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::{
  16     self, DefIdTree, IsSuggestable, Ty, TyCtxt, TypeFolder, TypeSuperFoldable, TypeVisitable,
  17 };
  18 use rustc_session::errors::ExprParenthesesNeeded;
  19 use rustc_span::source_map::Spanned;
  20 use rustc_span::symbol::{sym, Ident};
  21 use rustc_span::Span;
  22 use rustc_trait_selection::infer::InferCtxtExt;
  23 use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt as _;
  24 use rustc_trait_selection::traits::{self, FulfillmentError};
  25 use rustc_type_ir::sty::TyKind::*;
  26
  27 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  28     /// Checks a `a <op>= b`
  29     pub fn check_binop_assign(
  30         &self,
  31         expr: &'tcx hir::Expr<'tcx>,
  32         op: hir::BinOp,
  33         lhs: &'tcx hir::Expr<'tcx>,
  34         rhs: &'tcx hir::Expr<'tcx>,
  35         expected: Expectation<'tcx>,
  36     ) -> Ty<'tcx> {
  37         let (lhs_ty, rhs_ty, return_ty) =
  38             self.check_overloaded_binop(expr, lhs, rhs, op, IsAssign::Yes, expected);
  39
  40         let ty =
  41             if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() && is_builtin_binop(lhs_ty, rhs_ty, op) {
  42                 self.enforce_builtin_binop_types(lhs.span, lhs_ty, rhs.span, rhs_ty, op);
  43                 self.tcx.mk_unit()
  44             } else {
  45                 return_ty
  46             };
  47
  48         self.check_lhs_assignable(lhs, "E0067", op.span, |err| {
  49             if let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
  50                 if self
  51                     .lookup_op_method(
  52                         lhs_deref_ty,
  53                         Some((rhs, rhs_ty)),
  54                         Op::Binary(op, IsAssign::Yes),
  55                         expected,
  56                     )
  57                     .is_ok()
  58                 {
  59                     // If LHS += RHS is an error, but *LHS += RHS is successful, then we will have
  60                     // emitted a better suggestion during error handling in check_overloaded_binop.
  61                     if self
  62                         .lookup_op_method(
  63                             lhs_ty,
  64                             Some((rhs, rhs_ty)),
  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_expr, rhs_ty_var)),
 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 = AutoBorrowMutability::new(*mutbl, AllowTwoPhase::Yes);
 266                         let autoref = Adjustment {
 267                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 268                             target: method.sig.inputs()[0],
 269                         };
 270                         self.apply_adjustments(lhs_expr, vec![autoref]);
 271                     }
 272                 }
 273                 if by_ref_binop {
 274                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 275                         // Allow two-phase borrows for binops in initial deployment
 276                         // since they desugar to methods
 277                         let mutbl = AutoBorrowMutability::new(*mutbl, AllowTwoPhase::Yes);
 278
 279                         let autoref = Adjustment {
 280                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 281                             target: method.sig.inputs()[1],
 282                         };
 283                         // HACK(eddyb) Bypass checks due to reborrows being in
 284                         // some cases applied on the RHS, on top of which we need
 285                         // to autoref, which is not allowed by apply_adjustments.
