crates/hir_ty/src/infer/expr.rs

   1 //! Type inference for expressions.
   2
   3 use std::{
   4     iter::{repeat, repeat_with},
   5     mem,
   6     sync::Arc,
   7 };
   8
   9 use chalk_ir::{cast::Cast, fold::Shift, Mutability, TyVariableKind};
  10 use hir_def::{
  11     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
  12     path::{GenericArg, GenericArgs},
  13     resolver::resolver_for_expr,
  14     AssocContainerId, FieldId, Lookup,
  15 };
  16 use hir_expand::name::{name, Name};
  17 use stdx::always;
  18 use syntax::ast::RangeOp;
  19
  20 use crate::{
  21     autoderef::{self, Autoderef},
  22     consteval,
  23     infer::coerce::CoerceMany,
  24     lower::lower_to_chalk_mutability,
  25     mapping::from_chalk,
  26     method_resolution, op,
  27     primitive::{self, UintTy},
  28     static_lifetime, to_chalk_trait_id,
  29     traits::FnTrait,
  30     utils::{generics, Generics},
  31     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
  32     ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  33 };
  34
  35 use super::{
  36     find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
  37     InferenceDiagnostic, TypeMismatch,
  38 };
  39
  40 impl<'a> InferenceContext<'a> {
  41     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  42         let ty = self.infer_expr_inner(tgt_expr, expected);
  43         if self.resolve_ty_shallow(&ty).is_never() {
  44             // Any expression that produces a value of type `!` must have diverged
  45             self.diverges = Diverges::Always;
  46         }
  47         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  48             let could_unify = self.unify(&ty, &expected_ty);
  49             if !could_unify {
  50                 self.result.type_mismatches.insert(
  51                     tgt_expr.into(),
  52                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  53                 );
  54             }
  55         }
  56         ty
  57     }
  58
  59     /// Infer type of expression with possibly implicit coerce to the expected type.
  60     /// Return the type after possible coercion.
  61     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  62         let ty = self.infer_expr_inner(expr, expected);
  63         let ty = if let Some(target) = expected.only_has_type(&mut self.table) {
  64             match self.coerce(Some(expr), &ty, &target) {
  65                 Ok(res) => res.value,
  66                 Err(_) => {
  67                     self.result
  68                         .type_mismatches
  69                         .insert(expr.into(), TypeMismatch { expected: target, actual: ty.clone() });
  70                     // Return actual type when type mismatch.
  71                     // This is needed for diagnostic when return type mismatch.
  72                     ty
  73                 }
  74             }
  75         } else {
  76             ty
  77         };
  78
  79         ty
  80     }
  81
  82     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
  83         let krate = self.resolver.krate()?;
  84         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
  85         let output_assoc_type =
  86             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
  87
  88         let mut arg_tys = vec![];
  89         let arg_ty = TyBuilder::tuple(num_args)
  90             .fill(repeat_with(|| {
  91                 let arg = self.table.new_type_var();
  92                 arg_tys.push(arg.clone());
  93                 arg
  94             }))
  95             .build();
  96
  97         let projection = {
  98             let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
  99             if b.remaining() != 2 {
 100                 return None;
 101             }
 102             b.push(ty.clone()).push(arg_ty).build()
 103         };
 104
 105         let trait_env = self.trait_env.env.clone();
 106         let obligation = InEnvironment {
 107             goal: projection.trait_ref(self.db).cast(&Interner),
 108             environment: trait_env,
 109         };
 110         let canonical = self.canonicalize(obligation.clone());
 111         if self.db.trait_solve(krate, canonical.value.cast(&Interner)).is_some() {
 112             self.push_obligation(obligation.goal);
 113             let return_ty = self.table.normalize_projection_ty(projection);
 114             Some((arg_tys, return_ty))
 115         } else {
 116             None
 117         }
 118     }
 119
 120     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 121         match ty.callable_sig(self.db) {
 122             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 123             None => self.callable_sig_from_fn_trait(ty, num_args),
 124         }
 125     }
 126
 127     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 128         self.db.unwind_if_cancelled();
 129
 130         let body = Arc::clone(&self.body); // avoid borrow checker problem
 131         let ty = match &body[tgt_expr] {
 132             Expr::Missing => self.err_ty(),
 133             &Expr::If { condition, then_branch, else_branch } => {
 134                 // if let is desugared to match, so this is always simple if
 135                 self.infer_expr(
 136                     condition,
 137                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 138                 );
 139
 140                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 141                 let mut both_arms_diverge = Diverges::Always;
 142
 143                 let result_ty = self.table.new_type_var();
 144                 let then_ty = self.infer_expr_inner(then_branch, expected);
 145                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 146                 let mut coerce = CoerceMany::new(result_ty);
 147                 coerce.coerce(self, Some(then_branch), &then_ty);
 148                 let else_ty = match else_branch {
 149                     Some(else_branch) => self.infer_expr_inner(else_branch, expected),
 150                     None => TyBuilder::unit(),
 151                 };
 152                 both_arms_diverge &= self.diverges;
 153                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 154                 coerce.coerce(self, else_branch, &else_ty);
 155
 156                 self.diverges = condition_diverges | both_arms_diverge;
 157
 158                 coerce.complete()
 159             }
 160             Expr::Block { statements, tail, label, id: _ } => {
 161                 let old_resolver = mem::replace(
 162                     &mut self.resolver,
