src/librustc_typeck/check/op.rs

   1 // Copyright 2014 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 //! Code related to processing overloaded binary and unary operators.
  12
  13 use super::{FnCtxt, Needs};
  14 use super::method::MethodCallee;
  15 use rustc::ty::{self, Ty, TypeFoldable};
  16 use rustc::ty::TyKind::{Ref, Adt, Str, Uint, Never, Tuple, Char, Array};
  17 use rustc::ty::adjustment::{Adjustment, Adjust, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
  18 use rustc::infer::type_variable::TypeVariableOrigin;
  19 use errors::{self,Applicability};
  20 use syntax_pos::Span;
  21 use syntax::ast::Ident;
  22 use rustc::hir;
  23
  24 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  25     /// Check a `a <op>= b`
  26     pub fn check_binop_assign(&self,
  27                               expr: &'gcx hir::Expr,
  28                               op: hir::BinOp,
  29                               lhs_expr: &'gcx hir::Expr,
  30                               rhs_expr: &'gcx hir::Expr) -> Ty<'tcx>
  31     {
  32         let (lhs_ty, rhs_ty, return_ty) =
  33             self.check_overloaded_binop(expr, lhs_expr, rhs_expr, op, IsAssign::Yes);
  34
  35         let ty = if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var()
  36                     && is_builtin_binop(lhs_ty, rhs_ty, op) {
  37             self.enforce_builtin_binop_types(lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
  38             self.tcx.mk_unit()
  39         } else {
  40             return_ty
  41         };
  42
  43         if !lhs_expr.is_place_expr() {
  44             struct_span_err!(
  45                 self.tcx.sess, lhs_expr.span,
  46                 E0067, "invalid left-hand side expression")
  47             .span_label(
  48                 lhs_expr.span,
  49                 "invalid expression for left-hand side")
  50             .emit();
  51         }
  52         ty
  53     }
  54
  55     /// Check a potentially overloaded binary operator.
  56     pub fn check_binop(&self,
  57                        expr: &'gcx hir::Expr,
  58                        op: hir::BinOp,
  59                        lhs_expr: &'gcx hir::Expr,
  60                        rhs_expr: &'gcx hir::Expr) -> Ty<'tcx>
  61     {
  62         let tcx = self.tcx;
  63
  64         debug!("check_binop(expr.id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  65                expr.id,
  66                expr,
  67                op,
  68                lhs_expr,
  69                rhs_expr);
  70
  71         match BinOpCategory::from(op) {
  72             BinOpCategory::Shortcircuit => {
  73                 // && and || are a simple case.
  74                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool);
  75                 let lhs_diverges = self.diverges.get();
  76                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool);
  77
  78                 // Depending on the LHS' value, the RHS can never execute.
  79                 self.diverges.set(lhs_diverges);
  80
  81                 tcx.types.bool
  82             }
  83             _ => {
  84                 // Otherwise, we always treat operators as if they are
  85                 // overloaded. This is the way to be most flexible w/r/t
  86                 // types that get inferred.
  87                 let (lhs_ty, rhs_ty, return_ty) =
  88                     self.check_overloaded_binop(expr, lhs_expr,
  89                                                 rhs_expr, op, IsAssign::No);
  90
  91                 // Supply type inference hints if relevant. Probably these
  92                 // hints should be enforced during select as part of the
  93                 // `consider_unification_despite_ambiguity` routine, but this
  94                 // more convenient for now.
  95                 //
  96                 // The basic idea is to help type inference by taking
  97                 // advantage of things we know about how the impls for
  98                 // scalar types are arranged. This is important in a
  99                 // scenario like `1_u32 << 2`, because it lets us quickly
 100                 // deduce that the result type should be `u32`, even
 101                 // though we don't know yet what type 2 has and hence
 102                 // can't pin this down to a specific impl.