 286                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 287                         self.typeck_results
 288                             .borrow_mut()
 289                             .adjustments_mut()
 290                             .entry(rhs_expr.hir_id)
 291                             .or_default()
 292                             .push(autoref);
 293                     }
 294                 }
 295                 self.write_method_call(expr.hir_id, method);
 296
 297                 method.sig.output()
 298             }
 299             // error types are considered "builtin"
 300             Err(_) if lhs_ty.references_error() || rhs_ty.references_error() => self.tcx.ty_error(),
 301             Err(errors) => {
 302                 let (_, trait_def_id) =
 303                     lang_item_for_op(self.tcx, Op::Binary(op, is_assign), op.span);
 304                 let missing_trait = trait_def_id
 305                     .map(|def_id| with_no_trimmed_paths!(self.tcx.def_path_str(def_id)));
 306                 let (mut err, output_def_id) = match is_assign {
 307                     IsAssign::Yes => {
 308                         let mut err = struct_span_err!(
 309                             self.tcx.sess,
 310                             expr.span,
 311                             E0368,
 312                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 313                             op.node.as_str(),
 314                             lhs_ty,
 315                         );
 316                         err.span_label(
 317                             lhs_expr.span,
 318                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 319                         );
 320                         self.note_unmet_impls_on_type(&mut err, errors);
 321                         (err, None)
 322                     }
 323                     IsAssign::No => {
 324                         let message = match op.node {
 325                             hir::BinOpKind::Add => {
 326                                 format!("cannot add `{rhs_ty}` to `{lhs_ty}`")
 327                             }
 328                             hir::BinOpKind::Sub => {
 329                                 format!("cannot subtract `{rhs_ty}` from `{lhs_ty}`")
 330                             }
 331                             hir::BinOpKind::Mul => {
 332                                 format!("cannot multiply `{lhs_ty}` by `{rhs_ty}`")
 333                             }
 334                             hir::BinOpKind::Div => {
 335                                 format!("cannot divide `{lhs_ty}` by `{rhs_ty}`")
 336                             }
 337                             hir::BinOpKind::Rem => {
 338                                 format!(
 339                                     "cannot calculate the remainder of `{lhs_ty}` divided by `{rhs_ty}`"
 340                                 )
 341                             }
 342                             hir::BinOpKind::BitAnd => {
 343                                 format!("no implementation for `{lhs_ty} & {rhs_ty}`")
 344                             }
 345                             hir::BinOpKind::BitXor => {
 346                                 format!("no implementation for `{lhs_ty} ^ {rhs_ty}`")
 347                             }
 348                             hir::BinOpKind::BitOr => {
 349                                 format!("no implementation for `{lhs_ty} | {rhs_ty}`")
 350                             }
 351                             hir::BinOpKind::Shl => {
 352                                 format!("no implementation for `{lhs_ty} << {rhs_ty}`")
 353                             }
 354                             hir::BinOpKind::Shr => {
 355                                 format!("no implementation for `{lhs_ty} >> {rhs_ty}`")
 356                             }
 357                             _ => format!(
 358                                 "binary operation `{}` cannot be applied to type `{}`",
 359                                 op.node.as_str(),
 360                                 lhs_ty
 361                             ),
 362                         };
 363                         let output_def_id = trait_def_id.and_then(|def_id| {
 364                             self.tcx
 365                                 .associated_item_def_ids(def_id)
 366                                 .iter()
 367                                 .find(|item_def_id| {
 368                                     self.tcx.associated_item(*item_def_id).name == sym::Output
 369                                 })
 370                                 .cloned()
 371                         });
 372                         let mut err = struct_span_err!(self.tcx.sess, op.span, E0369, "{message}");
 373                         if !lhs_expr.span.eq(&rhs_expr.span) {
 374                             err.span_label(lhs_expr.span, lhs_ty.to_string());
 375                             err.span_label(rhs_expr.span, rhs_ty.to_string());
 376                         }
 377                         self.note_unmet_impls_on_type(&mut err, errors);
 378                         (err, output_def_id)
 379                     }
 380                 };
 381
 382                 let mut suggest_deref_binop = |lhs_deref_ty: Ty<'tcx>| {
 383                     if self
 384                         .lookup_op_method(
 385                             lhs_deref_ty,
 386                             Some((rhs_expr, rhs_ty)),
 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_expr, rhs_ty)),
 414                         Op::Binary(op, is_assign),
 415                         expected,
 416                     )
 417                     .is_ok()
 418                 };
 419
 420                 // We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
 421                 // `a += b` => `*a += b` if a is a mut ref.
 422                 if !op.span.can_be_used_for_suggestions() {
 423                     // Suppress suggestions when lhs and rhs are not in the same span as the error
 424                 } else if is_assign == IsAssign::Yes
 425                     && let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty)
 426                 {
 427                     suggest_deref_binop(lhs_deref_ty);
 428                 } else if is_assign == IsAssign::No
 429                     && let Ref(_, lhs_deref_ty, _) = lhs_ty.kind()
 430                 {
 431                     if self.type_is_copy_modulo_regions(
 432                         self.param_env,
 433                         *lhs_deref_ty,
 434                         lhs_expr.span,
 435                     ) {
 436                         suggest_deref_binop(*lhs_deref_ty);
 437                     }
 438                 } else if self.suggest_fn_call(&mut err, lhs_expr, lhs_ty, |lhs_ty| {
 439                     is_compatible(lhs_ty, rhs_ty)
 440                 }) || self.suggest_fn_call(&mut err, rhs_expr, rhs_ty, |rhs_ty| {
 441                     is_compatible(lhs_ty, rhs_ty)
 442                 }) || self.suggest_two_fn_call(
 443                     &mut err,
 444                     rhs_expr,
 445                     rhs_ty,
 446                     lhs_expr,
 447                     lhs_ty,
 448                     |lhs_ty, rhs_ty| is_compatible(lhs_ty, rhs_ty),
 449                 ) {
 450                     // Cool
 451                 }
 452
 453                 if let Some(missing_trait) = missing_trait {
 454                     if op.node == hir::BinOpKind::Add
 455                         && self.check_str_addition(
 456                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 457                         )
 458                     {
 459                         // This has nothing here because it means we did string
 460                         // concatenation (e.g., "Hello " + "World!"). This means
 461                         // we don't want the note in the else clause to be emitted
 462                     } else if lhs_ty.has_non_region_param() {
 463                         // Look for a TraitPredicate in the Fulfillment errors,
 464                         // and use it to generate a suggestion.
