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
  22 use std::ops::ControlFlow;
  23
  24 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  25     /// Checks a `a <op>= b`
  26     pub fn check_binop_assign(
  27         &self,
  28         expr: &'tcx hir::Expr<'tcx>,
  29         op: hir::BinOp,
  30         lhs: &'tcx hir::Expr<'tcx>,
  31         rhs: &'tcx hir::Expr<'tcx>,
  32     ) -> Ty<'tcx> {
  33         let (lhs_ty, rhs_ty, return_ty) =
  34             self.check_overloaded_binop(expr, lhs, rhs, op, IsAssign::Yes);
  35
  36         let ty =
  37             if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() && is_builtin_binop(lhs_ty, rhs_ty, op) {
  38                 self.enforce_builtin_binop_types(&lhs.span, lhs_ty, &rhs.span, rhs_ty, op);
  39                 self.tcx.mk_unit()
  40             } else {
  41                 return_ty
  42             };
  43
  44         self.check_lhs_assignable(lhs, "E0067", &op.span);
  45
  46         ty
  47     }
  48
  49     /// Checks a potentially overloaded binary operator.
  50     pub fn check_binop(
  51         &self,
  52         expr: &'tcx hir::Expr<'tcx>,
  53         op: hir::BinOp,
  54         lhs_expr: &'tcx hir::Expr<'tcx>,
  55         rhs_expr: &'tcx hir::Expr<'tcx>,
  56     ) -> Ty<'tcx> {
  57         let tcx = self.tcx;
  58
  59         debug!(
  60             "check_binop(expr.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
  61             expr.hir_id, expr, op, lhs_expr, rhs_expr
  62         );
  63
  64         match BinOpCategory::from(op) {
  65             BinOpCategory::Shortcircuit => {
  66                 // && and || are a simple case.
  67                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool, None);
  68                 let lhs_diverges = self.diverges.get();
  69                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool, None);
  70
  71                 // Depending on the LHS' value, the RHS can never execute.
  72                 self.diverges.set(lhs_diverges);
  73
  74                 tcx.types.bool
  75             }
  76             _ => {
  77                 // Otherwise, we always treat operators as if they are
  78                 // overloaded. This is the way to be most flexible w/r/t
  79                 // types that get inferred.
  80                 let (lhs_ty, rhs_ty, return_ty) =
  81                     self.check_overloaded_binop(expr, lhs_expr, rhs_expr, op, IsAssign::No);
  82
  83                 // Supply type inference hints if relevant. Probably these
  84                 // hints should be enforced during select as part of the
  85                 // `consider_unification_despite_ambiguity` routine, but this
  86                 // more convenient for now.
  87                 //
  88                 // The basic idea is to help type inference by taking
  89                 // advantage of things we know about how the impls for
  90                 // scalar types are arranged. This is important in a
  91                 // scenario like `1_u32 << 2`, because it lets us quickly
  92                 // deduce that the result type should be `u32`, even
  93                 // though we don't know yet what type 2 has and hence
  94                 // can't pin this down to a specific impl.
  95                 if !lhs_ty.is_ty_var()
  96                     && !rhs_ty.is_ty_var()
  97                     && is_builtin_binop(lhs_ty, rhs_ty, op)
  98                 {
  99                     let builtin_return_ty = self.enforce_builtin_binop_types(
 100                         &lhs_expr.span,
 101                         lhs_ty,
 102                         &rhs_expr.span,
 103                         rhs_ty,
 104                         op,
 105                     );
 106                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 107                 }
 108
 109                 return_ty
 110             }
 111         }
 112     }
 113
 114     fn enforce_builtin_binop_types(
 115         &self,
 116         lhs_span: &Span,
 117         lhs_ty: Ty<'tcx>,
 118         rhs_span: &Span,
 119         rhs_ty: Ty<'tcx>,
 120         op: hir::BinOp,
 121     ) -> Ty<'tcx> {
 122         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 123
 124         // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 125         // (See https://github.com/rust-lang/rust/issues/57447.)
