compiler/rustc_typeck/src/check/op.rs

   1 //! Code related to processing overloaded binary and unary operators.
   2
   3 use super::method::MethodCallee;
   4 use super::{has_expected_num_generic_args, FnCtxt};
   5 use crate::check::Expectation;
   6 use rustc_ast as ast;
   7 use rustc_errors::{self, struct_span_err, Applicability, Diagnostic};
   8 use rustc_hir as hir;
   9 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  10 use rustc_infer::traits::ObligationCauseCode;
  11 use rustc_middle::ty::adjustment::{
  12     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  13 };
  14 use rustc_middle::ty::print::with_no_trimmed_paths;
  15 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt, TypeFolder, TypeSuperFoldable, TypeVisitable};
  16 use rustc_span::source_map::Spanned;
  17 use rustc_span::symbol::{sym, Ident};
  18 use rustc_span::Span;
  19 use rustc_trait_selection::infer::InferCtxtExt;
  20 use rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt as _;
  21 use rustc_trait_selection::traits::{FulfillmentError, TraitEngine, TraitEngineExt};
  22 use rustc_type_ir::sty::TyKind::*;
  23
  24 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  25     /// Checks a `a <op>= b`
  26     pub fn check_binop_assign(
  27         &self,
  28         expr: &'tcx hir::Expr<'tcx>,
  29         op: hir::BinOp,
  30         lhs: &'tcx hir::Expr<'tcx>,
  31         rhs: &'tcx hir::Expr<'tcx>,
  32         expected: Expectation<'tcx>,
  33     ) -> Ty<'tcx> {
  34         let (lhs_ty, rhs_ty, return_ty) =
  35             self.check_overloaded_binop(expr, lhs, rhs, op, IsAssign::Yes, expected);
  36
  37         let ty =
  38             if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() && is_builtin_binop(lhs_ty, rhs_ty, op) {
  39                 self.enforce_builtin_binop_types(lhs.span, lhs_ty, rhs.span, rhs_ty, op);
  40                 self.tcx.mk_unit()
  41             } else {
  42                 return_ty
  43             };
  44
  45         self.check_lhs_assignable(lhs, "E0067", op.span, |err| {
  46             if let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
  47                 if self
  48                     .lookup_op_method(
  49                         lhs_deref_ty,
  50                         Some(rhs_ty),
  51                         Some(rhs),
  52                         Op::Binary(op, IsAssign::Yes),
  53                         expected,
  54                     )
  55                     .is_ok()
  56                 {
  57                     // If LHS += RHS is an error, but *LHS += RHS is successful, then we will have
  58                     // emitted a better suggestion during error handling in check_overloaded_binop.
  59                     if self
  60                         .lookup_op_method(
  61                             lhs_ty,
  62                             Some(rhs_ty),
  63                             Some(rhs),
  64                             Op::Binary(op, IsAssign::Yes),
  65                             expected,
  66                         )
  67                         .is_err()
  68                     {
  69                         err.downgrade_to_delayed_bug();
  70                     } else {
  71                         // Otherwise, it's valid to suggest dereferencing the LHS here.
  72                         err.span_suggestion_verbose(
  73                             lhs.span.shrink_to_lo(),
  74                             "consider dereferencing the left-hand side of this operation",
  75                             "*",
  76                             Applicability::MaybeIncorrect,
  77                         );
  78                     }
  79                 }
  80             }
  81         });
  82
  83         ty
  84     }
  85
  86     /// Checks a potentially overloaded binary operator.
  87     pub fn check_binop(
  88         &self,
  89         expr: &'tcx hir::Expr<'tcx>,
  90         op: hir::BinOp,
  91         lhs_expr: &'tcx hir::Expr<'tcx>,
  92         rhs_expr: &'tcx hir::Expr<'tcx>,
  93         expected: Expectation<'tcx>,
  94     ) -> Ty<'tcx> {
  95         let tcx = self.tcx;
  96
  97         debug!(
  98             "check_binop(expr.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  99             expr.hir_id, expr, op, lhs_expr, rhs_expr
 100         );
 101
 102         match BinOpCategory::from(op) {
 103             BinOpCategory::Shortcircuit => {
 104                 // && and || are a simple case.
 105                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool, None);
 106                 let lhs_diverges = self.diverges.get();
 107                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool, None);
 108
 109                 // Depending on the LHS' value, the RHS can never execute.
