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.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 } => 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.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.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.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::RecordLit { path, fields, spread } => {
 371                 let (ty, def_id) = self.resolve_variant(path.as_ref());
 372                 if let Some(variant) = def_id {
 373                     self.write_variant_resolution(tgt_expr.into(), variant);
 374                 }
 375
 376                 self.unify(&ty, &expected.ty);
 377
 378                 let substs = ty.substs().unwrap_or_else(Substs::empty);
 379                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 380                 let variant_data = def_id.map(|it| variant_data(self.db.upcast(), it));
 381                 for (field_idx, field) in fields.iter().enumerate() {
 382                     let field_def =
 383                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 384                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 385                             None => {
 386                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 387                                     expr: tgt_expr,
 388                                     field: field_idx,
 389                                 });
 390                                 None
 391                             }
 392                         });
 393                     if let Some(field_def) = field_def {
 394                         self.result.record_field_resolutions.insert(field.expr, field_def);
 395                     }
 396                     let field_ty = field_def
 397                         .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
 398                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 399                 }
 400                 if let Some(expr) = spread {
 401                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 402                 }
 403                 ty
 404             }
 405             Expr::Field { expr, name } => {
 406                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 407                 let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
 408                 let ty = autoderef::autoderef(
 409                     self.db,
 410                     self.resolver.krate(),
 411                     InEnvironment {
 412                         value: canonicalized.value.clone(),
 413                         environment: self.trait_env.clone(),
 414                     },
 415                 )
 416                 .find_map(|derefed_ty| match canonicalized.decanonicalize_ty(derefed_ty.value) {
 417                     Ty::Apply(a_ty) => match a_ty.ctor {
 418                         TypeCtor::Tuple { .. } => name
 419                             .as_tuple_index()
 420                             .and_then(|idx| a_ty.parameters.0.get(idx).cloned()),
 421                         TypeCtor::Adt(AdtId::StructId(s)) => {
 422                             self.db.struct_data(s).variant_data.field(name).map(|local_id| {
 423                                 let field = FieldId { parent: s.into(), local_id };
 424                                 self.write_field_resolution(tgt_expr, field);
 425                                 self.db.field_types(s.into())[field.local_id]
 426                                     .clone()
 427                                     .subst(&a_ty.parameters)
 428                             })
 429                         }
 430                         TypeCtor::Adt(AdtId::UnionId(u)) => {
 431                             self.db.union_data(u).variant_data.field(name).map(|local_id| {
 432                                 let field = FieldId { parent: u.into(), local_id };
 433                                 self.write_field_resolution(tgt_expr, field);
 434                                 self.db.field_types(u.into())[field.local_id]
 435                                     .clone()
 436                                     .subst(&a_ty.parameters)
 437                             })
 438                         }
 439                         _ => None,
 440                     },
 441                     _ => None,
 442                 })
 443                 .unwrap_or(Ty::Unknown);
 444                 let ty = self.insert_type_vars(ty);
 445                 self.normalize_associated_types_in(ty)
 446             }
 447             Expr::Await { expr } => {
 448                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 449                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 450             }
 451             Expr::Try { expr } => {
 452                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 453                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 454             }
 455             Expr::Cast { expr, type_ref } => {
 456                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 457                 let cast_ty = self.make_ty(type_ref);
 458                 // FIXME check the cast...
