crates/hir_ty/src/infer/expr.rs

   1 //! Type inference for expressions.
   2
   3 use std::iter::{repeat, repeat_with};
   4 use std::{mem, sync::Arc};
   5
   6 use hir_def::{
   7     builtin_type::Signedness,
   8     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
   9     path::{GenericArg, GenericArgs},
  10     resolver::resolver_for_expr,
  11     AdtId, AssocContainerId, FieldId, Lookup,
  12 };
  13 use hir_expand::name::{name, Name};
  14 use syntax::ast::RangeOp;
  15 use test_utils::mark;
  16
  17 use crate::{
  18     autoderef, method_resolution, op,
  19     traits::{FnTrait, InEnvironment},
  20     utils::{generics, variant_data, Generics},
  21     ApplicationTy, Binders, CallableDefId, InferTy, IntTy, Mutability, Obligation, OpaqueTyId,
  22     Rawness, Substs, TraitRef, Ty, TypeCtor,
  23 };
  24
  25 use super::{
  26     find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
  27     InferenceDiagnostic, TypeMismatch,
  28 };
  29
  30 impl<'a> InferenceContext<'a> {
  31     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  32         let ty = self.infer_expr_inner(tgt_expr, expected);
  33         if ty.is_never() {
  34             // Any expression that produces a value of type `!` must have diverged
  35             self.diverges = Diverges::Always;
  36         }
  37         let could_unify = self.unify(&ty, &expected.ty);
  38         if !could_unify {
  39             self.result.type_mismatches.insert(
  40                 tgt_expr,
  41                 TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() },
  42             );
  43         }
  44         self.resolve_ty_as_possible(ty)
  45     }
  46
  47     /// Infer type of expression with possibly implicit coerce to the expected type.
  48     /// Return the type after possible coercion.
  49     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  50         let ty = self.infer_expr_inner(expr, &expected);
  51         let ty = if !self.coerce(&ty, &expected.coercion_target()) {
  52             self.result
  53                 .type_mismatches
  54                 .insert(expr, TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() });
  55             // Return actual type when type mismatch.
  56             // This is needed for diagnostic when return type mismatch.
  57             ty
  58         } else if expected.coercion_target() == &Ty::Unknown {
  59             ty
  60         } else {
  61             expected.ty.clone()
  62         };
  63
  64         self.resolve_ty_as_possible(ty)
  65     }
  66
  67     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
  68         let krate = self.resolver.krate()?;
  69         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
  70         let output_assoc_type =
  71             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
  72         let generic_params = generics(self.db.upcast(), fn_once_trait.into());
  73         if generic_params.len() != 2 {
  74             return None;
  75         }
  76
  77         let mut param_builder = Substs::builder(num_args);
  78         let mut arg_tys = vec![];
  79         for _ in 0..num_args {
  80             let arg = self.table.new_type_var();
  81             param_builder = param_builder.push(arg.clone());
  82             arg_tys.push(arg);
  83         }
  84         let parameters = param_builder.build();
  85         let arg_ty = Ty::Apply(ApplicationTy {
  86             ctor: TypeCtor::Tuple { cardinality: num_args as u16 },
  87             parameters,
  88         });
  89         let substs =
  90             Substs::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
  91
  92         let trait_env = Arc::clone(&self.trait_env);
  93         let implements_fn_trait =
  94             Obligation::Trait(TraitRef { trait_: fn_once_trait, substs: substs.clone() });
  95         let goal = self.canonicalizer().canonicalize_obligation(InEnvironment {
  96             value: implements_fn_trait.clone(),
  97             environment: trait_env,
  98         });
  99         if self.db.trait_solve(krate, goal.value).is_some() {
 100             self.obligations.push(implements_fn_trait);
 101             let output_proj_ty =
 102                 crate::ProjectionTy { associated_ty: output_assoc_type, parameters: substs };
 103             let return_ty = self.normalize_projection_ty(output_proj_ty);
 104             Some((arg_tys, return_ty))
 105         } else {
 106             None
 107         }
 108     }
 109
 110     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 111         match ty.callable_sig(self.db) {
 112             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 113             None => self.callable_sig_from_fn_trait(ty, num_args),
 114         }
 115     }
 116
 117     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 118         let body = Arc::clone(&self.body); // avoid borrow checker problem
 119         let ty = match &body[tgt_expr] {
 120             Expr::Missing => Ty::Unknown,
 121             Expr::If { condition, then_branch, else_branch } => {
 122                 // if let is desugared to match, so this is always simple if
 123                 self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
 124
 125                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 126                 let mut both_arms_diverge = Diverges::Always;
 127
 128                 let then_ty = self.infer_expr_inner(*then_branch, &expected);
 129                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 130                 let else_ty = match else_branch {
 131                     Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