 110                 self.diverges.set(lhs_diverges);
 111
 112                 tcx.types.bool
 113             }
 114             _ => {
 115                 // Otherwise, we always treat operators as if they are
 116                 // overloaded. This is the way to be most flexible w/r/t
 117                 // types that get inferred.
 118                 let (lhs_ty, rhs_ty, return_ty) = self.check_overloaded_binop(
 119                     expr,
 120                     lhs_expr,
 121                     rhs_expr,
 122                     op,
 123                     IsAssign::No,
 124                     expected,
 125                 );
 126
 127                 // Supply type inference hints if relevant. Probably these
 128                 // hints should be enforced during select as part of the
 129                 // `consider_unification_despite_ambiguity` routine, but this
 130                 // more convenient for now.
 131                 //
 132                 // The basic idea is to help type inference by taking
 133                 // advantage of things we know about how the impls for
 134                 // scalar types are arranged. This is important in a
 135                 // scenario like `1_u32 << 2`, because it lets us quickly
 136                 // deduce that the result type should be `u32`, even
 137                 // though we don't know yet what type 2 has and hence
 138                 // can't pin this down to a specific impl.
 139                 if !lhs_ty.is_ty_var()
 140                     && !rhs_ty.is_ty_var()
 141                     && is_builtin_binop(lhs_ty, rhs_ty, op)
 142                 {
 143                     let builtin_return_ty = self.enforce_builtin_binop_types(
 144                         lhs_expr.span,
 145                         lhs_ty,
 146                         rhs_expr.span,
 147                         rhs_ty,
 148                         op,
 149                     );
 150                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 151                 }
 152
 153                 return_ty
 154             }
 155         }
 156     }
 157
 158     fn enforce_builtin_binop_types(
 159         &self,
 160         lhs_span: Span,
 161         lhs_ty: Ty<'tcx>,
 162         rhs_span: Span,
 163         rhs_ty: Ty<'tcx>,
 164         op: hir::BinOp,
 165     ) -> Ty<'tcx> {
 166         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 167
 168         // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 169         // (See https://github.com/rust-lang/rust/issues/57447.)
 170         let (lhs_ty, rhs_ty) = (deref_ty_if_possible(lhs_ty), deref_ty_if_possible(rhs_ty));
 171
 172         let tcx = self.tcx;
 173         match BinOpCategory::from(op) {
 174             BinOpCategory::Shortcircuit => {
 175                 self.demand_suptype(lhs_span, tcx.types.bool, lhs_ty);
 176                 self.demand_suptype(rhs_span, tcx.types.bool, rhs_ty);
 177                 tcx.types.bool
 178             }
 179
 180             BinOpCategory::Shift => {
 181                 // result type is same as LHS always
 182                 lhs_ty
 183             }
 184
 185             BinOpCategory::Math | BinOpCategory::Bitwise => {
 186                 // both LHS and RHS and result will have the same type
 187                 self.demand_suptype(rhs_span, lhs_ty, rhs_ty);
 188                 lhs_ty
 189             }
 190
 191             BinOpCategory::Comparison => {
 192                 // both LHS and RHS and result will have the same type
 193                 self.demand_suptype(rhs_span, lhs_ty, rhs_ty);
 194                 tcx.types.bool
 195             }
 196         }
 197     }
 198
 199     fn check_overloaded_binop(
 200         &self,
 201         expr: &'tcx hir::Expr<'tcx>,
 202         lhs_expr: &'tcx hir::Expr<'tcx>,
 203         rhs_expr: &'tcx hir::Expr<'tcx>,
 204         op: hir::BinOp,
 205         is_assign: IsAssign,
 206         expected: Expectation<'tcx>,
 207     ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
 208         debug!(
 209             "check_overloaded_binop(expr.hir_id={}, op={:?}, is_assign={:?})",
 210             expr.hir_id, op, is_assign
 211         );
 212
 213         let lhs_ty = match is_assign {
 214             IsAssign::No => {
 215                 // Find a suitable supertype of the LHS expression's type, by coercing to
 216                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 217                 // trait matching creating lifetime constraints that are too strict.
 218                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 219                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 220                 let lhs_ty = self.check_expr(lhs_expr);
 221                 let fresh_var = self.next_ty_var(TypeVariableOrigin {
 222                     kind: TypeVariableOriginKind::MiscVariable,
 223                     span: lhs_expr.span,
 224                 });
 225                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var, Some(rhs_expr), AllowTwoPhase::No)
 226             }
 227             IsAssign::Yes => {
 228                 // rust-lang/rust#52126: We have to use strict
 229                 // equivalence on the LHS of an assign-op like `+=`;
 230                 // overwritten or mutably-borrowed places cannot be
 231                 // coerced to a supertype.
