crates/hir_ty/src/infer/expr.rs

   1 //! Type inference for expressions.
   2
   3 use std::{
   4     collections::hash_map::Entry,
   5     iter::{repeat, repeat_with},
   6     mem,
   7     sync::Arc,
   8 };
   9
  10 use chalk_ir::{
  11     cast::Cast, fold::Shift, DebruijnIndex, GenericArgData, Mutability, TyVariableKind,
  12 };
  13 use hir_def::{
  14     expr::{ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, Ordering, Statement, UnaryOp},
  15     generics::TypeOrConstParamData,
  16     path::{GenericArg, GenericArgs},
  17     resolver::resolver_for_expr,
  18     ConstParamId, FieldId, FunctionId, ItemContainerId, Lookup,
  19 };
  20 use hir_expand::name::{name, Name};
  21 use stdx::always;
  22 use syntax::ast::RangeOp;
  23
  24 use crate::{
  25     autoderef::{self, Autoderef},
  26     consteval,
  27     infer::coerce::CoerceMany,
  28     lower::{
  29         const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
  30     },
  31     mapping::{from_chalk, ToChalk},
  32     method_resolution,
  33     primitive::{self, UintTy},
  34     static_lifetime, to_chalk_trait_id,
  35     utils::{generics, Generics},
  36     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, Interner, Rawness, Scalar,
  37     Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  38 };
  39
  40 use super::{
  41     coerce::auto_deref_adjust_steps, find_breakable, BindingMode, BreakableContext, Diverges,
  42     Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch,
  43 };
  44
  45 impl<'a> InferenceContext<'a> {
  46     pub(crate) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  47         let ty = self.infer_expr_inner(tgt_expr, expected);
  48         if self.resolve_ty_shallow(&ty).is_never() {
  49             // Any expression that produces a value of type `!` must have diverged
  50             self.diverges = Diverges::Always;
  51         }
  52         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  53             let could_unify = self.unify(&ty, &expected_ty);
  54             if !could_unify {
  55                 self.result.type_mismatches.insert(
  56                     tgt_expr.into(),
  57                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  58                 );
  59             }
  60         }
  61         ty
  62     }
  63
  64     /// Infer type of expression with possibly implicit coerce to the expected type.
  65     /// Return the type after possible coercion.
  66     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  67         let ty = self.infer_expr_inner(expr, expected);
  68         if let Some(target) = expected.only_has_type(&mut self.table) {
  69             match self.coerce(Some(expr), &ty, &target) {
  70                 Ok(res) => res,
  71                 Err(_) => {
  72                     self.result
  73                         .type_mismatches
  74                         .insert(expr.into(), TypeMismatch { expected: target, actual: ty.clone() });
  75                     // Return actual type when type mismatch.
  76                     // This is needed for diagnostic when return type mismatch.
  77                     ty
  78                 }
  79             }
  80         } else {
  81             ty
  82         }
  83     }
  84
  85     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  86         self.db.unwind_if_cancelled();
  87
  88         let body = Arc::clone(&self.body); // avoid borrow checker problem
  89         let ty = match &body[tgt_expr] {
  90             Expr::Missing => self.err_ty(),
  91             &Expr::If { condition, then_branch, else_branch } => {
  92                 self.infer_expr(
  93                     condition,
  94                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
  95                 );
  96
  97                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
  98                 let mut both_arms_diverge = Diverges::Always;
  99
 100                 let result_ty = self.table.new_type_var();
 101                 let then_ty = self.infer_expr_inner(then_branch, expected);
 102                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 103                 let mut coerce = CoerceMany::new(result_ty);
 104                 coerce.coerce(self, Some(then_branch), &then_ty);
 105                 let else_ty = match else_branch {
 106                     Some(else_branch) => self.infer_expr_inner(else_branch, expected),
 107                     None => TyBuilder::unit(),
 108                 };
 109                 both_arms_diverge &= self.diverges;
 110                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 111                 coerce.coerce(self, else_branch, &else_ty);
 112
 113                 self.diverges = condition_diverges | both_arms_diverge;
 114
 115                 coerce.complete()
 116             }
 117             &Expr::Let { pat, expr } => {
 118                 let input_ty = self.infer_expr(expr, &Expectation::none());
 119                 self.infer_pat(pat, &input_ty, BindingMode::default());
 120                 TyKind::Scalar(Scalar::Bool).intern(Interner)
 121             }
 122             Expr::Block { statements, tail, label, id: _ } => {
 123                 let old_resolver = mem::replace(
 124                     &mut self.resolver,
 125                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 126                 );
 127                 let ty = match label {
 128                     Some(_) => {
 129                         let break_ty = self.table.new_type_var();
 130                         self.breakables.push(BreakableContext {
 131                             may_break: false,
 132                             coerce: CoerceMany::new(break_ty.clone()),
 133                             label: label.map(|label| self.body[label].name.clone()),
 134                         });
 135                         let ty = self.infer_block(
 136                             tgt_expr,
 137                             statements,
 138                             *tail,
 139                             &Expectation::has_type(break_ty),
