crates/hir_ty/src/infer/expr.rs

   1 //! Type inference for expressions.
   2
   3 use std::{
   4     collections::hash_map::Entry,
   5     iter::{repeat, repeat_with},
   6     mem,
   7     sync::Arc,
   8 };
   9
  10 use chalk_ir::{
  11     cast::Cast, fold::Shift, DebruijnIndex, GenericArgData, Mutability, TyVariableKind,
  12 };
  13 use hir_def::{
  14     expr::{ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, Ordering, Statement, UnaryOp},
  15     generics::TypeOrConstParamData,
  16     path::{GenericArg, GenericArgs},
  17     resolver::resolver_for_expr,
  18     ConstParamId, FieldId, FunctionId, ItemContainerId, Lookup,
  19 };
  20 use hir_expand::name::{name, Name};
  21 use stdx::always;
  22 use syntax::ast::RangeOp;
  23
  24 use crate::{
  25     autoderef::{self, Autoderef},
  26     consteval,
  27     infer::coerce::CoerceMany,
  28     lower::{
  29         const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
  30     },
  31     mapping::from_chalk,
  32     method_resolution,
  33     primitive::{self, UintTy},
  34     static_lifetime, to_chalk_trait_id,
  35     utils::{generics, Generics},
  36     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, Interner, Rawness, Scalar,
  37     Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  38 };
  39
  40 use super::{
  41     coerce::auto_deref_adjust_steps, find_breakable, BindingMode, BreakableContext, Diverges,
  42     Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch,
  43 };
  44
  45 impl<'a> InferenceContext<'a> {
  46     pub(crate) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  47         let ty = self.infer_expr_inner(tgt_expr, expected);
  48         if self.resolve_ty_shallow(&ty).is_never() {
  49             // Any expression that produces a value of type `!` must have diverged
  50             self.diverges = Diverges::Always;
  51         }
  52         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  53             let could_unify = self.unify(&ty, &expected_ty);
  54             if !could_unify {
  55                 self.result.type_mismatches.insert(
  56                     tgt_expr.into(),
  57                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  58                 );
  59             }
  60         }
  61         ty
  62     }
  63
  64     /// Infer type of expression with possibly implicit coerce to the expected type.
  65     /// Return the type after possible coercion.
  66     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  67         let ty = self.infer_expr_inner(expr, expected);
  68         if let Some(target) = expected.only_has_type(&mut self.table) {
  69             match self.coerce(Some(expr), &ty, &target) {
  70                 Ok(res) => res.value,
  71                 Err(_) => {
  72                     self.result
  73                         .type_mismatches
  74                         .insert(expr.into(), TypeMismatch { expected: target, actual: ty.clone() });
  75                     // Return actual type when type mismatch.
  76                     // This is needed for diagnostic when return type mismatch.
  77                     ty
  78                 }
  79             }
  80         } else {
  81             ty
  82         }
  83     }
  84
  85     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  86         self.db.unwind_if_cancelled();
  87
  88         let body = Arc::clone(&self.body); // avoid borrow checker problem
  89         let ty = match &body[tgt_expr] {
  90             Expr::Missing => self.err_ty(),
  91             &Expr::If { condition, then_branch, else_branch } => {
  92                 self.infer_expr(
  93                     condition,
  94                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
  95                 );
  96
  97                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
  98                 let mut both_arms_diverge = Diverges::Always;
  99
 100                 let result_ty = self.table.new_type_var();
 101                 let then_ty = self.infer_expr_inner(then_branch, expected);
 102                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 103                 let mut coerce = CoerceMany::new(result_ty);
 104                 coerce.coerce(self, Some(then_branch), &then_ty);
 105                 let else_ty = match else_branch {
 106                     Some(else_branch) => self.infer_expr_inner(else_branch, expected),
 107                     None => TyBuilder::unit(),
 108                 };
 109                 both_arms_diverge &= self.diverges;
 110                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 111                 coerce.coerce(self, else_branch, &else_ty);
 112
 113                 self.diverges = condition_diverges | both_arms_diverge;
 114
 115                 coerce.complete()
 116             }
 117             &Expr::Let { pat, expr } => {
 118                 let input_ty = self.infer_expr(expr, &Expectation::none());
 119                 self.infer_pat(pat, &input_ty, BindingMode::default());
 120                 TyKind::Scalar(Scalar::Bool).intern(Interner)
 121             }
 122             Expr::Block { statements, tail, label, id: _ } => {
 123                 let old_resolver = mem::replace(
 124                     &mut self.resolver,
 125                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 126                 );
 127                 let ty = match label {
 128                     Some(_) => {
 129                         let break_ty = self.table.new_type_var();
 130                         self.breakables.push(BreakableContext {
 131                             may_break: false,
 132                             coerce: CoerceMany::new(break_ty.clone()),
 133                             label: label.map(|label| self.body[label].name.clone()),
 134                         });
 135                         let ty = self.infer_block(
 136                             tgt_expr,
 137                             statements,
 138                             *tail,
 139                             &Expectation::has_type(break_ty),
 140                         );
 141                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 142                         if ctxt.may_break {
 143                             ctxt.coerce.complete()
 144                         } else {
 145                             ty
 146                         }
 147                     }
 148                     None => self.infer_block(tgt_expr, statements, *tail, expected),
 149                 };
 150                 self.resolver = old_resolver;
 151                 ty
 152             }
 153             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 154             Expr::TryBlock { body } => {
 155                 let _inner = self.infer_expr(*body, expected);
 156                 // FIXME should be std::result::Result<{inner}, _>
 157                 self.err_ty()
 158             }
 159             Expr::Async { body } => {
 160                 // Use the first type parameter as the output type of future.
