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, Diagnostic};
   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(
 205             lhs_ty,
 206             Some(rhs_ty_var),
 207             Some(rhs_expr),
 208             Op::Binary(op, is_assign),
 209         );
 210
 211         // see `NB` above
 212         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var, Some(lhs_expr));
 213         let rhs_ty = self.resolve_vars_with_obligations(rhs_ty);
 214
 215         let return_ty = match result {
 216             Ok(method) => {
 217                 let by_ref_binop = !op.node.is_by_value();
 218                 if is_assign == IsAssign::Yes || by_ref_binop {
 219                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() {
 220                         let mutbl = match mutbl {
 221                             hir::Mutability::Not => AutoBorrowMutability::Not,
 222                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 223                                 // Allow two-phase borrows for binops in initial deployment
 224                                 // since they desugar to methods
 225                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 226                             },
 227                         };
 228                         let autoref = Adjustment {
 229                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 230                             target: method.sig.inputs()[0],
 231                         };
 232                         self.apply_adjustments(lhs_expr, vec![autoref]);
 233                     }
 234                 }
 235                 if by_ref_binop {
 236                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 237                         let mutbl = match mutbl {
 238                             hir::Mutability::Not => AutoBorrowMutability::Not,
 239                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 240                                 // Allow two-phase borrows for binops in initial deployment
 241                                 // since they desugar to methods
 242                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 243                             },
 244                         };
 245                         let autoref = Adjustment {
 246                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 247                             target: method.sig.inputs()[1],
 248                         };
 249                         // HACK(eddyb) Bypass checks due to reborrows being in
 250                         // some cases applied on the RHS, on top of which we need
 251                         // to autoref, which is not allowed by apply_adjustments.
 252                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 253                         self.typeck_results
 254                             .borrow_mut()
 255                             .adjustments_mut()
 256                             .entry(rhs_expr.hir_id)
 257                             .or_default()
 258                             .push(autoref);
 259                     }
 260                 }
 261                 self.write_method_call(expr.hir_id, method);
 262
 263                 method.sig.output()
 264             }
 265             // error types are considered "builtin"
 266             Err(_) if lhs_ty.references_error() || rhs_ty.references_error() => self.tcx.ty_error(),
 267             Err(errors) => {
 268                 let source_map = self.tcx.sess.source_map();
 269                 let (mut err, missing_trait, use_output) = match is_assign {
 270                     IsAssign::Yes => {
 271                         let mut err = struct_span_err!(
 272                             self.tcx.sess,
 273                             expr.span,
 274                             E0368,
 275                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 276                             op.node.as_str(),
 277                             lhs_ty,
 278                         );
 279                         err.span_label(
 280                             lhs_expr.span,
 281                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 282                         );
 283                         let missing_trait = match op.node {
 284                             hir::BinOpKind::Add => Some("std::ops::AddAssign"),
 285                             hir::BinOpKind::Sub => Some("std::ops::SubAssign"),
 286                             hir::BinOpKind::Mul => Some("std::ops::MulAssign"),
 287                             hir::BinOpKind::Div => Some("std::ops::DivAssign"),
 288                             hir::BinOpKind::Rem => Some("std::ops::RemAssign"),
 289                             hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 290                             hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 291                             hir::BinOpKind::BitOr => Some("std::ops::BitOrAssign"),
 292                             hir::BinOpKind::Shl => Some("std::ops::ShlAssign"),
 293                             hir::BinOpKind::Shr => Some("std::ops::ShrAssign"),
 294                             _ => None,
 295                         };
 296                         self.note_unmet_impls_on_type(&mut err, errors);
 297                         (err, missing_trait, false)
 298                     }
 299                     IsAssign::No => {
 300                         let (message, missing_trait, use_output) = match op.node {
 301                             hir::BinOpKind::Add => (
 302                                 format!("cannot add `{}` to `{}`", rhs_ty, lhs_ty),