 103                 if
 104                     !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() &&
 105                     is_builtin_binop(lhs_ty, rhs_ty, op)
 106                 {
 107                     let builtin_return_ty =
 108                         self.enforce_builtin_binop_types(lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
 109                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 110                 }
 111
 112                 return_ty
 113             }
 114         }
 115     }
 116
 117     fn enforce_builtin_binop_types(&self,
 118                                    lhs_expr: &'gcx hir::Expr,
 119                                    lhs_ty: Ty<'tcx>,
 120                                    rhs_expr: &'gcx hir::Expr,
 121                                    rhs_ty: Ty<'tcx>,
 122                                    op: hir::BinOp)
 123                                    -> Ty<'tcx>
 124     {
 125         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 126
 127         let tcx = self.tcx;
 128         match BinOpCategory::from(op) {
 129             BinOpCategory::Shortcircuit => {
 130                 self.demand_suptype(lhs_expr.span, tcx.mk_bool(), lhs_ty);
 131                 self.demand_suptype(rhs_expr.span, tcx.mk_bool(), rhs_ty);
 132                 tcx.mk_bool()
 133             }
 134
 135             BinOpCategory::Shift => {
 136                 // result type is same as LHS always
 137                 lhs_ty
 138             }
 139
 140             BinOpCategory::Math |
 141             BinOpCategory::Bitwise => {
 142                 // both LHS and RHS and result will have the same type
 143                 self.demand_suptype(rhs_expr.span, lhs_ty, rhs_ty);
 144                 lhs_ty
 145             }
 146
 147             BinOpCategory::Comparison => {
 148                 // both LHS and RHS and result will have the same type
 149                 self.demand_suptype(rhs_expr.span, lhs_ty, rhs_ty);
 150                 tcx.mk_bool()
 151             }
 152         }
 153     }
 154
 155     fn check_overloaded_binop(&self,
 156                               expr: &'gcx hir::Expr,
 157                               lhs_expr: &'gcx hir::Expr,
 158                               rhs_expr: &'gcx hir::Expr,
 159                               op: hir::BinOp,
 160                               is_assign: IsAssign)
 161                               -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>)
 162     {
 163         debug!("check_overloaded_binop(expr.id={}, op={:?}, is_assign={:?})",
 164                expr.id,
 165                op,
 166                is_assign);
 167
 168         let lhs_ty = match is_assign {
 169             IsAssign::No => {
 170                 // Find a suitable supertype of the LHS expression's type, by coercing to
 171                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 172                 // trait matching creating lifetime constraints that are too strict.
 173                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 174                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 175                 let lhs_ty = self.check_expr_with_needs(lhs_expr, Needs::None);
 176                 let fresh_var = self.next_ty_var(TypeVariableOrigin::MiscVariable(lhs_expr.span));
 177                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var,  AllowTwoPhase::No)
 178             }
 179             IsAssign::Yes => {
 180                 // rust-lang/rust#52126: We have to use strict
 181                 // equivalence on the LHS of an assign-op like `+=`;
 182                 // overwritten or mutably-borrowed places cannot be
 183                 // coerced to a supertype.
 184                 self.check_expr_with_needs(lhs_expr, Needs::MutPlace)
 185             }
 186         };
 187         let lhs_ty = self.resolve_type_vars_with_obligations(lhs_ty);
 188
 189         // N.B., as we have not yet type-checked the RHS, we don't have the
 190         // type at hand. Make a variable to represent it. The whole reason
 191         // for this indirection is so that, below, we can check the expr
 192         // using this variable as the expected type, which sometimes lets
 193         // us do better coercions than we would be able to do otherwise,
 194         // particularly for things like `String + &String`.
 195         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin::MiscVariable(rhs_expr.span));
 196
 197         let result = self.lookup_op_method(lhs_ty, &[rhs_ty_var], Op::Binary(op, is_assign));
 198
 199         // see `NB` above
 200         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var);
 201         let rhs_ty = self.resolve_type_vars_with_obligations(rhs_ty);
 202
 203         let return_ty = match result {
 204             Ok(method) => {
 205                 let by_ref_binop = !op.node.is_by_value();
 206                 if is_assign == IsAssign::Yes || by_ref_binop {
 207                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].sty {
 208                         let mutbl = match mutbl {
 209                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 210                             hir::MutMutable => AutoBorrowMutability::Mutable {
 211                                 // Allow two-phase borrows for binops in initial deployment
 212                                 // since they desugar to methods
 213                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 214                             }
 215                         };
 216                         let autoref = Adjustment {
 217                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 218                             target: method.sig.inputs()[0]
 219                         };
 220                         self.apply_adjustments(lhs_expr, vec![autoref]);
 221                     }
 222                 }
 223                 if by_ref_binop {
 224                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].sty {
 225                         let mutbl = match mutbl {
 226                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 227                             hir::MutMutable => AutoBorrowMutability::Mutable {
 228                                 // Allow two-phase borrows for binops in initial deployment
 229                                 // since they desugar to methods
 230                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 231                             }
 232                         };
 233                         let autoref = Adjustment {
 234                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 235                             target: method.sig.inputs()[1]
 236                         };
 237                         // HACK(eddyb) Bypass checks due to reborrows being in
 238                         // some cases applied on the RHS, on top of which we need
 239                         // to autoref, which is not allowed by apply_adjustments.