 459                 cast_ty
 460             }
 461             Expr::Ref { expr, rawness, mutability } => {
 462                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
 463                     &expected.ty.as_reference_or_ptr()
 464                 {
 465                     if *exp_mutability == Mutability::Mut && *mutability == Mutability::Shared {
 466                         // FIXME: throw type error - expected mut reference but found shared ref,
 467                         // which cannot be coerced
 468                     }
 469                     if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 470                         // FIXME: throw type error - expected reference but found ptr,
 471                         // which cannot be coerced
 472                     }
 473                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 474                 } else {
 475                     Expectation::none()
 476                 };
 477                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 478                 let ty = match rawness {
 479                     Rawness::RawPtr => TypeCtor::RawPtr(*mutability),
 480                     Rawness::Ref => TypeCtor::Ref(*mutability),
 481                 };
 482                 Ty::apply_one(ty, inner_ty)
 483             }
 484             Expr::Box { expr } => {
 485                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 486                 if let Some(box_) = self.resolve_boxed_box() {
 487                     Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
 488                 } else {
 489                     Ty::Unknown
 490                 }
 491             }
 492             Expr::UnaryOp { expr, op } => {
 493                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 494                 match op {
 495                     UnaryOp::Deref => match self.resolver.krate() {
 496                         Some(krate) => {
 497                             let canonicalized = self.canonicalizer().canonicalize_ty(inner_ty);
 498                             match autoderef::deref(
 499                                 self.db,
 500                                 krate,
 501                                 InEnvironment {
 502                                     value: &canonicalized.value,
 503                                     environment: self.trait_env.clone(),
 504                                 },
 505                             ) {
 506                                 Some(derefed_ty) => {
 507                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 508                                 }
 509                                 None => Ty::Unknown,
 510                             }
 511                         }
 512                         None => Ty::Unknown,
 513                     },
 514                     UnaryOp::Neg => {
 515                         match &inner_ty {
 516                             // Fast path for builtins
 517                             Ty::Apply(ApplicationTy {
 518                                 ctor: TypeCtor::Int(IntTy { signedness: Signedness::Signed, .. }),
 519                                 ..
 520                             })
 521                             | Ty::Apply(ApplicationTy { ctor: TypeCtor::Float(_), .. })
 522                             | Ty::Infer(InferTy::IntVar(..))
 523                             | Ty::Infer(InferTy::FloatVar(..)) => inner_ty,
 524                             // Otherwise we resolve via the std::ops::Neg trait
 525                             _ => self
 526                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 527                         }
 528                     }
 529                     UnaryOp::Not => {
 530                         match &inner_ty {
 531                             // Fast path for builtins
 532                             Ty::Apply(ApplicationTy { ctor: TypeCtor::Bool, .. })
 533                             | Ty::Apply(ApplicationTy { ctor: TypeCtor::Int(_), .. })
 534                             | Ty::Infer(InferTy::IntVar(..)) => inner_ty,
 535                             // Otherwise we resolve via the std::ops::Not trait
 536                             _ => self
 537                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 538                         }
 539                     }
 540                 }
 541             }
 542             Expr::BinaryOp { lhs, rhs, op } => match op {
 543                 Some(op) => {
 544                     let lhs_expectation = match op {
 545                         BinaryOp::LogicOp(..) => Expectation::has_type(Ty::simple(TypeCtor::Bool)),
 546                         _ => Expectation::none(),
 547                     };
 548                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 549                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 550                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 551
 552                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 553
 554                     if ret == Ty::Unknown {
 555                         mark::hit!(infer_expr_inner_binary_operator_overload);
 556
 557                         self.resolve_associated_type_with_params(
 558                             lhs_ty,
 559                             self.resolve_binary_op_output(op),
 560                             &[rhs_ty],
 561                         )
 562                     } else {
 563                         ret
 564                     }
 565                 }
 566                 _ => Ty::Unknown,
 567             },
 568             Expr::Range { lhs, rhs, range_type } => {
 569                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 570                 let rhs_expect = lhs_ty
 571                     .as_ref()
