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 rustc_ast as ast;
   6 use rustc_errors::{self, struct_span_err, Applicability, DiagnosticBuilder};
   7 use rustc_hir as hir;
   8 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
   9 use rustc_middle::ty::adjustment::{
  10     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  11 };
  12 use rustc_middle::ty::fold::TypeFolder;
  13 use rustc_middle::ty::TyKind::{Adt, Array, Char, FnDef, Never, Ref, Str, Tuple, Uint};
  14 use rustc_middle::ty::{
  15     self, suggest_constraining_type_param, Ty, TyCtxt, TypeFoldable, 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::{FulfillmentError, TraitEngine, TraitEngineExt};
  22
  23 use std::ops::ControlFlow;
  24
  25 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  26     /// Checks a `a <op>= b`
  27     pub fn check_binop_assign(
  28         &self,
  29         expr: &'tcx hir::Expr<'tcx>,
  30         op: hir::BinOp,
  31         lhs: &'tcx hir::Expr<'tcx>,
  32         rhs: &'tcx hir::Expr<'tcx>,
  33     ) -> Ty<'tcx> {
  34         let (lhs_ty, rhs_ty, return_ty) =
  35             self.check_overloaded_binop(expr, lhs, rhs, op, IsAssign::Yes);
  36
  37         let ty =
  38             if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() && is_builtin_binop(lhs_ty, rhs_ty, op) {
  39                 self.enforce_builtin_binop_types(&lhs.span, lhs_ty, &rhs.span, rhs_ty, op);
  40                 self.tcx.mk_unit()
  41             } else {
  42                 return_ty
  43             };
  44
  45         self.check_lhs_assignable(lhs, "E0067", op.span);
  46
  47         ty
  48     }
  49
  50     /// Checks a potentially overloaded binary operator.
  51     pub fn check_binop(
  52         &self,
  53         expr: &'tcx hir::Expr<'tcx>,
  54         op: hir::BinOp,
  55         lhs_expr: &'tcx hir::Expr<'tcx>,
  56         rhs_expr: &'tcx hir::Expr<'tcx>,
  57     ) -> Ty<'tcx> {
  58         let tcx = self.tcx;
  59
  60         debug!(
  61             "check_binop(expr.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  62             expr.hir_id, expr, op, lhs_expr, rhs_expr
  63         );
  64
  65         match BinOpCategory::from(op) {
  66             BinOpCategory::Shortcircuit => {
  67                 // && and || are a simple case.
  68                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool, None);
  69                 let lhs_diverges = self.diverges.get();
  70                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool, None);
  71
  72                 // Depending on the LHS' value, the RHS can never execute.
  73                 self.diverges.set(lhs_diverges);
  74
  75                 tcx.types.bool
  76             }
  77             _ => {
  78                 // Otherwise, we always treat operators as if they are
  79                 // overloaded. This is the way to be most flexible w/r/t
  80                 // types that get inferred.
  81                 let (lhs_ty, rhs_ty, return_ty) =
  82                     self.check_overloaded_binop(expr, lhs_expr, rhs_expr, op, IsAssign::No);
  83
  84                 // Supply type inference hints if relevant. Probably these
  85                 // hints should be enforced during select as part of the
  86                 // `consider_unification_despite_ambiguity` routine, but this
  87                 // more convenient for now.
  88                 //
  89                 // The basic idea is to help type inference by taking
  90                 // advantage of things we know about how the impls for
  91                 // scalar types are arranged. This is important in a
  92                 // scenario like `1_u32 << 2`, because it lets us quickly
  93                 // deduce that the result type should be `u32`, even
  94                 // though we don't know yet what type 2 has and hence
  95                 // can't pin this down to a specific impl.
  96                 if !lhs_ty.is_ty_var()
  97                     && !rhs_ty.is_ty_var()
  98                     && is_builtin_binop(lhs_ty, rhs_ty, op)
  99                 {
 100                     let builtin_return_ty = self.enforce_builtin_binop_types(
 101                         &lhs_expr.span,
 102                         lhs_ty,
 103                         &rhs_expr.span,
 104                         rhs_ty,
 105                         op,
 106                     );
 107                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 108                 }
 109
 110                 return_ty
 111             }
 112         }
 113     }
 114
 115     fn enforce_builtin_binop_types(
 116         &self,
 117         lhs_span: &Span,
 118         lhs_ty: Ty<'tcx>,
 119         rhs_span: &Span,
 120         rhs_ty: Ty<'tcx>,
 121         op: hir::BinOp,
 122     ) -> Ty<'tcx> {
 123         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 124
 125         // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 126         // (See https://github.com/rust-lang/rust/issues/57447.)
