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, FnDef, Str, Uint, Never, Tuple, Char, Array};
   7 use rustc::ty::adjustment::{Adjustment, Adjust, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
   8 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
   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     /// Checks 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     /// Checks 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.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  55                expr.hir_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.hir_id={}, op={:?}, is_assign={:?})",
 154                expr.hir_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 {
 167                     kind: TypeVariableOriginKind::MiscVariable,
 168                     span: lhs_expr.span,
 169                 });
 170                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var,  AllowTwoPhase::No)
 171             }
 172             IsAssign::Yes => {
 173                 // rust-lang/rust#52126: We have to use strict
 174                 // equivalence on the LHS of an assign-op like `+=`;
 175                 // overwritten or mutably-borrowed places cannot be
 176                 // coerced to a supertype.
 177                 self.check_expr_with_needs(lhs_expr, Needs::MutPlace)
 178             }
 179         };
 180         let lhs_ty = self.resolve_type_vars_with_obligations(lhs_ty);
 181
 182         // N.B., as we have not yet type-checked the RHS, we don't have the
 183         // type at hand. Make a variable to represent it. The whole reason
 184         // for this indirection is so that, below, we can check the expr
 185         // using this variable as the expected type, which sometimes lets
 186         // us do better coercions than we would be able to do otherwise,
 187         // particularly for things like `String + &String`.
 188         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 189             kind: TypeVariableOriginKind::MiscVariable,
 190             span: rhs_expr.span,
 191         });
 192
 193         let result = self.lookup_op_method(lhs_ty, &[rhs_ty_var], Op::Binary(op, is_assign));
 194
 195         // see `NB` above
 196         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var);
 197         let rhs_ty = self.resolve_type_vars_with_obligations(rhs_ty);
 198
 199         let return_ty = match result {
 200             Ok(method) => {
 201                 let by_ref_binop = !op.node.is_by_value();
 202                 if is_assign == IsAssign::Yes || by_ref_binop {
 203                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].sty {
 204                         let mutbl = match mutbl {
 205                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 206                             hir::MutMutable => AutoBorrowMutability::Mutable {
 207                                 // Allow two-phase borrows for binops in initial deployment
 208                                 // since they desugar to methods
 209                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 210                             }
 211                         };
 212                         let autoref = Adjustment {
 213                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 214                             target: method.sig.inputs()[0]
 215                         };
 216                         self.apply_adjustments(lhs_expr, vec![autoref]);
 217                     }
 218                 }
 219                 if by_ref_binop {
 220                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].sty {
 221                         let mutbl = match mutbl {
 222                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 223                             hir::MutMutable => AutoBorrowMutability::Mutable {
 224                                 // Allow two-phase borrows for binops in initial deployment
 225                                 // since they desugar to methods
 226                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 227                             }
 228                         };
 229                         let autoref = Adjustment {
 230                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 231                             target: method.sig.inputs()[1]
 232                         };
 233                         // HACK(eddyb) Bypass checks due to reborrows being in
 234                         // some cases applied on the RHS, on top of which we need
 235                         // to autoref, which is not allowed by apply_adjustments.
