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, fold::Shift, 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, dummy_usize_const,
  19     lower::lower_to_chalk_mutability,
  20     method_resolution, op,
  21     primitive::{self, UintTy},
  22     static_lifetime, to_chalk_trait_id,
  23     traits::{chalk::from_chalk, FnTrait},
  24     utils::{generics, Generics},
  25     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
  26     ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, 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
  77         let mut arg_tys = vec![];
  78         let arg_ty = TyBuilder::tuple(num_args)
  79             .fill(repeat_with(|| {
  80                 let arg = self.table.new_type_var();
  81                 arg_tys.push(arg.clone());
  82                 arg
  83             }))
  84             .build();
  85
  86         let projection = {
  87             let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
  88             if b.remaining() != 2 {
  89                 return None;
  90             }
  91             b.push(ty.clone()).push(arg_ty).build()
  92         };
  93
  94         let trait_env = self.trait_env.env.clone();
  95         let obligation = InEnvironment {
  96             goal: projection.trait_ref(self.db).cast(&Interner),
  97             environment: trait_env,
  98         };
  99         let canonical = self.canonicalizer().canonicalize_obligation(obligation.clone());
 100         if self.db.trait_solve(krate, canonical.value).is_some() {
 101             self.push_obligation(obligation.goal);
 102             let return_ty = self.normalize_projection_ty(projection);
 103             Some((arg_tys, return_ty))
 104         } else {
 105             None
 106         }
 107     }
 108
 109     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 110         match ty.callable_sig(self.db) {
 111             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 112             None => self.callable_sig_from_fn_trait(ty, num_args),
 113         }
 114     }
 115
 116     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 117         self.db.check_canceled();
 118
 119         let body = Arc::clone(&self.body); // avoid borrow checker problem
 120         let ty = match &body[tgt_expr] {
 121             Expr::Missing => self.err_ty(),
 122             Expr::If { condition, then_branch, else_branch } => {
 123                 // if let is desugared to match, so this is always simple if
 124                 self.infer_expr(
 125                     *condition,
 126                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 127                 );
 128
 129                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 130                 let mut both_arms_diverge = Diverges::Always;
 131
 132                 let then_ty = self.infer_expr_inner(*then_branch, &expected);
 133                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 134                 let else_ty = match else_branch {
 135                     Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
 136                     None => TyBuilder::unit(),
 137                 };
 138                 both_arms_diverge &= self.diverges;
 139
 140                 self.diverges = condition_diverges | both_arms_diverge;
 141
 142                 self.coerce_merge_branch(&then_ty, &else_ty)
 143             }
 144             Expr::Block { statements, tail, label, id: _ } => {
 145                 let old_resolver = mem::replace(
 146                     &mut self.resolver,
 147                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 148                 );
 149                 let ty = match label {
 150                     Some(_) => {
 151                         let break_ty = self.table.new_type_var();
 152                         self.breakables.push(BreakableContext {
 153                             may_break: false,
 154                             break_ty: break_ty.clone(),
 155                             label: label.map(|label| self.body[label].name.clone()),
 156                         });
 157                         let ty =
 158                             self.infer_block(statements, *tail, &Expectation::has_type(break_ty));
 159                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 160                         if ctxt.may_break {
 161                             ctxt.break_ty
 162                         } else {
 163                             ty
 164                         }
 165                     }
 166                     None => self.infer_block(statements, *tail, expected),
 167                 };
 168                 self.resolver = old_resolver;
 169                 ty
 170             }
 171             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 172             Expr::TryBlock { body } => {
 173                 let _inner = self.infer_expr(*body, expected);
 174                 // FIXME should be std::result::Result<{inner}, _>
 175                 self.err_ty()
 176             }
 177             Expr::Async { body } => {
 178                 // Use the first type parameter as the output type of future.
