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, 'tcx> FnCtxt<'a, 'tcx> {
  15     /// Checks a `a <op>= b`
  16     pub fn check_binop_assign(
  17         &self,
  18         expr: &'tcx hir::Expr,
  19         op: hir::BinOp,
  20         lhs_expr: &'tcx hir::Expr,
  21         rhs_expr: &'tcx hir::Expr,
  22     ) -> Ty<'tcx> {
  23         let (lhs_ty, rhs_ty, return_ty) =
  24             self.check_overloaded_binop(expr, lhs_expr, rhs_expr, op, IsAssign::Yes);
  25
  26         let ty = if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var()
  27                     && is_builtin_binop(lhs_ty, rhs_ty, op) {
  28             self.enforce_builtin_binop_types(lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
  29             self.tcx.mk_unit()
  30         } else {
  31             return_ty
  32         };
  33
  34         if !lhs_expr.is_place_expr() {
  35             struct_span_err!(
  36                 self.tcx.sess, lhs_expr.span,
  37                 E0067, "invalid left-hand side expression")
  38             .span_label(
  39                 lhs_expr.span,
  40                 "invalid expression for left-hand side")
  41             .emit();
  42         }
  43         ty
  44     }
  45
  46     /// Checks a potentially overloaded binary operator.
  47     pub fn check_binop(
  48         &self,
  49         expr: &'tcx hir::Expr,
  50         op: hir::BinOp,
  51         lhs_expr: &'tcx hir::Expr,
  52         rhs_expr: &'tcx hir::Expr,
  53     ) -> Ty<'tcx> {
  54         let tcx = self.tcx;
  55
  56         debug!("check_binop(expr.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  57                expr.hir_id,
  58                expr,
  59                op,
  60                lhs_expr,
  61                rhs_expr);
  62
  63         match BinOpCategory::from(op) {
  64             BinOpCategory::Shortcircuit => {
  65                 // && and || are a simple case.
  66                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool);
  67                 let lhs_diverges = self.diverges.get();
  68                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool);
  69
  70                 // Depending on the LHS' value, the RHS can never execute.
  71                 self.diverges.set(lhs_diverges);
  72
  73                 tcx.types.bool
  74             }
  75             _ => {
  76                 // Otherwise, we always treat operators as if they are
  77                 // overloaded. This is the way to be most flexible w/r/t
  78                 // types that get inferred.
  79                 let (lhs_ty, rhs_ty, return_ty) =
  80                     self.check_overloaded_binop(expr, lhs_expr,
  81                                                 rhs_expr, op, IsAssign::No);
  82
  83                 // Supply type inference hints if relevant. Probably these
  84                 // hints should be enforced during select as part of the
  85                 // `consider_unification_despite_ambiguity` routine, but this
  86                 // more convenient for now.
  87                 //
  88                 // The basic idea is to help type inference by taking
  89                 // advantage of things we know about how the impls for
  90                 // scalar types are arranged. This is important in a
  91                 // scenario like `1_u32 << 2`, because it lets us quickly
  92                 // deduce that the result type should be `u32`, even
  93                 // though we don't know yet what type 2 has and hence
  94                 // can't pin this down to a specific impl.
