src/librustc_typeck/check/op.rs

   1 //! Code related to processing overloaded binary and unary operators.
   2
   3 use super::{FnCtxt, Needs};
   4 use super::method::MethodCallee;
   5 use rustc::ty::{self, Ty, TypeFoldable};
   6 use rustc::ty::TyKind::{Ref, Adt, Str, Uint, Never, Tuple, Char, Array};
   7 use rustc::ty::adjustment::{Adjustment, Adjust, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
   8 use rustc::infer::type_variable::TypeVariableOrigin;
   9 use errors::{self,Applicability};
  10 use syntax_pos::Span;
  11 use syntax::ast::Ident;
  12 use rustc::hir;
  13
  14 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  15     /// Check a `a <op>= b`
  16     pub fn check_binop_assign(&self,
  17                               expr: &'gcx hir::Expr,
  18                               op: hir::BinOp,
  19                               lhs_expr: &'gcx hir::Expr,
  20                               rhs_expr: &'gcx hir::Expr) -> Ty<'tcx>
  21     {
  22         let (lhs_ty, rhs_ty, return_ty) =
  23             self.check_overloaded_binop(expr, lhs_expr, rhs_expr, op, IsAssign::Yes);
  24
  25         let ty = if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var()
  26                     && is_builtin_binop(lhs_ty, rhs_ty, op) {
  27             self.enforce_builtin_binop_types(lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
  28             self.tcx.mk_unit()
  29         } else {
  30             return_ty
  31         };
  32
  33         if !lhs_expr.is_place_expr() {
  34             struct_span_err!(
  35                 self.tcx.sess, lhs_expr.span,
  36                 E0067, "invalid left-hand side expression")
  37             .span_label(
  38                 lhs_expr.span,
  39                 "invalid expression for left-hand side")
  40             .emit();
  41         }
  42         ty
  43     }
  44
  45     /// Check a potentially overloaded binary operator.
  46     pub fn check_binop(&self,
  47                        expr: &'gcx hir::Expr,
  48                        op: hir::BinOp,
  49                        lhs_expr: &'gcx hir::Expr,
  50                        rhs_expr: &'gcx hir::Expr) -> Ty<'tcx>
  51     {
  52         let tcx = self.tcx;
  53
  54         debug!("check_binop(expr.id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  55                expr.id,
  56                expr,
  57                op,
  58                lhs_expr,
  59                rhs_expr);
  60
  61         match BinOpCategory::from(op) {
  62             BinOpCategory::Shortcircuit => {
  63                 // && and || are a simple case.
  64                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool);
  65                 let lhs_diverges = self.diverges.get();
  66                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool);
  67
  68                 // Depending on the LHS' value, the RHS can never execute.
  69                 self.diverges.set(lhs_diverges);
  70
  71                 tcx.types.bool
  72             }
  73             _ => {
  74                 // Otherwise, we always treat operators as if they are
  75                 // overloaded. This is the way to be most flexible w/r/t
  76                 // types that get inferred.
  77                 let (lhs_ty, rhs_ty, return_ty) =
  78                     self.check_overloaded_binop(expr, lhs_expr,
  79                                                 rhs_expr, op, IsAssign::No);
  80
  81                 // Supply type inference hints if relevant. Probably these
  82                 // hints should be enforced during select as part of the
  83                 // `consider_unification_despite_ambiguity` routine, but this
  84                 // more convenient for now.
  85                 //
  86                 // The basic idea is to help type inference by taking
  87                 // advantage of things we know about how the impls for
  88                 // scalar types are arranged. This is important in a
  89                 // scenario like `1_u32 << 2`, because it lets us quickly
  90                 // deduce that the result type should be `u32`, even
  91                 // though we don't know yet what type 2 has and hence
  92                 // can't pin this down to a specific impl.