 303                                 Some("std::ops::Add"),
 304                                 true,
 305                             ),
 306                             hir::BinOpKind::Sub => (
 307                                 format!("cannot subtract `{}` from `{}`", rhs_ty, lhs_ty),
 308                                 Some("std::ops::Sub"),
 309                                 true,
 310                             ),
 311                             hir::BinOpKind::Mul => (
 312                                 format!("cannot multiply `{}` by `{}`", lhs_ty, rhs_ty),
 313                                 Some("std::ops::Mul"),
 314                                 true,
 315                             ),
 316                             hir::BinOpKind::Div => (
 317                                 format!("cannot divide `{}` by `{}`", lhs_ty, rhs_ty),
 318                                 Some("std::ops::Div"),
 319                                 true,
 320                             ),
 321                             hir::BinOpKind::Rem => (
 322                                 format!("cannot mod `{}` by `{}`", lhs_ty, rhs_ty),
 323                                 Some("std::ops::Rem"),
 324                                 true,
 325                             ),
 326                             hir::BinOpKind::BitAnd => (
 327                                 format!("no implementation for `{} & {}`", lhs_ty, rhs_ty),
 328                                 Some("std::ops::BitAnd"),
 329                                 true,
 330                             ),
 331                             hir::BinOpKind::BitXor => (
 332                                 format!("no implementation for `{} ^ {}`", lhs_ty, rhs_ty),
 333                                 Some("std::ops::BitXor"),
 334                                 true,
 335                             ),
 336                             hir::BinOpKind::BitOr => (
 337                                 format!("no implementation for `{} | {}`", lhs_ty, rhs_ty),
 338                                 Some("std::ops::BitOr"),
 339                                 true,
 340                             ),
 341                             hir::BinOpKind::Shl => (
 342                                 format!("no implementation for `{} << {}`", lhs_ty, rhs_ty),
 343                                 Some("std::ops::Shl"),
 344                                 true,
 345                             ),
 346                             hir::BinOpKind::Shr => (
 347                                 format!("no implementation for `{} >> {}`", lhs_ty, rhs_ty),
 348                                 Some("std::ops::Shr"),
 349                                 true,
 350                             ),
 351                             hir::BinOpKind::Eq | hir::BinOpKind::Ne => (
 352                                 format!(
 353                                     "binary operation `{}` cannot be applied to type `{}`",
 354                                     op.node.as_str(),
 355                                     lhs_ty
 356                                 ),
 357                                 Some("std::cmp::PartialEq"),
 358                                 false,
 359                             ),
 360                             hir::BinOpKind::Lt
 361                             | hir::BinOpKind::Le
 362                             | hir::BinOpKind::Gt
 363                             | hir::BinOpKind::Ge => (
 364                                 format!(
 365                                     "binary operation `{}` cannot be applied to type `{}`",
 366                                     op.node.as_str(),
 367                                     lhs_ty
 368                                 ),
 369                                 Some("std::cmp::PartialOrd"),
 370                                 false,
 371                             ),
 372                             _ => (
 373                                 format!(
 374                                     "binary operation `{}` cannot be applied to type `{}`",
 375                                     op.node.as_str(),
 376                                     lhs_ty
 377                                 ),
 378                                 None,
 379                                 false,
 380                             ),
 381                         };
 382                         let mut err =
 383                             struct_span_err!(self.tcx.sess, op.span, E0369, "{}", message.as_str());
 384                         if !lhs_expr.span.eq(&rhs_expr.span) {
 385                             self.add_type_neq_err_label(
 386                                 &mut err,
 387                                 lhs_expr.span,
 388                                 lhs_ty,
 389                                 rhs_ty,
 390                                 rhs_expr,
 391                                 op,
 392                                 is_assign,
 393                             );
 394                             self.add_type_neq_err_label(
 395                                 &mut err,
 396                                 rhs_expr.span,
 397                                 rhs_ty,
 398                                 lhs_ty,
 399                                 lhs_expr,
 400                                 op,
 401                                 is_assign,
 402                             );
 403                         }
 404                         self.note_unmet_impls_on_type(&mut err, errors);
 405                         (err, missing_trait, use_output)
 406                     }
 407                 };
