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 chalk_ir::{cast::Cast, Mutability, TyVariableKind};
   7 use hir_def::{
   8     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
   9     path::{GenericArg, GenericArgs},
  10     resolver::resolver_for_expr,
  11     AssocContainerId, FieldId, Lookup,
  12 };
  13 use hir_expand::name::{name, Name};
  14 use stdx::always;
  15 use syntax::ast::RangeOp;
  16
  17 use crate::{
  18     autoderef,
  19     lower::lower_to_chalk_mutability,
  20     method_resolution, op,
  21     primitive::{self, UintTy},
  22     to_assoc_type_id, to_chalk_trait_id,
  23     traits::{chalk::from_chalk, FnTrait, InEnvironment},
  24     utils::{generics, variant_data, Generics},
  25     AdtId, Binders, CallableDefId, DomainGoal, FnPointer, FnSig, Interner, Rawness, Scalar,
  26     Substitution, TraitRef, Ty, TyKind,
  27 };
  28
  29 use super::{
  30     find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
  31     InferenceDiagnostic, TypeMismatch,
  32 };
  33
  34 impl<'a> InferenceContext<'a> {
  35     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  36         let ty = self.infer_expr_inner(tgt_expr, expected);
  37         if ty.is_never() {
  38             // Any expression that produces a value of type `!` must have diverged
  39             self.diverges = Diverges::Always;
  40         }
  41         let could_unify = self.unify(&ty, &expected.ty);
  42         if !could_unify {
  43             self.result.type_mismatches.insert(
  44                 tgt_expr,
  45                 TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() },
  46             );
  47         }
  48         self.resolve_ty_as_possible(ty)
  49     }
  50
  51     /// Infer type of expression with possibly implicit coerce to the expected type.
  52     /// Return the type after possible coercion.
  53     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  54         let ty = self.infer_expr_inner(expr, &expected);
  55         let ty = if !self.coerce(&ty, &expected.coercion_target()) {
  56             self.result
  57                 .type_mismatches
  58                 .insert(expr, TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() });
  59             // Return actual type when type mismatch.
  60             // This is needed for diagnostic when return type mismatch.
  61             ty
  62         } else if expected.coercion_target().is_unknown() {
  63             ty
  64         } else {
  65             expected.ty.clone()
  66         };
  67
  68         self.resolve_ty_as_possible(ty)
  69     }
  70
  71     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
  72         let krate = self.resolver.krate()?;
  73         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
  74         let output_assoc_type =
  75             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
  76         let generic_params = generics(self.db.upcast(), fn_once_trait.into());
  77         if generic_params.len() != 2 {
  78             return None;
  79         }
  80
  81         let mut param_builder = Substitution::builder(num_args);
  82         let mut arg_tys = vec![];
  83         for _ in 0..num_args {
  84             let arg = self.table.new_type_var();
  85             param_builder = param_builder.push(arg.clone());
  86             arg_tys.push(arg);
  87         }
  88         let parameters = param_builder.build();
  89         let arg_ty = TyKind::Tuple(num_args, parameters).intern(&Interner);
  90         let substs =
  91             Substitution::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
  92
  93         let trait_env = self.trait_env.env.clone();
  94         let implements_fn_trait: DomainGoal =
  95             TraitRef { trait_id: to_chalk_trait_id(fn_once_trait), substitution: substs.clone() }
  96                 .cast(&Interner);
  97         let goal = self.canonicalizer().canonicalize_obligation(InEnvironment {
  98             goal: implements_fn_trait.clone(),
  99             environment: trait_env,
 100         });
 101         if self.db.trait_solve(krate, goal.value).is_some() {
 102             self.push_obligation(implements_fn_trait);
 103             let output_proj_ty = crate::ProjectionTy {
 104                 associated_ty_id: to_assoc_type_id(output_assoc_type),
 105                 substitution: substs,
 106             };
 107             let return_ty = self.normalize_projection_ty(output_proj_ty);
 108             Some((arg_tys, return_ty))
 109         } else {
 110             None
 111         }
 112     }
 113
 114     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 115         match ty.callable_sig(self.db) {
 116             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 117             None => self.callable_sig_from_fn_trait(ty, num_args),
 118         }
 119     }
 120
 121     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 122         self.db.check_canceled();
 123
 124         let body = Arc::clone(&self.body); // avoid borrow checker problem
 125         let ty = match &body[tgt_expr] {
 126             Expr::Missing => self.err_ty(),
 127             Expr::If { condition, then_branch, else_branch } => {
 128                 // if let is desugared to match, so this is always simple if
 129                 self.infer_expr(
 130                     *condition,
 131                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 132                 );