 232                 self.check_expr(lhs_expr)
 233             }
 234         };
 235         let lhs_ty = self.resolve_vars_with_obligations(lhs_ty);
 236
 237         // N.B., as we have not yet type-checked the RHS, we don't have the
 238         // type at hand. Make a variable to represent it. The whole reason
 239         // for this indirection is so that, below, we can check the expr
 240         // using this variable as the expected type, which sometimes lets
 241         // us do better coercions than we would be able to do otherwise,
 242         // particularly for things like `String + &String`.
 243         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 244             kind: TypeVariableOriginKind::MiscVariable,
 245             span: rhs_expr.span,
 246         });
 247
 248         let result = self.lookup_op_method(
 249             lhs_ty,
 250             Some(rhs_ty_var),
 251             Some(rhs_expr),
 252             Op::Binary(op, is_assign),
 253             expected,
 254         );
 255
 256         // see `NB` above
 257         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var, Some(lhs_expr));
 258         let rhs_ty = self.resolve_vars_with_obligations(rhs_ty);
 259
 260         let return_ty = match result {
 261             Ok(method) => {
 262                 let by_ref_binop = !op.node.is_by_value();
 263                 if is_assign == IsAssign::Yes || by_ref_binop {
 264                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() {
 265                         let mutbl = match mutbl {
 266                             hir::Mutability::Not => AutoBorrowMutability::Not,
 267                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 268                                 // Allow two-phase borrows for binops in initial deployment
 269                                 // since they desugar to methods
 270                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 271                             },
 272                         };
 273                         let autoref = Adjustment {
 274                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 275                             target: method.sig.inputs()[0],
 276                         };
 277                         self.apply_adjustments(lhs_expr, vec![autoref]);
 278                     }
 279                 }
 280                 if by_ref_binop {
 281                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 282                         let mutbl = match mutbl {
 283                             hir::Mutability::Not => AutoBorrowMutability::Not,
 284                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 285                                 // Allow two-phase borrows for binops in initial deployment
 286                                 // since they desugar to methods
 287                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 288                             },
 289                         };
 290                         let autoref = Adjustment {
 291                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 292                             target: method.sig.inputs()[1],
 293                         };
 294                         // HACK(eddyb) Bypass checks due to reborrows being in
 295                         // some cases applied on the RHS, on top of which we need
 296                         // to autoref, which is not allowed by apply_adjustments.
 297                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 298                         self.typeck_results
 299                             .borrow_mut()
 300                             .adjustments_mut()
 301                             .entry(rhs_expr.hir_id)
 302                             .or_default()
 303                             .push(autoref);
 304                     }
 305                 }
 306                 self.write_method_call(expr.hir_id, method);
 307
 308                 method.sig.output()
 309             }
 310             // error types are considered "builtin"
 311             Err(_) if lhs_ty.references_error() || rhs_ty.references_error() => self.tcx.ty_error(),
 312             Err(errors) => {
 313                 let (_, trait_def_id) =
 314                     lang_item_for_op(self.tcx, Op::Binary(op, is_assign), op.span);
 315                 let missing_trait = trait_def_id
 316                     .map(|def_id| with_no_trimmed_paths!(self.tcx.def_path_str(def_id)));
 317                 let (mut err, output_def_id) = match is_assign {
 318                     IsAssign::Yes => {
 319                         let mut err = struct_span_err!(
 320                             self.tcx.sess,
 321                             expr.span,
 322                             E0368,
 323                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 324                             op.node.as_str(),
 325                             lhs_ty,
 326                         );
 327                         err.span_label(
 328                             lhs_expr.span,
 329                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 330                         );
 331                         self.note_unmet_impls_on_type(&mut err, errors);
