src/tools/rust-analyzer/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::{
  14         ArithOp, Array, BinaryOp, ClosureKind, CmpOp, Expr, ExprId, LabelId, Literal, Statement,
  15         UnaryOp,
  16     },
  17     generics::TypeOrConstParamData,
  18     path::{GenericArg, GenericArgs},
  19     resolver::resolver_for_expr,
  20     ConstParamId, FieldId, ItemContainerId, Lookup,
  21 };
  22 use hir_expand::name::Name;
  23 use stdx::always;
  24 use syntax::ast::RangeOp;
  25
  26 use crate::{
  27     autoderef::{self, Autoderef},
  28     consteval,
  29     infer::{coerce::CoerceMany, find_continuable, BreakableKind},
  30     lower::{
  31         const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
  32     },
  33     mapping::{from_chalk, ToChalk},
  34     method_resolution::{self, lang_names_for_bin_op, VisibleFromModule},
  35     primitive::{self, UintTy},
  36     static_lifetime, to_chalk_trait_id,
  37     utils::{generics, Generics},
  38     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, Interner, Rawness, Scalar,
  39     Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  40 };
  41
  42 use super::{
  43     coerce::auto_deref_adjust_steps, find_breakable, BindingMode, BreakableContext, Diverges,
  44     Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch,
  45 };
  46
  47 impl<'a> InferenceContext<'a> {
  48     pub(crate) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  49         let ty = self.infer_expr_inner(tgt_expr, expected);
  50         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  51             let could_unify = self.unify(&ty, &expected_ty);
  52             if !could_unify {
  53                 self.result.type_mismatches.insert(
  54                     tgt_expr.into(),
  55                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  56                 );
  57             }
  58         }
  59         ty
  60     }
  61
  62     /// Infer type of expression with possibly implicit coerce to the expected type.
  63     /// Return the type after possible coercion.
  64     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  65         let ty = self.infer_expr_inner(expr, expected);
  66         if let Some(target) = expected.only_has_type(&mut self.table) {
  67             match self.coerce(Some(expr), &ty, &target) {
  68                 Ok(res) => res,
  69                 Err(_) => {
  70                     self.result.type_mismatches.insert(
  71                         expr.into(),
  72                         TypeMismatch { expected: target.clone(), actual: ty.clone() },
  73                     );
  74                     target
  75                 }
  76             }
  77         } else {
  78             ty
  79         }
  80     }
  81
  82     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  83         self.db.unwind_if_cancelled();
  84
  85         let ty = match &self.body[tgt_expr] {
  86             Expr::Missing => self.err_ty(),
  87             &Expr::If { condition, then_branch, else_branch } => {
  88                 self.infer_expr(
  89                     condition,
  90                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
  91                 );
  92
  93                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
  94                 let mut both_arms_diverge = Diverges::Always;
  95
  96                 let result_ty = self.table.new_type_var();
  97                 let then_ty = self.infer_expr_inner(then_branch, expected);
  98                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
  99                 let mut coerce = CoerceMany::new(result_ty);
 100                 coerce.coerce(self, Some(then_branch), &then_ty);
 101                 let else_ty = match else_branch {
 102                     Some(else_branch) => self.infer_expr_inner(else_branch, expected),
 103                     None => TyBuilder::unit(),
 104                 };
 105                 both_arms_diverge &= self.diverges;
 106                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 107                 coerce.coerce(self, else_branch, &else_ty);
 108
 109                 self.diverges = condition_diverges | both_arms_diverge;
 110
 111                 coerce.complete()
 112             }
 113             &Expr::Let { pat, expr } => {
 114                 let input_ty = self.infer_expr(expr, &Expectation::none());
 115                 self.infer_pat(pat, &input_ty, BindingMode::default());
 116                 TyKind::Scalar(Scalar::Bool).intern(Interner)
 117             }
 118             Expr::Block { statements, tail, label, id: _ } => {
 119                 let old_resolver = mem::replace(
 120                     &mut self.resolver,
 121                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 122                 );
 123                 let ty = match label {
 124                     Some(_) => {
 125                         let break_ty = self.table.new_type_var();
 126                         let (breaks, ty) = self.with_breakable_ctx(
 127                             BreakableKind::Block,
 128                             break_ty.clone(),
 129                             *label,
 130                             |this| {
 131                                 this.infer_block(
 132                                     tgt_expr,
 133                                     statements,
 134                                     *tail,
 135                                     &Expectation::has_type(break_ty),
 136                                 )
 137                             },
 138                         );
 139                         breaks.unwrap_or(ty)
 140                     }
 141                     None => self.infer_block(tgt_expr, statements, *tail, expected),
 142                 };
 143                 self.resolver = old_resolver;
 144                 ty
 145             }
 146             Expr::Unsafe { body } => self.infer_expr(*body, expected),
 147             Expr::Const { body } => {
 148                 self.with_breakable_ctx(BreakableKind::Border, self.err_ty(), None, |this| {
 149                     this.infer_expr(*body, expected)
 150                 })
 151                 .1
 152             }
 153             Expr::TryBlock { body } => {
 154                 self.with_breakable_ctx(BreakableKind::Border, self.err_ty(), None, |this| {
 155                     let _inner = this.infer_expr(*body, expected);
 156                 });
 157                 // FIXME should be std::result::Result<{inner}, _>
 158                 self.err_ty()
 159             }
 160             Expr::Async { body } => {
 161                 let ret_ty = self.table.new_type_var();
 162                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 163                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 164
 165                 let (_, inner_ty) =
 166                     self.with_breakable_ctx(BreakableKind::Border, self.err_ty(), None, |this| {
 167                         this.infer_expr_coerce(*body, &Expectation::has_type(ret_ty))
 168                     });
 169
 170                 self.diverges = prev_diverges;
 171                 self.return_ty = prev_ret_ty;
 172
 173                 // Use the first type parameter as the output type of future.