 133
 134                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 135                 let mut both_arms_diverge = Diverges::Always;
 136
 137                 let then_ty = self.infer_expr_inner(*then_branch, &expected);
 138                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 139                 let else_ty = match else_branch {
 140                     Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
 141                     None => Ty::unit(),
 142                 };
 143                 both_arms_diverge &= self.diverges;
 144
 145                 self.diverges = condition_diverges | both_arms_diverge;
 146
 147                 self.coerce_merge_branch(&then_ty, &else_ty)
 148             }
 149             Expr::Block { statements, tail, label, id: _ } => {
 150                 let old_resolver = mem::replace(
 151                     &mut self.resolver,
 152                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 153                 );
 154                 let ty = match label {
 155                     Some(_) => {
 156                         let break_ty = self.table.new_type_var();
 157                         self.breakables.push(BreakableContext {
 158                             may_break: false,
 159                             break_ty: break_ty.clone(),
 160                             label: label.map(|label| self.body[label].name.clone()),
 161                         });
 162                         let ty =
 163                             self.infer_block(statements, *tail, &Expectation::has_type(break_ty));
 164                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 165                         if ctxt.may_break {
 166                             ctxt.break_ty
 167                         } else {
 168                             ty
 169                         }
 170                     }
 171                     None => self.infer_block(statements, *tail, expected),
 172                 };
 173                 self.resolver = old_resolver;
 174                 ty
 175             }
 176             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 177             Expr::TryBlock { body } => {
 178                 let _inner = self.infer_expr(*body, expected);
 179                 // FIXME should be std::result::Result<{inner}, _>
 180                 self.err_ty()
 181             }
 182             Expr::Async { body } => {
 183                 // Use the first type parameter as the output type of future.
 184                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 185                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 186                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 187                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 188                 TyKind::OpaqueType(opaque_ty_id, Substitution::single(inner_ty)).intern(&Interner)
 189             }
 190             Expr::Loop { body, label } => {
 191                 self.breakables.push(BreakableContext {
 192                     may_break: false,
 193                     break_ty: self.table.new_type_var(),
 194                     label: label.map(|label| self.body[label].name.clone()),
 195                 });
 196                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 197
 198                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 199                 if ctxt.may_break {
 200                     self.diverges = Diverges::Maybe;
 201                 }
 202
 203                 if ctxt.may_break {
 204                     ctxt.break_ty
 205                 } else {
 206                     TyKind::Never.intern(&Interner)
 207                 }
 208             }
 209             Expr::While { condition, body, label } => {
 210                 self.breakables.push(BreakableContext {
 211                     may_break: false,
 212                     break_ty: self.err_ty(),
 213                     label: label.map(|label| self.body[label].name.clone()),
 214                 });
 215                 // while let is desugared to a match loop, so this is always simple while
 216                 self.infer_expr(
 217                     *condition,
 218                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 219                 );
 220                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 221                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 222                 // the body may not run, so it diverging doesn't mean we diverge
 223                 self.diverges = Diverges::Maybe;
 224                 Ty::unit()
 225             }
 226             Expr::For { iterable, body, pat, label } => {
 227                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 228
 229                 self.breakables.push(BreakableContext {
 230                     may_break: false,
 231                     break_ty: self.err_ty(),
 232                     label: label.map(|label| self.body[label].name.clone()),
 233                 });
 234                 let pat_ty =
 235                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 236
 237                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 238
 239                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 240                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 241                 // the body may not run, so it diverging doesn't mean we diverge