 126         let (lhs_ty, rhs_ty) = (deref_ty_if_possible(lhs_ty), deref_ty_if_possible(rhs_ty));
 127
 128         let tcx = self.tcx;
 129         match BinOpCategory::from(op) {
 130             BinOpCategory::Shortcircuit => {
 131                 self.demand_suptype(*lhs_span, tcx.types.bool, lhs_ty);
 132                 self.demand_suptype(*rhs_span, tcx.types.bool, rhs_ty);
 133                 tcx.types.bool
 134             }
 135
 136             BinOpCategory::Shift => {
 137                 // result type is same as LHS always
 138                 lhs_ty
 139             }
 140
 141             BinOpCategory::Math | BinOpCategory::Bitwise => {
 142                 // both LHS and RHS and result will have the same type
 143                 self.demand_suptype(*rhs_span, lhs_ty, rhs_ty);
 144                 lhs_ty
 145             }
 146
 147             BinOpCategory::Comparison => {
 148                 // both LHS and RHS and result will have the same type
 149                 self.demand_suptype(*rhs_span, lhs_ty, rhs_ty);
 150                 tcx.types.bool
 151             }
 152         }
 153     }
 154
 155     fn check_overloaded_binop(
 156         &self,
 157         expr: &'tcx hir::Expr<'tcx>,
 158         lhs_expr: &'tcx hir::Expr<'tcx>,
 159         rhs_expr: &'tcx hir::Expr<'tcx>,
 160         op: hir::BinOp,
 161         is_assign: IsAssign,
 162     ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
 163         debug!(
 164             "check_overloaded_binop(expr.hir_id={}, op={:?}, is_assign={:?})",
 165             expr.hir_id, op, is_assign
 166         );
 167
 168         let lhs_ty = match is_assign {
 169             IsAssign::No => {
 170                 // Find a suitable supertype of the LHS expression's type, by coercing to
 171                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 172                 // trait matching creating lifetime constraints that are too strict.
 173                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 174                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 175                 let lhs_ty = self.check_expr(lhs_expr);
 176                 let fresh_var = self.next_ty_var(TypeVariableOrigin {
 177                     kind: TypeVariableOriginKind::MiscVariable,
 178                     span: lhs_expr.span,
 179                 });
 180                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var, Some(rhs_expr), AllowTwoPhase::No)
 181             }
 182             IsAssign::Yes => {
 183                 // rust-lang/rust#52126: We have to use strict
 184                 // equivalence on the LHS of an assign-op like `+=`;
 185                 // overwritten or mutably-borrowed places cannot be
 186                 // coerced to a supertype.
 187                 self.check_expr(lhs_expr)
 188             }
 189         };
 190         let lhs_ty = self.resolve_vars_with_obligations(lhs_ty);
 191
 192         // N.B., as we have not yet type-checked the RHS, we don't have the
 193         // type at hand. Make a variable to represent it. The whole reason
 194         // for this indirection is so that, below, we can check the expr
 195         // using this variable as the expected type, which sometimes lets
 196         // us do better coercions than we would be able to do otherwise,
 197         // particularly for things like `String + &String`.
 198         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 199             kind: TypeVariableOriginKind::MiscVariable,
 200             span: rhs_expr.span,
 201         });
 202
 203         let result = self.lookup_op_method(lhs_ty, &[rhs_ty_var], Op::Binary(op, is_assign));
 204
 205         // see `NB` above
 206         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var, Some(lhs_expr));
 207         let rhs_ty = self.resolve_vars_with_obligations(rhs_ty);
 208
 209         let return_ty = match result {
 210             Ok(method) => {
 211                 let by_ref_binop = !op.node.is_by_value();
 212                 if is_assign == IsAssign::Yes || by_ref_binop {
 213                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() {
 214                         let mutbl = match mutbl {
 215                             hir::Mutability::Not => AutoBorrowMutability::Not,
 216                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 217                                 // Allow two-phase borrows for binops in initial deployment
 218                                 // since they desugar to methods
 219                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 220                             },
 221                         };
 222                         let autoref = Adjustment {
 223                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 224                             target: method.sig.inputs()[0],
 225                         };
 226                         self.apply_adjustments(lhs_expr, vec![autoref]);
 227                     }
 228                 }
 229                 if by_ref_binop {
 230                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 231                         let mutbl = match mutbl {
 232                             hir::Mutability::Not => AutoBorrowMutability::Not,
 233                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 234                                 // Allow two-phase borrows for binops in initial deployment
 235                                 // since they desugar to methods
 236                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 237                             },
 238                         };
 239                         let autoref = Adjustment {
 240                             kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl)),
 241                             target: method.sig.inputs()[1],
 242                         };
 243                         // HACK(eddyb) Bypass checks due to reborrows being in
 244                         // some cases applied on the RHS, on top of which we need
 245                         // to autoref, which is not allowed by apply_adjustments.