 161                 // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 162                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 163                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 164                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 165                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
 166                     .intern(Interner)
 167             }
 168             Expr::Loop { body, label } => {
 169                 self.breakables.push(BreakableContext {
 170                     may_break: false,
 171                     coerce: CoerceMany::new(self.table.new_type_var()),
 172                     label: label.map(|label| self.body[label].name.clone()),
 173                 });
 174                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 175
 176                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 177
 178                 if ctxt.may_break {
 179                     self.diverges = Diverges::Maybe;
 180                     ctxt.coerce.complete()
 181                 } else {
 182                     TyKind::Never.intern(Interner)
 183                 }
 184             }
 185             Expr::While { condition, body, label } => {
 186                 self.breakables.push(BreakableContext {
 187                     may_break: false,
 188                     coerce: CoerceMany::new(self.err_ty()),
 189                     label: label.map(|label| self.body[label].name.clone()),
 190                 });
 191                 self.infer_expr(
 192                     *condition,
 193                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 194                 );
 195                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 196                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 197                 // the body may not run, so it diverging doesn't mean we diverge
 198                 self.diverges = Diverges::Maybe;
 199                 TyBuilder::unit()
 200             }
 201             Expr::For { iterable, body, pat, label } => {
 202                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 203
 204                 self.breakables.push(BreakableContext {
 205                     may_break: false,
 206                     coerce: CoerceMany::new(self.err_ty()),
 207                     label: label.map(|label| self.body[label].name.clone()),
 208                 });
 209                 let pat_ty =
 210                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 211
 212                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 213
 214                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 215                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 216                 // the body may not run, so it diverging doesn't mean we diverge
 217                 self.diverges = Diverges::Maybe;
 218                 TyBuilder::unit()
 219             }
 220             Expr::Lambda { body, args, ret_type, arg_types } => {
 221                 assert_eq!(args.len(), arg_types.len());
 222
 223                 let mut sig_tys = Vec::new();
 224
 225                 // collect explicitly written argument types
 226                 for arg_type in arg_types.iter() {
 227                     let arg_ty = match arg_type {
 228                         Some(type_ref) => self.make_ty(type_ref),
 229                         None => self.table.new_type_var(),
 230                     };
 231                     sig_tys.push(arg_ty);
 232                 }
 233
 234                 // add return type
 235                 let ret_ty = match ret_type {
 236                     Some(type_ref) => self.make_ty(type_ref),
 237                     None => self.table.new_type_var(),
 238                 };
 239                 sig_tys.push(ret_ty.clone());
 240                 let sig_ty = TyKind::Function(FnPointer {
 241                     num_binders: 0,
 242                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 243                     substitution: FnSubst(
 244                         Substitution::from_iter(Interner, sig_tys.clone()).shifted_in(Interner),
 245                     ),
 246                 })
 247                 .intern(Interner);
 248                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 249                 let closure_ty =
 250                     TyKind::Closure(closure_id, Substitution::from1(Interner, sig_ty.clone()))
 251                         .intern(Interner);
 252
 253                 // Eagerly try to relate the closure type with the expected
 254                 // type, otherwise we often won't have enough information to
 255                 // infer the body.
 256                 self.deduce_closure_type_from_expectations(
 257                     tgt_expr,
 258                     &closure_ty,
 259                     &sig_ty,
 260                     expected,
 261                 );
 262
 263                 // Now go through the argument patterns
 264                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 265                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 266                 }
 267
 268                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 269                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 270
 271                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 272
 273                 self.diverges = prev_diverges;
 274                 self.return_ty = prev_ret_ty;
 275
 276                 closure_ty
 277             }
 278             Expr::Call { callee, args } => {
 279                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 280                 let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone());
 281                 let mut res = None;
 282                 // manual loop to be able to access `derefs.table`
 283                 while let Some((callee_deref_ty, _)) = derefs.next() {
 284                     res = derefs.table.callable_sig(&callee_deref_ty, args.len());
 285                     if res.is_some() {
 286                         break;
 287                     }
 288                 }
 289                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = match res {
 290                     Some(res) => {
 291                         let adjustments = auto_deref_adjust_steps(&derefs);
 292                         self.write_expr_adj(*callee, adjustments);
 293                         res
 294                     }
 295                     None => (Vec::new(), self.err_ty()),
 296                 };
 297                 self.register_obligations_for_call(&callee_ty);
 298
 299                 let expected_inputs = self.expected_inputs_for_expected_output(
 300                     expected,
 301                     ret_ty.clone(),
 302                     param_tys.clone(),
 303                 );
 304
 305                 self.check_call_arguments(args, &expected_inputs, &param_tys);
 306                 self.normalize_associated_types_in(ret_ty)
 307             }
 308             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 309                 .infer_method_call(
 310                     tgt_expr,
 311                     *receiver,
 312                     args,
 313                     method_name,
 314                     generic_args.as_deref(),
 315                     expected,
 316                 ),
 317             Expr::Match { expr, arms } => {
 318                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 319
 320                 let expected = expected.adjust_for_branches(&mut self.table);
 321
 322                 let result_ty = if arms.is_empty() {
 323                     TyKind::Never.intern(Interner)
 324                 } else {
 325                     match &expected {
 326                         Expectation::HasType(ty) => ty.clone(),
 327                         _ => self.table.new_type_var(),
 328                     }
 329                 };
 330                 let mut coerce = CoerceMany::new(result_ty);
 331
 332                 let matchee_diverges = self.diverges;
 333                 let mut all_arms_diverge = Diverges::Always;
 334
 335                 for arm in arms.iter() {
 336                     self.diverges = Diverges::Maybe;
 337                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 338                     if let Some(guard_expr) = arm.guard {
 339                         self.infer_expr(
 340                             guard_expr,
 341                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 342                         );
 343                     }
 344
 345                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 346                     all_arms_diverge &= self.diverges;
 347                     coerce.coerce(self, Some(arm.expr), &arm_ty);
 348                 }
 349
 350                 self.diverges = matchee_diverges | all_arms_diverge;
 351
 352                 coerce.complete()
 353             }
 354             Expr::Path(p) => {
 355                 // FIXME this could be more efficient...