 242                 self.diverges = Diverges::Maybe;
 243                 Ty::unit()
 244             }
 245             Expr::Lambda { body, args, ret_type, arg_types } => {
 246                 assert_eq!(args.len(), arg_types.len());
 247
 248                 let mut sig_tys = Vec::new();
 249
 250                 // collect explicitly written argument types
 251                 for arg_type in arg_types.iter() {
 252                     let arg_ty = if let Some(type_ref) = arg_type {
 253                         self.make_ty(type_ref)
 254                     } else {
 255                         self.table.new_type_var()
 256                     };
 257                     sig_tys.push(arg_ty);
 258                 }
 259
 260                 // add return type
 261                 let ret_ty = match ret_type {
 262                     Some(type_ref) => self.make_ty(type_ref),
 263                     None => self.table.new_type_var(),
 264                 };
 265                 sig_tys.push(ret_ty.clone());
 266                 let sig_ty = TyKind::Function(FnPointer {
 267                     num_args: sig_tys.len() - 1,
 268                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 269                     substs: Substitution::from_iter(&Interner, sig_tys.clone()),
 270                 })
 271                 .intern(&Interner);
 272                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 273                 let closure_ty =
 274                     TyKind::Closure(closure_id, Substitution::single(sig_ty)).intern(&Interner);
 275
 276                 // Eagerly try to relate the closure type with the expected
 277                 // type, otherwise we often won't have enough information to
 278                 // infer the body.
 279                 self.coerce(&closure_ty, &expected.ty);
 280
 281                 // Now go through the argument patterns
 282                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 283                     let resolved = self.resolve_ty_as_possible(arg_ty);
 284                     self.infer_pat(*arg_pat, &resolved, BindingMode::default());
 285                 }
 286
 287                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 288                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 289
 290                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 291
 292                 self.diverges = prev_diverges;
 293                 self.return_ty = prev_ret_ty;
 294
 295                 closure_ty
 296             }
 297             Expr::Call { callee, args } => {
 298                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 299                 let canonicalized = self.canonicalizer().canonicalize_ty(callee_ty.clone());
 300                 let mut derefs = autoderef(
 301                     self.db,
 302                     self.resolver.krate(),
 303                     InEnvironment {
 304                         goal: canonicalized.value.clone(),
 305                         environment: self.trait_env.env.clone(),
 306                     },
 307                 );
 308                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
 309                     .find_map(|callee_deref_ty| {
 310                         self.callable_sig(
 311                             &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 312                             args.len(),
 313                         )
 314                     })
 315                     .unwrap_or((Vec::new(), self.err_ty()));
 316                 self.register_obligations_for_call(&callee_ty);
 317                 self.check_call_arguments(args, &param_tys);
 318                 self.normalize_associated_types_in(ret_ty)
 319             }
 320             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 321                 .infer_method_call(tgt_expr, *receiver, &args, &method_name, generic_args.as_ref()),
 322             Expr::Match { expr, arms } => {
 323                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 324
 325                 let mut result_ty = if arms.is_empty() {
 326                     TyKind::Never.intern(&Interner)
 327                 } else {
 328                     self.table.new_type_var()
 329                 };
 330
 331                 let matchee_diverges = self.diverges;
 332                 let mut all_arms_diverge = Diverges::Always;
 333
 334                 for arm in arms {
 335                     self.diverges = Diverges::Maybe;
 336                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 337                     if let Some(guard_expr) = arm.guard {
 338                         self.infer_expr(
 339                             guard_expr,
 340                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 341                         );
 342                     }
 343
 344                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 345                     all_arms_diverge &= self.diverges;
 346                     result_ty = self.coerce_merge_branch(&result_ty, &arm_ty);
 347                 }
 348
 349                 self.diverges = matchee_diverges | all_arms_diverge;
 350
 351                 result_ty
 352             }
 353             Expr::Path(p) => {
 354                 // FIXME this could be more efficient...