 174                 // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 175                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 176                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 177                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
 178                     .intern(Interner)
 179             }
 180             &Expr::Loop { body, label } => {
 181                 let ty = self.table.new_type_var();
 182                 let (breaks, ()) =
 183                     self.with_breakable_ctx(BreakableKind::Loop, ty, label, |this| {
 184                         this.infer_expr(body, &Expectation::has_type(TyBuilder::unit()));
 185                     });
 186
 187                 match breaks {
 188                     Some(breaks) => {
 189                         self.diverges = Diverges::Maybe;
 190                         breaks
 191                     }
 192                     None => TyKind::Never.intern(Interner),
 193                 }
 194             }
 195             &Expr::While { condition, body, label } => {
 196                 self.with_breakable_ctx(BreakableKind::Loop, self.err_ty(), label, |this| {
 197                     this.infer_expr(
 198                         condition,
 199                         &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 200                     );
 201                     this.infer_expr(body, &Expectation::has_type(TyBuilder::unit()));
 202                 });
 203
 204                 // the body may not run, so it diverging doesn't mean we diverge
 205                 self.diverges = Diverges::Maybe;
 206                 TyBuilder::unit()
 207             }
 208             &Expr::For { iterable, body, pat, label } => {
 209                 let iterable_ty = self.infer_expr(iterable, &Expectation::none());
 210                 let into_iter_ty =
 211                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 212                 let pat_ty =
 213                     self.resolve_associated_type(into_iter_ty, self.resolve_iterator_item());
 214
 215                 self.infer_pat(pat, &pat_ty, BindingMode::default());
 216                 self.with_breakable_ctx(BreakableKind::Loop, self.err_ty(), label, |this| {
 217                     this.infer_expr(body, &Expectation::has_type(TyBuilder::unit()));
 218                 });
 219
 220                 // the body may not run, so it diverging doesn't mean we diverge
 221                 self.diverges = Diverges::Maybe;
 222                 TyBuilder::unit()
 223             }
 224             Expr::Closure { body, args, ret_type, arg_types, closure_kind } => {
 225                 assert_eq!(args.len(), arg_types.len());
 226
 227                 let mut sig_tys = Vec::new();
 228
 229                 // collect explicitly written argument types
 230                 for arg_type in arg_types.iter() {
 231                     let arg_ty = match arg_type {
 232                         Some(type_ref) => self.make_ty(type_ref),
 233                         None => self.table.new_type_var(),
 234                     };
 235                     sig_tys.push(arg_ty);
 236                 }
 237
 238                 // add return type
 239                 let ret_ty = match ret_type {
 240                     Some(type_ref) => self.make_ty(type_ref),
 241                     None => self.table.new_type_var(),
 242                 };
 243                 sig_tys.push(ret_ty.clone());
 244                 let sig_ty = TyKind::Function(FnPointer {
 245                     num_binders: 0,
 246                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 247                     substitution: FnSubst(
 248                         Substitution::from_iter(Interner, sig_tys.clone()).shifted_in(Interner),
 249                     ),
 250                 })
 251                 .intern(Interner);
 252
 253                 let (ty, resume_yield_tys) = if matches!(closure_kind, ClosureKind::Generator(_)) {
 254                     // FIXME: report error when there are more than 1 parameter.
 255                     let resume_ty = match sig_tys.first() {
 256                         // When `sig_tys.len() == 1` the first type is the return type, not the
 257                         // first parameter type.
 258                         Some(ty) if sig_tys.len() > 1 => ty.clone(),
 259                         _ => self.result.standard_types.unit.clone(),
 260                     };
 261                     let yield_ty = self.table.new_type_var();
 262
 263                     let subst = TyBuilder::subst_for_generator(self.db, self.owner)
 264                         .push(resume_ty.clone())
 265                         .push(yield_ty.clone())
 266                         .push(ret_ty.clone())
 267                         .build();
 268
 269                     let generator_id = self.db.intern_generator((self.owner, tgt_expr)).into();
 270                     let generator_ty = TyKind::Generator(generator_id, subst).intern(Interner);
 271
 272                     (generator_ty, Some((resume_ty, yield_ty)))
 273                 } else {
 274                     let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 275                     let closure_ty =
 276                         TyKind::Closure(closure_id, Substitution::from1(Interner, sig_ty.clone()))
 277                             .intern(Interner);
 278
 279                     (closure_ty, None)
 280                 };
 281
 282                 // Eagerly try to relate the closure type with the expected
 283                 // type, otherwise we often won't have enough information to
 284                 // infer the body.
 285                 self.deduce_closure_type_from_expectations(tgt_expr, &ty, &sig_ty, expected);
 286
 287                 // Now go through the argument patterns
 288                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 289                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 290                 }
 291
 292                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 293                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 294                 let prev_resume_yield_tys =
 295                     mem::replace(&mut self.resume_yield_tys, resume_yield_tys);
 296
 297                 self.with_breakable_ctx(BreakableKind::Border, self.err_ty(), None, |this| {
 298                     this.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 299                 });
 300
 301                 self.diverges = prev_diverges;
 302                 self.return_ty = prev_ret_ty;
 303                 self.resume_yield_tys = prev_resume_yield_tys;
 304
 305                 ty
 306             }
 307             Expr::Call { callee, args, .. } => {
 308                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 309                 let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone());
 310                 let mut res = None;
 311                 let mut derefed_callee = callee_ty.clone();
 312                 // manual loop to be able to access `derefs.table`
 313                 while let Some((callee_deref_ty, _)) = derefs.next() {
 314                     res = derefs.table.callable_sig(&callee_deref_ty, args.len());
 315                     if res.is_some() {
 316                         derefed_callee = callee_deref_ty;
 317                         break;
 318                     }
 319                 }
 320                 // if the function is unresolved, we use is_varargs=true to
 321                 // suppress the arg count diagnostic here
 322                 let is_varargs =
 323                     derefed_callee.callable_sig(self.db).map_or(false, |sig| sig.is_varargs)
 324                         || res.is_none();
 325                 let (param_tys, ret_ty) = match res {
 326                     Some(res) => {
 327                         let adjustments = auto_deref_adjust_steps(&derefs);
 328                         self.write_expr_adj(*callee, adjustments);
 329                         res
 330                     }
 331                     None => (Vec::new(), self.err_ty()), // FIXME diagnostic
 332                 };
 333                 let indices_to_skip = self.check_legacy_const_generics(derefed_callee, args);
 334                 self.register_obligations_for_call(&callee_ty);
 335
 336                 let expected_inputs = self.expected_inputs_for_expected_output(
 337                     expected,
 338                     ret_ty.clone(),
 339                     param_tys.clone(),
 340                 );
 341
 342                 self.check_call_arguments(
 343                     tgt_expr,
 344                     args,
 345                     &expected_inputs,
 346                     &param_tys,
 347                     &indices_to_skip,
 348                     is_varargs,
 349                 );
 350                 self.normalize_associated_types_in(ret_ty)
 351             }
 352             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 353                 .infer_method_call(
 354                     tgt_expr,
 355                     *receiver,
 356                     args,
 357                     method_name,
 358                     generic_args.as_deref(),
 359                     expected,
 360                 ),
 361             Expr::Match { expr, arms } => {
 362                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 363
 364                 let expected = expected.adjust_for_branches(&mut self.table);
 365
 366                 let result_ty = if arms.is_empty() {
 367                     TyKind::Never.intern(Interner)
 368                 } else {
 369                     match &expected {
 370                         Expectation::HasType(ty) => ty.clone(),
 371                         _ => self.table.new_type_var(),
 372                     }
 373                 };
 374                 let mut coerce = CoerceMany::new(result_ty);
 375
 376                 let matchee_diverges = self.diverges;
 377                 let mut all_arms_diverge = Diverges::Always;
 378
 379                 for arm in arms.iter() {
 380                     self.diverges = Diverges::Maybe;
 381                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 382                     if let Some(guard_expr) = arm.guard {
 383                         self.infer_expr(
 384                             guard_expr,
 385                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 386                         );
 387                     }
 388
 389                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 390                     all_arms_diverge &= self.diverges;
 391                     coerce.coerce(self, Some(arm.expr), &arm_ty);
 392                 }
 393
 394                 self.diverges = matchee_diverges | all_arms_diverge;
 395
 396                 coerce.complete()
 397             }
 398             Expr::Path(p) => {
 399                 // FIXME this could be more efficient...