 127         let (lhs_ty, rhs_ty) = (deref_ty_if_possible(lhs_ty), deref_ty_if_possible(rhs_ty));
 128
 129         let tcx = self.tcx;
 130         match BinOpCategory::from(op) {
 131             BinOpCategory::Shortcircuit => {
 132                 self.demand_suptype(*lhs_span, tcx.types.bool, lhs_ty);
 133                 self.demand_suptype(*rhs_span, tcx.types.bool, rhs_ty);
 134                 tcx.types.bool
 135             }
 136
 137             BinOpCategory::Shift => {
 138                 // result type is same as LHS always
 139                 lhs_ty
 140             }
 141
 142             BinOpCategory::Math | BinOpCategory::Bitwise => {
 143                 // both LHS and RHS and result will have the same type
 144                 self.demand_suptype(*rhs_span, lhs_ty, rhs_ty);
 145                 lhs_ty
 146             }
 147
 148             BinOpCategory::Comparison => {
 149                 // both LHS and RHS and result will have the same type
 150                 self.demand_suptype(*rhs_span, lhs_ty, rhs_ty);
 151                 tcx.types.bool
 152             }
 153         }
 154     }
 155
 156     fn check_overloaded_binop(
 157         &self,
 158         expr: &'tcx hir::Expr<'tcx>,
 159         lhs_expr: &'tcx hir::Expr<'tcx>,
 160         rhs_expr: &'tcx hir::Expr<'tcx>,
 161         op: hir::BinOp,
 162         is_assign: IsAssign,
 163     ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
 164         debug!(
 165             "check_overloaded_binop(expr.hir_id={}, op={:?}, is_assign={:?})",
 166             expr.hir_id, op, is_assign
 167         );
 168
 169         let lhs_ty = match is_assign {
 170             IsAssign::No => {
 171                 // Find a suitable supertype of the LHS expression's type, by coercing to
 172                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 173                 // trait matching creating lifetime constraints that are too strict.
 174                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 175                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 176                 let lhs_ty = self.check_expr(lhs_expr);
 177                 let fresh_var = self.next_ty_var(TypeVariableOrigin {
 178                     kind: TypeVariableOriginKind::MiscVariable,
 179                     span: lhs_expr.span,
 180                 });
 181                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var, Some(rhs_expr), AllowTwoPhase::No)
 182             }
 183             IsAssign::Yes => {
 184                 // rust-lang/rust#52126: We have to use strict
 185                 // equivalence on the LHS of an assign-op like `+=`;
 186                 // overwritten or mutably-borrowed places cannot be
 187                 // coerced to a supertype.
 188                 self.check_expr(lhs_expr)
 189             }
 190         };
 191         let lhs_ty = self.resolve_vars_with_obligations(lhs_ty);
 192
 193         // N.B., as we have not yet type-checked the RHS, we don't have the
 194         // type at hand. Make a variable to represent it. The whole reason
 195         // for this indirection is so that, below, we can check the expr
 196         // using this variable as the expected type, which sometimes lets
 197         // us do better coercions than we would be able to do otherwise,
 198         // particularly for things like `String + &String`.
 199         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 200             kind: TypeVariableOriginKind::MiscVariable,
 201             span: rhs_expr.span,
 202         });
 203
 204         let result = self.lookup_op_method(lhs_ty, &[rhs_ty_var], Op::Binary(op, is_assign));
 205
 206         // see `NB` above
 207         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var, Some(lhs_expr));
 208         let rhs_ty = self.resolve_vars_with_obligations(rhs_ty);
 209
 210         let return_ty = match result {
 211             Ok(method) => {
 212                 let by_ref_binop = !op.node.is_by_value();
 213                 if is_assign == IsAssign::Yes || by_ref_binop {
 214                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() {
 215                         let mutbl = match mutbl {
 216                             hir::Mutability::Not => AutoBorrowMutability::Not,
 217                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 218                                 // Allow two-phase borrows for binops in initial deployment
 219                                 // since they desugar to methods
 220                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 221                             },
 222                         };
 223                         let autoref = Adjustment {
 224                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 225                             target: method.sig.inputs()[0],
 226                         };
 227                         self.apply_adjustments(lhs_expr, vec![autoref]);
 228                     }
 229                 }
 230                 if by_ref_binop {
 231                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 232                         let mutbl = match mutbl {
 233                             hir::Mutability::Not => AutoBorrowMutability::Not,
 234                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 235                                 // Allow two-phase borrows for binops in initial deployment
 236                                 // since they desugar to methods
 237                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 238                             },
 239                         };
 240                         let autoref = Adjustment {
 241                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 242                             target: method.sig.inputs()[1],
 243                         };
 244                         // HACK(eddyb) Bypass checks due to reborrows being in
 245                         // some cases applied on the RHS, on top of which we need
 246                         // to autoref, which is not allowed by apply_adjustments.
