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.delay_as_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                             self.add_type_neq_err_label(
 414                                 &mut err,
 415                                 lhs_expr.span,
 416                                 lhs_ty,
 417                                 rhs_ty,
 418                                 rhs_expr,
 419                                 op,
 420                                 is_assign,
 421                                 expected,
 422                             );
 423                             self.add_type_neq_err_label(
 424                                 &mut err,
 425                                 rhs_expr.span,
 426                                 rhs_ty,
 427                                 lhs_ty,
 428                                 lhs_expr,
 429                                 op,
 430                                 is_assign,
 431                                 expected,
 432                             );
 433                         }
 434                         self.note_unmet_impls_on_type(&mut err, errors);
 435                         (err, missing_trait, use_output)
 436                     }
 437                 };
 438
 439                 let mut suggest_deref_binop = |lhs_deref_ty: Ty<'tcx>| {
 440                     if self
 441                         .lookup_op_method(
 442                             lhs_deref_ty,
 443                             Some(rhs_ty),
 444                             Some(rhs_expr),
 445                             Op::Binary(op, is_assign),
 446                             expected,
 447                         )
 448                         .is_ok()
 449                     {
 450                         if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 451                             let msg = &format!(
 452                                 "`{}{}` can be used on `{}`, you can dereference `{}`",
 453                                 op.node.as_str(),
 454                                 match is_assign {
 455                                     IsAssign::Yes => "=",
 456                                     IsAssign::No => "",
 457                                 },
 458                                 lhs_deref_ty.peel_refs(),
 459                                 lstring,
 460                             );
 461                             err.span_suggestion_verbose(
 462                                 lhs_expr.span.shrink_to_lo(),
 463                                 msg,
 464                                 "*",
 465                                 rustc_errors::Applicability::MachineApplicable,
 466                             );
 467                         }
 468                     }
 469                 };
 470
 471                 // We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
 472                 // `a += b` => `*a += b` if a is a mut ref.
 473                 if is_assign == IsAssign::Yes
 474                     && let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
 475                         suggest_deref_binop(lhs_deref_ty);
 476                 } else if is_assign == IsAssign::No
 477                     && let Ref(_, lhs_deref_ty, _) = lhs_ty.kind() {
 478                     if self.type_is_copy_modulo_regions(self.param_env, *lhs_deref_ty, lhs_expr.span) {
 479                         suggest_deref_binop(*lhs_deref_ty);
 480                     }
 481                 }
 482                 if let Some(missing_trait) = missing_trait {
 483                     let mut visitor = TypeParamVisitor(vec![]);
 484                     visitor.visit_ty(lhs_ty);
 485
 486                     if op.node == hir::BinOpKind::Add
 487                         && self.check_str_addition(
 488                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 489                         )
 490                     {
 491                         // This has nothing here because it means we did string
 492                         // concatenation (e.g., "Hello " + "World!"). This means
 493                         // we don't want the note in the else clause to be emitted
 494                     } else if let [ty] = &visitor.0[..] {
 495                         // Look for a TraitPredicate in the Fulfillment errors,
 496                         // and use it to generate a suggestion.
 497                         //
 498                         // Note that lookup_op_method must be called again but
 499                         // with a specific rhs_ty instead of a placeholder so
 500                         // the resulting predicate generates a more specific
 501                         // suggestion for the user.
 502                         let errors = self
 503                             .lookup_op_method(
 504                                 lhs_ty,
 505                                 Some(rhs_ty),
 506                                 Some(rhs_expr),
 507                                 Op::Binary(op, is_assign),
 508                                 expected,
 509                             )
 510                             .unwrap_err();
 511                         if !errors.is_empty() {
 512                             for error in errors {
 513                                 if let Some(trait_pred) =
 514                                     error.obligation.predicate.to_opt_poly_trait_pred()
 515                                 {
 516                                     let proj_pred = match error.obligation.cause.code() {
 517                                         ObligationCauseCode::BinOp {
 518                                             output_pred: Some(output_pred),
 519                                             ..
 520                                         } if use_output => {
 521                                             output_pred.to_opt_poly_projection_pred()
 522                                         }
 523                                         _ => None,
 524                                     };
 525
 526                                     self.suggest_restricting_param_bound(
 527                                         &mut err,
 528                                         trait_pred,
 529                                         proj_pred,
 530                                         self.body_id,
 531                                     );
 532                                 }
 533                             }
 534                         } else if *ty != lhs_ty {
 535                             // When we know that a missing bound is responsible, we don't show
 536                             // this note as it is redundant.