 246                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 247                         self.typeck_results
 248                             .borrow_mut()
 249                             .adjustments_mut()
 250                             .entry(rhs_expr.hir_id)
 251                             .or_default()
 252                             .push(autoref);
 253                     }
 254                 }
 255                 self.write_method_call(expr.hir_id, method);
 256
 257                 method.sig.output()
 258             }
 259             // error types are considered "builtin"
 260             Err(()) if lhs_ty.references_error() || rhs_ty.references_error() => {
 261                 self.tcx.ty_error()
 262             }
 263             Err(()) => {
 264                 let source_map = self.tcx.sess.source_map();
 265                 let (mut err, missing_trait, use_output, involves_fn) = match is_assign {
 266                     IsAssign::Yes => {
 267                         let mut err = struct_span_err!(
 268                             self.tcx.sess,
 269                             expr.span,
 270                             E0368,
 271                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 272                             op.node.as_str(),
 273                             lhs_ty,
 274                         );
 275                         err.span_label(
 276                             lhs_expr.span,
 277                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 278                         );
 279                         let missing_trait = match op.node {
 280                             hir::BinOpKind::Add => Some("std::ops::AddAssign"),
 281                             hir::BinOpKind::Sub => Some("std::ops::SubAssign"),
 282                             hir::BinOpKind::Mul => Some("std::ops::MulAssign"),
 283                             hir::BinOpKind::Div => Some("std::ops::DivAssign"),
 284                             hir::BinOpKind::Rem => Some("std::ops::RemAssign"),
 285                             hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 286                             hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 287                             hir::BinOpKind::BitOr => Some("std::ops::BitOrAssign"),
 288                             hir::BinOpKind::Shl => Some("std::ops::ShlAssign"),
 289                             hir::BinOpKind::Shr => Some("std::ops::ShrAssign"),
 290                             _ => None,
 291                         };
 292                         (err, missing_trait, false, 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                         let mut involves_fn = false;
 380                         if !lhs_expr.span.eq(&rhs_expr.span) {
 381                             involves_fn |= self.add_type_neq_err_label(
 382                                 &mut err,
 383                                 lhs_expr.span,
 384                                 lhs_ty,
 385                                 rhs_ty,
 386                                 op,
 387                                 is_assign,
 388                             );
 389                             involves_fn |= self.add_type_neq_err_label(
 390                                 &mut err,
 391                                 rhs_expr.span,
 392                                 rhs_ty,
 393                                 lhs_ty,
 394                                 op,
 395                                 is_assign,
 396                             );
 397                         }
 398                         (err, missing_trait, use_output, involves_fn)
 399                     }
 400                 };
 401                 let mut suggested_deref = false;
 402                 if let Ref(_, rty, _) = lhs_ty.kind() {
 403                     if {
 404                         self.infcx.type_is_copy_modulo_regions(self.param_env, rty, lhs_expr.span)
 405                             && self
 406                                 .lookup_op_method(rty, &[rhs_ty], Op::Binary(op, is_assign))
 407                                 .is_ok()
 408                     } {
 409                         if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 410                             let msg = &format!(
 411                                 "`{}{}` can be used on `{}`, you can dereference `{}`",
 412                                 op.node.as_str(),
 413                                 match is_assign {
 414                                     IsAssign::Yes => "=",
 415                                     IsAssign::No => "",
 416                                 },
 417                                 rty.peel_refs(),
 418                                 lstring,
 419                             );
 420                             err.span_suggestion_verbose(
 421                                 lhs_expr.span.shrink_to_lo(),
 422                                 msg,
 423                                 "*".to_string(),
 424                                 rustc_errors::Applicability::MachineApplicable,
 425                             );
 426                             suggested_deref = true;
 427                         }
 428                     }
 429                 }
 430                 if let Some(missing_trait) = missing_trait {
 431                     let mut visitor = TypeParamVisitor(vec![]);
 432                     visitor.visit_ty(lhs_ty);
 433
 434                     if op.node == hir::BinOpKind::Add
 435                         && self.check_str_addition(
 436                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 437                         )
 438                     {
 439                         // This has nothing here because it means we did string
 440                         // concatenation (e.g., "Hello " + "World!"). This means
 441                         // we don't want the note in the else clause to be emitted
 442                     } else if let [ty] = &visitor.0[..] {
 443                         if let ty::Param(p) = *ty.kind() {
 444                             // Check if the method would be found if the type param wasn't
 445                             // involved. If so, it means that adding a trait bound to the param is
 446                             // enough. Otherwise we do not give the suggestion.