  93                 if
  94                     !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() &&
  95                     is_builtin_binop(lhs_ty, rhs_ty, op)
  96                 {
  97                     let builtin_return_ty =
  98                         self.enforce_builtin_binop_types(lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
  99                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 100                 }
 101
 102                 return_ty
 103             }
 104         }
 105     }
 106
 107     fn enforce_builtin_binop_types(&self,
 108                                    lhs_expr: &'gcx hir::Expr,
 109                                    lhs_ty: Ty<'tcx>,
 110                                    rhs_expr: &'gcx hir::Expr,
 111                                    rhs_ty: Ty<'tcx>,
 112                                    op: hir::BinOp)
 113                                    -> Ty<'tcx>
 114     {
 115         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 116
 117         let tcx = self.tcx;
 118         match BinOpCategory::from(op) {
 119             BinOpCategory::Shortcircuit => {
 120                 self.demand_suptype(lhs_expr.span, tcx.mk_bool(), lhs_ty);
 121                 self.demand_suptype(rhs_expr.span, tcx.mk_bool(), rhs_ty);
 122                 tcx.mk_bool()
 123             }
 124
 125             BinOpCategory::Shift => {
 126                 // result type is same as LHS always
 127                 lhs_ty
 128             }
 129
 130             BinOpCategory::Math |
 131             BinOpCategory::Bitwise => {
 132                 // both LHS and RHS and result will have the same type
 133                 self.demand_suptype(rhs_expr.span, lhs_ty, rhs_ty);
 134                 lhs_ty
 135             }
 136
 137             BinOpCategory::Comparison => {
 138                 // both LHS and RHS and result will have the same type
 139                 self.demand_suptype(rhs_expr.span, lhs_ty, rhs_ty);
 140                 tcx.mk_bool()
 141             }
 142         }
 143     }
 144
 145     fn check_overloaded_binop(&self,
 146                               expr: &'gcx hir::Expr,
 147                               lhs_expr: &'gcx hir::Expr,
 148                               rhs_expr: &'gcx hir::Expr,
 149                               op: hir::BinOp,
 150                               is_assign: IsAssign)
 151                               -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>)
 152     {
 153         debug!("check_overloaded_binop(expr.id={}, op={:?}, is_assign={:?})",
 154                expr.id,
 155                op,
 156                is_assign);
 157
 158         let lhs_ty = match is_assign {
 159             IsAssign::No => {
 160                 // Find a suitable supertype of the LHS expression's type, by coercing to
 161                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 162                 // trait matching creating lifetime constraints that are too strict.
 163                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 164                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 165                 let lhs_ty = self.check_expr_with_needs(lhs_expr, Needs::None);
 166                 let fresh_var = self.next_ty_var(TypeVariableOrigin::MiscVariable(lhs_expr.span));
 167                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var,  AllowTwoPhase::No)
 168             }
 169             IsAssign::Yes => {
 170                 // rust-lang/rust#52126: We have to use strict
 171                 // equivalence on the LHS of an assign-op like `+=`;
 172                 // overwritten or mutably-borrowed places cannot be
 173                 // coerced to a supertype.
 174                 self.check_expr_with_needs(lhs_expr, Needs::MutPlace)
 175             }
 176         };
 177         let lhs_ty = self.resolve_type_vars_with_obligations(lhs_ty);
 178
 179         // N.B., as we have not yet type-checked the RHS, we don't have the
 180         // type at hand. Make a variable to represent it. The whole reason
 181         // for this indirection is so that, below, we can check the expr
 182         // using this variable as the expected type, which sometimes lets
 183         // us do better coercions than we would be able to do otherwise,
 184         // particularly for things like `String + &String`.
 185         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin::MiscVariable(rhs_expr.span));
 186
 187         let result = self.lookup_op_method(lhs_ty, &[rhs_ty_var], Op::Binary(op, is_assign));
 188
 189         // see `NB` above
 190         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var);
 191         let rhs_ty = self.resolve_type_vars_with_obligations(rhs_ty);
 192
 193         let return_ty = match result {
 194             Ok(method) => {
 195                 let by_ref_binop = !op.node.is_by_value();
 196                 if is_assign == IsAssign::Yes || by_ref_binop {
 197                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].sty {
 198                         let mutbl = match mutbl {
 199                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 200                             hir::MutMutable => AutoBorrowMutability::Mutable {
 201                                 // Allow two-phase borrows for binops in initial deployment
 202                                 // since they desugar to methods
 203                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 204                             }
 205                         };
 206                         let autoref = Adjustment {
 207                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 208                             target: method.sig.inputs()[0]
 209                         };
 210                         self.apply_adjustments(lhs_expr, vec![autoref]);
 211                     }
 212                 }
 213                 if by_ref_binop {
 214                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].sty {
 215                         let mutbl = match mutbl {
 216                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 217                             hir::MutMutable => AutoBorrowMutability::Mutable {
 218                                 // Allow two-phase borrows for binops in initial deployment
 219                                 // since they desugar to methods
 220                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 221                             }
 222                         };
 223                         let autoref = Adjustment {
 224                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 225                             target: method.sig.inputs()[1]
 226                         };
 227                         // HACK(eddyb) Bypass checks due to reborrows being in
 228                         // some cases applied on the RHS, on top of which we need
 229                         // to autoref, which is not allowed by apply_adjustments.
