compiler/rustc_typeck/src/check/op.rs

   1 //! Code related to processing overloaded binary and unary operators.
   2
   3 use super::method::MethodCallee;
   4 use super::{has_expected_num_generic_args, FnCtxt};
   5 use crate::check::Expectation;
   6 use rustc_ast as ast;
   7 use rustc_errors::{self, struct_span_err, Applicability, Diagnostic};
   8 use rustc_hir as hir;
   9 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  10 use rustc_infer::traits::ObligationCauseCode;
  11 use rustc_middle::ty::adjustment::{
  12     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
  13 };
  14 use rustc_middle::ty::{
  15     self, Ty, TyCtxt, TypeFolder, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitor,
  16 };
  17 use rustc_span::source_map::Spanned;
  18 use rustc_span::symbol::{sym, Ident};
  19 use rustc_span::Span;
  20 use rustc_trait_selection::infer::InferCtxtExt;
  21 use rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt as _;
  22 use rustc_trait_selection::traits::{FulfillmentError, TraitEngine, TraitEngineExt};
  23 use rustc_type_ir::sty::TyKind::*;
  24
  25 use std::ops::ControlFlow;
  26
  27 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  28     /// Checks a `a <op>= b`
  29     pub fn check_binop_assign(
  30         &self,
  31         expr: &'tcx hir::Expr<'tcx>,
  32         op: hir::BinOp,
  33         lhs: &'tcx hir::Expr<'tcx>,
  34         rhs: &'tcx hir::Expr<'tcx>,
  35         expected: Expectation<'tcx>,
  36     ) -> Ty<'tcx> {
  37         let (lhs_ty, rhs_ty, return_ty) =
  38             self.check_overloaded_binop(expr, lhs, rhs, op, IsAssign::Yes, expected);
  39
  40         let ty =
  41             if !lhs_ty.is_ty_var() && !rhs_ty.is_ty_var() && is_builtin_binop(lhs_ty, rhs_ty, op) {
  42                 self.enforce_builtin_binop_types(lhs.span, lhs_ty, rhs.span, rhs_ty, op);
  43                 self.tcx.mk_unit()
  44             } else {
  45                 return_ty
  46             };
  47
  48         self.check_lhs_assignable(lhs, "E0067", op.span, |err| {
  49             if let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty) {
  50                 if self
  51                     .lookup_op_method(
  52                         lhs_deref_ty,
  53                         Some(rhs_ty),
  54                         Some(rhs),
  55                         Op::Binary(op, IsAssign::Yes),
  56                         expected,
  57                     )
  58                     .is_ok()
  59                 {
  60                     // If LHS += RHS is an error, but *LHS += RHS is successful, then we will have
  61                     // emitted a better suggestion during error handling in check_overloaded_binop.
  62                     if self
  63                         .lookup_op_method(
  64                             lhs_ty,
  65                             Some(rhs_ty),
  66                             Some(rhs),
  67                             Op::Binary(op, IsAssign::Yes),
  68                             expected,
  69                         )
  70                         .is_err()
  71                     {
  72                         err.downgrade_to_delayed_bug();
  73                     } else {
  74                         // Otherwise, it's valid to suggest dereferencing the LHS here.
  75                         err.span_suggestion_verbose(
  76                             lhs.span.shrink_to_lo(),
  77                             "consider dereferencing the left-hand side of this operation",
  78                             "*",
  79                             Applicability::MaybeIncorrect,
  80                         );
  81                     }
  82                 }
  83             }
  84         });
  85
  86         ty
  87     }
  88
  89     /// Checks a potentially overloaded binary operator.
  90     pub fn check_binop(
  91         &self,
  92         expr: &'tcx hir::Expr<'tcx>,
  93         op: hir::BinOp,
  94         lhs_expr: &'tcx hir::Expr<'tcx>,
  95         rhs_expr: &'tcx hir::Expr<'tcx>,
  96         expected: Expectation<'tcx>,
  97     ) -> Ty<'tcx> {
  98         let tcx = self.tcx;
  99
 100         debug!(
 101             "check_binop(expr.hir_id={}, expr={:?}, op={:?}, lhs_expr={:?}, rhs_expr={:?})",
 102             expr.hir_id, expr, op, lhs_expr, rhs_expr
 103         );
 104
 105         match BinOpCategory::from(op) {
 106             BinOpCategory::Shortcircuit => {
 107                 // && and || are a simple case.
 108                 self.check_expr_coercable_to_type(lhs_expr, tcx.types.bool, None);
 109                 let lhs_diverges = self.diverges.get();
 110                 self.check_expr_coercable_to_type(rhs_expr, tcx.types.bool, None);
 111
 112                 // Depending on the LHS' value, the RHS can never execute.
 113                 self.diverges.set(lhs_diverges);
 114
 115                 tcx.types.bool
 116             }
 117             _ => {
 118                 // Otherwise, we always treat operators as if they are
 119                 // overloaded. This is the way to be most flexible w/r/t
 120                 // types that get inferred.
 121                 let (lhs_ty, rhs_ty, return_ty) = self.check_overloaded_binop(
 122                     expr,
 123                     lhs_expr,
 124                     rhs_expr,
 125                     op,
 126                     IsAssign::No,
 127                     expected,
 128                 );
 129
 130                 // Supply type inference hints if relevant. Probably these
 131                 // hints should be enforced during select as part of the
 132                 // `consider_unification_despite_ambiguity` routine, but this
 133                 // more convenient for now.