 447                             let mut eraser = TypeParamEraser(&self, expr.span);
 448                             let needs_bound = self
 449                                 .lookup_op_method(
 450                                     eraser.fold_ty(lhs_ty),
 451                                     &[eraser.fold_ty(rhs_ty)],
 452                                     Op::Binary(op, is_assign),
 453                                 )
 454                                 .is_ok();
 455                             if needs_bound {
 456                                 suggest_constraining_param(
 457                                     self.tcx,
 458                                     self.body_id,
 459                                     &mut err,
 460                                     ty,
 461                                     rhs_ty,
 462                                     missing_trait,
 463                                     p,
 464                                     use_output,
 465                                 );
 466                             } else if *ty != lhs_ty {
 467                                 // When we know that a missing bound is responsible, we don't show
 468                                 // this note as it is redundant.
 469                                 err.note(&format!(
 470                                     "the trait `{}` is not implemented for `{}`",
 471                                     missing_trait, lhs_ty
 472                                 ));
 473                             }
 474                         } else {
 475                             bug!("type param visitor stored a non type param: {:?}", ty.kind());
 476                         }
 477                     } else if !suggested_deref && !involves_fn {
 478                         suggest_impl_missing(&mut err, lhs_ty, &missing_trait);
 479                     }
 480                 }
 481                 err.emit();
 482                 self.tcx.ty_error()
 483             }
 484         };
 485
 486         (lhs_ty, rhs_ty, return_ty)
 487     }
 488
 489     /// If one of the types is an uncalled function and calling it would yield the other type,
 490     /// suggest calling the function. Returns `true` if suggestion would apply (even if not given).
 491     fn add_type_neq_err_label(
 492         &self,
 493         err: &mut rustc_errors::DiagnosticBuilder<'_>,
 494         span: Span,
 495         ty: Ty<'tcx>,
 496         other_ty: Ty<'tcx>,
 497         op: hir::BinOp,
 498         is_assign: IsAssign,
 499     ) -> bool /* did we suggest to call a function because of missing parenthesis? */ {
 500         err.span_label(span, ty.to_string());
 501         if let FnDef(def_id, _) = *ty.kind() {
 502             let source_map = self.tcx.sess.source_map();
 503             if !self.tcx.has_typeck_results(def_id) {
 504                 return false;
 505             }
 506             // FIXME: Instead of exiting early when encountering bound vars in
 507             // the function signature, consider keeping the binder here and
 508             // propagating it downwards.
 509             let fn_sig = if let Some(fn_sig) = self.tcx.fn_sig(def_id).no_bound_vars() {
 510                 fn_sig
 511             } else {
 512                 return false;
 513             };
 514
 515             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
 516                 if !self.tcx.has_typeck_results(def_id) {
 517                     return false;
 518                 }
 519                 // We're emitting a suggestion, so we can just ignore regions
 520                 self.tcx.fn_sig(def_id).skip_binder().output()
 521             } else {
 522                 other_ty
 523             };
 524
 525             if self
 526                 .lookup_op_method(fn_sig.output(), &[other_ty], Op::Binary(op, is_assign))
 527                 .is_ok()
 528             {
 529                 if let Ok(snippet) = source_map.span_to_snippet(span) {
 530                     let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
 531                         (format!("{}( /* arguments */ )", snippet), Applicability::HasPlaceholders)
 532                     } else {
 533                         (format!("{}()", snippet), Applicability::MaybeIncorrect)
 534                     };
 535
 536                     err.span_suggestion(
 537                         span,
 538                         "you might have forgotten to call this function",
 539                         variable_snippet,
 540                         applicability,
 541                     );
 542                 }
 543                 return true;
 544             }
 545         }
 546         false
 547     }
 548
 549     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 550     /// like `&str + &str`, `String + String` and `&str + &String`.
