 242                     let self_ref = cx.expr_addr_of(span, self_expr.clone());
 243                     let enc =
 244                         cx.expr_call(span, fn_path.clone(), vec![self_ref, blkencoder.clone()]);
 245                     let lambda = cx.lambda1(span, enc, blkarg);
 246
 247                     let call = cx.expr_call_global(
 248                         span,
 249                         fn_emit_enum_variant_arg_path.clone(),
 250                         vec![blkencoder.clone(), cx.expr_usize(span, i), lambda],
 251                     );
 252                     let call = if i != last {
 253                         cx.expr_try(span, call)
 254                     } else {
 255                         cx.expr(span, ExprKind::Ret(Some(call)))
 256                     };
 257                     stmts.push(cx.stmt_expr(call));
 258                 }
 259             } else {
 260                 let ok = cx.expr_ok(trait_span, cx.expr_tuple(trait_span, vec![]));
 261                 let ret_ok = cx.expr(trait_span, ExprKind::Ret(Some(ok)));
 262                 stmts.push(cx.stmt_expr(ret_ok));
 263             }
 264
 265             let blk = cx.lambda_stmts_1(trait_span, stmts, blkarg);
 266             let name = cx.expr_str(trait_span, variant.ident.name);
 267
 268             let fn_emit_enum_variant_path: Vec<_> =
 269                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum_variant]);
 270
 271             let call = cx.expr_call_global(
 272                 trait_span,
 273                 fn_emit_enum_variant_path,
 274                 vec![
 275                     blkencoder,
 276                     name,
 277                     cx.expr_usize(trait_span, *idx),
 278                     cx.expr_usize(trait_span, fields.len()),
 279                     blk,
 280                 ],
 281             );
 282
 283             let blk = cx.lambda1(trait_span, call, blkarg);
 284             let fn_emit_enum_path: Vec<_> =
 285                 cx.def_site_path(&[sym::rustc_serialize, sym::Encoder, sym::emit_enum]);
 286             let expr = cx.expr_call_global(
 287                 trait_span,
 288                 fn_emit_enum_path,
 289                 vec![encoder, cx.expr_str(trait_span, substr.type_ident.name), blk],
 290             );
 291             BlockOrExpr::new_mixed(vec![me], Some(expr))
 292         }
 293
 294         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)"),
 295     }
 296 }