  95                 if
  96                     !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() &&
  97                     is_builtin_binop(lhs_ty, rhs_ty, op)
  98                 {
  99                     let builtin_return_ty =
 100                         self.enforce_builtin_binop_types(lhs_expr, lhs_ty, rhs_expr, rhs_ty, op);
 101                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 102                 }
 103
 104                 return_ty
 105             }
 106         }
 107     }
 108
 109     fn enforce_builtin_binop_types(
 110         &self,
 111         lhs_expr: &'tcx hir::Expr,
 112         lhs_ty: Ty<'tcx>,
 113         rhs_expr: &'tcx hir::Expr,
 114         rhs_ty: Ty<'tcx>,
 115         op: hir::BinOp,
 116     ) -> Ty<'tcx> {
 117         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 118
 119         let tcx = self.tcx;
 120         match BinOpCategory::from(op) {
 121             BinOpCategory::Shortcircuit => {
 122                 self.demand_suptype(lhs_expr.span, tcx.mk_bool(), lhs_ty);
 123                 self.demand_suptype(rhs_expr.span, tcx.mk_bool(), rhs_ty);
 124                 tcx.mk_bool()
 125             }
 126
 127             BinOpCategory::Shift => {
 128                 // result type is same as LHS always
 129                 lhs_ty
 130             }
 131
 132             BinOpCategory::Math |
 133             BinOpCategory::Bitwise => {
 134                 // both LHS and RHS and result will have the same type
 135                 self.demand_suptype(rhs_expr.span, lhs_ty, rhs_ty);
 136                 lhs_ty
 137             }
 138
 139             BinOpCategory::Comparison => {
 140                 // both LHS and RHS and result will have the same type
 141                 self.demand_suptype(rhs_expr.span, lhs_ty, rhs_ty);
 142                 tcx.mk_bool()
 143             }
 144         }
 145     }
 146
 147     fn check_overloaded_binop(
 148         &self,
 149         expr: &'tcx hir::Expr,
 150         lhs_expr: &'tcx hir::Expr,
 151         rhs_expr: &'tcx hir::Expr,
 152         op: hir::BinOp,
 153         is_assign: IsAssign,
 154     ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
 155         debug!("check_overloaded_binop(expr.hir_id={}, op={:?}, is_assign={:?})",
 156                expr.hir_id,
 157                op,
 158                is_assign);
 159
 160         let lhs_ty = match is_assign {
 161             IsAssign::No => {
 162                 // Find a suitable supertype of the LHS expression's type, by coercing to
 163                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 164                 // trait matching creating lifetime constraints that are too strict.
 165                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 166                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 167                 let lhs_ty = self.check_expr_with_needs(lhs_expr, Needs::None);
 168                 let fresh_var = self.next_ty_var(TypeVariableOrigin {
 169                     kind: TypeVariableOriginKind::MiscVariable,
 170                     span: lhs_expr.span,
 171                 });
 172                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var,  AllowTwoPhase::No)
 173             }
 174             IsAssign::Yes => {
 175                 // rust-lang/rust#52126: We have to use strict
 176                 // equivalence on the LHS of an assign-op like `+=`;
 177                 // overwritten or mutably-borrowed places cannot be
 178                 // coerced to a supertype.
 179                 self.check_expr_with_needs(lhs_expr, Needs::MutPlace)
 180             }
 181         };
 182         let lhs_ty = self.resolve_type_vars_with_obligations(lhs_ty);
 183
 184         // N.B., as we have not yet type-checked the RHS, we don't have the
 185         // type at hand. Make a variable to represent it. The whole reason
 186         // for this indirection is so that, below, we can check the expr
 187         // using this variable as the expected type, which sometimes lets
 188         // us do better coercions than we would be able to do otherwise,
 189         // particularly for things like `String + &String`.
 190         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 191             kind: TypeVariableOriginKind::MiscVariable,
 192             span: rhs_expr.span,
 193         });
 194
 195         let result = self.lookup_op_method(lhs_ty, &[rhs_ty_var], Op::Binary(op, is_assign));
 196
 197         // see `NB` above
 198         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var);
 199         let rhs_ty = self.resolve_type_vars_with_obligations(rhs_ty);
 200
 201         let return_ty = match result {
 202             Ok(method) => {
 203                 let by_ref_binop = !op.node.is_by_value();
 204                 if is_assign == IsAssign::Yes || by_ref_binop {
 205                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].sty {
 206                         let mutbl = match mutbl {
 207                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 208                             hir::MutMutable => AutoBorrowMutability::Mutable {
 209                                 // Allow two-phase borrows for binops in initial deployment
 210                                 // since they desugar to methods
 211                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 212                             }
 213                         };
 214                         let autoref = Adjustment {
 215                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 216                             target: method.sig.inputs()[0]
 217                         };
 218                         self.apply_adjustments(lhs_expr, vec![autoref]);
 219                     }
 220                 }
 221                 if by_ref_binop {
 222                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].sty {
 223                         let mutbl = match mutbl {
 224                             hir::MutImmutable => AutoBorrowMutability::Immutable,
 225                             hir::MutMutable => AutoBorrowMutability::Mutable {
 226                                 // Allow two-phase borrows for binops in initial deployment
 227                                 // since they desugar to methods
 228                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 229                             }
 230                         };
 231                         let autoref = Adjustment {
 232                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 233                             target: method.sig.inputs()[1]
 234                         };
 235                         // HACK(eddyb) Bypass checks due to reborrows being in
 236                         // some cases applied on the RHS, on top of which we need
 237                         // to autoref, which is not allowed by apply_adjustments.
