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 syntax::ast::RangeOp;
  15
  16 use crate::{
  17     autoderef,
  18     lower::lower_to_chalk_mutability,
  19     method_resolution, op,
  20     primitive::{self, UintTy},
  21     to_assoc_type_id, to_chalk_trait_id,
  22     traits::{chalk::from_chalk, FnTrait, InEnvironment},
  23     utils::{generics, variant_data, Generics},
  24     AdtId, Binders, CallableDefId, DomainGoal, FnPointer, FnSig, Interner, Rawness, Scalar,
  25     Substitution, TraitRef, Ty, TyKind,
  26 };
  27
  28 use super::{
  29     find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
  30     InferenceDiagnostic, TypeMismatch,
  31 };
  32
  33 impl<'a> InferenceContext<'a> {
  34     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  35         let ty = self.infer_expr_inner(tgt_expr, expected);
  36         if ty.is_never() {
  37             // Any expression that produces a value of type `!` must have diverged
  38             self.diverges = Diverges::Always;
  39         }
  40         let could_unify = self.unify(&ty, &expected.ty);
  41         if !could_unify {
  42             self.result.type_mismatches.insert(
  43                 tgt_expr,
  44                 TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() },
  45             );
  46         }
  47         self.resolve_ty_as_possible(ty)
  48     }
  49
  50     /// Infer type of expression with possibly implicit coerce to the expected type.
  51     /// Return the type after possible coercion.
  52     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  53         let ty = self.infer_expr_inner(expr, &expected);
  54         let ty = if !self.coerce(&ty, &expected.coercion_target()) {
  55             self.result
  56                 .type_mismatches
  57                 .insert(expr, TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() });
  58             // Return actual type when type mismatch.
  59             // This is needed for diagnostic when return type mismatch.
  60             ty
  61         } else if expected.coercion_target().is_unknown() {
  62             ty
  63         } else {
  64             expected.ty.clone()
  65         };
  66
  67         self.resolve_ty_as_possible(ty)
  68     }
  69
  70     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
  71         let krate = self.resolver.krate()?;
  72         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
  73         let output_assoc_type =
  74             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
  75         let generic_params = generics(self.db.upcast(), fn_once_trait.into());
  76         if generic_params.len() != 2 {
  77             return None;
  78         }
  79
  80         let mut param_builder = Substitution::builder(num_args);
  81         let mut arg_tys = vec![];
  82         for _ in 0..num_args {
  83             let arg = self.table.new_type_var();
  84             param_builder = param_builder.push(arg.clone());
  85             arg_tys.push(arg);
  86         }
  87         let parameters = param_builder.build();
  88         let arg_ty = TyKind::Tuple(num_args, parameters).intern(&Interner);
  89         let substs =
  90             Substitution::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
  91
  92         let trait_env = Arc::clone(&self.trait_env);
  93         let implements_fn_trait: DomainGoal =
  94             TraitRef { trait_id: to_chalk_trait_id(fn_once_trait), substitution: substs.clone() }
  95                 .cast(&Interner);
  96         let goal = self.canonicalizer().canonicalize_obligation(InEnvironment {
  97             value: implements_fn_trait.clone(),
  98             environment: trait_env,
  99         });
 100         if self.db.trait_solve(krate, goal.value).is_some() {
 101             self.obligations.push(implements_fn_trait);
 102             let output_proj_ty = crate::ProjectionTy {
 103                 associated_ty_id: to_assoc_type_id(output_assoc_type),
 104                 substitution: substs,
 105             };
 106             let return_ty = self.normalize_projection_ty(output_proj_ty);
 107             Some((arg_tys, return_ty))
 108         } else {
 109             None
 110         }
 111     }
 112
 113     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 114         match ty.callable_sig(self.db) {
 115             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 116             None => self.callable_sig_from_fn_trait(ty, num_args),
 117         }
 118     }
 119
 120     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 121         let body = Arc::clone(&self.body); // avoid borrow checker problem
 122         let ty = match &body[tgt_expr] {
 123             Expr::Missing => self.err_ty(),
 124             Expr::If { condition, then_branch, else_branch } => {
 125                 // if let is desugared to match, so this is always simple if
 126                 self.infer_expr(
 127                     *condition,
 128                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 129                 );
 130
 131                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 132                 let mut both_arms_diverge = Diverges::Always;
 133
 134                 let then_ty = self.infer_expr_inner(*then_branch, &expected);
 135                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 136                 let else_ty = match else_branch {
 137                     Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
 138                     None => Ty::unit(),
 139                 };
 140                 both_arms_diverge &= self.diverges;
 141
 142                 self.diverges = condition_diverges | both_arms_diverge;
 143
 144                 self.coerce_merge_branch(&then_ty, &else_ty)
 145             }
 146             Expr::Block { statements, tail, label, id: _ } => {
 147                 let old_resolver = mem::replace(
 148                     &mut self.resolver,
 149                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 150                 );
 151                 let ty = match label {
 152                     Some(_) => {
