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 };
   8
   9 use chalk_ir::{
  10     cast::Cast, fold::Shift, DebruijnIndex, GenericArgData, Mutability, TyVariableKind,
  11 };
  12 use hir_def::{
  13     expr::{ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, Statement, UnaryOp},
  14     generics::TypeOrConstParamData,
  15     path::{GenericArg, GenericArgs},
  16     resolver::resolver_for_expr,
  17     ConstParamId, FieldId, ItemContainerId, Lookup,
  18 };
  19 use hir_expand::name::Name;
  20 use stdx::always;
  21 use syntax::ast::RangeOp;
  22
  23 use crate::{
  24     autoderef::{self, Autoderef},
  25     consteval,
  26     infer::coerce::CoerceMany,
  27     lower::{
  28         const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
  29     },
  30     mapping::{from_chalk, ToChalk},
  31     method_resolution::{self, lang_names_for_bin_op, VisibleFromModule},
  32     primitive::{self, UintTy},
  33     static_lifetime, to_chalk_trait_id,
  34     utils::{generics, Generics},
  35     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, Interner, Rawness, Scalar,
  36     Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  37 };
  38
  39 use super::{
  40     coerce::auto_deref_adjust_steps, find_breakable, BindingMode, BreakableContext, Diverges,
  41     Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch,
  42 };
  43
  44 impl<'a> InferenceContext<'a> {
  45     pub(crate) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  46         let ty = self.infer_expr_inner(tgt_expr, expected);
  47         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  48             let could_unify = self.unify(&ty, &expected_ty);
  49             if !could_unify {
  50                 self.result.type_mismatches.insert(
  51                     tgt_expr.into(),
  52                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  53                 );
  54             }
  55         }
  56         ty
  57     }
  58
  59     /// Infer type of expression with possibly implicit coerce to the expected type.
  60     /// Return the type after possible coercion.
  61     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  62         let ty = self.infer_expr_inner(expr, expected);
  63         if let Some(target) = expected.only_has_type(&mut self.table) {
  64             match self.coerce(Some(expr), &ty, &target) {
  65                 Ok(res) => res,
  66                 Err(_) => {
  67                     self.result.type_mismatches.insert(
  68                         expr.into(),
  69                         TypeMismatch { expected: target.clone(), actual: ty.clone() },
  70                     );
  71                     target
  72                 }
  73             }
  74         } else {
  75             ty
  76         }
  77     }
  78
  79     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  80         self.db.unwind_if_cancelled();
  81
  82         let ty = match &self.body[tgt_expr] {
  83             Expr::Missing => self.err_ty(),
  84             &Expr::If { condition, then_branch, else_branch } => {
  85                 self.infer_expr(
  86                     condition,
  87                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
  88                 );
  89
  90                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
  91                 let mut both_arms_diverge = Diverges::Always;
  92
  93                 let result_ty = self.table.new_type_var();
  94                 let then_ty = self.infer_expr_inner(then_branch, expected);
  95                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
  96                 let mut coerce = CoerceMany::new(result_ty);
  97                 coerce.coerce(self, Some(then_branch), &then_ty);
  98                 let else_ty = match else_branch {
  99                     Some(else_branch) => self.infer_expr_inner(else_branch, expected),
 100                     None => TyBuilder::unit(),
 101                 };
 102                 both_arms_diverge &= self.diverges;
 103                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 104                 coerce.coerce(self, else_branch, &else_ty);
 105
 106                 self.diverges = condition_diverges | both_arms_diverge;
 107
 108                 coerce.complete()
 109             }
 110             &Expr::Let { pat, expr } => {
 111                 let input_ty = self.infer_expr(expr, &Expectation::none());
 112                 self.infer_pat(pat, &input_ty, BindingMode::default());
 113                 TyKind::Scalar(Scalar::Bool).intern(Interner)
 114             }
 115             Expr::Block { statements, tail, label, id: _ } => {
 116                 let old_resolver = mem::replace(
 117                     &mut self.resolver,
 118                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 119                 );
 120                 let ty = match label {
 121                     Some(_) => {
 122                         let break_ty = self.table.new_type_var();
 123                         self.breakables.push(BreakableContext {
 124                             may_break: false,
 125                             coerce: CoerceMany::new(break_ty.clone()),
 126                             label: label.map(|label| self.body[label].name.clone()),
 127                         });
 128                         let ty = self.infer_block(
 129                             tgt_expr,
 130                             statements,
 131                             *tail,
 132                             &Expectation::has_type(break_ty),
 133                         );
 134                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 135                         if ctxt.may_break {
 136                             ctxt.coerce.complete()
 137                         } else {
 138                             ty
 139                         }
 140                     }
 141                     None => self.infer_block(tgt_expr, statements, *tail, expected),
 142                 };
 143                 self.resolver = old_resolver;
 144                 ty
 145             }
 146             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 147             Expr::TryBlock { body } => {
 148                 let _inner = self.infer_expr(*body, expected);
 149                 // FIXME should be std::result::Result<{inner}, _>
 150                 self.err_ty()
 151             }
 152             Expr::Async { body } => {
 153                 let ret_ty = self.table.new_type_var();
 154                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 155                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 156
 157                 let inner_ty = self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 158
 159                 self.diverges = prev_diverges;
 160                 self.return_ty = prev_ret_ty;
 161
 162                 // Use the first type parameter as the output type of future.