 247                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 248                         self.typeck_results
 249                             .borrow_mut()
 250                             .adjustments_mut()
 251                             .entry(rhs_expr.hir_id)
 252                             .or_default()
 253                             .push(autoref);
 254                     }
 255                 }
 256                 self.write_method_call(expr.hir_id, method);
 257
 258                 method.sig.output()
 259             }
 260             // error types are considered "builtin"
 261             Err(_) if lhs_ty.references_error() || rhs_ty.references_error() => self.tcx.ty_error(),
 262             Err(errors) => {
 263                 let source_map = self.tcx.sess.source_map();
 264                 let (mut err, missing_trait, use_output) = match is_assign {
 265                     IsAssign::Yes => {
 266                         let mut err = struct_span_err!(
 267                             self.tcx.sess,
 268                             expr.span,
 269                             E0368,
 270                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 271                             op.node.as_str(),
 272                             lhs_ty,
 273                         );
 274                         err.span_label(
 275                             lhs_expr.span,
 276                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 277                         );
 278                         let missing_trait = match op.node {
 279                             hir::BinOpKind::Add => Some("std::ops::AddAssign"),
 280                             hir::BinOpKind::Sub => Some("std::ops::SubAssign"),
 281                             hir::BinOpKind::Mul => Some("std::ops::MulAssign"),
 282                             hir::BinOpKind::Div => Some("std::ops::DivAssign"),
 283                             hir::BinOpKind::Rem => Some("std::ops::RemAssign"),
 284                             hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 285                             hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 286                             hir::BinOpKind::BitOr => Some("std::ops::BitOrAssign"),
 287                             hir::BinOpKind::Shl => Some("std::ops::ShlAssign"),
 288                             hir::BinOpKind::Shr => Some("std::ops::ShrAssign"),
 289                             _ => None,
 290                         };
 291                         self.note_unmet_impls_on_type(&mut err, errors);
 292                         (err, missing_trait, false)
 293                     }
 294                     IsAssign::No => {
 295                         let (message, missing_trait, use_output) = match op.node {
 296                             hir::BinOpKind::Add => (
 297                                 format!("cannot add `{}` to `{}`", rhs_ty, lhs_ty),
 298                                 Some("std::ops::Add"),
 299                                 true,
 300                             ),
 301                             hir::BinOpKind::Sub => (
 302                                 format!("cannot subtract `{}` from `{}`", rhs_ty, lhs_ty),
 303                                 Some("std::ops::Sub"),
 304                                 true,
 305                             ),
 306                             hir::BinOpKind::Mul => (
 307                                 format!("cannot multiply `{}` by `{}`", lhs_ty, rhs_ty),
 308                                 Some("std::ops::Mul"),
 309                                 true,
 310                             ),
 311                             hir::BinOpKind::Div => (
 312                                 format!("cannot divide `{}` by `{}`", lhs_ty, rhs_ty),
 313                                 Some("std::ops::Div"),
 314                                 true,
 315                             ),
 316                             hir::BinOpKind::Rem => (
 317                                 format!("cannot mod `{}` by `{}`", lhs_ty, rhs_ty),
 318                                 Some("std::ops::Rem"),
 319                                 true,
 320                             ),
 321                             hir::BinOpKind::BitAnd => (
 322                                 format!("no implementation for `{} & {}`", lhs_ty, rhs_ty),
 323                                 Some("std::ops::BitAnd"),
 324                                 true,
 325                             ),
 326                             hir::BinOpKind::BitXor => (
 327                                 format!("no implementation for `{} ^ {}`", lhs_ty, rhs_ty),
 328                                 Some("std::ops::BitXor"),
 329                                 true,
 330                             ),
 331                             hir::BinOpKind::BitOr => (
 332                                 format!("no implementation for `{} | {}`", lhs_ty, rhs_ty),
 333                                 Some("std::ops::BitOr"),
 334                                 true,
 335                             ),
 336                             hir::BinOpKind::Shl => (
 337                                 format!("no implementation for `{} << {}`", lhs_ty, rhs_ty),
 338                                 Some("std::ops::Shl"),
 339                                 true,
 340                             ),
 341                             hir::BinOpKind::Shr => (
 342                                 format!("no implementation for `{} >> {}`", lhs_ty, rhs_ty),
 343                                 Some("std::ops::Shr"),
 344                                 true,
 345                             ),
 346                             hir::BinOpKind::Eq | hir::BinOpKind::Ne => (
 347                                 format!(
 348                                     "binary operation `{}` cannot be applied to type `{}`",
 349                                     op.node.as_str(),
 350                                     lhs_ty
 351                                 ),
 352                                 Some("std::cmp::PartialEq"),
