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;
   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::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(
 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(
 309                                         lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, true, op) {
 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, op.span, E0369,
 331                                 "binary operation `{}` cannot be applied to type `{}`",
 332                                 op.node.as_str(),
 333                                 lhs_ty);
 334
 335                             let mut involves_fn = false;
 336                             if !lhs_expr.span.eq(&rhs_expr.span) {
 337                                 involves_fn |= self.add_type_neq_err_label(
 338                                     &mut err,
 339                                     lhs_expr.span,
 340                                     lhs_ty,
 341                                     rhs_ty,
 342                                     op,
 343                                     is_assign
 344                                 );
 345                                 involves_fn |= self.add_type_neq_err_label(
 346                                     &mut err,
 347                                     rhs_expr.span,
 348                                     rhs_ty,
 349                                     lhs_ty,
 350                                     op,
 351                                     is_assign
 352                                 );
 353                             }
 354
 355                             let mut suggested_deref = false;
 356                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 357                                 if {
 358                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 359                                                                            rty,
 360                                                                            lhs_expr.span) &&
 361                                         self.lookup_op_method(rty,
 362                                                               &[rhs_ty],
 363                                                               Op::Binary(op, is_assign))
 364                                             .is_ok()
 365                                 } {
 366                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 367                                         while let Ref(_, rty_inner, _) = rty.sty {
 368                                             rty = rty_inner;
 369                                         }
 370                                         let msg = &format!(
 371                                                 "`{}` can be used on '{}', you can \
 372                                                 dereference `{2}`: `*{2}`",
 373                                                 op.node.as_str(),
 374                                                 rty,
 375                                                 lstring
 376                                         );
 377                                         err.help(msg);
 378                                         suggested_deref = true;
 379                                     }
 380                                 }
 381                             }
 382                             let missing_trait = match op.node {
 383                                 hir::BinOpKind::Add    => Some("std::ops::Add"),
 384                                 hir::BinOpKind::Sub    => Some("std::ops::Sub"),
 385                                 hir::BinOpKind::Mul    => Some("std::ops::Mul"),
 386                                 hir::BinOpKind::Div    => Some("std::ops::Div"),
 387                                 hir::BinOpKind::Rem    => Some("std::ops::Rem"),
 388                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAnd"),
 389                                 hir::BinOpKind::BitXor => Some("std::ops::BitXor"),
 390                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOr"),
 391                                 hir::BinOpKind::Shl    => Some("std::ops::Shl"),
 392                                 hir::BinOpKind::Shr    => Some("std::ops::Shr"),
 393                                 hir::BinOpKind::Eq |
 394                                 hir::BinOpKind::Ne => Some("std::cmp::PartialEq"),
 395                                 hir::BinOpKind::Lt |
 396                                 hir::BinOpKind::Le |
 397                                 hir::BinOpKind::Gt |
 398                                 hir::BinOpKind::Ge => Some("std::cmp::PartialOrd"),
 399                                 _ => None
 400                             };
 401                             if let Some(missing_trait) = missing_trait {
 402                                 if op.node == hir::BinOpKind::Add &&
 403                                     self.check_str_addition(
 404                                         lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, false, op) {
 405                                     // This has nothing here because it means we did string
 406                                     // concatenation (e.g., "Hello " + "World!"). This means
 407                                     // we don't want the note in the else clause to be emitted
 408                                 } else if let ty::Param(_) = lhs_ty.sty {
 409                                     // FIXME: point to span of param
 410                                     err.note(&format!(
 411                                         "`{}` might need a bound for `{}`",
 412                                         lhs_ty, missing_trait
 413                                     ));
 414                                 } else if !suggested_deref && !involves_fn {
 415                                     err.note(&format!(
 416                                         "an implementation of `{}` might \
 417                                          be missing for `{}`",
 418                                         missing_trait, lhs_ty
 419                                     ));
 420                                 }
 421                             }
 422                             err.emit();
 423                         }
 424                     }
 425                 }
 426                 self.tcx.types.err
 427             }
 428         };
 429
 430         (lhs_ty, rhs_ty, return_ty)
 431     }
 432
 433     /// If one of the types is an uncalled function and calling it would yield the other type,
 434     /// suggest calling the function. Returns wether a suggestion was given.