 465                         //
 466                         // Note that lookup_op_method must be called again but
 467                         // with a specific rhs_ty instead of a placeholder so
 468                         // the resulting predicate generates a more specific
 469                         // suggestion for the user.
 470                         let errors = self
 471                             .lookup_op_method(
 472                                 lhs_ty,
 473                                 Some((rhs_expr, rhs_ty)),
 474                                 Op::Binary(op, is_assign),
 475                                 expected,
 476                             )
 477                             .unwrap_err();
 478                         if !errors.is_empty() {
 479                             for error in errors {
 480                                 if let Some(trait_pred) =
 481                                     error.obligation.predicate.to_opt_poly_trait_pred()
 482                                 {
 483                                     let output_associated_item = match error.obligation.cause.code()
 484                                     {
 485                                         ObligationCauseCode::BinOp {
 486                                             output_ty: Some(output_ty),
 487                                             ..
 488                                         } => {
 489                                             // Make sure that we're attaching `Output = ..` to the right trait predicate
 490                                             if let Some(output_def_id) = output_def_id
 491                                                 && let Some(trait_def_id) = trait_def_id
 492                                                 && self.tcx.parent(output_def_id) == trait_def_id
 493                                                 && output_ty.is_suggestable(self.tcx, false)
 494                                             {
 495                                                 Some(("Output", *output_ty))
 496                                             } else {
 497                                                 None
 498                                             }
 499                                         }
 500                                         _ => None,
 501                                     };
 502
 503                                     self.err_ctxt().suggest_restricting_param_bound(
 504                                         &mut err,
 505                                         trait_pred,
 506                                         output_associated_item,
 507                                         self.body_id,
 508                                     );
 509                                 }
 510                             }
 511                         } else {
 512                             // When we know that a missing bound is responsible, we don't show
 513                             // this note as it is redundant.
 514                             err.note(&format!(
 515                                 "the trait `{missing_trait}` is not implemented for `{lhs_ty}`"
 516                             ));
 517                         }
 518                     }
 519                 }
 520                 let reported = err.emit();
 521                 self.tcx.ty_error_with_guaranteed(reported)
 522             }
 523         };
 524
 525         (lhs_ty, rhs_ty, return_ty)
 526     }
 527
 528     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 529     /// like `&str + &str`, `String + String` and `&str + &String`.
 530     ///
 531     /// If this function returns `true` it means a note was printed, so we don't need
 532     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 533     fn check_str_addition(
 534         &self,
 535         lhs_expr: &'tcx hir::Expr<'tcx>,
 536         rhs_expr: &'tcx hir::Expr<'tcx>,
 537         lhs_ty: Ty<'tcx>,
 538         rhs_ty: Ty<'tcx>,
 539         err: &mut Diagnostic,
 540         is_assign: IsAssign,
 541         op: hir::BinOp,
 542     ) -> bool {
 543         let str_concat_note = "string concatenation requires an owned `String` on the left";
 544         let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
 545         let to_owned_msg = "create an owned `String` from a string reference";
 546
 547         let string_type = self.tcx.lang_items().string();
 548         let is_std_string = |ty: Ty<'tcx>| {
 549             ty.ty_adt_def().map_or(false, |ty_def| Some(ty_def.did()) == string_type)
 550         };
 551
 552         match (lhs_ty.kind(), rhs_ty.kind()) {
 553             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 554                 if (*l_ty.kind() == Str || is_std_string(l_ty))
 555                     && (*r_ty.kind() == Str
 556                         || is_std_string(r_ty)
 557                         || matches!(
 558                             r_ty.kind(), Ref(_, inner_ty, _) if *inner_ty.kind() == Str
 559                         )) =>
 560             {
 561                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 562                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 563                     err.note(str_concat_note);
 564                     if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 565                         err.span_suggestion_verbose(
 566                             lhs_expr.span.until(lhs_inner_expr.span),
 567                             rm_borrow_msg,