 353                                 false,
 354                             ),
 355                             hir::BinOpKind::Lt
 356                             | hir::BinOpKind::Le
 357                             | hir::BinOpKind::Gt
 358                             | hir::BinOpKind::Ge => (
 359                                 format!(
 360                                     "binary operation `{}` cannot be applied to type `{}`",
 361                                     op.node.as_str(),
 362                                     lhs_ty
 363                                 ),
 364                                 Some("std::cmp::PartialOrd"),
 365                                 false,
 366                             ),
 367                             _ => (
 368                                 format!(
 369                                     "binary operation `{}` cannot be applied to type `{}`",
 370                                     op.node.as_str(),
 371                                     lhs_ty
 372                                 ),
 373                                 None,
 374                                 false,
 375                             ),
 376                         };
 377                         let mut err =
 378                             struct_span_err!(self.tcx.sess, op.span, E0369, "{}", message.as_str());
 379                         if !lhs_expr.span.eq(&rhs_expr.span) {
 380                             self.add_type_neq_err_label(
 381                                 &mut err,
 382                                 lhs_expr.span,
 383                                 lhs_ty,
 384                                 rhs_ty,
 385                                 op,
 386                                 is_assign,
 387                             );
 388                             self.add_type_neq_err_label(
 389                                 &mut err,
 390                                 rhs_expr.span,
 391                                 rhs_ty,
 392                                 lhs_ty,
 393                                 op,
 394                                 is_assign,
 395                             );
 396                         }
 397                         self.note_unmet_impls_on_type(&mut err, errors);
 398                         (err, missing_trait, use_output)
 399                     }
 400                 };
 401                 if let Ref(_, rty, _) = lhs_ty.kind() {
 402                     if self.infcx.type_is_copy_modulo_regions(self.param_env, rty, lhs_expr.span)
 403                         && self.lookup_op_method(rty, &[rhs_ty], Op::Binary(op, is_assign)).is_ok()
 404                     {
 405                         if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 406                             let msg = &format!(
 407                                 "`{}{}` can be used on `{}`, you can dereference `{}`",
 408                                 op.node.as_str(),
 409                                 match is_assign {
 410                                     IsAssign::Yes => "=",
 411                                     IsAssign::No => "",
 412                                 },
 413                                 rty.peel_refs(),
 414                                 lstring,
 415                             );
 416                             err.span_suggestion_verbose(
 417                                 lhs_expr.span.shrink_to_lo(),
 418                                 msg,
 419                                 "*".to_string(),
 420                                 rustc_errors::Applicability::MachineApplicable,
 421                             );
 422                         }
 423                     }
 424                 }
 425                 if let Some(missing_trait) = missing_trait {
 426                     let mut visitor = TypeParamVisitor(self.tcx, vec![]);
 427                     visitor.visit_ty(lhs_ty);
 428
 429                     if op.node == hir::BinOpKind::Add
 430                         && self.check_str_addition(
 431                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 432                         )
 433                     {
 434                         // This has nothing here because it means we did string
 435                         // concatenation (e.g., "Hello " + "World!"). This means
 436                         // we don't want the note in the else clause to be emitted
 437                     } else if let [ty] = &visitor.1[..] {
 438                         if let ty::Param(p) = *ty.kind() {
 439                             // Check if the method would be found if the type param wasn't
 440                             // involved. If so, it means that adding a trait bound to the param is
 441                             // enough. Otherwise we do not give the suggestion.
 442                             let mut eraser = TypeParamEraser(self, expr.span);
 443                             let needs_bound = self
 444                                 .lookup_op_method(
 445                                     eraser.fold_ty(lhs_ty),
 446                                     &[eraser.fold_ty(rhs_ty)],
 447                                     Op::Binary(op, is_assign),
 448                                 )
 449                                 .is_ok();
 450                             if needs_bound {
 451                                 suggest_constraining_param(
 452                                     self.tcx,
 453                                     self.body_id,
 454                                     &mut err,
 455                                     ty,
 456                                     rhs_ty,
 457                                     missing_trait,
 458                                     p,
 459                                     use_output,
 460                                 );
 461                             } else if *ty != lhs_ty {
 462                                 // When we know that a missing bound is responsible, we don't show
 463                                 // this note as it is redundant.