 400                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 401                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
 402             }
 403             Expr::Continue { label } => {
 404                 if let None = find_continuable(&mut self.breakables, label.as_ref()) {
 405                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 406                         expr: tgt_expr,
 407                         is_break: false,
 408                     });
 409                 };
 410                 TyKind::Never.intern(Interner)
 411             }
 412             Expr::Break { expr, label } => {
 413                 let val_ty = if let Some(expr) = *expr {
 414                     self.infer_expr(expr, &Expectation::none())
 415                 } else {
 416                     TyBuilder::unit()
 417                 };
 418
 419                 match find_breakable(&mut self.breakables, label.as_ref()) {
 420                     Some(ctxt) => {
 421                         // avoiding the borrowck
 422                         let mut coerce = mem::replace(
 423                             &mut ctxt.coerce,
 424                             CoerceMany::new(self.result.standard_types.unknown.clone()),
 425                         );
 426
 427                         // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 428                         coerce.coerce(self, *expr, &val_ty);
 429
 430                         let ctxt = find_breakable(&mut self.breakables, label.as_ref())
 431                             .expect("breakable stack changed during coercion");
 432                         ctxt.coerce = coerce;
 433                         ctxt.may_break = true;
 434                     }
 435                     None => {
 436                         self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 437                             expr: tgt_expr,
 438                             is_break: true,
 439                         });
 440                     }
 441                 }
 442                 TyKind::Never.intern(Interner)
 443             }
 444             Expr::Return { expr } => {
 445                 if let Some(expr) = expr {
 446                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 447                 } else {
 448                     let unit = TyBuilder::unit();
 449                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
 450                 }
 451                 TyKind::Never.intern(Interner)
 452             }
 453             Expr::Yield { expr } => {
 454                 if let Some((resume_ty, yield_ty)) = self.resume_yield_tys.clone() {
 455                     if let Some(expr) = expr {
 456                         self.infer_expr_coerce(*expr, &Expectation::has_type(yield_ty));
 457                     } else {
 458                         let unit = self.result.standard_types.unit.clone();
 459                         let _ = self.coerce(Some(tgt_expr), &unit, &yield_ty);
 460                     }
 461                     resume_ty
 462                 } else {
 463                     // FIXME: report error (yield expr in non-generator)
 464                     TyKind::Error.intern(Interner)
 465                 }
 466             }
 467             Expr::RecordLit { path, fields, spread, .. } => {
 468                 let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
 469                 if let Some(variant) = def_id {
 470                     self.write_variant_resolution(tgt_expr.into(), variant);
 471                 }
 472
 473                 if let Some(t) = expected.only_has_type(&mut self.table) {
 474                     self.unify(&ty, &t);
 475                 }
 476
 477                 let substs = ty
 478                     .as_adt()
 479                     .map(|(_, s)| s.clone())
 480                     .unwrap_or_else(|| Substitution::empty(Interner));
 481                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 482                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 483                 for field in fields.iter() {
 484                     let field_def =
 485                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 486                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 487                             None => {
 488                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 489                                     expr: field.expr,
 490                                 });
 491                                 None
 492                             }
 493                         });
 494                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 495                         field_types[it.local_id].clone().substitute(Interner, &substs)
 496                     });
 497                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 498                 }
 499                 if let Some(expr) = spread {
 500                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 501                 }
 502                 ty
 503             }
 504             Expr::Field { expr, name } => {
 505                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 506
 507                 let mut autoderef = Autoderef::new(&mut self.table, receiver_ty);
 508                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
 509                     let (field_id, parameters) = match derefed_ty.kind(Interner) {
 510                         TyKind::Tuple(_, substs) => {
 511                             return name.as_tuple_index().and_then(|idx| {
 512                                 substs
 513                                     .as_slice(Interner)
 514                                     .get(idx)
 515                                     .map(|a| a.assert_ty_ref(Interner))
 516                                     .cloned()
 517                             });
 518                         }
 519                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 520                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 521                             let field = FieldId { parent: (*s).into(), local_id };
 522                             (field, parameters.clone())
 523                         }
 524                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 525                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 526                             let field = FieldId { parent: (*u).into(), local_id };
 527                             (field, parameters.clone())
 528                         }
 529                         _ => return None,
 530                     };
 531                     let is_visible = self.db.field_visibilities(field_id.parent)[field_id.local_id]
 532                         .is_visible_from(self.db.upcast(), self.resolver.module());
 533                     if !is_visible {
 534                         // Write down the first field resolution even if it is not visible
 535                         // This aids IDE features for private fields like goto def and in
 536                         // case of autoderef finding an applicable field, this will be
 537                         // overwritten in a following cycle
 538                         if let Entry::Vacant(entry) = self.result.field_resolutions.entry(tgt_expr)
 539                         {
 540                             entry.insert(field_id);
 541                         }
 542                         return None;
 543                     }
 544                     // can't have `write_field_resolution` here because `self.table` is borrowed :(
 545                     self.result.field_resolutions.insert(tgt_expr, field_id);
 546                     let ty = self.db.field_types(field_id.parent)[field_id.local_id]
 547                         .clone()
 548                         .substitute(Interner, &parameters);
 549                     Some(ty)
 550                 });
 551                 let ty = match ty {
 552                     Some(ty) => {
 553                         let adjustments = auto_deref_adjust_steps(&autoderef);
 554                         self.write_expr_adj(*expr, adjustments);
 555                         let ty = self.insert_type_vars(ty);
 556                         let ty = self.normalize_associated_types_in(ty);
 557                         ty
 558                     }
 559                     _ => self.err_ty(),
 560                 };
 561                 ty
 562             }
 563             Expr::Await { expr } => {
 564                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 565                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 566             }
 567             Expr::Try { expr } => {
 568                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 569                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 570             }
 571             Expr::Cast { expr, type_ref } => {
 572                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 573                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 574                 let cast_ty = self.make_ty(type_ref);
 575                 // FIXME check the cast...