 153                         let break_ty = self.table.new_type_var();
 154                         self.breakables.push(BreakableContext {
 155                             may_break: false,
 156                             break_ty: break_ty.clone(),
 157                             label: label.map(|label| self.body[label].name.clone()),
 158                         });
 159                         let ty =
 160                             self.infer_block(statements, *tail, &Expectation::has_type(break_ty));
 161                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 162                         if ctxt.may_break {
 163                             ctxt.break_ty
 164                         } else {
 165                             ty
 166                         }
 167                     }
 168                     None => self.infer_block(statements, *tail, expected),
 169                 };
 170                 self.resolver = old_resolver;
 171                 ty
 172             }
 173             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 174             Expr::TryBlock { body } => {
 175                 let _inner = self.infer_expr(*body, expected);
 176                 // FIXME should be std::result::Result<{inner}, _>
 177                 self.err_ty()
 178             }
 179             Expr::Async { body } => {
 180                 // Use the first type parameter as the output type of future.
 181                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 182                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 183                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 184                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 185                 TyKind::OpaqueType(opaque_ty_id, Substitution::single(inner_ty)).intern(&Interner)
 186             }
 187             Expr::Loop { body, label } => {
 188                 self.breakables.push(BreakableContext {
 189                     may_break: false,
 190                     break_ty: self.table.new_type_var(),
 191                     label: label.map(|label| self.body[label].name.clone()),
 192                 });
 193                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 194
 195                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 196                 if ctxt.may_break {
 197                     self.diverges = Diverges::Maybe;
 198                 }
 199
 200                 if ctxt.may_break {
 201                     ctxt.break_ty
 202                 } else {
 203                     TyKind::Never.intern(&Interner)
 204                 }
 205             }
 206             Expr::While { condition, body, label } => {
 207                 self.breakables.push(BreakableContext {
 208                     may_break: false,
 209                     break_ty: self.err_ty(),
 210                     label: label.map(|label| self.body[label].name.clone()),
 211                 });
 212                 // while let is desugared to a match loop, so this is always simple while
 213                 self.infer_expr(
 214                     *condition,
 215                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 216                 );
 217                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 218                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 219                 // the body may not run, so it diverging doesn't mean we diverge
 220                 self.diverges = Diverges::Maybe;
 221                 Ty::unit()
 222             }
 223             Expr::For { iterable, body, pat, label } => {
 224                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 225
 226                 self.breakables.push(BreakableContext {
 227                     may_break: false,
 228                     break_ty: self.err_ty(),
 229                     label: label.map(|label| self.body[label].name.clone()),
 230                 });
 231                 let pat_ty =
 232                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 233
 234                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 235
 236                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 237                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 238                 // the body may not run, so it diverging doesn't mean we diverge
 239                 self.diverges = Diverges::Maybe;
 240                 Ty::unit()
 241             }
 242             Expr::Lambda { body, args, ret_type, arg_types } => {
 243                 assert_eq!(args.len(), arg_types.len());
 244
 245                 let mut sig_tys = Vec::new();
 246
 247                 // collect explicitly written argument types
 248                 for arg_type in arg_types.iter() {
 249                     let arg_ty = if let Some(type_ref) = arg_type {
 250                         self.make_ty(type_ref)
 251                     } else {
 252                         self.table.new_type_var()
 253                     };
 254                     sig_tys.push(arg_ty);
 255                 }
 256
 257                 // add return type
 258                 let ret_ty = match ret_type {
 259                     Some(type_ref) => self.make_ty(type_ref),
 260                     None => self.table.new_type_var(),
 261                 };
 262                 sig_tys.push(ret_ty.clone());
 263                 let sig_ty = TyKind::Function(FnPointer {
 264                     num_args: sig_tys.len() - 1,
 265                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 266                     substs: Substitution(sig_tys.clone().into()),
 267                 })
 268                 .intern(&Interner);
 269                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 270                 let closure_ty =
 271                     TyKind::Closure(closure_id, Substitution::single(sig_ty)).intern(&Interner);
 272
 273                 // Eagerly try to relate the closure type with the expected
 274                 // type, otherwise we often won't have enough information to
 275                 // infer the body.