 163                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 164                 );
 165                 let ty = match label {
 166                     Some(_) => {
 167                         let break_ty = self.table.new_type_var();
 168                         self.breakables.push(BreakableContext {
 169                             may_break: false,
 170                             coerce: CoerceMany::new(break_ty.clone()),
 171                             label: label.map(|label| self.body[label].name.clone()),
 172                         });
 173                         let ty = self.infer_block(
 174                             tgt_expr,
 175                             statements,
 176                             *tail,
 177                             &Expectation::has_type(break_ty),
 178                         );
 179                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 180                         if ctxt.may_break {
 181                             ctxt.coerce.complete()
 182                         } else {
 183                             ty
 184                         }
 185                     }
 186                     None => self.infer_block(tgt_expr, statements, *tail, expected),
 187                 };
 188                 self.resolver = old_resolver;
 189                 ty
 190             }
 191             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 192             Expr::TryBlock { body } => {
 193                 let _inner = self.infer_expr(*body, expected);
 194                 // FIXME should be std::result::Result<{inner}, _>
 195                 self.err_ty()
 196             }
 197             Expr::Async { body } => {
 198                 // Use the first type parameter as the output type of future.
 199                 // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 200                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 201                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 202                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 203                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(&Interner, inner_ty))
 204                     .intern(&Interner)
 205             }
 206             Expr::Loop { body, label } => {
 207                 self.breakables.push(BreakableContext {
 208                     may_break: false,
 209                     coerce: CoerceMany::new(self.table.new_type_var()),
 210                     label: label.map(|label| self.body[label].name.clone()),
 211                 });
 212                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 213
 214                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 215
 216                 if ctxt.may_break {
 217                     self.diverges = Diverges::Maybe;
 218                     ctxt.coerce.complete()
 219                 } else {
 220                     TyKind::Never.intern(&Interner)
 221                 }
 222             }
 223             Expr::While { condition, body, label } => {
 224                 self.breakables.push(BreakableContext {
 225                     may_break: false,
 226                     coerce: CoerceMany::new(self.err_ty()),
 227                     label: label.map(|label| self.body[label].name.clone()),
 228                 });
 229                 // while let is desugared to a match loop, so this is always simple while
 230                 self.infer_expr(
 231                     *condition,
 232                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 233                 );
 234                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 235                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 236                 // the body may not run, so it diverging doesn't mean we diverge
 237                 self.diverges = Diverges::Maybe;
 238                 TyBuilder::unit()
 239             }
 240             Expr::For { iterable, body, pat, label } => {
 241                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 242
 243                 self.breakables.push(BreakableContext {
 244                     may_break: false,
 245                     coerce: CoerceMany::new(self.err_ty()),
 246                     label: label.map(|label| self.body[label].name.clone()),
 247                 });
 248                 let pat_ty =
 249                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 250
 251                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 252
 253                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 254                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 255                 // the body may not run, so it diverging doesn't mean we diverge
 256                 self.diverges = Diverges::Maybe;
 257                 TyBuilder::unit()
 258             }
 259             Expr::Lambda { body, args, ret_type, arg_types } => {
 260                 assert_eq!(args.len(), arg_types.len());
 261
 262                 let mut sig_tys = Vec::new();
 263
 264                 // collect explicitly written argument types
 265                 for arg_type in arg_types.iter() {
 266                     let arg_ty = if let Some(type_ref) = arg_type {
 267                         self.make_ty(type_ref)
 268                     } else {
 269                         self.table.new_type_var()
 270                     };
 271                     sig_tys.push(arg_ty);
 272                 }
 273
 274                 // add return type
 275                 let ret_ty = match ret_type {
 276                     Some(type_ref) => self.make_ty(type_ref),
 277                     None => self.table.new_type_var(),
 278                 };
 279                 sig_tys.push(ret_ty.clone());
 280                 let sig_ty = TyKind::Function(FnPointer {
 281                     num_binders: 0,
 282                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 283                     substitution: FnSubst(
 284                         Substitution::from_iter(&Interner, sig_tys.clone()).shifted_in(&Interner),
 285                     ),
 286                 })
 287                 .intern(&Interner);
 288                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 289                 let closure_ty =
 290                     TyKind::Closure(closure_id, Substitution::from1(&Interner, sig_ty.clone()))
 291                         .intern(&Interner);
 292
 293                 // Eagerly try to relate the closure type with the expected
 294                 // type, otherwise we often won't have enough information to
 295                 // infer the body.