 163                 // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 164                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 165                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 166                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
 167                     .intern(Interner)
 168             }
 169             Expr::Loop { body, label } => {
 170                 self.breakables.push(BreakableContext {
 171                     may_break: false,
 172                     coerce: CoerceMany::new(self.table.new_type_var()),
 173                     label: label.map(|label| self.body[label].name.clone()),
 174                 });
 175                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 176
 177                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 178
 179                 if ctxt.may_break {
 180                     self.diverges = Diverges::Maybe;
 181                     ctxt.coerce.complete()
 182                 } else {
 183                     TyKind::Never.intern(Interner)
 184                 }
 185             }
 186             Expr::While { condition, body, label } => {
 187                 self.breakables.push(BreakableContext {
 188                     may_break: false,
 189                     coerce: CoerceMany::new(self.err_ty()),
 190                     label: label.map(|label| self.body[label].name.clone()),
 191                 });
 192                 self.infer_expr(
 193                     *condition,
 194                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 195                 );
 196                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 197                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 198                 // the body may not run, so it diverging doesn't mean we diverge
 199                 self.diverges = Diverges::Maybe;
 200                 TyBuilder::unit()
 201             }
 202             Expr::For { iterable, body, pat, label } => {
 203                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 204
 205                 self.breakables.push(BreakableContext {
 206                     may_break: false,
 207                     coerce: CoerceMany::new(self.err_ty()),
 208                     label: label.map(|label| self.body[label].name.clone()),
 209                 });
 210                 let pat_ty =
 211                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 212
 213                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 214
 215                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 216                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 217                 // the body may not run, so it diverging doesn't mean we diverge
 218                 self.diverges = Diverges::Maybe;
 219                 TyBuilder::unit()
 220             }
 221             Expr::Closure { body, args, ret_type, arg_types } => {
 222                 assert_eq!(args.len(), arg_types.len());
 223
 224                 let mut sig_tys = Vec::new();
 225
 226                 // collect explicitly written argument types
 227                 for arg_type in arg_types.iter() {
 228                     let arg_ty = match arg_type {
 229                         Some(type_ref) => self.make_ty(type_ref),
 230                         None => self.table.new_type_var(),
 231                     };
 232                     sig_tys.push(arg_ty);
 233                 }
 234
 235                 // add return type
 236                 let ret_ty = match ret_type {
 237                     Some(type_ref) => self.make_ty(type_ref),
 238                     None => self.table.new_type_var(),
 239                 };
 240                 sig_tys.push(ret_ty.clone());
 241                 let sig_ty = TyKind::Function(FnPointer {
 242                     num_binders: 0,
 243                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 244                     substitution: FnSubst(
 245                         Substitution::from_iter(Interner, sig_tys.clone()).shifted_in(Interner),
 246                     ),
 247                 })
 248                 .intern(Interner);
 249                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 250                 let closure_ty =
 251                     TyKind::Closure(closure_id, Substitution::from1(Interner, sig_ty.clone()))
 252                         .intern(Interner);
 253
 254                 // Eagerly try to relate the closure type with the expected
 255                 // type, otherwise we often won't have enough information to
 256                 // infer the body.
 257                 self.deduce_closure_type_from_expectations(
 258                     tgt_expr,
 259                     &closure_ty,
 260                     &sig_ty,
 261                     expected,
 262                 );
 263
 264                 // Now go through the argument patterns
 265                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 266                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 267                 }
 268
 269                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 270                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 271
 272                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 273
 274                 self.diverges = prev_diverges;
 275                 self.return_ty = prev_ret_ty;
 276
 277                 closure_ty
 278             }
 279             Expr::Call { callee, args, .. } => {
 280                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 281                 let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone());
 282                 let mut res = None;
 283                 let mut derefed_callee = callee_ty.clone();
 284                 // manual loop to be able to access `derefs.table`
 285                 while let Some((callee_deref_ty, _)) = derefs.next() {
 286                     res = derefs.table.callable_sig(&callee_deref_ty, args.len());
 287                     if res.is_some() {
 288                         derefed_callee = callee_deref_ty;
 289                         break;
 290                     }
 291                 }
 292                 // if the function is unresolved, we use is_varargs=true to
 293                 // suppress the arg count diagnostic here
 294                 let is_varargs =
 295                     derefed_callee.callable_sig(self.db).map_or(false, |sig| sig.is_varargs)
 296                         || res.is_none();
 297                 let (param_tys, ret_ty) = match res {
 298                     Some(res) => {
 299                         let adjustments = auto_deref_adjust_steps(&derefs);
 300                         self.write_expr_adj(*callee, adjustments);
 301                         res
 302                     }
 303                     None => (Vec::new(), self.err_ty()), // FIXME diagnostic
 304                 };
 305                 let indices_to_skip = self.check_legacy_const_generics(derefed_callee, args);
 306                 self.register_obligations_for_call(&callee_ty);
 307
 308                 let expected_inputs = self.expected_inputs_for_expected_output(
 309                     expected,
 310                     ret_ty.clone(),
 311                     param_tys.clone(),
 312                 );
 313
 314                 self.check_call_arguments(
 315                     tgt_expr,
 316                     args,
 317                     &expected_inputs,
 318                     &param_tys,
 319                     &indices_to_skip,
 320                     is_varargs,
 321                 );
 322                 self.normalize_associated_types_in(ret_ty)
 323             }
 324             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 325                 .infer_method_call(
 326                     tgt_expr,
 327                     *receiver,
 328                     args,
 329                     method_name,
 330                     generic_args.as_deref(),
 331                     expected,
 332                 ),
 333             Expr::Match { expr, arms } => {
 334                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 335
 336                 let expected = expected.adjust_for_branches(&mut self.table);
 337
 338                 let result_ty = if arms.is_empty() {
 339                     TyKind::Never.intern(Interner)
 340                 } else {
 341                     match &expected {
 342                         Expectation::HasType(ty) => ty.clone(),
 343                         _ => self.table.new_type_var(),
 344                     }
 345                 };
 346                 let mut coerce = CoerceMany::new(result_ty);
 347
 348                 let matchee_diverges = self.diverges;
 349                 let mut all_arms_diverge = Diverges::Always;
 350
 351                 for arm in arms.iter() {
 352                     self.diverges = Diverges::Maybe;
 353                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 354                     if let Some(guard_expr) = arm.guard {
 355                         self.infer_expr(
 356                             guard_expr,
 357                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 358                         );
 359                     }
 360
 361                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 362                     all_arms_diverge &= self.diverges;
 363                     coerce.coerce(self, Some(arm.expr), &arm_ty);
 364                 }
 365
 366                 self.diverges = matchee_diverges | all_arms_diverge;
 367
 368                 coerce.complete()
 369             }
 370             Expr::Path(p) => {
 371                 // FIXME this could be more efficient...