 132                     None => Ty::unit(),
 133                 };
 134                 both_arms_diverge &= self.diverges;
 135
 136                 self.diverges = condition_diverges | both_arms_diverge;
 137
 138                 self.coerce_merge_branch(&then_ty, &else_ty)
 139             }
 140             Expr::Block { statements, tail, label } => match label {
 141                 Some(_) => {
 142                     let break_ty = self.table.new_type_var();
 143                     self.breakables.push(BreakableContext {
 144                         may_break: false,
 145                         break_ty: break_ty.clone(),
 146                         label: label.map(|label| self.body[label].name.clone()),
 147                     });
 148                     let ty = self.infer_block(statements, *tail, &Expectation::has_type(break_ty));
 149                     let ctxt = self.breakables.pop().expect("breakable stack broken");
 150                     if ctxt.may_break {
 151                         ctxt.break_ty
 152                     } else {
 153                         ty
 154                     }
 155                 }
 156                 None => self.infer_block(statements, *tail, expected),
 157             },
 158             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 159             Expr::TryBlock { body } => {
 160                 let _inner = self.infer_expr(*body, expected);
 161                 // FIXME should be std::result::Result<{inner}, _>
 162                 Ty::Unknown
 163             }
 164             Expr::Async { body } => {
 165                 // Use the first type parameter as the output type of future.
 166                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 167                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 168                 let opaque_ty_id = OpaqueTyId::AsyncBlockTypeImplTrait(self.owner, *body);
 169                 Ty::apply_one(TypeCtor::OpaqueType(opaque_ty_id), inner_ty)
 170             }
 171             Expr::Loop { body, label } => {
 172                 self.breakables.push(BreakableContext {
 173                     may_break: false,
 174                     break_ty: self.table.new_type_var(),
 175                     label: label.map(|label| self.body[label].name.clone()),
 176                 });
 177                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 178
 179                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 180                 if ctxt.may_break {
 181                     self.diverges = Diverges::Maybe;
 182                 }
 183
 184                 if ctxt.may_break {
 185                     ctxt.break_ty
 186                 } else {
 187                     Ty::simple(TypeCtor::Never)
 188                 }
 189             }
 190             Expr::While { condition, body, label } => {
 191                 self.breakables.push(BreakableContext {
 192                     may_break: false,
 193                     break_ty: Ty::Unknown,
 194                     label: label.map(|label| self.body[label].name.clone()),
 195                 });
 196                 // while let is desugared to a match loop, so this is always simple while
 197                 self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
 198                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 199                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 200                 // the body may not run, so it diverging doesn't mean we diverge
 201                 self.diverges = Diverges::Maybe;
 202                 Ty::unit()
 203             }
 204             Expr::For { iterable, body, pat, label } => {
 205                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 206
 207                 self.breakables.push(BreakableContext {
 208                     may_break: false,
 209                     break_ty: Ty::Unknown,
 210                     label: label.map(|label| self.body[label].name.clone()),
 211                 });
 212                 let pat_ty =
 213                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 214
 215                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 216
 217                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 218                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 219                 // the body may not run, so it diverging doesn't mean we diverge
 220                 self.diverges = Diverges::Maybe;
 221                 Ty::unit()
 222             }
 223             Expr::Lambda { body, args, ret_type, arg_types } => {
 224                 assert_eq!(args.len(), arg_types.len());
 225
 226                 let mut sig_tys = Vec::new();
 227
 228                 // collect explicitly written argument types
 229                 for arg_type in arg_types.iter() {
 230                     let arg_ty = if let Some(type_ref) = arg_type {
 231                         self.make_ty(type_ref)
 232                     } else {
 233                         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 = Ty::apply(
 245                     TypeCtor::FnPtr { num_args: sig_tys.len() as u16 - 1, is_varargs: false },
 246                     Substs(sig_tys.clone().into()),
 247                 );
 248                 let closure_ty =
 249                     Ty::apply_one(TypeCtor::Closure { def: self.owner, expr: tgt_expr }, sig_ty);
 250
 251                 // Eagerly try to relate the closure type with the expected
 252                 // type, otherwise we often won't have enough information to
 253                 // infer the body.