 296                 self.deduce_closure_type_from_expectations(
 297                     tgt_expr,
 298                     &closure_ty,
 299                     &sig_ty,
 300                     expected,
 301                 );
 302
 303                 // Now go through the argument patterns
 304                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 305                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 306                 }
 307
 308                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 309                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 310
 311                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 312
 313                 self.diverges = prev_diverges;
 314                 self.return_ty = prev_ret_ty;
 315
 316                 closure_ty
 317             }
 318             Expr::Call { callee, args } => {
 319                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 320                 let canonicalized = self.canonicalize(callee_ty.clone());
 321                 let mut derefs = Autoderef::new(
 322                     self.db,
 323                     self.resolver.krate(),
 324                     InEnvironment {
 325                         goal: canonicalized.value.clone(),
 326                         environment: self.table.trait_env.env.clone(),
 327                     },
 328                 );
 329                 let res = derefs.by_ref().find_map(|(callee_deref_ty, _)| {
 330                     self.callable_sig(
 331                         &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 332                         args.len(),
 333                     )
 334                 });
 335                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = match res {
 336                     Some(res) => {
 337                         self.write_expr_adj(*callee, self.auto_deref_adjust_steps(&derefs));
 338                         res
 339                     }
 340                     None => (Vec::new(), self.err_ty()),
 341                 };
 342                 self.register_obligations_for_call(&callee_ty);
 343
 344                 let expected_inputs = self.expected_inputs_for_expected_output(
 345                     expected,
 346                     ret_ty.clone(),
 347                     param_tys.clone(),
 348                 );
 349
 350                 self.check_call_arguments(args, &expected_inputs, &param_tys);
 351                 self.normalize_associated_types_in(ret_ty)
 352             }
 353             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 354                 .infer_method_call(
 355                     tgt_expr,
 356                     *receiver,
 357                     args,
 358                     method_name,
 359                     generic_args.as_deref(),
 360                     expected,
 361                 ),
 362             Expr::Match { expr, arms } => {
 363                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 364
 365                 let expected = expected.adjust_for_branches(&mut self.table);
 366
 367                 let result_ty = if arms.is_empty() {
 368                     TyKind::Never.intern(&Interner)
 369                 } else {
 370                     match &expected {
 371                         Expectation::HasType(ty) => ty.clone(),
 372                         _ => self.table.new_type_var(),
 373                     }
 374                 };
 375                 let mut coerce = CoerceMany::new(result_ty);
 376
 377                 let matchee_diverges = self.diverges;
 378                 let mut all_arms_diverge = Diverges::Always;
 379
 380                 for arm in arms {
 381                     self.diverges = Diverges::Maybe;
 382                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 383                     if let Some(guard_expr) = arm.guard {
 384                         self.infer_expr(
 385                             guard_expr,
 386                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 387                         );
 388                     }
 389
 390                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 391                     all_arms_diverge &= self.diverges;
 392                     coerce.coerce(self, Some(arm.expr), &arm_ty);
 393                 }
 394
 395                 self.diverges = matchee_diverges | all_arms_diverge;
 396
 397                 coerce.complete()
 398             }
 399             Expr::Path(p) => {
 400                 // FIXME this could be more efficient...