 355                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 356                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
 357             }
 358             Expr::Continue { .. } => TyKind::Never.intern(&Interner),
 359             Expr::Break { expr, label } => {
 360                 let val_ty = if let Some(expr) = expr {
 361                     self.infer_expr(*expr, &Expectation::none())
 362                 } else {
 363                     Ty::unit()
 364                 };
 365
 366                 let last_ty =
 367                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 368                         ctxt.break_ty.clone()
 369                     } else {
 370                         self.err_ty()
 371                     };
 372
 373                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
 374
 375                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 376                     ctxt.break_ty = merged_type;
 377                     ctxt.may_break = true;
 378                 } else {
 379                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 380                         expr: tgt_expr,
 381                     });
 382                 }
 383                 TyKind::Never.intern(&Interner)
 384             }
 385             Expr::Return { expr } => {
 386                 if let Some(expr) = expr {
 387                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 388                 } else {
 389                     let unit = Ty::unit();
 390                     self.coerce(&unit, &self.return_ty.clone());
 391                 }
 392                 TyKind::Never.intern(&Interner)
 393             }
 394             Expr::Yield { expr } => {
 395                 // FIXME: track yield type for coercion
 396                 if let Some(expr) = expr {
 397                     self.infer_expr(*expr, &Expectation::none());
 398                 }
 399                 TyKind::Never.intern(&Interner)
 400             }
 401             Expr::RecordLit { path, fields, spread } => {
 402                 let (ty, def_id) = self.resolve_variant(path.as_ref());
 403                 if let Some(variant) = def_id {
 404                     self.write_variant_resolution(tgt_expr.into(), variant);
 405                 }
 406
 407                 self.unify(&ty, &expected.ty);
 408
 409                 let substs = ty.substs().cloned().unwrap_or_else(|| Substitution::empty(&Interner));
 410                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 411                 let variant_data = def_id.map(|it| variant_data(self.db.upcast(), it));
 412                 for field in fields.iter() {
 413                     let field_def =
 414                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 415                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 416                             None => {
 417                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 418                                     expr: field.expr,
 419                                 });
 420                                 None
 421                             }
 422                         });
 423                     if let Some(field_def) = field_def {
 424                         self.result.record_field_resolutions.insert(field.expr, field_def);
 425                     }
 426                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 427                         field_types[it.local_id].clone().subst(&substs)
 428                     });
 429                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 430                 }
 431                 if let Some(expr) = spread {
 432                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 433                 }
 434                 ty
 435             }
 436             Expr::Field { expr, name } => {
 437                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 438                 let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
 439                 let ty = autoderef::autoderef(
 440                     self.db,
 441                     self.resolver.krate(),
 442                     InEnvironment {
 443                         goal: canonicalized.value.clone(),
 444                         environment: self.trait_env.env.clone(),
 445                     },
 446                 )
 447                 .find_map(|derefed_ty| {
 448                     let def_db = self.db.upcast();
 449                     let module = self.resolver.module();
 450                     let is_visible = |field_id: &FieldId| {
 451                         module
 452                             .map(|mod_id| {
 453                                 self.db.field_visibilities(field_id.parent)[field_id.local_id]
 454                                     .is_visible_from(def_db, mod_id)
 455                             })
 456                             .unwrap_or(true)
 457                     };
 458                     match canonicalized.decanonicalize_ty(derefed_ty.value).interned(&Interner) {
 459                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
 460                             substs
 461                                 .interned(&Interner)
 462                                 .get(idx)
 463                                 .map(|a| a.assert_ty_ref(&Interner))
 464                                 .cloned()
 465                         }),
 466                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 467                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 468                             let field = FieldId { parent: (*s).into(), local_id };
 469                             if is_visible(&field) {
 470                                 self.write_field_resolution(tgt_expr, field);
 471                                 Some(
 472                                     self.db.field_types((*s).into())[field.local_id]
 473                                         .clone()
 474                                         .subst(&parameters),
 475                                 )
 476                             } else {
 477                                 None
 478                             }
 479                         }
 480                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 481                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 482                             let field = FieldId { parent: (*u).into(), local_id };
 483                             if is_visible(&field) {
 484                                 self.write_field_resolution(tgt_expr, field);
 485                                 Some(
 486                                     self.db.field_types((*u).into())[field.local_id]
 487                                         .clone()
 488                                         .subst(&parameters),
 489                                 )
 490                             } else {
 491                                 None
 492                             }
 493                         }
 494                         _ => None,
 495                     }
 496                 })
 497                 .unwrap_or(self.err_ty());
 498                 let ty = self.insert_type_vars(ty);
 499                 self.normalize_associated_types_in(ty)
 500             }
 501             Expr::Await { expr } => {
 502                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 503                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 504             }
 505             Expr::Try { expr } => {
 506                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 507                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 508             }
 509             Expr::Cast { expr, type_ref } => {
 510                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 511                 let cast_ty = self.make_ty(type_ref);
 512                 // FIXME check the cast...