 238                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 239                         self.tables
 240                             .borrow_mut()
 241                             .adjustments_mut()
 242                             .entry(rhs_expr.hir_id)
 243                             .or_default()
 244                             .push(autoref);
 245                     }
 246                 }
 247                 self.write_method_call(expr.hir_id, method);
 248
 249                 method.sig.output()
 250             }
 251             Err(()) => {
 252                 // error types are considered "builtin"
 253                 if !lhs_ty.references_error() {
 254                     let source_map = self.tcx.sess.source_map();
 255                     match is_assign {
 256                         IsAssign::Yes => {
 257                             let mut err = struct_span_err!(
 258                                 self.tcx.sess,
 259                                 expr.span,
 260                                 E0368,
 261                                 "binary assignment operation `{}=` cannot be applied to type `{}`",
 262                                 op.node.as_str(),
 263                                 lhs_ty,
 264                             );
 265                             err.span_label(
 266                                 lhs_expr.span,
 267                                 format!("cannot use `{}=` on type `{}`",
 268                                 op.node.as_str(), lhs_ty),
 269                             );
 270                             let mut suggested_deref = false;
 271                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 272                                 if {
 273                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 274                                                                            rty,
 275                                                                            lhs_expr.span) &&
 276                                         self.lookup_op_method(rty,
 277                                                               &[rhs_ty],
 278                                                               Op::Binary(op, is_assign))
 279                                             .is_ok()
 280                                 } {
 281                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 282                                         while let Ref(_, rty_inner, _) = rty.sty {
 283                                             rty = rty_inner;
 284                                         }
 285                                         let msg = &format!(
 286                                             "`{}=` can be used on '{}', you can dereference `{}`",
 287                                             op.node.as_str(),
 288                                             rty,
 289                                             lstring,
 290                                         );
 291                                         err.span_suggestion(
 292                                             lhs_expr.span,
 293                                             msg,
 294                                             format!("*{}", lstring),
 295                                             errors::Applicability::MachineApplicable,
 296                                         );
 297                                         suggested_deref = true;
 298                                     }
 299                                 }
 300                             }
 301                             let missing_trait = match op.node {
 302                                 hir::BinOpKind::Add    => Some("std::ops::AddAssign"),
 303                                 hir::BinOpKind::Sub    => Some("std::ops::SubAssign"),
 304                                 hir::BinOpKind::Mul    => Some("std::ops::MulAssign"),
 305                                 hir::BinOpKind::Div    => Some("std::ops::DivAssign"),
 306                                 hir::BinOpKind::Rem    => Some("std::ops::RemAssign"),
 307                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 308                                 hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 309                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOrAssign"),
 310                                 hir::BinOpKind::Shl    => Some("std::ops::ShlAssign"),
 311                                 hir::BinOpKind::Shr    => Some("std::ops::ShrAssign"),
 312                                 _                      => None
 313                             };
 314                             if let Some(missing_trait) = missing_trait {
 315                                 if op.node == hir::BinOpKind::Add &&
 316                                     self.check_str_addition(
 317                                         lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, true, op) {
 318                                     // This has nothing here because it means we did string
 319                                     // concatenation (e.g., "Hello " += "World!"). This means
 320                                     // we don't want the note in the else clause to be emitted
 321                                 } else if let ty::Param(_) = lhs_ty.sty {
 322                                     // FIXME: point to span of param
 323                                     err.note(&format!(
 324                                         "`{}` might need a bound for `{}`",
 325                                         lhs_ty, missing_trait
 326                                     ));
 327                                 } else if !suggested_deref {
 328                                     err.note(&format!(
 329                                         "an implementation of `{}` might \
 330                                          be missing for `{}`",
 331                                         missing_trait, lhs_ty
 332                                     ));
 333                                 }
 334                             }
 335                             err.emit();
 336                         }
 337                         IsAssign::No => {
 338                             let mut err = struct_span_err!(self.tcx.sess, op.span, E0369,