 332                         (err, None)
 333                     }
 334                     IsAssign::No => {
 335                         let message = match op.node {
 336                             hir::BinOpKind::Add => {
 337                                 format!("cannot add `{rhs_ty}` to `{lhs_ty}`")
 338                             }
 339                             hir::BinOpKind::Sub => {
 340                                 format!("cannot subtract `{rhs_ty}` from `{lhs_ty}`")
 341                             }
 342                             hir::BinOpKind::Mul => {
 343                                 format!("cannot multiply `{lhs_ty}` by `{rhs_ty}`")
 344                             }
 345                             hir::BinOpKind::Div => {
 346                                 format!("cannot divide `{lhs_ty}` by `{rhs_ty}`")
 347                             }
 348                             hir::BinOpKind::Rem => {
 349                                 format!("cannot mod `{lhs_ty}` by `{rhs_ty}`")
 350                             }
 351                             hir::BinOpKind::BitAnd => {
 352                                 format!("no implementation for `{lhs_ty} & {rhs_ty}`")
 353                             }
 354                             hir::BinOpKind::BitXor => {
 355                                 format!("no implementation for `{lhs_ty} ^ {rhs_ty}`")
 356                             }
 357                             hir::BinOpKind::BitOr => {
 358                                 format!("no implementation for `{lhs_ty} | {rhs_ty}`")
 359                             }
 360                             hir::BinOpKind::Shl => {
 361                                 format!("no implementation for `{lhs_ty} << {rhs_ty}`")
 362                             }
 363                             hir::BinOpKind::Shr => {
 364                                 format!("no implementation for `{lhs_ty} >> {rhs_ty}`")
 365                             }
 366                             _ => format!(
 367                                 "binary operation `{}` cannot be applied to type `{}`",
 368                                 op.node.as_str(),
 369                                 lhs_ty
 370                             ),
 371                         };
 372                         let output_def_id = trait_def_id.and_then(|def_id| {
 373                             self.tcx
 374                                 .associated_item_def_ids(def_id)
 375                                 .iter()
 376                                 .find(|item_def_id| {
 377                                     self.tcx.associated_item(*item_def_id).name == sym::Output
 378                                 })
 379                                 .cloned()
 380                         });
 381                         let mut err = struct_span_err!(self.tcx.sess, op.span, E0369, "{message}");
 382                         if !lhs_expr.span.eq(&rhs_expr.span) {
 383                             err.span_label(lhs_expr.span, lhs_ty.to_string());
 384                             err.span_label(rhs_expr.span, rhs_ty.to_string());
 385                         }
 386                         self.note_unmet_impls_on_type(&mut err, errors);
 387                         (err, output_def_id)
 388                     }
 389                 };
 390
 391                 let mut suggest_deref_binop = |lhs_deref_ty: Ty<'tcx>| {
 392                     if self
 393                         .lookup_op_method(
 394                             lhs_deref_ty,
 395                             Some(rhs_ty),
 396                             Some(rhs_expr),
 397                             Op::Binary(op, is_assign),
 398                             expected,
 399                         )
 400                         .is_ok()
 401                     {
 402                         let msg = &format!(
 403                             "`{}{}` can be used on `{}` if you dereference the left-hand side",
 404                             op.node.as_str(),
 405                             match is_assign {
 406                                 IsAssign::Yes => "=",
 407                                 IsAssign::No => "",
 408                             },
 409                             lhs_deref_ty,
 410                         );
 411                         err.span_suggestion_verbose(
 412                             lhs_expr.span.shrink_to_lo(),
 413                             msg,
 414                             "*",
 415                             rustc_errors::Applicability::MachineApplicable,
 416                         );
 417                     }
 418                 };
 419
 420                 let is_compatible = |lhs_ty, rhs_ty| {
 421                     self.lookup_op_method(
 422                         lhs_ty,
 423                         Some(rhs_ty),
 424                         Some(rhs_expr),
 425                         Op::Binary(op, is_assign),
 426                         expected,
 427                     )
 428                     .is_ok()
 429                 };
 430
 431                 // We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
 432                 // `a += b` => `*a += b` if a is a mut ref.