 134                 //
 135                 // The basic idea is to help type inference by taking
 136                 // advantage of things we know about how the impls for
 137                 // scalar types are arranged. This is important in a
 138                 // scenario like `1_u32 << 2`, because it lets us quickly
 139                 // deduce that the result type should be `u32`, even
 140                 // though we don't know yet what type 2 has and hence
 141                 // can't pin this down to a specific impl.
 142                 if !lhs_ty.is_ty_var()
 143                     && !rhs_ty.is_ty_var()
 144                     && is_builtin_binop(lhs_ty, rhs_ty, op)
 145                 {
 146                     let builtin_return_ty = self.enforce_builtin_binop_types(
 147                         lhs_expr.span,
 148                         lhs_ty,
 149                         rhs_expr.span,
 150                         rhs_ty,
 151                         op,
 152                     );
 153                     self.demand_suptype(expr.span, builtin_return_ty, return_ty);
 154                 }
 155
 156                 return_ty
 157             }
 158         }
 159     }
 160
 161     fn enforce_builtin_binop_types(
 162         &self,
 163         lhs_span: Span,
 164         lhs_ty: Ty<'tcx>,
 165         rhs_span: Span,
 166         rhs_ty: Ty<'tcx>,
 167         op: hir::BinOp,
 168     ) -> Ty<'tcx> {
 169         debug_assert!(is_builtin_binop(lhs_ty, rhs_ty, op));
 170
 171         // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 172         // (See https://github.com/rust-lang/rust/issues/57447.)
 173         let (lhs_ty, rhs_ty) = (deref_ty_if_possible(lhs_ty), deref_ty_if_possible(rhs_ty));
 174
 175         let tcx = self.tcx;
 176         match BinOpCategory::from(op) {
 177             BinOpCategory::Shortcircuit => {
 178                 self.demand_suptype(lhs_span, tcx.types.bool, lhs_ty);
 179                 self.demand_suptype(rhs_span, tcx.types.bool, rhs_ty);
 180                 tcx.types.bool
 181             }
 182
 183             BinOpCategory::Shift => {
 184                 // result type is same as LHS always
 185                 lhs_ty
 186             }
 187
 188             BinOpCategory::Math | BinOpCategory::Bitwise => {
 189                 // both LHS and RHS and result will have the same type
 190                 self.demand_suptype(rhs_span, lhs_ty, rhs_ty);
 191                 lhs_ty
 192             }
 193
 194             BinOpCategory::Comparison => {
 195                 // both LHS and RHS and result will have the same type
 196                 self.demand_suptype(rhs_span, lhs_ty, rhs_ty);
 197                 tcx.types.bool
 198             }
 199         }
 200     }
 201
 202     fn check_overloaded_binop(
 203         &self,
 204         expr: &'tcx hir::Expr<'tcx>,
 205         lhs_expr: &'tcx hir::Expr<'tcx>,
 206         rhs_expr: &'tcx hir::Expr<'tcx>,
 207         op: hir::BinOp,
 208         is_assign: IsAssign,
 209         expected: Expectation<'tcx>,
 210     ) -> (Ty<'tcx>, Ty<'tcx>, Ty<'tcx>) {
 211         debug!(
 212             "check_overloaded_binop(expr.hir_id={}, op={:?}, is_assign={:?})",
 213             expr.hir_id, op, is_assign
 214         );
 215
 216         let lhs_ty = match is_assign {
 217             IsAssign::No => {
 218                 // Find a suitable supertype of the LHS expression's type, by coercing to
 219                 // a type variable, to pass as the `Self` to the trait, avoiding invariant
 220                 // trait matching creating lifetime constraints that are too strict.
 221                 // e.g., adding `&'a T` and `&'b T`, given `&'x T: Add<&'x T>`, will result
 222                 // in `&'a T <: &'x T` and `&'b T <: &'x T`, instead of `'a = 'b = 'x`.
 223                 let lhs_ty = self.check_expr(lhs_expr);
 224                 let fresh_var = self.next_ty_var(TypeVariableOrigin {
 225                     kind: TypeVariableOriginKind::MiscVariable,
 226                     span: lhs_expr.span,
 227                 });
 228                 self.demand_coerce(lhs_expr, lhs_ty, fresh_var, Some(rhs_expr), AllowTwoPhase::No)
 229             }
 230             IsAssign::Yes => {
 231                 // rust-lang/rust#52126: We have to use strict
 232                 // equivalence on the LHS of an assign-op like `+=`;
 233                 // overwritten or mutably-borrowed places cannot be
 234                 // coerced to a supertype.
 235                 self.check_expr(lhs_expr)
 236             }
 237         };
 238         let lhs_ty = self.resolve_vars_with_obligations(lhs_ty);
 239
 240         // N.B., as we have not yet type-checked the RHS, we don't have the
 241         // type at hand. Make a variable to represent it. The whole reason
 242         // for this indirection is so that, below, we can check the expr
 243         // using this variable as the expected type, which sometimes lets
 244         // us do better coercions than we would be able to do otherwise,
 245         // particularly for things like `String + &String`.