 236                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 237                         self.tables
 238                             .borrow_mut()
 239                             .adjustments_mut()
 240                             .entry(rhs_expr.hir_id)
 241                             .or_default()
 242                             .push(autoref);
 243                     }
 244                 }
 245                 self.write_method_call(expr.hir_id, method);
 246
 247                 method.sig.output()
 248             }
 249             Err(()) => {
 250                 // error types are considered "builtin"
 251                 if !lhs_ty.references_error() {
 252                     let source_map = self.tcx.sess.source_map();
 253                     match is_assign {
 254                         IsAssign::Yes => {
 255                             let mut err = struct_span_err!(
 256                                 self.tcx.sess,
 257                                 expr.span,
 258                                 E0368,
 259                                 "binary assignment operation `{}=` cannot be applied to type `{}`",
 260                                 op.node.as_str(),
 261                                 lhs_ty,
 262                             );
 263                             err.span_label(
 264                                 lhs_expr.span,
 265                                 format!("cannot use `{}=` on type `{}`",
 266                                 op.node.as_str(), lhs_ty),
 267                             );
 268                             let mut suggested_deref = false;
 269                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 270                                 if {
 271                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 272                                                                            rty,
 273                                                                            lhs_expr.span) &&
 274                                         self.lookup_op_method(rty,
 275                                                               &[rhs_ty],
 276                                                               Op::Binary(op, is_assign))
 277                                             .is_ok()
 278                                 } {
 279                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 280                                         while let Ref(_, rty_inner, _) = rty.sty {
 281                                             rty = rty_inner;
 282                                         }
 283                                         let msg = &format!(
 284                                             "`{}=` can be used on '{}', you can dereference `{}`",
 285                                             op.node.as_str(),
 286                                             rty,
 287                                             lstring,
 288                                         );
 289                                         err.span_suggestion(
 290                                             lhs_expr.span,
 291                                             msg,
 292                                             format!("*{}", lstring),
 293                                             errors::Applicability::MachineApplicable,
 294                                         );
 295                                         suggested_deref = true;
 296                                     }
 297                                 }
 298                             }
 299                             let missing_trait = match op.node {
 300                                 hir::BinOpKind::Add    => Some("std::ops::AddAssign"),
 301                                 hir::BinOpKind::Sub    => Some("std::ops::SubAssign"),
 302                                 hir::BinOpKind::Mul    => Some("std::ops::MulAssign"),
 303                                 hir::BinOpKind::Div    => Some("std::ops::DivAssign"),
 304                                 hir::BinOpKind::Rem    => Some("std::ops::RemAssign"),
 305                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 306                                 hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 307                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOrAssign"),
 308                                 hir::BinOpKind::Shl    => Some("std::ops::ShlAssign"),
 309                                 hir::BinOpKind::Shr    => Some("std::ops::ShrAssign"),
 310                                 _                      => None
 311                             };
 312                             if let Some(missing_trait) = missing_trait {
 313                                 if op.node == hir::BinOpKind::Add &&
 314                                     self.check_str_addition(
 315                                         lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, true, op) {
 316                                     // This has nothing here because it means we did string
 317                                     // concatenation (e.g., "Hello " += "World!"). This means
 318                                     // we don't want the note in the else clause to be emitted
 319                                 } else if let ty::Param(_) = lhs_ty.sty {
 320                                     // FIXME: point to span of param
 321                                     err.note(&format!(
 322                                         "`{}` might need a bound for `{}`",
 323                                         lhs_ty, missing_trait
 324                                     ));
 325                                 } else if !suggested_deref {
 326                                     err.note(&format!(
 327                                         "an implementation of `{}` might \
 328                                          be missing for `{}`",
 329                                         missing_trait, lhs_ty
 330                                     ));
 331                                 }
 332                             }
 333                             err.emit();
 334                         }
 335                         IsAssign::No => {
 336                             let mut err = struct_span_err!(self.tcx.sess, op.span, E0369,