 568                             "",
 569                             Applicability::MachineApplicable
 570                         );
 571                     } else {
 572                         err.span_suggestion_verbose(
 573                             lhs_expr.span.shrink_to_hi(),
 574                             to_owned_msg,
 575                             ".to_owned()",
 576                             Applicability::MachineApplicable
 577                         );
 578                     }
 579                 }
 580                 true
 581             }
 582             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 583                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 584             {
 585                 err.span_label(
 586                     op.span,
 587                     "`+` cannot be used to concatenate a `&str` with a `String`",
 588                 );
 589                 match is_assign {
 590                     IsAssign::No => {
 591                         let sugg_msg;
 592                         let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 593                             sugg_msg = "remove the borrow on the left and add one on the right";
 594                             (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 595                         } else {
 596                             sugg_msg = "create an owned `String` on the left and add a borrow on the right";
 597                             (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 598                         };
 599                         let suggestions = vec![
 600                             lhs_sugg,
 601                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 602                         ];
 603                         err.multipart_suggestion_verbose(
 604                             sugg_msg,
 605                             suggestions,
 606                             Applicability::MachineApplicable,
 607                         );
 608                     }
 609                     IsAssign::Yes => {
 610                         err.note(str_concat_note);
 611                     }
 612                 }
 613                 true
 614             }
 615             _ => false,
 616         }
 617     }
 618
 619     pub fn check_user_unop(
 620         &self,
 621         ex: &'tcx hir::Expr<'tcx>,
 622         operand_ty: Ty<'tcx>,
 623         op: hir::UnOp,
 624         expected: Expectation<'tcx>,
 625     ) -> Ty<'tcx> {
 626         assert!(op.is_by_value());
 627         match self.lookup_op_method(operand_ty, None, Op::Unary(op, ex.span), expected) {
 628             Ok(method) => {
 629                 self.write_method_call(ex.hir_id, method);
 630                 method.sig.output()
 631             }
 632             Err(errors) => {
 633                 let actual = self.resolve_vars_if_possible(operand_ty);
 634                 if !actual.references_error() {
 635                     let mut err = struct_span_err!(
 636                         self.tcx.sess,
 637                         ex.span,
 638                         E0600,
 639                         "cannot apply unary operator `{}` to type `{}`",
 640                         op.as_str(),
 641                         actual
 642                     );
 643                     err.span_label(
 644                         ex.span,
 645                         format!("cannot apply unary operator `{}`", op.as_str()),
 646                     );
 647
 648                     if operand_ty.has_non_region_param() {
 649                         let predicates = errors.iter().filter_map(|error| {
 650                             error.obligation.predicate.to_opt_poly_trait_pred()
 651                         });
 652                         for pred in predicates {
 653                             self.err_ctxt().suggest_restricting_param_bound(
 654                                 &mut err,
 655                                 pred,
 656                                 None,
 657                                 self.body_id,
 658                             );
 659                         }
 660                     }
 661
 662                     let sp = self.tcx.sess.source_map().start_point(ex.span).with_parent(None);
 663                     if let Some(sp) =
 664                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 665                     {
 666                         // If the previous expression was a block expression, suggest parentheses
 667                         // (turning this into a binary subtraction operation instead.)
 668                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 669                         err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
 670                     } else {
 671                         match actual.kind() {
 672                             Uint(_) if op == hir::UnOp::Neg => {
 673                                 err.note("unsigned values cannot be negated");
 674
 675                                 if let hir::ExprKind::Unary(
 676                                     _,
 677                                     hir::Expr {
 678                                         kind:
 679                                             hir::ExprKind::Lit(Spanned {
 680                                                 node: ast::LitKind::Int(1, _),
 681                                                 ..
 682                                             }),
 683                                         ..