 339                                 "binary operation `{}` cannot be applied to type `{}`",
 340                                 op.node.as_str(),
 341                                 lhs_ty);
 342
 343                             let mut involves_fn = false;
 344                             if !lhs_expr.span.eq(&rhs_expr.span) {
 345                                 involves_fn |= self.add_type_neq_err_label(
 346                                     &mut err,
 347                                     lhs_expr.span,
 348                                     lhs_ty,
 349                                     rhs_ty,
 350                                     op,
 351                                     is_assign
 352                                 );
 353                                 involves_fn |= self.add_type_neq_err_label(
 354                                     &mut err,
 355                                     rhs_expr.span,
 356                                     rhs_ty,
 357                                     lhs_ty,
 358                                     op,
 359                                     is_assign
 360                                 );
 361                             }
 362
 363                             let mut suggested_deref = false;
 364                             if let Ref(_, mut rty, _) = lhs_ty.sty {
 365                                 if {
 366                                     self.infcx.type_is_copy_modulo_regions(self.param_env,
 367                                                                            rty,
 368                                                                            lhs_expr.span) &&
 369                                         self.lookup_op_method(rty,
 370                                                               &[rhs_ty],
 371                                                               Op::Binary(op, is_assign))
 372                                             .is_ok()
 373                                 } {
 374                                     if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 375                                         while let Ref(_, rty_inner, _) = rty.sty {
 376                                             rty = rty_inner;
 377                                         }
 378                                         let msg = &format!(
 379                                                 "`{}` can be used on '{}', you can \
 380                                                 dereference `{2}`: `*{2}`",
 381                                                 op.node.as_str(),
 382                                                 rty,
 383                                                 lstring
 384                                         );
 385                                         err.help(msg);
 386                                         suggested_deref = true;
 387                                     }
 388                                 }
 389                             }
 390                             let missing_trait = match op.node {
 391                                 hir::BinOpKind::Add    => Some("std::ops::Add"),
 392                                 hir::BinOpKind::Sub    => Some("std::ops::Sub"),
 393                                 hir::BinOpKind::Mul    => Some("std::ops::Mul"),
 394                                 hir::BinOpKind::Div    => Some("std::ops::Div"),
 395                                 hir::BinOpKind::Rem    => Some("std::ops::Rem"),
 396                                 hir::BinOpKind::BitAnd => Some("std::ops::BitAnd"),
 397                                 hir::BinOpKind::BitXor => Some("std::ops::BitXor"),
 398                                 hir::BinOpKind::BitOr  => Some("std::ops::BitOr"),
 399                                 hir::BinOpKind::Shl    => Some("std::ops::Shl"),
 400                                 hir::BinOpKind::Shr    => Some("std::ops::Shr"),
 401                                 hir::BinOpKind::Eq |
 402                                 hir::BinOpKind::Ne => Some("std::cmp::PartialEq"),
 403                                 hir::BinOpKind::Lt |
 404                                 hir::BinOpKind::Le |
 405                                 hir::BinOpKind::Gt |
 406                                 hir::BinOpKind::Ge => Some("std::cmp::PartialOrd"),
 407                                 _ => None
 408                             };
 409                             if let Some(missing_trait) = missing_trait {
 410                                 if op.node == hir::BinOpKind::Add &&
 411                                     self.check_str_addition(
 412                                         lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, false, op) {
 413                                     // This has nothing here because it means we did string
 414                                     // concatenation (e.g., "Hello " + "World!"). This means
 415                                     // we don't want the note in the else clause to be emitted
 416                                 } else if let ty::Param(_) = lhs_ty.sty {
 417                                     // FIXME: point to span of param
 418                                     err.note(&format!(
 419                                         "`{}` might need a bound for `{}`",
 420                                         lhs_ty, missing_trait
 421                                     ));
 422                                 } else if !suggested_deref && !involves_fn {
 423                                     err.note(&format!(
 424                                         "an implementation of `{}` might \
 425                                          be missing for `{}`",
 426                                         missing_trait, lhs_ty
 427                                     ));
 428                                 }
 429                             }
 430                             err.emit();
 431                         }
 432                     }
 433                 }
 434                 self.tcx.types.err
 435             }
 436         };
 437
 438         (lhs_ty, rhs_ty, return_ty)
 439     }
 440
 441     /// If one of the types is an uncalled function and calling it would yield the other type,
 442     /// suggest calling the function. Returns wether a suggestion was given.