 372                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 373                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
 374             }
 375             Expr::Continue { .. } => TyKind::Never.intern(Interner),
 376             Expr::Break { expr, label } => {
 377                 let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
 378                     Some(ctxt) => {
 379                         // avoiding the borrowck
 380                         mem::replace(
 381                             &mut ctxt.coerce,
 382                             CoerceMany::new(self.result.standard_types.unknown.clone()),
 383                         )
 384                     }
 385                     None => CoerceMany::new(self.result.standard_types.unknown.clone()),
 386                 };
 387
 388                 let val_ty = if let Some(expr) = *expr {
 389                     self.infer_expr(expr, &Expectation::none())
 390                 } else {
 391                     TyBuilder::unit()
 392                 };
 393
 394                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 395                 coerce.coerce(self, *expr, &val_ty);
 396
 397                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 398                     ctxt.coerce = coerce;
 399                     ctxt.may_break = true;
 400                 } else {
 401                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 402                         expr: tgt_expr,
 403                     });
 404                 };
 405
 406                 TyKind::Never.intern(Interner)
 407             }
 408             Expr::Return { expr } => {
 409                 if let Some(expr) = expr {
 410                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 411                 } else {
 412                     let unit = TyBuilder::unit();
 413                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
 414                 }
 415                 TyKind::Never.intern(Interner)
 416             }
 417             Expr::Yield { expr } => {
 418                 // FIXME: track yield type for coercion
 419                 if let Some(expr) = expr {
 420                     self.infer_expr(*expr, &Expectation::none());
 421                 }
 422                 TyKind::Never.intern(Interner)
 423             }
 424             Expr::RecordLit { path, fields, spread, .. } => {
 425                 let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
 426                 if let Some(variant) = def_id {
 427                     self.write_variant_resolution(tgt_expr.into(), variant);
 428                 }
 429
 430                 if let Some(t) = expected.only_has_type(&mut self.table) {
 431                     self.unify(&ty, &t);
 432                 }
 433
 434                 let substs = ty
 435                     .as_adt()
 436                     .map(|(_, s)| s.clone())
 437                     .unwrap_or_else(|| Substitution::empty(Interner));
 438                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 439                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 440                 for field in fields.iter() {
 441                     let field_def =
 442                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 443                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 444                             None => {
 445                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 446                                     expr: field.expr,
 447                                 });
 448                                 None
 449                             }
 450                         });
 451                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 452                         field_types[it.local_id].clone().substitute(Interner, &substs)
 453                     });
 454                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 455                 }
 456                 if let Some(expr) = spread {
 457                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 458                 }
 459                 ty
 460             }
 461             Expr::Field { expr, name } => {
 462                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 463
 464                 let mut autoderef = Autoderef::new(&mut self.table, receiver_ty);
 465                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
 466                     let (field_id, parameters) = match derefed_ty.kind(Interner) {
 467                         TyKind::Tuple(_, substs) => {
 468                             return name.as_tuple_index().and_then(|idx| {
 469                                 substs
 470                                     .as_slice(Interner)
 471                                     .get(idx)
 472                                     .map(|a| a.assert_ty_ref(Interner))
 473                                     .cloned()
 474                             });
 475                         }
 476                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 477                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 478                             let field = FieldId { parent: (*s).into(), local_id };
 479                             (field, parameters.clone())
 480                         }
 481                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 482                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 483                             let field = FieldId { parent: (*u).into(), local_id };
 484                             (field, parameters.clone())
 485                         }
 486                         _ => return None,
 487                     };
 488                     let is_visible = self.db.field_visibilities(field_id.parent)[field_id.local_id]
 489                         .is_visible_from(self.db.upcast(), self.resolver.module());
 490                     if !is_visible {
 491                         // Write down the first field resolution even if it is not visible
 492                         // This aids IDE features for private fields like goto def and in
 493                         // case of autoderef finding an applicable field, this will be
 494                         // overwritten in a following cycle
 495                         if let Entry::Vacant(entry) = self.result.field_resolutions.entry(tgt_expr)
 496                         {
 497                             entry.insert(field_id);
 498                         }
 499                         return None;
 500                     }
 501                     // can't have `write_field_resolution` here because `self.table` is borrowed :(
 502                     self.result.field_resolutions.insert(tgt_expr, field_id);
 503                     let ty = self.db.field_types(field_id.parent)[field_id.local_id]
 504                         .clone()
 505                         .substitute(Interner, &parameters);
 506                     Some(ty)
 507                 });
 508                 let ty = match ty {
 509                     Some(ty) => {
 510                         let adjustments = auto_deref_adjust_steps(&autoderef);
 511                         self.write_expr_adj(*expr, adjustments);
 512                         let ty = self.insert_type_vars(ty);
 513                         let ty = self.normalize_associated_types_in(ty);
 514                         ty
 515                     }
 516                     _ => self.err_ty(),
 517                 };
 518                 ty
 519             }
 520             Expr::Await { expr } => {
 521                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 522                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 523             }
 524             Expr::Try { expr } => {
 525                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 526                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 527             }
 528             Expr::Cast { expr, type_ref } => {
 529                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 530                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 531                 let cast_ty = self.make_ty(type_ref);
 532                 // FIXME check the cast...
 533                 cast_ty
 534             }
 535             Expr::Ref { expr, rawness, mutability } => {
 536                 let mutability = lower_to_chalk_mutability(*mutability);
 537                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 538                     .only_has_type(&mut self.table)
 539                     .as_ref()
 540                     .and_then(|t| t.as_reference_or_ptr())
 541                 {
 542                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 543                         // FIXME: record type error - expected mut reference but found shared ref,
 544                         // which cannot be coerced
 545                     }
 546                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 547                         // FIXME: record type error - expected reference but found ptr,
 548                         // which cannot be coerced
 549                     }
 550                     Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
 551                 } else {
 552                     Expectation::none()
 553                 };
 554                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 555                 match rawness {
 556                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 557                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 558                 }
 559                 .intern(Interner)
 560             }
 561             &Expr::Box { expr } => self.infer_expr_box(expr, expected),
 562             Expr::UnaryOp { expr, op } => {
 563                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 564                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 565                 match op {
 566                     UnaryOp::Deref => {
 567                         autoderef::deref(&mut self.table, inner_ty).unwrap_or_else(|| self.err_ty())
 568                     }
 569                     UnaryOp::Neg => {
 570                         match inner_ty.kind(Interner) {
 571                             // Fast path for builtins
 572                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
 573                             | TyKind::InferenceVar(
 574                                 _,
 575                                 TyVariableKind::Integer | TyVariableKind::Float,
 576                             ) => inner_ty,
 577                             // Otherwise we resolve via the std::ops::Neg trait
 578                             _ => self
 579                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 580                         }
 581                     }
 582                     UnaryOp::Not => {
 583                         match inner_ty.kind(Interner) {
 584                             // Fast path for builtins
 585                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
 586                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 587                             // Otherwise we resolve via the std::ops::Not trait
 588                             _ => self
 589                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 590                         }
 591                     }
 592                 }
 593             }
 594             Expr::BinaryOp { lhs, rhs, op } => match op {
 595                 Some(BinaryOp::Assignment { op: None }) => {
 596                     let lhs = *lhs;
 597                     let is_ordinary = match &self.body[lhs] {
 598                         Expr::Array(_)
 599                         | Expr::RecordLit { .. }
 600                         | Expr::Tuple { .. }
 601                         | Expr::Underscore => false,
 602                         Expr::Call { callee, .. } => !matches!(&self.body[*callee], Expr::Path(_)),
 603                         _ => true,
 604                     };
 605
 606                     // In ordinary (non-destructuring) assignments, the type of
 607                     // `lhs` must be inferred first so that the ADT fields
 608                     // instantiations in RHS can be coerced to it. Note that this
 609                     // cannot happen in destructuring assignments because of how
 610                     // they are desugared.