 179                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 180                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 181                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 182                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 183                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(&Interner, inner_ty))
 184                     .intern(&Interner)
 185             }
 186             Expr::Loop { body, label } => {
 187                 self.breakables.push(BreakableContext {
 188                     may_break: false,
 189                     break_ty: self.table.new_type_var(),
 190                     label: label.map(|label| self.body[label].name.clone()),
 191                 });
 192                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 193
 194                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 195                 if ctxt.may_break {
 196                     self.diverges = Diverges::Maybe;
 197                 }
 198
 199                 if ctxt.may_break {
 200                     ctxt.break_ty
 201                 } else {
 202                     TyKind::Never.intern(&Interner)
 203                 }
 204             }
 205             Expr::While { condition, body, label } => {
 206                 self.breakables.push(BreakableContext {
 207                     may_break: false,
 208                     break_ty: self.err_ty(),
 209                     label: label.map(|label| self.body[label].name.clone()),
 210                 });
 211                 // while let is desugared to a match loop, so this is always simple while
 212                 self.infer_expr(
 213                     *condition,
 214                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 215                 );
 216                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 217                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 218                 // the body may not run, so it diverging doesn't mean we diverge
 219                 self.diverges = Diverges::Maybe;
 220                 TyBuilder::unit()
 221             }
 222             Expr::For { iterable, body, pat, label } => {
 223                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 224
 225                 self.breakables.push(BreakableContext {
 226                     may_break: false,
 227                     break_ty: self.err_ty(),
 228                     label: label.map(|label| self.body[label].name.clone()),
 229                 });
 230                 let pat_ty =
 231                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 232
 233                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 234
 235                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 236                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 237                 // the body may not run, so it diverging doesn't mean we diverge
 238                 self.diverges = Diverges::Maybe;
 239                 TyBuilder::unit()
 240             }
 241             Expr::Lambda { body, args, ret_type, arg_types } => {
 242                 assert_eq!(args.len(), arg_types.len());
 243
 244                 let mut sig_tys = Vec::new();
 245
 246                 // collect explicitly written argument types
 247                 for arg_type in arg_types.iter() {
 248                     let arg_ty = if let Some(type_ref) = arg_type {
 249                         self.make_ty(type_ref)
 250                     } else {
 251                         self.table.new_type_var()
 252                     };
 253                     sig_tys.push(arg_ty);
 254                 }
 255
 256                 // add return type
 257                 let ret_ty = match ret_type {
 258                     Some(type_ref) => self.make_ty(type_ref),
 259                     None => self.table.new_type_var(),
 260                 };
 261                 sig_tys.push(ret_ty.clone());
 262                 let sig_ty = TyKind::Function(FnPointer {
 263                     num_binders: 0,
 264                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 265                     substitution: FnSubst(
 266                         Substitution::from_iter(&Interner, sig_tys.clone()).shifted_in(&Interner),
 267                     ),
 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::from1(&Interner, sig_ty))
 273                         .intern(&Interner);
 274
 275                 // Eagerly try to relate the closure type with the expected
 276                 // type, otherwise we often won't have enough information to
 277                 // infer the body.
 278                 self.coerce(&closure_ty, &expected.ty);
 279
 280                 // Now go through the argument patterns
 281                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 282                     let resolved = self.resolve_ty_as_possible(arg_ty);
 283                     self.infer_pat(*arg_pat, &resolved, BindingMode::default());
 284                 }
 285
 286                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 287                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 288
 289                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 290
 291                 self.diverges = prev_diverges;
 292                 self.return_ty = prev_ret_ty;
 293
 294                 closure_ty
 295             }
 296             Expr::Call { callee, args } => {
 297                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 298                 let canonicalized = self.canonicalizer().canonicalize_ty(callee_ty.clone());
 299                 let mut derefs = autoderef(
 300                     self.db,
 301                     self.resolver.krate(),
 302                     InEnvironment {
 303                         goal: canonicalized.value.clone(),
 304                         environment: self.trait_env.env.clone(),
 305                     },
 306                 );
 307                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
 308                     .find_map(|callee_deref_ty| {
 309                         self.callable_sig(
 310                             &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 311                             args.len(),
 312                         )
 313                     })
 314                     .unwrap_or((Vec::new(), self.err_ty()));
 315                 self.register_obligations_for_call(&callee_ty);
 316                 self.check_call_arguments(args, &param_tys);
 317                 self.normalize_associated_types_in(ret_ty)
 318             }
 319             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 320                 .infer_method_call(
 321                     tgt_expr,
 322                     *receiver,
 323                     &args,
 324                     &method_name,
 325                     generic_args.as_deref(),
 326                 ),
 327             Expr::Match { expr, arms } => {
 328                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 329
 330                 let mut result_ty = if arms.is_empty() {
 331                     TyKind::Never.intern(&Interner)
 332                 } else {
 333                     self.table.new_type_var()
 334                 };
 335
 336                 let matchee_diverges = self.diverges;
 337                 let mut all_arms_diverge = Diverges::Always;
 338
 339                 for arm in arms {
 340                     self.diverges = Diverges::Maybe;
 341                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 342                     if let Some(guard_expr) = arm.guard {
 343                         self.infer_expr(
 344                             guard_expr,
 345                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 346                         );
 347                     }
 348
 349                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 350                     all_arms_diverge &= self.diverges;
 351                     result_ty = self.coerce_merge_branch(&result_ty, &arm_ty);
 352                 }
 353
 354                 self.diverges = matchee_diverges | all_arms_diverge;
 355
 356                 result_ty
 357             }
 358             Expr::Path(p) => {
 359                 // FIXME this could be more efficient...