 240                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 241                         self.tables
 242                             .borrow_mut()
 243                             .adjustments_mut()
 244                             .entry(rhs_expr.hir_id)
 245                             .or_default()
 246                             .push(autoref);
 247                     }
 248                 }
 249                 self.write_method_call(expr.hir_id, method);
 250
 251                 method.sig.output()
 252             }
 253             Err(()) => {
 254                 // error types are considered "builtin"
 255                 if !lhs_ty.references_error() {
 256                     let source_map = self.tcx.sess.source_map();
 257                     match is_assign {
 258                         IsAssign::Yes => {
 259                             let mut err = struct_span_err!(
 260                                 self.tcx.sess,
 261                                 expr.span,
 262                                 E0368,
 263                                 "binary assignment operation `{}=` cannot be applied to type `{}`",
 264                                 op.node.as_str(),
 265                                 lhs_ty,
 266                             );
 267                             err.span_label(
 268                                 lhs_expr.span,
 269                                 format!("cannot use `{}=` on type `{}`",
 270                                 op.node.as_str(), lhs_ty),
 271                             );
 272                             let mut suggested_deref = false;
 273                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 274                                 if {
 275                                     !self.infcx.type_moves_by_default(self.param_env,
 276                                                                         rty,
 277                                                                         lhs_expr.span) &&
 278                                         self.lookup_op_method(rty,
 279                                                               &[rhs_ty],
 280                                                               Op::Binary(op, is_assign))
 281                                             .is_ok()
 282                                 } {
 283                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 284                                         while let Ref(_, rty_inner, _) = rty.sty {
 285                                             rty = rty_inner;
 286                                         }
 287                                         let msg = &format!(
 288                                             "`{}=` can be used on '{}', you can dereference `{}`",
 289                                             op.node.as_str(),
 290                                             rty,
 291                                             lstring,
 292                                         );
 293                                         err.span_suggestion_with_applicability(
 294                                             lhs_expr.span,
 295                                             msg,
 296                                             format!("*{}", lstring),
 297                                             errors::Applicability::MachineApplicable,
 298                                         );
 299                                         suggested_deref = true;
 300                                     }
 301                                 }
 302                             }
 303                             let missing_trait = match op.node {
 304                                 hir::BinOpKind::Add    => Some("std::ops::AddAssign"),
 305                                 hir::BinOpKind::Sub    => Some("std::ops::SubAssign"),
 306                                 hir::BinOpKind::Mul    => Some("std::ops::MulAssign"),
 307                                 hir::BinOpKind::Div    => Some("std::ops::DivAssign"),
 308                                 hir::BinOpKind::Rem    => Some("std::ops::RemAssign"),
 309                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 310                                 hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 311                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOrAssign"),
 312                                 hir::BinOpKind::Shl    => Some("std::ops::ShlAssign"),
 313                                 hir::BinOpKind::Shr    => Some("std::ops::ShrAssign"),
 314                                 _                      => None
 315                             };
 316                             if let Some(missing_trait) = missing_trait {
 317                                 if op.node == hir::BinOpKind::Add &&
 318                                     self.check_str_addition(expr, lhs_expr, rhs_expr, lhs_ty,
 319                                                             rhs_ty, &mut err, true) {
 320                                     // This has nothing here because it means we did string
 321                                     // concatenation (e.g., "Hello " += "World!"). This means
 322                                     // we don't want the note in the else clause to be emitted