 254                 self.coerce(&closure_ty, &expected.ty);
 255
 256                 // Now go through the argument patterns
 257                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 258                     let resolved = self.resolve_ty_as_possible(arg_ty);
 259                     self.infer_pat(*arg_pat, &resolved, BindingMode::default());
 260                 }
 261
 262                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 263                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 264
 265                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 266
 267                 self.diverges = prev_diverges;
 268                 self.return_ty = prev_ret_ty;
 269
 270                 closure_ty
 271             }
 272             Expr::Call { callee, args } => {
 273                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 274                 let canonicalized = self.canonicalizer().canonicalize_ty(callee_ty.clone());
 275                 let mut derefs = autoderef(
 276                     self.db,
 277                     self.resolver.krate(),
 278                     InEnvironment {
 279                         value: canonicalized.value.clone(),
 280                         environment: self.trait_env.clone(),
 281                     },
 282                 );
 283                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
 284                     .find_map(|callee_deref_ty| {
 285                         self.callable_sig(
 286                             &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 287                             args.len(),
 288                         )
 289                     })
 290                     .unwrap_or((Vec::new(), Ty::Unknown));
 291                 self.register_obligations_for_call(&callee_ty);
 292                 self.check_call_arguments(args, &param_tys);
 293                 self.normalize_associated_types_in(ret_ty)
 294             }
 295             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 296                 .infer_method_call(tgt_expr, *receiver, &args, &method_name, generic_args.as_ref()),
 297             Expr::Match { expr, arms } => {
 298                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 299
 300                 let mut result_ty = if arms.is_empty() {
 301                     Ty::simple(TypeCtor::Never)
 302                 } else {
 303                     self.table.new_type_var()
 304                 };
 305
 306                 let matchee_diverges = self.diverges;
 307                 let mut all_arms_diverge = Diverges::Always;
 308
 309                 for arm in arms {
 310                     self.diverges = Diverges::Maybe;
 311                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 312                     if let Some(guard_expr) = arm.guard {
 313                         self.infer_expr(
 314                             guard_expr,
 315                             &Expectation::has_type(Ty::simple(TypeCtor::Bool)),
 316                         );
 317                     }
 318
 319                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 320                     all_arms_diverge &= self.diverges;
 321                     result_ty = self.coerce_merge_branch(&result_ty, &arm_ty);
 322                 }
 323
 324                 self.diverges = matchee_diverges | all_arms_diverge;
 325
 326                 result_ty
 327             }
 328             Expr::Path(p) => {
 329                 // FIXME this could be more efficient...