 537                             err.note(&format!(
 538                                 "the trait `{missing_trait}` is not implemented for `{lhs_ty}`"
 539                             ));
 540                         }
 541                     }
 542                 }
 543                 err.emit();
 544                 self.tcx.ty_error()
 545             }
 546         };
 547
 548         (lhs_ty, rhs_ty, return_ty)
 549     }
 550
 551     /// If one of the types is an uncalled function and calling it would yield the other type,
 552     /// suggest calling the function. Returns `true` if suggestion would apply (even if not given).
 553     fn add_type_neq_err_label(
 554         &self,
 555         err: &mut Diagnostic,
 556         span: Span,
 557         ty: Ty<'tcx>,
 558         other_ty: Ty<'tcx>,
 559         other_expr: &'tcx hir::Expr<'tcx>,
 560         op: hir::BinOp,
 561         is_assign: IsAssign,
 562         expected: Expectation<'tcx>,
 563     ) -> bool /* did we suggest to call a function because of missing parentheses? */ {
 564         err.span_label(span, ty.to_string());
 565         if let FnDef(def_id, _) = *ty.kind() {
 566             if !self.tcx.has_typeck_results(def_id) {
 567                 return false;
 568             }
 569             // FIXME: Instead of exiting early when encountering bound vars in
 570             // the function signature, consider keeping the binder here and
 571             // propagating it downwards.
 572             let Some(fn_sig) = self.tcx.fn_sig(def_id).no_bound_vars() else {
 573                 return false;
 574             };
 575
 576             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
 577                 if !self.tcx.has_typeck_results(def_id) {
 578                     return false;
 579                 }
 580                 // We're emitting a suggestion, so we can just ignore regions
 581                 self.tcx.fn_sig(def_id).skip_binder().output()
 582             } else {
 583                 other_ty
 584             };
 585
 586             if self
 587                 .lookup_op_method(
 588                     fn_sig.output(),
 589                     Some(other_ty),
 590                     Some(other_expr),
 591                     Op::Binary(op, is_assign),
 592                     expected,
 593                 )
 594                 .is_ok()
 595             {
 596                 let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
 597                     ("( /* arguments */ )", Applicability::HasPlaceholders)
 598                 } else {
 599                     ("()", Applicability::MaybeIncorrect)
 600                 };
 601
 602                 err.span_suggestion_verbose(
 603                     span.shrink_to_hi(),
 604                     "you might have forgotten to call this function",
 605                     variable_snippet,
 606                     applicability,
 607                 );
 608                 return true;
 609             }
 610         }
 611         false
 612     }
 613
 614     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 615     /// like `&str + &str`, `String + String` and `&str + &String`.
 616     ///
 617     /// If this function returns `true` it means a note was printed, so we don't need
 618     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 619     fn check_str_addition(
 620         &self,
 621         lhs_expr: &'tcx hir::Expr<'tcx>,
 622         rhs_expr: &'tcx hir::Expr<'tcx>,
 623         lhs_ty: Ty<'tcx>,
 624         rhs_ty: Ty<'tcx>,
 625         err: &mut Diagnostic,
 626         is_assign: IsAssign,
 627         op: hir::BinOp,
 628     ) -> bool {
 629         let str_concat_note = "string concatenation requires an owned `String` on the left";
 630         let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
 631         let to_owned_msg = "create an owned `String` from a string reference";
 632
 633         let is_std_string = |ty: Ty<'tcx>| {
 634             ty.ty_adt_def()
 635                 .map_or(false, |ty_def| self.tcx.is_diagnostic_item(sym::String, ty_def.did()))
 636         };
 637
 638         match (lhs_ty.kind(), rhs_ty.kind()) {
 639             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 640                 if (*l_ty.kind() == Str || is_std_string(l_ty))
 641                     && (*r_ty.kind() == Str
 642                         || is_std_string(r_ty)
 643                         || matches!(
 644                             r_ty.kind(), Ref(_, inner_ty, _) if *inner_ty.kind() == Str
 645                         )) =>
 646             {
 647                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 648                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 649                     err.note(str_concat_note);
 650                     if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 651                         err.span_suggestion_verbose(
 652                             lhs_expr.span.until(lhs_inner_expr.span),
 653                             rm_borrow_msg,
 654                             "",
 655                             Applicability::MachineApplicable
 656                         );
 657                     } else {
 658                         err.span_suggestion_verbose(
 659                             lhs_expr.span.shrink_to_hi(),
 660                             to_owned_msg,
 661                             ".to_owned()",