 356                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 357                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
 358             }
 359             Expr::Continue { .. } => TyKind::Never.intern(Interner),
 360             Expr::Break { expr, label } => {
 361                 let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
 362                     Some(ctxt) => {
 363                         // avoiding the borrowck
 364                         mem::replace(
 365                             &mut ctxt.coerce,
 366                             CoerceMany::new(self.result.standard_types.unknown.clone()),
 367                         )
 368                     }
 369                     None => CoerceMany::new(self.result.standard_types.unknown.clone()),
 370                 };
 371
 372                 let val_ty = if let Some(expr) = *expr {
 373                     self.infer_expr(expr, &Expectation::none())
 374                 } else {
 375                     TyBuilder::unit()
 376                 };
 377
 378                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 379                 coerce.coerce(self, *expr, &val_ty);
 380
 381                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 382                     ctxt.coerce = coerce;
 383                     ctxt.may_break = true;
 384                 } else {
 385                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 386                         expr: tgt_expr,
 387                     });
 388                 };
 389
 390                 TyKind::Never.intern(Interner)
 391             }
 392             Expr::Return { expr } => {
 393                 if let Some(expr) = expr {
 394                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 395                 } else {
 396                     let unit = TyBuilder::unit();
 397                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
 398                 }
 399                 TyKind::Never.intern(Interner)
 400             }
 401             Expr::Yield { expr } => {
 402                 // FIXME: track yield type for coercion
 403                 if let Some(expr) = expr {
 404                     self.infer_expr(*expr, &Expectation::none());
 405                 }
 406                 TyKind::Never.intern(Interner)
 407             }
 408             Expr::RecordLit { path, fields, spread } => {
 409                 let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
 410                 if let Some(variant) = def_id {
 411                     self.write_variant_resolution(tgt_expr.into(), variant);
 412                 }
 413
 414                 if let Some(t) = expected.only_has_type(&mut self.table) {
 415                     self.unify(&ty, &t);
 416                 }
 417
 418                 let substs = ty
 419                     .as_adt()
 420                     .map(|(_, s)| s.clone())
 421                     .unwrap_or_else(|| Substitution::empty(Interner));
 422                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 423                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 424                 for field in fields.iter() {
 425                     let field_def =
 426                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 427                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 428                             None => {
 429                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 430                                     expr: field.expr,
 431                                 });
 432                                 None
 433                             }
 434                         });
 435                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 436                         field_types[it.local_id].clone().substitute(Interner, &substs)
 437                     });
 438                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 439                 }
 440                 if let Some(expr) = spread {
 441                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 442                 }
 443                 ty
 444             }
 445             Expr::Field { expr, name } => {
 446                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 447
 448                 let mut autoderef = Autoderef::new(&mut self.table, receiver_ty);
 449                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
 450                     let (field_id, parameters) = match derefed_ty.kind(Interner) {
 451                         TyKind::Tuple(_, substs) => {
 452                             return name.as_tuple_index().and_then(|idx| {
 453                                 substs
 454                                     .as_slice(Interner)
 455                                     .get(idx)
 456                                     .map(|a| a.assert_ty_ref(Interner))
 457                                     .cloned()
 458                             });
 459                         }
 460                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 461                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 462                             let field = FieldId { parent: (*s).into(), local_id };
 463                             (field, parameters.clone())
 464                         }
 465                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 466                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 467                             let field = FieldId { parent: (*u).into(), local_id };
 468                             (field, parameters.clone())
 469                         }
 470                         _ => return None,
 471                     };
 472                     let module = self.resolver.module();
 473                     let is_visible = module
 474                         .map(|mod_id| {
 475                             self.db.field_visibilities(field_id.parent)[field_id.local_id]
 476                                 .is_visible_from(self.db.upcast(), mod_id)
 477                         })
 478                         .unwrap_or(true);
 479                     if !is_visible {
 480                         // Write down the first field resolution even if it is not visible
 481                         // This aids IDE features for private fields like goto def and in
 482                         // case of autoderef finding an applicable field, this will be
 483                         // overwritten in a following cycle
 484                         if let Entry::Vacant(entry) = self.result.field_resolutions.entry(tgt_expr)
 485                         {
 486                             entry.insert(field_id);
 487                         }
 488                         return None;
 489                     }
 490                     // can't have `write_field_resolution` here because `self.table` is borrowed :(
 491                     self.result.field_resolutions.insert(tgt_expr, field_id);
 492                     let ty = self.db.field_types(field_id.parent)[field_id.local_id]
 493                         .clone()
 494                         .substitute(Interner, &parameters);
 495                     Some(ty)
 496                 });
 497                 let ty = match ty {
 498                     Some(ty) => {
 499                         let adjustments = auto_deref_adjust_steps(&autoderef);
 500                         self.write_expr_adj(*expr, adjustments);
 501                         let ty = self.insert_type_vars(ty);
 502                         let ty = self.normalize_associated_types_in(ty);
 503                         ty
 504                     }
 505                     _ => self.err_ty(),
 506                 };
 507                 ty
 508             }
 509             Expr::Await { expr } => {
 510                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 511                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 512             }
 513             Expr::Try { expr } => {
 514                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 515                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 516             }
 517             Expr::Cast { expr, type_ref } => {
 518                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 519                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 520                 let cast_ty = self.make_ty(type_ref);
 521                 // FIXME check the cast...