 464                                 err.note(&format!(
 465                                     "the trait `{}` is not implemented for `{}`",
 466                                     missing_trait, lhs_ty
 467                                 ));
 468                             }
 469                         } else {
 470                             bug!("type param visitor stored a non type param: {:?}", ty.kind());
 471                         }
 472                     }
 473                 }
 474                 err.emit();
 475                 self.tcx.ty_error()
 476             }
 477         };
 478
 479         (lhs_ty, rhs_ty, return_ty)
 480     }
 481
 482     /// If one of the types is an uncalled function and calling it would yield the other type,
 483     /// suggest calling the function. Returns `true` if suggestion would apply (even if not given).
 484     fn add_type_neq_err_label(
 485         &self,
 486         err: &mut rustc_errors::DiagnosticBuilder<'_>,
 487         span: Span,
 488         ty: Ty<'tcx>,
 489         other_ty: Ty<'tcx>,
 490         op: hir::BinOp,
 491         is_assign: IsAssign,
 492     ) -> bool /* did we suggest to call a function because of missing parentheses? */ {
 493         err.span_label(span, ty.to_string());
 494         if let FnDef(def_id, _) = *ty.kind() {
 495             if !self.tcx.has_typeck_results(def_id) {
 496                 return false;
 497             }
 498             // FIXME: Instead of exiting early when encountering bound vars in
 499             // the function signature, consider keeping the binder here and
 500             // propagating it downwards.
 501             let Some(fn_sig) = self.tcx.fn_sig(def_id).no_bound_vars() else {
 502                 return false;
 503             };
 504
 505             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
 506                 if !self.tcx.has_typeck_results(def_id) {
 507                     return false;
 508                 }
 509                 // We're emitting a suggestion, so we can just ignore regions
 510                 self.tcx.fn_sig(def_id).skip_binder().output()
 511             } else {
 512                 other_ty
 513             };
 514
 515             if self
 516                 .lookup_op_method(fn_sig.output(), &[other_ty], Op::Binary(op, is_assign))
 517                 .is_ok()
 518             {
 519                 let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
 520                     ("( /* arguments */ )".to_string(), Applicability::HasPlaceholders)
 521                 } else {
 522                     ("()".to_string(), Applicability::MaybeIncorrect)
 523                 };
 524
 525                 err.span_suggestion_verbose(
 526                     span.shrink_to_hi(),
 527                     "you might have forgotten to call this function",
 528                     variable_snippet,
 529                     applicability,
 530                 );
 531                 return true;
 532             }
 533         }
 534         false
 535     }
 536
 537     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 538     /// like `&str + &str`, `String + String` and `&str + &String`.
 539     ///
 540     /// If this function returns `true` it means a note was printed, so we don't need
 541     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 542     fn check_str_addition(
 543         &self,
 544         lhs_expr: &'tcx hir::Expr<'tcx>,
 545         rhs_expr: &'tcx hir::Expr<'tcx>,
 546         lhs_ty: Ty<'tcx>,
 547         rhs_ty: Ty<'tcx>,
 548         err: &mut rustc_errors::DiagnosticBuilder<'_>,
 549         is_assign: IsAssign,
 550         op: hir::BinOp,
 551     ) -> bool {
 552         let remove_borrow_msg = "String concatenation appends the string on the right to the \
 553                                  string on the left and may require reallocation. This \
 554                                  requires ownership of the string on the left";
 555
 556         let msg = "`to_owned()` can be used to create an owned `String` \
 557                    from a string reference. String concatenation \
 558                    appends the string on the right to the string \
 559                    on the left and may require reallocation. This \
 560                    requires ownership of the string on the left";
 561
 562         let string_type = self.tcx.get_diagnostic_item(sym::String);
 563         let is_std_string = |ty: Ty<'tcx>| match ty.ty_adt_def() {
 564             Some(ty_def) => Some(ty_def.did) == string_type,
 565             None => false,
 566         };
 567
 568         match (lhs_ty.kind(), rhs_ty.kind()) {
 569             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 570                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && (
 571                         *r_ty.kind() == Str || is_std_string(r_ty) ||
 572                         &format!("{:?}", rhs_ty) == "&&str"
 573                     ) =>
 574             {
 575                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 576                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 577                     if let hir::ExprKind::AddrOf(_,_,lhs_inner_expr) = lhs_expr.kind {
 578                         err.span_suggestion(
 579                             lhs_expr.span.until(lhs_inner_expr.span),
 580                             remove_borrow_msg,
 581                             "".to_owned(),
 582                             Applicability::MachineApplicable
 583                         );
 584                     } else {
 585                         err.span_suggestion(
 586                             lhs_expr.span.shrink_to_hi(),
 587                             msg,
 588                             ".to_owned()".to_owned(),
 589                             Applicability::MachineApplicable
 590                         );
 591                     }
 592                 }
 593                 true
 594             }
 595             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 596                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 597             {
 598                 err.span_label(
 599                     op.span,
 600                     "`+` cannot be used to concatenate a `&str` with a `String`",
 601                 );
 602                 match is_assign {
 603                     IsAssign::No => {
 604                         let suggestions = vec![
 605                             if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 606                                 (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 607                             } else {
 608                                 (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 609                             },
 610                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 611                         ];
 612                         err.multipart_suggestion(msg, suggestions, Applicability::MachineApplicable);
 613                     }
 614                     IsAssign::Yes => {
 615                         err.help(msg);
 616                     }
 617                 }
 618                 true
 619             }
 620             _ => false,
 621         }
 622     }
 623
 624     pub fn check_user_unop(
 625         &self,
 626         ex: &'tcx hir::Expr<'tcx>,
 627         operand_ty: Ty<'tcx>,
 628         op: hir::UnOp,
 629     ) -> Ty<'tcx> {
 630         assert!(op.is_by_value());