 443     fn add_type_neq_err_label(
 444         &self,
 445         err: &mut errors::DiagnosticBuilder<'_>,
 446         span: Span,
 447         ty: Ty<'tcx>,
 448         other_ty: Ty<'tcx>,
 449         op: hir::BinOp,
 450         is_assign: IsAssign,
 451     ) -> bool /* did we suggest to call a function because of missing parenthesis? */ {
 452         err.span_label(span, ty.to_string());
 453         if let FnDef(def_id, _) = ty.sty {
 454             let source_map = self.tcx.sess.source_map();
 455             let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
 456                 Some(hir_id) => hir_id,
 457                 None => return false,
 458             };
 459             if self.tcx.has_typeck_tables(def_id) == false {
 460                 return false;
 461             }
 462             let fn_sig = {
 463                 match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(hir_id) {
 464                     Some(f) => f.clone(),
 465                     None => {
 466                         bug!("No fn-sig entry for def_id={:?}", def_id);
 467                     }
 468                 }
 469             };
 470
 471             let other_ty = if let FnDef(def_id, _) = other_ty.sty {
 472                 let hir_id = match self.tcx.hir().as_local_hir_id(def_id) {
 473                     Some(hir_id) => hir_id,
 474                     None => return false,
 475                 };
 476                 if self.tcx.has_typeck_tables(def_id) == false {
 477                     return false;
 478                 }
 479                 match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(hir_id) {
 480                     Some(f) => f.clone().output(),
 481                     None => {
 482                         bug!("No fn-sig entry for def_id={:?}", def_id);
 483                     }
 484                 }
 485             } else {
 486                 other_ty
 487             };
 488
 489             if self.lookup_op_method(fn_sig.output(),
 490                                     &[other_ty],
 491                                     Op::Binary(op, is_assign))
 492                     .is_ok() {
 493                 let (variable_snippet, applicability) = if fn_sig.inputs().len() > 0 {
 494                     (format!("{}( /* arguments */ )", source_map.span_to_snippet(span).unwrap()),
 495                     Applicability::HasPlaceholders)
 496                 } else {
 497                     (format!("{}()", source_map.span_to_snippet(span).unwrap()),
 498                     Applicability::MaybeIncorrect)
 499                 };
 500
 501                 err.span_suggestion(
 502                     span,
 503                     "you might have forgotten to call this function",
 504                     variable_snippet,
 505                     applicability,
 506                 );
 507                 return true;
 508             }
 509         }
 510         false
 511     }
 512
 513     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 514     /// like `&str + &str`, `String + String` and `&str + &String`.
 515     ///
 516     /// If this function returns `true` it means a note was printed, so we don't need
 517     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 518     fn check_str_addition(
 519         &self,
 520         lhs_expr: &'tcx hir::Expr,
 521         rhs_expr: &'tcx hir::Expr,
 522         lhs_ty: Ty<'tcx>,
 523         rhs_ty: Ty<'tcx>,
 524         err: &mut errors::DiagnosticBuilder<'_>,
 525         is_assign: bool,
 526         op: hir::BinOp,
 527     ) -> bool {
 528         let source_map = self.tcx.sess.source_map();
 529         let remove_borrow_msg = "String concatenation appends the string on the right to the \
 530                                  string on the left and may require reallocation. This \
 531                                  requires ownership of the string on the left";
 532
 533         let msg = "`to_owned()` can be used to create an owned `String` \
 534                    from a string reference. String concatenation \
 535                    appends the string on the right to the string \
 536                    on the left and may require reallocation. This \
 537                    requires ownership of the string on the left";
 538
 539         let is_std_string = |ty| &format!("{:?}", ty) == "std::string::String";
 540
 541         match (&lhs_ty.sty, &rhs_ty.sty) {
 542             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 543                 if (l_ty.sty == Str || is_std_string(l_ty)) && (
 544                         r_ty.sty == Str || is_std_string(r_ty) ||
 545                         &format!("{:?}", rhs_ty) == "&&str"
 546                     ) =>
 547             {
 548                 if !is_assign { // Do not supply this message if `&str += &str`
 549                     err.span_label(
 550                         op.span,
 551                         "`+` cannot be used to concatenate two `&str` strings",
 552                     );
 553                     match source_map.span_to_snippet(lhs_expr.span) {
 554                         Ok(lstring) => {
 555                             err.span_suggestion(
 556                                 lhs_expr.span,
 557                                 if lstring.starts_with("&") {
 558                                     remove_borrow_msg
 559                                 } else {
 560                                     msg
 561                                 },
 562                                 if lstring.starts_with("&") {
 563                                     // let a = String::new();
 564                                     // let _ = &a + "bar";
 565                                     format!("{}", &lstring[1..])