 337                                 "binary operation `{}` cannot be applied to type `{}`",
 338                                 op.node.as_str(),
 339                                 lhs_ty);
 340
 341                             let mut involves_fn = false;
 342                             if !lhs_expr.span.eq(&rhs_expr.span) {
 343                                 involves_fn |= self.add_type_neq_err_label(
 344                                     &mut err,
 345                                     lhs_expr.span,
 346                                     lhs_ty,
 347                                     rhs_ty,
 348                                     op,
 349                                     is_assign
 350                                 );
 351                                 involves_fn |= self.add_type_neq_err_label(
 352                                     &mut err,
 353                                     rhs_expr.span,
 354                                     rhs_ty,
 355                                     lhs_ty,
 356                                     op,
 357                                     is_assign
 358                                 );
 359                             }
 360
 361                             let mut suggested_deref = false;
 362                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 363                                 if {
 364                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 365                                                                            rty,
 366                                                                            lhs_expr.span) &&
 367                                         self.lookup_op_method(rty,
 368                                                               &[rhs_ty],
 369                                                               Op::Binary(op, is_assign))
 370                                             .is_ok()
 371                                 } {
 372                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 373                                         while let Ref(_, rty_inner, _) = rty.sty {
 374                                             rty = rty_inner;
 375                                         }
 376                                         let msg = &format!(
 377                                                 "`{}` can be used on '{}', you can \
 378                                                 dereference `{2}`: `*{2}`",
 379                                                 op.node.as_str(),
 380                                                 rty,
 381                                                 lstring
 382                                         );
 383                                         err.help(msg);
 384                                         suggested_deref = true;
 385                                     }
 386                                 }
 387                             }
 388                             let missing_trait = match op.node {
 389                                 hir::BinOpKind::Add    => Some("std::ops::Add"),
 390                                 hir::BinOpKind::Sub    => Some("std::ops::Sub"),
 391                                 hir::BinOpKind::Mul    => Some("std::ops::Mul"),
 392                                 hir::BinOpKind::Div    => Some("std::ops::Div"),
 393                                 hir::BinOpKind::Rem    => Some("std::ops::Rem"),
 394                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAnd"),
 395                                 hir::BinOpKind::BitXor => Some("std::ops::BitXor"),
 396                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOr"),
 397                                 hir::BinOpKind::Shl    => Some("std::ops::Shl"),
 398                                 hir::BinOpKind::Shr    => Some("std::ops::Shr"),
 399                                 hir::BinOpKind::Eq |
 400                                 hir::BinOpKind::Ne => Some("std::cmp::PartialEq"),
 401                                 hir::BinOpKind::Lt |
 402                                 hir::BinOpKind::Le |
 403                                 hir::BinOpKind::Gt |
 404                                 hir::BinOpKind::Ge => Some("std::cmp::PartialOrd"),
 405                                 _ => None
 406                             };
 407                             if let Some(missing_trait) = missing_trait {
 408                                 if op.node == hir::BinOpKind::Add &&
 409                                     self.check_str_addition(
 410                                         lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, false, op) {
 411                                     // This has nothing here because it means we did string
 412                                     // concatenation (e.g., "Hello " + "World!"). This means
 413                                     // we don't want the note in the else clause to be emitted
 414                                 } else if let ty::Param(_) = lhs_ty.sty {
 415                                     // FIXME: point to span of param
 416                                     err.note(&format!(
 417                                         "`{}` might need a bound for `{}`",
 418                                         lhs_ty, missing_trait
 419                                     ));
 420                                 } else if !suggested_deref && !involves_fn {
 421                                     err.note(&format!(
 422                                         "an implementation of `{}` might \
 423                                          be missing for `{}`",
 424                                         missing_trait, lhs_ty
 425                                     ));
 426                                 }
 427                             }
 428                             err.emit();
 429                         }
 430                     }
 431                 }
 432                 self.tcx.types.err
 433             }
 434         };
 435
 436         (lhs_ty, rhs_ty, return_ty)
 437     }
 438
 439     /// If one of the types is an uncalled function and calling it would yield the other type,
 440     /// suggest calling the function. Returns wether a suggestion was given.