 408                 if let Ref(_, rty, _) = lhs_ty.kind() {
 409                     if self.infcx.type_is_copy_modulo_regions(self.param_env, *rty, lhs_expr.span)
 410                         && self
 411                             .lookup_op_method(
 412                                 *rty,
 413                                 Some(rhs_ty),
 414                                 Some(rhs_expr),
 415                                 Op::Binary(op, is_assign),
 416                             )
 417                             .is_ok()
 418                     {
 419                         if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 420                             let msg = &format!(
 421                                 "`{}{}` can be used on `{}`, you can dereference `{}`",
 422                                 op.node.as_str(),
 423                                 match is_assign {
 424                                     IsAssign::Yes => "=",
 425                                     IsAssign::No => "",
 426                                 },
 427                                 rty.peel_refs(),
 428                                 lstring,
 429                             );
 430                             err.span_suggestion_verbose(
 431                                 lhs_expr.span.shrink_to_lo(),
 432                                 msg,
 433                                 "*".to_string(),
 434                                 rustc_errors::Applicability::MachineApplicable,
 435                             );
 436                         }
 437                     }
 438                 }
 439                 if let Some(missing_trait) = missing_trait {
 440                     let mut visitor = TypeParamVisitor(vec![]);
 441                     visitor.visit_ty(lhs_ty);
 442
 443                     if op.node == hir::BinOpKind::Add
 444                         && self.check_str_addition(
 445                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 446                         )
 447                     {
 448                         // This has nothing here because it means we did string
 449                         // concatenation (e.g., "Hello " + "World!"). This means
 450                         // we don't want the note in the else clause to be emitted
 451                     } else if let [ty] = &visitor.0[..] {
 452                         if let ty::Param(p) = *ty.kind() {
 453                             // Check if the method would be found if the type param wasn't
 454                             // involved. If so, it means that adding a trait bound to the param is
 455                             // enough. Otherwise we do not give the suggestion.
 456                             let mut eraser = TypeParamEraser(self, expr.span);
 457                             let needs_bound = self
 458                                 .lookup_op_method(
 459                                     eraser.fold_ty(lhs_ty),
 460                                     Some(eraser.fold_ty(rhs_ty)),
 461                                     Some(rhs_expr),
 462                                     Op::Binary(op, is_assign),
 463                                 )
 464                                 .is_ok();
 465                             if needs_bound {
 466                                 suggest_constraining_param(
 467                                     self.tcx,
 468                                     self.body_id,
 469                                     &mut err,
 470                                     *ty,
 471                                     rhs_ty,
 472                                     missing_trait,
 473                                     p,
 474                                     use_output,
 475                                 );
 476                             } else if *ty != lhs_ty {
 477                                 // When we know that a missing bound is responsible, we don't show
 478                                 // this note as it is redundant.
 479                                 err.note(&format!(
 480                                     "the trait `{}` is not implemented for `{}`",
 481                                     missing_trait, lhs_ty
 482                                 ));
 483                             }
 484                         } else {
 485                             bug!("type param visitor stored a non type param: {:?}", ty.kind());
 486                         }
 487                     }
 488                 }
 489                 err.emit();
 490                 self.tcx.ty_error()
 491             }
 492         };
 493
 494         (lhs_ty, rhs_ty, return_ty)
 495     }
 496
 497     /// If one of the types is an uncalled function and calling it would yield the other type,
 498     /// suggest calling the function. Returns `true` if suggestion would apply (even if not given).
 499     fn add_type_neq_err_label(
 500         &self,
 501         err: &mut Diagnostic,
 502         span: Span,
 503         ty: Ty<'tcx>,
 504         other_ty: Ty<'tcx>,
 505         other_expr: &'tcx hir::Expr<'tcx>,
 506         op: hir::BinOp,
 507         is_assign: IsAssign,
 508     ) -> bool /* did we suggest to call a function because of missing parentheses? */ {
 509         err.span_label(span, ty.to_string());
 510         if let FnDef(def_id, _) = *ty.kind() {
 511             if !self.tcx.has_typeck_results(def_id) {
 512                 return false;
 513             }
 514             // FIXME: Instead of exiting early when encountering bound vars in
 515             // the function signature, consider keeping the binder here and
 516             // propagating it downwards.