 566                                 } else {
 567                                     format!("{}.to_owned()", lstring)
 568                                 },
 569                                 Applicability::MachineApplicable,
 570                             )
 571                         }
 572                         _ => err.help(msg),
 573                     };
 574                 }
 575                 true
 576             }
 577             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 578                 if (l_ty.sty == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 579             {
 580                 err.span_label(
 581                     op.span,
 582                     "`+` cannot be used to concatenate a `&str` with a `String`",
 583                 );
 584                 match (
 585                     source_map.span_to_snippet(lhs_expr.span),
 586                     source_map.span_to_snippet(rhs_expr.span),
 587                     is_assign,
 588                 ) {
 589                     (Ok(l), Ok(r), false) => {
 590                         let to_string = if l.starts_with("&") {
 591                             // let a = String::new(); let b = String::new();
 592                             // let _ = &a + b;
 593                             format!("{}", &l[1..])
 594                         } else {
 595                             format!("{}.to_owned()", l)
 596                         };
 597                         err.multipart_suggestion(
 598                             msg,
 599                             vec![
 600                                 (lhs_expr.span, to_string),
 601                                 (rhs_expr.span, format!("&{}", r)),
 602                             ],
 603                             Applicability::MachineApplicable,
 604                         );
 605                     }
 606                     _ => {
 607                         err.help(msg);
 608                     }
 609                 };
 610                 true
 611             }
 612             _ => false,
 613         }
 614     }
 615
 616     pub fn check_user_unop(
 617         &self,
 618         ex: &'tcx hir::Expr,
 619         operand_ty: Ty<'tcx>,
 620         op: hir::UnOp,
 621     ) -> Ty<'tcx> {
 622         assert!(op.is_by_value());
 623         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 624             Ok(method) => {
 625                 self.write_method_call(ex.hir_id, method);
 626                 method.sig.output()
 627             }
 628             Err(()) => {
 629                 let actual = self.resolve_vars_if_possible(&operand_ty);
 630                 if !actual.references_error() {
 631                     let mut err = struct_span_err!(self.tcx.sess, ex.span, E0600,
 632                                      "cannot apply unary operator `{}` to type `{}`",
 633                                      op.as_str(), actual);
 634                     err.span_label(ex.span, format!("cannot apply unary \
 635                                                     operator `{}`", op.as_str()));
 636                     match actual.sty {
 637                         Uint(_) if op == hir::UnNeg => {
 638                             err.note("unsigned values cannot be negated");
 639                         },
 640                         Str | Never | Char | Tuple(_) | Array(_,_) => {},
 641                         Ref(_, ref lty, _) if lty.sty == Str => {},
 642                         _ => {
 643                             let missing_trait = match op {
 644                                 hir::UnNeg => "std::ops::Neg",
 645                                 hir::UnNot => "std::ops::Not",
 646                                 hir::UnDeref => "std::ops::UnDerf"
 647                             };
 648                             err.note(&format!("an implementation of `{}` might \
 649                                                 be missing for `{}`",
 650                                              missing_trait, operand_ty));
 651                         }
 652                     }
 653                     err.emit();
 654                 }
 655                 self.tcx.types.err
 656             }
 657         }
 658     }
 659
 660     fn lookup_op_method(&self, lhs_ty: Ty<'tcx>, other_tys: &[Ty<'tcx>], op: Op)
