compiler/rustc_typeck/src/check/op.rs

   1 //! Code related to processing overloaded binary and unary operators.
   2
   3 use super::method::MethodCallee;
   4 use super::{has_expected_num_generic_args, FnCtxt};
   5 use crate::check::Expectation;
   6 use rustc_ast as ast;
   7 use rustc_errors::{self, struct_span_err, Applicability, Diagnostic};
   8 use rustc_hir as hir;
   9 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  10 use rustc_infer::traits::ObligationCauseCode;
  11 use rustc_middle::ty::adjustment::{
  12     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  13 };
  14 use rustc_middle::ty::{
  15     self, Ty, TyCtxt, TypeFolder, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitor,
  16 };
  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::InferCtxtExt as _;
  22 use rustc_trait_selection::traits::{FulfillmentError, TraitEngine, TraitEngineExt};
  23 use rustc_type_ir::sty::TyKind::*;
  24
  25 use std::ops::ControlFlow;
  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_ty),
  54                         Some(rhs),
  55                         Op::Binary(op, IsAssign::Yes),
  56                         expected,
  57                     )
  58                     .is_ok()
  59                 {
  60                     // Suppress this error, since we already emitted
  61                     // a deref suggestion in check_overloaded_binop
  62                     err.downgrade_to_delayed_bug();
  63                 }
  64             }
  65         });
  66
  67         ty
  68     }
  69
  70     /// Checks a potentially overloaded binary operator.
  71     pub fn check_binop(
  72         &self,
  73         expr: &'tcx hir::Expr<'tcx>,
  74         op: hir::BinOp,
  75         lhs_expr: &'tcx hir::Expr<'tcx>,
  76         rhs_expr: &'tcx hir::Expr<'tcx>,
  77         expected: Expectation<'tcx>,
  78     ) -> Ty<'tcx> {
  79         let tcx = self.tcx;
  80
  81         debug!(
  82             "check_binop(expr.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  83             expr.hir_id, expr, op, lhs_expr, rhs_expr
  84         );
  85
  86         match BinOpCategory::from(op) {
  87             BinOpCategory::Shortcircuit => {
  88                 // && and || are a simple case.
  89                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool, None);
  90                 let lhs_diverges = self.diverges.get();
  91                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool, None);
  92
  93                 // Depending on the LHS' value, the RHS can never execute.
  94                 self.diverges.set(lhs_diverges);
  95
  96                 tcx.types.bool
  97             }
  98             _ => {
  99                 // Otherwise, we always treat operators as if they are
 100                 // overloaded. This is the way to be most flexible w/r/t
 101                 // types that get inferred.
 102                 let (lhs_ty, rhs_ty, return_ty) = self.check_overloaded_binop(
 103                     expr,
 104                     lhs_expr,
 105                     rhs_expr,
 106                     op,
 107                     IsAssign::No,
 108                     expected,
 109                 );
 110
 111                 // Supply type inference hints if relevant. Probably these
 112                 // hints should be enforced during select as part of the
 113                 // `consider_unification_despite_ambiguity` routine, but this
 114                 // more convenient for now.
 115                 //
 116                 // The basic idea is to help type inference by taking
 117                 // advantage of things we know about how the impls for
 118                 // scalar types are arranged. This is important in a
 119                 // scenario like `1_u32 << 2`, because it lets us quickly
 120                 // deduce that the result type should be `u32`, even
 121                 // though we don't know yet what type 2 has and hence
 122                 // can't pin this down to a specific impl.
 123                 if !lhs_ty.is_ty_var()
 124                     && !rhs_ty.is_ty_var()
 125                     && is_builtin_binop(lhs_ty, rhs_ty, op)
 126                 {
 127                     let builtin_return_ty = self.enforce_builtin_binop_types(
 128                         lhs_expr.span,
 129                         lhs_ty,
 130                         rhs_expr.span,
 131                         rhs_ty,
 132                         op,
 133                     );
 134                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 135                 }
 136
 137                 return_ty
 138             }
 139         }
 140     }
 141
 142     fn enforce_builtin_binop_types(
 143         &self,
 144         lhs_span: Span,
 145         lhs_ty: Ty<'tcx>,
 146         rhs_span: Span,
 147         rhs_ty: Ty<'tcx>,
 148         op: hir::BinOp,
 149     ) -> Ty<'tcx> {
 150         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 151
 152         // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 153         // (See https://github.com/rust-lang/rust/issues/57447.)