 576                 cast_ty
 577             }
 578             Expr::Ref { expr, rawness, mutability } => {
 579                 let mutability = lower_to_chalk_mutability(*mutability);
 580                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 581                     .only_has_type(&mut self.table)
 582                     .as_ref()
 583                     .and_then(|t| t.as_reference_or_ptr())
 584                 {
 585                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 586                         // FIXME: record type error - expected mut reference but found shared ref,
 587                         // which cannot be coerced
 588                     }
 589                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 590                         // FIXME: record type error - expected reference but found ptr,
 591                         // which cannot be coerced
 592                     }
 593                     Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
 594                 } else {
 595                     Expectation::none()
 596                 };
 597                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 598                 match rawness {
 599                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 600                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 601                 }
 602                 .intern(Interner)
 603             }
 604             &Expr::Box { expr } => self.infer_expr_box(expr, expected),
 605             Expr::UnaryOp { expr, op } => {
 606                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 607                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 608                 match op {
 609                     UnaryOp::Deref => {
 610                         autoderef::deref(&mut self.table, inner_ty).unwrap_or_else(|| self.err_ty())
 611                     }
 612                     UnaryOp::Neg => {
 613                         match inner_ty.kind(Interner) {
 614                             // Fast path for builtins
 615                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
 616                             | TyKind::InferenceVar(
 617                                 _,
 618                                 TyVariableKind::Integer | TyVariableKind::Float,
 619                             ) => inner_ty,
 620                             // Otherwise we resolve via the std::ops::Neg trait
 621                             _ => self
 622                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 623                         }
 624                     }
 625                     UnaryOp::Not => {
 626                         match inner_ty.kind(Interner) {
 627                             // Fast path for builtins
 628                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
 629                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 630                             // Otherwise we resolve via the std::ops::Not trait
 631                             _ => self
 632                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 633                         }
 634                     }
 635                 }
 636             }
 637             Expr::BinaryOp { lhs, rhs, op } => match op {
 638                 Some(BinaryOp::Assignment { op: None }) => {
 639                     let lhs = *lhs;
 640                     let is_ordinary = match &self.body[lhs] {
 641                         Expr::Array(_)
 642                         | Expr::RecordLit { .. }
 643                         | Expr::Tuple { .. }
 644                         | Expr::Underscore => false,
 645                         Expr::Call { callee, .. } => !matches!(&self.body[*callee], Expr::Path(_)),
 646                         _ => true,
 647                     };
 648
 649                     // In ordinary (non-destructuring) assignments, the type of
 650                     // `lhs` must be inferred first so that the ADT fields
 651                     // instantiations in RHS can be coerced to it. Note that this
 652                     // cannot happen in destructuring assignments because of how
 653                     // they are desugared.
 654                     if is_ordinary {
 655                         let lhs_ty = self.infer_expr(lhs, &Expectation::none());
 656                         self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
 657                     } else {
 658                         let rhs_ty = self.infer_expr(*rhs, &Expectation::none());
 659                         self.infer_assignee_expr(lhs, &rhs_ty);
 660                     }
 661                     self.result.standard_types.unit.clone()
 662                 }
 663                 Some(BinaryOp::LogicOp(_)) => {
 664                     let bool_ty = self.result.standard_types.bool_.clone();
 665                     self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
 666                     let lhs_diverges = self.diverges;
 667                     self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
 668                     // Depending on the LHS' value, the RHS can never execute.
 669                     self.diverges = lhs_diverges;
 670                     bool_ty
 671                 }
 672                 Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
 673                 _ => self.err_ty(),
 674             },
 675             Expr::Range { lhs, rhs, range_type } => {
 676                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 677                 let rhs_expect = lhs_ty
 678                     .as_ref()
 679                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 680                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 681                 match (range_type, lhs_ty, rhs_ty) {
 682                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 683                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 684                         None => self.err_ty(),
 685                     },
 686                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 687                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 688                         None => self.err_ty(),
 689                     },
 690                     (RangeOp::Inclusive, None, Some(ty)) => {
 691                         match self.resolve_range_to_inclusive() {
 692                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 693                             None => self.err_ty(),
 694                         }
 695                     }
 696                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 697                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 698                         None => self.err_ty(),
 699                     },
 700                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 701                         match self.resolve_range_inclusive() {
 702                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 703                             None => self.err_ty(),
 704                         }
 705                     }
 706                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 707                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 708                         None => self.err_ty(),
 709                     },
 710                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 711                 }
 712             }
 713             Expr::Index { base, index } => {
 714                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 715                 let index_ty = self.infer_expr(*index, &Expectation::none());
 716
 717                 if let Some(index_trait) = self.resolve_ops_index() {
 718                     let canonicalized = self.canonicalize(base_ty.clone());
 719                     let receiver_adjustments = method_resolution::resolve_indexing_op(
 720                         self.db,
 721                         self.trait_env.clone(),
 722                         canonicalized.value,
 723                         index_trait,
 724                     );
 725                     let (self_ty, adj) = receiver_adjustments
 726                         .map_or((self.err_ty(), Vec::new()), |adj| {
 727                             adj.apply(&mut self.table, base_ty)
 728                         });
 729                     self.write_expr_adj(*base, adj);
 730                     self.resolve_associated_type_with_params(
 731                         self_ty,
 732                         self.resolve_ops_index_output(),
 733                         &[GenericArgData::Ty(index_ty).intern(Interner)],
 734                     )
 735                 } else {
 736                     self.err_ty()
 737                 }
 738             }
 739             Expr::Tuple { exprs, .. } => {
 740                 let mut tys = match expected
 741                     .only_has_type(&mut self.table)
 742                     .as_ref()
 743                     .map(|t| t.kind(Interner))
 744                 {
 745                     Some(TyKind::Tuple(_, substs)) => substs
 746                         .iter(Interner)
 747                         .map(|a| a.assert_ty_ref(Interner).clone())
 748                         .chain(repeat_with(|| self.table.new_type_var()))
 749                         .take(exprs.len())
 750                         .collect::<Vec<_>>(),
 751                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 752                 };
 753
 754                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 755                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 756                 }
 757
 758                 TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
 759             }
 760             Expr::Array(array) => {
 761                 let elem_ty =
 762                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
 763                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
 764                         _ => self.table.new_type_var(),
 765                     };
 766                 let mut coerce = CoerceMany::new(elem_ty.clone());
 767
 768                 let expected = Expectation::has_type(elem_ty.clone());
 769                 let len = match array {
 770                     Array::ElementList { elements, .. } => {
 771                         for &expr in elements.iter() {
 772                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
 773                             coerce.coerce(self, Some(expr), &cur_elem_ty);
 774                         }
 775                         consteval::usize_const(Some(elements.len() as u128))
 776                     }
 777                     &Array::Repeat { initializer, repeat } => {
 778                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
 779                         self.infer_expr(
 780                             repeat,
 781                             &Expectation::has_type(
 782                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
 783                             ),
 784                         );
 785
 786                         if let Some(g_def) = self.owner.as_generic_def_id() {
 787                             let generics = generics(self.db.upcast(), g_def);
 788                             consteval::eval_to_const(
 789                                 repeat,
 790                                 ParamLoweringMode::Placeholder,
 791                                 self,
 792                                 || generics,
 793                                 DebruijnIndex::INNERMOST,
 794                             )
 795                         } else {
 796                             consteval::usize_const(None)
 797                         }
 798                     }
 799                 };
 800
 801                 TyKind::Array(coerce.complete(), len).intern(Interner)
 802             }
 803             Expr::Literal(lit) => match lit {
 804                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
 805                 Literal::String(..) => {
 806                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
 807                         .intern(Interner)
 808                 }
 809                 Literal::ByteString(bs) => {
 810                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 811
 812                     let len = consteval::usize_const(Some(bs.len() as u128));
 813
 814                     let array_type = TyKind::Array(byte_type, len).intern(Interner);
 815                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
 816                 }
 817                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
 818                 Literal::Int(_v, ty) => match ty {
 819                     Some(int_ty) => {
 820                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 821                             .intern(Interner)
 822                     }
 823                     None => self.table.new_integer_var(),
 824                 },
 825                 Literal::Uint(_v, ty) => match ty {
 826                     Some(int_ty) => {
 827                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 828                             .intern(Interner)
 829                     }
 830                     None => self.table.new_integer_var(),
 831                 },
 832                 Literal::Float(_v, ty) => match ty {
 833                     Some(float_ty) => {
 834                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 835                             .intern(Interner)
 836                     }
 837                     None => self.table.new_float_var(),
 838                 },
 839             },
 840             Expr::Underscore => {
 841                 // Underscore expressions may only appear in assignee expressions,
 842                 // which are handled by `infer_assignee_expr()`, so any underscore
 843                 // expression reaching this branch is an error.