 611                     if is_ordinary {
 612                         let lhs_ty = self.infer_expr(lhs, &Expectation::none());
 613                         self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
 614                     } else {
 615                         let rhs_ty = self.infer_expr(*rhs, &Expectation::none());
 616                         self.infer_assignee_expr(lhs, &rhs_ty);
 617                     }
 618                     self.result.standard_types.unit.clone()
 619                 }
 620                 Some(BinaryOp::LogicOp(_)) => {
 621                     let bool_ty = self.result.standard_types.bool_.clone();
 622                     self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
 623                     let lhs_diverges = self.diverges;
 624                     self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
 625                     // Depending on the LHS' value, the RHS can never execute.
 626                     self.diverges = lhs_diverges;
 627                     bool_ty
 628                 }
 629                 Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
 630                 _ => self.err_ty(),
 631             },
 632             Expr::Range { lhs, rhs, range_type } => {
 633                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 634                 let rhs_expect = lhs_ty
 635                     .as_ref()
 636                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 637                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 638                 match (range_type, lhs_ty, rhs_ty) {
 639                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 640                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 641                         None => self.err_ty(),
 642                     },
 643                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 644                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 645                         None => self.err_ty(),
 646                     },
 647                     (RangeOp::Inclusive, None, Some(ty)) => {
 648                         match self.resolve_range_to_inclusive() {
 649                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 650                             None => self.err_ty(),
 651                         }
 652                     }
 653                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 654                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 655                         None => self.err_ty(),
 656                     },
 657                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 658                         match self.resolve_range_inclusive() {
 659                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 660                             None => self.err_ty(),
 661                         }
 662                     }
 663                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 664                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 665                         None => self.err_ty(),
 666                     },
 667                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 668                 }
 669             }
 670             Expr::Index { base, index } => {
 671                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 672                 let index_ty = self.infer_expr(*index, &Expectation::none());
 673
 674                 if let Some(index_trait) = self.resolve_ops_index() {
 675                     let canonicalized = self.canonicalize(base_ty.clone());
 676                     let receiver_adjustments = method_resolution::resolve_indexing_op(
 677                         self.db,
 678                         self.trait_env.clone(),
 679                         canonicalized.value,
 680                         index_trait,
 681                     );
 682                     let (self_ty, adj) = receiver_adjustments
 683                         .map_or((self.err_ty(), Vec::new()), |adj| {
 684                             adj.apply(&mut self.table, base_ty)
 685                         });
 686                     self.write_expr_adj(*base, adj);
 687                     self.resolve_associated_type_with_params(
 688                         self_ty,
 689                         self.resolve_ops_index_output(),
 690                         &[GenericArgData::Ty(index_ty).intern(Interner)],
 691                     )
 692                 } else {
 693                     self.err_ty()
 694                 }
 695             }
 696             Expr::Tuple { exprs, .. } => {
 697                 let mut tys = match expected
 698                     .only_has_type(&mut self.table)
 699                     .as_ref()
 700                     .map(|t| t.kind(Interner))
 701                 {
 702                     Some(TyKind::Tuple(_, substs)) => substs
 703                         .iter(Interner)
 704                         .map(|a| a.assert_ty_ref(Interner).clone())
 705                         .chain(repeat_with(|| self.table.new_type_var()))
 706                         .take(exprs.len())
 707                         .collect::<Vec<_>>(),
 708                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 709                 };
 710
 711                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 712                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 713                 }
 714
 715                 TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
 716             }
 717             Expr::Array(array) => {
 718                 let elem_ty =
 719                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
 720                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
 721                         _ => self.table.new_type_var(),
 722                     };
 723                 let mut coerce = CoerceMany::new(elem_ty.clone());
 724
 725                 let expected = Expectation::has_type(elem_ty.clone());
 726                 let len = match array {
 727                     Array::ElementList { elements, .. } => {
 728                         for &expr in elements.iter() {
 729                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
 730                             coerce.coerce(self, Some(expr), &cur_elem_ty);
 731                         }
 732                         consteval::usize_const(Some(elements.len() as u128))
 733                     }
 734                     &Array::Repeat { initializer, repeat } => {
 735                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
 736                         self.infer_expr(
 737                             repeat,
 738                             &Expectation::has_type(
 739                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
 740                             ),
 741                         );
 742
 743                         if let Some(g_def) = self.owner.as_generic_def_id() {
 744                             let generics = generics(self.db.upcast(), g_def);
 745                             consteval::eval_to_const(
 746                                 repeat,
 747                                 ParamLoweringMode::Placeholder,
 748                                 self,
 749                                 || generics,
 750                                 DebruijnIndex::INNERMOST,
 751                             )
 752                         } else {
 753                             consteval::usize_const(None)
 754                         }
 755                     }
 756                 };
 757
 758                 TyKind::Array(coerce.complete(), len).intern(Interner)
 759             }
 760             Expr::Literal(lit) => match lit {
 761                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
 762                 Literal::String(..) => {
 763                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
 764                         .intern(Interner)
 765                 }
 766                 Literal::ByteString(bs) => {
 767                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 768
 769                     let len = consteval::usize_const(Some(bs.len() as u128));
 770
 771                     let array_type = TyKind::Array(byte_type, len).intern(Interner);
 772                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
 773                 }
 774                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
 775                 Literal::Int(_v, ty) => match ty {
 776                     Some(int_ty) => {
 777                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 778                             .intern(Interner)
 779                     }
 780                     None => self.table.new_integer_var(),
 781                 },
 782                 Literal::Uint(_v, ty) => match ty {
 783                     Some(int_ty) => {
 784                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 785                             .intern(Interner)
 786                     }
 787                     None => self.table.new_integer_var(),
 788                 },
 789                 Literal::Float(_v, ty) => match ty {
 790                     Some(float_ty) => {
 791                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 792                             .intern(Interner)
 793                     }
 794                     None => self.table.new_float_var(),
 795                 },
 796             },
 797             Expr::MacroStmts { tail, statements } => {
 798                 self.infer_block(tgt_expr, statements, *tail, expected)
 799             }
 800             Expr::Underscore => {
 801                 // Underscore expressions may only appear in assignee expressions,
 802                 // which are handled by `infer_assignee_expr()`, so any underscore
 803                 // expression reaching this branch is an error.