 401                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 402                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
 403             }
 404             Expr::Continue { .. } => TyKind::Never.intern(&Interner),
 405             Expr::Break { expr, label } => {
 406                 let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
 407                     Some(ctxt) => {
 408                         // avoiding the borrowck
 409                         mem::replace(
 410                             &mut ctxt.coerce,
 411                             CoerceMany::new(self.result.standard_types.unknown.clone()),
 412                         )
 413                     }
 414                     None => CoerceMany::new(self.result.standard_types.unknown.clone()),
 415                 };
 416
 417                 let val_ty = if let Some(expr) = *expr {
 418                     self.infer_expr(expr, &Expectation::none())
 419                 } else {
 420                     TyBuilder::unit()
 421                 };
 422
 423                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 424                 coerce.coerce(self, *expr, &val_ty);
 425
 426                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 427                     ctxt.coerce = coerce;
 428                     ctxt.may_break = true;
 429                 } else {
 430                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 431                         expr: tgt_expr,
 432                     });
 433                 };
 434
 435                 TyKind::Never.intern(&Interner)
 436             }
 437             Expr::Return { expr } => {
 438                 if let Some(expr) = expr {
 439                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 440                 } else {
 441                     let unit = TyBuilder::unit();
 442                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
 443                 }
 444                 TyKind::Never.intern(&Interner)
 445             }
 446             Expr::Yield { expr } => {
 447                 // FIXME: track yield type for coercion
 448                 if let Some(expr) = expr {
 449                     self.infer_expr(*expr, &Expectation::none());
 450                 }
 451                 TyKind::Never.intern(&Interner)
 452             }
 453             Expr::RecordLit { path, fields, spread } => {
 454                 let (ty, def_id) = self.resolve_variant(path.as_deref());
 455                 if let Some(variant) = def_id {
 456                     self.write_variant_resolution(tgt_expr.into(), variant);
 457                 }
 458
 459                 if let Some(t) = expected.only_has_type(&mut self.table) {
 460                     self.unify(&ty, &t);
 461                 }
 462
 463                 let substs = ty
 464                     .as_adt()
 465                     .map(|(_, s)| s.clone())
 466                     .unwrap_or_else(|| Substitution::empty(&Interner));
 467                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 468                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 469                 for field in fields.iter() {
 470                     let field_def =
 471                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 472                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 473                             None => {
 474                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 475                                     expr: field.expr,
 476                                 });
 477                                 None
 478                             }
 479                         });
 480                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 481                         field_types[it.local_id].clone().substitute(&Interner, &substs)
 482                     });
 483                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 484                 }
 485                 if let Some(expr) = spread {
 486                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 487                 }
 488                 ty
 489             }
 490             Expr::Field { expr, name } => {
 491                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 492                 let canonicalized = self.canonicalize(receiver_ty);
 493
 494                 let mut autoderef = Autoderef::new(
 495                     self.db,
 496                     self.resolver.krate(),
 497                     InEnvironment {
 498                         goal: canonicalized.value.clone(),
 499                         environment: self.trait_env.env.clone(),
 500                     },
 501                 );
 502                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
 503                     let def_db = self.db.upcast();
 504                     let module = self.resolver.module();
 505                     let is_visible = |field_id: &FieldId| {
 506                         module
 507                             .map(|mod_id| {
 508                                 self.db.field_visibilities(field_id.parent)[field_id.local_id]
 509                                     .is_visible_from(def_db, mod_id)
 510                             })
 511                             .unwrap_or(true)
 512                     };
 513                     match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
 514                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
 515                             substs
 516                                 .as_slice(&Interner)
 517                                 .get(idx)
 518                                 .map(|a| a.assert_ty_ref(&Interner))
 519                                 .cloned()
 520                         }),
 521                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 522                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 523                             let field = FieldId { parent: (*s).into(), local_id };
 524                             if is_visible(&field) {
 525                                 self.write_field_resolution(tgt_expr, field);
 526                                 Some(
 527                                     self.db.field_types((*s).into())[field.local_id]
 528                                         .clone()
 529                                         .substitute(&Interner, &parameters),
 530                                 )
 531                             } else {
 532                                 None
 533                             }
 534                         }
 535                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 536                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 537                             let field = FieldId { parent: (*u).into(), local_id };
 538                             if is_visible(&field) {
 539                                 self.write_field_resolution(tgt_expr, field);
 540                                 Some(
 541                                     self.db.field_types((*u).into())[field.local_id]
 542                                         .clone()
 543                                         .substitute(&Interner, &parameters),
 544                                 )
 545                             } else {
 546                                 None
 547                             }
 548                         }
 549                         _ => None,
 550                     }
 551                 });
 552                 let ty = match ty {
 553                     Some(ty) => {
 554                         self.write_expr_adj(*expr, self.auto_deref_adjust_steps(&autoderef));
 555                         ty
 556                     }
 557                     None => self.err_ty(),
 558                 };
 559                 let ty = self.insert_type_vars(ty);
 560                 self.normalize_associated_types_in(ty)
 561             }
 562             Expr::Await { expr } => {
 563                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 564                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 565             }
 566             Expr::Try { expr } => {
 567                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 568                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 569             }
 570             Expr::Cast { expr, type_ref } => {
 571                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 572                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 573                 let cast_ty = self.make_ty(type_ref);
 574                 // FIXME check the cast...