 684                                     },
 685                                 ) = ex.kind
 686                                 {
 687                                     err.span_suggestion(
 688                                         ex.span,
 689                                         &format!(
 690                                             "you may have meant the maximum value of `{actual}`",
 691                                         ),
 692                                         format!("{actual}::MAX"),
 693                                         Applicability::MaybeIncorrect,
 694                                     );
 695                                 }
 696                             }
 697                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 698                             Ref(_, lty, _) if *lty.kind() == Str => {}
 699                             _ => {
 700                                 self.note_unmet_impls_on_type(&mut err, errors);
 701                             }
 702                         }
 703                     }
 704                     err.emit();
 705                 }
 706                 self.tcx.ty_error()
 707             }
 708         }
 709     }
 710
 711     fn lookup_op_method(
 712         &self,
 713         lhs_ty: Ty<'tcx>,
 714         opt_rhs: Option<(&'tcx hir::Expr<'tcx>, Ty<'tcx>)>,
 715         op: Op,
 716         expected: Expectation<'tcx>,
 717     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 718         let span = match op {
 719             Op::Binary(op, _) => op.span,
 720             Op::Unary(_, span) => span,
 721         };
 722         let (opname, trait_did) = lang_item_for_op(self.tcx, op, span);
 723
 724         debug!(
 725             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 726             lhs_ty, op, opname, trait_did
 727         );
 728
 729         // Catches cases like #83893, where a lang item is declared with the
 730         // wrong number of generic arguments. Should have yielded an error
 731         // elsewhere by now, but we have to catch it here so that we do not
 732         // index `other_tys` out of bounds (if the lang item has too many
 733         // generic arguments, `other_tys` is too short).
 734         if !has_expected_num_generic_args(
 735             self.tcx,
 736             trait_did,
 737             match op {
 738                 // Binary ops have a generic right-hand side, unary ops don't
 739                 Op::Binary(..) => 1,
 740                 Op::Unary(..) => 0,
 741             },
 742         ) {
 743             self.tcx
 744                 .sess
 745                 .delay_span_bug(span, "operator didn't have the right number of generic args");
 746             return Err(vec![]);
 747         }
 748
 749         let opname = Ident::with_dummy_span(opname);
 750         let input_types =
 751             opt_rhs.as_ref().map(|(_, ty)| std::slice::from_ref(ty)).unwrap_or_default();
 752         let cause = self.cause(
 753             span,
 754             traits::BinOp {
 755                 rhs_span: opt_rhs.map(|(expr, _)| expr.span),
 756                 is_lit: opt_rhs
 757                     .map_or(false, |(expr, _)| matches!(expr.kind, hir::ExprKind::Lit(_))),
 758                 output_ty: expected.only_has_type(self),
 759             },
 760         );
 761
 762         let method = trait_did.and_then(|trait_did| {
 763             self.lookup_method_in_trait(cause.clone(), opname, trait_did, lhs_ty, Some(input_types))
 764         });
 765
 766         match (method, trait_did) {
 767             (Some(ok), _) => {
 768                 let method = self.register_infer_ok_obligations(ok);
 769                 self.select_obligations_where_possible(|_| {});
 770                 Ok(method)
 771             }
 772             (None, None) => Err(vec![]),
 773             (None, Some(trait_did)) => {
 774                 let (obligation, _) =
 775                     self.obligation_for_method(cause, trait_did, lhs_ty, Some(input_types));
 776                 Err(rustc_trait_selection::traits::fully_solve_obligation(self, obligation))
 777             }
 778         }
 779     }
 780 }
 781
 782 fn lang_item_for_op(
 783     tcx: TyCtxt<'_>,
 784     op: Op,
 785     span: Span,
 786 ) -> (rustc_span::Symbol, Option<hir::def_id::DefId>) {
 787     let lang = tcx.lang_items();
 788     if let Op::Binary(op, IsAssign::Yes) = op {
 789         match op.node {
 790             hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 791             hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 792             hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 793             hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 794             hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 795             hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 796             hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 797             hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 798             hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 799             hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 800             hir::BinOpKind::Lt
 801             | hir::BinOpKind::Le
 802             | hir::BinOpKind::Ge
 803             | hir::BinOpKind::Gt
 804             | hir::BinOpKind::Eq
 805             | hir::BinOpKind::Ne
 806             | hir::BinOpKind::And
 807             | hir::BinOpKind::Or => {
 808                 span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 809             }
 810         }
 811     } else if let Op::Binary(op, IsAssign::No) = op {
 812         match op.node {
 813             hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 814             hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 815             hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 816             hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 817             hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 818             hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 819             hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 820             hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 821             hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 822             hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 823             hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 824             hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 825             hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 826             hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 827             hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 828             hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 829             hir::BinOpKind::And | hir::BinOpKind::Or => {
 830                 span_bug!(span, "&& and || are not overloadable")
 831             }
 832         }
 833     } else if let Op::Unary(hir::UnOp::Not, _) = op {
 834         (sym::not, lang.not_trait())
 835     } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 836         (sym::neg, lang.neg_trait())
 837     } else {
 838         bug!("lookup_op_method: op not supported: {:?}", op)
 839     }
 840 }
 841
 842 // Binary operator categories. These categories summarize the behavior
 843 // with respect to the builtin operations supported.