 276                 self.coerce(&closure_ty, &expected.ty);
 277
 278                 // Now go through the argument patterns
 279                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 280                     let resolved = self.resolve_ty_as_possible(arg_ty);
 281                     self.infer_pat(*arg_pat, &resolved, BindingMode::default());
 282                 }
 283
 284                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 285                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 286
 287                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 288
 289                 self.diverges = prev_diverges;
 290                 self.return_ty = prev_ret_ty;
 291
 292                 closure_ty
 293             }
 294             Expr::Call { callee, args } => {
 295                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 296                 let canonicalized = self.canonicalizer().canonicalize_ty(callee_ty.clone());
 297                 let mut derefs = autoderef(
 298                     self.db,
 299                     self.resolver.krate(),
 300                     InEnvironment {
 301                         value: canonicalized.value.clone(),
 302                         environment: self.trait_env.clone(),
 303                     },
 304                 );
 305                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
 306                     .find_map(|callee_deref_ty| {
 307                         self.callable_sig(
 308                             &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 309                             args.len(),
 310                         )
 311                     })
 312                     .unwrap_or((Vec::new(), self.err_ty()));
 313                 self.register_obligations_for_call(&callee_ty);
 314                 self.check_call_arguments(args, &param_tys);
 315                 self.normalize_associated_types_in(ret_ty)
 316             }
 317             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 318                 .infer_method_call(tgt_expr, *receiver, &args, &method_name, generic_args.as_ref()),
 319             Expr::Match { expr, arms } => {
 320                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 321
 322                 let mut result_ty = if arms.is_empty() {
 323                     TyKind::Never.intern(&Interner)
 324                 } else {
 325                     self.table.new_type_var()
 326                 };
 327
 328                 let matchee_diverges = self.diverges;
 329                 let mut all_arms_diverge = Diverges::Always;
 330
 331                 for arm in arms {
 332                     self.diverges = Diverges::Maybe;
 333                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 334                     if let Some(guard_expr) = arm.guard {
 335                         self.infer_expr(
 336                             guard_expr,
 337                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 338                         );
 339                     }
 340
 341                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 342                     all_arms_diverge &= self.diverges;
 343                     result_ty = self.coerce_merge_branch(&result_ty, &arm_ty);
 344                 }
 345
 346                 self.diverges = matchee_diverges | all_arms_diverge;
 347
 348                 result_ty
 349             }
 350             Expr::Path(p) => {
 351                 // FIXME this could be more efficient...