 441     fn add_type_neq_err_label(
 442         &self,
 443         err: &mut errors::DiagnosticBuilder<'_>,
 444         span: Span,
 445         ty: Ty<'tcx>,
 446         other_ty: Ty<'tcx>,
 447         op: hir::BinOp,
 448         is_assign: IsAssign,
 449     ) -> bool /* did we suggest to call a function because of missing parenthesis? */ {
 450         err.span_label(span, ty.to_string());
 451         if let FnDef(def_id, _) = ty.sty {
 452             let source_map = self.tcx.sess.source_map();
 453             let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
 454                 Some(hir_id) => hir_id,
 455                 None => return false,
 456             };
 457             if self.tcx.has_typeck_tables(def_id) == false {
 458                 return false;
 459             }
 460             let fn_sig = {
 461                 match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(hir_id) {
 462                     Some(f) => f.clone(),
 463                     None => {
 464                         bug!("No fn-sig entry for def_id={:?}", def_id);
 465                     }
 466                 }
 467             };
 468
 469             let other_ty = if let FnDef(def_id, _) = other_ty.sty {
 470                 let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
 471                     Some(hir_id) => hir_id,
 472                     None => return false,
 473                 };
 474                 if self.tcx.has_typeck_tables(def_id) == false {
 475                     return false;
 476                 }
 477                 match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(hir_id) {
 478                     Some(f) => f.clone().output(),
 479                     None => {
 480                         bug!("No fn-sig entry for def_id={:?}", def_id);
 481                     }
 482                 }
 483             } else {
 484                 other_ty
 485             };
 486
 487             if self.lookup_op_method(fn_sig.output(),
 488                                     &[other_ty],
 489                                     Op::Binary(op, is_assign))
 490                     .is_ok() {
 491                 let (variable_snippet, applicability) = if fn_sig.inputs().len() > 0 {
 492                     (format!("{}( /* arguments */ )", source_map.span_to_snippet(span).unwrap()),
 493                     Applicability::HasPlaceholders)
 494                 } else {
 495                     (format!("{}()", source_map.span_to_snippet(span).unwrap()),
 496                     Applicability::MaybeIncorrect)
 497                 };
 498
 499                 err.span_suggestion(
 500                     span,
 501                     "you might have forgotten to call this function",
 502                     variable_snippet,
 503                     applicability,
 504                 );
 505                 return true;
 506             }
 507         }
 508         false
 509     }
 510
 511     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 512     /// like `&str + &str`, `String + String` and `&str + &String`.
 513     ///
 514     /// If this function returns `true` it means a note was printed, so we don't need
 515     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 516     fn check_str_addition(
 517         &self,
 518         lhs_expr: &'gcx hir::Expr,
 519         rhs_expr: &'gcx hir::Expr,
 520         lhs_ty: Ty<'tcx>,
 521         rhs_ty: Ty<'tcx>,
 522         err: &mut errors::DiagnosticBuilder<'_>,
 523         is_assign: bool,
 524         op: hir::BinOp,
 525     ) -> bool {
 526         let source_map = self.tcx.sess.source_map();
 527         let remove_borrow_msg = "String concatenation appends the string on the right to the \
 528                                  string on the left and may require reallocation. This \
 529                                  requires ownership of the string on the left";
 530
 531         let msg = "`to_owned()` can be used to create an owned `String` \
 532                    from a string reference. String concatenation \
 533                    appends the string on the right to the string \
 534                    on the left and may require reallocation. This \
 535                    requires ownership of the string on the left";
 536
 537         let is_std_string = |ty| &format!("{:?}", ty) == "std::string::String";
 538
 539         match (&lhs_ty.sty, &rhs_ty.sty) {
 540             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 541                 if (l_ty.sty == Str || is_std_string(l_ty)) && (
 542                         r_ty.sty == Str || is_std_string(r_ty) ||
 543                         &format!("{:?}", rhs_ty) == "&&str"
 544                     ) =>
 545             {
 546                 if !is_assign { // Do not supply this message if `&str += &str`
 547                     err.span_label(
 548                         op.span,
 549                         "`+` cannot be used to concatenate two `&str` strings",
 550                     );
 551                     match source_map.span_to_snippet(lhs_expr.span) {
 552                         Ok(lstring) => {
 553                             err.span_suggestion(
 554                                 lhs_expr.span,
 555                                 if lstring.starts_with("&") {
 556                                     remove_borrow_msg
 557                                 } else {
 558                                     msg
 559                                 },
 560                                 if lstring.starts_with("&") {
 561                                     // let a = String::new();
 562                                     // let _ = &a + "bar";
 563                                     format!("{}", &lstring[1..])