 323                                 } else if let ty::Param(_) = lhs_ty.sty {
 324                                     // FIXME: point to span of param
 325                                     err.note(&format!(
 326                                         "`{}` might need a bound for `{}`",
 327                                         lhs_ty, missing_trait
 328                                     ));
 329                                 } else if !suggested_deref {
 330                                     err.note(&format!(
 331                                         "an implementation of `{}` might \
 332                                          be missing for `{}`",
 333                                         missing_trait, lhs_ty
 334                                     ));
 335                                 }
 336                             }
 337                             err.emit();
 338                         }
 339                         IsAssign::No => {
 340                             let mut err = struct_span_err!(self.tcx.sess, expr.span, E0369,
 341                                 "binary operation `{}` cannot be applied to type `{}`",
 342                                 op.node.as_str(),
 343                                 lhs_ty);
 344                             let mut suggested_deref = false;
 345                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 346                                 if {
 347                                     !self.infcx.type_moves_by_default(self.param_env,
 348                                                                       rty,
 349                                                                       lhs_expr.span) &&
 350                                         self.lookup_op_method(rty,
 351                                                               &[rhs_ty],
 352                                                               Op::Binary(op, is_assign))
 353                                             .is_ok()
 354                                 } {
 355                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 356                                         while let Ref(_, rty_inner, _) = rty.sty {
 357                                             rty = rty_inner;
 358                                         }
 359                                         let msg = &format!(
 360                                                 "`{}` can be used on '{}', you can \
 361                                                 dereference `{2}`: `*{2}`",
 362                                                 op.node.as_str(),
 363                                                 rty,
 364                                                 lstring
 365                                         );
 366                                         err.help(msg);
 367                                         suggested_deref = true;
 368                                     }
 369                                 }
 370                             }
 371                             let missing_trait = match op.node {
 372                                 hir::BinOpKind::Add    => Some("std::ops::Add"),
 373                                 hir::BinOpKind::Sub    => Some("std::ops::Sub"),
 374                                 hir::BinOpKind::Mul    => Some("std::ops::Mul"),
 375                                 hir::BinOpKind::Div    => Some("std::ops::Div"),
 376                                 hir::BinOpKind::Rem    => Some("std::ops::Rem"),
 377                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAnd"),
 378                                 hir::BinOpKind::BitXor => Some("std::ops::BitXor"),
 379                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOr"),
 380                                 hir::BinOpKind::Shl    => Some("std::ops::Shl"),
 381                                 hir::BinOpKind::Shr    => Some("std::ops::Shr"),
 382                                 hir::BinOpKind::Eq |
 383                                 hir::BinOpKind::Ne => Some("std::cmp::PartialEq"),
 384                                 hir::BinOpKind::Lt |
 385                                 hir::BinOpKind::Le |
 386                                 hir::BinOpKind::Gt |
 387                                 hir::BinOpKind::Ge => Some("std::cmp::PartialOrd"),
 388                                 _ => None
 389                             };
 390                             if let Some(missing_trait) = missing_trait {
 391                                 if op.node == hir::BinOpKind::Add &&
 392                                     self.check_str_addition(expr, lhs_expr, rhs_expr, lhs_ty,
 393                                                             rhs_ty, &mut err, false) {
 394                                     // This has nothing here because it means we did string
 395                                     // concatenation (e.g., "Hello " + "World!"). This means
 396                                     // we don't want the note in the else clause to be emitted
 397                                 } else if let ty::Param(_) = lhs_ty.sty {
 398                                     // FIXME: point to span of param
 399                                     err.note(&format!(