 804                 self.err_ty()
 805             }
 806         };
 807         // use a new type variable if we got unknown here
 808         let ty = self.insert_type_vars_shallow(ty);
 809         self.write_expr_ty(tgt_expr, ty.clone());
 810         if self.resolve_ty_shallow(&ty).is_never() {
 811             // Any expression that produces a value of type `!` must have diverged
 812             self.diverges = Diverges::Always;
 813         }
 814         ty
 815     }
 816
 817     fn infer_expr_box(&mut self, inner_expr: ExprId, expected: &Expectation) -> Ty {
 818         if let Some(box_id) = self.resolve_boxed_box() {
 819             let table = &mut self.table;
 820             let inner_exp = expected
 821                 .to_option(table)
 822                 .as_ref()
 823                 .map(|e| e.as_adt())
 824                 .flatten()
 825                 .filter(|(e_adt, _)| e_adt == &box_id)
 826                 .map(|(_, subts)| {
 827                     let g = subts.at(Interner, 0);
 828                     Expectation::rvalue_hint(table, Ty::clone(g.assert_ty_ref(Interner)))
 829                 })
 830                 .unwrap_or_else(Expectation::none);
 831
 832             let inner_ty = self.infer_expr_inner(inner_expr, &inner_exp);
 833             TyBuilder::adt(self.db, box_id)
 834                 .push(inner_ty)
 835                 .fill_with_defaults(self.db, || self.table.new_type_var())
 836                 .build()
 837         } else {
 838             self.err_ty()
 839         }
 840     }
 841
 842     pub(super) fn infer_assignee_expr(&mut self, lhs: ExprId, rhs_ty: &Ty) -> Ty {
 843         let is_rest_expr = |expr| {
 844             matches!(
 845                 &self.body[expr],
 846                 Expr::Range { lhs: None, rhs: None, range_type: RangeOp::Exclusive },
 847             )
 848         };
 849
 850         let rhs_ty = self.resolve_ty_shallow(rhs_ty);
 851
 852         let ty = match &self.body[lhs] {
 853             Expr::Tuple { exprs, .. } => {
 854                 // We don't consider multiple ellipses. This is analogous to
 855                 // `hir_def::body::lower::ExprCollector::collect_tuple_pat()`.
 856                 let ellipsis = exprs.iter().position(|e| is_rest_expr(*e));
 857                 let exprs: Vec<_> = exprs.iter().filter(|e| !is_rest_expr(**e)).copied().collect();
 858
 859                 self.infer_tuple_pat_like(&rhs_ty, (), ellipsis, &exprs)
 860             }
 861             Expr::Call { callee, args, .. } => {
 862                 // Tuple structs
 863                 let path = match &self.body[*callee] {
 864                     Expr::Path(path) => Some(path),
 865                     _ => None,
 866                 };
 867
 868                 // We don't consider multiple ellipses. This is analogous to
 869                 // `hir_def::body::lower::ExprCollector::collect_tuple_pat()`.
 870                 let ellipsis = args.iter().position(|e| is_rest_expr(*e));
 871                 let args: Vec<_> = args.iter().filter(|e| !is_rest_expr(**e)).copied().collect();
 872
 873                 self.infer_tuple_struct_pat_like(path, &rhs_ty, (), lhs, ellipsis, &args)
 874             }
 875             Expr::Array(Array::ElementList { elements, .. }) => {
 876                 let elem_ty = match rhs_ty.kind(Interner) {
 877                     TyKind::Array(st, _) => st.clone(),
 878                     _ => self.err_ty(),
 879                 };
 880
 881                 // There's no need to handle `..` as it cannot be bound.
 882                 let sub_exprs = elements.iter().filter(|e| !is_rest_expr(**e));
 883
 884                 for e in sub_exprs {
 885                     self.infer_assignee_expr(*e, &elem_ty);
 886                 }
 887
 888                 match rhs_ty.kind(Interner) {
 889                     TyKind::Array(_, _) => rhs_ty.clone(),
 890                     // Even when `rhs_ty` is not an array type, this assignee
 891                     // expression is inferred to be an array (of unknown element
 892                     // type and length). This should not be just an error type,
 893                     // because we are to compute the unifiability of this type and
 894                     // `rhs_ty` in the end of this function to issue type mismatches.
 895                     _ => TyKind::Array(self.err_ty(), crate::consteval::usize_const(None))
 896                         .intern(Interner),
 897                 }
 898             }
 899             Expr::RecordLit { path, fields, .. } => {
 900                 let subs = fields.iter().map(|f| (f.name.clone(), f.expr));
 901
 902                 self.infer_record_pat_like(path.as_deref(), &rhs_ty, (), lhs.into(), subs)
 903             }
 904             Expr::Underscore => rhs_ty.clone(),
 905             _ => {
 906                 // `lhs` is a place expression, a unit struct, or an enum variant.
 907                 let lhs_ty = self.infer_expr(lhs, &Expectation::none());
 908
 909                 // This is the only branch where this function may coerce any type.
 910                 // We are returning early to avoid the unifiability check below.
 911                 let lhs_ty = self.insert_type_vars_shallow(lhs_ty);
 912                 let ty = match self.coerce(None, &rhs_ty, &lhs_ty) {
 913                     Ok(ty) => ty,
 914                     Err(_) => {
 915                         self.result.type_mismatches.insert(
 916                             lhs.into(),
 917                             TypeMismatch { expected: rhs_ty.clone(), actual: lhs_ty.clone() },
 918                         );
 919                         // `rhs_ty` is returned so no further type mismatches are
 920                         // reported because of this mismatch.