 572                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 573                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 574                 match (range_type, lhs_ty, rhs_ty) {
 575                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 576                         Some(adt) => Ty::simple(TypeCtor::Adt(adt)),
 577                         None => Ty::Unknown,
 578                     },
 579                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 580                         Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 581                         None => Ty::Unknown,
 582                     },
 583                     (RangeOp::Inclusive, None, Some(ty)) => {
 584                         match self.resolve_range_to_inclusive() {
 585                             Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 586                             None => Ty::Unknown,
 587                         }
 588                     }
 589                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 590                         Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 591                         None => Ty::Unknown,
 592                     },
 593                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 594                         match self.resolve_range_inclusive() {
 595                             Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 596                             None => Ty::Unknown,
 597                         }
 598                     }
 599                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 600                         Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
 601                         None => Ty::Unknown,
 602                     },
 603                     (RangeOp::Inclusive, _, None) => Ty::Unknown,
 604                 }
 605             }
 606             Expr::Index { base, index } => {
 607                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 608                 let index_ty = self.infer_expr(*index, &Expectation::none());
 609
 610                 if let (Some(index_trait), Some(krate)) =
 611                     (self.resolve_ops_index(), self.resolver.krate())
 612                 {
 613                     let canonicalized = self.canonicalizer().canonicalize_ty(base_ty);
 614                     let self_ty = method_resolution::resolve_indexing_op(
 615                         self.db,
 616                         &canonicalized.value,
 617                         self.trait_env.clone(),
 618                         krate,
 619                         index_trait,
 620                     );
 621                     let self_ty =
 622                         self_ty.map_or(Ty::Unknown, |t| canonicalized.decanonicalize_ty(t.value));
 623                     self.resolve_associated_type_with_params(
 624                         self_ty,
 625                         self.resolve_ops_index_output(),
 626                         &[index_ty],
 627                     )
 628                 } else {
 629                     Ty::Unknown
 630                 }
 631             }
 632             Expr::Tuple { exprs } => {
 633                 let mut tys = match &expected.ty {
 634                     ty_app!(TypeCtor::Tuple { .. }, st) => st
 635                         .iter()
 636                         .cloned()
 637                         .chain(repeat_with(|| self.table.new_type_var()))
 638                         .take(exprs.len())
 639                         .collect::<Vec<_>>(),
 640                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 641                 };
 642
 643                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 644                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 645                 }
 646
 647                 Ty::apply(TypeCtor::Tuple { cardinality: tys.len() as u16 }, Substs(tys.into()))
 648             }
 649             Expr::Array(array) => {
 650                 let elem_ty = match &expected.ty {
 651                     ty_app!(TypeCtor::Array, st) | ty_app!(TypeCtor::Slice, st) => {
 652                         st.as_single().clone()
 653                     }
 654                     _ => self.table.new_type_var(),
 655                 };
 656
 657                 match array {
 658                     Array::ElementList(items) => {
 659                         for expr in items.iter() {
 660                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
 661                         }
 662                     }
 663                     Array::Repeat { initializer, repeat } => {
 664                         self.infer_expr_coerce(
 665                             *initializer,
 666                             &Expectation::has_type(elem_ty.clone()),
 667                         );
 668                         self.infer_expr(
 669                             *repeat,
 670                             &Expectation::has_type(Ty::simple(TypeCtor::Int(IntTy::usize()))),
 671                         );
 672                     }
 673                 }
 674
 675                 Ty::apply_one(TypeCtor::Array, elem_ty)
 676             }
 677             Expr::Literal(lit) => match lit {
 678                 Literal::Bool(..) => Ty::simple(TypeCtor::Bool),
 679                 Literal::String(..) => {
 680                     Ty::apply_one(TypeCtor::Ref(Mutability::Shared), Ty::simple(TypeCtor::Str))
 681                 }
 682                 Literal::ByteString(..) => {
 683                     let byte_type = Ty::simple(TypeCtor::Int(IntTy::u8()));
 684                     let array_type = Ty::apply_one(TypeCtor::Array, byte_type);
 685                     Ty::apply_one(TypeCtor::Ref(Mutability::Shared), array_type)
 686                 }
 687                 Literal::Char(..) => Ty::simple(TypeCtor::Char),
 688                 Literal::Int(_v, ty) => match ty {