 575                 cast_ty
 576             }
 577             Expr::Ref { expr, rawness, mutability } => {
 578                 let mutability = lower_to_chalk_mutability(*mutability);
 579                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 580                     .only_has_type(&mut self.table)
 581                     .as_ref()
 582                     .and_then(|t| t.as_reference_or_ptr())
 583                 {
 584                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 585                         // FIXME: record type error - expected mut reference but found shared ref,
 586                         // which cannot be coerced
 587                     }
 588                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 589                         // FIXME: record type error - expected reference but found ptr,
 590                         // which cannot be coerced
 591                     }
 592                     Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
 593                 } else {
 594                     Expectation::none()
 595                 };
 596                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 597                 match rawness {
 598                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 599                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 600                 }
 601                 .intern(&Interner)
 602             }
 603             Expr::Box { expr } => {
 604                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 605                 if let Some(box_) = self.resolve_boxed_box() {
 606                     TyBuilder::adt(self.db, box_)
 607                         .push(inner_ty)
 608                         .fill_with_defaults(self.db, || self.table.new_type_var())
 609                         .build()
 610                 } else {
 611                     self.err_ty()
 612                 }
 613             }
 614             Expr::UnaryOp { expr, op } => {
 615                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 616                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 617                 match op {
 618                     UnaryOp::Deref => match self.resolver.krate() {
 619                         Some(krate) => {
 620                             let canonicalized = self.canonicalize(inner_ty);
 621                             match autoderef::deref(
 622                                 self.db,
 623                                 krate,
 624                                 InEnvironment {
 625                                     goal: &canonicalized.value,
 626                                     environment: self.trait_env.env.clone(),
 627                                 },
 628                             ) {
 629                                 Some(derefed_ty) => {
 630                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 631                                 }
 632                                 None => self.err_ty(),
 633                             }
 634                         }
 635                         None => self.err_ty(),
 636                     },
 637                     UnaryOp::Neg => {
 638                         match inner_ty.kind(&Interner) {
 639                             // Fast path for builtins
 640                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
 641                             | TyKind::InferenceVar(
 642                                 _,
 643                                 TyVariableKind::Integer | TyVariableKind::Float,
 644                             ) => inner_ty,
 645                             // Otherwise we resolve via the std::ops::Neg trait
 646                             _ => self
 647                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 648                         }
 649                     }
 650                     UnaryOp::Not => {
 651                         match inner_ty.kind(&Interner) {
 652                             // Fast path for builtins
 653                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
 654                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 655                             // Otherwise we resolve via the std::ops::Not trait
 656                             _ => self
 657                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 658                         }
 659                     }
 660                 }
 661             }
 662             Expr::BinaryOp { lhs, rhs, op } => match op {
 663                 Some(op) => {
 664                     let lhs_expectation = match op {
 665                         BinaryOp::LogicOp(..) => {
 666                             Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
 667                         }
 668                         _ => Expectation::none(),
 669                     };
 670                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 671                     let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
 672                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 673                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 674                     let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
 675
 676                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 677
 678                     if ret.is_unknown() {
 679                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 680
 681                         self.resolve_associated_type_with_params(
 682                             lhs_ty,
 683                             self.resolve_binary_op_output(op),
 684                             &[rhs_ty],
 685                         )
 686                     } else {
 687                         ret
 688                     }
 689                 }
 690                 _ => self.err_ty(),
 691             },
 692             Expr::Range { lhs, rhs, range_type } => {
 693                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 694                 let rhs_expect = lhs_ty
 695                     .as_ref()
 696                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 697                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 698                 match (range_type, lhs_ty, rhs_ty) {
 699                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 700                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 701                         None => self.err_ty(),
 702                     },
 703                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 704                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 705                         None => self.err_ty(),
 706                     },
 707                     (RangeOp::Inclusive, None, Some(ty)) => {
 708                         match self.resolve_range_to_inclusive() {
 709                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 710                             None => self.err_ty(),
 711                         }
 712                     }
 713                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 714                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 715                         None => self.err_ty(),
 716                     },
 717                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 718                         match self.resolve_range_inclusive() {
 719                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 720                             None => self.err_ty(),
 721                         }
 722                     }
 723                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 724                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 725                         None => self.err_ty(),
 726                     },