 246         let rhs_ty_var = self.next_ty_var(TypeVariableOrigin {
 247             kind: TypeVariableOriginKind::MiscVariable,
 248             span: rhs_expr.span,
 249         });
 250
 251         let result = self.lookup_op_method(
 252             lhs_ty,
 253             Some(rhs_ty_var),
 254             Some(rhs_expr),
 255             Op::Binary(op, is_assign),
 256             expected,
 257         );
 258
 259         // see `NB` above
 260         let rhs_ty = self.check_expr_coercable_to_type(rhs_expr, rhs_ty_var, Some(lhs_expr));
 261         let rhs_ty = self.resolve_vars_with_obligations(rhs_ty);
 262
 263         let return_ty = match result {
 264             Ok(method) => {
 265                 let by_ref_binop = !op.node.is_by_value();
 266                 if is_assign == IsAssign::Yes || by_ref_binop {
 267                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[0].kind() {
 268                         let mutbl = match mutbl {
 269                             hir::Mutability::Not => AutoBorrowMutability::Not,
 270                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 271                                 // Allow two-phase borrows for binops in initial deployment
 272                                 // since they desugar to methods
 273                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 274                             },
 275                         };
 276                         let autoref = Adjustment {
 277                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 278                             target: method.sig.inputs()[0],
 279                         };
 280                         self.apply_adjustments(lhs_expr, vec![autoref]);
 281                     }
 282                 }
 283                 if by_ref_binop {
 284                     if let ty::Ref(region, _, mutbl) = method.sig.inputs()[1].kind() {
 285                         let mutbl = match mutbl {
 286                             hir::Mutability::Not => AutoBorrowMutability::Not,
 287                             hir::Mutability::Mut => AutoBorrowMutability::Mut {
 288                                 // Allow two-phase borrows for binops in initial deployment
 289                                 // since they desugar to methods
 290                                 allow_two_phase_borrow: AllowTwoPhase::Yes,
 291                             },
 292                         };
 293                         let autoref = Adjustment {
 294                             kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
 295                             target: method.sig.inputs()[1],
 296                         };
 297                         // HACK(eddyb) Bypass checks due to reborrows being in
 298                         // some cases applied on the RHS, on top of which we need
 299                         // to autoref, which is not allowed by apply_adjustments.
 300                         // self.apply_adjustments(rhs_expr, vec![autoref]);
 301                         self.typeck_results
 302                             .borrow_mut()
 303                             .adjustments_mut()
 304                             .entry(rhs_expr.hir_id)
 305                             .or_default()
 306                             .push(autoref);
 307                     }
 308                 }
 309                 self.write_method_call(expr.hir_id, method);
 310
 311                 method.sig.output()
 312             }
 313             // error types are considered "builtin"
 314             Err(_) if lhs_ty.references_error() || rhs_ty.references_error() => self.tcx.ty_error(),
 315             Err(errors) => {
 316                 let source_map = self.tcx.sess.source_map();
 317                 let (mut err, missing_trait, use_output) = match is_assign {
 318                     IsAssign::Yes => {
 319                         let mut err = struct_span_err!(
 320                             self.tcx.sess,
 321                             expr.span,
 322                             E0368,
 323                             "binary assignment operation `{}=` cannot be applied to type `{}`",
 324                             op.node.as_str(),
 325                             lhs_ty,
 326                         );
 327                         err.span_label(
 328                             lhs_expr.span,
 329                             format!("cannot use `{}=` on type `{}`", op.node.as_str(), lhs_ty),
 330                         );
 331                         let missing_trait = match op.node {
 332                             hir::BinOpKind::Add => Some("std::ops::AddAssign"),
 333                             hir::BinOpKind::Sub => Some("std::ops::SubAssign"),
 334                             hir::BinOpKind::Mul => Some("std::ops::MulAssign"),
 335                             hir::BinOpKind::Div => Some("std::ops::DivAssign"),
 336                             hir::BinOpKind::Rem => Some("std::ops::RemAssign"),
 337                             hir::BinOpKind::BitAnd => Some("std::ops::BitAndAssign"),
 338                             hir::BinOpKind::BitXor => Some("std::ops::BitXorAssign"),
 339                             hir::BinOpKind::BitOr => Some("std::ops::BitOrAssign"),
 340                             hir::BinOpKind::Shl => Some("std::ops::ShlAssign"),
 341                             hir::BinOpKind::Shr => Some("std::ops::ShrAssign"),
 342                             _ => None,
 343                         };
 344                         self.note_unmet_impls_on_type(&mut err, errors);
 345                         (err, missing_trait, false)
 346                     }
 347                     IsAssign::No => {
 348                         let (message, missing_trait, use_output) = match op.node {
 349                             hir::BinOpKind::Add => (
 350                                 format!("cannot add `{rhs_ty}` to `{lhs_ty}`"),
 351                                 Some("std::ops::Add"),
 352                                 true,
 353                             ),
 354                             hir::BinOpKind::Sub => (
 355                                 format!("cannot subtract `{rhs_ty}` from `{lhs_ty}`"),
 356                                 Some("std::ops::Sub"),
 357                                 true,
 358                             ),
 359                             hir::BinOpKind::Mul => (
 360                                 format!("cannot multiply `{lhs_ty}` by `{rhs_ty}`"),
 361                                 Some("std::ops::Mul"),
 362                                 true,
 363                             ),
 364                             hir::BinOpKind::Div => (
 365                                 format!("cannot divide `{lhs_ty}` by `{rhs_ty}`"),
 366                                 Some("std::ops::Div"),
 367                                 true,
 368                             ),
 369                             hir::BinOpKind::Rem => (
 370                                 format!("cannot mod `{lhs_ty}` by `{rhs_ty}`"),
 371                                 Some("std::ops::Rem"),
 372                                 true,
 373                             ),
 374                             hir::BinOpKind::BitAnd => (
 375                                 format!("no implementation for `{lhs_ty} & {rhs_ty}`"),
 376                                 Some("std::ops::BitAnd"),
 377                                 true,
 378                             ),
 379                             hir::BinOpKind::BitXor => (
 380                                 format!("no implementation for `{lhs_ty} ^ {rhs_ty}`"),
 381                                 Some("std::ops::BitXor"),