 435     fn add_type_neq_err_label(
 436         &self,
 437         err: &mut errors::DiagnosticBuilder<'_>,
 438         span: Span,
 439         ty: Ty<'tcx>,
 440         other_ty: Ty<'tcx>,
 441         op: hir::BinOp,
 442         is_assign: IsAssign,
 443     ) -> bool /* did we suggest to call a function because of missing parenthesis? */ {
 444         err.span_label(span, ty.to_string());
 445         if let FnDef(def_id, _) = ty.sty {
 446             let source_map = self.tcx.sess.source_map();
 447             let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
 448                 Some(hir_id) => hir_id,
 449                 None => return false,
 450             };
 451             if self.tcx.has_typeck_tables(def_id) == false {
 452                 return false;
 453             }
 454             let fn_sig = {
 455                 match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(hir_id) {
 456                     Some(f) => f.clone(),
 457                     None => {
 458                         bug!("No fn-sig entry for def_id={:?}", def_id);
 459                     }
 460                 }
 461             };
 462
 463             let other_ty = if let FnDef(def_id, _) = other_ty.sty {
 464                 let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
 465                     Some(hir_id) => hir_id,
 466                     None => return false,
 467                 };
 468                 if self.tcx.has_typeck_tables(def_id) == false {
 469                     return false;
 470                 }
 471                 match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(hir_id) {
 472                     Some(f) => f.clone().output(),
 473                     None => {
 474                         bug!("No fn-sig entry for def_id={:?}", def_id);
 475                     }
 476                 }
 477             } else {
 478                 other_ty
 479             };
 480
 481             if self.lookup_op_method(fn_sig.output(),
 482                                     &[other_ty],
 483                                     Op::Binary(op, is_assign))
 484                     .is_ok() {
 485                 let (variable_snippet, applicability) = if fn_sig.inputs().len() > 0 {
 486                     (format!("{}( /* arguments */ )", source_map.span_to_snippet(span).unwrap()),
 487                     Applicability::HasPlaceholders)
 488                 } else {
 489                     (format!("{}()", source_map.span_to_snippet(span).unwrap()),
 490                     Applicability::MaybeIncorrect)
 491                 };
 492
 493                 err.span_suggestion(
 494                     span,
 495                     "you might have forgotten to call this function",
 496                     variable_snippet,
 497                     applicability,
 498                 );
 499                 return true;
 500             }
 501         }
 502         false
 503     }
 504
 505     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 506     /// like `&str + &str`, `String + String` and `&str + &String`.
 507     ///
 508     /// If this function returns `true` it means a note was printed, so we don't need
 509     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 510     fn check_str_addition(
 511         &self,
 512         lhs_expr: &'gcx hir::Expr,
 513         rhs_expr: &'gcx hir::Expr,
 514         lhs_ty: Ty<'tcx>,
 515         rhs_ty: Ty<'tcx>,
 516         err: &mut errors::DiagnosticBuilder<'_>,
 517         is_assign: bool,
 518         op: hir::BinOp,
 519     ) -> bool {
 520         let source_map = self.tcx.sess.source_map();
 521         let remove_borrow_msg = "String concatenation appends the string on the right to the \
 522                                  string on the left and may require reallocation. This \
 523                                  requires ownership of the string on the left";
 524
 525         let msg = "`to_owned()` can be used to create an owned `String` \
 526                    from a string reference. String concatenation \
 527                    appends the string on the right to the string \
 528                    on the left and may require reallocation. This \
 529                    requires ownership of the string on the left";
 530
 531         let is_std_string = |ty| &format!("{:?}", ty) == "std::string::String";
 532
 533         match (&lhs_ty.sty, &rhs_ty.sty) {
 534             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 535                 if (l_ty.sty == Str || is_std_string(l_ty)) && (
 536                         r_ty.sty == Str || is_std_string(r_ty) ||
 537                         &format!("{:?}", rhs_ty) == "&&str"
 538                     ) =>
 539             {
 540                 if !is_assign { // Do not supply this message if `&str += &str`
 541                     err.span_label(
 542                         op.span,
 543                         "`+` cannot be used to concatenate two `&str` strings",
 544                     );
 545                     match source_map.span_to_snippet(lhs_expr.span) {
 546                         Ok(lstring) => {
 547                             err.span_suggestion(
 548                                 lhs_expr.span,
 549                                 if lstring.starts_with("&") {
 550                                     remove_borrow_msg
 551                                 } else {
 552                                     msg
 553                                 },
 554                                 if lstring.starts_with("&") {
 555                                     // let a = String::new();
 556                                     // let _ = &a + "bar";
 557                                     format!("{}", &lstring[1..])