 433                 if !op.span.can_be_used_for_suggestions() {
 434                     // Suppress suggestions when lhs and rhs are not in the same span as the error
 435                 } else if is_assign == IsAssign::Yes
 436                     && let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty)
 437                 {
 438                     suggest_deref_binop(lhs_deref_ty);
 439                 } else if is_assign == IsAssign::No
 440                     && let Ref(_, lhs_deref_ty, _) = lhs_ty.kind()
 441                 {
 442                     if self.type_is_copy_modulo_regions(
 443                         self.param_env,
 444                         *lhs_deref_ty,
 445                         lhs_expr.span,
 446                     ) {
 447                         suggest_deref_binop(*lhs_deref_ty);
 448                     }
 449                 } else if self.suggest_fn_call(&mut err, lhs_expr, lhs_ty, |lhs_ty| {
 450                     is_compatible(lhs_ty, rhs_ty)
 451                 }) || self.suggest_fn_call(&mut err, rhs_expr, rhs_ty, |rhs_ty| {
 452                     is_compatible(lhs_ty, rhs_ty)
 453                 }) || self.suggest_two_fn_call(
 454                     &mut err,
 455                     rhs_expr,
 456                     rhs_ty,
 457                     lhs_expr,
 458                     lhs_ty,
 459                     |lhs_ty, rhs_ty| is_compatible(lhs_ty, rhs_ty),
 460                 ) {
 461                     // Cool
 462                 }
 463
 464                 if let Some(missing_trait) = missing_trait {
 465                     if op.node == hir::BinOpKind::Add
 466                         && self.check_str_addition(
 467                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 468                         )
 469                     {
 470                         // This has nothing here because it means we did string
 471                         // concatenation (e.g., "Hello " + "World!"). This means
 472                         // we don't want the note in the else clause to be emitted
 473                     } else if lhs_ty.has_param_types_or_consts() {
 474                         // Look for a TraitPredicate in the Fulfillment errors,
 475                         // and use it to generate a suggestion.
 476                         //
 477                         // Note that lookup_op_method must be called again but
 478                         // with a specific rhs_ty instead of a placeholder so
 479                         // the resulting predicate generates a more specific
 480                         // suggestion for the user.
 481                         let errors = self
 482                             .lookup_op_method(
 483                                 lhs_ty,
 484                                 Some(rhs_ty),
 485                                 Some(rhs_expr),
 486                                 Op::Binary(op, is_assign),
 487                                 expected,
 488                             )
 489                             .unwrap_err();
 490                         if !errors.is_empty() {
 491                             for error in errors {
 492                                 if let Some(trait_pred) =
 493                                     error.obligation.predicate.to_opt_poly_trait_pred()
 494                                 {
 495                                     let output_associated_item = match error.obligation.cause.code()
 496                                     {
 497                                         ObligationCauseCode::BinOp {
 498                                             output_ty: Some(output_ty),
 499                                             ..
 500                                         } => {
 501                                             // Make sure that we're attaching `Output = ..` to the right trait predicate
 502                                             if let Some(output_def_id) = output_def_id
 503                                                 && let Some(trait_def_id) = trait_def_id
 504                                                 && self.tcx.parent(output_def_id) == trait_def_id
 505                                             {
 506                                                 Some(("Output", *output_ty))
 507                                             } else {
 508                                                 None
 509                                             }
 510                                         }
 511                                         _ => None,
 512                                     };
 513
 514                                     self.suggest_restricting_param_bound(
 515                                         &mut err,
 516                                         trait_pred,
 517                                         output_associated_item,
 518                                         self.body_id,
 519                                     );
 520                                 }
 521                             }
 522                         } else {
 523                             // When we know that a missing bound is responsible, we don't show
 524                             // this note as it is redundant.
 525                             err.note(&format!(
 526                                 "the trait `{missing_trait}` is not implemented for `{lhs_ty}`"
 527                             ));
 528                         }
 529                     }
 530                 }
 531                 err.emit();
 532                 self.tcx.ty_error()
 533             }
 534         };
 535
 536         (lhs_ty, rhs_ty, return_ty)
 537     }
 538
 539     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 540     /// like `&str + &str`, `String + String` and `&str + &String`.