 382                                 true,
 383                             ),
 384                             hir::BinOpKind::BitOr => (
 385                                 format!("no implementation for `{lhs_ty} | {rhs_ty}`"),
 386                                 Some("std::ops::BitOr"),
 387                                 true,
 388                             ),
 389                             hir::BinOpKind::Shl => (
 390                                 format!("no implementation for `{lhs_ty} << {rhs_ty}`"),
 391                                 Some("std::ops::Shl"),
 392                                 true,
 393                             ),
 394                             hir::BinOpKind::Shr => (
 395                                 format!("no implementation for `{lhs_ty} >> {rhs_ty}`"),
 396                                 Some("std::ops::Shr"),
 397                                 true,
 398                             ),
 399                             hir::BinOpKind::Eq | hir::BinOpKind::Ne => (
 400                                 format!(
 401                                     "binary operation `{}` cannot be applied to type `{}`",
 402                                     op.node.as_str(),
 403                                     lhs_ty
 404                                 ),
 405                                 Some("std::cmp::PartialEq"),
 406                                 false,
 407                             ),
 408                             hir::BinOpKind::Lt
 409                             | hir::BinOpKind::Le
 410                             | hir::BinOpKind::Gt
 411                             | hir::BinOpKind::Ge => (
 412                                 format!(
 413                                     "binary operation `{}` cannot be applied to type `{}`",
 414                                     op.node.as_str(),
 415                                     lhs_ty
 416                                 ),
 417                                 Some("std::cmp::PartialOrd"),
 418                                 false,
 419                             ),
 420                             _ => (
 421                                 format!(
 422                                     "binary operation `{}` cannot be applied to type `{}`",
 423                                     op.node.as_str(),
 424                                     lhs_ty
 425                                 ),
 426                                 None,
 427                                 false,
 428                             ),
 429                         };
 430                         let mut err = struct_span_err!(self.tcx.sess, op.span, E0369, "{message}");
 431                         if !lhs_expr.span.eq(&rhs_expr.span) {
 432                             err.span_label(lhs_expr.span, lhs_ty.to_string());
 433                             err.span_label(rhs_expr.span, rhs_ty.to_string());
 434                         }
 435                         self.note_unmet_impls_on_type(&mut err, errors);
 436                         (err, missing_trait, use_output)
 437                     }
 438                 };
 439
 440                 let mut suggest_deref_binop = |lhs_deref_ty: Ty<'tcx>| {
 441                     if self
 442                         .lookup_op_method(
 443                             lhs_deref_ty,
 444                             Some(rhs_ty),
 445                             Some(rhs_expr),
 446                             Op::Binary(op, is_assign),
 447                             expected,
 448                         )
 449                         .is_ok()
 450                     {
 451                         if let Ok(lstring) = source_map.span_to_snippet(lhs_expr.span) {
 452                             let msg = &format!(
 453                                 "`{}{}` can be used on `{}`, you can dereference `{}`",
 454                                 op.node.as_str(),
 455                                 match is_assign {
 456                                     IsAssign::Yes => "=",
 457                                     IsAssign::No => "",
 458                                 },
 459                                 lhs_deref_ty.peel_refs(),
 460                                 lstring,
 461                             );
 462                             err.span_suggestion_verbose(
 463                                 lhs_expr.span.shrink_to_lo(),
 464                                 msg,
 465                                 "*",
 466                                 rustc_errors::Applicability::MachineApplicable,
 467                             );
 468                         }
 469                     }
 470                 };
 471
 472                 let is_compatible = |lhs_ty, rhs_ty| {
 473                     self.lookup_op_method(
 474                         lhs_ty,
 475                         Some(rhs_ty),
 476                         Some(rhs_expr),
 477                         Op::Binary(op, is_assign),
 478                         expected,
 479                     )
 480                     .is_ok()
 481                 };
 482
 483                 // We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
 484                 // `a += b` => `*a += b` if a is a mut ref.
 485                 if !op.span.can_be_used_for_suggestions() {
 486                     // Suppress suggestions when lhs and rhs are not in the same span as the error
 487                 } else if is_assign == IsAssign::Yes
 488                     && let Some(lhs_deref_ty) = self.deref_once_mutably_for_diagnostic(lhs_ty)
 489                 {
 490                     suggest_deref_binop(lhs_deref_ty);
 491                 } else if is_assign == IsAssign::No
 492                     && let Ref(_, lhs_deref_ty, _) = lhs_ty.kind()
 493                 {
 494                     if self.type_is_copy_modulo_regions(
 495                         self.param_env,
 496                         *lhs_deref_ty,
 497                         lhs_expr.span,
 498                     ) {
 499                         suggest_deref_binop(*lhs_deref_ty);
 500                     }
 501                 } else if self.suggest_fn_call(&mut err, lhs_expr, lhs_ty, |lhs_ty| {
 502                     is_compatible(lhs_ty, rhs_ty)
 503                 }) || self.suggest_fn_call(&mut err, rhs_expr, rhs_ty, |rhs_ty| {
 504                     is_compatible(lhs_ty, rhs_ty)
 505                 }) || self.suggest_two_fn_call(
 506                     &mut err,
 507                     rhs_expr,
 508                     rhs_ty,
 509                     lhs_expr,
 510                     lhs_ty,
 511                     |lhs_ty, rhs_ty| is_compatible(lhs_ty, rhs_ty),
 512                 ) {
 513                     // Cool
 514                 }
 515
 516                 if let Some(missing_trait) = missing_trait {
 517                     let mut visitor = TypeParamVisitor(vec![]);
 518                     visitor.visit_ty(lhs_ty);
 519
 520                     if op.node == hir::BinOpKind::Add
 521                         && self.check_str_addition(
 522                             lhs_expr, rhs_expr, lhs_ty, rhs_ty, &mut err, is_assign, op,
 523                         )
 524                     {
 525                         // This has nothing here because it means we did string
 526                         // concatenation (e.g., "Hello " + "World!"). This means
 527                         // we don't want the note in the else clause to be emitted
 528                     } else if let [ty] = &visitor.0[..] {
 529                         // Look for a TraitPredicate in the Fulfillment errors,
 530                         // and use it to generate a suggestion.