 661                         -> Result<MethodCallee<'tcx>, ()>
 662     {
 663         let lang = self.tcx.lang_items();
 664
 665         let span = match op {
 666             Op::Binary(op, _) => op.span,
 667             Op::Unary(_, span) => span
 668         };
 669         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 670             match op.node {
 671                 hir::BinOpKind::Add => ("add_assign", lang.add_assign_trait()),
 672                 hir::BinOpKind::Sub => ("sub_assign", lang.sub_assign_trait()),
 673                 hir::BinOpKind::Mul => ("mul_assign", lang.mul_assign_trait()),
 674                 hir::BinOpKind::Div => ("div_assign", lang.div_assign_trait()),
 675                 hir::BinOpKind::Rem => ("rem_assign", lang.rem_assign_trait()),
 676                 hir::BinOpKind::BitXor => ("bitxor_assign", lang.bitxor_assign_trait()),
 677                 hir::BinOpKind::BitAnd => ("bitand_assign", lang.bitand_assign_trait()),
 678                 hir::BinOpKind::BitOr => ("bitor_assign", lang.bitor_assign_trait()),
 679                 hir::BinOpKind::Shl => ("shl_assign", lang.shl_assign_trait()),
 680                 hir::BinOpKind::Shr => ("shr_assign", lang.shr_assign_trait()),
 681                 hir::BinOpKind::Lt | hir::BinOpKind::Le |
 682                 hir::BinOpKind::Ge | hir::BinOpKind::Gt |
 683                 hir::BinOpKind::Eq | hir::BinOpKind::Ne |
 684                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 685                     span_bug!(span,
 686                               "impossible assignment operation: {}=",
 687                               op.node.as_str())
 688                 }
 689             }
 690         } else if let Op::Binary(op, IsAssign::No) = op {
 691             match op.node {
 692                 hir::BinOpKind::Add => ("add", lang.add_trait()),
 693                 hir::BinOpKind::Sub => ("sub", lang.sub_trait()),
 694                 hir::BinOpKind::Mul => ("mul", lang.mul_trait()),
 695                 hir::BinOpKind::Div => ("div", lang.div_trait()),
 696                 hir::BinOpKind::Rem => ("rem", lang.rem_trait()),
 697                 hir::BinOpKind::BitXor => ("bitxor", lang.bitxor_trait()),
 698                 hir::BinOpKind::BitAnd => ("bitand", lang.bitand_trait()),
 699                 hir::BinOpKind::BitOr => ("bitor", lang.bitor_trait()),
 700                 hir::BinOpKind::Shl => ("shl", lang.shl_trait()),
 701                 hir::BinOpKind::Shr => ("shr", lang.shr_trait()),
 702                 hir::BinOpKind::Lt => ("lt", lang.partial_ord_trait()),
 703                 hir::BinOpKind::Le => ("le", lang.partial_ord_trait()),
 704                 hir::BinOpKind::Ge => ("ge", lang.partial_ord_trait()),
 705                 hir::BinOpKind::Gt => ("gt", lang.partial_ord_trait()),
 706                 hir::BinOpKind::Eq => ("eq", lang.eq_trait()),
 707                 hir::BinOpKind::Ne => ("ne", lang.eq_trait()),
 708                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 709                     span_bug!(span, "&& and || are not overloadable")
 710                 }
 711             }
 712         } else if let Op::Unary(hir::UnNot, _) = op {
 713             ("not", lang.not_trait())
 714         } else if let Op::Unary(hir::UnNeg, _) = op {
 715             ("neg", lang.neg_trait())
 716         } else {
 717             bug!("lookup_op_method: op not supported: {:?}", op)
 718         };
 719
 720         debug!("lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 721                lhs_ty,
 722                op,
 723                opname,
 724                trait_did);
 725
 726         let method = trait_did.and_then(|trait_did| {
 727             let opname = Ident::from_str(opname);
 728             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 729         });
 730
 731         match method {
 732             Some(ok) => {
 733                 let method = self.register_infer_ok_obligations(ok);
 734                 self.select_obligations_where_possible(false);
 735
 736                 Ok(method)
 737             }
 738             None => {
 739                 Err(())
 740             }
 741         }
 742     }
 743 }
 744
 745 // Binary operator categories. These categories summarize the behavior
 746 // with respect to the builtin operationrs supported.