 551     ///
 552     /// If this function returns `true` it means a note was printed, so we don't need
 553     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 554     fn check_str_addition(
 555         &self,
 556         lhs_expr: &'tcx hir::Expr<'tcx>,
 557         rhs_expr: &'tcx hir::Expr<'tcx>,
 558         lhs_ty: Ty<'tcx>,
 559         rhs_ty: Ty<'tcx>,
 560         err: &mut rustc_errors::DiagnosticBuilder<'_>,
 561         is_assign: IsAssign,
 562         op: hir::BinOp,
 563     ) -> bool {
 564         let source_map = self.tcx.sess.source_map();
 565         let remove_borrow_msg = "String concatenation appends the string on the right to the \
 566                                  string on the left and may require reallocation. This \
 567                                  requires ownership of the string on the left";
 568
 569         let msg = "`to_owned()` can be used to create an owned `String` \
 570                    from a string reference. String concatenation \
 571                    appends the string on the right to the string \
 572                    on the left and may require reallocation. This \
 573                    requires ownership of the string on the left";
 574
 575         let string_type = self.tcx.get_diagnostic_item(sym::string_type);
 576         let is_std_string = |ty: Ty<'tcx>| match ty.ty_adt_def() {
 577             Some(ty_def) => Some(ty_def.did) == string_type,
 578             None => false,
 579         };
 580
 581         match (lhs_ty.kind(), rhs_ty.kind()) {
 582             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 583                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && (
 584                         *r_ty.kind() == Str || is_std_string(r_ty) ||
 585                         &format!("{:?}", rhs_ty) == "&&str"
 586                     ) =>
 587             {
 588                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 589                     err.span_label(
 590                         op.span,
 591                         "`+` cannot be used to concatenate two `&str` strings",
 592                     );
 593                     match source_map.span_to_snippet(lhs_expr.span) {
 594                         Ok(lstring) => {
 595                             err.span_suggestion(
 596                                 lhs_expr.span,
 597                                 if lstring.starts_with('&') {
 598                                     remove_borrow_msg
 599                                 } else {
 600                                     msg
 601                                 },
 602                                 if let Some(stripped) = lstring.strip_prefix('&') {
 603                                     // let a = String::new();
 604                                     // let _ = &a + "bar";
 605                                     stripped.to_string()
 606                                 } else {
 607                                     format!("{}.to_owned()", lstring)
 608                                 },
 609                                 Applicability::MachineApplicable,
 610                             )
 611                         }
 612                         _ => err.help(msg),
 613                     };
 614                 }
 615                 true
 616             }
 617             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 618                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 619             {
 620                 err.span_label(
 621                     op.span,
 622                     "`+` cannot be used to concatenate a `&str` with a `String`",
 623                 );
 624                 match (
 625                     source_map.span_to_snippet(lhs_expr.span),
 626                     source_map.span_to_snippet(rhs_expr.span),
 627                     is_assign,
 628                 ) {
 629                     (Ok(l), Ok(r), IsAssign::No) => {
 630                         let to_string = if let Some(stripped) = l.strip_prefix('&') {
 631                             // let a = String::new(); let b = String::new();
 632                             // let _ = &a + b;
 633                             stripped.to_string()
 634                         } else {
 635                             format!("{}.to_owned()", l)
 636                         };
 637                         err.multipart_suggestion(
 638                             msg,
 639                             vec![
 640                                 (lhs_expr.span, to_string),
 641                                 (rhs_expr.span, format!("&{}", r)),
 642                             ],
 643                             Applicability::MachineApplicable,
 644                         );
 645                     }
 646                     _ => {
 647                         err.help(msg);
 648                     }
 649                 };
 650                 true
 651             }
 652             _ => false,
 653         }
 654     }
 655
 656     pub fn check_user_unop(
 657         &self,
 658         ex: &'tcx hir::Expr<'tcx>,
 659         operand_ty: Ty<'tcx>,
 660         op: hir::UnOp,
 661     ) -> Ty<'tcx> {
 662         assert!(op.is_by_value());
 663         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 664             Ok(method) => {
 665                 self.write_method_call(ex.hir_id, method);
 666                 method.sig.output()
 667             }
 668             Err(()) => {
 669                 let actual = self.resolve_vars_if_possible(operand_ty);
 670                 if !actual.references_error() {
 671                     let mut err = struct_span_err!(
 672                         self.tcx.sess,
 673                         ex.span,
 674                         E0600,
 675                         "cannot apply unary operator `{}` to type `{}`",
 676                         op.as_str(),
 677                         actual
 678                     );
 679                     err.span_label(
 680                         ex.span,
 681                         format!("cannot apply unary operator `{}`", op.as_str()),
 682                     );