 531                         //
 532                         // Note that lookup_op_method must be called again but
 533                         // with a specific rhs_ty instead of a placeholder so
 534                         // the resulting predicate generates a more specific
 535                         // suggestion for the user.
 536                         let errors = self
 537                             .lookup_op_method(
 538                                 lhs_ty,
 539                                 Some(rhs_ty),
 540                                 Some(rhs_expr),
 541                                 Op::Binary(op, is_assign),
 542                                 expected,
 543                             )
 544                             .unwrap_err();
 545                         if !errors.is_empty() {
 546                             for error in errors {
 547                                 if let Some(trait_pred) =
 548                                     error.obligation.predicate.to_opt_poly_trait_pred()
 549                                 {
 550                                     let proj_pred = match error.obligation.cause.code() {
 551                                         ObligationCauseCode::BinOp {
 552                                             output_pred: Some(output_pred),
 553                                             ..
 554                                         } if use_output => {
 555                                             output_pred.to_opt_poly_projection_pred()
 556                                         }
 557                                         _ => None,
 558                                     };
 559
 560                                     self.suggest_restricting_param_bound(
 561                                         &mut err,
 562                                         trait_pred,
 563                                         proj_pred,
 564                                         self.body_id,
 565                                     );
 566                                 }
 567                             }
 568                         } else if *ty != lhs_ty {
 569                             // When we know that a missing bound is responsible, we don't show
 570                             // this note as it is redundant.
 571                             err.note(&format!(
 572                                 "the trait `{missing_trait}` is not implemented for `{lhs_ty}`"
 573                             ));
 574                         }
 575                     }
 576                 }
 577                 err.emit();
 578                 self.tcx.ty_error()
 579             }
 580         };
 581
 582         (lhs_ty, rhs_ty, return_ty)
 583     }
 584
 585     /// Provide actionable suggestions when trying to add two strings with incorrect types,
 586     /// like `&str + &str`, `String + String` and `&str + &String`.
 587     ///
 588     /// If this function returns `true` it means a note was printed, so we don't need
 589     /// to print the normal "implementation of `std::ops::Add` might be missing" note
 590     fn check_str_addition(
 591         &self,
 592         lhs_expr: &'tcx hir::Expr<'tcx>,
 593         rhs_expr: &'tcx hir::Expr<'tcx>,
 594         lhs_ty: Ty<'tcx>,
 595         rhs_ty: Ty<'tcx>,
 596         err: &mut Diagnostic,
 597         is_assign: IsAssign,
 598         op: hir::BinOp,
 599     ) -> bool {
 600         let str_concat_note = "string concatenation requires an owned `String` on the left";
 601         let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
 602         let to_owned_msg = "create an owned `String` from a string reference";
 603
 604         let is_std_string = |ty: Ty<'tcx>| {
 605             ty.ty_adt_def()
 606                 .map_or(false, |ty_def| self.tcx.is_diagnostic_item(sym::String, ty_def.did()))
 607         };
 608
 609         match (lhs_ty.kind(), rhs_ty.kind()) {
 610             (&Ref(_, l_ty, _), &Ref(_, r_ty, _)) // &str or &String + &str, &String or &&str
 611                 if (*l_ty.kind() == Str || is_std_string(l_ty))
 612                     && (*r_ty.kind() == Str
 613                         || is_std_string(r_ty)
 614                         || matches!(
 615                             r_ty.kind(), Ref(_, inner_ty, _) if *inner_ty.kind() == Str
 616                         )) =>
 617             {
 618                 if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
 619                     err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
 620                     err.note(str_concat_note);
 621                     if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 622                         err.span_suggestion_verbose(
 623                             lhs_expr.span.until(lhs_inner_expr.span),
 624                             rm_borrow_msg,
 625                             "",
 626                             Applicability::MachineApplicable
 627                         );
 628                     } else {
 629                         err.span_suggestion_verbose(
 630                             lhs_expr.span.shrink_to_hi(),
 631                             to_owned_msg,
 632                             ".to_owned()",
 633                             Applicability::MachineApplicable
 634                         );
 635                     }
 636                 }
 637                 true
 638             }
 639             (&Ref(_, l_ty, _), &Adt(..)) // Handle `&str` & `&String` + `String`
 640                 if (*l_ty.kind() == Str || is_std_string(l_ty)) && is_std_string(rhs_ty) =>
 641             {
 642                 err.span_label(
 643                     op.span,
 644                     "`+` cannot be used to concatenate a `&str` with a `String`",
 645                 );
 646                 match is_assign {
 647                     IsAssign::No => {
 648                         let sugg_msg;
 649                         let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
 650                             sugg_msg = "remove the borrow on the left and add one on the right";