 541     ///
 542     /// If this function returns `true` it means a note was printed, so we don't need
 543     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 544     fn check_str_addition(
 545         &self,
 546         lhs_expr: &'tcx hir::Expr<'tcx>,
 547         rhs_expr: &'tcx hir::Expr<'tcx>,
 548         lhs_ty: Ty<'tcx>,
 549         rhs_ty: Ty<'tcx>,
 550         err: &mut Diagnostic,
 551         is_assign: IsAssign,
 552         op: hir::BinOp,
 553     ) -> bool {
 554         let str_concat_note = "string concatenation requires an owned `String` on the left";
 555         let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
 556         let to_owned_msg = "create an owned `String` from a string reference";
 557
 558         let is_std_string = |ty: Ty<'tcx>| {
 559             ty.ty_adt_def()
 560                 .map_or(false, |ty_def| self.tcx.is_diagnostic_item(sym::String, ty_def.did()))
 561         };
 562
 563         match (lhs_ty.kind(), rhs_ty.kind()) {
 564             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 565                 if (*l_ty.kind() == Str || is_std_string(l_ty))
 566                     && (*r_ty.kind() == Str
 567                         || is_std_string(r_ty)
 568                         || matches!(
 569                             r_ty.kind(), Ref(_, inner_ty, _) if *inner_ty.kind() == Str
 570                         )) =>
 571             {
 572                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 573                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 574                     err.note(str_concat_note);
 575                     if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 576                         err.span_suggestion_verbose(
 577                             lhs_expr.span.until(lhs_inner_expr.span),
 578                             rm_borrow_msg,
 579                             "",
 580                             Applicability::MachineApplicable
 581                         );
 582                     } else {
 583                         err.span_suggestion_verbose(
 584                             lhs_expr.span.shrink_to_hi(),
 585                             to_owned_msg,
 586                             ".to_owned()",
 587                             Applicability::MachineApplicable
 588                         );
 589                     }
 590                 }
 591                 true
 592             }
 593             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 594                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 595             {
 596                 err.span_label(
 597                     op.span,
 598                     "`+` cannot be used to concatenate a `&str` with a `String`",
 599                 );
 600                 match is_assign {
 601                     IsAssign::No => {
 602                         let sugg_msg;
 603                         let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 604                             sugg_msg = "remove the borrow on the left and add one on the right";
 605                             (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 606                         } else {
 607                             sugg_msg = "create an owned `String` on the left and add a borrow on the right";
 608                             (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 609                         };
 610                         let suggestions = vec![
 611                             lhs_sugg,
 612                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 613                         ];
 614                         err.multipart_suggestion_verbose(
 615                             sugg_msg,
 616                             suggestions,
 617                             Applicability::MachineApplicable,
 618                         );
 619                     }
 620                     IsAssign::Yes => {
 621                         err.note(str_concat_note);
 622                     }
 623                 }
 624                 true
 625             }
 626             _ => false,
 627         }
 628     }
 629
 630     pub fn check_user_unop(
 631         &self,
 632         ex: &'tcx hir::Expr<'tcx>,
 633         operand_ty: Ty<'tcx>,
 634         op: hir::UnOp,
 635         expected: Expectation<'tcx>,
 636     ) -> Ty<'tcx> {
 637         assert!(op.is_by_value());
 638         match self.lookup_op_method(operand_ty, None, None, Op::Unary(op, ex.span), expected) {
 639             Ok(method) => {
 640                 self.write_method_call(ex.hir_id, method);
 641                 method.sig.output()
 642             }
 643             Err(errors) => {
 644                 let actual = self.resolve_vars_if_possible(operand_ty);
 645                 if !actual.references_error() {
 646                     let mut err = struct_span_err!(
 647                         self.tcx.sess,
 648                         ex.span,
 649                         E0600,
 650                         "cannot apply unary operator `{}` to type `{}`",
 651                         op.as_str(),
 652                         actual
 653                     );
 654                     err.span_label(
 655                         ex.span,
 656                         format!("cannot apply unary operator `{}`", op.as_str()),
 657                     );
 658
 659                     if operand_ty.has_param_types_or_consts() {
 660                         let predicates = errors.iter().filter_map(|error| {
 661                             error.obligation.predicate.to_opt_poly_trait_pred()
 662                         });
 663                         for pred in predicates {
 664                             self.suggest_restricting_param_bound(
 665                                 &mut err,
 666                                 pred,
 667                                 None,
 668                                 self.body_id,
 669                             );
 670                         }
 671                     }
 672
 673                     let sp = self.tcx.sess.source_map().start_point(ex.span);
 674                     if let Some(sp) =
 675                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 676                     {
 677                         // If the previous expression was a block expression, suggest parentheses
 678                         // (turning this into a binary subtraction operation instead.)
 679                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 680                         self.tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 681                     } else {
 682                         match actual.kind() {
 683                             Uint(_) if op == hir::UnOp::Neg => {
 684                                 err.note("unsigned values cannot be negated");
 685
 686                                 if let hir::ExprKind::Unary(
 687                                     _,
 688                                     hir::Expr {
 689                                         kind:
 690                                             hir::ExprKind::Lit(Spanned {
 691                                                 node: ast::LitKind::Int(1, _),
 692                                                 ..
 693                                             }),
 694                                         ..