 154         let (lhs_ty, rhs_ty) = (deref_ty_if_possible(lhs_ty), deref_ty_if_possible(rhs_ty));
 155
 156         let tcx = self.tcx;
 157         match BinOpCategory::from(op) {
 158             BinOpCategory::Shortcircuit => {
 159                 self.demand_suptype(lhs_span, tcx.types.bool, lhs_ty);
 160                 self.demand_suptype(rhs_span, tcx.types.bool, rhs_ty);
 161                 tcx.types.bool
 162             }
 163
 164             BinOpCategory::Shift => {
 165                 // result type is same as LHS always
 166                 lhs_ty
 167             }
 168
 169             BinOpCategory::Math | BinOpCategory::Bitwise => {
 170                 // both LHS and RHS and result will have the same type
 171                 self.demand_suptype(rhs_span, lhs_ty, rhs_ty);
 172                 lhs_ty
 173             }
 174
 175             BinOpCategory::Comparison => {
 176                 // both LHS and RHS and result will have the same type
 177                 self.demand_suptype(rhs_span, lhs_ty, rhs_ty);
 178                 tcx.types.bool
 179             }
 180         }
 181     }
 182
 183     fn check_overloaded_binop(
 184         &self,
 185         expr: &'tcx hir::Expr<'tcx>,
 186         lhs_expr: &'tcx hir::Expr<'tcx>,
 187         rhs_expr: &'tcx hir::Expr<'tcx>,
 188         op: hir::BinOp,
 189         is_assign: IsAssign,
 190         expected: Expectation<'tcx>,
 191     ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
 192         debug!(
 193             "check_overloaded_binop(expr.hir_id={}, op={:?}, is_assign={:?})",
 194             expr.hir_id, op, is_assign
 195         );
 196
 197         let lhs_ty = match is_assign {
 198             IsAssign::No => {
 199                 // Find a suitable supertype of the LHS expression's type, by coercing to
 200                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 201                 // trait matching creating lifetime constraints that are too strict.
 202                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 203                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 204                 let lhs_ty = self.check_expr(lhs_expr);
 205                 let fresh_var = self.next_ty_var(TypeVariableOrigin {
 206                     kind: TypeVariableOriginKind::MiscVariable,
 207                     span: lhs_expr.span,
 208                 });
 209                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var, Some(rhs_expr), AllowTwoPhase::No)
 210             }
 211             IsAssign::Yes => {
 212                 // rust-lang/rust#52126: We have to use strict
 213                 // equivalence on the LHS of an assign-op like `+=`;
 214                 // overwritten or mutably-borrowed places cannot be
 215                 // coerced to a supertype.
 216                 self.check_expr(lhs_expr)
 217             }
 218         };
 219         let lhs_ty = self.resolve_vars_with_obligations(lhs_ty);
 220
 221         // N.B., as we have not yet type-checked the RHS, we don't have the
 222         // type at hand. Make a variable to represent it. The whole reason
 223         // for this indirection is so that, below, we can check the expr
 224         // using this variable as the expected type, which sometimes lets
 225         // us do better coercions than we would be able to do otherwise,
 226         // particularly for things like `String + &String`.
 227         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 228             kind: TypeVariableOriginKind::MiscVariable,
 229             span: rhs_expr.span,
 230         });
 231
 232         let result = self.lookup_op_method(
 233             lhs_ty,
 234             Some(rhs_ty_var),
 235             Some(rhs_expr),
 236             Op::Binary(op, is_assign),
 237             expected,
 238         );
 239
 240         // see `NB` above
 241         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var, Some(lhs_expr));
 242         let rhs_ty = self.resolve_vars_with_obligations(rhs_ty);
 243
 244         let return_ty = match result {
 245             Ok(method) => {
 246                 let by_ref_binop = !op.node.is_by_value();
 247                 if is_assign == IsAssign::Yes || by_ref_binop {
 248                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() {
 249                         let mutbl = match mutbl {
 250                             hir::Mutability::Not => AutoBorrowMutability::Not,
 251                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 252                                 // Allow two-phase borrows for binops in initial deployment
 253                                 // since they desugar to methods
 254                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 255                             },
 256                         };
 257                         let autoref = Adjustment {
 258                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 259                             target: method.sig.inputs()[0],
 260                         };
 261                         self.apply_adjustments(lhs_expr, vec![autoref]);
 262                     }
 263                 }
 264                 if by_ref_binop {
 265                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 266                         let mutbl = match mutbl {
 267                             hir::Mutability::Not => AutoBorrowMutability::Not,
 268                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 269                                 // Allow two-phase borrows for binops in initial deployment
 270                                 // since they desugar to methods
 271                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 272                             },
 273                         };
 274                         let autoref = Adjustment {
 275                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 276                             target: method.sig.inputs()[1],
 277                         };
 278                         // HACK(eddyb) Bypass checks due to reborrows being in
 279                         // some cases applied on the RHS, on top of which we need
 280                         // to autoref, which is not allowed by apply_adjustments.