 330                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 331                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
 332             }
 333             Expr::Continue { .. } => Ty::simple(TypeCtor::Never),
 334             Expr::Break { expr, label } => {
 335                 let val_ty = if let Some(expr) = expr {
 336                     self.infer_expr(*expr, &Expectation::none())
 337                 } else {
 338                     Ty::unit()
 339                 };
 340
 341                 let last_ty =
 342                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 343                         ctxt.break_ty.clone()
 344                     } else {
 345                         Ty::Unknown
 346                     };
 347
 348                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
 349
 350                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 351                     ctxt.break_ty = merged_type;
 352                     ctxt.may_break = true;
 353                 } else {
 354                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 355                         expr: tgt_expr,
 356                     });
 357                 }
 358
 359                 Ty::simple(TypeCtor::Never)
 360             }
 361             Expr::Return { expr } => {
 362                 if let Some(expr) = expr {
 363                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 364                 } else {
 365                     let unit = Ty::unit();
 366                     self.coerce(&unit, &self.return_ty.clone());
 367                 }
 368                 Ty::simple(TypeCtor::Never)
 369             }
 370             Expr::Yield { expr } => {
 371                 // FIXME: track yield type for coercion
 372                 if let Some(expr) = expr {
 373                     self.infer_expr(*expr, &Expectation::none());
 374                 }
 375                 Ty::simple(TypeCtor::Never)
 376             }
 377             Expr::RecordLit { path, fields, spread } => {
 378                 let (ty, def_id) = self.resolve_variant(path.as_ref());
 379                 if let Some(variant) = def_id {
 380                     self.write_variant_resolution(tgt_expr.into(), variant);
 381                 }
 382
 383                 self.unify(&ty, &expected.ty);
 384
 385                 let substs = ty.substs().unwrap_or_else(Substs::empty);
 386                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 387                 let variant_data = def_id.map(|it| variant_data(self.db.upcast(), it));
 388                 for (field_idx, field) in fields.iter().enumerate() {
 389                     let field_def =
 390                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 391                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 392                             None => {
 393                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 394                                     expr: tgt_expr,
 395                                     field: field_idx,
 396                                 });
 397                                 None
 398                             }
 399                         });
 400                     if let Some(field_def) = field_def {
 401                         self.result.record_field_resolutions.insert(field.expr, field_def);
 402                     }
 403                     let field_ty = field_def
 404                         .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
 405                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 406                 }
 407                 if let Some(expr) = spread {
 408                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 409                 }
 410                 ty
 411             }
 412             Expr::Field { expr, name } => {
 413                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 414                 let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
 415                 let ty = autoderef::autoderef(
 416                     self.db,
 417                     self.resolver.krate(),
 418                     InEnvironment {
 419                         value: canonicalized.value.clone(),
 420                         environment: self.trait_env.clone(),
 421                     },
 422                 )
 423                 .find_map(|derefed_ty| match canonicalized.decanonicalize_ty(derefed_ty.value) {
 424                     Ty::Apply(a_ty) => match a_ty.ctor {
 425                         TypeCtor::Tuple { .. } => name
 426                             .as_tuple_index()
 427                             .and_then(|idx| a_ty.parameters.0.get(idx).cloned()),
 428                         TypeCtor::Adt(AdtId::StructId(s)) => {
 429                             self.db.struct_data(s).variant_data.field(name).map(|local_id| {
 430                                 let field = FieldId { parent: s.into(), local_id };
 431                                 self.write_field_resolution(tgt_expr, field);
 432                                 self.db.field_types(s.into())[field.local_id]
 433                                     .clone()
 434                                     .subst(&a_ty.parameters)
 435                             })
 436                         }
 437                         TypeCtor::Adt(AdtId::UnionId(u)) => {
 438                             self.db.union_data(u).variant_data.field(name).map(|local_id| {
 439                                 let field = FieldId { parent: u.into(), local_id };
 440                                 self.write_field_resolution(tgt_expr, field);
 441                                 self.db.field_types(u.into())[field.local_id]
 442                                     .clone()
 443                                     .subst(&a_ty.parameters)
 444                             })
 445                         }
 446                         _ => None,
 447                     },
 448                     _ => None,
 449                 })
 450                 .unwrap_or(Ty::Unknown);
 451                 let ty = self.insert_type_vars(ty);
 452                 self.normalize_associated_types_in(ty)
 453             }
 454             Expr::Await { expr } => {
 455                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 456                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 457             }
 458             Expr::Try { expr } => {
 459                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 460                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 461             }
 462             Expr::Cast { expr, type_ref } => {
 463                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 464                 let cast_ty = self.make_ty(type_ref);
 465                 // FIXME check the cast...