 651                             (lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
 652                         } else {
 653                             sugg_msg = "create an owned `String` on the left and add a borrow on the right";
 654                             (lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
 655                         };
 656                         let suggestions = vec![
 657                             lhs_sugg,
 658                             (rhs_expr.span.shrink_to_lo(), "&".to_owned()),
 659                         ];
 660                         err.multipart_suggestion_verbose(
 661                             sugg_msg,
 662                             suggestions,
 663                             Applicability::MachineApplicable,
 664                         );
 665                     }
 666                     IsAssign::Yes => {
 667                         err.note(str_concat_note);
 668                     }
 669                 }
 670                 true
 671             }
 672             _ => false,
 673         }
 674     }
 675
 676     pub fn check_user_unop(
 677         &self,
 678         ex: &'tcx hir::Expr<'tcx>,
 679         operand_ty: Ty<'tcx>,
 680         op: hir::UnOp,
 681         expected: Expectation<'tcx>,
 682     ) -> Ty<'tcx> {
 683         assert!(op.is_by_value());
 684         match self.lookup_op_method(operand_ty, None, None, Op::Unary(op, ex.span), expected) {
 685             Ok(method) => {
 686                 self.write_method_call(ex.hir_id, method);
 687                 method.sig.output()
 688             }
 689             Err(errors) => {
 690                 let actual = self.resolve_vars_if_possible(operand_ty);
 691                 if !actual.references_error() {
 692                     let mut err = struct_span_err!(
 693                         self.tcx.sess,
 694                         ex.span,
 695                         E0600,
 696                         "cannot apply unary operator `{}` to type `{}`",
 697                         op.as_str(),
 698                         actual
 699                     );
 700                     err.span_label(
 701                         ex.span,
 702                         format!("cannot apply unary operator `{}`", op.as_str()),
 703                     );
 704
 705                     let mut visitor = TypeParamVisitor(vec![]);
 706                     visitor.visit_ty(operand_ty);
 707                     if let [_] = &visitor.0[..] && let ty::Param(_) = *operand_ty.kind() {
 708                         let predicates = errors
 709                             .iter()
 710                             .filter_map(|error| {
 711                                 error.obligation.predicate.to_opt_poly_trait_pred()
 712                             });
 713                         for pred in predicates {
 714                             self.suggest_restricting_param_bound(
 715                                 &mut err,
 716                                 pred,
 717                                 None,
 718                                 self.body_id,
 719                             );
 720                         }
 721                     }
 722
 723                     let sp = self.tcx.sess.source_map().start_point(ex.span);
 724                     if let Some(sp) =
 725                         self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
 726                     {
 727                         // If the previous expression was a block expression, suggest parentheses
 728                         // (turning this into a binary subtraction operation instead.)
 729                         // for example, `{2} - 2` -> `({2}) - 2` (see src\test\ui\parser\expr-as-stmt.rs)
 730                         self.tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp);
 731                     } else {
 732                         match actual.kind() {
 733                             Uint(_) if op == hir::UnOp::Neg => {
 734                                 err.note("unsigned values cannot be negated");
 735
 736                                 if let hir::ExprKind::Unary(
 737                                     _,
 738                                     hir::Expr {
 739                                         kind:
 740                                             hir::ExprKind::Lit(Spanned {
 741                                                 node: ast::LitKind::Int(1, _),
 742                                                 ..
 743                                             }),
 744                                         ..
 745                                     },
 746                                 ) = ex.kind
 747                                 {
 748                                     err.span_suggestion(
 749                                         ex.span,
 750                                         &format!(
 751                                             "you may have meant the maximum value of `{actual}`",
 752                                         ),
 753                                         format!("{actual}::MAX"),
 754                                         Applicability::MaybeIncorrect,
 755                                     );
 756                                 }
 757                             }
 758                             Str | Never | Char | Tuple(_) | Array(_, _) => {}
 759                             Ref(_, lty, _) if *lty.kind() == Str => {}
 760                             _ => {
 761                                 self.note_unmet_impls_on_type(&mut err, errors);
 762                             }
 763                         }
 764                     }
 765                     err.emit();
 766                 }
 767                 self.tcx.ty_error()
 768             }
 769         }
 770     }
 771
 772     fn lookup_op_method(
 773         &self,
 774         lhs_ty: Ty<'tcx>,
 775         other_ty: Option<Ty<'tcx>>,
 776         other_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
 777         op: Op,
 778         expected: Expectation<'tcx>,
 779     ) -> Result<MethodCallee<'tcx>, Vec<FulfillmentError<'tcx>>> {