 695                                     },
 696                                 ) = ex.kind
 697                                 {
 698                                     err.span_suggestion(
 699                                         ex.span,
 700                                         &format!(
 701                                             "you may have meant the maximum value of `{actual}`",
 702                                         ),
 703                                         format!("{actual}::MAX"),
 704                                         Applicability::MaybeIncorrect,
 705                                     );
 706                                 }
 707                             }
 708                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 709                             Ref(_, lty, _) if *lty.kind() == Str => {}
 710                             _ => {
 711                                 self.note_unmet_impls_on_type(&mut err, errors);
 712                             }
 713                         }
 714                     }
 715                     err.emit();
 716                 }
 717                 self.tcx.ty_error()
 718             }
 719         }
 720     }
 721
 722     fn lookup_op_method(
 723         &self,
 724         lhs_ty: Ty<'tcx>,
 725         other_ty: Option<Ty<'tcx>>,
 726         other_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 727         op: Op,
 728         expected: Expectation<'tcx>,
 729     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 730         let span = match op {
 731             Op::Binary(op, _) => op.span,
 732             Op::Unary(_, span) => span,
 733         };
 734         let (opname, trait_did) = lang_item_for_op(self.tcx, op, span);
 735
 736         debug!(
 737             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 738             lhs_ty, op, opname, trait_did
 739         );
 740
 741         // Catches cases like #83893, where a lang item is declared with the
 742         // wrong number of generic arguments. Should have yielded an error
 743         // elsewhere by now, but we have to catch it here so that we do not
 744         // index `other_tys` out of bounds (if the lang item has too many
 745         // generic arguments, `other_tys` is too short).
 746         if !has_expected_num_generic_args(
 747             self.tcx,
 748             trait_did,
 749             match op {
 750                 // Binary ops have a generic right-hand side, unary ops don't
 751                 Op::Binary(..) => 1,
 752                 Op::Unary(..) => 0,
 753             },
 754         ) {
 755             return Err(vec![]);
 756         }
 757
 758         let opname = Ident::with_dummy_span(opname);
 759         let method = trait_did.and_then(|trait_did| {
 760             self.lookup_op_method_in_trait(
 761                 span,
 762                 opname,
 763                 trait_did,
 764                 lhs_ty,
 765                 other_ty,
 766                 other_ty_expr,
 767                 expected,
 768             )
 769         });
 770
 771         match (method, trait_did) {
 772             (Some(ok), _) => {
 773                 let method = self.register_infer_ok_obligations(ok);
 774                 self.select_obligations_where_possible(false, |_| {});
 775                 Ok(method)
 776             }
 777             (None, None) => Err(vec![]),
 778             (None, Some(trait_did)) => {
 779                 let (obligation, _) = self.obligation_for_op_method(
 780                     span,
 781                     trait_did,
 782                     lhs_ty,
 783                     other_ty,
 784                     other_ty_expr,
 785                     expected,
 786                 );
 787                 let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 788                 fulfill.register_predicate_obligation(self, obligation);
 789                 Err(fulfill.select_where_possible(&self.infcx))
 790             }
 791         }
 792     }
 793 }
 794
 795 fn lang_item_for_op(
 796     tcx: TyCtxt<'_>,
 797     op: Op,
 798     span: Span,
 799 ) -> (rustc_span::Symbol, Option<hir::def_id::DefId>) {
 800     let lang = tcx.lang_items();
 801     if let Op::Binary(op, IsAssign::Yes) = op {
 802         match op.node {
 803             hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 804             hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 805             hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 806             hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 807             hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 808             hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 809             hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 810             hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 811             hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 812             hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 813             hir::BinOpKind::Lt
 814             | hir::BinOpKind::Le
 815             | hir::BinOpKind::Ge
 816             | hir::BinOpKind::Gt
 817             | hir::BinOpKind::Eq
 818             | hir::BinOpKind::Ne
 819             | hir::BinOpKind::And
 820             | hir::BinOpKind::Or => {
 821                 span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 822             }
 823         }
 824     } else if let Op::Binary(op, IsAssign::No) = op {
 825         match op.node {
 826             hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 827             hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 828             hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 829             hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 830             hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 831             hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 832             hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 833             hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 834             hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 835             hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 836             hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 837             hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 838             hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 839             hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 840             hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 841             hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 842             hir::BinOpKind::And | hir::BinOpKind::Or => {
 843                 span_bug!(span, "&& and || are not overloadable")
 844             }
 845         }
 846     } else if let Op::Unary(hir::UnOp::Not, _) = op {
 847         (sym::not, lang.not_trait())
 848     } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 849         (sym::neg, lang.neg_trait())
 850     } else {
 851         bug!("lookup_op_method: op not supported: {:?}", op)
 852     }
 853 }
 854
 855 // Binary operator categories. These categories summarize the behavior
 856 // with respect to the builtin operations supported.