 140                         );
 141                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 142                         if ctxt.may_break {
 143                             ctxt.coerce.complete()
 144                         } else {
 145                             ty
 146                         }
 147                     }
 148                     None => self.infer_block(tgt_expr, statements, *tail, expected),
 149                 };
 150                 self.resolver = old_resolver;
 151                 ty
 152             }
 153             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 154             Expr::TryBlock { body } => {
 155                 let _inner = self.infer_expr(*body, expected);
 156                 // FIXME should be std::result::Result<{inner}, _>
 157                 self.err_ty()
 158             }
 159             Expr::Async { body } => {
 160                 let ret_ty = self.table.new_type_var();
 161                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 162                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 163
 164                 let inner_ty = self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 165
 166                 self.diverges = prev_diverges;
 167                 self.return_ty = prev_ret_ty;
 168
 169                 // Use the first type parameter as the output type of future.
 170                 // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 171                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 172                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 173                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
 174                     .intern(Interner)
 175             }
 176             Expr::Loop { body, label } => {
 177                 self.breakables.push(BreakableContext {
 178                     may_break: false,
 179                     coerce: CoerceMany::new(self.table.new_type_var()),
 180                     label: label.map(|label| self.body[label].name.clone()),
 181                 });
 182                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 183
 184                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 185
 186                 if ctxt.may_break {
 187                     self.diverges = Diverges::Maybe;
 188                     ctxt.coerce.complete()
 189                 } else {
 190                     TyKind::Never.intern(Interner)
 191                 }
 192             }
 193             Expr::While { condition, body, label } => {
 194                 self.breakables.push(BreakableContext {
 195                     may_break: false,
 196                     coerce: CoerceMany::new(self.err_ty()),
 197                     label: label.map(|label| self.body[label].name.clone()),
 198                 });
 199                 self.infer_expr(
 200                     *condition,
 201                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 202                 );
 203                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 204                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 205                 // the body may not run, so it diverging doesn't mean we diverge
 206                 self.diverges = Diverges::Maybe;
 207                 TyBuilder::unit()
 208             }
 209             Expr::For { iterable, body, pat, label } => {
 210                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 211
 212                 self.breakables.push(BreakableContext {
 213                     may_break: false,
 214                     coerce: CoerceMany::new(self.err_ty()),
 215                     label: label.map(|label| self.body[label].name.clone()),
 216                 });
 217                 let pat_ty =
 218                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 219
 220                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 221
 222                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 223                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 224                 // the body may not run, so it diverging doesn't mean we diverge
 225                 self.diverges = Diverges::Maybe;
 226                 TyBuilder::unit()
 227             }
 228             Expr::Lambda { body, args, ret_type, arg_types } => {
 229                 assert_eq!(args.len(), arg_types.len());
 230
 231                 let mut sig_tys = Vec::new();
 232
 233                 // collect explicitly written argument types
 234                 for arg_type in arg_types.iter() {
 235                     let arg_ty = match arg_type {
 236                         Some(type_ref) => self.make_ty(type_ref),
 237                         None => self.table.new_type_var(),
 238                     };
 239                     sig_tys.push(arg_ty);
 240                 }
 241
 242                 // add return type
 243                 let ret_ty = match ret_type {
 244                     Some(type_ref) => self.make_ty(type_ref),
 245                     None => self.table.new_type_var(),
 246                 };
 247                 sig_tys.push(ret_ty.clone());
 248                 let sig_ty = TyKind::Function(FnPointer {
 249                     num_binders: 0,
 250                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 251                     substitution: FnSubst(
 252                         Substitution::from_iter(Interner, sig_tys.clone()).shifted_in(Interner),
 253                     ),
 254                 })
 255                 .intern(Interner);
 256                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 257                 let closure_ty =
 258                     TyKind::Closure(closure_id, Substitution::from1(Interner, sig_ty.clone()))
 259                         .intern(Interner);
 260
 261                 // Eagerly try to relate the closure type with the expected
 262                 // type, otherwise we often won't have enough information to
 263                 // infer the body.