 558                                 } else {
 559                                     format!("{}.to_owned()", lstring)
 560                                 },
 561                                 Applicability::MachineApplicable,
 562                             )
 563                         }
 564                         _ => err.help(msg),
 565                     };
 566                 }
 567                 true
 568             }
 569             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 570                 if (l_ty.sty == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 571             {
 572                 err.span_label(
 573                     op.span,
 574                     "`+` cannot be used to concatenate a `&str` with a `String`",
 575                 );
 576                 match (
 577                     source_map.span_to_snippet(lhs_expr.span),
 578                     source_map.span_to_snippet(rhs_expr.span),
 579                     is_assign,
 580                 ) {
 581                     (Ok(l), Ok(r), false) => {
 582                         err.multipart_suggestion(
 583                             msg,
 584                             vec![
 585                                 (lhs_expr.span, format!("{}.to_owned()", l)),
 586                                 (rhs_expr.span, format!("&{}", r)),
 587                             ],
 588                             Applicability::MachineApplicable,
 589                         );
 590                     }
 591                     _ => {
 592                         err.help(msg);
 593                     }
 594                 };
 595                 true
 596             }
 597             _ => false,
 598         }
 599     }
 600
 601     pub fn check_user_unop(&self,
 602                            ex: &'gcx hir::Expr,
 603                            operand_ty: Ty<'tcx>,
 604                            op: hir::UnOp)
 605                            -> Ty<'tcx>
 606     {
 607         assert!(op.is_by_value());
 608         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 609             Ok(method) => {
 610                 self.write_method_call(ex.hir_id, method);
 611                 method.sig.output()
 612             }
 613             Err(()) => {
 614                 let actual = self.resolve_type_vars_if_possible(&operand_ty);
 615                 if !actual.references_error() {
 616                     let mut err = struct_span_err!(self.tcx.sess, ex.span, E0600,
 617                                      "cannot apply unary operator `{}` to type `{}`",
 618                                      op.as_str(), actual);
 619                     err.span_label(ex.span, format!("cannot apply unary \
 620                                                     operator `{}`", op.as_str()));
 621                     match actual.sty {
 622                         Uint(_) if op == hir::UnNeg => {
 623                             err.note("unsigned values cannot be negated");
 624                         },
 625                         Str | Never | Char | Tuple(_) | Array(_,_) => {},
 626                         Ref(_, ref lty, _) if lty.sty == Str => {},
 627                         _ => {
 628                             let missing_trait = match op {
 629                                 hir::UnNeg => "std::ops::Neg",
 630                                 hir::UnNot => "std::ops::Not",
 631                                 hir::UnDeref => "std::ops::UnDerf"
 632                             };
 633                             err.note(&format!("an implementation of `{}` might \
 634                                                 be missing for `{}`",
 635                                              missing_trait, operand_ty));
 636                         }
 637                     }
 638                     err.emit();
 639                 }
 640                 self.tcx.types.err
 641             }
 642         }
 643     }
 644
 645     fn lookup_op_method(&self, lhs_ty: Ty<'tcx>, other_tys: &[Ty<'tcx>], op: Op)
 646                         -> Result<MethodCallee<'tcx>, ()>
 647     {
 648         let lang = self.tcx.lang_items();
 649
 650         let span = match op {