 522                 cast_ty
 523             }
 524             Expr::Ref { expr, rawness, mutability } => {
 525                 let mutability = lower_to_chalk_mutability(*mutability);
 526                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 527                     .only_has_type(&mut self.table)
 528                     .as_ref()
 529                     .and_then(|t| t.as_reference_or_ptr())
 530                 {
 531                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 532                         // FIXME: record type error - expected mut reference but found shared ref,
 533                         // which cannot be coerced
 534                     }
 535                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 536                         // FIXME: record type error - expected reference but found ptr,
 537                         // which cannot be coerced
 538                     }
 539                     Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
 540                 } else {
 541                     Expectation::none()
 542                 };
 543                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 544                 match rawness {
 545                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 546                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 547                 }
 548                 .intern(Interner)
 549             }
 550             Expr::Box { expr } => {
 551                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 552                 if let Some(box_) = self.resolve_boxed_box() {
 553                     TyBuilder::adt(self.db, box_)
 554                         .push(inner_ty)
 555                         .fill_with_defaults(self.db, || self.table.new_type_var())
 556                         .build()
 557                 } else {
 558                     self.err_ty()
 559                 }
 560             }
 561             Expr::UnaryOp { expr, op } => {
 562                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 563                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 564                 match op {
 565                     UnaryOp::Deref => {
 566                         autoderef::deref(&mut self.table, inner_ty).unwrap_or_else(|| self.err_ty())
 567                     }
 568                     UnaryOp::Neg => {
 569                         match inner_ty.kind(Interner) {
 570                             // Fast path for builtins
 571                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
 572                             | TyKind::InferenceVar(
 573                                 _,
 574                                 TyVariableKind::Integer | TyVariableKind::Float,
 575                             ) => inner_ty,
 576                             // Otherwise we resolve via the std::ops::Neg trait
 577                             _ => self
 578                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 579                         }
 580                     }
 581                     UnaryOp::Not => {
 582                         match inner_ty.kind(Interner) {
 583                             // Fast path for builtins
 584                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
 585                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 586                             // Otherwise we resolve via the std::ops::Not trait
 587                             _ => self
 588                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 589                         }
 590                     }
 591                 }
 592             }
 593             Expr::BinaryOp { lhs, rhs, op } => match op {
 594                 Some(BinaryOp::Assignment { op: None }) => {
 595                     let lhs_ty = self.infer_expr(*lhs, &Expectation::none());
 596                     self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
 597                     self.result.standard_types.unit.clone()
 598                 }
 599                 Some(BinaryOp::LogicOp(_)) => {
 600                     let bool_ty = self.result.standard_types.bool_.clone();
 601                     self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
 602                     let lhs_diverges = self.diverges;
 603                     self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
 604                     // Depending on the LHS' value, the RHS can never execute.