 517             let Some(fn_sig) = self.tcx.fn_sig(def_id).no_bound_vars() else {
 518                 return false;
 519             };
 520
 521             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
 522                 if !self.tcx.has_typeck_results(def_id) {
 523                     return false;
 524                 }
 525                 // We're emitting a suggestion, so we can just ignore regions
 526                 self.tcx.fn_sig(def_id).skip_binder().output()
 527             } else {
 528                 other_ty
 529             };
 530
 531             if self
 532                 .lookup_op_method(
 533                     fn_sig.output(),
 534                     Some(other_ty),
 535                     Some(other_expr),
 536                     Op::Binary(op, is_assign),
 537                 )
 538                 .is_ok()
 539             {
 540                 let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
 541                     ("( /* arguments */ )".to_string(), Applicability::HasPlaceholders)
 542                 } else {
 543                     ("()".to_string(), Applicability::MaybeIncorrect)
 544                 };
 545
 546                 err.span_suggestion_verbose(
 547                     span.shrink_to_hi(),
 548                     "you might have forgotten to call this function",
 549                     variable_snippet,
 550                     applicability,
 551                 );
 552                 return true;
 553             }
 554         }
 555         false
 556     }
 557
 558     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 559     /// like `&str + &str`, `String + String` and `&str + &String`.
 560     ///
 561     /// If this function returns `true` it means a note was printed, so we don't need
 562     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 563     fn check_str_addition(
 564         &self,
 565         lhs_expr: &'tcx hir::Expr<'tcx>,
 566         rhs_expr: &'tcx hir::Expr<'tcx>,
 567         lhs_ty: Ty<'tcx>,
 568         rhs_ty: Ty<'tcx>,
 569         err: &mut Diagnostic,
 570         is_assign: IsAssign,
 571         op: hir::BinOp,
 572     ) -> bool {
 573         let str_concat_note = "string concatenation requires an owned `String` on the left";
 574         let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
 575         let to_owned_msg = "create an owned `String` from a string reference";
 576
 577         let string_type = self.tcx.get_diagnostic_item(sym::String);
 578         let is_std_string = |ty: Ty<'tcx>| match ty.ty_adt_def() {
 579             Some(ty_def) => Some(ty_def.did) == string_type,
 580             None => false,
 581         };
 582
 583         match (lhs_ty.kind(), rhs_ty.kind()) {
 584             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 585                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && (
 586                         *r_ty.kind() == Str || is_std_string(r_ty) ||
 587                         &format!("{:?}", rhs_ty) == "&&str"
 588                     ) =>
 589             {
 590                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 591                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 592                     err.note(str_concat_note);
 593                     if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 594                         err.span_suggestion_verbose(
 595                             lhs_expr.span.until(lhs_inner_expr.span),
 596                             rm_borrow_msg,
 597                             "".to_owned(),
 598                             Applicability::MachineApplicable
 599                         );
 600                     } else {
 601                         err.span_suggestion_verbose(
 602                             lhs_expr.span.shrink_to_hi(),
 603                             to_owned_msg,
 604                             ".to_owned()".to_owned(),
 605                             Applicability::MachineApplicable
 606                         );
 607                     }
 608                 }
 609                 true
 610             }
 611             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 612                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 613             {
 614                 err.span_label(
 615                     op.span,
 616                     "`+` cannot be used to concatenate a `&str` with a `String`",
 617                 );
 618                 match is_assign {
 619                     IsAssign::No => {
 620                         let sugg_msg;
 621                         let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 622                             sugg_msg = "remove the borrow on the left and add one on the right";
 623                             (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 624                         } else {
 625                             sugg_msg = "create an owned `String` on the left and add a borrow on the right";
 626                             (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 627                         };
 628                         let suggestions = vec![
 629                             lhs_sugg,
 630                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 631                         ];
 632                         err.multipart_suggestion_verbose(
 633                             sugg_msg,
 634                             suggestions,
 635                             Applicability::MachineApplicable,
 636                         );
 637                     }
 638                     IsAssign::Yes => {
 639                         err.note(str_concat_note);
 640                     }
 641                 }
 642                 true
 643             }
 644             _ => false,
 645         }
 646     }
 647
 648     pub fn check_user_unop(
 649         &self,
 650         ex: &'tcx hir::Expr<'tcx>,
 651         operand_ty: Ty<'tcx>,
 652         op: hir::UnOp,
 653     ) -> Ty<'tcx> {
 654         assert!(op.is_by_value());
 655         match self.lookup_op_method(operand_ty, None, None, Op::Unary(op, ex.span)) {
 656             Ok(method) => {
 657                 self.write_method_call(ex.hir_id, method);
 658                 method.sig.output()
 659             }
 660             Err(errors) => {
 661                 let actual = self.resolve_vars_if_possible(operand_ty);
 662                 if !actual.references_error() {
 663                     let mut err = struct_span_err!(
 664                         self.tcx.sess,
 665                         ex.span,
 666                         E0600,
 667                         "cannot apply unary operator `{}` to type `{}`",
 668                         op.as_str(),
 669                         actual
 670                     );