 780         let lang = self.tcx.lang_items();
 781
 782         let span = match op {
 783             Op::Binary(op, _) => op.span,
 784             Op::Unary(_, span) => span,
 785         };
 786         let (opname, trait_did) = if let Op::Binary(op, IsAssign::Yes) = op {
 787             match op.node {
 788                 hir::BinOpKind::Add => (sym::add_assign, lang.add_assign_trait()),
 789                 hir::BinOpKind::Sub => (sym::sub_assign, lang.sub_assign_trait()),
 790                 hir::BinOpKind::Mul => (sym::mul_assign, lang.mul_assign_trait()),
 791                 hir::BinOpKind::Div => (sym::div_assign, lang.div_assign_trait()),
 792                 hir::BinOpKind::Rem => (sym::rem_assign, lang.rem_assign_trait()),
 793                 hir::BinOpKind::BitXor => (sym::bitxor_assign, lang.bitxor_assign_trait()),
 794                 hir::BinOpKind::BitAnd => (sym::bitand_assign, lang.bitand_assign_trait()),
 795                 hir::BinOpKind::BitOr => (sym::bitor_assign, lang.bitor_assign_trait()),
 796                 hir::BinOpKind::Shl => (sym::shl_assign, lang.shl_assign_trait()),
 797                 hir::BinOpKind::Shr => (sym::shr_assign, lang.shr_assign_trait()),
 798                 hir::BinOpKind::Lt
 799                 | hir::BinOpKind::Le
 800                 | hir::BinOpKind::Ge
 801                 | hir::BinOpKind::Gt
 802                 | hir::BinOpKind::Eq
 803                 | hir::BinOpKind::Ne
 804                 | hir::BinOpKind::And
 805                 | hir::BinOpKind::Or => {
 806                     span_bug!(span, "impossible assignment operation: {}=", op.node.as_str())
 807                 }
 808             }
 809         } else if let Op::Binary(op, IsAssign::No) = op {
 810             match op.node {
 811                 hir::BinOpKind::Add => (sym::add, lang.add_trait()),
 812                 hir::BinOpKind::Sub => (sym::sub, lang.sub_trait()),
 813                 hir::BinOpKind::Mul => (sym::mul, lang.mul_trait()),
 814                 hir::BinOpKind::Div => (sym::div, lang.div_trait()),
 815                 hir::BinOpKind::Rem => (sym::rem, lang.rem_trait()),
 816                 hir::BinOpKind::BitXor => (sym::bitxor, lang.bitxor_trait()),
 817                 hir::BinOpKind::BitAnd => (sym::bitand, lang.bitand_trait()),
 818                 hir::BinOpKind::BitOr => (sym::bitor, lang.bitor_trait()),
 819                 hir::BinOpKind::Shl => (sym::shl, lang.shl_trait()),
 820                 hir::BinOpKind::Shr => (sym::shr, lang.shr_trait()),
 821                 hir::BinOpKind::Lt => (sym::lt, lang.partial_ord_trait()),
 822                 hir::BinOpKind::Le => (sym::le, lang.partial_ord_trait()),
 823                 hir::BinOpKind::Ge => (sym::ge, lang.partial_ord_trait()),
 824                 hir::BinOpKind::Gt => (sym::gt, lang.partial_ord_trait()),
 825                 hir::BinOpKind::Eq => (sym::eq, lang.eq_trait()),
 826                 hir::BinOpKind::Ne => (sym::ne, lang.eq_trait()),
 827                 hir::BinOpKind::And | hir::BinOpKind::Or => {
 828                     span_bug!(span, "&& and || are not overloadable")
 829                 }
 830             }
 831         } else if let Op::Unary(hir::UnOp::Not, _) = op {
 832             (sym::not, lang.not_trait())
 833         } else if let Op::Unary(hir::UnOp::Neg, _) = op {
 834             (sym::neg, lang.neg_trait())
 835         } else {
 836             bug!("lookup_op_method: op not supported: {:?}", op)
 837         };
 838
 839         debug!(
 840             "lookup_op_method(lhs_ty={:?}, op={:?}, opname={:?}, trait_did={:?})",
 841             lhs_ty, op, opname, trait_did
 842         );
 843
 844         // Catches cases like #83893, where a lang item is declared with the
 845         // wrong number of generic arguments. Should have yielded an error
 846         // elsewhere by now, but we have to catch it here so that we do not
 847         // index `other_tys` out of bounds (if the lang item has too many
 848         // generic arguments, `other_tys` is too short).
 849         if !has_expected_num_generic_args(
 850             self.tcx,
 851             trait_did,
 852             match op {
 853                 // Binary ops have a generic right-hand side, unary ops don't
 854                 Op::Binary(..) => 1,
 855                 Op::Unary(..) => 0,
 856             },
 857         ) {
 858             return Err(vec![]);
 859         }
 860
 861         let opname = Ident::with_dummy_span(opname);
 862         let method = trait_did.and_then(|trait_did| {
 863             self.lookup_op_method_in_trait(
 864                 span,
 865                 opname,
 866                 trait_did,
 867                 lhs_ty,
 868                 other_ty,
 869                 other_ty_expr,
 870                 expected,
 871             )
 872         });
 873
 874         match (method, trait_did) {
 875             (Some(ok), _) => {
 876                 let method = self.register_infer_ok_obligations(ok);
 877                 self.select_obligations_where_possible(false, |_| {});
 878                 Ok(method)
 879             }
 880             (None, None) => Err(vec![]),
 881             (None, Some(trait_did)) => {
 882                 let (obligation, _) = self.obligation_for_op_method(
 883                     span,
 884                     trait_did,
 885                     lhs_ty,
 886                     other_ty,
 887                     other_ty_expr,
 888                     expected,
 889                 );
 890                 let mut fulfill = <dyn TraitEngine<'_>>::new(self.tcx);
 891                 fulfill.register_predicate_obligation(self, obligation);
 892                 Err(fulfill.select_where_possible(&self.infcx))
 893             }
 894         }
 895     }
 896 }
 897
 898 // Binary operator categories. These categories summarize the behavior
 899 // with respect to the builtin operations supported.
 900 enum BinOpCategory {
 901     /// &&, || -- cannot be overridden
 902     Shortcircuit,
 903
 904     /// <<, >> -- when shifting a single integer, rhs can be any
 905     /// integer type. For simd, types must match.