 466                 cast_ty
 467             }
 468             Expr::Ref { expr, rawness, mutability } => {
 469                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
 470                     &expected.ty.as_reference_or_ptr()
 471                 {
 472                     if *exp_mutability == Mutability::Mut && *mutability == Mutability::Shared {
 473                         // FIXME: throw type error - expected mut reference but found shared ref,
 474                         // which cannot be coerced
 475                     }
 476                     if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 477                         // FIXME: throw type error - expected reference but found ptr,
 478                         // which cannot be coerced
 479                     }
 480                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 481                 } else {
 482                     Expectation::none()
 483                 };
 484                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 485                 let ty = match rawness {
 486                     Rawness::RawPtr => TypeCtor::RawPtr(*mutability),
 487                     Rawness::Ref => TypeCtor::Ref(*mutability),
 488                 };
 489                 Ty::apply_one(ty, inner_ty)
 490             }
 491             Expr::Box { expr } => {
 492                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 493                 if let Some(box_) = self.resolve_boxed_box() {
 494                     Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
 495                 } else {
 496                     Ty::Unknown
 497                 }
 498             }
 499             Expr::UnaryOp { expr, op } => {
 500                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 501                 match op {
 502                     UnaryOp::Deref => match self.resolver.krate() {
 503                         Some(krate) => {
 504                             let canonicalized = self.canonicalizer().canonicalize_ty(inner_ty);
 505                             match autoderef::deref(
 506                                 self.db,
 507                                 krate,
 508                                 InEnvironment {
 509                                     value: &canonicalized.value,
 510                                     environment: self.trait_env.clone(),
 511                                 },
 512                             ) {
 513                                 Some(derefed_ty) => {
 514                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 515                                 }
 516                                 None => Ty::Unknown,
 517                             }
 518                         }
 519                         None => Ty::Unknown,
 520                     },
 521                     UnaryOp::Neg => {
 522                         match &inner_ty {
 523                             // Fast path for builtins
 524                             Ty::Apply(ApplicationTy {
 525                                 ctor: TypeCtor::Int(IntTy { signedness: Signedness::Signed, .. }),
 526                                 ..
 527                             })
 528                             | Ty::Apply(ApplicationTy { ctor: TypeCtor::Float(_), .. })
 529                             | Ty::Infer(InferTy::IntVar(..))
 530                             | Ty::Infer(InferTy::FloatVar(..)) => inner_ty,
 531                             // Otherwise we resolve via the std::ops::Neg trait
 532                             _ => self
 533                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 534                         }
 535                     }
 536                     UnaryOp::Not => {
 537                         match &inner_ty {
 538                             // Fast path for builtins
 539                             Ty::Apply(ApplicationTy { ctor: TypeCtor::Bool, .. })
 540                             | Ty::Apply(ApplicationTy { ctor: TypeCtor::Int(_), .. })
 541                             | Ty::Infer(InferTy::IntVar(..)) => inner_ty,
 542                             // Otherwise we resolve via the std::ops::Not trait
 543                             _ => self
 544                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 545                         }
 546                     }
 547                 }
 548             }
 549             Expr::BinaryOp { lhs, rhs, op } => match op {
 550                 Some(op) => {
 551                     let lhs_expectation = match op {
 552                         BinaryOp::LogicOp(..) => Expectation::has_type(Ty::simple(TypeCtor::Bool)),
 553                         _ => Expectation::none(),
 554                     };
 555                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 556                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 557                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 558
 559                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 560
 561                     if ret == Ty::Unknown {
 562                         mark::hit!(infer_expr_inner_binary_operator_overload);
 563
 564                         self.resolve_associated_type_with_params(
 565                             lhs_ty,
 566                             self.resolve_binary_op_output(op),
 567                             &[rhs_ty],
 568                         )
 569                     } else {
 570                         ret
 571                     }
 572                 }
 573                 _ => Ty::Unknown,
 574             },
 575             Expr::Range { lhs, rhs, range_type } => {
 576                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 577                 let rhs_expect = lhs_ty
 578                     .as_ref()
 579                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 580                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 581                 match (range_type, lhs_ty, rhs_ty) {