 662                             Applicability::MachineApplicable
 663                         );
 664                     }
 665                 }
 666                 true
 667             }
 668             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 669                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 670             {
 671                 err.span_label(
 672                     op.span,
 673                     "`+` cannot be used to concatenate a `&str` with a `String`",
 674                 );
 675                 match is_assign {
 676                     IsAssign::No => {
 677                         let sugg_msg;
 678                         let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 679                             sugg_msg = "remove the borrow on the left and add one on the right";
 680                             (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 681                         } else {
 682                             sugg_msg = "create an owned `String` on the left and add a borrow on the right";
 683                             (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 684                         };
 685                         let suggestions = vec![
 686                             lhs_sugg,
 687                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 688                         ];
 689                         err.multipart_suggestion_verbose(
 690                             sugg_msg,
 691                             suggestions,
 692                             Applicability::MachineApplicable,
 693                         );
 694                     }
 695                     IsAssign::Yes => {
 696                         err.note(str_concat_note);
 697                     }
 698                 }
 699                 true
 700             }
 701             _ => false,
 702         }
 703     }
 704
 705     pub fn check_user_unop(
 706         &self,
 707         ex: &'tcx hir::Expr<'tcx>,
 708         operand_ty: Ty<'tcx>,
 709         op: hir::UnOp,
 710         expected: Expectation<'tcx>,
 711     ) -> Ty<'tcx> {
 712         assert!(op.is_by_value());
 713         match self.lookup_op_method(operand_ty, None, None, Op::Unary(op, ex.span), expected) {
 714             Ok(method) => {
 715                 self.write_method_call(ex.hir_id, method);
 716                 method.sig.output()
 717             }
 718             Err(errors) => {
 719                 let actual = self.resolve_vars_if_possible(operand_ty);
 720                 if !actual.references_error() {
 721                     let mut err = struct_span_err!(
 722                         self.tcx.sess,
 723                         ex.span,
 724                         E0600,
 725                         "cannot apply unary operator `{}` to type `{}`",
 726                         op.as_str(),
 727                         actual
 728                     );
 729                     err.span_label(
 730                         ex.span,
 731                         format!("cannot apply unary operator `{}`", op.as_str()),
 732                     );
 733
 734                     let mut visitor = TypeParamVisitor(vec![]);
 735                     visitor.visit_ty(operand_ty);
 736                     if let [_] = &visitor.0[..] && let ty::Param(_) = *operand_ty.kind() {
 737                         let predicates = errors
 738                             .iter()
 739                             .filter_map(|error| {
 740                                 error.obligation.predicate.to_opt_poly_trait_pred()
 741                             });
 742                         for pred in predicates {
 743                             self.suggest_restricting_param_bound(
 744                                 &mut err,
 745                                 pred,
 746                                 None,
 747                                 self.body_id,
 748                             );
 749                         }
 750                     }
 751
 752                     let sp = self.tcx.sess.source_map().start_point(ex.span);
 753                     if let Some(sp) =
 754                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 755                     {
 756                         // If the previous expression was a block expression, suggest parentheses
 757                         // (turning this into a binary subtraction operation instead.)
 758                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 759                         self.tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 760                     } else {
 761                         match actual.kind() {
 762                             Uint(_) if op == hir::UnOp::Neg => {
 763                                 err.note("unsigned values cannot be negated");
 764
 765                                 if let hir::ExprKind::Unary(
 766                                     _,
 767                                     hir::Expr {
 768                                         kind:
 769                                             hir::ExprKind::Lit(Spanned {
 770                                                 node: ast::LitKind::Int(1, _),
 771                                                 ..
 772                                             }),
 773                                         ..