 844                 self.err_ty()
 845             }
 846         };
 847         // use a new type variable if we got unknown here
 848         let ty = self.insert_type_vars_shallow(ty);
 849         self.write_expr_ty(tgt_expr, ty.clone());
 850         if self.resolve_ty_shallow(&ty).is_never() {
 851             // Any expression that produces a value of type `!` must have diverged
 852             self.diverges = Diverges::Always;
 853         }
 854         ty
 855     }
 856
 857     fn infer_expr_box(&mut self, inner_expr: ExprId, expected: &Expectation) -> Ty {
 858         if let Some(box_id) = self.resolve_boxed_box() {
 859             let table = &mut self.table;
 860             let inner_exp = expected
 861                 .to_option(table)
 862                 .as_ref()
 863                 .map(|e| e.as_adt())
 864                 .flatten()
 865                 .filter(|(e_adt, _)| e_adt == &box_id)
 866                 .map(|(_, subts)| {
 867                     let g = subts.at(Interner, 0);
 868                     Expectation::rvalue_hint(table, Ty::clone(g.assert_ty_ref(Interner)))
 869                 })
 870                 .unwrap_or_else(Expectation::none);
 871
 872             let inner_ty = self.infer_expr_inner(inner_expr, &inner_exp);
 873             TyBuilder::adt(self.db, box_id)
 874                 .push(inner_ty)
 875                 .fill_with_defaults(self.db, || self.table.new_type_var())
 876                 .build()
 877         } else {
 878             self.err_ty()
 879         }
 880     }
 881
 882     pub(super) fn infer_assignee_expr(&mut self, lhs: ExprId, rhs_ty: &Ty) -> Ty {
 883         let is_rest_expr = |expr| {
 884             matches!(
 885                 &self.body[expr],
 886                 Expr::Range { lhs: None, rhs: None, range_type: RangeOp::Exclusive },
 887             )
 888         };
 889
 890         let rhs_ty = self.resolve_ty_shallow(rhs_ty);
 891
 892         let ty = match &self.body[lhs] {
 893             Expr::Tuple { exprs, .. } => {
 894                 // We don't consider multiple ellipses. This is analogous to
 895                 // `hir_def::body::lower::ExprCollector::collect_tuple_pat()`.
 896                 let ellipsis = exprs.iter().position(|e| is_rest_expr(*e));
 897                 let exprs: Vec<_> = exprs.iter().filter(|e| !is_rest_expr(**e)).copied().collect();
 898
 899                 self.infer_tuple_pat_like(&rhs_ty, (), ellipsis, &exprs)
 900             }
 901             Expr::Call { callee, args, .. } => {
 902                 // Tuple structs
 903                 let path = match &self.body[*callee] {
 904                     Expr::Path(path) => Some(path),
 905                     _ => None,
 906                 };
 907
 908                 // We don't consider multiple ellipses. This is analogous to
 909                 // `hir_def::body::lower::ExprCollector::collect_tuple_pat()`.
 910                 let ellipsis = args.iter().position(|e| is_rest_expr(*e));
 911                 let args: Vec<_> = args.iter().filter(|e| !is_rest_expr(**e)).copied().collect();
 912
 913                 self.infer_tuple_struct_pat_like(path, &rhs_ty, (), lhs, ellipsis, &args)
 914             }
 915             Expr::Array(Array::ElementList { elements, .. }) => {
 916                 let elem_ty = match rhs_ty.kind(Interner) {
 917                     TyKind::Array(st, _) => st.clone(),
 918                     _ => self.err_ty(),
 919                 };
 920
 921                 // There's no need to handle `..` as it cannot be bound.
 922                 let sub_exprs = elements.iter().filter(|e| !is_rest_expr(**e));
 923
 924                 for e in sub_exprs {
 925                     self.infer_assignee_expr(*e, &elem_ty);
 926                 }
 927
 928                 match rhs_ty.kind(Interner) {
 929                     TyKind::Array(_, _) => rhs_ty.clone(),
 930                     // Even when `rhs_ty` is not an array type, this assignee
 931                     // expression is inferred to be an array (of unknown element
 932                     // type and length). This should not be just an error type,
 933                     // because we are to compute the unifiability of this type and
 934                     // `rhs_ty` in the end of this function to issue type mismatches.
 935                     _ => TyKind::Array(self.err_ty(), crate::consteval::usize_const(None))
 936                         .intern(Interner),
 937                 }
 938             }
 939             Expr::RecordLit { path, fields, .. } => {
 940                 let subs = fields.iter().map(|f| (f.name.clone(), f.expr));
 941
 942                 self.infer_record_pat_like(path.as_deref(), &rhs_ty, (), lhs.into(), subs)
 943             }
 944             Expr::Underscore => rhs_ty.clone(),
 945             _ => {
 946                 // `lhs` is a place expression, a unit struct, or an enum variant.
 947                 let lhs_ty = self.infer_expr(lhs, &Expectation::none());
 948
 949                 // This is the only branch where this function may coerce any type.
 950                 // We are returning early to avoid the unifiability check below.