 582                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 583                         Some(adt) => Ty::simple(TypeCtor::Adt(adt)),
 584                         None => Ty::Unknown,
 585                     },
 586                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 587                         Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 588                         None => Ty::Unknown,
 589                     },
 590                     (RangeOp::Inclusive, None, Some(ty)) => {
 591                         match self.resolve_range_to_inclusive() {
 592                             Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 593                             None => Ty::Unknown,
 594                         }
 595                     }
 596                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 597                         Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 598                         None => Ty::Unknown,
 599                     },
 600                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 601                         match self.resolve_range_inclusive() {
 602                             Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 603                             None => Ty::Unknown,
 604                         }
 605                     }
 606                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 607                         Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 608                         None => Ty::Unknown,
 609                     },
 610                     (RangeOp::Inclusive, _, None) => Ty::Unknown,
 611                 }
 612             }
 613             Expr::Index { base, index } => {
 614                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 615                 let index_ty = self.infer_expr(*index, &Expectation::none());
 616
 617                 if let (Some(index_trait), Some(krate)) =
 618                     (self.resolve_ops_index(), self.resolver.krate())
 619                 {
 620                     let canonicalized = self.canonicalizer().canonicalize_ty(base_ty);
 621                     let self_ty = method_resolution::resolve_indexing_op(
 622                         self.db,
 623                         &canonicalized.value,
 624                         self.trait_env.clone(),
 625                         krate,
 626                         index_trait,
 627                     );
 628                     let self_ty =
 629                         self_ty.map_or(Ty::Unknown, |t| canonicalized.decanonicalize_ty(t.value));
 630                     self.resolve_associated_type_with_params(
 631                         self_ty,
 632                         self.resolve_ops_index_output(),
 633                         &[index_ty],
 634                     )
 635                 } else {
 636                     Ty::Unknown
 637                 }
 638             }
 639             Expr::Tuple { exprs } => {
 640                 let mut tys = match &expected.ty {
 641                     ty_app!(TypeCtor::Tuple { .. }, st) => st
 642                         .iter()
 643                         .cloned()
 644                         .chain(repeat_with(|| self.table.new_type_var()))
 645                         .take(exprs.len())
 646                         .collect::<Vec<_>>(),
 647                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 648                 };
 649
 650                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 651                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 652                 }
 653
 654                 Ty::apply(TypeCtor::Tuple { cardinality: tys.len() as u16 }, Substs(tys.into()))
 655             }
 656             Expr::Array(array) => {
 657                 let elem_ty = match &expected.ty {
 658                     // FIXME: remove when https://github.com/rust-lang/rust/issues/80501 is fixed
 659                     #[allow(unreachable_patterns)]
 660                     ty_app!(TypeCtor::Array, st) | ty_app!(TypeCtor::Slice, st) => {
 661                         st.as_single().clone()
 662                     }
 663                     _ => self.table.new_type_var(),
 664                 };
 665
 666                 match array {
 667                     Array::ElementList(items) => {
 668                         for expr in items.iter() {
 669                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
 670                         }
 671                     }
 672                     Array::Repeat { initializer, repeat } => {
 673                         self.infer_expr_coerce(
 674                             *initializer,
 675                             &Expectation::has_type(elem_ty.clone()),
 676                         );
 677                         self.infer_expr(
 678                             *repeat,
 679                             &Expectation::has_type(Ty::simple(TypeCtor::Int(IntTy::usize()))),
 680                         );
 681                     }
 682                 }
 683
 684                 Ty::apply_one(TypeCtor::Array, elem_ty)
 685             }
 686             Expr::Literal(lit) => match lit {
 687                 Literal::Bool(..) => Ty::simple(TypeCtor::Bool),
 688                 Literal::String(..) => {
 689                     Ty::apply_one(TypeCtor::Ref(Mutability::Shared), Ty::simple(TypeCtor::Str))
 690                 }
 691                 Literal::ByteString(..) => {
 692                     let byte_type = Ty::simple(TypeCtor::Int(IntTy::u8()));
 693                     let array_type = Ty::apply_one(TypeCtor::Array, byte_type);
 694                     Ty::apply_one(TypeCtor::Ref(Mutability::Shared), array_type)
 695                 }
 696                 Literal::Char(..) => Ty::simple(TypeCtor::Char),