 605                     self.diverges = lhs_diverges;
 606                     bool_ty
 607                 }
 608                 Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
 609                 _ => self.err_ty(),
 610             },
 611             Expr::Range { lhs, rhs, range_type } => {
 612                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 613                 let rhs_expect = lhs_ty
 614                     .as_ref()
 615                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 616                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 617                 match (range_type, lhs_ty, rhs_ty) {
 618                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 619                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 620                         None => self.err_ty(),
 621                     },
 622                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 623                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 624                         None => self.err_ty(),
 625                     },
 626                     (RangeOp::Inclusive, None, Some(ty)) => {
 627                         match self.resolve_range_to_inclusive() {
 628                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 629                             None => self.err_ty(),
 630                         }
 631                     }
 632                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 633                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 634                         None => self.err_ty(),
 635                     },
 636                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 637                         match self.resolve_range_inclusive() {
 638                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 639                             None => self.err_ty(),
 640                         }
 641                     }
 642                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 643                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 644                         None => self.err_ty(),
 645                     },
 646                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 647                 }
 648             }
 649             Expr::Index { base, index } => {
 650                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 651                 let index_ty = self.infer_expr(*index, &Expectation::none());
 652
 653                 if let Some(index_trait) = self.resolve_ops_index() {
 654                     let canonicalized = self.canonicalize(base_ty.clone());
 655                     let receiver_adjustments = method_resolution::resolve_indexing_op(
 656                         self.db,
 657                         self.trait_env.clone(),
 658                         canonicalized.value,
 659                         index_trait,
 660                     );
 661                     let (self_ty, adj) = receiver_adjustments
 662                         .map_or((self.err_ty(), Vec::new()), |adj| {
 663                             adj.apply(&mut self.table, base_ty)
 664                         });
 665                     self.write_expr_adj(*base, adj);
 666                     self.resolve_associated_type_with_params(
 667                         self_ty,
 668                         self.resolve_ops_index_output(),
 669                         &[GenericArgData::Ty(index_ty).intern(Interner)],
 670                     )
 671                 } else {
 672                     self.err_ty()
 673                 }
 674             }
 675             Expr::Tuple { exprs } => {
 676                 let mut tys = match expected
 677                     .only_has_type(&mut self.table)
 678                     .as_ref()
 679                     .map(|t| t.kind(Interner))
 680                 {
 681                     Some(TyKind::Tuple(_, substs)) => substs
 682                         .iter(Interner)
 683                         .map(|a| a.assert_ty_ref(Interner).clone())
 684                         .chain(repeat_with(|| self.table.new_type_var()))
 685                         .take(exprs.len())
 686                         .collect::<Vec<_>>(),
 687                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 688                 };
 689
 690                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 691                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 692                 }
 693
 694                 TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
 695             }
 696             Expr::Array(array) => {
 697                 let elem_ty =
 698                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
 699                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
 700                         _ => self.table.new_type_var(),
 701                     };
 702                 let mut coerce = CoerceMany::new(elem_ty.clone());
 703
 704                 let expected = Expectation::has_type(elem_ty.clone());
 705                 let len = match array {
 706                     Array::ElementList(items) => {
 707                         for &expr in items.iter() {
 708                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
 709                             coerce.coerce(self, Some(expr), &cur_elem_ty);
 710                         }
 711                         consteval::usize_const(Some(items.len() as u64))
 712                     }
 713                     &Array::Repeat { initializer, repeat } => {
 714                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
 715                         self.infer_expr(
 716                             repeat,
 717                             &Expectation::has_type(
 718                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
 719                             ),
 720                         );
 721
 722                         if let Some(g_def) = self.owner.as_generic_def_id() {
 723                             let generics = generics(self.db.upcast(), g_def);
 724                             consteval::eval_to_const(
 725                                 repeat,
 726                                 ParamLoweringMode::Placeholder,
 727                                 self,
 728                                 || generics,
 729                                 DebruijnIndex::INNERMOST,
 730                             )
 731                         } else {
 732                             consteval::usize_const(None)
 733                         }
 734                     }
 735                 };
 736
 737                 TyKind::Array(coerce.complete(), len).intern(Interner)
 738             }
 739             Expr::Literal(lit) => match lit {
 740                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
 741                 Literal::String(..) => {
 742                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
 743                         .intern(Interner)
 744                 }
 745                 Literal::ByteString(bs) => {
 746                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 747
 748                     let len = consteval::usize_const(Some(bs.len() as u64));
 749
 750                     let array_type = TyKind::Array(byte_type, len).intern(Interner);
 751                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
 752                 }
 753                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
 754                 Literal::Int(_v, ty) => match ty {
 755                     Some(int_ty) => {
 756                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 757                             .intern(Interner)
 758                     }
 759                     None => self.table.new_integer_var(),
 760                 },
 761                 Literal::Uint(_v, ty) => match ty {
 762                     Some(int_ty) => {
 763                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 764                             .intern(Interner)
 765                     }
 766                     None => self.table.new_integer_var(),
 767                 },
 768                 Literal::Float(_v, ty) => match ty {
 769                     Some(float_ty) => {
 770                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 771                             .intern(Interner)
 772                     }
 773                     None => self.table.new_float_var(),
 774                 },
 775             },
 776             Expr::MacroStmts { tail } => self.infer_expr_inner(*tail, expected),
 777         };
 778         // use a new type variable if we got unknown here
 779         let ty = self.insert_type_vars_shallow(ty);
 780         self.write_expr_ty(tgt_expr, ty.clone());