 951                 let lhs_ty = self.insert_type_vars_shallow(lhs_ty);
 952                 let ty = match self.coerce(None, &rhs_ty, &lhs_ty) {
 953                     Ok(ty) => ty,
 954                     Err(_) => {
 955                         self.result.type_mismatches.insert(
 956                             lhs.into(),
 957                             TypeMismatch { expected: rhs_ty.clone(), actual: lhs_ty.clone() },
 958                         );
 959                         // `rhs_ty` is returned so no further type mismatches are
 960                         // reported because of this mismatch.
 961                         rhs_ty
 962                     }
 963                 };
 964                 self.write_expr_ty(lhs, ty.clone());
 965                 return ty;
 966             }
 967         };
 968
 969         let ty = self.insert_type_vars_shallow(ty);
 970         if !self.unify(&ty, &rhs_ty) {
 971             self.result
 972                 .type_mismatches
 973                 .insert(lhs.into(), TypeMismatch { expected: rhs_ty.clone(), actual: ty.clone() });
 974         }
 975         self.write_expr_ty(lhs, ty.clone());
 976         ty
 977     }
 978
 979     fn infer_overloadable_binop(
 980         &mut self,
 981         lhs: ExprId,
 982         op: BinaryOp,
 983         rhs: ExprId,
 984         tgt_expr: ExprId,
 985     ) -> Ty {
 986         let lhs_expectation = Expectation::none();
 987         let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
 988         let rhs_ty = self.table.new_type_var();
 989
 990         let trait_func = lang_names_for_bin_op(op).and_then(|(name, lang_item)| {
 991             let trait_id = self.resolve_lang_item(lang_item)?.as_trait()?;
 992             let func = self.db.trait_data(trait_id).method_by_name(&name)?;
 993             Some((trait_id, func))
 994         });
 995         let (trait_, func) = match trait_func {
 996             Some(it) => it,
 997             None => {
 998                 let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
 999                 let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
1000                 return self
1001                     .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
1002                     .unwrap_or_else(|| self.err_ty());
1003             }
1004         };
1005
1006         // HACK: We can use this substitution for the function because the function itself doesn't
1007         // have its own generic parameters.
1008         let subst = TyBuilder::subst_for_def(self.db, trait_, None)
1009             .push(lhs_ty.clone())
1010             .push(rhs_ty.clone())
1011             .build();
1012         self.write_method_resolution(tgt_expr, func, subst.clone());
1013
1014         let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
1015         self.register_obligations_for_call(&method_ty);
1016
1017         self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
1018
1019         let ret_ty = match method_ty.callable_sig(self.db) {
1020             Some(sig) => sig.ret().clone(),
1021             None => self.err_ty(),
1022         };
1023
1024         let ret_ty = self.normalize_associated_types_in(ret_ty);
1025
1026         // FIXME: record autoref adjustments
1027
1028         // use knowledge of built-in binary ops, which can sometimes help inference
1029         if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
1030             self.unify(&builtin_rhs, &rhs_ty);
1031         }
1032         if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
1033             self.unify(&builtin_ret, &ret_ty);
1034         }
1035
1036         ret_ty
1037     }
1038
1039     fn infer_block(
1040         &mut self,
1041         expr: ExprId,
1042         statements: &[Statement],
1043         tail: Option<ExprId>,
1044         expected: &Expectation,
1045     ) -> Ty {
1046         for stmt in statements {
1047             match stmt {
1048                 Statement::Let { pat, type_ref, initializer, else_branch } => {
1049                     let decl_ty = type_ref
1050                         .as_ref()
1051                         .map(|tr| self.make_ty(tr))
1052                         .unwrap_or_else(|| self.err_ty());
1053
1054                     // Always use the declared type when specified
1055                     let mut ty = decl_ty.clone();
1056
1057                     if let Some(expr) = initializer {
1058                         let actual_ty =
1059                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
1060                         if decl_ty.is_unknown() {
1061                             ty = actual_ty;
1062                         }
1063                     }
1064
1065                     if let Some(expr) = else_branch {
1066                         self.infer_expr_coerce(
1067                             *expr,
1068                             &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
1069                         );
1070                     }
1071
1072                     self.infer_pat(*pat, &ty, BindingMode::default());
1073                 }
1074                 Statement::Expr { expr, .. } => {
1075                     self.infer_expr(*expr, &Expectation::none());
1076                 }
1077             }
1078         }
1079
1080         if let Some(expr) = tail {
1081             self.infer_expr_coerce(expr, expected)
1082         } else {
1083             // Citing rustc: if there is no explicit tail expression,
1084             // that is typically equivalent to a tail expression
1085             // of `()` -- except if the block diverges. In that
1086             // case, there is no value supplied from the tail
1087             // expression (assuming there are no other breaks,
1088             // this implies that the type of the block will be
1089             // `!`).
1090             if self.diverges.is_always() {
1091                 // we don't even make an attempt at coercion
1092                 self.table.new_maybe_never_var()
1093             } else {
1094                 if let Some(t) = expected.only_has_type(&mut self.table) {
1095                     if self.coerce(Some(expr), &TyBuilder::unit(), &t).is_err() {
1096                         self.result.type_mismatches.insert(
1097                             expr.into(),
1098                             TypeMismatch { expected: t.clone(), actual: TyBuilder::unit() },
1099                         );
1100                     }
1101                     t
1102                 } else {
1103                     TyBuilder::unit()
1104                 }
1105             }
1106         }
1107     }
1108
1109     fn infer_method_call(
1110         &mut self,
1111         tgt_expr: ExprId,
1112         receiver: ExprId,
1113         args: &[ExprId],
1114         method_name: &Name,
1115         generic_args: Option<&GenericArgs>,
1116         expected: &Expectation,
1117     ) -> Ty {
1118         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
1119         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
1120
1121         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
1122
1123         let resolved = method_resolution::lookup_method(
1124             &canonicalized_receiver.value,
1125             self.db,
1126             self.trait_env.clone(),
1127             &traits_in_scope,
1128             VisibleFromModule::Filter(self.resolver.module()),
1129             method_name,
1130         );
1131         let (receiver_ty, method_ty, substs) = match resolved {
1132             Some((adjust, func)) => {
1133                 let (ty, adjustments) = adjust.apply(&mut self.table, receiver_ty);
1134                 let generics = generics(self.db.upcast(), func.into());
1135                 let substs = self.substs_for_method_call(generics, generic_args);
1136                 self.write_expr_adj(receiver, adjustments);
1137                 self.write_method_resolution(tgt_expr, func, substs.clone());
1138                 (ty, self.db.value_ty(func.into()), substs)
1139             }
1140             None => (
1141                 receiver_ty,
1142                 Binders::empty(Interner, self.err_ty()),
1143                 Substitution::empty(Interner),
1144             ),
1145         };
1146         let method_ty = method_ty.substitute(Interner, &substs);