 727                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 728                 }
 729             }
 730             Expr::Index { base, index } => {
 731                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 732                 let index_ty = self.infer_expr(*index, &Expectation::none());
 733
 734                 if let (Some(index_trait), Some(krate)) =
 735                     (self.resolve_ops_index(), self.resolver.krate())
 736                 {
 737                     let canonicalized = self.canonicalize(base_ty);
 738                     let self_ty = method_resolution::resolve_indexing_op(
 739                         self.db,
 740                         &canonicalized.value,
 741                         self.trait_env.clone(),
 742                         krate,
 743                         index_trait,
 744                     );
 745                     let self_ty =
 746                         self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
 747                     self.resolve_associated_type_with_params(
 748                         self_ty,
 749                         self.resolve_ops_index_output(),
 750                         &[index_ty],
 751                     )
 752                 } else {
 753                     self.err_ty()
 754                 }
 755             }
 756             Expr::Tuple { exprs } => {
 757                 let mut tys = match expected
 758                     .only_has_type(&mut self.table)
 759                     .as_ref()
 760                     .map(|t| t.kind(&Interner))
 761                 {
 762                     Some(TyKind::Tuple(_, substs)) => substs
 763                         .iter(&Interner)
 764                         .map(|a| a.assert_ty_ref(&Interner).clone())
 765                         .chain(repeat_with(|| self.table.new_type_var()))
 766                         .take(exprs.len())
 767                         .collect::<Vec<_>>(),
 768                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 769                 };
 770
 771                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 772                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 773                 }
 774
 775                 TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
 776             }
 777             Expr::Array(array) => {
 778                 let elem_ty =
 779                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(&Interner)) {
 780                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
 781                         _ => self.table.new_type_var(),
 782                     };
 783                 let mut coerce = CoerceMany::new(elem_ty.clone());
 784
 785                 let expected = Expectation::has_type(elem_ty.clone());
 786                 let len = match array {
 787                     Array::ElementList(items) => {
 788                         for &expr in items.iter() {
 789                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
 790                             coerce.coerce(self, Some(expr), &cur_elem_ty);
 791                         }
 792                         Some(items.len() as u64)
 793                     }
 794                     &Array::Repeat { initializer, repeat } => {
 795                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
 796                         self.infer_expr(
 797                             repeat,
 798                             &Expectation::has_type(
 799                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
 800                             ),
 801                         );
 802
 803                         let repeat_expr = &self.body.exprs[repeat];
 804                         consteval::eval_usize(repeat_expr)
 805                     }
 806                 };
 807
 808                 TyKind::Array(coerce.complete(), consteval::usize_const(len)).intern(&Interner)
 809             }
 810             Expr::Literal(lit) => match lit {
 811                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
 812                 Literal::String(..) => {
 813                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(&Interner))
 814                         .intern(&Interner)
 815                 }
 816                 Literal::ByteString(bs) => {
 817                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
 818
 819                     let len = consteval::usize_const(Some(bs.len() as u64));
 820
 821                     let array_type = TyKind::Array(byte_type, len).intern(&Interner);
 822                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
 823                 }
 824                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
 825                 Literal::Int(_v, ty) => match ty {
 826                     Some(int_ty) => {
 827                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 828                             .intern(&Interner)
 829                     }
 830                     None => self.table.new_integer_var(),
 831                 },
 832                 Literal::Uint(_v, ty) => match ty {
 833                     Some(int_ty) => {
 834                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 835                             .intern(&Interner)
 836                     }
 837                     None => self.table.new_integer_var(),
 838                 },
 839                 Literal::Float(_v, ty) => match ty {
 840                     Some(float_ty) => {
 841                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 842                             .intern(&Interner)
 843                     }
 844                     None => self.table.new_float_var(),
 845                 },
 846             },
 847             Expr::MacroStmts { tail } => self.infer_expr_inner(*tail, expected),
 848         };
 849         // use a new type variable if we got unknown here
 850         let ty = self.insert_type_vars_shallow(ty);
 851         self.write_expr_ty(tgt_expr, ty.clone());
 852         ty
 853     }
 854
 855     fn infer_block(
 856         &mut self,
 857         expr: ExprId,
 858         statements: &[Statement],
 859         tail: Option<ExprId>,
 860         expected: &Expectation,
 861     ) -> Ty {
 862         for stmt in statements {
 863             match stmt {
 864                 Statement::Let { pat, type_ref, initializer } => {
 865                     let decl_ty = type_ref
 866                         .as_ref()
 867                         .map(|tr| self.make_ty(tr))
 868                         .unwrap_or_else(|| self.err_ty());
 869
 870                     // Always use the declared type when specified
 871                     let mut ty = decl_ty.clone();
 872
 873                     if let Some(expr) = initializer {
 874                         let actual_ty =
 875                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 876                         if decl_ty.is_unknown() {
 877                             ty = actual_ty;
 878                         }
 879                     }
 880
 881                     self.infer_pat(*pat, &ty, BindingMode::default());
 882                 }
 883                 Statement::Expr { expr, .. } => {
 884                     self.infer_expr(*expr, &Expectation::none());
 885                 }
 886             }
 887         }
 888
 889         let ty = if let Some(expr) = tail {
 890             self.infer_expr_coerce(expr, expected)
 891         } else {
 892             // Citing rustc: if there is no explicit tail expression,
 893             // that is typically equivalent to a tail expression
 894             // of `()` -- except if the block diverges. In that
 895             // case, there is no value supplied from the tail
 896             // expression (assuming there are no other breaks,
 897             // this implies that the type of the block will be
 898             // `!`).