 281                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 282                         self.typeck_results
 283                             .borrow_mut()
 284                             .adjustments_mut()
 285                             .entry(rhs_expr.hir_id)
 286                             .or_default()
 287                             .push(autoref);
 288                     }
 289                 }
 290                 self.write_method_call(expr.hir_id, method);
 291
 292                 method.sig.output()
 293             }
 294             // error types are considered "builtin"
 295             Err(_) if lhs_ty.references_error() || rhs_ty.references_error() => self.tcx.ty_error(),
 296             Err(errors) => {
 297                 let source_map = self.tcx.sess.source_map();
 298                 let (mut err, missing_trait, use_output) = match is_assign {
 299                     IsAssign::Yes => {
 300                         let mut err = struct_span_err!(
 301                             self.tcx.sess,
 302                             expr.span,
 303                             E0368,
 304                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 305                             op.node.as_str(),
 306                             lhs_ty,
 307                         );
 308                         err.span_label(
 309                             lhs_expr.span,
 310                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 311                         );
 312                         let missing_trait = match op.node {
 313                             hir::BinOpKind::Add => Some("std::ops::AddAssign"),
 314                             hir::BinOpKind::Sub => Some("std::ops::SubAssign"),
 315                             hir::BinOpKind::Mul => Some("std::ops::MulAssign"),
 316                             hir::BinOpKind::Div => Some("std::ops::DivAssign"),
 317                             hir::BinOpKind::Rem => Some("std::ops::RemAssign"),
 318                             hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 319                             hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 320                             hir::BinOpKind::BitOr => Some("std::ops::BitOrAssign"),
 321                             hir::BinOpKind::Shl => Some("std::ops::ShlAssign"),
 322                             hir::BinOpKind::Shr => Some("std::ops::ShrAssign"),
 323                             _ => None,
 324                         };
 325                         self.note_unmet_impls_on_type(&mut err, errors);
 326                         (err, missing_trait, false)
 327                     }
 328                     IsAssign::No => {
 329                         let (message, missing_trait, use_output) = match op.node {
 330                             hir::BinOpKind::Add => (
 331                                 format!("cannot add `{rhs_ty}` to `{lhs_ty}`"),
 332                                 Some("std::ops::Add"),
 333                                 true,
 334                             ),
 335                             hir::BinOpKind::Sub => (
 336                                 format!("cannot subtract `{rhs_ty}` from `{lhs_ty}`"),
 337                                 Some("std::ops::Sub"),
 338                                 true,
 339                             ),
 340                             hir::BinOpKind::Mul => (
 341                                 format!("cannot multiply `{lhs_ty}` by `{rhs_ty}`"),
 342                                 Some("std::ops::Mul"),
 343                                 true,
 344                             ),
 345                             hir::BinOpKind::Div => (
 346                                 format!("cannot divide `{lhs_ty}` by `{rhs_ty}`"),
 347                                 Some("std::ops::Div"),
 348                                 true,
 349                             ),
 350                             hir::BinOpKind::Rem => (
 351                                 format!("cannot mod `{lhs_ty}` by `{rhs_ty}`"),
 352                                 Some("std::ops::Rem"),
 353                                 true,
 354                             ),
 355                             hir::BinOpKind::BitAnd => (
 356                                 format!("no implementation for `{lhs_ty} & {rhs_ty}`"),
 357                                 Some("std::ops::BitAnd"),
 358                                 true,
 359                             ),
 360                             hir::BinOpKind::BitXor => (
 361                                 format!("no implementation for `{lhs_ty} ^ {rhs_ty}`"),
 362                                 Some("std::ops::BitXor"),
 363                                 true,
 364                             ),
 365                             hir::BinOpKind::BitOr => (
 366                                 format!("no implementation for `{lhs_ty} | {rhs_ty}`"),
 367                                 Some("std::ops::BitOr"),