 774                                     },
 775                                 ) = ex.kind
 776                                 {
 777                                     err.span_suggestion(
 778                                         ex.span,
 779                                         &format!(
 780                                             "you may have meant the maximum value of `{actual}`",
 781                                         ),
 782                                         format!("{actual}::MAX"),
 783                                         Applicability::MaybeIncorrect,
 784                                     );
 785                                 }
 786                             }
 787                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 788                             Ref(_, lty, _) if *lty.kind() == Str => {}
 789                             _ => {
 790                                 self.note_unmet_impls_on_type(&mut err, errors);
 791                             }
 792                         }
 793                     }
 794                     err.emit();
 795                 }
 796                 self.tcx.ty_error()
 797             }
 798         }
 799     }
 800
 801     fn lookup_op_method(
 802         &self,
 803         lhs_ty: Ty<'tcx>,
 804         other_ty: Option<Ty<'tcx>>,
 805         other_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 806         op: Op,
 807         expected: Expectation<'tcx>,
 808     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 809         let lang = self.tcx.lang_items();
 810
 811         let span = match op {
 812             Op::Binary(op, _) => op.span,
 813             Op::Unary(_, span) => span,
 814         };
 815         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 816             match op.node {
 817                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 818                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 819                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 820                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 821                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 822                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 823                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 824                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 825                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 826                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 827                 hir::BinOpKind::Lt
 828                 | hir::BinOpKind::Le
 829                 | hir::BinOpKind::Ge
 830                 | hir::BinOpKind::Gt
 831                 | hir::BinOpKind::Eq
 832                 | hir::BinOpKind::Ne
 833                 | hir::BinOpKind::And
 834                 | hir::BinOpKind::Or => {
 835                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 836                 }
 837             }
 838         } else if let Op::Binary(op, IsAssign::No) = op {
 839             match op.node {
 840                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 841                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 842                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 843                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 844                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 845                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 846                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 847                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 848                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 849                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 850                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 851                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 852                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 853                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 854                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 855                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 856                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 857                     span_bug!(span, "&& and || are not overloadable")
 858                 }
 859             }
 860         } else if let Op::Unary(hir::UnOp::Not, _) = op {
 861             (sym::not, lang.not_trait())
 862         } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 863             (sym::neg, lang.neg_trait())
 864         } else {
 865             bug!("lookup_op_method: op not supported: {:?}", op)
 866         };
 867
 868         debug!(
 869             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 870             lhs_ty, op, opname, trait_did
 871         );
 872
 873         // Catches cases like #83893, where a lang item is declared with the
 874         // wrong number of generic arguments. Should have yielded an error
 875         // elsewhere by now, but we have to catch it here so that we do not
 876         // index `other_tys` out of bounds (if the lang item has too many
 877         // generic arguments, `other_tys` is too short).
 878         if !has_expected_num_generic_args(
 879             self.tcx,
 880             trait_did,
 881             match op {
 882                 // Binary ops have a generic right-hand side, unary ops don't
 883                 Op::Binary(..) => 1,
 884                 Op::Unary(..) => 0,
 885             },
 886         ) {
 887             return Err(vec![]);
 888         }
 889
 890         let opname = Ident::with_dummy_span(opname);
 891         let method = trait_did.and_then(|trait_did| {
 892             self.lookup_op_method_in_trait(
 893                 span,
 894                 opname,
 895                 trait_did,
 896                 lhs_ty,
 897                 other_ty,
 898                 other_ty_expr,
 899                 expected,
 900             )
 901         });
 902
 903         match (method, trait_did) {
 904             (Some(ok), _) => {
 905                 let method = self.register_infer_ok_obligations(ok);
 906                 self.select_obligations_where_possible(false, |_| {});
 907                 Ok(method)
 908             }
 909             (None, None) => Err(vec![]),
 910             (None, Some(trait_did)) => {
 911                 let (obligation, _) = self.obligation_for_op_method(
 912                     span,
 913                     trait_did,
 914                     lhs_ty,
 915                     other_ty,
 916                     other_ty_expr,
 917                     expected,
 918                 );
 919                 let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 920                 fulfill.register_predicate_obligation(self, obligation);
 921                 Err(fulfill.select_where_possible(&self.infcx))
 922             }
 923         }
 924     }
 925 }
 926
 927 // Binary operator categories. These categories summarize the behavior
 928 // with respect to the builtin operations supported.
 929 enum BinOpCategory {
 930     /// &&, || -- cannot be overridden
 931     Shortcircuit,
 932
 933     /// <<, >> -- when shifting a single integer, rhs can be any
 934     /// integer type. For simd, types must match.