 631         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 632             Ok(method) => {
 633                 self.write_method_call(ex.hir_id, method);
 634                 method.sig.output()
 635             }
 636             Err(errors) => {
 637                 let actual = self.resolve_vars_if_possible(operand_ty);
 638                 if !actual.references_error() {
 639                     let mut err = struct_span_err!(
 640                         self.tcx.sess,
 641                         ex.span,
 642                         E0600,
 643                         "cannot apply unary operator `{}` to type `{}`",
 644                         op.as_str(),
 645                         actual
 646                     );
 647                     err.span_label(
 648                         ex.span,
 649                         format!("cannot apply unary operator `{}`", op.as_str()),
 650                     );
 651
 652                     let sp = self.tcx.sess.source_map().start_point(ex.span);
 653                     if let Some(sp) =
 654                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 655                     {
 656                         // If the previous expression was a block expression, suggest parentheses
 657                         // (turning this into a binary subtraction operation instead.)
 658                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 659                         self.tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 660                     } else {
 661                         match actual.kind() {
 662                             Uint(_) if op == hir::UnOp::Neg => {
 663                                 err.note("unsigned values cannot be negated");
 664
 665                                 if let hir::ExprKind::Unary(
 666                                     _,
 667                                     hir::Expr {
 668                                         kind:
 669                                             hir::ExprKind::Lit(Spanned {
 670                                                 node: ast::LitKind::Int(1, _),
 671                                                 ..
 672                                             }),
 673                                         ..
 674                                     },
 675                                 ) = ex.kind
 676                                 {
 677                                     err.span_suggestion(
 678                                         ex.span,
 679                                         &format!(
 680                                             "you may have meant the maximum value of `{}`",
 681                                             actual
 682                                         ),
 683                                         format!("{}::MAX", actual),
 684                                         Applicability::MaybeIncorrect,
 685                                     );
 686                                 }
 687                             }
 688                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 689                             Ref(_, lty, _) if *lty.kind() == Str => {}
 690                             _ => {
 691                                 self.note_unmet_impls_on_type(&mut err, errors);
 692                             }
 693                         }
 694                     }
 695                     err.emit();
 696                 }
 697                 self.tcx.ty_error()
 698             }
 699         }
 700     }
 701
 702     fn lookup_op_method(
 703         &self,
 704         lhs_ty: Ty<'tcx>,
 705         other_tys: &[Ty<'tcx>],
 706         op: Op,
 707     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 708         let lang = self.tcx.lang_items();
 709
 710         let span = match op {
 711             Op::Binary(op, _) => op.span,
 712             Op::Unary(_, span) => span,
 713         };
 714         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 715             match op.node {
 716                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 717                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 718                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 719                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 720                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 721                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 722                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 723                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 724                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 725                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 726                 hir::BinOpKind::Lt
 727                 | hir::BinOpKind::Le
 728                 | hir::BinOpKind::Ge
 729                 | hir::BinOpKind::Gt
 730                 | hir::BinOpKind::Eq
 731                 | hir::BinOpKind::Ne
 732                 | hir::BinOpKind::And
 733                 | hir::BinOpKind::Or => {
 734                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 735                 }
 736             }
 737         } else if let Op::Binary(op, IsAssign::No) = op {
 738             match op.node {
 739                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 740                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 741                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 742                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 743                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 744                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 745                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 746                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 747                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 748                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 749                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 750                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 751                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 752                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 753                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 754                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 755                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 756                     span_bug!(span, "&& and || are not overloadable")
 757                 }
 758             }
 759         } else if let Op::Unary(hir::UnOp::Not, _) = op {
 760             (sym::not, lang.not_trait())
 761         } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 762             (sym::neg, lang.neg_trait())
 763         } else {
 764             bug!("lookup_op_method: op not supported: {:?}", op)
 765         };
 766
 767         debug!(
 768             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 769             lhs_ty, op, opname, trait_did
 770         );
 771
 772         // Catches cases like #83893, where a lang item is declared with the
 773         // wrong number of generic arguments. Should have yielded an error
 774         // elsewhere by now, but we have to catch it here so that we do not
 775         // index `other_tys` out of bounds (if the lang item has too many
 776         // generic arguments, `other_tys` is too short).