 747 enum BinOpCategory {
 748     /// &&, || -- cannot be overridden
 749     Shortcircuit,
 750
 751     /// <<, >> -- when shifting a single integer, rhs can be any
 752     /// integer type. For simd, types must match.
 753     Shift,
 754
 755     /// +, -, etc -- takes equal types, produces same type as input,
 756     /// applicable to ints/floats/simd
 757     Math,
 758
 759     /// &, |, ^ -- takes equal types, produces same type as input,
 760     /// applicable to ints/floats/simd/bool
 761     Bitwise,
 762
 763     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 764     /// which produce the input type
 765     Comparison,
 766 }
 767
 768 impl BinOpCategory {
 769     fn from(op: hir::BinOp) -> BinOpCategory {
 770         match op.node {
 771             hir::BinOpKind::Shl | hir::BinOpKind::Shr =>
 772                 BinOpCategory::Shift,
 773
 774             hir::BinOpKind::Add |
 775             hir::BinOpKind::Sub |
 776             hir::BinOpKind::Mul |
 777             hir::BinOpKind::Div |
 778             hir::BinOpKind::Rem =>
 779                 BinOpCategory::Math,
 780
 781             hir::BinOpKind::BitXor |
 782             hir::BinOpKind::BitAnd |
 783             hir::BinOpKind::BitOr =>
 784                 BinOpCategory::Bitwise,
 785
 786             hir::BinOpKind::Eq |
 787             hir::BinOpKind::Ne |
 788             hir::BinOpKind::Lt |
 789             hir::BinOpKind::Le |
 790             hir::BinOpKind::Ge |
 791             hir::BinOpKind::Gt =>
 792                 BinOpCategory::Comparison,
 793
 794             hir::BinOpKind::And |
 795             hir::BinOpKind::Or =>
 796                 BinOpCategory::Shortcircuit,
 797         }
 798     }
 799 }
 800
 801 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 802 #[derive(Clone, Copy, Debug, PartialEq)]
 803 enum IsAssign {
 804     No,
 805     Yes,
 806 }
 807
 808 #[derive(Clone, Copy, Debug)]
 809 enum Op {
 810     Binary(hir::BinOp, IsAssign),
 811     Unary(hir::UnOp, Span),
 812 }
 813
 814 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 815 /// + u32, i16x4 == i16x4) and false if these types would have to be
 816 /// overloaded to be legal. There are two reasons that we distinguish
 817 /// builtin operations from overloaded ones (vs trying to drive
 818 /// everything uniformly through the trait system and intrinsics or
 819 /// something like that):
 820 ///
 821 /// 1. Builtin operations can trivially be evaluated in constants.
 822 /// 2. For comparison operators applied to SIMD types the result is
 823 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 824 ///    type like `i16x4`. This means that the overloaded trait
 825 ///    `PartialEq` is not applicable.
 826 ///
 827 /// Reason #2 is the killer. I tried for a while to always use
 828 /// overloaded logic and just check the types in constants/codegen after
 829 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 830 fn is_builtin_binop(lhs: Ty<'_>, rhs: Ty<'_>, op: hir::BinOp) -> bool {
 831     match BinOpCategory::from(op) {
 832         BinOpCategory::Shortcircuit => {
 833             true
 834         }
 835
 836         BinOpCategory::Shift => {
 837             lhs.references_error() || rhs.references_error() ||
 838                 lhs.is_integral() && rhs.is_integral()
 839         }
 840
 841         BinOpCategory::Math => {
 842             lhs.references_error() || rhs.references_error() ||
 843                 lhs.is_integral() && rhs.is_integral() ||
 844                 lhs.is_floating_point() && rhs.is_floating_point()
 845         }
 846
 847         BinOpCategory::Bitwise => {
 848             lhs.references_error() || rhs.references_error() ||
 849                 lhs.is_integral() && rhs.is_integral() ||
 850                 lhs.is_floating_point() && rhs.is_floating_point() ||
 851                 lhs.is_bool() && rhs.is_bool()
 852         }
 853
 854         BinOpCategory::Comparison => {
 855             lhs.references_error() || rhs.references_error() ||
 856                 lhs.is_scalar() && rhs.is_scalar()
 857         }
 858     }
 859 }