 368                                 true,
 369                             ),
 370                             hir::BinOpKind::Shl => (
 371                                 format!("no implementation for `{lhs_ty} << {rhs_ty}`"),
 372                                 Some("std::ops::Shl"),
 373                                 true,
 374                             ),
 375                             hir::BinOpKind::Shr => (
 376                                 format!("no implementation for `{lhs_ty} >> {rhs_ty}`"),
 377                                 Some("std::ops::Shr"),
 378                                 true,
 379                             ),
 380                             hir::BinOpKind::Eq | hir::BinOpKind::Ne => (
 381                                 format!(
 382                                     "binary operation `{}` cannot be applied to type `{}`",
 383                                     op.node.as_str(),
 384                                     lhs_ty
 385                                 ),
 386                                 Some("std::cmp::PartialEq"),
 387                                 false,
 388                             ),
 389                             hir::BinOpKind::Lt
 390                             | hir::BinOpKind::Le
 391                             | hir::BinOpKind::Gt
 392                             | hir::BinOpKind::Ge => (
 393                                 format!(
 394                                     "binary operation `{}` cannot be applied to type `{}`",
 395                                     op.node.as_str(),
 396                                     lhs_ty
 397                                 ),
 398                                 Some("std::cmp::PartialOrd"),
 399                                 false,
 400                             ),
 401                             _ => (
 402                                 format!(
 403                                     "binary operation `{}` cannot be applied to type `{}`",
 404                                     op.node.as_str(),
 405                                     lhs_ty
 406                                 ),
 407                                 None,
 408                                 false,
 409                             ),
 410                         };
 411                         let mut err = struct_span_err!(self.tcx.sess, op.span, E0369, "{message}");
 412                         if !lhs_expr.span.eq(&rhs_expr.span) {
 413                             err.span_label(lhs_expr.span, lhs_ty.to_string());
 414                             err.span_label(rhs_expr.span, rhs_ty.to_string());
 415                         }
 416                         self.note_unmet_impls_on_type(&mut err, errors);
 417                         (err, missing_trait, use_output)
 418                     }
 419                 };
 420
 421                 let mut suggest_deref_binop = |lhs_deref_ty: Ty<'tcx>| {
 422                     if self
 423                         .lookup_op_method(
 424                             lhs_deref_ty,
 425                             Some(rhs_ty),
 426                             Some(rhs_expr),
 427                             Op::Binary(op, is_assign),
 428                             expected,
 429                         )
 430                         .is_ok()
 431                     {
 432                         if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 433                             let msg = &format!(
 434                                 "`{}{}` can be used on `{}`, you can dereference `{}`",
 435                                 op.node.as_str(),
 436                                 match is_assign {
 437                                     IsAssign::Yes => "=",
 438                                     IsAssign::No => "",
 439                                 },
 440                                 lhs_deref_ty.peel_refs(),
 441                                 lstring,
 442                             );
 443                             err.span_suggestion_verbose(
 444                                 lhs_expr.span.shrink_to_lo(),
 445                                 msg,
 446                                 "*",
 447                                 rustc_errors::Applicability::MachineApplicable,
 448                             );
 449                         }
 450                     }
 451                 };
 452
 453                 let is_compatible = |lhs_ty, rhs_ty| {
 454                     self.lookup_op_method(
 455                         lhs_ty,
 456                         Some(rhs_ty),
 457                         Some(rhs_expr),
 458                         Op::Binary(op, is_assign),
 459                         expected,
 460                     )
 461                     .is_ok()
 462                 };
 463
 464                 // We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
 465                 // `a += b` => `*a += b` if a is a mut ref.