 935     Shift,
 936
 937     /// +, -, etc -- takes equal types, produces same type as input,
 938     /// applicable to ints/floats/simd
 939     Math,
 940
 941     /// &, |, ^ -- takes equal types, produces same type as input,
 942     /// applicable to ints/floats/simd/bool
 943     Bitwise,
 944
 945     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 946     /// which produce the input type
 947     Comparison,
 948 }
 949
 950 impl BinOpCategory {
 951     fn from(op: hir::BinOp) -> BinOpCategory {
 952         match op.node {
 953             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 954
 955             hir::BinOpKind::Add
 956             | hir::BinOpKind::Sub
 957             | hir::BinOpKind::Mul
 958             | hir::BinOpKind::Div
 959             | hir::BinOpKind::Rem => BinOpCategory::Math,
 960
 961             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 962                 BinOpCategory::Bitwise
 963             }
 964
 965             hir::BinOpKind::Eq
 966             | hir::BinOpKind::Ne
 967             | hir::BinOpKind::Lt
 968             | hir::BinOpKind::Le
 969             | hir::BinOpKind::Ge
 970             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 971
 972             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 973         }
 974     }
 975 }
 976
 977 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 978 #[derive(Clone, Copy, Debug, PartialEq)]
 979 enum IsAssign {
 980     No,
 981     Yes,
 982 }
 983
 984 #[derive(Clone, Copy, Debug)]
 985 enum Op {
 986     Binary(hir::BinOp, IsAssign),
 987     Unary(hir::UnOp, Span),
 988 }
 989
 990 /// Dereferences a single level of immutable referencing.
 991 fn deref_ty_if_possible<'tcx>(ty: Ty<'tcx>) -> Ty<'tcx> {
 992     match ty.kind() {
 993         ty::Ref(_, ty, hir::Mutability::Not) => *ty,
 994         _ => ty,
 995     }
 996 }
 997
 998 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 999 /// + u32, i16x4 == i16x4) and false if these types would have to be
1000 /// overloaded to be legal. There are two reasons that we distinguish
1001 /// builtin operations from overloaded ones (vs trying to drive
1002 /// everything uniformly through the trait system and intrinsics or
1003 /// something like that):
1004 ///
1005 /// 1. Builtin operations can trivially be evaluated in constants.
1006 /// 2. For comparison operators applied to SIMD types the result is
1007 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
1008 ///    type like `i16x4`. This means that the overloaded trait
1009 ///    `PartialEq` is not applicable.
1010 ///
1011 /// Reason #2 is the killer. I tried for a while to always use
1012 /// overloaded logic and just check the types in constants/codegen after
1013 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
1014 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
1015     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
1016     // (See https://github.com/rust-lang/rust/issues/57447.)
1017     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
1018
1019     match BinOpCategory::from(op) {
1020         BinOpCategory::Shortcircuit => true,
1021
1022         BinOpCategory::Shift => {
1023             lhs.references_error()
1024                 || rhs.references_error()
1025                 || lhs.is_integral() && rhs.is_integral()
1026         }
1027
1028         BinOpCategory::Math => {
1029             lhs.references_error()
1030                 || rhs.references_error()
1031                 || lhs.is_integral() && rhs.is_integral()
1032                 || lhs.is_floating_point() && rhs.is_floating_point()
1033         }
1034
1035         BinOpCategory::Bitwise => {
1036             lhs.references_error()
1037                 || rhs.references_error()
1038                 || lhs.is_integral() && rhs.is_integral()
1039                 || lhs.is_floating_point() && rhs.is_floating_point()
1040                 || lhs.is_bool() && rhs.is_bool()
1041         }
1042
1043         BinOpCategory::Comparison => {
1044             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
1045         }
1046     }
1047 }
1048
1049 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
1050
1051 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
1052     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1053         if let ty::Param(_) = ty.kind() {
1054             self.0.push(ty);
1055         }
1056         ty.super_visit_with(self)
1057     }
1058 }
1059
1060 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
1061
1062 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
1063     fn tcx(&self) -> TyCtxt<'tcx> {
1064         self.0.tcx
1065     }
1066
1067     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1068         match ty.kind() {
1069             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
1070                 kind: TypeVariableOriginKind::MiscVariable,
1071                 span: self.1,
1072             }),
1073             _ => ty.super_fold_with(self),
1074         }
1075     }
1076 }