 921                         rhs_ty
 922                     }
 923                 };
 924                 self.write_expr_ty(lhs, ty.clone());
 925                 return ty;
 926             }
 927         };
 928
 929         let ty = self.insert_type_vars_shallow(ty);
 930         if !self.unify(&ty, &rhs_ty) {
 931             self.result
 932                 .type_mismatches
 933                 .insert(lhs.into(), TypeMismatch { expected: rhs_ty.clone(), actual: ty.clone() });
 934         }
 935         self.write_expr_ty(lhs, ty.clone());
 936         ty
 937     }
 938
 939     fn infer_overloadable_binop(
 940         &mut self,
 941         lhs: ExprId,
 942         op: BinaryOp,
 943         rhs: ExprId,
 944         tgt_expr: ExprId,
 945     ) -> Ty {
 946         let lhs_expectation = Expectation::none();
 947         let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
 948         let rhs_ty = self.table.new_type_var();
 949
 950         let func = lang_names_for_bin_op(op).and_then(|(name, lang_item)| {
 951             self.db.trait_data(self.resolve_lang_item(lang_item)?.as_trait()?).method_by_name(&name)
 952         });
 953         let func = match func {
 954             Some(func) => func,
 955             None => {
 956                 let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
 957                 let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
 958                 return self
 959                     .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
 960                     .unwrap_or_else(|| self.err_ty());
 961             }
 962         };
 963
 964         let subst = TyBuilder::subst_for_def(self.db, func)
 965             .push(lhs_ty.clone())
 966             .push(rhs_ty.clone())
 967             .build();
 968         self.write_method_resolution(tgt_expr, func, subst.clone());
 969
 970         let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
 971         self.register_obligations_for_call(&method_ty);
 972
 973         self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
 974
 975         let ret_ty = match method_ty.callable_sig(self.db) {
 976             Some(sig) => sig.ret().clone(),
 977             None => self.err_ty(),
 978         };
 979
 980         let ret_ty = self.normalize_associated_types_in(ret_ty);
 981
 982         // FIXME: record autoref adjustments
 983
 984         // use knowledge of built-in binary ops, which can sometimes help inference
 985         if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
 986             self.unify(&builtin_rhs, &rhs_ty);
 987         }
 988         if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
 989             self.unify(&builtin_ret, &ret_ty);
 990         }
 991
 992         ret_ty
 993     }
 994
 995     fn infer_block(
 996         &mut self,
 997         expr: ExprId,
 998         statements: &[Statement],
 999         tail: Option<ExprId>,
1000         expected: &Expectation,
1001     ) -> Ty {
1002         for stmt in statements {
1003             match stmt {
1004                 Statement::Let { pat, type_ref, initializer, else_branch } => {
1005                     let decl_ty = type_ref
1006                         .as_ref()
1007                         .map(|tr| self.make_ty(tr))
1008                         .unwrap_or_else(|| self.err_ty());
1009
1010                     // Always use the declared type when specified
1011                     let mut ty = decl_ty.clone();
1012
1013                     if let Some(expr) = initializer {
1014                         let actual_ty =
1015                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
1016                         if decl_ty.is_unknown() {
1017                             ty = actual_ty;
1018                         }
1019                     }
1020
1021                     if let Some(expr) = else_branch {
1022                         self.infer_expr_coerce(
1023                             *expr,
1024                             &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
1025                         );
1026                     }
1027
1028                     self.infer_pat(*pat, &ty, BindingMode::default());
1029                 }
1030                 Statement::Expr { expr, .. } => {
1031                     self.infer_expr(*expr, &Expectation::none());
1032                 }
1033             }
1034         }
1035
1036         if let Some(expr) = tail {
1037             self.infer_expr_coerce(expr, expected)
1038         } else {
1039             // Citing rustc: if there is no explicit tail expression,
1040             // that is typically equivalent to a tail expression
1041             // of `()` -- except if the block diverges. In that
1042             // case, there is no value supplied from the tail
1043             // expression (assuming there are no other breaks,
1044             // this implies that the type of the block will be
1045             // `!`).
1046             if self.diverges.is_always() {
1047                 // we don't even make an attempt at coercion
1048                 self.table.new_maybe_never_var()
1049             } else {
1050                 if let Some(t) = expected.only_has_type(&mut self.table) {
1051                     if self.coerce(Some(expr), &TyBuilder::unit(), &t).is_err() {
1052                         self.result.type_mismatches.insert(
1053                             expr.into(),
1054                             TypeMismatch { expected: t.clone(), actual: TyBuilder::unit() },
1055                         );
1056                     }
1057                     t
1058                 } else {
1059                     TyBuilder::unit()
1060                 }
1061             }
1062         }
1063     }
1064
1065     fn infer_method_call(
1066         &mut self,
1067         tgt_expr: ExprId,
1068         receiver: ExprId,
1069         args: &[ExprId],
1070         method_name: &Name,
1071         generic_args: Option<&GenericArgs>,
1072         expected: &Expectation,
1073     ) -> Ty {
1074         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
1075         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
1076
1077         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
1078
1079         let resolved = method_resolution::lookup_method(
1080             &canonicalized_receiver.value,
1081             self.db,
1082             self.trait_env.clone(),
1083             &traits_in_scope,
1084             VisibleFromModule::Filter(self.resolver.module()),
1085             method_name,
1086         );
1087         let (receiver_ty, method_ty, substs) = match resolved {
1088             Some((adjust, func)) => {
1089                 let (ty, adjustments) = adjust.apply(&mut self.table, receiver_ty);
1090                 let generics = generics(self.db.upcast(), func.into());
1091                 let substs = self.substs_for_method_call(generics, generic_args);
1092                 self.write_expr_adj(receiver, adjustments);
1093                 self.write_method_resolution(tgt_expr, func, substs.clone());
1094                 (ty, self.db.value_ty(func.into()), substs)
1095             }
1096             None => (
1097                 receiver_ty,
1098                 Binders::empty(Interner, self.err_ty()),
1099                 Substitution::empty(Interner),
1100             ),
1101         };
1102         let method_ty = method_ty.substitute(Interner, &substs);
1103         self.register_obligations_for_call(&method_ty);
1104         let (formal_receiver_ty, param_tys, ret_ty, is_varargs) =
1105             match method_ty.callable_sig(self.db) {
1106                 Some(sig) => {
1107                     if !sig.params().is_empty() {
1108                         (
1109                             sig.params()[0].clone(),
1110                             sig.params()[1..].to_vec(),
1111                             sig.ret().clone(),
1112                             sig.is_varargs,
1113                         )
1114                     } else {
1115                         (self.err_ty(), Vec::new(), sig.ret().clone(), sig.is_varargs)
1116                     }
1117                 }
1118                 None => (self.err_ty(), Vec::new(), self.err_ty(), true),
1119             };
1120         self.unify(&formal_receiver_ty, &receiver_ty);
1121
1122         let expected_inputs =
1123             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
1124