 264                 self.deduce_closure_type_from_expectations(
 265                     tgt_expr,
 266                     &closure_ty,
 267                     &sig_ty,
 268                     expected,
 269                 );
 270
 271                 // Now go through the argument patterns
 272                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 273                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 274                 }
 275
 276                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 277                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 278
 279                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 280
 281                 self.diverges = prev_diverges;
 282                 self.return_ty = prev_ret_ty;
 283
 284                 closure_ty
 285             }
 286             Expr::Call { callee, args } => {
 287                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 288                 let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone());
 289                 let mut res = None;
 290                 let mut derefed_callee = callee_ty.clone();
 291                 // manual loop to be able to access `derefs.table`
 292                 while let Some((callee_deref_ty, _)) = derefs.next() {
 293                     res = derefs.table.callable_sig(&callee_deref_ty, args.len());
 294                     if res.is_some() {
 295                         derefed_callee = callee_deref_ty;
 296                         break;
 297                     }
 298                 }
 299                 let (param_tys, ret_ty) = match res {
 300                     Some(res) => {
 301                         let adjustments = auto_deref_adjust_steps(&derefs);
 302                         self.write_expr_adj(*callee, adjustments);
 303                         res
 304                     }
 305                     None => (Vec::new(), self.err_ty()),
 306                 };
 307                 let indices_to_skip = self.check_legacy_const_generics(derefed_callee, args);
 308                 self.register_obligations_for_call(&callee_ty);
 309
 310                 let expected_inputs = self.expected_inputs_for_expected_output(
 311                     expected,
 312                     ret_ty.clone(),
 313                     param_tys.clone(),
 314                 );
 315
 316                 self.check_call_arguments(args, &expected_inputs, &param_tys, &indices_to_skip);
 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                     expected,
 327                 ),
 328             Expr::Match { expr, arms } => {
 329                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 330
 331                 let expected = expected.adjust_for_branches(&mut self.table);
 332
 333                 let result_ty = if arms.is_empty() {
 334                     TyKind::Never.intern(Interner)
 335                 } else {
 336                     match &expected {
 337                         Expectation::HasType(ty) => ty.clone(),
 338                         _ => self.table.new_type_var(),
 339                     }
 340                 };
 341                 let mut coerce = CoerceMany::new(result_ty);
 342
 343                 let matchee_diverges = self.diverges;
 344                 let mut all_arms_diverge = Diverges::Always;
 345
 346                 for arm in arms.iter() {
 347                     self.diverges = Diverges::Maybe;
 348                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 349                     if let Some(guard_expr) = arm.guard {
 350                         self.infer_expr(
 351                             guard_expr,
 352                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 353                         );
 354                     }
 355
 356                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 357                     all_arms_diverge &= self.diverges;
 358                     coerce.coerce(self, Some(arm.expr), &arm_ty);
 359                 }
 360
 361                 self.diverges = matchee_diverges | all_arms_diverge;
 362
 363                 coerce.complete()
 364             }
 365             Expr::Path(p) => {
 366                 // FIXME this could be more efficient...