 697                 Literal::Int(_v, ty) => match ty {
 698                     Some(int_ty) => Ty::simple(TypeCtor::Int((*int_ty).into())),
 699                     None => self.table.new_integer_var(),
 700                 },
 701                 Literal::Float(_v, ty) => match ty {
 702                     Some(float_ty) => Ty::simple(TypeCtor::Float((*float_ty).into())),
 703                     None => self.table.new_float_var(),
 704                 },
 705             },
 706         };
 707         // use a new type variable if we got Ty::Unknown here
 708         let ty = self.insert_type_vars_shallow(ty);
 709         let ty = self.resolve_ty_as_possible(ty);
 710         self.write_expr_ty(tgt_expr, ty.clone());
 711         ty
 712     }
 713
 714     fn infer_block(
 715         &mut self,
 716         statements: &[Statement],
 717         tail: Option<ExprId>,
 718         expected: &Expectation,
 719     ) -> Ty {
 720         for stmt in statements {
 721             match stmt {
 722                 Statement::Let { pat, type_ref, initializer } => {
 723                     let decl_ty =
 724                         type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(Ty::Unknown);
 725
 726                     // Always use the declared type when specified
 727                     let mut ty = decl_ty.clone();
 728
 729                     if let Some(expr) = initializer {
 730                         let actual_ty =
 731                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 732                         if decl_ty == Ty::Unknown {
 733                             ty = actual_ty;
 734                         }
 735                     }
 736
 737                     let ty = self.resolve_ty_as_possible(ty);
 738                     self.infer_pat(*pat, &ty, BindingMode::default());
 739                 }
 740                 Statement::Expr(expr) => {
 741                     self.infer_expr(*expr, &Expectation::none());
 742                 }
 743             }
 744         }
 745
 746         let ty = if let Some(expr) = tail {
 747             self.infer_expr_coerce(expr, expected)
 748         } else {
 749             // Citing rustc: if there is no explicit tail expression,
 750             // that is typically equivalent to a tail expression
 751             // of `()` -- except if the block diverges. In that
 752             // case, there is no value supplied from the tail
 753             // expression (assuming there are no other breaks,
 754             // this implies that the type of the block will be
 755             // `!`).
 756             if self.diverges.is_always() {
 757                 // we don't even make an attempt at coercion
 758                 self.table.new_maybe_never_type_var()
 759             } else {
 760                 self.coerce(&Ty::unit(), expected.coercion_target());
 761                 Ty::unit()
 762             }
 763         };
 764         ty
 765     }
 766
 767     fn infer_method_call(
 768         &mut self,
 769         tgt_expr: ExprId,
 770         receiver: ExprId,
 771         args: &[ExprId],
 772         method_name: &Name,
 773         generic_args: Option<&GenericArgs>,
 774     ) -> Ty {
 775         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 776         let canonicalized_receiver = self.canonicalizer().canonicalize_ty(receiver_ty.clone());
 777
 778         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 779
 780         let resolved = self.resolver.krate().and_then(|krate| {
 781             method_resolution::lookup_method(
 782                 &canonicalized_receiver.value,
 783                 self.db,
 784                 self.trait_env.clone(),
 785                 krate,
 786                 &traits_in_scope,
 787                 method_name,
 788             )
 789         });
 790         let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
 791             Some((ty, func)) => {
 792                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 793                 self.write_method_resolution(tgt_expr, func);
 794                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
 795             }
 796             None => (receiver_ty, Binders::new(0, Ty::Unknown), None),
 797         };
 798         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
 799         let method_ty = method_ty.subst(&substs);
 800         let method_ty = self.insert_type_vars(method_ty);
 801         self.register_obligations_for_call(&method_ty);
 802         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 803             Some(sig) => {
 804                 if !sig.params().is_empty() {
 805                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 806                 } else {
 807                     (Ty::Unknown, Vec::new(), sig.ret().clone())
 808                 }
 809             }
 810             None => (Ty::Unknown, Vec::new(), Ty::Unknown),
 811         };
 812         // Apply autoref so the below unification works correctly
 813         // FIXME: return correct autorefs from lookup_method
 814         let actual_receiver_ty = match expected_receiver_ty.as_reference() {
 815             Some((_, mutability)) => Ty::apply_one(TypeCtor::Ref(mutability), derefed_receiver_ty),
 816             _ => derefed_receiver_ty,
 817         };
 818         self.unify(&expected_receiver_ty, &actual_receiver_ty);
 819
 820         self.check_call_arguments(args, &param_tys);
 821         self.normalize_associated_types_in(ret_ty)
 822     }
 823
 824     fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
 825         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 826         // We do this in a pretty awful way: first we type-check any arguments
 827         // that are not closures, then we type-check the closures. This is so
 828         // that we have more information about the types of arguments when we
 829         // type-check the functions. This isn't really the right way to do this.