1125         self.check_call_arguments(tgt_expr, args, &expected_inputs, &param_tys, &[], is_varargs);
1126         self.normalize_associated_types_in(ret_ty)
1127     }
1128
1129     fn expected_inputs_for_expected_output(
1130         &mut self,
1131         expected_output: &Expectation,
1132         output: Ty,
1133         inputs: Vec<Ty>,
1134     ) -> Vec<Ty> {
1135         if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
1136             self.table.fudge_inference(|table| {
1137                 if table.try_unify(&expected_ty, &output).is_ok() {
1138                     table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
1139                         chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
1140                         chalk_ir::VariableKind::Lifetime => {
1141                             var.to_lifetime(Interner).cast(Interner)
1142                         }
1143                         chalk_ir::VariableKind::Const(ty) => {
1144                             var.to_const(Interner, ty).cast(Interner)
1145                         }
1146                     })
1147                 } else {
1148                     Vec::new()
1149                 }
1150             })
1151         } else {
1152             Vec::new()
1153         }
1154     }
1155
1156     fn check_call_arguments(
1157         &mut self,
1158         expr: ExprId,
1159         args: &[ExprId],
1160         expected_inputs: &[Ty],
1161         param_tys: &[Ty],
1162         skip_indices: &[u32],
1163         is_varargs: bool,
1164     ) {
1165         if args.len() != param_tys.len() + skip_indices.len() && !is_varargs {
1166             self.push_diagnostic(InferenceDiagnostic::MismatchedArgCount {
1167                 call_expr: expr,
1168                 expected: param_tys.len() + skip_indices.len(),
1169                 found: args.len(),
1170             });
1171         }
1172
1173         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
1174         // We do this in a pretty awful way: first we type-check any arguments
1175         // that are not closures, then we type-check the closures. This is so
1176         // that we have more information about the types of arguments when we
1177         // type-check the functions. This isn't really the right way to do this.
1178         for &check_closures in &[false, true] {
1179             let mut skip_indices = skip_indices.into_iter().copied().fuse().peekable();
1180             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
1181             let expected_iter = expected_inputs
1182                 .iter()
1183                 .cloned()
1184                 .chain(param_iter.clone().skip(expected_inputs.len()));
1185             for (idx, ((&arg, param_ty), expected_ty)) in
1186                 args.iter().zip(param_iter).zip(expected_iter).enumerate()
1187             {
1188                 let is_closure = matches!(&self.body[arg], Expr::Closure { .. });
1189                 if is_closure != check_closures {
1190                     continue;
1191                 }
1192
1193                 while skip_indices.peek().map_or(false, |i| *i < idx as u32) {
1194                     skip_indices.next();
1195                 }
1196                 if skip_indices.peek().copied() == Some(idx as u32) {
1197                     continue;
1198                 }
1199
1200                 // the difference between param_ty and expected here is that
1201                 // expected is the parameter when the expected *return* type is
1202                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
1203                 // the expected type is already `&[i32]`, whereas param_ty is
1204                 // still an unbound type variable. We don't always want to force
1205                 // the parameter to coerce to the expected type (for example in
1206                 // `coerce_unsize_expected_type_4`).
1207                 let param_ty = self.normalize_associated_types_in(param_ty);
1208                 let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
1209                 // infer with the expected type we have...
1210                 let ty = self.infer_expr_inner(arg, &expected);
1211
1212                 // then coerce to either the expected type or just the formal parameter type
1213                 let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
1214                     // if we are coercing to the expectation, unify with the
1215                     // formal parameter type to connect everything
1216                     self.unify(&ty, &param_ty);
1217                     ty
1218                 } else {
1219                     param_ty
1220                 };
1221                 if !coercion_target.is_unknown() {
1222                     if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
1223                         self.result.type_mismatches.insert(
1224                             arg.into(),
1225                             TypeMismatch { expected: coercion_target, actual: ty.clone() },
1226                         );
1227                     }
1228                 }
1229             }
1230         }
1231     }
1232
1233     fn substs_for_method_call(
1234         &mut self,
1235         def_generics: Generics,
1236         generic_args: Option<&GenericArgs>,
1237     ) -> Substitution {
1238         let (parent_params, self_params, type_params, const_params, impl_trait_params) =
1239             def_generics.provenance_split();
1240         assert_eq!(self_params, 0); // method shouldn't have another Self param
1241         let total_len = parent_params + type_params + const_params + impl_trait_params;
1242         let mut substs = Vec::with_capacity(total_len);
1243         // Parent arguments are unknown
1244         for (id, param) in def_generics.iter_parent() {
1245             match param {
1246                 TypeOrConstParamData::TypeParamData(_) => {
1247                     substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner));
1248                 }
1249                 TypeOrConstParamData::ConstParamData(_) => {
1250                     let ty = self.db.const_param_ty(ConstParamId::from_unchecked(id));
1251                     substs
1252                         .push(GenericArgData::Const(self.table.new_const_var(ty)).intern(Interner));
1253                 }
1254             }
1255         }
1256         // handle provided arguments
1257         if let Some(generic_args) = generic_args {
1258             // if args are provided, it should be all of them, but we can't rely on that
1259             for (arg, kind_id) in generic_args
1260                 .args
1261                 .iter()
1262                 .filter(|arg| !matches!(arg, GenericArg::Lifetime(_)))
1263                 .take(type_params + const_params)
1264                 .zip(def_generics.iter_id().skip(parent_params))
1265             {
1266                 if let Some(g) = generic_arg_to_chalk(
1267                     self.db,
1268                     kind_id,
1269                     arg,
1270                     self,
1271                     |this, type_ref| this.make_ty(type_ref),
1272                     |this, c, ty| {
1273                         const_or_path_to_chalk(
1274                             this.db,
1275                             &this.resolver,
1276                             ty,
1277                             c,
1278                             ParamLoweringMode::Placeholder,
1279                             || generics(this.db.upcast(), (&this.resolver).generic_def().unwrap()),
1280                             DebruijnIndex::INNERMOST,
1281                         )
1282                     },
1283                 ) {
1284                     substs.push(g);
1285                 }
1286             }
1287         };
1288         for (id, data) in def_generics.iter().skip(substs.len()) {
1289             match data {
1290                 TypeOrConstParamData::TypeParamData(_) => {
1291                     substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner))
1292                 }
1293                 TypeOrConstParamData::ConstParamData(_) => {
1294                     substs.push(
1295                         GenericArgData::Const(self.table.new_const_var(
1296                             self.db.const_param_ty(ConstParamId::from_unchecked(id)),
1297                         ))
1298                         .intern(Interner),
1299                     )
1300                 }