 844 enum BinOpCategory {
 845     /// &&, || -- cannot be overridden
 846     Shortcircuit,
 847
 848     /// <<, >> -- when shifting a single integer, rhs can be any
 849     /// integer type. For simd, types must match.
 850     Shift,
 851
 852     /// +, -, etc -- takes equal types, produces same type as input,
 853     /// applicable to ints/floats/simd
 854     Math,
 855
 856     /// &, |, ^ -- takes equal types, produces same type as input,
 857     /// applicable to ints/floats/simd/bool
 858     Bitwise,
 859
 860     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 861     /// which produce the input type
 862     Comparison,
 863 }
 864
 865 impl BinOpCategory {
 866     fn from(op: hir::BinOp) -> BinOpCategory {
 867         match op.node {
 868             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 869
 870             hir::BinOpKind::Add
 871             | hir::BinOpKind::Sub
 872             | hir::BinOpKind::Mul
 873             | hir::BinOpKind::Div
 874             | hir::BinOpKind::Rem => BinOpCategory::Math,
 875
 876             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 877                 BinOpCategory::Bitwise
 878             }
 879
 880             hir::BinOpKind::Eq
 881             | hir::BinOpKind::Ne
 882             | hir::BinOpKind::Lt
 883             | hir::BinOpKind::Le
 884             | hir::BinOpKind::Ge
 885             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 886
 887             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 888         }
 889     }
 890 }
 891
 892 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 893 #[derive(Clone, Copy, Debug, PartialEq)]
 894 enum IsAssign {
 895     No,
 896     Yes,
 897 }
 898
 899 #[derive(Clone, Copy, Debug)]
 900 enum Op {
 901     Binary(hir::BinOp, IsAssign),
 902     Unary(hir::UnOp, Span),
 903 }
 904
 905 /// Dereferences a single level of immutable referencing.
 906 fn deref_ty_if_possible(ty: Ty<'_>) -> Ty<'_> {
 907     match ty.kind() {
 908         ty::Ref(_, ty, hir::Mutability::Not) => *ty,
 909         _ => ty,
 910     }
 911 }
 912
 913 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 914 /// + u32, i16x4 == i16x4) and false if these types would have to be
 915 /// overloaded to be legal. There are two reasons that we distinguish
 916 /// builtin operations from overloaded ones (vs trying to drive
 917 /// everything uniformly through the trait system and intrinsics or
 918 /// something like that):
 919 ///
 920 /// 1. Builtin operations can trivially be evaluated in constants.
 921 /// 2. For comparison operators applied to SIMD types the result is
 922 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 923 ///    type like `i16x4`. This means that the overloaded trait
 924 ///    `PartialEq` is not applicable.
 925 ///
 926 /// Reason #2 is the killer. I tried for a while to always use
 927 /// overloaded logic and just check the types in constants/codegen after
 928 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 929 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 930     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 931     // (See https://github.com/rust-lang/rust/issues/57447.)
 932     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 933
 934     match BinOpCategory::from(op) {
 935         BinOpCategory::Shortcircuit => true,
 936
 937         BinOpCategory::Shift => {
 938             lhs.references_error()
 939                 || rhs.references_error()
 940                 || lhs.is_integral() && rhs.is_integral()
 941         }
 942
 943         BinOpCategory::Math => {
 944             lhs.references_error()
 945                 || rhs.references_error()
 946                 || lhs.is_integral() && rhs.is_integral()
 947                 || lhs.is_floating_point() && rhs.is_floating_point()
 948         }
 949
 950         BinOpCategory::Bitwise => {
 951             lhs.references_error()
 952                 || rhs.references_error()
 953                 || lhs.is_integral() && rhs.is_integral()
 954                 || lhs.is_floating_point() && rhs.is_floating_point()
 955                 || lhs.is_bool() && rhs.is_bool()
 956         }
 957
 958         BinOpCategory::Comparison => {
 959             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 960         }
 961     }
 962 }
 963
 964 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
 965
 966 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
 967     fn tcx(&self) -> TyCtxt<'tcx> {
 968         self.0.tcx
 969     }
 970
 971     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 972         match ty.kind() {
 973             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
 974                 kind: TypeVariableOriginKind::MiscVariable,
 975                 span: self.1,
 976             }),
 977             _ => ty.super_fold_with(self),
 978         }
 979     }
 980 }