 671                     err.span_label(
 672                         ex.span,
 673                         format!("cannot apply unary operator `{}`", op.as_str()),
 674                     );
 675
 676                     let sp = self.tcx.sess.source_map().start_point(ex.span);
 677                     if let Some(sp) =
 678                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 679                     {
 680                         // If the previous expression was a block expression, suggest parentheses
 681                         // (turning this into a binary subtraction operation instead.)
 682                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 683                         self.tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 684                     } else {
 685                         match actual.kind() {
 686                             Uint(_) if op == hir::UnOp::Neg => {
 687                                 err.note("unsigned values cannot be negated");
 688
 689                                 if let hir::ExprKind::Unary(
 690                                     _,
 691                                     hir::Expr {
 692                                         kind:
 693                                             hir::ExprKind::Lit(Spanned {
 694                                                 node: ast::LitKind::Int(1, _),
 695                                                 ..
 696                                             }),
 697                                         ..
 698                                     },
 699                                 ) = ex.kind
 700                                 {
 701                                     err.span_suggestion(
 702                                         ex.span,
 703                                         &format!(
 704                                             "you may have meant the maximum value of `{}`",
 705                                             actual
 706                                         ),
 707                                         format!("{}::MAX", actual),
 708                                         Applicability::MaybeIncorrect,
 709                                     );
 710                                 }
 711                             }
 712                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 713                             Ref(_, lty, _) if *lty.kind() == Str => {}
 714                             _ => {
 715                                 self.note_unmet_impls_on_type(&mut err, errors);
 716                             }
 717                         }
 718                     }
 719                     err.emit();
 720                 }
 721                 self.tcx.ty_error()
 722             }
 723         }
 724     }
 725
 726     fn lookup_op_method(
 727         &self,
 728         lhs_ty: Ty<'tcx>,
 729         other_ty: Option<Ty<'tcx>>,
 730         other_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 731         op: Op,
 732     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 733         let lang = self.tcx.lang_items();
 734
 735         let span = match op {
 736             Op::Binary(op, _) => op.span,
 737             Op::Unary(_, span) => span,
 738         };
 739         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 740             match op.node {
 741                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 742                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 743                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 744                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 745                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 746                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 747                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 748                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 749                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 750                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 751                 hir::BinOpKind::Lt
 752                 | hir::BinOpKind::Le
 753                 | hir::BinOpKind::Ge
 754                 | hir::BinOpKind::Gt
 755                 | hir::BinOpKind::Eq
 756                 | hir::BinOpKind::Ne
 757                 | hir::BinOpKind::And
 758                 | hir::BinOpKind::Or => {
 759                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 760                 }
 761             }
 762         } else if let Op::Binary(op, IsAssign::No) = op {
 763             match op.node {
 764                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 765                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 766                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 767                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 768                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 769                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 770                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 771                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 772                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 773                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 774                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 775                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 776                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 777                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 778                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 779                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 780                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 781                     span_bug!(span, "&& and || are not overloadable")
 782                 }
 783             }
 784         } else if let Op::Unary(hir::UnOp::Not, _) = op {
 785             (sym::not, lang.not_trait())
 786         } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 787             (sym::neg, lang.neg_trait())
 788         } else {
 789             bug!("lookup_op_method: op not supported: {:?}", op)
 790         };
 791
 792         debug!(
 793             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 794             lhs_ty, op, opname, trait_did
 795         );
 796
 797         // Catches cases like #83893, where a lang item is declared with the
 798         // wrong number of generic arguments. Should have yielded an error
 799         // elsewhere by now, but we have to catch it here so that we do not
 800         // index `other_tys` out of bounds (if the lang item has too many
 801         // generic arguments, `other_tys` is too short).