 781         ty
 782     }
 783
 784     fn infer_overloadable_binop(
 785         &mut self,
 786         lhs: ExprId,
 787         op: BinaryOp,
 788         rhs: ExprId,
 789         tgt_expr: ExprId,
 790     ) -> Ty {
 791         let lhs_expectation = Expectation::none();
 792         let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
 793         let rhs_ty = self.table.new_type_var();
 794
 795         let func = self.resolve_binop_method(op);
 796         let func = match func {
 797             Some(func) => func,
 798             None => {
 799                 let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
 800                 let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
 801                 return self
 802                     .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
 803                     .unwrap_or_else(|| self.err_ty());
 804             }
 805         };
 806
 807         let subst = TyBuilder::subst_for_def(self.db, func)
 808             .push(lhs_ty.clone())
 809             .push(rhs_ty.clone())
 810             .build();
 811         self.write_method_resolution(tgt_expr, func, subst.clone());
 812
 813         let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
 814         self.register_obligations_for_call(&method_ty);
 815
 816         self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
 817
 818         let ret_ty = match method_ty.callable_sig(self.db) {
 819             Some(sig) => sig.ret().clone(),
 820             None => self.err_ty(),
 821         };
 822
 823         let ret_ty = self.normalize_associated_types_in(ret_ty);
 824
 825         // FIXME: record autoref adjustments
 826
 827         // use knowledge of built-in binary ops, which can sometimes help inference
 828         if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
 829             self.unify(&builtin_rhs, &rhs_ty);
 830         }
 831         if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
 832             self.unify(&builtin_ret, &ret_ty);
 833         }
 834
 835         ret_ty
 836     }
 837
 838     fn infer_block(
 839         &mut self,
 840         expr: ExprId,
 841         statements: &[Statement],
 842         tail: Option<ExprId>,
 843         expected: &Expectation,
 844     ) -> Ty {
 845         for stmt in statements {
 846             match stmt {
 847                 Statement::Let { pat, type_ref, initializer, else_branch } => {
 848                     let decl_ty = type_ref
 849                         .as_ref()
 850                         .map(|tr| self.make_ty(tr))
 851                         .unwrap_or_else(|| self.err_ty());
 852
 853                     // Always use the declared type when specified
 854                     let mut ty = decl_ty.clone();
 855
 856                     if let Some(expr) = initializer {
 857                         let actual_ty =
 858                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 859                         if decl_ty.is_unknown() {
 860                             ty = actual_ty;
 861                         }
 862                     }
 863
 864                     if let Some(expr) = else_branch {
 865                         self.infer_expr_coerce(
 866                             *expr,
 867                             &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
 868                         );
 869                     }
 870
 871                     self.infer_pat(*pat, &ty, BindingMode::default());
 872                 }
 873                 Statement::Expr { expr, .. } => {
 874                     self.infer_expr(*expr, &Expectation::none());
 875                 }
 876             }
 877         }
 878
 879         if let Some(expr) = tail {
 880             self.infer_expr_coerce(expr, expected)
 881         } else {
 882             // Citing rustc: if there is no explicit tail expression,
 883             // that is typically equivalent to a tail expression
 884             // of `()` -- except if the block diverges. In that
 885             // case, there is no value supplied from the tail
 886             // expression (assuming there are no other breaks,
 887             // this implies that the type of the block will be
 888             // `!`).
 889             if self.diverges.is_always() {
 890                 // we don't even make an attempt at coercion
 891                 self.table.new_maybe_never_var()
 892             } else {
 893                 if let Some(t) = expected.only_has_type(&mut self.table) {
 894                     let _ = self.coerce(Some(expr), &TyBuilder::unit(), &t);
 895                 }
 896                 TyBuilder::unit()
 897             }
 898         }
 899     }
 900
 901     fn infer_method_call(
 902         &mut self,
 903         tgt_expr: ExprId,
 904         receiver: ExprId,
 905         args: &[ExprId],
 906         method_name: &Name,
 907         generic_args: Option<&GenericArgs>,
 908         expected: &Expectation,
 909     ) -> Ty {
 910         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 911         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
 912
 913         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 914
 915         let resolved = method_resolution::lookup_method(
 916             &canonicalized_receiver.value,
 917             self.db,
 918             self.trait_env.clone(),
 919             &traits_in_scope,
 920             self.resolver.module().into(),
 921             method_name,
 922         );
 923         let (receiver_ty, method_ty, substs) = match resolved {
 924             Some((adjust, func)) => {
 925                 let (ty, adjustments) = adjust.apply(&mut self.table, receiver_ty);
 926                 let generics = generics(self.db.upcast(), func.into());
 927                 let substs = self.substs_for_method_call(generics, generic_args);
 928                 self.write_expr_adj(receiver, adjustments);
 929                 self.write_method_resolution(tgt_expr, func, substs.clone());
 930                 (ty, self.db.value_ty(func.into()), substs)
 931             }
 932             None => (
 933                 receiver_ty,
 934                 Binders::empty(Interner, self.err_ty()),
 935                 Substitution::empty(Interner),
 936             ),
 937         };
 938         let method_ty = method_ty.substitute(Interner, &substs);
 939         self.register_obligations_for_call(&method_ty);
 940         let (formal_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 941             Some(sig) => {
 942                 if !sig.params().is_empty() {
 943                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 944                 } else {
 945                     (self.err_ty(), Vec::new(), sig.ret().clone())
 946                 }
 947             }
 948             None => (self.err_ty(), Vec::new(), self.err_ty()),
 949         };
 950         self.unify(&formal_receiver_ty, &receiver_ty);
 951
 952         let expected_inputs =
 953             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
 954
 955         self.check_call_arguments(args, &expected_inputs, &param_tys);
 956         self.normalize_associated_types_in(ret_ty)
 957     }
 958
 959     fn expected_inputs_for_expected_output(
 960         &mut self,
 961         expected_output: &Expectation,
 962         output: Ty,
 963         inputs: Vec<Ty>,
 964     ) -> Vec<Ty> {
 965         if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
 966             self.table.fudge_inference(|table| {
 967                 if table.try_unify(&expected_ty, &output).is_ok() {
 968                     table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
 969                         chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
 970                         chalk_ir::VariableKind::Lifetime => {
 971                             var.to_lifetime(Interner).cast(Interner)
 972                         }
 973                         chalk_ir::VariableKind::Const(ty) => {
 974                             var.to_const(Interner, ty).cast(Interner)
 975                         }
 976                     })
 977                 } else {
 978                     Vec::new()
 979                 }
 980             })
 981         } else {
 982             Vec::new()
 983         }
 984     }
 985
 986     fn check_call_arguments(&mut self, args: &[ExprId], expected_inputs: &[Ty], param_tys: &[Ty]) {
 987         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 988         // We do this in a pretty awful way: first we type-check any arguments
 989         // that are not closures, then we type-check the closures. This is so
 990         // that we have more information about the types of arguments when we
 991         // type-check the functions. This isn't really the right way to do this.