 360                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 361                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
 362             }
 363             Expr::Continue { .. } => TyKind::Never.intern(&Interner),
 364             Expr::Break { expr, label } => {
 365                 let val_ty = if let Some(expr) = expr {
 366                     self.infer_expr(*expr, &Expectation::none())
 367                 } else {
 368                     TyBuilder::unit()
 369                 };
 370
 371                 let last_ty =
 372                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 373                         ctxt.break_ty.clone()
 374                     } else {
 375                         self.err_ty()
 376                     };
 377
 378                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
 379
 380                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 381                     ctxt.break_ty = merged_type;
 382                     ctxt.may_break = true;
 383                 } else {
 384                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 385                         expr: tgt_expr,
 386                     });
 387                 }
 388                 TyKind::Never.intern(&Interner)
 389             }
 390             Expr::Return { expr } => {
 391                 if let Some(expr) = expr {
 392                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 393                 } else {
 394                     let unit = TyBuilder::unit();
 395                     self.coerce(&unit, &self.return_ty.clone());
 396                 }
 397                 TyKind::Never.intern(&Interner)
 398             }
 399             Expr::Yield { expr } => {
 400                 // FIXME: track yield type for coercion
 401                 if let Some(expr) = expr {
 402                     self.infer_expr(*expr, &Expectation::none());
 403                 }
 404                 TyKind::Never.intern(&Interner)
 405             }
 406             Expr::RecordLit { path, fields, spread } => {
 407                 let (ty, def_id) = self.resolve_variant(path.as_deref());
 408                 if let Some(variant) = def_id {
 409                     self.write_variant_resolution(tgt_expr.into(), variant);
 410                 }
 411
 412                 self.unify(&ty, &expected.ty);
 413
 414                 let substs = ty
 415                     .as_adt()
 416                     .map(|(_, s)| s.clone())
 417                     .unwrap_or_else(|| Substitution::empty(&Interner));
 418                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 419                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 420                 for field in fields.iter() {
 421                     let field_def =
 422                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 423                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 424                             None => {
 425                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 426                                     expr: field.expr,
 427                                 });
 428                                 None
 429                             }
 430                         });
 431                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 432                         field_types[it.local_id].clone().substitute(&Interner, &substs)
 433                     });
 434                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 435                 }
 436                 if let Some(expr) = spread {
 437                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 438                 }
 439                 ty
 440             }
 441             Expr::Field { expr, name } => {
 442                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 443                 let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
 444                 let ty = autoderef::autoderef(
 445                     self.db,
 446                     self.resolver.krate(),
 447                     InEnvironment {
 448                         goal: canonicalized.value.clone(),
 449                         environment: self.trait_env.env.clone(),
 450                     },
 451                 )
 452                 .find_map(|derefed_ty| {
 453                     let def_db = self.db.upcast();
 454                     let module = self.resolver.module();
 455                     let is_visible = |field_id: &FieldId| {
 456                         module
 457                             .map(|mod_id| {
 458                                 self.db.field_visibilities(field_id.parent)[field_id.local_id]
 459                                     .is_visible_from(def_db, mod_id)
 460                             })
 461                             .unwrap_or(true)
 462                     };
 463                     match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
 464                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
 465                             substs.interned().get(idx).map(|a| a.assert_ty_ref(&Interner)).cloned()
 466                         }),
 467                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 468                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 469                             let field = FieldId { parent: (*s).into(), local_id };
 470                             if is_visible(&field) {
 471                                 self.write_field_resolution(tgt_expr, field);
 472                                 Some(
 473                                     self.db.field_types((*s).into())[field.local_id]
 474                                         .clone()
 475                                         .substitute(&Interner, &parameters),
 476                                 )
 477                             } else {
 478                                 None
 479                             }
 480                         }
 481                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 482                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 483                             let field = FieldId { parent: (*u).into(), local_id };
 484                             if is_visible(&field) {