 683                     match actual.kind() {
 684                         Uint(_) if op == hir::UnOp::Neg => {
 685                             err.note("unsigned values cannot be negated");
 686
 687                             if let hir::ExprKind::Unary(
 688                                 _,
 689                                 hir::Expr {
 690                                     kind:
 691                                         hir::ExprKind::Lit(Spanned {
 692                                             node: ast::LitKind::Int(1, _),
 693                                             ..
 694                                         }),
 695                                     ..
 696                                 },
 697                             ) = ex.kind
 698                             {
 699                                 err.span_suggestion(
 700                                     ex.span,
 701                                     &format!(
 702                                         "you may have meant the maximum value of `{}`",
 703                                         actual
 704                                     ),
 705                                     format!("{}::MAX", actual),
 706                                     Applicability::MaybeIncorrect,
 707                                 );
 708                             }
 709                         }
 710                         Str | Never | Char | Tuple(_) | Array(_, _) => {}
 711                         Ref(_, ref lty, _) if *lty.kind() == Str => {}
 712                         _ => {
 713                             let missing_trait = match op {
 714                                 hir::UnOp::Neg => "std::ops::Neg",
 715                                 hir::UnOp::Not => "std::ops::Not",
 716                                 hir::UnOp::Deref => "std::ops::UnDerf",
 717                             };
 718                             suggest_impl_missing(&mut err, operand_ty, &missing_trait);
 719                         }
 720                     }
 721                     err.emit();
 722                 }
 723                 self.tcx.ty_error()
 724             }
 725         }
 726     }
 727
 728     fn lookup_op_method(
 729         &self,
 730         lhs_ty: Ty<'tcx>,
 731         other_tys: &[Ty<'tcx>],
 732         op: Op,
 733     ) -> Result<MethodCallee<'tcx>, ()> {
 734         let lang = self.tcx.lang_items();
 735
 736         let span = match op {
 737             Op::Binary(op, _) => op.span,
 738             Op::Unary(_, span) => span,
 739         };
 740         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 741             match op.node {
 742                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 743                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 744                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 745                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 746                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 747                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 748                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 749                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 750                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 751                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 752                 hir::BinOpKind::Lt
 753                 | hir::BinOpKind::Le
 754                 | hir::BinOpKind::Ge
 755                 | hir::BinOpKind::Gt
 756                 | hir::BinOpKind::Eq
 757                 | hir::BinOpKind::Ne
 758                 | hir::BinOpKind::And
 759                 | hir::BinOpKind::Or => {
 760                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 761                 }
 762             }
 763         } else if let Op::Binary(op, IsAssign::No) = op {
 764             match op.node {
 765                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 766                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 767                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 768                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 769                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 770                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 771                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 772                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 773                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 774                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 775                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 776                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 777                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 778                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 779                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 780                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 781                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 782                     span_bug!(span, "&& and || are not overloadable")
 783                 }
 784             }
 785         } else if let Op::Unary(hir::UnOp::Not, _) = op {
 786             (sym::not, lang.not_trait())
 787         } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 788             (sym::neg, lang.neg_trait())
 789         } else {
 790             bug!("lookup_op_method: op not supported: {:?}", op)
 791         };
 792
 793         debug!(
 794             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 795             lhs_ty, op, opname, trait_did
 796         );
 797
 798         // Catches cases like #83893, where a lang item is declared with the
 799         // wrong number of generic arguments. Should have yielded an error
 800         // elsewhere by now, but we have to catch it here so that we do not
 801         // index `other_tys` out of bounds (if the lang item has too many
 802         // generic arguments, `other_tys` is too short).