 352                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 353                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
 354             }
 355             Expr::Continue { .. } => TyKind::Never.intern(&Interner),
 356             Expr::Break { expr, label } => {
 357                 let val_ty = if let Some(expr) = expr {
 358                     self.infer_expr(*expr, &Expectation::none())
 359                 } else {
 360                     Ty::unit()
 361                 };
 362
 363                 let last_ty =
 364                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 365                         ctxt.break_ty.clone()
 366                     } else {
 367                         self.err_ty()
 368                     };
 369
 370                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
 371
 372                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 373                     ctxt.break_ty = merged_type;
 374                     ctxt.may_break = true;
 375                 } else {
 376                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 377                         expr: tgt_expr,
 378                     });
 379                 }
 380                 TyKind::Never.intern(&Interner)
 381             }
 382             Expr::Return { expr } => {
 383                 if let Some(expr) = expr {
 384                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 385                 } else {
 386                     let unit = Ty::unit();
 387                     self.coerce(&unit, &self.return_ty.clone());
 388                 }
 389                 TyKind::Never.intern(&Interner)
 390             }
 391             Expr::Yield { expr } => {
 392                 // FIXME: track yield type for coercion
 393                 if let Some(expr) = expr {
 394                     self.infer_expr(*expr, &Expectation::none());
 395                 }
 396                 TyKind::Never.intern(&Interner)
 397             }
 398             Expr::RecordLit { path, fields, spread } => {
 399                 let (ty, def_id) = self.resolve_variant(path.as_ref());
 400                 if let Some(variant) = def_id {
 401                     self.write_variant_resolution(tgt_expr.into(), variant);
 402                 }
 403
 404                 self.unify(&ty, &expected.ty);
 405
 406                 let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
 407                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 408                 let variant_data = def_id.map(|it| variant_data(self.db.upcast(), it));
 409                 for field in fields.iter() {
 410                     let field_def =
 411                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 412                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 413                             None => {
 414                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 415                                     expr: field.expr,
 416                                 });
 417                                 None
 418                             }
 419                         });
 420                     if let Some(field_def) = field_def {
 421                         self.result.record_field_resolutions.insert(field.expr, field_def);
 422                     }
 423                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 424                         field_types[it.local_id].clone().subst(&substs)
 425                     });
 426                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 427                 }
 428                 if let Some(expr) = spread {
 429                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 430                 }
 431                 ty
 432             }
 433             Expr::Field { expr, name } => {
 434                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 435                 let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
 436                 let ty = autoderef::autoderef(
 437                     self.db,
 438                     self.resolver.krate(),
 439                     InEnvironment {
 440                         value: canonicalized.value.clone(),
 441                         environment: self.trait_env.clone(),
 442                     },
 443                 )
 444                 .find_map(|derefed_ty| {
 445                     let def_db = self.db.upcast();
 446                     let module = self.resolver.module();
 447                     let is_visible = |field_id: &FieldId| {
 448                         module
 449                             .map(|mod_id| {
 450                                 self.db.field_visibilities(field_id.parent)[field_id.local_id]
 451                                     .is_visible_from(def_db, mod_id)
 452                             })
 453                             .unwrap_or(true)
 454                     };
 455                     match canonicalized.decanonicalize_ty(derefed_ty.value).interned(&Interner) {
 456                         TyKind::Tuple(_, substs) => {
 457                             name.as_tuple_index().and_then(|idx| substs.0.get(idx).cloned())
 458                         }
 459                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 460                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 461                             let field = FieldId { parent: (*s).into(), local_id };
 462                             let is_visible_in_ctx = is_visible(&field);
 463                             self.write_field_resolution(tgt_expr, field);
 464                             if is_visible_in_ctx {
 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                             let is_visible_in_ctx = is_visible(&field);
 478                             self.write_field_resolution(tgt_expr, field);
 479                             if is_visible_in_ctx {
 480                                 Some(
 481                                     self.db.field_types((*u).into())[field.local_id]
 482                                         .clone()
 483                                         .subst(&parameters),
 484                                 )
 485                             } else {
 486                                 None
 487                             }
 488                         }
 489                         _ => None,
 490                     }
 491                 })
 492                 .unwrap_or(self.err_ty());
 493                 let ty = self.insert_type_vars(ty);
 494                 self.normalize_associated_types_in(ty)
 495             }
 496             Expr::Await { expr } => {
 497                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 498                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 499             }
 500             Expr::Try { expr } => {
 501                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 502                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 503             }
 504             Expr::Cast { expr, type_ref } => {
 505                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 506                 let cast_ty = self.make_ty(type_ref);
 507                 // FIXME check the cast...