1147         self.register_obligations_for_call(&method_ty);
1148         let (formal_receiver_ty, param_tys, ret_ty, is_varargs) =
1149             match method_ty.callable_sig(self.db) {
1150                 Some(sig) => {
1151                     if !sig.params().is_empty() {
1152                         (
1153                             sig.params()[0].clone(),
1154                             sig.params()[1..].to_vec(),
1155                             sig.ret().clone(),
1156                             sig.is_varargs,
1157                         )
1158                     } else {
1159                         (self.err_ty(), Vec::new(), sig.ret().clone(), sig.is_varargs)
1160                     }
1161                 }
1162                 None => (self.err_ty(), Vec::new(), self.err_ty(), true),
1163             };
1164         self.unify(&formal_receiver_ty, &receiver_ty);
1165
1166         let expected_inputs =
1167             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
1168
1169         self.check_call_arguments(tgt_expr, args, &expected_inputs, &param_tys, &[], is_varargs);
1170         self.normalize_associated_types_in(ret_ty)
1171     }
1172
1173     fn expected_inputs_for_expected_output(
1174         &mut self,
1175         expected_output: &Expectation,
1176         output: Ty,
1177         inputs: Vec<Ty>,
1178     ) -> Vec<Ty> {
1179         if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
1180             self.table.fudge_inference(|table| {
1181                 if table.try_unify(&expected_ty, &output).is_ok() {
1182                     table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
1183                         chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
1184                         chalk_ir::VariableKind::Lifetime => {
1185                             var.to_lifetime(Interner).cast(Interner)
1186                         }
1187                         chalk_ir::VariableKind::Const(ty) => {
1188                             var.to_const(Interner, ty).cast(Interner)
1189                         }
1190                     })
1191                 } else {
1192                     Vec::new()
1193                 }
1194             })
1195         } else {
1196             Vec::new()
1197         }
1198     }
1199
1200     fn check_call_arguments(
1201         &mut self,
1202         expr: ExprId,
1203         args: &[ExprId],
1204         expected_inputs: &[Ty],
1205         param_tys: &[Ty],
1206         skip_indices: &[u32],
1207         is_varargs: bool,
1208     ) {
1209         if args.len() != param_tys.len() + skip_indices.len() && !is_varargs {
1210             self.push_diagnostic(InferenceDiagnostic::MismatchedArgCount {
1211                 call_expr: expr,
1212                 expected: param_tys.len() + skip_indices.len(),
1213                 found: args.len(),
1214             });
1215         }
1216
1217         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
1218         // We do this in a pretty awful way: first we type-check any arguments
1219         // that are not closures, then we type-check the closures. This is so
1220         // that we have more information about the types of arguments when we
1221         // type-check the functions. This isn't really the right way to do this.
1222         for &check_closures in &[false, true] {
1223             let mut skip_indices = skip_indices.into_iter().copied().fuse().peekable();
1224             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
1225             let expected_iter = expected_inputs
1226                 .iter()
1227                 .cloned()
1228                 .chain(param_iter.clone().skip(expected_inputs.len()));
1229             for (idx, ((&arg, param_ty), expected_ty)) in
1230                 args.iter().zip(param_iter).zip(expected_iter).enumerate()
1231             {
1232                 let is_closure = matches!(&self.body[arg], Expr::Closure { .. });
1233                 if is_closure != check_closures {
1234                     continue;
1235                 }
1236
1237                 while skip_indices.peek().map_or(false, |i| *i < idx as u32) {
1238                     skip_indices.next();
1239                 }
1240                 if skip_indices.peek().copied() == Some(idx as u32) {
1241                     continue;
1242                 }
1243
1244                 // the difference between param_ty and expected here is that
1245                 // expected is the parameter when the expected *return* type is
1246                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
1247                 // the expected type is already `&[i32]`, whereas param_ty is
1248                 // still an unbound type variable. We don't always want to force
1249                 // the parameter to coerce to the expected type (for example in
1250                 // `coerce_unsize_expected_type_4`).
1251                 let param_ty = self.normalize_associated_types_in(param_ty);
1252                 let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
1253                 // infer with the expected type we have...
1254                 let ty = self.infer_expr_inner(arg, &expected);
1255
1256                 // then coerce to either the expected type or just the formal parameter type
1257                 let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
1258                     // if we are coercing to the expectation, unify with the
1259                     // formal parameter type to connect everything
1260                     self.unify(&ty, &param_ty);
1261                     ty
1262                 } else {
1263                     param_ty
1264                 };
1265                 if !coercion_target.is_unknown() {
1266                     if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
1267                         self.result.type_mismatches.insert(
1268                             arg.into(),
1269                             TypeMismatch { expected: coercion_target, actual: ty.clone() },
1270                         );
1271                     }
1272                 }
1273             }
1274         }
1275     }
1276
1277     fn substs_for_method_call(
1278         &mut self,
1279         def_generics: Generics,
1280         generic_args: Option<&GenericArgs>,
1281     ) -> Substitution {
1282         let (parent_params, self_params, type_params, const_params, impl_trait_params) =
1283             def_generics.provenance_split();
1284         assert_eq!(self_params, 0); // method shouldn't have another Self param
1285         let total_len = parent_params + type_params + const_params + impl_trait_params;
1286         let mut substs = Vec::with_capacity(total_len);
1287
1288         // handle provided arguments
1289         if let Some(generic_args) = generic_args {
1290             // if args are provided, it should be all of them, but we can't rely on that
1291             for (arg, kind_id) in generic_args
1292                 .args
1293                 .iter()
1294                 .filter(|arg| !matches!(arg, GenericArg::Lifetime(_)))
1295                 .take(type_params + const_params)
1296                 .zip(def_generics.iter_id())
1297             {
1298                 if let Some(g) = generic_arg_to_chalk(
1299                     self.db,
1300                     kind_id,
1301                     arg,
1302                     self,
1303                     |this, type_ref| this.make_ty(type_ref),
1304                     |this, c, ty| {
1305                         const_or_path_to_chalk(
1306                             this.db,
1307                             &this.resolver,
1308                             ty,
1309                             c,
1310                             ParamLoweringMode::Placeholder,
1311                             || generics(this.db.upcast(), (&this.resolver).generic_def().unwrap()),
1312                             DebruijnIndex::INNERMOST,
1313                         )
1314                     },
1315                 ) {
1316                     substs.push(g);
1317                 }
1318             }
1319         };
1320
1321         // Handle everything else as unknown. This also handles generic arguments for the method's
1322         // parent (impl or trait), which should come after those for the method.