 803         if !has_expected_num_generic_args(
 804             self.tcx,
 805             trait_did,
 806             match op {
 807                 // Binary ops have a generic right-hand side, unary ops don't
 808                 Op::Binary(..) => 1,
 809                 Op::Unary(..) => 0,
 810             },
 811         ) {
 812             return Err(());
 813         }
 814
 815         let method = trait_did.and_then(|trait_did| {
 816             let opname = Ident::with_dummy_span(opname);
 817             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 818         });
 819
 820         match method {
 821             Some(ok) => {
 822                 let method = self.register_infer_ok_obligations(ok);
 823                 self.select_obligations_where_possible(false, |_| {});
 824
 825                 Ok(method)
 826             }
 827             None => Err(()),
 828         }
 829     }
 830 }
 831
 832 // Binary operator categories. These categories summarize the behavior
 833 // with respect to the builtin operationrs supported.
 834 enum BinOpCategory {
 835     /// &&, || -- cannot be overridden
 836     Shortcircuit,
 837
 838     /// <<, >> -- when shifting a single integer, rhs can be any
 839     /// integer type. For simd, types must match.
 840     Shift,
 841
 842     /// +, -, etc -- takes equal types, produces same type as input,
 843     /// applicable to ints/floats/simd
 844     Math,
 845
 846     /// &, |, ^ -- takes equal types, produces same type as input,
 847     /// applicable to ints/floats/simd/bool
 848     Bitwise,
 849
 850     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 851     /// which produce the input type
 852     Comparison,
 853 }
 854
 855 impl BinOpCategory {
 856     fn from(op: hir::BinOp) -> BinOpCategory {
 857         match op.node {
 858             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 859
 860             hir::BinOpKind::Add
 861             | hir::BinOpKind::Sub
 862             | hir::BinOpKind::Mul
 863             | hir::BinOpKind::Div
 864             | hir::BinOpKind::Rem => BinOpCategory::Math,
 865
 866             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 867                 BinOpCategory::Bitwise
 868             }
 869
 870             hir::BinOpKind::Eq
 871             | hir::BinOpKind::Ne
 872             | hir::BinOpKind::Lt
 873             | hir::BinOpKind::Le
 874             | hir::BinOpKind::Ge
 875             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 876
 877             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 878         }
 879     }
 880 }
 881
 882 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 883 #[derive(Clone, Copy, Debug, PartialEq)]
 884 enum IsAssign {
 885     No,
 886     Yes,
 887 }
 888
 889 #[derive(Clone, Copy, Debug)]
 890 enum Op {
 891     Binary(hir::BinOp, IsAssign),
 892     Unary(hir::UnOp, Span),
 893 }
 894
 895 /// Dereferences a single level of immutable referencing.
 896 fn deref_ty_if_possible(ty: Ty<'tcx>) -> Ty<'tcx> {
 897     match ty.kind() {
 898         ty::Ref(_, ty, hir::Mutability::Not) => ty,
 899         _ => ty,
 900     }
 901 }
 902
 903 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 904 /// + u32, i16x4 == i16x4) and false if these types would have to be
 905 /// overloaded to be legal. There are two reasons that we distinguish
 906 /// builtin operations from overloaded ones (vs trying to drive
 907 /// everything uniformly through the trait system and intrinsics or
 908 /// something like that):
 909 ///
 910 /// 1. Builtin operations can trivially be evaluated in constants.
 911 /// 2. For comparison operators applied to SIMD types the result is
 912 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 913 ///    type like `i16x4`. This means that the overloaded trait
 914 ///    `PartialEq` is not applicable.