 689                     Some(int_ty) => Ty::simple(TypeCtor::Int((*int_ty).into())),
 690                     None => self.table.new_integer_var(),
 691                 },
 692                 Literal::Float(_v, ty) => match ty {
 693                     Some(float_ty) => Ty::simple(TypeCtor::Float((*float_ty).into())),
 694                     None => self.table.new_float_var(),
 695                 },
 696             },
 697         };
 698         // use a new type variable if we got Ty::Unknown here
 699         let ty = self.insert_type_vars_shallow(ty);
 700         let ty = self.resolve_ty_as_possible(ty);
 701         self.write_expr_ty(tgt_expr, ty.clone());
 702         ty
 703     }
 704
 705     fn infer_block(
 706         &mut self,
 707         statements: &[Statement],
 708         tail: Option<ExprId>,
 709         expected: &Expectation,
 710     ) -> Ty {
 711         for stmt in statements {
 712             match stmt {
 713                 Statement::Let { pat, type_ref, initializer } => {
 714                     let decl_ty =
 715                         type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(Ty::Unknown);
 716
 717                     // Always use the declared type when specified
 718                     let mut ty = decl_ty.clone();
 719
 720                     if let Some(expr) = initializer {
 721                         let actual_ty =
 722                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 723                         if decl_ty == Ty::Unknown {
 724                             ty = actual_ty;
 725                         }
 726                     }
 727
 728                     let ty = self.resolve_ty_as_possible(ty);
 729                     self.infer_pat(*pat, &ty, BindingMode::default());
 730                 }
 731                 Statement::Expr(expr) => {
 732                     self.infer_expr(*expr, &Expectation::none());
 733                 }
 734             }
 735         }
 736
 737         let ty = if let Some(expr) = tail {
 738             self.infer_expr_coerce(expr, expected)
 739         } else {
 740             // Citing rustc: if there is no explicit tail expression,
 741             // that is typically equivalent to a tail expression
 742             // of `()` -- except if the block diverges. In that
 743             // case, there is no value supplied from the tail
 744             // expression (assuming there are no other breaks,
 745             // this implies that the type of the block will be
 746             // `!`).
 747             if self.diverges.is_always() {
 748                 // we don't even make an attempt at coercion
 749                 self.table.new_maybe_never_type_var()
 750             } else {
 751                 self.coerce(&Ty::unit(), expected.coercion_target());
 752                 Ty::unit()
 753             }
 754         };
 755         ty
 756     }
 757
 758     fn infer_method_call(
 759         &mut self,
 760         tgt_expr: ExprId,
 761         receiver: ExprId,
 762         args: &[ExprId],
 763         method_name: &Name,
 764         generic_args: Option<&GenericArgs>,
 765     ) -> Ty {
 766         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 767         let canonicalized_receiver = self.canonicalizer().canonicalize_ty(receiver_ty.clone());
 768
 769         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 770
 771         let resolved = self.resolver.krate().and_then(|krate| {
 772             method_resolution::lookup_method(
 773                 &canonicalized_receiver.value,
 774                 self.db,
 775                 self.trait_env.clone(),
 776                 krate,
 777                 &traits_in_scope,
 778                 method_name,
 779             )
 780         });
 781         let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
 782             Some((ty, func)) => {
 783                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 784                 self.write_method_resolution(tgt_expr, func);
 785                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
 786             }
 787             None => (receiver_ty, Binders::new(0, Ty::Unknown), None),
 788         };
 789         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
 790         let method_ty = method_ty.subst(&substs);
 791         let method_ty = self.insert_type_vars(method_ty);
 792         self.register_obligations_for_call(&method_ty);
 793         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 794             Some(sig) => {
 795                 if !sig.params().is_empty() {
 796                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 797                 } else {
 798                     (Ty::Unknown, Vec::new(), sig.ret().clone())
 799                 }
 800             }
 801             None => (Ty::Unknown, Vec::new(), Ty::Unknown),
 802         };
 803         // Apply autoref so the below unification works correctly
 804         // FIXME: return correct autorefs from lookup_method
 805         let actual_receiver_ty = match expected_receiver_ty.as_reference() {
 806             Some((_, mutability)) => Ty::apply_one(TypeCtor::Ref(mutability), derefed_receiver_ty),
 807             _ => derefed_receiver_ty,
 808         };
 809         self.unify(&expected_receiver_ty, &actual_receiver_ty);
 810
 811         self.check_call_arguments(args, &param_tys);
 812         self.normalize_associated_types_in(ret_ty)
 813     }
 814
 815     fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
 816         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 817         // We do this in a pretty awful way: first we type-check any arguments
 818         // that are not closures, then we type-check the closures. This is so
 819         // that we have more information about the types of arguments when we
 820         // type-check the functions. This isn't really the right way to do this.