 466                 if !op.span.can_be_used_for_suggestions() {
 467                     // Suppress suggestions when lhs and rhs are not in the same span as the error
 468                 } else if is_assign == IsAssign::Yes
 469                     && let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty)
 470                 {
 471                     suggest_deref_binop(lhs_deref_ty);
 472                 } else if is_assign == IsAssign::No
 473                     && let Ref(_, lhs_deref_ty, _) = lhs_ty.kind()
 474                 {
 475                     if self.type_is_copy_modulo_regions(
 476                         self.param_env,
 477                         *lhs_deref_ty,
 478                         lhs_expr.span,
 479                     ) {
 480                         suggest_deref_binop(*lhs_deref_ty);
 481                     }
 482                 } else if self.suggest_fn_call(&mut err, lhs_expr, lhs_ty, |lhs_ty| {
 483                     is_compatible(lhs_ty, rhs_ty)
 484                 }) || self.suggest_fn_call(&mut err, rhs_expr, rhs_ty, |rhs_ty| {
 485                     is_compatible(lhs_ty, rhs_ty)
 486                 }) || self.suggest_two_fn_call(
 487                     &mut err,
 488                     rhs_expr,
 489                     rhs_ty,
 490                     lhs_expr,
 491                     lhs_ty,
 492                     |lhs_ty, rhs_ty| is_compatible(lhs_ty, rhs_ty),
 493                 ) {
 494                     // Cool
 495                 }
 496
 497                 if let Some(missing_trait) = missing_trait {
 498                     let mut visitor = TypeParamVisitor(vec![]);
 499                     visitor.visit_ty(lhs_ty);
 500
 501                     if op.node == hir::BinOpKind::Add
 502                         && self.check_str_addition(
 503                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 504                         )
 505                     {
 506                         // This has nothing here because it means we did string
 507                         // concatenation (e.g., "Hello " + "World!"). This means
 508                         // we don't want the note in the else clause to be emitted
 509                     } else if let [ty] = &visitor.0[..] {
 510                         // Look for a TraitPredicate in the Fulfillment errors,
 511                         // and use it to generate a suggestion.
 512                         //
 513                         // Note that lookup_op_method must be called again but
 514                         // with a specific rhs_ty instead of a placeholder so
 515                         // the resulting predicate generates a more specific
 516                         // suggestion for the user.
 517                         let errors = self
 518                             .lookup_op_method(
 519                                 lhs_ty,
 520                                 Some(rhs_ty),
 521                                 Some(rhs_expr),
 522                                 Op::Binary(op, is_assign),
 523                                 expected,
 524                             )
 525                             .unwrap_err();
 526                         if !errors.is_empty() {
 527                             for error in errors {
 528                                 if let Some(trait_pred) =
 529                                     error.obligation.predicate.to_opt_poly_trait_pred()
 530                                 {
 531                                     let proj_pred = match error.obligation.cause.code() {
 532                                         ObligationCauseCode::BinOp {
 533                                             output_pred: Some(output_pred),
 534                                             ..
 535                                         } if use_output => {
 536                                             output_pred.to_opt_poly_projection_pred()
 537                                         }
 538                                         _ => None,
 539                                     };
 540
 541                                     self.suggest_restricting_param_bound(
 542                                         &mut err,
 543                                         trait_pred,
 544                                         proj_pred,
 545                                         self.body_id,
 546                                     );
 547                                 }
 548                             }
 549                         } else if *ty != lhs_ty {
 550                             // When we know that a missing bound is responsible, we don't show
 551                             // this note as it is redundant.
 552                             err.note(&format!(
 553                                 "the trait `{missing_trait}` is not implemented for `{lhs_ty}`"
 554                             ));
 555                         }
 556                     }
 557                 }
 558                 err.emit();
 559                 self.tcx.ty_error()
 560             }
 561         };
 562
 563         (lhs_ty, rhs_ty, return_ty)
 564     }
 565
 566     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 567     /// like `&str + &str`, `String + String` and `&str + &String`.