 564                                 } else {
 565                                     format!("{}.to_owned()", lstring)
 566                                 },
 567                                 Applicability::MachineApplicable,
 568                             )
 569                         }
 570                         _ => err.help(msg),
 571                     };
 572                 }
 573                 true
 574             }
 575             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 576                 if (l_ty.sty == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 577             {
 578                 err.span_label(
 579                     op.span,
 580                     "`+` cannot be used to concatenate a `&str` with a `String`",
 581                 );
 582                 match (
 583                     source_map.span_to_snippet(lhs_expr.span),
 584                     source_map.span_to_snippet(rhs_expr.span),
 585                     is_assign,
 586                 ) {
 587                     (Ok(l), Ok(r), false) => {
 588                         let to_string = if l.starts_with("&") {
 589                             // let a = String::new(); let b = String::new();
 590                             // let _ = &a + b;
 591                             format!("{}", &l[1..])
 592                         } else {
 593                             format!("{}.to_owned()", l)
 594                         };
 595                         err.multipart_suggestion(
 596                             msg,
 597                             vec![
 598                                 (lhs_expr.span, to_string),
 599                                 (rhs_expr.span, format!("&{}", r)),
 600                             ],
 601                             Applicability::MachineApplicable,
 602                         );
 603                     }
 604                     _ => {
 605                         err.help(msg);
 606                     }
 607                 };
 608                 true
 609             }
 610             _ => false,
 611         }
 612     }
 613
 614     pub fn check_user_unop(&self,
 615                            ex: &'gcx hir::Expr,
 616                            operand_ty: Ty<'tcx>,
 617                            op: hir::UnOp)
 618                            -> Ty<'tcx>
 619     {
 620         assert!(op.is_by_value());
 621         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 622             Ok(method) => {
 623                 self.write_method_call(ex.hir_id, method);
 624                 method.sig.output()
 625             }
 626             Err(()) => {
 627                 let actual = self.resolve_vars_if_possible(&operand_ty);
 628                 if !actual.references_error() {
 629                     let mut err = struct_span_err!(self.tcx.sess, ex.span, E0600,
 630                                      "cannot apply unary operator `{}` to type `{}`",
 631                                      op.as_str(), actual);
 632                     err.span_label(ex.span, format!("cannot apply unary \
 633                                                     operator `{}`", op.as_str()));
 634                     match actual.sty {
 635                         Uint(_) if op == hir::UnNeg => {
 636                             err.note("unsigned values cannot be negated");
 637                         },
 638                         Str | Never | Char | Tuple(_) | Array(_,_) => {},
 639                         Ref(_, ref lty, _) if lty.sty == Str => {},
 640                         _ => {
 641                             let missing_trait = match op {
 642                                 hir::UnNeg => "std::ops::Neg",
 643                                 hir::UnNot => "std::ops::Not",
 644                                 hir::UnDeref => "std::ops::UnDerf"
 645                             };
 646                             err.note(&format!("an implementation of `{}` might \
 647                                                 be missing for `{}`",
 648                                              missing_trait, operand_ty));
 649                         }
 650                     }
 651                     err.emit();
 652                 }
 653                 self.tcx.types.err
 654             }
 655         }
 656     }
 657
 658     fn lookup_op_method(&self, lhs_ty: Ty<'tcx>, other_tys: &[Ty<'tcx>], op: Op)
 659                         -> Result<MethodCallee<'tcx>, ()>
 660     {