 899             if self.diverges.is_always() {
 900                 // we don't even make an attempt at coercion
 901                 self.table.new_maybe_never_var()
 902             } else {
 903                 if let Some(t) = expected.only_has_type(&mut self.table) {
 904                     let _ = self.coerce(Some(expr), &TyBuilder::unit(), &t);
 905                 }
 906                 TyBuilder::unit()
 907             }
 908         };
 909         ty
 910     }
 911
 912     fn infer_method_call(
 913         &mut self,
 914         tgt_expr: ExprId,
 915         receiver: ExprId,
 916         args: &[ExprId],
 917         method_name: &Name,
 918         generic_args: Option<&GenericArgs>,
 919         expected: &Expectation,
 920     ) -> Ty {
 921         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 922         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
 923
 924         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 925
 926         let resolved = self.resolver.krate().and_then(|krate| {
 927             method_resolution::lookup_method(
 928                 &canonicalized_receiver.value,
 929                 self.db,
 930                 self.trait_env.clone(),
 931                 krate,
 932                 &traits_in_scope,
 933                 self.resolver.module(),
 934                 method_name,
 935             )
 936         });
 937         let (receiver_ty, method_ty, substs) = match resolved {
 938             Some((ty, func)) => {
 939                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 940                 let generics = generics(self.db.upcast(), func.into());
 941                 let substs = self.substs_for_method_call(generics, generic_args, &ty);
 942                 self.write_method_resolution(tgt_expr, func, substs.clone());
 943                 (ty, self.db.value_ty(func.into()), substs)
 944             }
 945             None => (
 946                 receiver_ty,
 947                 Binders::empty(&Interner, self.err_ty()),
 948                 Substitution::empty(&Interner),
 949             ),
 950         };
 951         let method_ty = method_ty.substitute(&Interner, &substs);
 952         self.register_obligations_for_call(&method_ty);
 953         let (formal_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 954             Some(sig) => {
 955                 if !sig.params().is_empty() {
 956                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 957                 } else {
 958                     (self.err_ty(), Vec::new(), sig.ret().clone())
 959                 }
 960             }
 961             None => (self.err_ty(), Vec::new(), self.err_ty()),
 962         };
 963         self.unify(&formal_receiver_ty, &receiver_ty);
 964
 965         let expected_inputs =
 966             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
 967
 968         self.check_call_arguments(args, &expected_inputs, &param_tys);
 969         self.normalize_associated_types_in(ret_ty)
 970     }
 971
 972     fn expected_inputs_for_expected_output(
 973         &mut self,
 974         expected_output: &Expectation,
 975         output: Ty,
 976         inputs: Vec<Ty>,
 977     ) -> Vec<Ty> {
 978         // rustc does a snapshot here and rolls back the unification, but since
 979         // we actually want to keep unbound variables in the result it then
 980         // needs to do 'fudging' to recreate them. So I'm not sure rustc's
 981         // approach is cleaner than ours, which is to create independent copies
 982         // of the variables before unifying. It might be more performant though,
 983         // so we might want to benchmark when we can actually do
 984         // snapshot/rollback.
 985         if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
 986             let (expected_ret_ty, expected_params) = self.table.reinstantiate((output, inputs));
 987             if self.table.try_unify(&expected_ty, &expected_ret_ty).is_ok() {
 988                 expected_params
 989             } else {
 990                 Vec::new()
 991             }
 992         } else {
 993             Vec::new()
 994         }
 995     }
 996
 997     fn check_call_arguments(&mut self, args: &[ExprId], expected_inputs: &[Ty], param_tys: &[Ty]) {
 998         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 999         // We do this in a pretty awful way: first we type-check any arguments
1000         // that are not closures, then we type-check the closures. This is so
1001         // that we have more information about the types of arguments when we
1002         // type-check the functions. This isn't really the right way to do this.