 400                                         "`{}` might need a bound for `{}`",
 401                                         lhs_ty, missing_trait
 402                                     ));
 403                                 } else if !suggested_deref {
 404                                     err.note(&format!(
 405                                         "an implementation of `{}` might \
 406                                          be missing for `{}`",
 407                                         missing_trait, lhs_ty
 408                                     ));
 409                                 }
 410                             }
 411                             err.emit();
 412                         }
 413                     }
 414                 }
 415                 self.tcx.types.err
 416             }
 417         };
 418
 419         (lhs_ty, rhs_ty, return_ty)
 420     }
 421
 422     fn check_str_addition(
 423         &self,
 424         expr: &'gcx hir::Expr,
 425         lhs_expr: &'gcx hir::Expr,
 426         rhs_expr: &'gcx hir::Expr,
 427         lhs_ty: Ty<'tcx>,
 428         rhs_ty: Ty<'tcx>,
 429         err: &mut errors::DiagnosticBuilder,
 430         is_assign: bool,
 431     ) -> bool {
 432         let source_map = self.tcx.sess.source_map();
 433         let msg = "`to_owned()` can be used to create an owned `String` \
 434                    from a string reference. String concatenation \
 435                    appends the string on the right to the string \
 436                    on the left and may require reallocation. This \
 437                    requires ownership of the string on the left";
 438         // If this function returns true it means a note was printed, so we don't need
 439         // to print the normal "implementation of `std::ops::Add` might be missing" note
 440         match (&lhs_ty.sty, &rhs_ty.sty) {
 441             (&Ref(_, l_ty, _), &Ref(_, r_ty, _))
 442             if l_ty.sty == Str && r_ty.sty == Str => {
 443                 if !is_assign {
 444                     err.span_label(expr.span,
 445                                    "`+` can't be used to concatenate two `&str` strings");
 446                     match source_map.span_to_snippet(lhs_expr.span) {
 447                         Ok(lstring) => err.span_suggestion_with_applicability(
 448                             lhs_expr.span,
 449                             msg,
 450                             format!("{}.to_owned()", lstring),
 451                             Applicability::MachineApplicable,
 452                         ),
 453                         _ => err.help(msg),
 454                     };
 455                 }
 456                 true
 457             }
 458             (&Ref(_, l_ty, _), &Adt(..))
 459             if l_ty.sty == Str && &format!("{:?}", rhs_ty) == "std::string::String" => {
 460                 err.span_label(expr.span,
 461                     "`+` can't be used to concatenate a `&str` with a `String`");
 462                 match (
 463                     source_map.span_to_snippet(lhs_expr.span),
 464                     source_map.span_to_snippet(rhs_expr.span),
 465                     is_assign,
 466                 ) {
 467                     (Ok(l), Ok(r), false) => {
 468                         err.multipart_suggestion_with_applicability(
 469                             msg,
 470                             vec![
 471                                 (lhs_expr.span, format!("{}.to_owned()", l)),
 472                                 (rhs_expr.span, format!("&{}", r)),
 473                             ],
 474                             Applicability::MachineApplicable,
 475                         );
 476                     }
 477                     _ => {
 478                         err.help(msg);
 479                     }
 480                 };
 481                 true
 482             }
 483             _ => false,
 484         }
 485     }
 486
 487     pub fn check_user_unop(&self,
 488                            ex: &'gcx hir::Expr,
 489                            operand_ty: Ty<'tcx>,
 490                            op: hir::UnOp)
 491                            -> Ty<'tcx>
 492     {
 493         assert!(op.is_by_value());
 494         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 495             Ok(method) => {
 496                 self.write_method_call(ex.hir_id, method);
 497                 method.sig.output()
 498             }
 499             Err(()) => {
 500                 let actual = self.resolve_type_vars_if_possible(&operand_ty);
 501                 if !actual.references_error() {
 502                     let mut err = struct_span_err!(self.tcx.sess, ex.span, E0600,
 503                                      "cannot apply unary operator `{}` to type `{}`",
 504                                      op.as_str(), actual);
 505                     err.span_label(ex.span, format!("cannot apply unary \
 506                                                     operator `{}`", op.as_str()));
 507                     match actual.sty {
 508                         Uint(_) if op == hir::UnNeg => {
 509                             err.note("unsigned values cannot be negated");
 510                         },
 511                         Str | Never | Char | Tuple(_) | Array(_,_) => {},