 485                                 self.write_field_resolution(tgt_expr, field);
 486                                 Some(
 487                                     self.db.field_types((*u).into())[field.local_id]
 488                                         .clone()
 489                                         .substitute(&Interner, &parameters),
 490                                 )
 491                             } else {
 492                                 None
 493                             }
 494                         }
 495                         _ => None,
 496                     }
 497                 })
 498                 .unwrap_or(self.err_ty());
 499                 let ty = self.insert_type_vars(ty);
 500                 self.normalize_associated_types_in(ty)
 501             }
 502             Expr::Await { expr } => {
 503                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 504                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 505             }
 506             Expr::Try { expr } => {
 507                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 508                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 509             }
 510             Expr::Cast { expr, type_ref } => {
 511                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 512                 let cast_ty = self.make_ty(type_ref);
 513                 // FIXME check the cast...
 514                 cast_ty
 515             }
 516             Expr::Ref { expr, rawness, mutability } => {
 517                 let mutability = lower_to_chalk_mutability(*mutability);
 518                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
 519                     &expected.ty.as_reference_or_ptr()
 520                 {
 521                     if *exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 522                         // FIXME: throw type error - expected mut reference but found shared ref,
 523                         // which cannot be coerced
 524                     }
 525                     if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 526                         // FIXME: throw type error - expected reference but found ptr,
 527                         // which cannot be coerced
 528                     }
 529                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 530                 } else {
 531                     Expectation::none()
 532                 };
 533                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 534                 match rawness {
 535                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 536                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 537                 }
 538                 .intern(&Interner)
 539             }
 540             Expr::Box { expr } => {
 541                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 542                 if let Some(box_) = self.resolve_boxed_box() {
 543                     TyBuilder::adt(self.db, box_)
 544                         .push(inner_ty)
 545                         .fill_with_defaults(self.db, || self.table.new_type_var())
 546                         .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.kind(&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.kind(&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) => TyBuilder::adt(self.db, adt).build(),
 637                         None => self.err_ty(),
 638                     },
 639                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 640                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 641                         None => self.err_ty(),
 642                     },
 643                     (RangeOp::Inclusive, None, Some(ty)) => {
 644                         match self.resolve_range_to_inclusive() {
 645                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 646                             None => self.err_ty(),
 647                         }
 648                     }
 649                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 650                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 651                         None => self.err_ty(),
 652                     },
 653                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 654                         match self.resolve_range_inclusive() {
 655                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 656                             None => self.err_ty(),
 657                         }
 658                     }
 659                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 660                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 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.kind(&Interner) {
 694                     TyKind::Tuple(_, substs) => substs
 695                         .iter(&Interner)
 696                         .map(|a| a.assert_ty_ref(&Interner).clone())
 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::from_iter(&Interner, tys)).intern(&Interner)
 708             }
 709             Expr::Array(array) => {
 710                 let elem_ty = match expected.ty.kind(&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, dummy_usize_const()).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, static_lifetime(), TyKind::Str.intern(&Interner))
 741                         .intern(&Interner)
 742                 }
 743                 Literal::ByteString(..) => {
 744                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
 745                     let array_type =
 746                         TyKind::Array(byte_type, dummy_usize_const()).intern(&Interner);
 747                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
 748                 }
 749                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
 750                 Literal::Int(_v, ty) => match ty {
 751                     Some(int_ty) => {
 752                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 753                             .intern(&Interner)
 754                     }
 755                     None => self.table.new_integer_var(),
 756                 },
 757                 Literal::Uint(_v, ty) => match ty {
 758                     Some(int_ty) => {