 230                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 231                         self.tables
 232                             .borrow_mut()
 233                             .adjustments_mut()
 234                             .entry(rhs_expr.hir_id)
 235                             .or_default()
 236                             .push(autoref);
 237                     }
 238                 }
 239                 self.write_method_call(expr.hir_id, method);
 240
 241                 method.sig.output()
 242             }
 243             Err(()) => {
 244                 // error types are considered "builtin"
 245                 if !lhs_ty.references_error() {
 246                     let source_map = self.tcx.sess.source_map();
 247                     match is_assign {
 248                         IsAssign::Yes => {
 249                             let mut err = struct_span_err!(
 250                                 self.tcx.sess,
 251                                 expr.span,
 252                                 E0368,
 253                                 "binary assignment operation `{}=` cannot be applied to type `{}`",
 254                                 op.node.as_str(),
 255                                 lhs_ty,
 256                             );
 257                             err.span_label(
 258                                 lhs_expr.span,
 259                                 format!("cannot use `{}=` on type `{}`",
 260                                 op.node.as_str(), lhs_ty),
 261                             );
 262                             let mut suggested_deref = false;
 263                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 264                                 if {
 265                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 266                                                                            rty,
 267                                                                            lhs_expr.span) &&
 268                                         self.lookup_op_method(rty,
 269                                                               &[rhs_ty],
 270                                                               Op::Binary(op, is_assign))
 271                                             .is_ok()
 272                                 } {
 273                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 274                                         while let Ref(_, rty_inner, _) = rty.sty {
 275                                             rty = rty_inner;
 276                                         }
 277                                         let msg = &format!(
 278                                             "`{}=` can be used on '{}', you can dereference `{}`",
 279                                             op.node.as_str(),
 280                                             rty,
 281                                             lstring,
 282                                         );
 283                                         err.span_suggestion_with_applicability(
 284                                             lhs_expr.span,
 285                                             msg,
 286                                             format!("*{}", lstring),
 287                                             errors::Applicability::MachineApplicable,
 288                                         );
 289                                         suggested_deref = true;
 290                                     }
 291                                 }
 292                             }
 293                             let missing_trait = match op.node {
 294                                 hir::BinOpKind::Add    => Some("std::ops::AddAssign"),
 295                                 hir::BinOpKind::Sub    => Some("std::ops::SubAssign"),
 296                                 hir::BinOpKind::Mul    => Some("std::ops::MulAssign"),
 297                                 hir::BinOpKind::Div    => Some("std::ops::DivAssign"),
 298                                 hir::BinOpKind::Rem    => Some("std::ops::RemAssign"),
 299                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 300                                 hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 301                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOrAssign"),
 302                                 hir::BinOpKind::Shl    => Some("std::ops::ShlAssign"),
 303                                 hir::BinOpKind::Shr    => Some("std::ops::ShrAssign"),
 304                                 _                      => None
 305                             };
 306                             if let Some(missing_trait) = missing_trait {
 307                                 if op.node == hir::BinOpKind::Add &&
 308                                     self.check_str_addition(expr, lhs_expr, rhs_expr, lhs_ty,
 309                                                             rhs_ty, &mut err, true) {
 310                                     // This has nothing here because it means we did string
 311                                     // concatenation (e.g., "Hello " += "World!"). This means
 312                                     // we don't want the note in the else clause to be emitted
 313                                 } else if let ty::Param(_) = lhs_ty.sty {
 314                                     // FIXME: point to span of param
 315                                     err.note(&format!(
 316                                         "`{}` might need a bound for `{}`",
 317                                         lhs_ty, missing_trait
 318                                     ));
 319                                 } else if !suggested_deref {
 320                                     err.note(&format!(
 321                                         "an implementation of `{}` might \
 322                                          be missing for `{}`",
 323                                         missing_trait, lhs_ty
 324                                     ));
 325                                 }
 326                             }
 327                             err.emit();
 328                         }
 329                         IsAssign::No => {
 330                             let mut err = struct_span_err!(self.tcx.sess, expr.span, E0369,
 331                                 "binary operation `{}` cannot be applied to type `{}`",
 332                                 op.node.as_str(),
 333                                 lhs_ty);
 334                             let mut suggested_deref = false;
