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::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             // We're emitting a suggestion, so we can just ignore regions
 507             let fn_sig = self.tcx.fn_sig(def_id).skip_binder();
 508
 509             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
 510                 if !self.tcx.has_typeck_results(def_id) {
 511                     return false;
 512                 }
 513                 // We're emitting a suggestion, so we can just ignore regions
 514                 self.tcx.fn_sig(def_id).skip_binder().output()
 515             } else {
 516                 other_ty
 517             };
 518
 519             if self
 520                 .lookup_op_method(fn_sig.output(), &[other_ty], Op::Binary(op, is_assign))
 521                 .is_ok()
 522             {
 523                 if let Ok(snippet) = source_map.span_to_snippet(span) {
 524                     let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
 525                         (format!("{}( /* arguments */ )", snippet), Applicability::HasPlaceholders)
 526                     } else {
 527                         (format!("{}()", snippet), Applicability::MaybeIncorrect)
 528                     };
 529
 530                     err.span_suggestion(
 531                         span,
 532                         "you might have forgotten to call this function",
 533                         variable_snippet,
 534                         applicability,
 535                     );
 536                 }
 537                 return true;
 538             }
 539         }
 540         false
 541     }
 542
 543     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 544     /// like `&str + &str`, `String + String` and `&str + &String`.
 545     ///
 546     /// If this function returns `true` it means a note was printed, so we don't need
 547     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 548     fn check_str_addition(
 549         &self,
 550         lhs_expr: &'tcx hir::Expr<'tcx>,
 551         rhs_expr: &'tcx hir::Expr<'tcx>,
 552         lhs_ty: Ty<'tcx>,
 553         rhs_ty: Ty<'tcx>,
 554         err: &mut rustc_errors::DiagnosticBuilder<'_>,
 555         is_assign: IsAssign,
 556         op: hir::BinOp,
 557     ) -> bool {
 558         let source_map = self.tcx.sess.source_map();
 559         let remove_borrow_msg = "String concatenation appends the string on the right to the \
 560                                  string on the left and may require reallocation. This \
 561                                  requires ownership of the string on the left";
 562
 563         let msg = "`to_owned()` can be used to create an owned `String` \
 564                    from a string reference. String concatenation \
 565                    appends the string on the right to the string \
 566                    on the left and may require reallocation. This \
 567                    requires ownership of the string on the left";
 568
 569         let string_type = self.tcx.get_diagnostic_item(sym::string_type);
 570         let is_std_string = |ty: Ty<'tcx>| match ty.ty_adt_def() {
 571             Some(ty_def) => Some(ty_def.did) == string_type,
 572             None => false,
 573         };
 574
 575         match (lhs_ty.kind(), rhs_ty.kind()) {
 576             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 577                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && (
 578                         *r_ty.kind() == Str || is_std_string(r_ty) ||
 579                         &format!("{:?}", rhs_ty) == "&&str"
 580                     ) =>
 581             {
 582                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 583                     err.span_label(
 584                         op.span,
 585                         "`+` cannot be used to concatenate two `&str` strings",
 586                     );
 587                     match source_map.span_to_snippet(lhs_expr.span) {
 588                         Ok(lstring) => {
 589                             err.span_suggestion(
 590                                 lhs_expr.span,
 591                                 if lstring.starts_with('&') {
 592                                     remove_borrow_msg
 593                                 } else {
 594                                     msg
 595                                 },
 596                                 if let Some(stripped) = lstring.strip_prefix('&') {
 597                                     // let a = String::new();
 598                                     // let _ = &a + "bar";
 599                                     stripped.to_string()
 600                                 } else {
 601                                     format!("{}.to_owned()", lstring)
 602                                 },
 603                                 Applicability::MachineApplicable,
 604                             )
 605                         }
 606                         _ => err.help(msg),
 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 (
 619                     source_map.span_to_snippet(lhs_expr.span),
 620                     source_map.span_to_snippet(rhs_expr.span),
 621                     is_assign,
 622                 ) {
 623                     (Ok(l), Ok(r), IsAssign::No) => {
 624                         let to_string = if let Some(stripped) = l.strip_prefix('&') {
 625                             // let a = String::new(); let b = String::new();
 626                             // let _ = &a + b;
 627                             stripped.to_string()