 992         for &check_closures in &[false, true] {
 993             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
 994             let expected_iter = expected_inputs
 995                 .iter()
 996                 .cloned()
 997                 .chain(param_iter.clone().skip(expected_inputs.len()));
 998             for ((&arg, param_ty), expected_ty) in args.iter().zip(param_iter).zip(expected_iter) {
 999                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
1000                 if is_closure != check_closures {
1001                     continue;
1002                 }
1003
1004                 // the difference between param_ty and expected here is that
1005                 // expected is the parameter when the expected *return* type is
1006                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
1007                 // the expected type is already `&[i32]`, whereas param_ty is
1008                 // still an unbound type variable. We don't always want to force
1009                 // the parameter to coerce to the expected type (for example in
1010                 // `coerce_unsize_expected_type_4`).
1011                 let param_ty = self.normalize_associated_types_in(param_ty);
1012                 let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
1013                 // infer with the expected type we have...
1014                 let ty = self.infer_expr_inner(arg, &expected);
1015
1016                 // then coerce to either the expected type or just the formal parameter type
1017                 let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
1018                     // if we are coercing to the expectation, unify with the
1019                     // formal parameter type to connect everything
1020                     self.unify(&ty, &param_ty);
1021                     ty
1022                 } else {
1023                     param_ty
1024                 };
1025                 if !coercion_target.is_unknown() {
1026                     if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
1027                         self.result.type_mismatches.insert(
1028                             arg.into(),
1029                             TypeMismatch { expected: coercion_target, actual: ty.clone() },
1030                         );
1031                     }
1032                 }
1033             }
1034         }
1035     }
1036
1037     fn substs_for_method_call(
1038         &mut self,
1039         def_generics: Generics,
1040         generic_args: Option<&GenericArgs>,
1041     ) -> Substitution {
1042         let (parent_params, self_params, type_params, const_params, impl_trait_params) =
1043             def_generics.provenance_split();
1044         assert_eq!(self_params, 0); // method shouldn't have another Self param
1045         let total_len = parent_params + type_params + const_params + impl_trait_params;
1046         let mut substs = Vec::with_capacity(total_len);
1047         // Parent arguments are unknown
1048         for (id, param) in def_generics.iter_parent() {
1049             match param {
1050                 TypeOrConstParamData::TypeParamData(_) => {
1051                     substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner));
1052                 }
1053                 TypeOrConstParamData::ConstParamData(_) => {
1054                     let ty = self.db.const_param_ty(ConstParamId::from_unchecked(id));
1055                     substs
1056                         .push(GenericArgData::Const(self.table.new_const_var(ty)).intern(Interner));
1057                 }
1058             }
1059         }
1060         // handle provided arguments
1061         if let Some(generic_args) = generic_args {
1062             // if args are provided, it should be all of them, but we can't rely on that
1063             for (arg, kind_id) in generic_args
1064                 .args
1065                 .iter()
1066                 .filter(|arg| !matches!(arg, GenericArg::Lifetime(_)))
1067                 .take(type_params + const_params)
1068                 .zip(def_generics.iter_id().skip(parent_params))
1069             {
1070                 if let Some(g) = generic_arg_to_chalk(
1071                     self.db,
1072                     kind_id,
1073                     arg,
1074                     self,
1075                     |this, type_ref| this.make_ty(type_ref),
1076                     |this, c| {
1077                         const_or_path_to_chalk(
1078                             this.db,
1079                             &this.resolver,
1080                             c,
1081                             ParamLoweringMode::Placeholder,
1082                             || generics(this.db.upcast(), (&this.resolver).generic_def().unwrap()),
1083                             DebruijnIndex::INNERMOST,
1084                         )
1085                     },
1086                 ) {
1087                     substs.push(g);
1088                 }
1089             }
1090         };
1091         let supplied_params = substs.len();
1092         for _ in supplied_params..total_len {
1093             substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner));
1094         }
1095         assert_eq!(substs.len(), total_len);
1096         Substitution::from_iter(Interner, substs)
1097     }
1098
1099     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1100         let callable_ty = self.resolve_ty_shallow(callable_ty);
1101         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(Interner) {
1102             let def: CallableDefId = from_chalk(self.db, *fn_def);
1103             let generic_predicates = self.db.generic_predicates(def.into());
1104             for predicate in generic_predicates.iter() {
1105                 let (predicate, binders) = predicate
1106                     .clone()
1107                     .substitute(Interner, parameters)
1108                     .into_value_and_skipped_binders();
1109                 always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
1110                 self.push_obligation(predicate.cast(Interner));
1111             }
1112             // add obligation for trait implementation, if this is a trait method
1113             match def {
1114                 CallableDefId::FunctionId(f) => {
1115                     if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
1116                         // construct a TraitRef
1117                         let substs = crate::subst_prefix(
1118                             &*parameters,
1119                             generics(self.db.upcast(), trait_.into()).len(),
1120                         );
1121                         self.push_obligation(
1122                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1123                                 .cast(Interner),
1124                         );
1125                     }
1126                 }
1127                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1128             }
1129         }
1130     }
1131
1132     fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