 513                 cast_ty
 514             }
 515             Expr::Ref { expr, rawness, mutability } => {
 516                 let mutability = lower_to_chalk_mutability(*mutability);
 517                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
 518                     &expected.ty.as_reference_or_ptr()
 519                 {
 520                     if *exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 521                         // FIXME: throw type error - expected mut reference but found shared ref,
 522                         // which cannot be coerced
 523                     }
 524                     if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 525                         // FIXME: throw type error - expected reference but found ptr,
 526                         // which cannot be coerced
 527                     }
 528                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 529                 } else {
 530                     Expectation::none()
 531                 };
 532                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 533                 match rawness {
 534                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 535                     Rawness::Ref => TyKind::Ref(mutability, inner_ty),
 536                 }
 537                 .intern(&Interner)
 538             }
 539             Expr::Box { expr } => {
 540                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 541                 if let Some(box_) = self.resolve_boxed_box() {
 542                     let mut sb =
 543                         Substitution::build_for_generics(&generics(self.db.upcast(), box_.into()));
 544                     sb = sb.push(inner_ty);
 545                     match self.db.generic_defaults(box_.into()).get(1) {
 546                         Some(alloc_ty) if !alloc_ty.value.is_unknown() && sb.remaining() > 0 => {
 547                             sb = sb.push(alloc_ty.value.clone());
 548                         }
 549                         _ => (),
 550                     }
 551                     sb = sb.fill(repeat_with(|| self.table.new_type_var()));
 552                     Ty::adt_ty(box_, sb.build())
 553                 } else {
 554                     self.err_ty()
 555                 }
 556             }
 557             Expr::UnaryOp { expr, op } => {
 558                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 559                 match op {
 560                     UnaryOp::Deref => match self.resolver.krate() {
 561                         Some(krate) => {
 562                             let canonicalized = self.canonicalizer().canonicalize_ty(inner_ty);
 563                             match autoderef::deref(
 564                                 self.db,
 565                                 krate,
 566                                 InEnvironment {
 567                                     goal: &canonicalized.value,
 568                                     environment: self.trait_env.env.clone(),
 569                                 },
 570                             ) {
 571                                 Some(derefed_ty) => {
 572                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 573                                 }
 574                                 None => self.err_ty(),
 575                             }
 576                         }
 577                         None => self.err_ty(),
 578                     },
 579                     UnaryOp::Neg => {
 580                         match inner_ty.interned(&Interner) {
 581                             // Fast path for builtins
 582                             TyKind::Scalar(Scalar::Int(_))
 583                             | TyKind::Scalar(Scalar::Uint(_))
 584                             | TyKind::Scalar(Scalar::Float(_))
 585                             | TyKind::InferenceVar(_, TyVariableKind::Integer)
 586                             | TyKind::InferenceVar(_, TyVariableKind::Float) => inner_ty,
 587                             // Otherwise we resolve via the std::ops::Neg trait
 588                             _ => self
 589                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 590                         }
 591                     }
 592                     UnaryOp::Not => {
 593                         match inner_ty.interned(&Interner) {
 594                             // Fast path for builtins
 595                             TyKind::Scalar(Scalar::Bool)
 596                             | TyKind::Scalar(Scalar::Int(_))
 597                             | TyKind::Scalar(Scalar::Uint(_))
 598                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 599                             // Otherwise we resolve via the std::ops::Not trait
 600                             _ => self
 601                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 602                         }
 603                     }
 604                 }
 605             }
 606             Expr::BinaryOp { lhs, rhs, op } => match op {
 607                 Some(op) => {
 608                     let lhs_expectation = match op {
 609                         BinaryOp::LogicOp(..) => {
 610                             Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
 611                         }
 612                         _ => Expectation::none(),
 613                     };
 614                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 615                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 616                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 617
 618                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 619
 620                     if ret.is_unknown() {
 621                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 622
 623                         self.resolve_associated_type_with_params(
 624                             lhs_ty,
 625                             self.resolve_binary_op_output(op),
 626                             &[rhs_ty],
 627                         )
 628                     } else {
 629                         ret
 630                     }
 631                 }
 632                 _ => self.err_ty(),
 633             },
 634             Expr::Range { lhs, rhs, range_type } => {