1301             }
1302         }
1303         assert_eq!(substs.len(), total_len);
1304         Substitution::from_iter(Interner, substs)
1305     }
1306
1307     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1308         let callable_ty = self.resolve_ty_shallow(callable_ty);
1309         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(Interner) {
1310             let def: CallableDefId = from_chalk(self.db, *fn_def);
1311             let generic_predicates = self.db.generic_predicates(def.into());
1312             for predicate in generic_predicates.iter() {
1313                 let (predicate, binders) = predicate
1314                     .clone()
1315                     .substitute(Interner, parameters)
1316                     .into_value_and_skipped_binders();
1317                 always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
1318                 self.push_obligation(predicate.cast(Interner));
1319             }
1320             // add obligation for trait implementation, if this is a trait method
1321             match def {
1322                 CallableDefId::FunctionId(f) => {
1323                     if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
1324                         // construct a TraitRef
1325                         let substs = crate::subst_prefix(
1326                             &*parameters,
1327                             generics(self.db.upcast(), trait_.into()).len(),
1328                         );
1329                         self.push_obligation(
1330                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1331                                 .cast(Interner),
1332                         );
1333                     }
1334                 }
1335                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1336             }
1337         }
1338     }
1339
1340     /// Returns the argument indices to skip.
1341     fn check_legacy_const_generics(&mut self, callee: Ty, args: &[ExprId]) -> Box<[u32]> {
1342         let (func, subst) = match callee.kind(Interner) {
1343             TyKind::FnDef(fn_id, subst) => {
1344                 let callable = CallableDefId::from_chalk(self.db, *fn_id);
1345                 let func = match callable {
1346                     CallableDefId::FunctionId(f) => f,
1347                     _ => return Default::default(),
1348                 };
1349                 (func, subst)
1350             }
1351             _ => return Default::default(),
1352         };
1353
1354         let data = self.db.function_data(func);
1355         if data.legacy_const_generics_indices.is_empty() {
1356             return Default::default();
1357         }
1358
1359         // only use legacy const generics if the param count matches with them
1360         if data.params.len() + data.legacy_const_generics_indices.len() != args.len() {
1361             if args.len() <= data.params.len() {
1362                 return Default::default();
1363             } else {
1364                 // there are more parameters than there should be without legacy
1365                 // const params; use them
1366                 let mut indices = data.legacy_const_generics_indices.clone();
1367                 indices.sort();
1368                 return indices;
1369             }
1370         }
1371
1372         // check legacy const parameters
1373         for (subst_idx, arg_idx) in data.legacy_const_generics_indices.iter().copied().enumerate() {
1374             let arg = match subst.at(Interner, subst_idx).constant(Interner) {
1375                 Some(c) => c,
1376                 None => continue, // not a const parameter?
1377             };
1378             if arg_idx >= args.len() as u32 {
1379                 continue;
1380             }
1381             let _ty = arg.data(Interner).ty.clone();
1382             let expected = Expectation::none(); // FIXME use actual const ty, when that is lowered correctly
1383             self.infer_expr(args[arg_idx as usize], &expected);
1384             // FIXME: evaluate and unify with the const
1385         }
1386         let mut indices = data.legacy_const_generics_indices.clone();
1387         indices.sort();
1388         indices
1389     }
1390
1391     fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
1392         let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
1393         let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
1394         match op {
1395             BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
1396                 Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
1397             }
1398             BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
1399             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
1400                 // all integer combinations are valid here
1401                 if matches!(
1402                     lhs_ty.kind(Interner),
1403                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1404                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1405                 ) && matches!(
1406                     rhs_ty.kind(Interner),
1407                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1408                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1409                 ) {
1410                     Some(lhs_ty)
1411                 } else {
1412                     None
1413                 }
1414             }
1415             BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
1416                 // (int, int) | (uint, uint) | (float, float)
1417                 (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
1418                 | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
1419                 | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
1420                     Some(rhs_ty)
1421                 }
1422                 // ({int}, int) | ({int}, uint)
1423                 (
1424                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1425                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1426                 ) => Some(rhs_ty),
1427                 // (int, {int}) | (uint, {int})
1428                 (
1429                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1430                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1431                 ) => Some(lhs_ty),
1432                 // ({float} | float)
1433                 (
1434                     TyKind::InferenceVar(_, TyVariableKind::Float),
1435                     TyKind::Scalar(Scalar::Float(_)),
1436                 ) => Some(rhs_ty),
1437                 // (float, {float})
1438                 (
1439                     TyKind::Scalar(Scalar::Float(_)),
1440                     TyKind::InferenceVar(_, TyVariableKind::Float),
1441                 ) => Some(lhs_ty),
1442                 // ({int}, {int}) | ({float}, {float})
1443                 (
1444                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1445                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1446                 )
1447                 | (
1448                     TyKind::InferenceVar(_, TyVariableKind::Float),
1449                     TyKind::InferenceVar(_, TyVariableKind::Float),
1450                 ) => Some(rhs_ty),
1451                 _ => None,
1452             },
1453         }
1454     }
1455
1456     fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
1457         Some(match op {
1458             BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
1459             BinaryOp::Assignment { op: None } => lhs_ty,
1460             BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
1461                 .resolve_ty_shallow(&lhs_ty)
1462                 .kind(Interner)
1463             {
1464                 TyKind::Scalar(_) | TyKind::Str => lhs_ty,
1465                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1466                 _ => return None,
1467             },
1468             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
1469             BinaryOp::CmpOp(CmpOp::Ord { .. })
1470             | BinaryOp::Assignment { op: Some(_) }
1471             | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
1472                 TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
1473                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1474                 _ => return None,
1475             },
1476         })
1477     }
1478 }