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