 635                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 636                 let rhs_expect = lhs_ty
 637                     .as_ref()
 638                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 639                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 640                 match (range_type, lhs_ty, rhs_ty) {
 641                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 642                         Some(adt) => Ty::adt_ty(adt, Substitution::empty(&Interner)),
 643                         None => self.err_ty(),
 644                     },
 645                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 646                         Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 647                         None => self.err_ty(),
 648                     },
 649                     (RangeOp::Inclusive, None, Some(ty)) => {
 650                         match self.resolve_range_to_inclusive() {
 651                             Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 652                             None => self.err_ty(),
 653                         }
 654                     }
 655                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 656                         Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 657                         None => self.err_ty(),
 658                     },
 659                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 660                         match self.resolve_range_inclusive() {
 661                             Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 662                             None => self.err_ty(),
 663                         }
 664                     }
 665                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 666                         Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 667                         None => self.err_ty(),
 668                     },
 669                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 670                 }
 671             }
 672             Expr::Index { base, index } => {
 673                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 674                 let index_ty = self.infer_expr(*index, &Expectation::none());
 675
 676                 if let (Some(index_trait), Some(krate)) =
 677                     (self.resolve_ops_index(), self.resolver.krate())
 678                 {
 679                     let canonicalized = self.canonicalizer().canonicalize_ty(base_ty);
 680                     let self_ty = method_resolution::resolve_indexing_op(
 681                         self.db,
 682                         &canonicalized.value,
 683                         self.trait_env.clone(),
 684                         krate,
 685                         index_trait,
 686                     );
 687                     let self_ty =
 688                         self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
 689                     self.resolve_associated_type_with_params(
 690                         self_ty,
 691                         self.resolve_ops_index_output(),
 692                         &[index_ty],
 693                     )
 694                 } else {
 695                     self.err_ty()
 696                 }
 697             }
 698             Expr::Tuple { exprs } => {
 699                 let mut tys = match expected.ty.interned(&Interner) {
 700                     TyKind::Tuple(_, substs) => substs
 701                         .iter(&Interner)
 702                         .map(|a| a.assert_ty_ref(&Interner).clone())
 703                         .chain(repeat_with(|| self.table.new_type_var()))
 704                         .take(exprs.len())
 705                         .collect::<Vec<_>>(),
 706                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 707                 };
 708
 709                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 710                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 711                 }
 712
 713                 TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
 714             }
 715             Expr::Array(array) => {
 716                 let elem_ty = match expected.ty.interned(&Interner) {
 717                     TyKind::Array(st) | TyKind::Slice(st) => st.clone(),
 718                     _ => self.table.new_type_var(),
 719                 };
 720
 721                 match array {
 722                     Array::ElementList(items) => {
 723                         for expr in items.iter() {
 724                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
 725                         }
 726                     }
 727                     Array::Repeat { initializer, repeat } => {
 728                         self.infer_expr_coerce(
 729                             *initializer,
 730                             &Expectation::has_type(elem_ty.clone()),
 731                         );
 732                         self.infer_expr(
 733                             *repeat,
 734                             &Expectation::has_type(
 735                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
 736                             ),
 737                         );
 738                     }
 739                 }
 740
 741                 TyKind::Array(elem_ty).intern(&Interner)
 742             }
 743             Expr::Literal(lit) => match lit {
 744                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
 745                 Literal::String(..) => {
 746                     TyKind::Ref(Mutability::Not, TyKind::Str.intern(&Interner)).intern(&Interner)
 747                 }
 748                 Literal::ByteString(..) => {
 749                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
 750                     let array_type = TyKind::Array(byte_type).intern(&Interner);
 751                     TyKind::Ref(Mutability::Not, array_type).intern(&Interner)
 752                 }
 753                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
 754                 Literal::Int(_v, ty) => match ty {
 755                     Some(int_ty) => {
 756                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 757                             .intern(&Interner)
 758                     }
 759                     None => self.table.new_integer_var(),