 335                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 336                                 if {
 337                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 338                                                                            rty,
 339                                                                            lhs_expr.span) &&
 340                                         self.lookup_op_method(rty,
 341                                                               &[rhs_ty],
 342                                                               Op::Binary(op, is_assign))
 343                                             .is_ok()
 344                                 } {
 345                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 346                                         while let Ref(_, rty_inner, _) = rty.sty {
 347                                             rty = rty_inner;
 348                                         }
 349                                         let msg = &format!(
 350                                                 "`{}` can be used on '{}', you can \
 351                                                 dereference `{2}`: `*{2}`",
 352                                                 op.node.as_str(),
 353                                                 rty,
 354                                                 lstring
 355                                         );
 356                                         err.help(msg);
 357                                         suggested_deref = true;
 358                                     }
 359                                 }
 360                             }
 361                             let missing_trait = match op.node {
 362                                 hir::BinOpKind::Add    => Some("std::ops::Add"),
 363                                 hir::BinOpKind::Sub    => Some("std::ops::Sub"),
 364                                 hir::BinOpKind::Mul    => Some("std::ops::Mul"),
 365                                 hir::BinOpKind::Div    => Some("std::ops::Div"),
 366                                 hir::BinOpKind::Rem    => Some("std::ops::Rem"),
 367                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAnd"),
 368                                 hir::BinOpKind::BitXor => Some("std::ops::BitXor"),
 369                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOr"),
 370                                 hir::BinOpKind::Shl    => Some("std::ops::Shl"),
 371                                 hir::BinOpKind::Shr    => Some("std::ops::Shr"),
 372                                 hir::BinOpKind::Eq |
 373                                 hir::BinOpKind::Ne => Some("std::cmp::PartialEq"),
 374                                 hir::BinOpKind::Lt |
 375                                 hir::BinOpKind::Le |
 376                                 hir::BinOpKind::Gt |
 377                                 hir::BinOpKind::Ge => Some("std::cmp::PartialOrd"),
 378                                 _ => None
 379                             };
 380                             if let Some(missing_trait) = missing_trait {
 381                                 if op.node == hir::BinOpKind::Add &&
 382                                     self.check_str_addition(expr, lhs_expr, rhs_expr, lhs_ty,
 383                                                             rhs_ty, &mut err, false) {
 384                                     // This has nothing here because it means we did string
 385                                     // concatenation (e.g., "Hello " + "World!"). This means
 386                                     // we don't want the note in the else clause to be emitted
 387                                 } else if let ty::Param(_) = lhs_ty.sty {
 388                                     // FIXME: point to span of param
 389                                     err.note(&format!(
 390                                         "`{}` might need a bound for `{}`",
 391                                         lhs_ty, missing_trait
 392                                     ));
 393                                 } else if !suggested_deref {
 394                                     err.note(&format!(
 395                                         "an implementation of `{}` might \
 396                                          be missing for `{}`",
 397                                         missing_trait, lhs_ty
 398                                     ));
 399                                 }
 400                             }
 401                             err.emit();
 402                         }
 403                     }
 404                 }
 405                 self.tcx.types.err
 406             }
 407         };
 408
 409         (lhs_ty, rhs_ty, return_ty)
 410     }
 411
 412     fn check_str_addition(
 413         &self,
 414         expr: &'gcx hir::Expr,
 415         lhs_expr: &'gcx hir::Expr,
 416         rhs_expr: &'gcx hir::Expr,
 417         lhs_ty: Ty<'tcx>,
 418         rhs_ty: Ty<'tcx>,
 419         err: &mut errors::DiagnosticBuilder,
 420         is_assign: bool,
 421     ) -> bool {
 422         let source_map = self.tcx.sess.source_map();
 423         let msg = "`to_owned()` can be used to create an owned `String` \
 424                    from a string reference. String concatenation \
 425                    appends the string on the right to the string \
 426                    on the left and may require reallocation. This \
 427                    requires ownership of the string on the left";
 428         // If this function returns true it means a note was printed, so we don't need
 429         // to print the normal "implementation of `std::ops::Add` might be missing" note
 430         match (&lhs_ty.sty, &rhs_ty.sty) {
 431             (&Ref(_, l_ty, _), &Ref(_, r_ty, _))
 432             if l_ty.sty == Str && r_ty.sty == Str => {
 433                 if !is_assign {
 434                     err.span_label(expr.span,
 435                                    "`+` can't be used to concatenate two `&str` strings");
 436                     match source_map.span_to_snippet(lhs_expr.span) {
 437                         Ok(lstring) => err.span_suggestion_with_applicability(
 438                             lhs_expr.span,
 439                             msg,
 440                             format!("{}.to_owned()", lstring),
 441                             Applicability::MachineApplicable,
 442                         ),
 443                         _ => err.help(msg),
 444                     };
 445                 }
 446                 true
 447             }
 448             (&Ref(_, l_ty, _), &Adt(..))