 915 ///
 916 /// Reason #2 is the killer. I tried for a while to always use
 917 /// overloaded logic and just check the types in constants/codegen after
 918 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 919 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 920     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 921     // (See https://github.com/rust-lang/rust/issues/57447.)
 922     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 923
 924     match BinOpCategory::from(op) {
 925         BinOpCategory::Shortcircuit => true,
 926
 927         BinOpCategory::Shift => {
 928             lhs.references_error()
 929                 || rhs.references_error()
 930                 || lhs.is_integral() && rhs.is_integral()
 931         }
 932
 933         BinOpCategory::Math => {
 934             lhs.references_error()
 935                 || rhs.references_error()
 936                 || lhs.is_integral() && rhs.is_integral()
 937                 || lhs.is_floating_point() && rhs.is_floating_point()
 938         }
 939
 940         BinOpCategory::Bitwise => {
 941             lhs.references_error()
 942                 || rhs.references_error()
 943                 || lhs.is_integral() && rhs.is_integral()
 944                 || lhs.is_floating_point() && rhs.is_floating_point()
 945                 || lhs.is_bool() && rhs.is_bool()
 946         }
 947
 948         BinOpCategory::Comparison => {
 949             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 950         }
 951     }
 952 }
 953
 954 /// If applicable, note that an implementation of `trait` for `ty` may fix the error.
 955 fn suggest_impl_missing(err: &mut DiagnosticBuilder<'_>, ty: Ty<'_>, missing_trait: &str) {
 956     if let Adt(def, _) = ty.peel_refs().kind() {
 957         if def.did.is_local() {
 958             err.note(&format!(
 959                 "an implementation of `{}` might be missing for `{}`",
 960                 missing_trait, ty
 961             ));
 962         }
 963     }
 964 }
 965
 966 fn suggest_constraining_param(
 967     tcx: TyCtxt<'_>,
 968     body_id: hir::HirId,
 969     mut err: &mut DiagnosticBuilder<'_>,
 970     lhs_ty: Ty<'_>,
 971     rhs_ty: Ty<'_>,
 972     missing_trait: &str,
 973     p: ty::ParamTy,
 974     set_output: bool,
 975 ) {
 976     let hir = tcx.hir();
 977     let msg = &format!("`{}` might need a bound for `{}`", lhs_ty, missing_trait);
 978     // Try to find the def-id and details for the parameter p. We have only the index,
 979     // so we have to find the enclosing function's def-id, then look through its declared
 980     // generic parameters to get the declaration.
 981     let def_id = hir.body_owner_def_id(hir::BodyId { hir_id: body_id });
 982     let generics = tcx.generics_of(def_id);
 983     let param_def_id = generics.type_param(&p, tcx).def_id;
 984     if let Some(generics) = param_def_id
 985         .as_local()
 986         .map(|id| hir.local_def_id_to_hir_id(id))
 987         .and_then(|id| hir.find(hir.get_parent_item(id)))
 988         .as_ref()
 989         .and_then(|node| node.generics())
 990     {
 991         let output = if set_output { format!("<Output = {}>", rhs_ty) } else { String::new() };
 992         suggest_constraining_type_param(
 993             tcx,
 994             generics,
 995             &mut err,
 996             &format!("{}", lhs_ty),
 997             &format!("{}{}", missing_trait, output),
 998             None,
 999         );
1000     } else {
1001         let span = tcx.def_span(param_def_id);
1002         err.span_label(span, msg);
1003     }
1004 }
1005
1006 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
1007
1008 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
1009     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1010         if let ty::Param(_) = ty.kind() {
1011             self.0.push(ty);
1012         }
1013         ty.super_visit_with(self)
1014     }
1015 }
1016
1017 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
1018
1019 impl TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
1020     fn tcx(&self) -> TyCtxt<'tcx> {
1021         self.0.tcx
1022     }
1023
1024     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1025         match ty.kind() {
1026             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
1027                 kind: TypeVariableOriginKind::MiscVariable,
1028                 span: self.1,
1029             }),
1030             _ => ty.super_fold_with(self),
1031         }
1032     }
1033 }