1133         let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
1134         let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
1135         match op {
1136             BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
1137                 Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
1138             }
1139             BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
1140             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
1141                 // all integer combinations are valid here
1142                 if matches!(
1143                     lhs_ty.kind(Interner),
1144                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1145                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1146                 ) && matches!(
1147                     rhs_ty.kind(Interner),
1148                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1149                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1150                 ) {
1151                     Some(lhs_ty)
1152                 } else {
1153                     None
1154                 }
1155             }
1156             BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
1157                 // (int, int) | (uint, uint) | (float, float)
1158                 (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
1159                 | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
1160                 | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
1161                     Some(rhs_ty)
1162                 }
1163                 // ({int}, int) | ({int}, uint)
1164                 (
1165                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1166                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1167                 ) => Some(rhs_ty),
1168                 // (int, {int}) | (uint, {int})
1169                 (
1170                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1171                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1172                 ) => Some(lhs_ty),
1173                 // ({float} | float)
1174                 (
1175                     TyKind::InferenceVar(_, TyVariableKind::Float),
1176                     TyKind::Scalar(Scalar::Float(_)),
1177                 ) => Some(rhs_ty),
1178                 // (float, {float})
1179                 (
1180                     TyKind::Scalar(Scalar::Float(_)),
1181                     TyKind::InferenceVar(_, TyVariableKind::Float),
1182                 ) => Some(lhs_ty),
1183                 // ({int}, {int}) | ({float}, {float})
1184                 (
1185                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1186                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1187                 )
1188                 | (
1189                     TyKind::InferenceVar(_, TyVariableKind::Float),
1190                     TyKind::InferenceVar(_, TyVariableKind::Float),
1191                 ) => Some(rhs_ty),
1192                 _ => None,
1193             },
1194         }
1195     }
1196
1197     fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
1198         Some(match op {
1199             BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
1200             BinaryOp::Assignment { op: None } => lhs_ty,
1201             BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
1202                 .resolve_ty_shallow(&lhs_ty)
1203                 .kind(Interner)
1204             {
1205                 TyKind::Scalar(_) | TyKind::Str => lhs_ty,
1206                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1207                 _ => return None,
1208             },
1209             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
1210             BinaryOp::CmpOp(CmpOp::Ord { .. })
1211             | BinaryOp::Assignment { op: Some(_) }
1212             | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
1213                 TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
1214                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1215                 _ => return None,
1216             },
1217         })
1218     }
1219
1220     fn resolve_binop_method(&self, op: BinaryOp) -> Option<FunctionId> {
1221         let (name, lang_item) = match op {
1222             BinaryOp::LogicOp(_) => return None,
1223             BinaryOp::ArithOp(aop) => match aop {
1224                 ArithOp::Add => (name!(add), name!(add)),
1225                 ArithOp::Mul => (name!(mul), name!(mul)),
1226                 ArithOp::Sub => (name!(sub), name!(sub)),
1227                 ArithOp::Div => (name!(div), name!(div)),
1228                 ArithOp::Rem => (name!(rem), name!(rem)),
1229                 ArithOp::Shl => (name!(shl), name!(shl)),
1230                 ArithOp::Shr => (name!(shr), name!(shr)),
1231                 ArithOp::BitXor => (name!(bitxor), name!(bitxor)),
1232                 ArithOp::BitOr => (name!(bitor), name!(bitor)),
1233                 ArithOp::BitAnd => (name!(bitand), name!(bitand)),
1234             },
1235             BinaryOp::Assignment { op: Some(aop) } => match aop {
1236                 ArithOp::Add => (name!(add_assign), name!(add_assign)),
1237                 ArithOp::Mul => (name!(mul_assign), name!(mul_assign)),
1238                 ArithOp::Sub => (name!(sub_assign), name!(sub_assign)),
1239                 ArithOp::Div => (name!(div_assign), name!(div_assign)),
1240                 ArithOp::Rem => (name!(rem_assign), name!(rem_assign)),
1241                 ArithOp::Shl => (name!(shl_assign), name!(shl_assign)),
1242                 ArithOp::Shr => (name!(shr_assign), name!(shr_assign)),
1243                 ArithOp::BitXor => (name!(bitxor_assign), name!(bitxor_assign)),
1244                 ArithOp::BitOr => (name!(bitor_assign), name!(bitor_assign)),
1245                 ArithOp::BitAnd => (name!(bitand_assign), name!(bitand_assign)),
1246             },
1247             BinaryOp::CmpOp(cop) => match cop {
1248                 CmpOp::Eq { negated: false } => (name!(eq), name!(eq)),
1249                 CmpOp::Eq { negated: true } => (name!(ne), name!(eq)),
1250                 CmpOp::Ord { ordering: Ordering::Less, strict: false } => {
1251                     (name!(le), name!(partial_ord))
1252                 }
1253                 CmpOp::Ord { ordering: Ordering::Less, strict: true } => {
1254                     (name!(lt), name!(partial_ord))
1255                 }
1256                 CmpOp::Ord { ordering: Ordering::Greater, strict: false } => {
1257                     (name!(ge), name!(partial_ord))
1258                 }
1259                 CmpOp::Ord { ordering: Ordering::Greater, strict: true } => {
1260                     (name!(gt), name!(partial_ord))
1261                 }
1262             },
1263             BinaryOp::Assignment { op: None } => return None,
1264         };
1265
1266         let trait_ = self.resolve_lang_item(lang_item)?.as_trait()?;
1267
1268         self.db.trait_data(trait_).method_by_name(&name)
1269     }
1270 }