 760                 },
 761                 Literal::Uint(_v, ty) => match ty {
 762                     Some(int_ty) => {
 763                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 764                             .intern(&Interner)
 765                     }
 766                     None => self.table.new_integer_var(),
 767                 },
 768                 Literal::Float(_v, ty) => match ty {
 769                     Some(float_ty) => {
 770                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 771                             .intern(&Interner)
 772                     }
 773                     None => self.table.new_float_var(),
 774                 },
 775             },
 776             Expr::MacroStmts { tail } => self.infer_expr(*tail, expected),
 777         };
 778         // use a new type variable if we got unknown here
 779         let ty = self.insert_type_vars_shallow(ty);
 780         let ty = self.resolve_ty_as_possible(ty);
 781         self.write_expr_ty(tgt_expr, ty.clone());
 782         ty
 783     }
 784
 785     fn infer_block(
 786         &mut self,
 787         statements: &[Statement],
 788         tail: Option<ExprId>,
 789         expected: &Expectation,
 790     ) -> Ty {
 791         for stmt in statements {
 792             match stmt {
 793                 Statement::Let { pat, type_ref, initializer } => {
 794                     let decl_ty =
 795                         type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(self.err_ty());
 796
 797                     // Always use the declared type when specified
 798                     let mut ty = decl_ty.clone();
 799
 800                     if let Some(expr) = initializer {
 801                         let actual_ty =
 802                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 803                         if decl_ty.is_unknown() {
 804                             ty = actual_ty;
 805                         }
 806                     }
 807
 808                     let ty = self.resolve_ty_as_possible(ty);
 809                     self.infer_pat(*pat, &ty, BindingMode::default());
 810                 }
 811                 Statement::Expr(expr) => {
 812                     self.infer_expr(*expr, &Expectation::none());
 813                 }
 814             }
 815         }
 816
 817         let ty = if let Some(expr) = tail {
 818             self.infer_expr_coerce(expr, expected)
 819         } else {
 820             // Citing rustc: if there is no explicit tail expression,
 821             // that is typically equivalent to a tail expression
 822             // of `()` -- except if the block diverges. In that
 823             // case, there is no value supplied from the tail
 824             // expression (assuming there are no other breaks,
 825             // this implies that the type of the block will be
 826             // `!`).
 827             if self.diverges.is_always() {
 828                 // we don't even make an attempt at coercion
 829                 self.table.new_maybe_never_var()
 830             } else {
 831                 self.coerce(&Ty::unit(), &expected.coercion_target());
 832                 Ty::unit()
 833             }
 834         };
 835         ty
 836     }
 837
 838     fn infer_method_call(
 839         &mut self,
 840         tgt_expr: ExprId,
 841         receiver: ExprId,
 842         args: &[ExprId],
 843         method_name: &Name,
 844         generic_args: Option<&GenericArgs>,
 845     ) -> Ty {
 846         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 847         let canonicalized_receiver = self.canonicalizer().canonicalize_ty(receiver_ty.clone());
 848
 849         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 850
 851         let resolved = self.resolver.krate().and_then(|krate| {
 852             method_resolution::lookup_method(
 853                 &canonicalized_receiver.value,
 854                 self.db,
 855                 self.trait_env.clone(),
 856                 krate,
 857                 &traits_in_scope,
 858                 self.resolver.module(),
 859                 method_name,
 860             )
 861         });
 862         let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
 863             Some((ty, func)) => {
 864                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 865                 self.write_method_resolution(tgt_expr, func);
 866                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
 867             }
 868             None => (receiver_ty, Binders::new(0, self.err_ty()), None),
 869         };
 870         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
 871         let method_ty = method_ty.subst(&substs);
 872         let method_ty = self.insert_type_vars(method_ty);
 873         self.register_obligations_for_call(&method_ty);
 874         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 875             Some(sig) => {
 876                 if !sig.params().is_empty() {
 877                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 878                 } else {
 879                     (self.err_ty(), Vec::new(), sig.ret().clone())
 880                 }
 881             }
 882             None => (self.err_ty(), Vec::new(), self.err_ty()),
 883         };
 884         // Apply autoref so the below unification works correctly
 885         // FIXME: return correct autorefs from lookup_method
 886         let actual_receiver_ty = match expected_receiver_ty.as_reference() {
 887             Some((_, mutability)) => TyKind::Ref(mutability, derefed_receiver_ty).intern(&Interner),
 888             _ => derefed_receiver_ty,
 889         };
 890         self.unify(&expected_receiver_ty, &actual_receiver_ty);
 891
 892         self.check_call_arguments(args, &param_tys);
 893         self.normalize_associated_types_in(ret_ty)
 894     }
 895
 896     fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
 897         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 898         // We do this in a pretty awful way: first we type-check any arguments
 899         // that are not closures, then we type-check the closures. This is so
 900         // that we have more information about the types of arguments when we
 901         // type-check the functions. This isn't really the right way to do this.