 449             if l_ty.sty == Str && &format!("{:?}", rhs_ty) == "std::string::String" => {
 450                 err.span_label(expr.span,
 451                     "`+` can't be used to concatenate a `&str` with a `String`");
 452                 match (
 453                     source_map.span_to_snippet(lhs_expr.span),
 454                     source_map.span_to_snippet(rhs_expr.span),
 455                     is_assign,
 456                 ) {
 457                     (Ok(l), Ok(r), false) => {
 458                         err.multipart_suggestion_with_applicability(
 459                             msg,
 460                             vec![
 461                                 (lhs_expr.span, format!("{}.to_owned()", l)),
 462                                 (rhs_expr.span, format!("&{}", r)),
 463                             ],
 464                             Applicability::MachineApplicable,
 465                         );
 466                     }
 467                     _ => {
 468                         err.help(msg);
 469                     }
 470                 };
 471                 true
 472             }
 473             _ => false,
 474         }
 475     }
 476
 477     pub fn check_user_unop(&self,
 478                            ex: &'gcx hir::Expr,
 479                            operand_ty: Ty<'tcx>,
 480                            op: hir::UnOp)
 481                            -> Ty<'tcx>
 482     {
 483         assert!(op.is_by_value());
 484         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 485             Ok(method) => {
 486                 self.write_method_call(ex.hir_id, method);
 487                 method.sig.output()
 488             }
 489             Err(()) => {
 490                 let actual = self.resolve_type_vars_if_possible(&operand_ty);
 491                 if !actual.references_error() {
 492                     let mut err = struct_span_err!(self.tcx.sess, ex.span, E0600,
 493                                      "cannot apply unary operator `{}` to type `{}`",
 494                                      op.as_str(), actual);
 495                     err.span_label(ex.span, format!("cannot apply unary \
 496                                                     operator `{}`", op.as_str()));
 497                     match actual.sty {
 498                         Uint(_) if op == hir::UnNeg => {
 499                             err.note("unsigned values cannot be negated");
 500                         },
 501                         Str | Never | Char | Tuple(_) | Array(_,_) => {},
 502                         Ref(_, ref lty, _) if lty.sty == Str => {},
 503                         _ => {
 504                             let missing_trait = match op {
 505                                 hir::UnNeg => "std::ops::Neg",
 506                                 hir::UnNot => "std::ops::Not",
 507                                 hir::UnDeref => "std::ops::UnDerf"
 508                             };
 509                             err.note(&format!("an implementation of `{}` might \
 510                                                 be missing for `{}`",
 511                                              missing_trait, operand_ty));
 512                         }
 513                     }
 514                     err.emit();
 515                 }
 516                 self.tcx.types.err
 517             }
 518         }
 519     }
 520
 521     fn lookup_op_method(&self, lhs_ty: Ty<'tcx>, other_tys: &[Ty<'tcx>], op: Op)
 522                         -> Result<MethodCallee<'tcx>, ()>
 523     {
 524         let lang = self.tcx.lang_items();
 525
 526         let span = match op {
 527             Op::Binary(op, _) => op.span,
 528             Op::Unary(_, span) => span
 529         };
 530         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 531             match op.node {
 532                 hir::BinOpKind::Add => ("add_assign", lang.add_assign_trait()),