 568     ///
 569     /// If this function returns `true` it means a note was printed, so we don't need
 570     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 571     fn check_str_addition(
 572         &self,
 573         lhs_expr: &'tcx hir::Expr<'tcx>,
 574         rhs_expr: &'tcx hir::Expr<'tcx>,
 575         lhs_ty: Ty<'tcx>,
 576         rhs_ty: Ty<'tcx>,
 577         err: &mut Diagnostic,
 578         is_assign: IsAssign,
 579         op: hir::BinOp,
 580     ) -> bool {
 581         let str_concat_note = "string concatenation requires an owned `String` on the left";
 582         let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
 583         let to_owned_msg = "create an owned `String` from a string reference";
 584
 585         let is_std_string = |ty: Ty<'tcx>| {
 586             ty.ty_adt_def()
 587                 .map_or(false, |ty_def| self.tcx.is_diagnostic_item(sym::String, ty_def.did()))
 588         };
 589
 590         match (lhs_ty.kind(), rhs_ty.kind()) {
 591             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 592                 if (*l_ty.kind() == Str || is_std_string(l_ty))
 593                     && (*r_ty.kind() == Str
 594                         || is_std_string(r_ty)
 595                         || matches!(
 596                             r_ty.kind(), Ref(_, inner_ty, _) if *inner_ty.kind() == Str
 597                         )) =>
 598             {
 599                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 600                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 601                     err.note(str_concat_note);
 602                     if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 603                         err.span_suggestion_verbose(
 604                             lhs_expr.span.until(lhs_inner_expr.span),
 605                             rm_borrow_msg,
 606                             "",
 607                             Applicability::MachineApplicable
 608                         );
 609                     } else {
 610                         err.span_suggestion_verbose(
 611                             lhs_expr.span.shrink_to_hi(),
 612                             to_owned_msg,
 613                             ".to_owned()",
 614                             Applicability::MachineApplicable
 615                         );
 616                     }
 617                 }
 618                 true
 619             }
 620             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 621                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 622             {
 623                 err.span_label(
 624                     op.span,
 625                     "`+` cannot be used to concatenate a `&str` with a `String`",
 626                 );
 627                 match is_assign {
 628                     IsAssign::No => {
 629                         let sugg_msg;
 630                         let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 631                             sugg_msg = "remove the borrow on the left and add one on the right";
 632                             (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 633                         } else {
 634                             sugg_msg = "create an owned `String` on the left and add a borrow on the right";
 635                             (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 636                         };
 637                         let suggestions = vec![
 638                             lhs_sugg,
 639                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 640                         ];
 641                         err.multipart_suggestion_verbose(
 642                             sugg_msg,
 643                             suggestions,
 644                             Applicability::MachineApplicable,
 645                         );
 646                     }
 647                     IsAssign::Yes => {
 648                         err.note(str_concat_note);
 649                     }
 650                 }
 651                 true
 652             }
 653             _ => false,
 654         }
 655     }
 656
 657     pub fn check_user_unop(
 658         &self,
 659         ex: &'tcx hir::Expr<'tcx>,
 660         operand_ty: Ty<'tcx>,
 661         op: hir::UnOp,
 662         expected: Expectation<'tcx>,
 663     ) -> Ty<'tcx> {
 664         assert!(op.is_by_value());
 665         match self.lookup_op_method(operand_ty, None, None, Op::Unary(op, ex.span), expected) {
 666             Ok(method) => {
 667                 self.write_method_call(ex.hir_id, method);
 668                 method.sig.output()
 669             }
 670             Err(errors) => {
 671                 let actual = self.resolve_vars_if_possible(operand_ty);
 672                 if !actual.references_error() {
 673                     let mut err = struct_span_err!(
 674                         self.tcx.sess,
 675                         ex.span,
 676                         E0600,
 677                         "cannot apply unary operator `{}` to type `{}`",
 678                         op.as_str(),
 679                         actual
 680                     );
 681                     err.span_label(
 682                         ex.span,
 683                         format!("cannot apply unary operator `{}`", op.as_str()),
 684                     );
 685
 686                     let mut visitor = TypeParamVisitor(vec![]);
 687                     visitor.visit_ty(operand_ty);
 688                     if let [_] = &visitor.0[..] && let ty::Param(_) = *operand_ty.kind() {
 689                         let predicates = errors
 690                             .iter()
 691                             .filter_map(|error| {
 692                                 error.obligation.predicate.to_opt_poly_trait_pred()
 693                             });
 694                         for pred in predicates {
 695                             self.suggest_restricting_param_bound(
 696                                 &mut err,
 697                                 pred,
 698                                 None,
 699                                 self.body_id,
 700                             );
 701                         }
 702                     }
 703
 704                     let sp = self.tcx.sess.source_map().start_point(ex.span);
 705                     if let Some(sp) =
 706                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 707                     {
 708                         // If the previous expression was a block expression, suggest parentheses
 709                         // (turning this into a binary subtraction operation instead.)
 710                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 711                         self.tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 712                     } else {
 713                         match actual.kind() {
 714                             Uint(_) if op == hir::UnOp::Neg => {
 715                                 err.note("unsigned values cannot be negated");
 716
 717                                 if let hir::ExprKind::Unary(
 718                                     _,
 719                                     hir::Expr {
 720                                         kind:
 721                                             hir::ExprKind::Lit(Spanned {
 722                                                 node: ast::LitKind::Int(1, _),
 723                                                 ..
 724                                             }),
 725                                         ..