 661         let lang = self.tcx.lang_items();
 662
 663         let span = match op {
 664             Op::Binary(op, _) => op.span,
 665             Op::Unary(_, span) => span
 666         };
 667         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 668             match op.node {
 669                 hir::BinOpKind::Add => ("add_assign", lang.add_assign_trait()),
 670                 hir::BinOpKind::Sub => ("sub_assign", lang.sub_assign_trait()),
 671                 hir::BinOpKind::Mul => ("mul_assign", lang.mul_assign_trait()),
 672                 hir::BinOpKind::Div => ("div_assign", lang.div_assign_trait()),
 673                 hir::BinOpKind::Rem => ("rem_assign", lang.rem_assign_trait()),
 674                 hir::BinOpKind::BitXor => ("bitxor_assign", lang.bitxor_assign_trait()),
 675                 hir::BinOpKind::BitAnd => ("bitand_assign", lang.bitand_assign_trait()),
 676                 hir::BinOpKind::BitOr => ("bitor_assign", lang.bitor_assign_trait()),
 677                 hir::BinOpKind::Shl => ("shl_assign", lang.shl_assign_trait()),
 678                 hir::BinOpKind::Shr => ("shr_assign", lang.shr_assign_trait()),
 679                 hir::BinOpKind::Lt | hir::BinOpKind::Le |
 680                 hir::BinOpKind::Ge | hir::BinOpKind::Gt |
 681                 hir::BinOpKind::Eq | hir::BinOpKind::Ne |
 682                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 683                     span_bug!(span,
 684                               "impossible assignment operation: {}=",
 685                               op.node.as_str())
 686                 }
 687             }
 688         } else if let Op::Binary(op, IsAssign::No) = op {
 689             match op.node {
 690                 hir::BinOpKind::Add => ("add", lang.add_trait()),
 691                 hir::BinOpKind::Sub => ("sub", lang.sub_trait()),
 692                 hir::BinOpKind::Mul => ("mul", lang.mul_trait()),
 693                 hir::BinOpKind::Div => ("div", lang.div_trait()),
 694                 hir::BinOpKind::Rem => ("rem", lang.rem_trait()),
 695                 hir::BinOpKind::BitXor => ("bitxor", lang.bitxor_trait()),
 696                 hir::BinOpKind::BitAnd => ("bitand", lang.bitand_trait()),
 697                 hir::BinOpKind::BitOr => ("bitor", lang.bitor_trait()),
 698                 hir::BinOpKind::Shl => ("shl", lang.shl_trait()),
 699                 hir::BinOpKind::Shr => ("shr", lang.shr_trait()),
 700                 hir::BinOpKind::Lt => ("lt", lang.partial_ord_trait()),
 701                 hir::BinOpKind::Le => ("le", lang.partial_ord_trait()),
 702                 hir::BinOpKind::Ge => ("ge", lang.partial_ord_trait()),
 703                 hir::BinOpKind::Gt => ("gt", lang.partial_ord_trait()),
 704                 hir::BinOpKind::Eq => ("eq", lang.eq_trait()),
 705                 hir::BinOpKind::Ne => ("ne", lang.eq_trait()),
 706                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 707                     span_bug!(span, "&& and || are not overloadable")
 708                 }
 709             }
 710         } else if let Op::Unary(hir::UnNot, _) = op {
 711             ("not", lang.not_trait())
 712         } else if let Op::Unary(hir::UnNeg, _) = op {
 713             ("neg", lang.neg_trait())
 714         } else {
 715             bug!("lookup_op_method: op not supported: {:?}", op)
 716         };
 717
 718         debug!("lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 719                lhs_ty,
 720                op,
 721                opname,
 722                trait_did);
 723
 724         let method = trait_did.and_then(|trait_did| {
 725             let opname = Ident::from_str(opname);
 726             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 727         });
 728
 729         match method {
 730             Some(ok) => {
 731                 let method = self.register_infer_ok_obligations(ok);
 732                 self.select_obligations_where_possible(false);
 733
 734                 Ok(method)
 735             }
 736             None => {
 737                 Err(())
 738             }
 739         }
 740     }
 741 }
 742
 743 // Binary operator categories. These categories summarize the behavior
 744 // with respect to the builtin operationrs supported.
 745 enum BinOpCategory {
 746     /// &&, || -- cannot be overridden
 747     Shortcircuit,
 748
 749     /// <<, >> -- when shifting a single integer, rhs can be any
 750     /// integer type. For simd, types must match.