 906     Shift,
 907
 908     /// +, -, etc -- takes equal types, produces same type as input,
 909     /// applicable to ints/floats/simd
 910     Math,
 911
 912     /// &, |, ^ -- takes equal types, produces same type as input,
 913     /// applicable to ints/floats/simd/bool
 914     Bitwise,
 915
 916     /// ==, !=, etc -- takes equal types, produces bools, except for simd,
 917     /// which produce the input type
 918     Comparison,
 919 }
 920
 921 impl BinOpCategory {
 922     fn from(op: hir::BinOp) -> BinOpCategory {
 923         match op.node {
 924             hir::BinOpKind::Shl | hir::BinOpKind::Shr => BinOpCategory::Shift,
 925
 926             hir::BinOpKind::Add
 927             | hir::BinOpKind::Sub
 928             | hir::BinOpKind::Mul
 929             | hir::BinOpKind::Div
 930             | hir::BinOpKind::Rem => BinOpCategory::Math,
 931
 932             hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => {
 933                 BinOpCategory::Bitwise
 934             }
 935
 936             hir::BinOpKind::Eq
 937             | hir::BinOpKind::Ne
 938             | hir::BinOpKind::Lt
 939             | hir::BinOpKind::Le
 940             | hir::BinOpKind::Ge
 941             | hir::BinOpKind::Gt => BinOpCategory::Comparison,
 942
 943             hir::BinOpKind::And | hir::BinOpKind::Or => BinOpCategory::Shortcircuit,
 944         }
 945     }
 946 }
 947
 948 /// Whether the binary operation is an assignment (`a += b`), or not (`a + b`)
 949 #[derive(Clone, Copy, Debug, PartialEq)]
 950 enum IsAssign {
 951     No,
 952     Yes,
 953 }
 954
 955 #[derive(Clone, Copy, Debug)]
 956 enum Op {
 957     Binary(hir::BinOp, IsAssign),
 958     Unary(hir::UnOp, Span),
 959 }
 960
 961 /// Dereferences a single level of immutable referencing.
 962 fn deref_ty_if_possible<'tcx>(ty: Ty<'tcx>) -> Ty<'tcx> {
 963     match ty.kind() {
 964         ty::Ref(_, ty, hir::Mutability::Not) => *ty,
 965         _ => ty,
 966     }
 967 }
 968
 969 /// Returns `true` if this is a built-in arithmetic operation (e.g., u32
 970 /// + u32, i16x4 == i16x4) and false if these types would have to be
 971 /// overloaded to be legal. There are two reasons that we distinguish
 972 /// builtin operations from overloaded ones (vs trying to drive
 973 /// everything uniformly through the trait system and intrinsics or
 974 /// something like that):
 975 ///
 976 /// 1. Builtin operations can trivially be evaluated in constants.
 977 /// 2. For comparison operators applied to SIMD types the result is
 978 ///    not of type `bool`. For example, `i16x4 == i16x4` yields a
 979 ///    type like `i16x4`. This means that the overloaded trait
 980 ///    `PartialEq` is not applicable.
 981 ///
 982 /// Reason #2 is the killer. I tried for a while to always use
 983 /// overloaded logic and just check the types in constants/codegen after
 984 /// the fact, and it worked fine, except for SIMD types. -nmatsakis
 985 fn is_builtin_binop<'tcx>(lhs: Ty<'tcx>, rhs: Ty<'tcx>, op: hir::BinOp) -> bool {
 986     // Special-case a single layer of referencing, so that things like `5.0 + &6.0f32` work.
 987     // (See https://github.com/rust-lang/rust/issues/57447.)
 988     let (lhs, rhs) = (deref_ty_if_possible(lhs), deref_ty_if_possible(rhs));
 989
 990     match BinOpCategory::from(op) {
 991         BinOpCategory::Shortcircuit => true,
 992
 993         BinOpCategory::Shift => {
 994             lhs.references_error()
 995                 || rhs.references_error()
 996                 || lhs.is_integral() && rhs.is_integral()
 997         }
 998
 999         BinOpCategory::Math => {
1000             lhs.references_error()
1001                 || rhs.references_error()
1002                 || lhs.is_integral() && rhs.is_integral()
1003                 || lhs.is_floating_point() && rhs.is_floating_point()
1004         }
1005
1006         BinOpCategory::Bitwise => {
1007             lhs.references_error()
1008                 || rhs.references_error()
1009                 || lhs.is_integral() && rhs.is_integral()
1010                 || lhs.is_floating_point() && rhs.is_floating_point()
1011                 || lhs.is_bool() && rhs.is_bool()
1012         }
1013
1014         BinOpCategory::Comparison => {
1015             lhs.references_error() || rhs.references_error() || lhs.is_scalar() && rhs.is_scalar()
1016         }
1017     }
1018 }
1019
1020 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
1021
1022 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
1023     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1024         if let ty::Param(_) = ty.kind() {
1025             self.0.push(ty);
1026         }
1027         ty.super_visit_with(self)
1028     }
1029 }
1030
1031 struct TypeParamEraser<'a, 'tcx>(&'a FnCtxt<'a, 'tcx>, Span);
1032
1033 impl<'tcx> TypeFolder<'tcx> for TypeParamEraser<'_, 'tcx> {
1034     fn tcx(&self) -> TyCtxt<'tcx> {
1035         self.0.tcx
1036     }
1037
1038     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
1039         match ty.kind() {
1040             ty::Param(_) => self.0.next_ty_var(TypeVariableOrigin {
1041                 kind: TypeVariableOriginKind::MiscVariable,
1042                 span: self.1,
1043             }),
1044             _ => ty.super_fold_with(self),
1045         }
1046     }
1047 }