 628                         } else {
 629                             format!("{}.to_owned()", l)
 630                         };
 631                         err.multipart_suggestion(
 632                             msg,
 633                             vec![
 634                                 (lhs_expr.span, to_string),
 635                                 (rhs_expr.span, format!("&{}", r)),
 636                             ],
 637                             Applicability::MachineApplicable,
 638                         );
 639                     }
 640                     _ => {
 641                         err.help(msg);
 642                     }
 643                 };
 644                 true
 645             }
 646             _ => false,
 647         }
 648     }
 649
 650     pub fn check_user_unop(
 651         &self,
 652         ex: &'tcx hir::Expr<'tcx>,
 653         operand_ty: Ty<'tcx>,
 654         op: hir::UnOp,
 655     ) -> Ty<'tcx> {
 656         assert!(op.is_by_value());
 657         match self.lookup_op_method(operand_ty, &[], Op::Unary(op, ex.span)) {
 658             Ok(method) => {
 659                 self.write_method_call(ex.hir_id, method);
 660                 method.sig.output()
 661             }
 662             Err(()) => {
 663                 let actual = self.resolve_vars_if_possible(operand_ty);
 664                 if !actual.references_error() {
 665                     let mut err = struct_span_err!(
 666                         self.tcx.sess,
 667                         ex.span,
 668                         E0600,
 669                         "cannot apply unary operator `{}` to type `{}`",
 670                         op.as_str(),
 671                         actual
 672                     );
 673                     err.span_label(
 674                         ex.span,
 675                         format!("cannot apply unary operator `{}`", op.as_str()),
 676                     );
 677                     match actual.kind() {
 678                         Uint(_) if op == hir::UnOp::UnNeg => {
 679                             err.note("unsigned values cannot be negated");
 680
 681                             if let hir::ExprKind::Unary(
 682                                 _,
 683                                 hir::Expr {
 684                                     kind:
 685                                         hir::ExprKind::Lit(Spanned {
 686                                             node: ast::LitKind::Int(1, _),
 687                                             ..
 688                                         }),
 689                                     ..
 690                                 },
 691                             ) = ex.kind
 692                             {
 693                                 err.span_suggestion(
 694                                     ex.span,
 695                                     &format!(
 696                                         "you may have meant the maximum value of `{}`",
 697                                         actual
 698                                     ),
 699                                     format!("{}::MAX", actual),
 700                                     Applicability::MaybeIncorrect,
 701                                 );
 702                             }
 703                         }
 704                         Str | Never | Char | Tuple(_) | Array(_, _) => {}
 705                         Ref(_, ref lty, _) if *lty.kind() == Str => {}
 706                         _ => {
 707                             let missing_trait = match op {
 708                                 hir::UnOp::UnNeg => "std::ops::Neg",
 709                                 hir::UnOp::UnNot => "std::ops::Not",
 710                                 hir::UnOp::UnDeref => "std::ops::UnDerf",
 711                             };
 712                             suggest_impl_missing(&mut err, operand_ty, &missing_trait);
 713                         }
 714                     }
 715                     err.emit();
 716                 }
 717                 self.tcx.ty_error()
 718             }
 719         }
 720     }
 721
 722     fn lookup_op_method(
 723         &self,
 724         lhs_ty: Ty<'tcx>,
 725         other_tys: &[Ty<'tcx>],
 726         op: Op,
 727     ) -> Result<MethodCallee<'tcx>, ()> {
 728         let lang = self.tcx.lang_items();
 729
 730         let span = match op {
 731             Op::Binary(op, _) => op.span,
 732             Op::Unary(_, span) => span,
 733         };
 734         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 735             match op.node {
 736                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 737                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 738                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 739                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 740                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 741                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 742                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 743                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 744                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 745                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 746                 hir::BinOpKind::Lt
 747                 | hir::BinOpKind::Le
 748                 | hir::BinOpKind::Ge
 749                 | hir::BinOpKind::Gt
 750                 | hir::BinOpKind::Eq
 751                 | hir::BinOpKind::Ne