 802         if !has_expected_num_generic_args(
 803             self.tcx,
 804             trait_did,
 805             match op {
 806                 // Binary ops have a generic right-hand side, unary ops don't
 807                 Op::Binary(..) => 1,
 808                 Op::Unary(..) => 0,
 809             },
 810         ) {
 811             return Err(vec![]);
 812         }
 813
 814         let opname = Ident::with_dummy_span(opname);
 815         let method = trait_did.and_then(|trait_did| {
 816             self.lookup_op_method_in_trait(span, opname, trait_did, lhs_ty, other_ty, other_ty_expr)
 817         });
 818
 819         match (method, trait_did) {
 820             (Some(ok), _) => {
 821                 let method = self.register_infer_ok_obligations(ok);
 822                 self.select_obligations_where_possible(false, |_| {});
 823                 Ok(method)
 824             }
 825             (None, None) => Err(vec![]),
 826             (None, Some(trait_did)) => {
 827                 let (obligation, _) =
 828                     self.obligation_for_op_method(span, trait_did, lhs_ty, other_ty, other_ty_expr);
 829                 let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 830                 fulfill.register_predicate_obligation(self, obligation);
 831                 Err(fulfill.select_where_possible(&self.infcx))
 832             }
 833         }
 834     }
 835 }
 836
 837 // Binary operator categories. These categories summarize the behavior
 838 // with respect to the builtin operationrs supported.
 839 enum BinOpCategory {
 840     /// &&, || -- cannot be overridden
 841     Shortcircuit,
 842
 843     /// <<, >> -- when shifting a single integer, rhs can be any
 844     /// integer type. For simd, types must match.
 845     Shift,
 846
 847     /// +, -, etc -- takes equal types, produces same type as input,
 848     /// applicable to ints/floats/simd
 849     Math,
 850
 851     /// &, |, ^ -- takes equal types, produces same type as input,
 852     /// applicable to ints/floats/simd/bool
 853     Bitwise,
 854
 855     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 856     /// which produce the input type
 857     Comparison,
 858 }
 859
 860 impl BinOpCategory {
 861     fn from(op: hir::BinOp) -> BinOpCategory {
 862         match op.node {
 863             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 864
 865             hir::BinOpKind::Add
 866             | hir::BinOpKind::Sub
 867             | hir::BinOpKind::Mul
 868             | hir::BinOpKind::Div
 869             | hir::BinOpKind::Rem => BinOpCategory::Math,
 870
 871             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 872                 BinOpCategory::Bitwise
 873             }
 874
 875             hir::BinOpKind::Eq
 876             | hir::BinOpKind::Ne
 877             | hir::BinOpKind::Lt
 878             | hir::BinOpKind::Le
 879             | hir::BinOpKind::Ge
 880             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 881
 882             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 883         }
 884     }
 885 }
 886
 887 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 888 #[derive(Clone, Copy, Debug, PartialEq)]
 889 enum IsAssign {
 890     No,
 891     Yes,
 892 }
 893
 894 #[derive(Clone, Copy, Debug)]
 895 enum Op {
 896     Binary(hir::BinOp, IsAssign),
 897     Unary(hir::UnOp, Span),
 898 }
 899
 900 /// Dereferences a single level of immutable referencing.