1003         for &check_closures in &[false, true] {
1004             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
1005             let expected_iter = expected_inputs
1006                 .iter()
1007                 .cloned()
1008                 .chain(param_iter.clone().skip(expected_inputs.len()));
1009             for ((&arg, param_ty), expected_ty) in args.iter().zip(param_iter).zip(expected_iter) {
1010                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
1011                 if is_closure != check_closures {
1012                     continue;
1013                 }
1014
1015                 // the difference between param_ty and expected here is that
1016                 // expected is the parameter when the expected *return* type is
1017                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
1018                 // the expected type is already `&[i32]`, whereas param_ty is
1019                 // still an unbound type variable. We don't always want to force
1020                 // the parameter to coerce to the expected type (for example in
1021                 // `coerce_unsize_expected_type_4`).
1022                 let param_ty = self.normalize_associated_types_in(param_ty);
1023                 let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
1024                 // infer with the expected type we have...
1025                 let ty = self.infer_expr_inner(arg, &expected);
1026
1027                 // then coerce to either the expected type or just the formal parameter type
1028                 let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
1029                     // if we are coercing to the expectation, unify with the
1030                     // formal parameter type to connect everything
1031                     self.unify(&ty, &param_ty);
1032                     ty
1033                 } else {
1034                     param_ty
1035                 };
1036                 if !coercion_target.is_unknown() {
1037                     if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
1038                         self.result.type_mismatches.insert(
1039                             arg.into(),
1040                             TypeMismatch { expected: coercion_target, actual: ty.clone() },
1041                         );
1042                     }
1043                 }
1044             }
1045         }
1046     }
1047
1048     fn substs_for_method_call(
1049         &mut self,
1050         def_generics: Generics,
1051         generic_args: Option<&GenericArgs>,
1052         receiver_ty: &Ty,
1053     ) -> Substitution {
1054         let (parent_params, self_params, type_params, impl_trait_params) =
1055             def_generics.provenance_split();
1056         assert_eq!(self_params, 0); // method shouldn't have another Self param
1057         let total_len = parent_params + type_params + impl_trait_params;
1058         let mut substs = Vec::with_capacity(total_len);
1059         // Parent arguments are unknown, except for the receiver type
1060         for (_id, param) in def_generics.iter_parent() {
1061             if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
1062                 substs.push(receiver_ty.clone());
1063             } else {
1064                 substs.push(self.table.new_type_var());
1065             }
1066         }
1067         // handle provided type arguments
1068         if let Some(generic_args) = generic_args {
1069             // if args are provided, it should be all of them, but we can't rely on that
1070             for arg in generic_args
1071                 .args
1072                 .iter()
1073                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
1074                 .take(type_params)
1075             {
1076                 match arg {
1077                     GenericArg::Type(type_ref) => {
1078                         let ty = self.make_ty(type_ref);
1079                         substs.push(ty);
1080                     }
1081                     GenericArg::Lifetime(_) => {}
1082                 }
1083             }
1084         };
1085         let supplied_params = substs.len();
1086         for _ in supplied_params..total_len {
1087             substs.push(self.table.new_type_var());
1088         }
1089         assert_eq!(substs.len(), total_len);
1090         Substitution::from_iter(&Interner, substs)
1091     }
1092
1093     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1094         let callable_ty = self.resolve_ty_shallow(callable_ty);
1095         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(&Interner) {
1096             let def: CallableDefId = from_chalk(self.db, *fn_def);
1097             let generic_predicates = self.db.generic_predicates(def.into());
1098             for predicate in generic_predicates.iter() {
1099                 let (predicate, binders) = predicate
1100                     .clone()
1101                     .substitute(&Interner, parameters)
1102                     .into_value_and_skipped_binders();
1103                 always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
1104                 self.push_obligation(predicate.cast(&Interner));
1105             }
1106             // add obligation for trait implementation, if this is a trait method
1107             match def {
1108                 CallableDefId::FunctionId(f) => {
1109                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
1110                     {
1111                         // construct a TraitRef
1112                         let substs = crate::subst_prefix(
1113                             &*parameters,
1114                             generics(self.db.upcast(), trait_.into()).len(),
1115                         );
1116                         self.push_obligation(
1117                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1118                                 .cast(&Interner),
1119                         );
1120                     }
1121                 }
1122                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1123             }
1124         }
1125     }
1126 }