 759                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 760                             .intern(&Interner)
 761                     }
 762                     None => self.table.new_integer_var(),
 763                 },
 764                 Literal::Float(_v, ty) => match ty {
 765                     Some(float_ty) => {
 766                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 767                             .intern(&Interner)
 768                     }
 769                     None => self.table.new_float_var(),
 770                 },
 771             },
 772             Expr::MacroStmts { tail } => self.infer_expr(*tail, expected),
 773         };
 774         // use a new type variable if we got unknown here
 775         let ty = self.insert_type_vars_shallow(ty);
 776         let ty = self.resolve_ty_as_possible(ty);
 777         self.write_expr_ty(tgt_expr, ty.clone());
 778         ty
 779     }
 780
 781     fn infer_block(
 782         &mut self,
 783         statements: &[Statement],
 784         tail: Option<ExprId>,
 785         expected: &Expectation,
 786     ) -> Ty {
 787         for stmt in statements {
 788             match stmt {
 789                 Statement::Let { pat, type_ref, initializer } => {
 790                     let decl_ty =
 791                         type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(self.err_ty());
 792
 793                     // Always use the declared type when specified
 794                     let mut ty = decl_ty.clone();
 795
 796                     if let Some(expr) = initializer {
 797                         let actual_ty =
 798                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 799                         if decl_ty.is_unknown() {
 800                             ty = actual_ty;
 801                         }
 802                     }
 803
 804                     let ty = self.resolve_ty_as_possible(ty);
 805                     self.infer_pat(*pat, &ty, BindingMode::default());
 806                 }
 807                 Statement::Expr(expr) => {
 808                     self.infer_expr(*expr, &Expectation::none());
 809                 }
 810             }
 811         }
 812
 813         let ty = if let Some(expr) = tail {
 814             self.infer_expr_coerce(expr, expected)
 815         } else {
 816             // Citing rustc: if there is no explicit tail expression,
 817             // that is typically equivalent to a tail expression
 818             // of `()` -- except if the block diverges. In that
 819             // case, there is no value supplied from the tail
 820             // expression (assuming there are no other breaks,
 821             // this implies that the type of the block will be
 822             // `!`).
 823             if self.diverges.is_always() {
 824                 // we don't even make an attempt at coercion
 825                 self.table.new_maybe_never_var()
 826             } else {
 827                 self.coerce(&TyBuilder::unit(), &expected.coercion_target());
 828                 TyBuilder::unit()
 829             }
 830         };
 831         ty
 832     }
 833
 834     fn infer_method_call(
 835         &mut self,
 836         tgt_expr: ExprId,
 837         receiver: ExprId,
 838         args: &[ExprId],
 839         method_name: &Name,
 840         generic_args: Option<&GenericArgs>,
 841     ) -> Ty {
 842         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 843         let canonicalized_receiver = self.canonicalizer().canonicalize_ty(receiver_ty.clone());
 844
 845         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 846
 847         let resolved = self.resolver.krate().and_then(|krate| {
 848             method_resolution::lookup_method(
 849                 &canonicalized_receiver.value,
 850                 self.db,
 851                 self.trait_env.clone(),
 852                 krate,
 853                 &traits_in_scope,
 854                 self.resolver.module(),
 855                 method_name,
 856             )
 857         });
 858         let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
 859             Some((ty, func)) => {
 860                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 861                 self.write_method_resolution(tgt_expr, func);
 862                 (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
 863             }
 864             None => (receiver_ty, Binders::empty(&Interner, self.err_ty()), None),
 865         };
 866         let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
 867         let method_ty = method_ty.substitute(&Interner, &substs);
 868         let method_ty = self.insert_type_vars(method_ty);
 869         self.register_obligations_for_call(&method_ty);
 870         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 871             Some(sig) => {
 872                 if !sig.params().is_empty() {
 873                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 874                 } else {
 875                     (self.err_ty(), Vec::new(), sig.ret().clone())
 876                 }
 877             }
 878             None => (self.err_ty(), Vec::new(), self.err_ty()),
 879         };
 880         // Apply autoref so the below unification works correctly
 881         // FIXME: return correct autorefs from lookup_method
 882         let actual_receiver_ty = match expected_receiver_ty.as_reference() {
 883             Some((_, lifetime, mutability)) => {
 884                 TyKind::Ref(mutability, lifetime, derefed_receiver_ty).intern(&Interner)
 885             }
 886             _ => derefed_receiver_ty,
 887         };
 888         self.unify(&expected_receiver_ty, &actual_receiver_ty);
 889
 890         self.check_call_arguments(args, &param_tys);
 891         self.normalize_associated_types_in(ret_ty)
 892     }
 893
 894     fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
 895         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 896         // We do this in a pretty awful way: first we type-check any arguments
 897         // that are not closures, then we type-check the closures. This is so
 898         // that we have more information about the types of arguments when we
 899         // type-check the functions. This isn't really the right way to do this.