 777         if !has_expected_num_generic_args(
 778             self.tcx,
 779             trait_did,
 780             match op {
 781                 // Binary ops have a generic right-hand side, unary ops don't
 782                 Op::Binary(..) => 1,
 783                 Op::Unary(..) => 0,
 784             },
 785         ) {
 786             return Err(vec![]);
 787         }
 788
 789         let opname = Ident::with_dummy_span(opname);
 790         let method = trait_did.and_then(|trait_did| {
 791             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 792         });
 793
 794         match (method, trait_did) {
 795             (Some(ok), _) => {
 796                 let method = self.register_infer_ok_obligations(ok);
 797                 self.select_obligations_where_possible(false, |_| {});
 798                 Ok(method)
 799             }
 800             (None, None) => Err(vec![]),
 801             (None, Some(trait_did)) => {
 802                 let (obligation, _) =
 803                     self.obligation_for_method(span, trait_did, lhs_ty, Some(other_tys));
 804                 let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 805                 fulfill.register_predicate_obligation(self, obligation);
 806                 Err(fulfill.select_where_possible(&self.infcx))
 807             }
 808         }
 809     }
 810 }
 811
 812 // Binary operator categories. These categories summarize the behavior
 813 // with respect to the builtin operationrs supported.
 814 enum BinOpCategory {
 815     /// &&, || -- cannot be overridden
 816     Shortcircuit,
 817
 818     /// <<, >> -- when shifting a single integer, rhs can be any
 819     /// integer type. For simd, types must match.
 820     Shift,
 821
 822     /// +, -, etc -- takes equal types, produces same type as input,
 823     /// applicable to ints/floats/simd
 824     Math,
 825
 826     /// &, |, ^ -- takes equal types, produces same type as input,
 827     /// applicable to ints/floats/simd/bool
 828     Bitwise,
 829
 830     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 831     /// which produce the input type
 832     Comparison,
 833 }
 834
 835 impl BinOpCategory {
 836     fn from(op: hir::BinOp) -> BinOpCategory {
 837         match op.node {
 838             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 839
 840             hir::BinOpKind::Add
 841             | hir::BinOpKind::Sub
 842             | hir::BinOpKind::Mul
 843             | hir::BinOpKind::Div
 844             | hir::BinOpKind::Rem => BinOpCategory::Math,
 845
 846             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 847                 BinOpCategory::Bitwise
 848             }
 849
 850             hir::BinOpKind::Eq
 851             | hir::BinOpKind::Ne
 852             | hir::BinOpKind::Lt
 853             | hir::BinOpKind::Le
 854             | hir::BinOpKind::Ge
 855             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 856
 857             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 858         }
 859     }
 860 }
 861
 862 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 863 #[derive(Clone, Copy, Debug, PartialEq)]
 864 enum IsAssign {
 865     No,
 866     Yes,
 867 }
 868
 869 #[derive(Clone, Copy, Debug)]
 870 enum Op {
 871     Binary(hir::BinOp, IsAssign),
 872     Unary(hir::UnOp, Span),
 873 }
 874
 875 /// Dereferences a single level of immutable referencing.