 752                 | hir::BinOpKind::And
 753                 | hir::BinOpKind::Or => {
 754                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 755                 }
 756             }
 757         } else if let Op::Binary(op, IsAssign::No) = op {
 758             match op.node {
 759                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 760                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 761                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 762                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 763                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 764                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 765                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 766                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 767                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 768                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 769                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 770                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 771                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 772                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 773                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 774                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 775                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 776                     span_bug!(span, "&& and || are not overloadable")
 777                 }
 778             }
 779         } else if let Op::Unary(hir::UnOp::UnNot, _) = op {
 780             (sym::not, lang.not_trait())
 781         } else if let Op::Unary(hir::UnOp::UnNeg, _) = op {
 782             (sym::neg, lang.neg_trait())
 783         } else {
 784             bug!("lookup_op_method: op not supported: {:?}", op)
 785         };
 786
 787         debug!(
 788             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 789             lhs_ty, op, opname, trait_did
 790         );
 791
 792         let method = trait_did.and_then(|trait_did| {
 793             let opname = Ident::with_dummy_span(opname);
 794             self.lookup_method_in_trait(span, opname, trait_did, lhs_ty, Some(other_tys))
 795         });
 796
 797         match method {
 798             Some(ok) => {
 799                 let method = self.register_infer_ok_obligations(ok);
 800                 self.select_obligations_where_possible(false, |_| {});
 801
 802                 Ok(method)
 803             }
 804             None => Err(()),
 805         }
 806     }
 807 }
 808
 809 // Binary operator categories. These categories summarize the behavior
 810 // with respect to the builtin operationrs supported.
 811 enum BinOpCategory {
 812     /// &&, || -- cannot be overridden
 813     Shortcircuit,
 814
 815     /// <<, >> -- when shifting a single integer, rhs can be any
 816     /// integer type. For simd, types must match.
 817     Shift,
 818
 819     /// +, -, etc -- takes equal types, produces same type as input,
 820     /// applicable to ints/floats/simd
 821     Math,
 822
 823     /// &, |, ^ -- takes equal types, produces same type as input,
 824     /// applicable to ints/floats/simd/bool
 825     Bitwise,
 826
 827     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 828     /// which produce the input type
 829     Comparison,
 830 }
 831
 832 impl BinOpCategory {
 833     fn from(op: hir::BinOp) -> BinOpCategory {
 834         match op.node {
 835             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 836
 837             hir::BinOpKind::Add
 838             | hir::BinOpKind::Sub
 839             | hir::BinOpKind::Mul
 840             | hir::BinOpKind::Div
 841             | hir::BinOpKind::Rem => BinOpCategory::Math,
 842
 843             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 844                 BinOpCategory::Bitwise
 845             }
 846
 847             hir::BinOpKind::Eq
 848             | hir::BinOpKind::Ne
 849             | hir::BinOpKind::Lt
 850             | hir::BinOpKind::Le
 851             | hir::BinOpKind::Ge
 852             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 853
 854             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 855         }
 856     }
 857 }
 858
 859 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 860 #[derive(Clone, Copy, Debug, PartialEq)]
 861 enum IsAssign {
 862     No,
 863     Yes,
 864 }
 865
 866 #[derive(Clone, Copy, Debug)]
 867 enum Op {
 868     Binary(hir::BinOp, IsAssign),
 869     Unary(hir::UnOp, Span),
 870 }
 871
 872 /// Dereferences a single level of immutable referencing.
 873 fn deref_ty_if_possible(ty: Ty<'tcx>) -> Ty<'tcx> {
 874     match ty.kind() {
 875         ty::Ref(_, ty, hir::Mutability::Not) => ty,
 876         _ => ty,
 877     }
 878 }
 879
 880 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 881 /// + u32, i16x4 == i16x4) and false if these types would have to be
 882 /// overloaded to be legal. There are two reasons that we distinguish
 883 /// builtin operations from overloaded ones (vs trying to drive
 884 /// everything uniformly through the trait system and intrinsics or
 885 /// something like that):
 886 ///
 887 /// 1. Builtin operations can trivially be evaluated in constants.
 888 /// 2. For comparison operators applied to SIMD types the result is
 889 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 890 ///    type like `i16x4`. This means that the overloaded trait
 891 ///    `PartialEq` is not applicable.