 900         for &check_closures in &[false, true] {
 901             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
 902             for (&arg, param_ty) in args.iter().zip(param_iter) {
 903                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
 904                 if is_closure != check_closures {
 905                     continue;
 906                 }
 907
 908                 let param_ty = self.normalize_associated_types_in(param_ty);
 909                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
 910             }
 911         }
 912     }
 913
 914     fn substs_for_method_call(
 915         &mut self,
 916         def_generics: Option<Generics>,
 917         generic_args: Option<&GenericArgs>,
 918         receiver_ty: &Ty,
 919     ) -> Substitution {
 920         let (parent_params, self_params, type_params, impl_trait_params) =
 921             def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
 922         assert_eq!(self_params, 0); // method shouldn't have another Self param
 923         let total_len = parent_params + type_params + impl_trait_params;
 924         let mut substs = Vec::with_capacity(total_len);
 925         // Parent arguments are unknown, except for the receiver type
 926         if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
 927             for (_id, param) in parent_generics {
 928                 if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
 929                     substs.push(receiver_ty.clone());
 930                 } else {
 931                     substs.push(self.err_ty());
 932                 }
 933             }
 934         }
 935         // handle provided type arguments
 936         if let Some(generic_args) = generic_args {
 937             // if args are provided, it should be all of them, but we can't rely on that
 938             for arg in generic_args
 939                 .args
 940                 .iter()
 941                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 942                 .take(type_params)
 943             {
 944                 match arg {
 945                     GenericArg::Type(type_ref) => {
 946                         let ty = self.make_ty(type_ref);
 947                         substs.push(ty);
 948                     }
 949                     GenericArg::Lifetime(_) => {}
 950                 }
 951             }
 952         };
 953         let supplied_params = substs.len();
 954         for _ in supplied_params..total_len {
 955             substs.push(self.err_ty());
 956         }
 957         assert_eq!(substs.len(), total_len);
 958         Substitution::from_iter(&Interner, substs)
 959     }
 960
 961     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
 962         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(&Interner) {
 963             let def: CallableDefId = from_chalk(self.db, *fn_def);
 964             let generic_predicates = self.db.generic_predicates(def.into());
 965             for predicate in generic_predicates.iter() {
 966                 let (predicate, binders) = predicate
 967                     .clone()
 968                     .substitute(&Interner, parameters)
 969                     .into_value_and_skipped_binders();
 970                 always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
 971                 self.push_obligation(predicate.cast(&Interner));
 972             }
 973             // add obligation for trait implementation, if this is a trait method
 974             match def {
 975                 CallableDefId::FunctionId(f) => {
 976                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
 977                     {
 978                         // construct a TraitRef
 979                         let substs = crate::subst_prefix(
 980                             &*parameters,
 981                             generics(self.db.upcast(), trait_.into()).len(),
 982                         );
 983                         self.push_obligation(
 984                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
 985                                 .cast(&Interner),
 986                         );
 987                     }
 988                 }
 989                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
 990             }
 991         }
 992     }
 993 }