 533                 hir::BinOpKind::Sub => ("sub_assign", lang.sub_assign_trait()),
 534                 hir::BinOpKind::Mul => ("mul_assign", lang.mul_assign_trait()),
 535                 hir::BinOpKind::Div => ("div_assign", lang.div_assign_trait()),
 536                 hir::BinOpKind::Rem => ("rem_assign", lang.rem_assign_trait()),
 537                 hir::BinOpKind::BitXor => ("bitxor_assign", lang.bitxor_assign_trait()),
 538                 hir::BinOpKind::BitAnd => ("bitand_assign", lang.bitand_assign_trait()),
 539                 hir::BinOpKind::BitOr => ("bitor_assign", lang.bitor_assign_trait()),
 540                 hir::BinOpKind::Shl => ("shl_assign", lang.shl_assign_trait()),
 541                 hir::BinOpKind::Shr => ("shr_assign", lang.shr_assign_trait()),
 542                 hir::BinOpKind::Lt | hir::BinOpKind::Le |
 543                 hir::BinOpKind::Ge | hir::BinOpKind::Gt |
 544                 hir::BinOpKind::Eq | hir::BinOpKind::Ne |
 545                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 546                     span_bug!(span,
 547                               "impossible assignment operation: {}=",
 548                               op.node.as_str())
 549                 }
 550             }
 551         } else if let Op::Binary(op, IsAssign::No) = op {
 552             match op.node {
 553                 hir::BinOpKind::Add => ("add", lang.add_trait()),
 554                 hir::BinOpKind::Sub => ("sub", lang.sub_trait()),
 555                 hir::BinOpKind::Mul => ("mul", lang.mul_trait()),
 556                 hir::BinOpKind::Div => ("div", lang.div_trait()),
 557                 hir::BinOpKind::Rem => ("rem", lang.rem_trait()),
 558                 hir::BinOpKind::BitXor => ("bitxor", lang.bitxor_trait()),
 559                 hir::BinOpKind::BitAnd => ("bitand", lang.bitand_trait()),
 560                 hir::BinOpKind::BitOr => ("bitor", lang.bitor_trait()),
 561                 hir::BinOpKind::Shl => ("shl", lang.shl_trait()),
 562                 hir::BinOpKind::Shr => ("shr", lang.shr_trait()),
 563                 hir::BinOpKind::Lt => ("lt", lang.partial_ord_trait()),
 564                 hir::BinOpKind::Le => ("le", lang.partial_ord_trait()),
 565                 hir::BinOpKind::Ge => ("ge", lang.partial_ord_trait()),
 566                 hir::BinOpKind::Gt => ("gt", lang.partial_ord_trait()),
 567                 hir::BinOpKind::Eq => ("eq", lang.eq_trait()),
 568                 hir::BinOpKind::Ne => ("ne", lang.eq_trait()),
 569                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 570                     span_bug!(span, "&& and || are not overloadable")
 571                 }
 572             }
 573         } else if let Op::Unary(hir::UnNot, _) = op {
 574             ("not", lang.not_trait())
 575         } else if let Op::Unary(hir::UnNeg, _) = op {
 576             ("neg", lang.neg_trait())
 577         } else {
 578             bug!("lookup_op_method: op not supported: {:?}", op)
 579         };
 580
 581         debug!("lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 582                lhs_ty,
 583                op,
 584                opname,
 585                trait_did);
 586
 587         let method = trait_did.and_then(|trait_did| {
 588             let opname = Ident::from_str(opname);
 589             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 590         });
 591
 592         match method {
 593             Some(ok) => {
 594                 let method = self.register_infer_ok_obligations(ok);
 595                 self.select_obligations_where_possible(false);
 596
 597                 Ok(method)
 598             }
 599             None => {
 600                 Err(())
 601             }
 602         }
 603     }
 604 }
 605
 606 // Binary operator categories. These categories summarize the behavior
 607 // with respect to the builtin operationrs supported.