 726                                     },
 727                                 ) = ex.kind
 728                                 {
 729                                     err.span_suggestion(
 730                                         ex.span,
 731                                         &format!(
 732                                             "you may have meant the maximum value of `{actual}`",
 733                                         ),
 734                                         format!("{actual}::MAX"),
 735                                         Applicability::MaybeIncorrect,
 736                                     );
 737                                 }
 738                             }
 739                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 740                             Ref(_, lty, _) if *lty.kind() == Str => {}
 741                             _ => {
 742                                 self.note_unmet_impls_on_type(&mut err, errors);
 743                             }
 744                         }
 745                     }
 746                     err.emit();
 747                 }
 748                 self.tcx.ty_error()
 749             }
 750         }
 751     }
 752
 753     fn lookup_op_method(
 754         &self,
 755         lhs_ty: Ty<'tcx>,
 756         other_ty: Option<Ty<'tcx>>,
 757         other_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 758         op: Op,
 759         expected: Expectation<'tcx>,
 760     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 761         let lang = self.tcx.lang_items();
 762
 763         let span = match op {
 764             Op::Binary(op, _) => op.span,
 765             Op::Unary(_, span) => span,
 766         };
 767         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 768             match op.node {
 769                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 770                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 771                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 772                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 773                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 774                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 775                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 776                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 777                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 778                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 779                 hir::BinOpKind::Lt
 780                 | hir::BinOpKind::Le
 781                 | hir::BinOpKind::Ge
 782                 | hir::BinOpKind::Gt
 783                 | hir::BinOpKind::Eq
 784                 | hir::BinOpKind::Ne
 785                 | hir::BinOpKind::And
 786                 | hir::BinOpKind::Or => {
 787                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 788                 }
 789             }
 790         } else if let Op::Binary(op, IsAssign::No) = op {
 791             match op.node {
 792                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 793                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 794                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 795                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 796                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 797                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 798                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 799                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 800                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 801                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 802                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 803                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 804                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 805                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 806                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 807                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 808                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 809                     span_bug!(span, "&& and || are not overloadable")
 810                 }
 811             }
 812         } else if let Op::Unary(hir::UnOp::Not, _) = op {
 813             (sym::not, lang.not_trait())
 814         } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 815             (sym::neg, lang.neg_trait())
 816         } else {
 817             bug!("lookup_op_method: op not supported: {:?}", op)
 818         };
 819
 820         debug!(
 821             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 822             lhs_ty, op, opname, trait_did
 823         );
 824
 825         // Catches cases like #83893, where a lang item is declared with the
 826         // wrong number of generic arguments. Should have yielded an error
 827         // elsewhere by now, but we have to catch it here so that we do not
 828         // index `other_tys` out of bounds (if the lang item has too many
 829         // generic arguments, `other_tys` is too short).
 830         if !has_expected_num_generic_args(
 831             self.tcx,
 832             trait_did,
 833             match op {
 834                 // Binary ops have a generic right-hand side, unary ops don't
 835                 Op::Binary(..) => 1,
 836                 Op::Unary(..) => 0,
 837             },
 838         ) {
 839             return Err(vec![]);
 840         }
 841
 842         let opname = Ident::with_dummy_span(opname);
 843         let method = trait_did.and_then(|trait_did| {
 844             self.lookup_op_method_in_trait(
 845                 span,
 846                 opname,
 847                 trait_did,
 848                 lhs_ty,
 849                 other_ty,
 850                 other_ty_expr,
 851                 expected,
 852             )
 853         });
 854
 855         match (method, trait_did) {
 856             (Some(ok), _) => {
 857                 let method = self.register_infer_ok_obligations(ok);
 858                 self.select_obligations_where_possible(false, |_| {});
 859                 Ok(method)
 860             }
 861             (None, None) => Err(vec![]),
 862             (None, Some(trait_did)) => {
 863                 let (obligation, _) = self.obligation_for_op_method(
 864                     span,
 865                     trait_did,
 866                     lhs_ty,
 867                     other_ty,
 868                     other_ty_expr,
 869                     expected,
 870                 );
 871                 let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 872                 fulfill.register_predicate_obligation(self, obligation);
 873                 Err(fulfill.select_where_possible(&self.infcx))
 874             }
 875         }
 876     }
 877 }
 878
 879 // Binary operator categories. These categories summarize the behavior
 880 // with respect to the builtin operations supported.
 881 enum BinOpCategory {
 882     /// &&, || -- cannot be overridden
 883     Shortcircuit,
 884
 885     /// <<, >> -- when shifting a single integer, rhs can be any
 886     /// integer type. For simd, types must match.