 651             Op::Binary(op, _) => op.span,
 652             Op::Unary(_, span) => span
 653         };
 654         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 655             match op.node {
 656                 hir::BinOpKind::Add => ("add_assign", lang.add_assign_trait()),
 657                 hir::BinOpKind::Sub => ("sub_assign", lang.sub_assign_trait()),
 658                 hir::BinOpKind::Mul => ("mul_assign", lang.mul_assign_trait()),
 659                 hir::BinOpKind::Div => ("div_assign", lang.div_assign_trait()),
 660                 hir::BinOpKind::Rem => ("rem_assign", lang.rem_assign_trait()),
 661                 hir::BinOpKind::BitXor => ("bitxor_assign", lang.bitxor_assign_trait()),
 662                 hir::BinOpKind::BitAnd => ("bitand_assign", lang.bitand_assign_trait()),
 663                 hir::BinOpKind::BitOr => ("bitor_assign", lang.bitor_assign_trait()),
 664                 hir::BinOpKind::Shl => ("shl_assign", lang.shl_assign_trait()),
 665                 hir::BinOpKind::Shr => ("shr_assign", lang.shr_assign_trait()),
 666                 hir::BinOpKind::Lt | hir::BinOpKind::Le |
 667                 hir::BinOpKind::Ge | hir::BinOpKind::Gt |
 668                 hir::BinOpKind::Eq | hir::BinOpKind::Ne |
 669                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 670                     span_bug!(span,
 671                               "impossible assignment operation: {}=",
 672                               op.node.as_str())
 673                 }
 674             }
 675         } else if let Op::Binary(op, IsAssign::No) = op {
 676             match op.node {
 677                 hir::BinOpKind::Add => ("add", lang.add_trait()),
 678                 hir::BinOpKind::Sub => ("sub", lang.sub_trait()),
 679                 hir::BinOpKind::Mul => ("mul", lang.mul_trait()),
 680                 hir::BinOpKind::Div => ("div", lang.div_trait()),
 681                 hir::BinOpKind::Rem => ("rem", lang.rem_trait()),
 682                 hir::BinOpKind::BitXor => ("bitxor", lang.bitxor_trait()),
 683                 hir::BinOpKind::BitAnd => ("bitand", lang.bitand_trait()),
 684                 hir::BinOpKind::BitOr => ("bitor", lang.bitor_trait()),
 685                 hir::BinOpKind::Shl => ("shl", lang.shl_trait()),
 686                 hir::BinOpKind::Shr => ("shr", lang.shr_trait()),
 687                 hir::BinOpKind::Lt => ("lt", lang.partial_ord_trait()),
 688                 hir::BinOpKind::Le => ("le", lang.partial_ord_trait()),
 689                 hir::BinOpKind::Ge => ("ge", lang.partial_ord_trait()),
 690                 hir::BinOpKind::Gt => ("gt", lang.partial_ord_trait()),
 691                 hir::BinOpKind::Eq => ("eq", lang.eq_trait()),
 692                 hir::BinOpKind::Ne => ("ne", lang.eq_trait()),
 693                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 694                     span_bug!(span, "&& and || are not overloadable")
 695                 }
 696             }
 697         } else if let Op::Unary(hir::UnNot, _) = op {
 698             ("not", lang.not_trait())
 699         } else if let Op::Unary(hir::UnNeg, _) = op {
 700             ("neg", lang.neg_trait())
 701         } else {
 702             bug!("lookup_op_method: op not supported: {:?}", op)
 703         };
 704
 705         debug!("lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 706                lhs_ty,
 707                op,
 708                opname,
 709                trait_did);
 710
 711         let method = trait_did.and_then(|trait_did| {
 712             let opname = Ident::from_str(opname);
 713             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 714         });
 715
 716         match method {
 717             Some(ok) => {
 718                 let method = self.register_infer_ok_obligations(ok);
 719                 self.select_obligations_where_possible(false);
 720
 721                 Ok(method)
 722             }
 723             None => {
 724                 Err(())
 725             }
 726         }
 727     }
 728 }
 729
 730 // Binary operator categories. These categories summarize the behavior
 731 // with respect to the builtin operationrs supported.