1323         for (id, data) in def_generics.iter().skip(substs.len()) {
1324             match data {
1325                 TypeOrConstParamData::TypeParamData(_) => {
1326                     substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner))
1327                 }
1328                 TypeOrConstParamData::ConstParamData(_) => {
1329                     substs.push(
1330                         GenericArgData::Const(self.table.new_const_var(
1331                             self.db.const_param_ty(ConstParamId::from_unchecked(id)),
1332                         ))
1333                         .intern(Interner),
1334                     )
1335                 }
1336             }
1337         }
1338         assert_eq!(substs.len(), total_len);
1339         Substitution::from_iter(Interner, substs)
1340     }
1341
1342     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1343         let callable_ty = self.resolve_ty_shallow(callable_ty);
1344         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(Interner) {
1345             let def: CallableDefId = from_chalk(self.db, *fn_def);
1346             let generic_predicates = self.db.generic_predicates(def.into());
1347             for predicate in generic_predicates.iter() {
1348                 let (predicate, binders) = predicate
1349                     .clone()
1350                     .substitute(Interner, parameters)
1351                     .into_value_and_skipped_binders();
1352                 always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
1353                 self.push_obligation(predicate.cast(Interner));
1354             }
1355             // add obligation for trait implementation, if this is a trait method
1356             match def {
1357                 CallableDefId::FunctionId(f) => {
1358                     if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
1359                         // construct a TraitRef
1360                         let params_len = parameters.len(Interner);
1361                         let trait_params_len = generics(self.db.upcast(), trait_.into()).len();
1362                         let substs = Substitution::from_iter(
1363                             Interner,
1364                             // The generic parameters for the trait come after those for the
1365                             // function.
1366                             &parameters.as_slice(Interner)[params_len - trait_params_len..],
1367                         );
1368                         self.push_obligation(
1369                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1370                                 .cast(Interner),
1371                         );
1372                     }
1373                 }
1374                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1375             }
1376         }
1377     }
1378
1379     /// Returns the argument indices to skip.
1380     fn check_legacy_const_generics(&mut self, callee: Ty, args: &[ExprId]) -> Box<[u32]> {
1381         let (func, subst) = match callee.kind(Interner) {
1382             TyKind::FnDef(fn_id, subst) => {
1383                 let callable = CallableDefId::from_chalk(self.db, *fn_id);
1384                 let func = match callable {
1385                     CallableDefId::FunctionId(f) => f,
1386                     _ => return Default::default(),
1387                 };
1388                 (func, subst)
1389             }
1390             _ => return Default::default(),
1391         };
1392
1393         let data = self.db.function_data(func);
1394         if data.legacy_const_generics_indices.is_empty() {
1395             return Default::default();
1396         }
1397
1398         // only use legacy const generics if the param count matches with them
1399         if data.params.len() + data.legacy_const_generics_indices.len() != args.len() {
1400             if args.len() <= data.params.len() {
1401                 return Default::default();
1402             } else {
1403                 // there are more parameters than there should be without legacy
1404                 // const params; use them
1405                 let mut indices = data.legacy_const_generics_indices.clone();
1406                 indices.sort();
1407                 return indices;
1408             }
1409         }
1410
1411         // check legacy const parameters
1412         for (subst_idx, arg_idx) in data.legacy_const_generics_indices.iter().copied().enumerate() {
1413             let arg = match subst.at(Interner, subst_idx).constant(Interner) {
1414                 Some(c) => c,
1415                 None => continue, // not a const parameter?
1416             };
1417             if arg_idx >= args.len() as u32 {
1418                 continue;
1419             }
1420             let _ty = arg.data(Interner).ty.clone();
1421             let expected = Expectation::none(); // FIXME use actual const ty, when that is lowered correctly
1422             self.infer_expr(args[arg_idx as usize], &expected);
1423             // FIXME: evaluate and unify with the const
1424         }
1425         let mut indices = data.legacy_const_generics_indices.clone();
1426         indices.sort();
1427         indices
1428     }
1429
1430     fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
1431         let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
1432         let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
1433         match op {
1434             BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
1435                 Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
1436             }
1437             BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
1438             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
1439                 // all integer combinations are valid here
1440                 if matches!(
1441                     lhs_ty.kind(Interner),
1442                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1443                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1444                 ) && matches!(
1445                     rhs_ty.kind(Interner),
1446                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1447                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1448                 ) {
1449                     Some(lhs_ty)
1450                 } else {
1451                     None
1452                 }
1453             }
1454             BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
1455                 // (int, int) | (uint, uint) | (float, float)
1456                 (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
1457                 | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
1458                 | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
1459                     Some(rhs_ty)
1460                 }
1461                 // ({int}, int) | ({int}, uint)
1462                 (
1463                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1464                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1465                 ) => Some(rhs_ty),
1466                 // (int, {int}) | (uint, {int})
1467                 (
1468                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1469                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1470                 ) => Some(lhs_ty),
1471                 // ({float} | float)
1472                 (
1473                     TyKind::InferenceVar(_, TyVariableKind::Float),
1474                     TyKind::Scalar(Scalar::Float(_)),
1475                 ) => Some(rhs_ty),
1476                 // (float, {float})
1477                 (
1478                     TyKind::Scalar(Scalar::Float(_)),
1479                     TyKind::InferenceVar(_, TyVariableKind::Float),
1480                 ) => Some(lhs_ty),
1481                 // ({int}, {int}) | ({float}, {float})
1482                 (
1483                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1484                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1485                 )
1486                 | (
1487                     TyKind::InferenceVar(_, TyVariableKind::Float),
1488                     TyKind::InferenceVar(_, TyVariableKind::Float),
1489                 ) => Some(rhs_ty),
1490                 _ => None,
1491             },
1492         }
1493     }
1494
1495     fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
1496         Some(match op {
1497             BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
1498             BinaryOp::Assignment { op: None } => lhs_ty,
1499             BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
1500                 .resolve_ty_shallow(&lhs_ty)
1501                 .kind(Interner)
1502             {
1503                 TyKind::Scalar(_) | TyKind::Str => lhs_ty,
1504                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1505                 _ => return None,
1506             },
1507             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
1508             BinaryOp::CmpOp(CmpOp::Ord { .. })
1509             | BinaryOp::Assignment { op: Some(_) }
1510             | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
1511                 TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
1512                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1513                 _ => return None,
1514             },
1515         })
1516     }
1517
1518     fn with_breakable_ctx<T>(
1519         &mut self,
1520         kind: BreakableKind,
1521         ty: Ty,
1522         label: Option<LabelId>,
1523         cb: impl FnOnce(&mut Self) -> T,
1524     ) -> (Option<Ty>, T) {
1525         self.breakables.push({
1526             let label = label.map(|label| self.body[label].name.clone());
1527             BreakableContext { kind, may_break: false, coerce: CoerceMany::new(ty), label }
1528         });
1529         let res = cb(self);
1530         let ctx = self.breakables.pop().expect("breakable stack broken");
1531         (ctx.may_break.then(|| ctx.coerce.complete()), res)
1532     }
1533 }