 876 fn deref_ty_if_possible<'tcx>(ty: Ty<'tcx>) -> Ty<'tcx> {
 877     match ty.kind() {
 878         ty::Ref(_, ty, hir::Mutability::Not) => ty,
 879         _ => ty,
 880     }
 881 }
 882
 883 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 884 /// + u32, i16x4 == i16x4) and false if these types would have to be
 885 /// overloaded to be legal. There are two reasons that we distinguish
 886 /// builtin operations from overloaded ones (vs trying to drive
 887 /// everything uniformly through the trait system and intrinsics or
 888 /// something like that):
 889 ///
 890 /// 1. Builtin operations can trivially be evaluated in constants.
 891 /// 2. For comparison operators applied to SIMD types the result is
 892 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 893 ///    type like `i16x4`. This means that the overloaded trait
 894 ///    `PartialEq` is not applicable.
 895 ///
 896 /// Reason #2 is the killer. I tried for a while to always use
 897 /// overloaded logic and just check the types in constants/codegen after
 898 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 899 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 900     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 901     // (See https://github.com/rust-lang/rust/issues/57447.)
 902     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 903
 904     match BinOpCategory::from(op) {
 905         BinOpCategory::Shortcircuit => true,
 906
 907         BinOpCategory::Shift => {
 908             lhs.references_error()
 909                 || rhs.references_error()
 910                 || lhs.is_integral() && rhs.is_integral()
 911         }
 912
 913         BinOpCategory::Math => {
 914             lhs.references_error()
 915                 || rhs.references_error()
 916                 || lhs.is_integral() && rhs.is_integral()
 917                 || lhs.is_floating_point() && rhs.is_floating_point()
 918         }
 919
 920         BinOpCategory::Bitwise => {
 921             lhs.references_error()
 922                 || rhs.references_error()
 923                 || lhs.is_integral() && rhs.is_integral()
 924                 || lhs.is_floating_point() && rhs.is_floating_point()
 925                 || lhs.is_bool() && rhs.is_bool()
 926         }
 927
 928         BinOpCategory::Comparison => {
 929             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 930         }
 931     }
 932 }
 933
 934 fn suggest_constraining_param(
 935     tcx: TyCtxt<'_>,
 936     body_id: hir::HirId,
 937     mut err: &mut DiagnosticBuilder<'_>,
 938     lhs_ty: Ty<'_>,
 939     rhs_ty: Ty<'_>,
 940     missing_trait: &str,
 941     p: ty::ParamTy,
 942     set_output: bool,
 943 ) {
 944     let hir = tcx.hir();
 945     let msg = &format!("`{}` might need a bound for `{}`", lhs_ty, missing_trait);
 946     // Try to find the def-id and details for the parameter p. We have only the index,
 947     // so we have to find the enclosing function's def-id, then look through its declared
 948     // generic parameters to get the declaration.
 949     let def_id = hir.body_owner_def_id(hir::BodyId { hir_id: body_id });
 950     let generics = tcx.generics_of(def_id);
 951     let param_def_id = generics.type_param(&p, tcx).def_id;
 952     if let Some(generics) = param_def_id
 953         .as_local()
 954         .map(|id| hir.local_def_id_to_hir_id(id))
 955         .and_then(|id| hir.find(hir.get_parent_item(id)))
 956         .as_ref()
 957         .and_then(|node| node.generics())
 958     {
 959         let output = if set_output { format!("<Output = {}>", rhs_ty) } else { String::new() };
 960         suggest_constraining_type_param(
 961             tcx,
 962             generics,
 963             &mut err,
 964             &format!("{}", lhs_ty),
 965             &format!("{}{}", missing_trait, output),
 966             None,
 967         );
 968     } else {
 969         let span = tcx.def_span(param_def_id);
 970         err.span_label(span, msg);
 971     }
 972 }
 973
 974 struct TypeParamVisitor<'tcx>(TyCtxt<'tcx>, Vec<Ty<'tcx>>);
 975
 976 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
 977     fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
 978         Some(self.0)
 979     }
 980     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 981         if let ty::Param(_) = ty.kind() {
 982             self.1.push(ty);
 983         }
 984         ty.super_visit_with(self)
 985     }
 986 }
 987
 988 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
 989
 990 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
 991     fn tcx(&self) -> TyCtxt<'tcx> {
 992         self.0.tcx
 993     }
 994
 995     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 996         match ty.kind() {
 997             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
 998                 kind: TypeVariableOriginKind::MiscVariable,
 999                 span: self.1,
1000             }),
1001             _ => ty.super_fold_with(self),
1002         }
1003     }
1004 }