 732 enum BinOpCategory {
 733     /// &&, || -- cannot be overridden
 734     Shortcircuit,
 735
 736     /// <<, >> -- when shifting a single integer, rhs can be any
 737     /// integer type. For simd, types must match.
 738     Shift,
 739
 740     /// +, -, etc -- takes equal types, produces same type as input,
 741     /// applicable to ints/floats/simd
 742     Math,
 743
 744     /// &, |, ^ -- takes equal types, produces same type as input,
 745     /// applicable to ints/floats/simd/bool
 746     Bitwise,
 747
 748     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 749     /// which produce the input type
 750     Comparison,
 751 }
 752
 753 impl BinOpCategory {
 754     fn from(op: hir::BinOp) -> BinOpCategory {
 755         match op.node {
 756             hir::BinOpKind::Shl | hir::BinOpKind::Shr =>
 757                 BinOpCategory::Shift,
 758
 759             hir::BinOpKind::Add |
 760             hir::BinOpKind::Sub |
 761             hir::BinOpKind::Mul |
 762             hir::BinOpKind::Div |
 763             hir::BinOpKind::Rem =>
 764                 BinOpCategory::Math,
 765
 766             hir::BinOpKind::BitXor |
 767             hir::BinOpKind::BitAnd |
 768             hir::BinOpKind::BitOr =>
 769                 BinOpCategory::Bitwise,
 770
 771             hir::BinOpKind::Eq |
 772             hir::BinOpKind::Ne |
 773             hir::BinOpKind::Lt |
 774             hir::BinOpKind::Le |
 775             hir::BinOpKind::Ge |
 776             hir::BinOpKind::Gt =>
 777                 BinOpCategory::Comparison,
 778
 779             hir::BinOpKind::And |
 780             hir::BinOpKind::Or =>
 781                 BinOpCategory::Shortcircuit,
 782         }
 783     }
 784 }
 785
 786 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 787 #[derive(Clone, Copy, Debug, PartialEq)]
 788 enum IsAssign {
 789     No,
 790     Yes,
 791 }
 792
 793 #[derive(Clone, Copy, Debug)]
 794 enum Op {
 795     Binary(hir::BinOp, IsAssign),
 796     Unary(hir::UnOp, Span),
 797 }
 798
 799 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 800 /// + u32, i16x4 == i16x4) and false if these types would have to be
 801 /// overloaded to be legal. There are two reasons that we distinguish
 802 /// builtin operations from overloaded ones (vs trying to drive
 803 /// everything uniformly through the trait system and intrinsics or
 804 /// something like that):
 805 ///
 806 /// 1. Builtin operations can trivially be evaluated in constants.
 807 /// 2. For comparison operators applied to SIMD types the result is
 808 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 809 ///    type like `i16x4`. This means that the overloaded trait
 810 ///    `PartialEq` is not applicable.
 811 ///
 812 /// Reason #2 is the killer. I tried for a while to always use
 813 /// overloaded logic and just check the types in constants/codegen after
 814 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 815 fn is_builtin_binop(lhs: Ty<'_>, rhs: Ty<'_>, op: hir::BinOp) -> bool {
 816     match BinOpCategory::from(op) {
 817         BinOpCategory::Shortcircuit => {
 818             true
 819         }
 820
 821         BinOpCategory::Shift => {
 822             lhs.references_error() || rhs.references_error() ||
 823                 lhs.is_integral() && rhs.is_integral()
 824         }
 825
 826         BinOpCategory::Math => {
 827             lhs.references_error() || rhs.references_error() ||
 828                 lhs.is_integral() && rhs.is_integral() ||
 829                 lhs.is_floating_point() && rhs.is_floating_point()
 830         }
 831
 832         BinOpCategory::Bitwise => {
 833             lhs.references_error() || rhs.references_error() ||
 834                 lhs.is_integral() && rhs.is_integral() ||
 835                 lhs.is_floating_point() && rhs.is_floating_point() ||
 836                 lhs.is_bool() && rhs.is_bool()
 837         }
 838
 839         BinOpCategory::Comparison => {
 840             lhs.references_error() || rhs.references_error() ||
 841                 lhs.is_scalar() && rhs.is_scalar()
 842         }
 843     }
 844 }