 508                 cast_ty
 509             }
 510             Expr::Ref { expr, rawness, mutability } => {
 511                 let mutability = lower_to_chalk_mutability(*mutability);
 512                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
 513                     &expected.ty.as_reference_or_ptr()
 514                 {
 515                     if *exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 516                         // FIXME: throw type error - expected mut reference but found shared ref,
 517                         // which cannot be coerced
 518                     }
 519                     if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 520                         // FIXME: throw type error - expected reference but found ptr,
 521                         // which cannot be coerced
 522                     }
 523                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 524                 } else {
 525                     Expectation::none()
 526                 };
 527                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 528                 match rawness {
 529                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 530                     Rawness::Ref => TyKind::Ref(mutability, inner_ty),
 531                 }
 532                 .intern(&Interner)
 533             }
 534             Expr::Box { expr } => {
 535                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 536                 if let Some(box_) = self.resolve_boxed_box() {
 537                     let mut sb =
 538                         Substitution::builder(generics(self.db.upcast(), box_.into()).len());
 539                     sb = sb.push(inner_ty);
 540                     match self.db.generic_defaults(box_.into()).as_ref() {
 541                         [_, alloc_ty, ..] if !alloc_ty.value.is_unknown() => {
 542                             sb = sb.push(alloc_ty.value.clone());
 543                         }
 544                         _ => (),
 545                     }
 546                     sb = sb.fill(repeat_with(|| self.table.new_type_var()));
 547                     Ty::adt_ty(box_, sb.build())
 548                 } else {
 549                     self.err_ty()
 550                 }
 551             }
 552             Expr::UnaryOp { expr, op } => {
 553                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 554                 match op {
 555                     UnaryOp::Deref => match self.resolver.krate() {
 556                         Some(krate) => {
 557                             let canonicalized = self.canonicalizer().canonicalize_ty(inner_ty);
 558                             match autoderef::deref(
 559                                 self.db,
 560                                 krate,
 561                                 InEnvironment {
 562                                     value: &canonicalized.value,
 563                                     environment: self.trait_env.clone(),
 564                                 },
 565                             ) {
 566                                 Some(derefed_ty) => {
 567                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 568                                 }
 569                                 None => self.err_ty(),
 570                             }
 571                         }
 572                         None => self.err_ty(),
 573                     },
 574                     UnaryOp::Neg => {
 575                         match inner_ty.interned(&Interner) {
 576                             // Fast path for builtins
 577                             TyKind::Scalar(Scalar::Int(_))
 578                             | TyKind::Scalar(Scalar::Uint(_))
 579                             | TyKind::Scalar(Scalar::Float(_))
 580                             | TyKind::InferenceVar(_, TyVariableKind::Integer)
 581                             | TyKind::InferenceVar(_, TyVariableKind::Float) => inner_ty,
 582                             // Otherwise we resolve via the std::ops::Neg trait
 583                             _ => self
 584                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 585                         }
 586                     }
 587                     UnaryOp::Not => {
 588                         match inner_ty.interned(&Interner) {
 589                             // Fast path for builtins
 590                             TyKind::Scalar(Scalar::Bool)
 591                             | TyKind::Scalar(Scalar::Int(_))
 592                             | TyKind::Scalar(Scalar::Uint(_))
 593                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 594                             // Otherwise we resolve via the std::ops::Not trait
 595                             _ => self
 596                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 597                         }
 598                     }
 599                 }
 600             }
 601             Expr::BinaryOp { lhs, rhs, op } => match op {
 602                 Some(op) => {
 603                     let lhs_expectation = match op {
 604                         BinaryOp::LogicOp(..) => {
 605                             Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
 606                         }
 607                         _ => Expectation::none(),
 608                     };
 609                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 610                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 611                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 612
 613                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 614
 615                     if ret.is_unknown() {
 616                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 617
 618                         self.resolve_associated_type_with_params(
 619                             lhs_ty,
 620                             self.resolve_binary_op_output(op),
 621                             &[rhs_ty],
 622                         )
 623                     } else {
 624                         ret
 625                     }
 626                 }
 627                 _ => self.err_ty(),
 628             },
 629             Expr::Range { lhs, rhs, range_type } => {
 630                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 631                 let rhs_expect = lhs_ty
 632                     .as_ref()
 633                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 634                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 635                 match (range_type, lhs_ty, rhs_ty) {
 636                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 637                         Some(adt) => Ty::adt_ty(adt, Substitution::empty()),
 638                         None => self.err_ty(),
 639                     },
 640                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 641                         Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 642                         None => self.err_ty(),
 643                     },
 644                     (RangeOp::Inclusive, None, Some(ty)) => {