 830         for &check_closures in &[false, true] {
 831             let param_iter = param_tys.iter().cloned().chain(repeat(Ty::Unknown));
 832             for (&arg, param_ty) in args.iter().zip(param_iter) {
 833                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
 834                 if is_closure != check_closures {
 835                     continue;
 836                 }
 837
 838                 let param_ty = self.normalize_associated_types_in(param_ty);
 839                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
 840             }
 841         }
 842     }
 843
 844     fn substs_for_method_call(
 845         &mut self,
 846         def_generics: Option<Generics>,
 847         generic_args: Option<&GenericArgs>,
 848         receiver_ty: &Ty,
 849     ) -> Substs {
 850         let (parent_params, self_params, type_params, impl_trait_params) =
 851             def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
 852         assert_eq!(self_params, 0); // method shouldn't have another Self param
 853         let total_len = parent_params + type_params + impl_trait_params;
 854         let mut substs = Vec::with_capacity(total_len);
 855         // Parent arguments are unknown, except for the receiver type
 856         if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
 857             for (_id, param) in parent_generics {
 858                 if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
 859                     substs.push(receiver_ty.clone());
 860                 } else {
 861                     substs.push(Ty::Unknown);
 862                 }
 863             }
 864         }
 865         // handle provided type arguments
 866         if let Some(generic_args) = generic_args {
 867             // if args are provided, it should be all of them, but we can't rely on that
 868             for arg in generic_args
 869                 .args
 870                 .iter()
 871                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 872                 .take(type_params)
 873             {
 874                 match arg {
 875                     GenericArg::Type(type_ref) => {
 876                         let ty = self.make_ty(type_ref);
 877                         substs.push(ty);
 878                     }
 879                     GenericArg::Lifetime(_) => {}
 880                 }
 881             }
 882         };
 883         let supplied_params = substs.len();
 884         for _ in supplied_params..total_len {
 885             substs.push(Ty::Unknown);
 886         }
 887         assert_eq!(substs.len(), total_len);
 888         Substs(substs.into())
 889     }
 890
 891     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
 892         if let Ty::Apply(a_ty) = callable_ty {
 893             if let TypeCtor::FnDef(def) = a_ty.ctor {
 894                 let generic_predicates = self.db.generic_predicates(def.into());
 895                 for predicate in generic_predicates.iter() {
 896                     let predicate = predicate.clone().subst(&a_ty.parameters);
 897                     if let Some(obligation) = Obligation::from_predicate(predicate) {
 898                         self.obligations.push(obligation);
 899                     }
 900                 }
 901                 // add obligation for trait implementation, if this is a trait method
 902                 match def {
 903                     CallableDefId::FunctionId(f) => {
 904                         if let AssocContainerId::TraitId(trait_) =
 905                             f.lookup(self.db.upcast()).container
 906                         {
 907                             // construct a TraitDef
 908                             let substs = a_ty
 909                                 .parameters
 910                                 .prefix(generics(self.db.upcast(), trait_.into()).len());
 911                             self.obligations.push(Obligation::Trait(TraitRef { trait_, substs }));
 912                         }
 913                     }
 914                     CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
 915                 }
 916             }
 917         }
 918     }
 919 }