 512                         Ref(_, ref lty, _) if lty.sty == Str => {},
 513                         _ => {
 514                             let missing_trait = match op {
 515                                 hir::UnNeg => "std::ops::Neg",
 516                                 hir::UnNot => "std::ops::Not",
 517                                 hir::UnDeref => "std::ops::UnDerf"
 518                             };
 519                             err.note(&format!("an implementation of `{}` might \
 520                                                 be missing for `{}`",
 521                                              missing_trait, operand_ty));
 522                         }
 523                     }
 524                     err.emit();
 525                 }
 526                 self.tcx.types.err
 527             }
 528         }
 529     }
 530
 531     fn lookup_op_method(&self, lhs_ty: Ty<'tcx>, other_tys: &[Ty<'tcx>], op: Op)
 532                         -> Result<MethodCallee<'tcx>, ()>
 533     {
 534         let lang = self.tcx.lang_items();
 535
 536         let span = match op {
 537             Op::Binary(op, _) => op.span,
 538             Op::Unary(_, span) => span
 539         };
 540         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 541             match op.node {
 542                 hir::BinOpKind::Add => ("add_assign", lang.add_assign_trait()),
 543                 hir::BinOpKind::Sub => ("sub_assign", lang.sub_assign_trait()),
 544                 hir::BinOpKind::Mul => ("mul_assign", lang.mul_assign_trait()),
 545                 hir::BinOpKind::Div => ("div_assign", lang.div_assign_trait()),
 546                 hir::BinOpKind::Rem => ("rem_assign", lang.rem_assign_trait()),
 547                 hir::BinOpKind::BitXor => ("bitxor_assign", lang.bitxor_assign_trait()),
 548                 hir::BinOpKind::BitAnd => ("bitand_assign", lang.bitand_assign_trait()),
 549                 hir::BinOpKind::BitOr => ("bitor_assign", lang.bitor_assign_trait()),
 550                 hir::BinOpKind::Shl => ("shl_assign", lang.shl_assign_trait()),
 551                 hir::BinOpKind::Shr => ("shr_assign", lang.shr_assign_trait()),
 552                 hir::BinOpKind::Lt | hir::BinOpKind::Le |
 553                 hir::BinOpKind::Ge | hir::BinOpKind::Gt |
 554                 hir::BinOpKind::Eq | hir::BinOpKind::Ne |
 555                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 556                     span_bug!(span,
 557                               "impossible assignment operation: {}=",
 558                               op.node.as_str())
 559                 }
 560             }
 561         } else if let Op::Binary(op, IsAssign::No) = op {
 562             match op.node {
 563                 hir::BinOpKind::Add => ("add", lang.add_trait()),
 564                 hir::BinOpKind::Sub => ("sub", lang.sub_trait()),
 565                 hir::BinOpKind::Mul => ("mul", lang.mul_trait()),
 566                 hir::BinOpKind::Div => ("div", lang.div_trait()),
 567                 hir::BinOpKind::Rem => ("rem", lang.rem_trait()),
 568                 hir::BinOpKind::BitXor => ("bitxor", lang.bitxor_trait()),
 569                 hir::BinOpKind::BitAnd => ("bitand", lang.bitand_trait()),
 570                 hir::BinOpKind::BitOr => ("bitor", lang.bitor_trait()),
 571                 hir::BinOpKind::Shl => ("shl", lang.shl_trait()),
 572                 hir::BinOpKind::Shr => ("shr", lang.shr_trait()),
 573                 hir::BinOpKind::Lt => ("lt", lang.partial_ord_trait()),
 574                 hir::BinOpKind::Le => ("le", lang.partial_ord_trait()),
 575                 hir::BinOpKind::Ge => ("ge", lang.partial_ord_trait()),
 576                 hir::BinOpKind::Gt => ("gt", lang.partial_ord_trait()),
 577                 hir::BinOpKind::Eq => ("eq", lang.eq_trait()),
 578                 hir::BinOpKind::Ne => ("ne", lang.eq_trait()),
 579                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 580                     span_bug!(span, "&& and || are not overloadable")
 581                 }
 582             }
 583         } else if let Op::Unary(hir::UnNot, _) = op {
 584             ("not", lang.not_trait())
 585         } else if let Op::Unary(hir::UnNeg, _) = op {
 586             ("neg", lang.neg_trait())
 587         } else {
 588             bug!("lookup_op_method: op not supported: {:?}", op)
 589         };
 590
 591         debug!("lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 592                lhs_ty,
 593                op,
 594                opname,
 595                trait_did);
 596
 597         let method = trait_did.and_then(|trait_did| {
 598             let opname = Ident::from_str(opname);
 599             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 600         });
 601
 602         match method {
 603             Some(ok) => {
 604                 let method = self.register_infer_ok_obligations(ok);
 605                 self.select_obligations_where_possible(false);
 606
 607                 Ok(method)
 608             }
 609             None => {
 610                 Err(())
 611             }
 612         }
 613     }
 614 }
 615
 616 // Binary operator categories. These categories summarize the behavior
 617 // with respect to the builtin operationrs supported.