 901 fn deref_ty_if_possible<'tcx>(ty: Ty<'tcx>) -> Ty<'tcx> {
 902     match ty.kind() {
 903         ty::Ref(_, ty, hir::Mutability::Not) => *ty,
 904         _ => ty,
 905     }
 906 }
 907
 908 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 909 /// + u32, i16x4 == i16x4) and false if these types would have to be
 910 /// overloaded to be legal. There are two reasons that we distinguish
 911 /// builtin operations from overloaded ones (vs trying to drive
 912 /// everything uniformly through the trait system and intrinsics or
 913 /// something like that):
 914 ///
 915 /// 1. Builtin operations can trivially be evaluated in constants.
 916 /// 2. For comparison operators applied to SIMD types the result is
 917 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 918 ///    type like `i16x4`. This means that the overloaded trait
 919 ///    `PartialEq` is not applicable.
 920 ///
 921 /// Reason #2 is the killer. I tried for a while to always use
 922 /// overloaded logic and just check the types in constants/codegen after
 923 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 924 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 925     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 926     // (See https://github.com/rust-lang/rust/issues/57447.)
 927     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 928
 929     match BinOpCategory::from(op) {
 930         BinOpCategory::Shortcircuit => true,
 931
 932         BinOpCategory::Shift => {
 933             lhs.references_error()
 934                 || rhs.references_error()
 935                 || lhs.is_integral() && rhs.is_integral()
 936         }
 937
 938         BinOpCategory::Math => {
 939             lhs.references_error()
 940                 || rhs.references_error()
 941                 || lhs.is_integral() && rhs.is_integral()
 942                 || lhs.is_floating_point() && rhs.is_floating_point()
 943         }
 944
 945         BinOpCategory::Bitwise => {
 946             lhs.references_error()
 947                 || rhs.references_error()
 948                 || lhs.is_integral() && rhs.is_integral()
 949                 || lhs.is_floating_point() && rhs.is_floating_point()
 950                 || lhs.is_bool() && rhs.is_bool()
 951         }
 952
 953         BinOpCategory::Comparison => {
 954             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 955         }
 956     }
 957 }
 958
 959 fn suggest_constraining_param(
 960     tcx: TyCtxt<'_>,
 961     body_id: hir::HirId,
 962     mut err: &mut Diagnostic,
 963     lhs_ty: Ty<'_>,
 964     rhs_ty: Ty<'_>,
 965     missing_trait: &str,
 966     p: ty::ParamTy,
 967     set_output: bool,
 968 ) {
 969     let hir = tcx.hir();
 970     let msg = &format!("`{}` might need a bound for `{}`", lhs_ty, missing_trait);
 971     // Try to find the def-id and details for the parameter p. We have only the index,
 972     // so we have to find the enclosing function's def-id, then look through its declared
 973     // generic parameters to get the declaration.
 974     let def_id = hir.body_owner_def_id(hir::BodyId { hir_id: body_id });
 975     let generics = tcx.generics_of(def_id);
 976     let param_def_id = generics.type_param(&p, tcx).def_id;
 977     if let Some(generics) = param_def_id
 978         .as_local()
 979         .map(|id| hir.local_def_id_to_hir_id(id))
 980         .and_then(|id| hir.find_by_def_id(hir.get_parent_item(id)))
 981         .as_ref()
 982         .and_then(|node| node.generics())
 983     {
 984         let output = if set_output { format!("<Output = {}>", rhs_ty) } else { String::new() };
 985         suggest_constraining_type_param(
 986             tcx,
 987             generics,
 988             &mut err,
 989             &format!("{}", lhs_ty),
 990             &format!("{}{}", missing_trait, output),
 991             None,
 992         );
 993     } else {
 994         let span = tcx.def_span(param_def_id);
 995         err.span_label(span, msg);
 996     }
 997 }
 998
 999 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
1000
1001 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
1002     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1003         if let ty::Param(_) = ty.kind() {
1004             self.0.push(ty);
1005         }
1006         ty.super_visit_with(self)
1007     }
1008 }
1009
1010 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
1011
1012 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
1013     fn tcx(&self) -> TyCtxt<'tcx> {
1014         self.0.tcx
1015     }
1016
1017     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1018         match ty.kind() {
1019             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
1020                 kind: TypeVariableOriginKind::MiscVariable,
1021                 span: self.1,
1022             }),
1023             _ => ty.super_fold_with(self),
1024         }
1025     }
1026 }