 887     Shift,
 888
 889     /// +, -, etc -- takes equal types, produces same type as input,
 890     /// applicable to ints/floats/simd
 891     Math,
 892
 893     /// &, |, ^ -- takes equal types, produces same type as input,
 894     /// applicable to ints/floats/simd/bool
 895     Bitwise,
 896
 897     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 898     /// which produce the input type
 899     Comparison,
 900 }
 901
 902 impl BinOpCategory {
 903     fn from(op: hir::BinOp) -> BinOpCategory {
 904         match op.node {
 905             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 906
 907             hir::BinOpKind::Add
 908             | hir::BinOpKind::Sub
 909             | hir::BinOpKind::Mul
 910             | hir::BinOpKind::Div
 911             | hir::BinOpKind::Rem => BinOpCategory::Math,
 912
 913             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 914                 BinOpCategory::Bitwise
 915             }
 916
 917             hir::BinOpKind::Eq
 918             | hir::BinOpKind::Ne
 919             | hir::BinOpKind::Lt
 920             | hir::BinOpKind::Le
 921             | hir::BinOpKind::Ge
 922             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 923
 924             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 925         }
 926     }
 927 }
 928
 929 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 930 #[derive(Clone, Copy, Debug, PartialEq)]
 931 enum IsAssign {
 932     No,
 933     Yes,
 934 }
 935
 936 #[derive(Clone, Copy, Debug)]
 937 enum Op {
 938     Binary(hir::BinOp, IsAssign),
 939     Unary(hir::UnOp, Span),
 940 }
 941
 942 /// Dereferences a single level of immutable referencing.
 943 fn deref_ty_if_possible<'tcx>(ty: Ty<'tcx>) -> Ty<'tcx> {
 944     match ty.kind() {
 945         ty::Ref(_, ty, hir::Mutability::Not) => *ty,
 946         _ => ty,
 947     }
 948 }
 949
 950 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 951 /// + u32, i16x4 == i16x4) and false if these types would have to be
 952 /// overloaded to be legal. There are two reasons that we distinguish
 953 /// builtin operations from overloaded ones (vs trying to drive
 954 /// everything uniformly through the trait system and intrinsics or
 955 /// something like that):
 956 ///
 957 /// 1. Builtin operations can trivially be evaluated in constants.
 958 /// 2. For comparison operators applied to SIMD types the result is
 959 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 960 ///    type like `i16x4`. This means that the overloaded trait
 961 ///    `PartialEq` is not applicable.
 962 ///
 963 /// Reason #2 is the killer. I tried for a while to always use
 964 /// overloaded logic and just check the types in constants/codegen after
 965 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 966 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 967     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 968     // (See https://github.com/rust-lang/rust/issues/57447.)
 969     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 970
 971     match BinOpCategory::from(op) {
 972         BinOpCategory::Shortcircuit => true,
 973
 974         BinOpCategory::Shift => {
 975             lhs.references_error()
 976                 || rhs.references_error()
 977                 || lhs.is_integral() && rhs.is_integral()
 978         }
 979
 980         BinOpCategory::Math => {
 981             lhs.references_error()
 982                 || rhs.references_error()
 983                 || lhs.is_integral() && rhs.is_integral()
 984                 || lhs.is_floating_point() && rhs.is_floating_point()
 985         }
 986
 987         BinOpCategory::Bitwise => {
 988             lhs.references_error()
 989                 || rhs.references_error()
 990                 || lhs.is_integral() && rhs.is_integral()
 991                 || lhs.is_floating_point() && rhs.is_floating_point()
 992                 || lhs.is_bool() && rhs.is_bool()
 993         }
 994
 995         BinOpCategory::Comparison => {
 996             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 997         }
 998     }
 999 }
1000
1001 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
1002
1003 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
1004     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1005         if let ty::Param(_) = ty.kind() {
1006             self.0.push(ty);
1007         }
1008         ty.super_visit_with(self)
1009     }
1010 }
1011
1012 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
1013
1014 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
1015     fn tcx(&self) -> TyCtxt<'tcx> {
1016         self.0.tcx
1017     }
1018
1019     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1020         match ty.kind() {
1021             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
1022                 kind: TypeVariableOriginKind::MiscVariable,
1023                 span: self.1,
1024             }),
1025             _ => ty.super_fold_with(self),
1026         }
1027     }
1028 }