 618 enum BinOpCategory {
 619     /// &&, || -- cannot be overridden
 620     Shortcircuit,
 621
 622     /// <<, >> -- when shifting a single integer, rhs can be any
 623     /// integer type. For simd, types must match.
 624     Shift,
 625
 626     /// +, -, etc -- takes equal types, produces same type as input,
 627     /// applicable to ints/floats/simd
 628     Math,
 629
 630     /// &, |, ^ -- takes equal types, produces same type as input,
 631     /// applicable to ints/floats/simd/bool
 632     Bitwise,
 633
 634     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 635     /// which produce the input type
 636     Comparison,
 637 }
 638
 639 impl BinOpCategory {
 640     fn from(op: hir::BinOp) -> BinOpCategory {
 641         match op.node {
 642             hir::BinOpKind::Shl | hir::BinOpKind::Shr =>
 643                 BinOpCategory::Shift,
 644
 645             hir::BinOpKind::Add |
 646             hir::BinOpKind::Sub |
 647             hir::BinOpKind::Mul |
 648             hir::BinOpKind::Div |
 649             hir::BinOpKind::Rem =>
 650                 BinOpCategory::Math,
 651
 652             hir::BinOpKind::BitXor |
 653             hir::BinOpKind::BitAnd |
 654             hir::BinOpKind::BitOr =>
 655                 BinOpCategory::Bitwise,
 656
 657             hir::BinOpKind::Eq |
 658             hir::BinOpKind::Ne |
 659             hir::BinOpKind::Lt |
 660             hir::BinOpKind::Le |
 661             hir::BinOpKind::Ge |
 662             hir::BinOpKind::Gt =>
 663                 BinOpCategory::Comparison,
 664
 665             hir::BinOpKind::And |
 666             hir::BinOpKind::Or =>
 667                 BinOpCategory::Shortcircuit,
 668         }
 669     }
 670 }
 671
 672 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 673 #[derive(Clone, Copy, Debug, PartialEq)]
 674 enum IsAssign {
 675     No,
 676     Yes,
 677 }
 678
 679 #[derive(Clone, Copy, Debug)]
 680 enum Op {
 681     Binary(hir::BinOp, IsAssign),
 682     Unary(hir::UnOp, Span),
 683 }
 684
 685 /// Returns true if this is a built-in arithmetic operation (e.g., u32
 686 /// + u32, i16x4 == i16x4) and false if these types would have to be
 687 /// overloaded to be legal. There are two reasons that we distinguish
 688 /// builtin operations from overloaded ones (vs trying to drive
 689 /// everything uniformly through the trait system and intrinsics or
 690 /// something like that):
 691 ///
 692 /// 1. Builtin operations can trivially be evaluated in constants.
 693 /// 2. For comparison operators applied to SIMD types the result is
 694 ///    not of type `bool`. For example, `i16x4==i16x4` yields a
 695 ///    type like `i16x4`. This means that the overloaded trait
 696 ///    `PartialEq` is not applicable.
 697 ///
 698 /// Reason #2 is the killer. I tried for a while to always use
 699 /// overloaded logic and just check the types in constants/codegen after
 700 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 701 fn is_builtin_binop(lhs: Ty, rhs: Ty, op: hir::BinOp) -> bool {
 702     match BinOpCategory::from(op) {
 703         BinOpCategory::Shortcircuit => {
 704             true
 705         }
 706
 707         BinOpCategory::Shift => {
 708             lhs.references_error() || rhs.references_error() ||
 709                 lhs.is_integral() && rhs.is_integral()
 710         }
 711
 712         BinOpCategory::Math => {
 713             lhs.references_error() || rhs.references_error() ||
 714                 lhs.is_integral() && rhs.is_integral() ||
 715                 lhs.is_floating_point() && rhs.is_floating_point()
 716         }
 717
 718         BinOpCategory::Bitwise => {
 719             lhs.references_error() || rhs.references_error() ||
 720                 lhs.is_integral() && rhs.is_integral() ||
 721                 lhs.is_floating_point() && rhs.is_floating_point() ||
 722                 lhs.is_bool() && rhs.is_bool()
 723         }
 724
 725         BinOpCategory::Comparison => {
 726             lhs.references_error() || rhs.references_error() ||
 727                 lhs.is_scalar() && rhs.is_scalar()
 728         }
 729     }
 730 }