 645                         match self.resolve_range_to_inclusive() {
 646                             Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 647                             None => self.err_ty(),
 648                         }
 649                     }
 650                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 651                         Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 652                         None => self.err_ty(),
 653                     },
 654                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 655                         match self.resolve_range_inclusive() {
 656                             Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 657                             None => self.err_ty(),
 658                         }
 659                     }
 660                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 661                         Some(adt) => Ty::adt_ty(adt, Substitution::single(ty)),
 662                         None => self.err_ty(),
 663                     },
 664                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 665                 }
 666             }
 667             Expr::Index { base, index } => {
 668                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 669                 let index_ty = self.infer_expr(*index, &Expectation::none());
 670
 671                 if let (Some(index_trait), Some(krate)) =
 672                     (self.resolve_ops_index(), self.resolver.krate())
 673                 {
 674                     let canonicalized = self.canonicalizer().canonicalize_ty(base_ty);
 675                     let self_ty = method_resolution::resolve_indexing_op(
 676                         self.db,
 677                         &canonicalized.value,
 678                         self.trait_env.clone(),
 679                         krate,
 680                         index_trait,
 681                     );
 682                     let self_ty =
 683                         self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
 684                     self.resolve_associated_type_with_params(
 685                         self_ty,
 686                         self.resolve_ops_index_output(),
 687                         &[index_ty],
 688                     )
 689                 } else {
 690                     self.err_ty()
 691                 }
 692             }
 693             Expr::Tuple { exprs } => {
 694                 let mut tys = match expected.ty.interned(&Interner) {
 695                     TyKind::Tuple(_, substs) => substs
 696                         .iter()
 697                         .cloned()
 698                         .chain(repeat_with(|| self.table.new_type_var()))
 699                         .take(exprs.len())
 700                         .collect::<Vec<_>>(),
 701                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 702                 };
 703
 704                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 705                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 706                 }
 707
 708                 TyKind::Tuple(tys.len(), Substitution(tys.into())).intern(&Interner)
 709             }
 710             Expr::Array(array) => {
 711                 let elem_ty = match expected.ty.interned(&Interner) {
 712                     TyKind::Array(st) | TyKind::Slice(st) => st.clone(),
 713                     _ => self.table.new_type_var(),
 714                 };
 715
 716                 match array {
 717                     Array::ElementList(items) => {
 718                         for expr in items.iter() {
 719                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
 720                         }
 721                     }
 722                     Array::Repeat { initializer, repeat } => {
 723                         self.infer_expr_coerce(
 724                             *initializer,
 725                             &Expectation::has_type(elem_ty.clone()),
 726                         );
 727                         self.infer_expr(
 728                             *repeat,
 729                             &Expectation::has_type(
 730                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
 731                             ),
 732                         );
 733                     }
 734                 }
 735
 736                 TyKind::Array(elem_ty).intern(&Interner)
 737             }
 738             Expr::Literal(lit) => match lit {
 739                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
 740                 Literal::String(..) => {
 741                     TyKind::Ref(Mutability::Not, TyKind::Str.intern(&Interner)).intern(&Interner)
 742                 }
 743                 Literal::ByteString(..) => {
 744                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
 745                     let array_type = TyKind::Array(byte_type).intern(&Interner);
 746                     TyKind::Ref(Mutability::Not, array_type).intern(&Interner)
 747                 }
 748                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
 749                 Literal::Int(_v, ty) => match ty {
 750                     Some(int_ty) => {
 751                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 752                             .intern(&Interner)
 753                     }
 754                     None => self.table.new_integer_var(),
 755                 },
 756                 Literal::Uint(_v, ty) => match ty {
 757                     Some(int_ty) => {
 758                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 759                             .intern(&Interner)
 760                     }
 761                     None => self.table.new_integer_var(),
 762                 },
 763                 Literal::Float(_v, ty) => match ty {
 764                     Some(float_ty) => {
 765                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 766                             .intern(&Interner)
 767                     }
 768                     None => self.table.new_float_var(),
 769                 },
 770             },
 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 = predicate.clone().subst(parameters);
 963                 self.obligations.push(predicate.cast(&Interner));
 964             }
 965             // add obligation for trait implementation, if this is a trait method
 966             match def {
 967                 CallableDefId::FunctionId(f) => {
 968                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
 969                     {
 970                         // construct a TraitRef
 971                         let substs =
 972                             parameters.prefix(generics(self.db.upcast(), trait_.into()).len());
 973                         self.obligations.push(
 974                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
 975                                 .cast(&Interner),
 976                         );
 977                     }
 978                 }
 979                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
 980             }
 981         }
 982     }
 983 }