 751     Shift,
 752
 753     /// +, -, etc -- takes equal types, produces same type as input,
 754     /// applicable to ints/floats/simd
 755     Math,
 756
 757     /// &, |, ^ -- takes equal types, produces same type as input,
 758     /// applicable to ints/floats/simd/bool
 759     Bitwise,
 760
 761     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 762     /// which produce the input type
 763     Comparison,
 764 }
 765
 766 impl BinOpCategory {
 767     fn from(op: hir::BinOp) -> BinOpCategory {
 768         match op.node {
 769             hir::BinOpKind::Shl | hir::BinOpKind::Shr =>
 770                 BinOpCategory::Shift,
 771
 772             hir::BinOpKind::Add |
 773             hir::BinOpKind::Sub |
 774             hir::BinOpKind::Mul |
 775             hir::BinOpKind::Div |
 776             hir::BinOpKind::Rem =>
 777                 BinOpCategory::Math,
 778
 779             hir::BinOpKind::BitXor |
 780             hir::BinOpKind::BitAnd |
 781             hir::BinOpKind::BitOr =>
 782                 BinOpCategory::Bitwise,
 783
 784             hir::BinOpKind::Eq |
 785             hir::BinOpKind::Ne |
 786             hir::BinOpKind::Lt |
 787             hir::BinOpKind::Le |
 788             hir::BinOpKind::Ge |
 789             hir::BinOpKind::Gt =>
 790                 BinOpCategory::Comparison,
 791
 792             hir::BinOpKind::And |
 793             hir::BinOpKind::Or =>
 794                 BinOpCategory::Shortcircuit,
 795         }
 796     }
 797 }
 798
 799 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 800 #[derive(Clone, Copy, Debug, PartialEq)]
 801 enum IsAssign {
 802     No,
 803     Yes,
 804 }
 805
 806 #[derive(Clone, Copy, Debug)]
 807 enum Op {
 808     Binary(hir::BinOp, IsAssign),
 809     Unary(hir::UnOp, Span),
 810 }
 811
 812 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 813 /// + u32, i16x4 == i16x4) and false if these types would have to be
 814 /// overloaded to be legal. There are two reasons that we distinguish
 815 /// builtin operations from overloaded ones (vs trying to drive
 816 /// everything uniformly through the trait system and intrinsics or
 817 /// something like that):
 818 ///
 819 /// 1. Builtin operations can trivially be evaluated in constants.
 820 /// 2. For comparison operators applied to SIMD types the result is
 821 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 822 ///    type like `i16x4`. This means that the overloaded trait
 823 ///    `PartialEq` is not applicable.
 824 ///
 825 /// Reason #2 is the killer. I tried for a while to always use
 826 /// overloaded logic and just check the types in constants/codegen after
 827 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 828 fn is_builtin_binop(lhs: Ty<'_>, rhs: Ty<'_>, op: hir::BinOp) -> bool {
 829     match BinOpCategory::from(op) {
 830         BinOpCategory::Shortcircuit => {
 831             true
 832         }
 833
 834         BinOpCategory::Shift => {
 835             lhs.references_error() || rhs.references_error() ||
 836                 lhs.is_integral() && rhs.is_integral()
 837         }
 838
 839         BinOpCategory::Math => {
 840             lhs.references_error() || rhs.references_error() ||
 841                 lhs.is_integral() && rhs.is_integral() ||
 842                 lhs.is_floating_point() && rhs.is_floating_point()
 843         }
 844
 845         BinOpCategory::Bitwise => {
 846             lhs.references_error() || rhs.references_error() ||
 847                 lhs.is_integral() && rhs.is_integral() ||
 848                 lhs.is_floating_point() && rhs.is_floating_point() ||
 849                 lhs.is_bool() && rhs.is_bool()
 850         }
 851
 852         BinOpCategory::Comparison => {
 853             lhs.references_error() || rhs.references_error() ||
 854                 lhs.is_scalar() && rhs.is_scalar()
 855         }
 856     }
 857 }