 902         for &check_closures in &[false, true] {
 903             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
 904             for (&arg, param_ty) in args.iter().zip(param_iter) {
 905                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
 906                 if is_closure != check_closures {
 907                     continue;
 908                 }
 909
 910                 let param_ty = self.normalize_associated_types_in(param_ty);
 911                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
 912             }
 913         }
 914     }
 915
 916     fn substs_for_method_call(
 917         &mut self,
 918         def_generics: Option<Generics>,
 919         generic_args: Option<&GenericArgs>,
 920         receiver_ty: &Ty,
 921     ) -> Substitution {
 922         let (parent_params, self_params, type_params, impl_trait_params) =
 923             def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
 924         assert_eq!(self_params, 0); // method shouldn't have another Self param
 925         let total_len = parent_params + type_params + impl_trait_params;
 926         let mut substs = Vec::with_capacity(total_len);
 927         // Parent arguments are unknown, except for the receiver type
 928         if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
 929             for (_id, param) in parent_generics {
 930                 if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
 931                     substs.push(receiver_ty.clone());
 932                 } else {
 933                     substs.push(self.err_ty());
 934                 }
 935             }
 936         }
 937         // handle provided type arguments
 938         if let Some(generic_args) = generic_args {
 939             // if args are provided, it should be all of them, but we can't rely on that
 940             for arg in generic_args
 941                 .args
 942                 .iter()
 943                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 944                 .take(type_params)
 945             {
 946                 match arg {
 947                     GenericArg::Type(type_ref) => {
 948                         let ty = self.make_ty(type_ref);
 949                         substs.push(ty);
 950                     }
 951                     GenericArg::Lifetime(_) => {}
 952                 }
 953             }
 954         };
 955         let supplied_params = substs.len();
 956         for _ in supplied_params..total_len {
 957             substs.push(self.err_ty());
 958         }
 959         assert_eq!(substs.len(), total_len);
 960         Substitution::from_iter(&Interner, substs)
 961     }
 962
 963     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
 964         if let TyKind::FnDef(fn_def, parameters) = callable_ty.interned(&Interner) {
 965             let def: CallableDefId = from_chalk(self.db, *fn_def);
 966             let generic_predicates = self.db.generic_predicates(def.into());
 967             for predicate in generic_predicates.iter() {
 968                 let (predicate, binders) =
 969                     predicate.clone().subst(parameters).into_value_and_skipped_binders();
 970                 always!(binders == 0); // quantified where clauses not yet handled
 971                 self.push_obligation(predicate.cast(&Interner));
 972             }
 973             // add obligation for trait implementation, if this is a trait method
 974             match def {
 975                 CallableDefId::FunctionId(f) => {
 976                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
 977                     {
 978                         // construct a TraitRef
 979                         let substs =
 980                             parameters.prefix(generics(self.db.upcast(), trait_.into()).len());
 981                         self.push_obligation(
 982                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
 983                                 .cast(&Interner),
 984                         );
 985                     }
 986                 }
 987                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
 988             }
 989         }
 990     }
 991 }