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