 857 enum BinOpCategory {
 858     /// &&, || -- cannot be overridden
 859     Shortcircuit,
 860
 861     /// <<, >> -- when shifting a single integer, rhs can be any
 862     /// integer type. For simd, types must match.
 863     Shift,
 864
 865     /// +, -, etc -- takes equal types, produces same type as input,
 866     /// applicable to ints/floats/simd
 867     Math,
 868
 869     /// &, |, ^ -- takes equal types, produces same type as input,
 870     /// applicable to ints/floats/simd/bool
 871     Bitwise,
 872
 873     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 874     /// which produce the input type
 875     Comparison,
 876 }
 877
 878 impl BinOpCategory {
 879     fn from(op: hir::BinOp) -> BinOpCategory {
 880         match op.node {
 881             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 882
 883             hir::BinOpKind::Add
 884             | hir::BinOpKind::Sub
 885             | hir::BinOpKind::Mul
 886             | hir::BinOpKind::Div
 887             | hir::BinOpKind::Rem => BinOpCategory::Math,
 888
 889             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 890                 BinOpCategory::Bitwise
 891             }
 892
 893             hir::BinOpKind::Eq
 894             | hir::BinOpKind::Ne
 895             | hir::BinOpKind::Lt
 896             | hir::BinOpKind::Le
 897             | hir::BinOpKind::Ge
 898             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 899
 900             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 901         }
 902     }
 903 }
 904
 905 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 906 #[derive(Clone, Copy, Debug, PartialEq)]
 907 enum IsAssign {
 908     No,
 909     Yes,
 910 }
 911
 912 #[derive(Clone, Copy, Debug)]
 913 enum Op {
 914     Binary(hir::BinOp, IsAssign),
 915     Unary(hir::UnOp, Span),
 916 }
 917
 918 /// Dereferences a single level of immutable referencing.
 919 fn deref_ty_if_possible<'tcx>(ty: Ty<'tcx>) -> Ty<'tcx> {
 920     match ty.kind() {
 921         ty::Ref(_, ty, hir::Mutability::Not) => *ty,
 922         _ => ty,
 923     }
 924 }
 925
 926 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 927 /// + u32, i16x4 == i16x4) and false if these types would have to be
 928 /// overloaded to be legal. There are two reasons that we distinguish
 929 /// builtin operations from overloaded ones (vs trying to drive
 930 /// everything uniformly through the trait system and intrinsics or
 931 /// something like that):
 932 ///
 933 /// 1. Builtin operations can trivially be evaluated in constants.
 934 /// 2. For comparison operators applied to SIMD types the result is
 935 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 936 ///    type like `i16x4`. This means that the overloaded trait
 937 ///    `PartialEq` is not applicable.
 938 ///
 939 /// Reason #2 is the killer. I tried for a while to always use
 940 /// overloaded logic and just check the types in constants/codegen after
 941 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 942 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 943     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 944     // (See https://github.com/rust-lang/rust/issues/57447.)
 945     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 946
 947     match BinOpCategory::from(op) {
 948         BinOpCategory::Shortcircuit => true,
 949
 950         BinOpCategory::Shift => {
 951             lhs.references_error()
 952                 || rhs.references_error()
 953                 || lhs.is_integral() && rhs.is_integral()
 954         }
 955
 956         BinOpCategory::Math => {
 957             lhs.references_error()
 958                 || rhs.references_error()
 959                 || lhs.is_integral() && rhs.is_integral()
 960                 || lhs.is_floating_point() && rhs.is_floating_point()
 961         }
 962
 963         BinOpCategory::Bitwise => {
 964             lhs.references_error()
 965                 || rhs.references_error()
 966                 || lhs.is_integral() && rhs.is_integral()
 967                 || lhs.is_floating_point() && rhs.is_floating_point()
 968                 || lhs.is_bool() && rhs.is_bool()
 969         }
 970
 971         BinOpCategory::Comparison => {
 972             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 973         }
 974     }
 975 }
 976
 977 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
 978
 979 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
 980     fn tcx(&self) -> TyCtxt<'tcx> {
 981         self.0.tcx
 982     }
 983
 984     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 985         match ty.kind() {
 986             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
 987                 kind: TypeVariableOriginKind::MiscVariable,
 988                 span: self.1,
 989             }),
 990             _ => ty.super_fold_with(self),
 991         }
 992     }
 993 }