 608 enum BinOpCategory {
 609     /// &&, || -- cannot be overridden
 610     Shortcircuit,
 611
 612     /// <<, >> -- when shifting a single integer, rhs can be any
 613     /// integer type. For simd, types must match.
 614     Shift,
 615
 616     /// +, -, etc -- takes equal types, produces same type as input,
 617     /// applicable to ints/floats/simd
 618     Math,
 619
 620     /// &, |, ^ -- takes equal types, produces same type as input,
 621     /// applicable to ints/floats/simd/bool
 622     Bitwise,
 623
 624     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 625     /// which produce the input type
 626     Comparison,
 627 }
 628
 629 impl BinOpCategory {
 630     fn from(op: hir::BinOp) -> BinOpCategory {
 631         match op.node {
 632             hir::BinOpKind::Shl | hir::BinOpKind::Shr =>
 633                 BinOpCategory::Shift,
 634
 635             hir::BinOpKind::Add |
 636             hir::BinOpKind::Sub |
 637             hir::BinOpKind::Mul |
 638             hir::BinOpKind::Div |
 639             hir::BinOpKind::Rem =>
 640                 BinOpCategory::Math,
 641
 642             hir::BinOpKind::BitXor |
 643             hir::BinOpKind::BitAnd |
 644             hir::BinOpKind::BitOr =>
 645                 BinOpCategory::Bitwise,
 646
 647             hir::BinOpKind::Eq |
 648             hir::BinOpKind::Ne |
 649             hir::BinOpKind::Lt |
 650             hir::BinOpKind::Le |
 651             hir::BinOpKind::Ge |
 652             hir::BinOpKind::Gt =>
 653                 BinOpCategory::Comparison,
 654
 655             hir::BinOpKind::And |
 656             hir::BinOpKind::Or =>
 657                 BinOpCategory::Shortcircuit,
 658         }
 659     }
 660 }
 661
 662 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 663 #[derive(Clone, Copy, Debug, PartialEq)]
 664 enum IsAssign {
 665     No,
 666     Yes,
 667 }
 668
 669 #[derive(Clone, Copy, Debug)]
 670 enum Op {
 671     Binary(hir::BinOp, IsAssign),
 672     Unary(hir::UnOp, Span),
 673 }
 674
 675 /// Returns true if this is a built-in arithmetic operation (e.g., u32
 676 /// + u32, i16x4 == i16x4) and false if these types would have to be
 677 /// overloaded to be legal. There are two reasons that we distinguish
 678 /// builtin operations from overloaded ones (vs trying to drive
 679 /// everything uniformly through the trait system and intrinsics or
 680 /// something like that):
 681 ///
 682 /// 1. Builtin operations can trivially be evaluated in constants.
 683 /// 2. For comparison operators applied to SIMD types the result is
 684 ///    not of type `bool`. For example, `i16x4==i16x4` yields a
 685 ///    type like `i16x4`. This means that the overloaded trait
 686 ///    `PartialEq` is not applicable.
 687 ///
 688 /// Reason #2 is the killer. I tried for a while to always use
 689 /// overloaded logic and just check the types in constants/codegen after
 690 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 691 fn is_builtin_binop(lhs: Ty, rhs: Ty, op: hir::BinOp) -> bool {
 692     match BinOpCategory::from(op) {
 693         BinOpCategory::Shortcircuit => {
 694             true
 695         }
 696
 697         BinOpCategory::Shift => {
 698             lhs.references_error() || rhs.references_error() ||
 699                 lhs.is_integral() && rhs.is_integral()
 700         }
 701
 702         BinOpCategory::Math => {
 703             lhs.references_error() || rhs.references_error() ||
 704                 lhs.is_integral() && rhs.is_integral() ||
 705                 lhs.is_floating_point() && rhs.is_floating_point()
 706         }
 707
 708         BinOpCategory::Bitwise => {
 709             lhs.references_error() || rhs.references_error() ||
 710                 lhs.is_integral() && rhs.is_integral() ||
 711                 lhs.is_floating_point() && rhs.is_floating_point() ||
 712                 lhs.is_bool() && rhs.is_bool()
 713         }
 714
 715         BinOpCategory::Comparison => {
 716             lhs.references_error() || rhs.references_error() ||
 717                 lhs.is_scalar() && rhs.is_scalar()
 718         }
 719     }
 720 }