 821         for &check_closures in &[false, true] {
 822             let param_iter = param_tys.iter().cloned().chain(repeat(Ty::Unknown));
 823             for (&arg, param_ty) in args.iter().zip(param_iter) {
 824                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
 825                 if is_closure != check_closures {
 826                     continue;
 827                 }
 828
 829                 let param_ty = self.normalize_associated_types_in(param_ty);
 830                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
 831             }
 832         }
 833     }
 834
 835     fn substs_for_method_call(
 836         &mut self,
 837         def_generics: Option<Generics>,
 838         generic_args: Option<&GenericArgs>,
 839         receiver_ty: &Ty,
 840     ) -> Substs {
 841         let (parent_params, self_params, type_params, impl_trait_params) =
 842             def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
 843         assert_eq!(self_params, 0); // method shouldn't have another Self param
 844         let total_len = parent_params + type_params + impl_trait_params;
 845         let mut substs = Vec::with_capacity(total_len);
 846         // Parent arguments are unknown, except for the receiver type
 847         if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
 848             for (_id, param) in parent_generics {
 849                 if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
 850                     substs.push(receiver_ty.clone());
 851                 } else {
 852                     substs.push(Ty::Unknown);
 853                 }
 854             }
 855         }
 856         // handle provided type arguments
 857         if let Some(generic_args) = generic_args {
 858             // if args are provided, it should be all of them, but we can't rely on that
 859             for arg in generic_args
 860                 .args
 861                 .iter()
 862                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 863                 .take(type_params)
 864             {
 865                 match arg {
 866                     GenericArg::Type(type_ref) => {
 867                         let ty = self.make_ty(type_ref);
 868                         substs.push(ty);
 869                     }
 870                     GenericArg::Lifetime(_) => {}
 871                 }
 872             }
 873         };
 874         let supplied_params = substs.len();
 875         for _ in supplied_params..total_len {
 876             substs.push(Ty::Unknown);
 877         }
 878         assert_eq!(substs.len(), total_len);
 879         Substs(substs.into())
 880     }
 881
 882     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
 883         if let Ty::Apply(a_ty) = callable_ty {
 884             if let TypeCtor::FnDef(def) = a_ty.ctor {
 885                 let generic_predicates = self.db.generic_predicates(def.into());
 886                 for predicate in generic_predicates.iter() {
 887                     let predicate = predicate.clone().subst(&a_ty.parameters);
 888                     if let Some(obligation) = Obligation::from_predicate(predicate) {
 889                         self.obligations.push(obligation);
 890                     }
 891                 }
 892                 // add obligation for trait implementation, if this is a trait method
 893                 match def {
 894                     CallableDefId::FunctionId(f) => {
 895                         if let AssocContainerId::TraitId(trait_) =
 896                             f.lookup(self.db.upcast()).container
 897                         {
 898                             // construct a TraitDef
 899                             let substs = a_ty
 900                                 .parameters
 901                                 .prefix(generics(self.db.upcast(), trait_.into()).len());
 902                             self.obligations.push(Obligation::Trait(TraitRef { trait_, substs }));
 903                         }
 904                     }
 905                     CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
 906                 }
 907             }
 908         }
 909     }
 910 }