 892 ///
 893 /// Reason #2 is the killer. I tried for a while to always use
 894 /// overloaded logic and just check the types in constants/codegen after
 895 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 896 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 897     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 898     // (See https://github.com/rust-lang/rust/issues/57447.)
 899     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 900
 901     match BinOpCategory::from(op) {
 902         BinOpCategory::Shortcircuit => true,
 903
 904         BinOpCategory::Shift => {
 905             lhs.references_error()
 906                 || rhs.references_error()
 907                 || lhs.is_integral() && rhs.is_integral()
 908         }
 909
 910         BinOpCategory::Math => {
 911             lhs.references_error()
 912                 || rhs.references_error()
 913                 || lhs.is_integral() && rhs.is_integral()
 914                 || lhs.is_floating_point() && rhs.is_floating_point()
 915         }
 916
 917         BinOpCategory::Bitwise => {
 918             lhs.references_error()
 919                 || rhs.references_error()
 920                 || lhs.is_integral() && rhs.is_integral()
 921                 || lhs.is_floating_point() && rhs.is_floating_point()
 922                 || lhs.is_bool() && rhs.is_bool()
 923         }
 924
 925         BinOpCategory::Comparison => {
 926             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
 927         }
 928     }
 929 }
 930
 931 /// If applicable, note that an implementation of `trait` for `ty` may fix the error.
 932 fn suggest_impl_missing(err: &mut DiagnosticBuilder<'_>, ty: Ty<'_>, missing_trait: &str) {
 933     if let Adt(def, _) = ty.peel_refs().kind() {
 934         if def.did.is_local() {
 935             err.note(&format!(
 936                 "an implementation of `{}` might be missing for `{}`",
 937                 missing_trait, ty
 938             ));
 939         }
 940     }
 941 }
 942
 943 fn suggest_constraining_param(
 944     tcx: TyCtxt<'_>,
 945     body_id: hir::HirId,
 946     mut err: &mut DiagnosticBuilder<'_>,
 947     lhs_ty: Ty<'_>,
 948     rhs_ty: Ty<'_>,
 949     missing_trait: &str,
 950     p: ty::ParamTy,
 951     set_output: bool,
 952 ) {
 953     let hir = tcx.hir();
 954     let msg = &format!("`{}` might need a bound for `{}`", lhs_ty, missing_trait);
 955     // Try to find the def-id and details for the parameter p. We have only the index,
 956     // so we have to find the enclosing function's def-id, then look through its declared
 957     // generic parameters to get the declaration.
 958     let def_id = hir.body_owner_def_id(hir::BodyId { hir_id: body_id });
 959     let generics = tcx.generics_of(def_id);
 960     let param_def_id = generics.type_param(&p, tcx).def_id;
 961     if let Some(generics) = param_def_id
 962         .as_local()
 963         .map(|id| hir.local_def_id_to_hir_id(id))
 964         .and_then(|id| hir.find(hir.get_parent_item(id)))
 965         .as_ref()
 966         .and_then(|node| node.generics())
 967     {
 968         let output = if set_output { format!("<Output = {}>", rhs_ty) } else { String::new() };
 969         suggest_constraining_type_param(
 970             tcx,
 971             generics,
 972             &mut err,
 973             &format!("{}", lhs_ty),
 974             &format!("{}{}", missing_trait, output),
 975             None,
 976         );
 977     } else {
 978         let span = tcx.def_span(param_def_id);
 979         err.span_label(span, msg);
 980     }
 981 }
 982
 983 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
 984
 985 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
 986     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 987         if let ty::Param(_) = ty.kind() {
 988             self.0.push(ty);
 989         }
 990         ty.super_visit_with(self)
 991     }
 992 }
 993
 994 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
 995
 996 impl TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
 997     fn tcx(&self) -> TyCtxt<'tcx> {
 998         self.0.tcx
 999     }
1000
1001     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1002         match ty.kind() {
1003             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
1004                 kind: TypeVariableOriginKind::MiscVariable,
1005                 span: self.1,
1006             }),
1007             _ => ty.super_fold_with(self),
1008         }
1009     }
1010 }