 367                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 368                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
 369             }
 370             Expr::Continue { .. } => TyKind::Never.intern(Interner),
 371             Expr::Break { expr, label } => {
 372                 let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
 373                     Some(ctxt) => {
 374                         // avoiding the borrowck
 375                         mem::replace(
 376                             &mut ctxt.coerce,
 377                             CoerceMany::new(self.result.standard_types.unknown.clone()),
 378                         )
 379                     }
 380                     None => CoerceMany::new(self.result.standard_types.unknown.clone()),
 381                 };
 382
 383                 let val_ty = if let Some(expr) = *expr {
 384                     self.infer_expr(expr, &Expectation::none())
 385                 } else {
 386                     TyBuilder::unit()
 387                 };
 388
 389                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 390                 coerce.coerce(self, *expr, &val_ty);
 391
 392                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 393                     ctxt.coerce = coerce;
 394                     ctxt.may_break = true;
 395                 } else {
 396                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 397                         expr: tgt_expr,
 398                     });
 399                 };
 400
 401                 TyKind::Never.intern(Interner)
 402             }
 403             Expr::Return { expr } => {
 404                 if let Some(expr) = expr {
 405                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 406                 } else {
 407                     let unit = TyBuilder::unit();
 408                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
 409                 }
 410                 TyKind::Never.intern(Interner)
 411             }
 412             Expr::Yield { expr } => {
 413                 // FIXME: track yield type for coercion
 414                 if let Some(expr) = expr {
 415                     self.infer_expr(*expr, &Expectation::none());
 416                 }
 417                 TyKind::Never.intern(Interner)
 418             }
 419             Expr::RecordLit { path, fields, spread } => {
 420                 let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
 421                 if let Some(variant) = def_id {
 422                     self.write_variant_resolution(tgt_expr.into(), variant);
 423                 }
 424
 425                 if let Some(t) = expected.only_has_type(&mut self.table) {
 426                     self.unify(&ty, &t);
 427                 }
 428
 429                 let substs = ty
 430                     .as_adt()
 431                     .map(|(_, s)| s.clone())
 432                     .unwrap_or_else(|| Substitution::empty(Interner));
 433                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 434                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 435                 for field in fields.iter() {
 436                     let field_def =
 437                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 438                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 439                             None => {
 440                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 441                                     expr: field.expr,
 442                                 });
 443                                 None
 444                             }
 445                         });
 446                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 447                         field_types[it.local_id].clone().substitute(Interner, &substs)
 448                     });
 449                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 450                 }
 451                 if let Some(expr) = spread {
 452                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 453                 }
 454                 ty
 455             }
 456             Expr::Field { expr, name } => {
 457                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 458
 459                 let mut autoderef = Autoderef::new(&mut self.table, receiver_ty);
 460                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
 461                     let (field_id, parameters) = match derefed_ty.kind(Interner) {
 462                         TyKind::Tuple(_, substs) => {
 463                             return name.as_tuple_index().and_then(|idx| {
 464                                 substs
 465                                     .as_slice(Interner)
 466                                     .get(idx)
 467                                     .map(|a| a.assert_ty_ref(Interner))
 468                                     .cloned()
 469                             });
 470                         }
 471                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 472                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 473                             let field = FieldId { parent: (*s).into(), local_id };
 474                             (field, parameters.clone())
 475                         }
 476                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 477                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 478                             let field = FieldId { parent: (*u).into(), local_id };
 479                             (field, parameters.clone())
 480                         }
 481                         _ => return None,
 482                     };
 483                     let module = self.resolver.module();
 484                     let is_visible = module
 485                         .map(|mod_id| {
 486                             self.db.field_visibilities(field_id.parent)[field_id.local_id]
 487                                 .is_visible_from(self.db.upcast(), mod_id)
 488                         })
 489                         .unwrap_or(true);
 490                     if !is_visible {
 491                         // Write down the first field resolution even if it is not visible
 492                         // This aids IDE features for private fields like goto def and in
 493                         // case of autoderef finding an applicable field, this will be
 494                         // overwritten in a following cycle
 495                         if let Entry::Vacant(entry) = self.result.field_resolutions.entry(tgt_expr)
 496                         {
 497                             entry.insert(field_id);
 498                         }
 499                         return None;
 500                     }
 501                     // can't have `write_field_resolution` here because `self.table` is borrowed :(
 502                     self.result.field_resolutions.insert(tgt_expr, field_id);
 503                     let ty = self.db.field_types(field_id.parent)[field_id.local_id]
 504                         .clone()
 505                         .substitute(Interner, &parameters);
 506                     Some(ty)
 507                 });
 508                 let ty = match ty {
 509                     Some(ty) => {
 510                         let adjustments = auto_deref_adjust_steps(&autoderef);
 511                         self.write_expr_adj(*expr, adjustments);
 512                         let ty = self.insert_type_vars(ty);
 513                         let ty = self.normalize_associated_types_in(ty);
 514                         ty
 515                     }
 516                     _ => self.err_ty(),
 517                 };
 518                 ty
 519             }
 520             Expr::Await { expr } => {
 521                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 522                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 523             }
 524             Expr::Try { expr } => {
 525                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 526                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 527             }
 528             Expr::Cast { expr, type_ref } => {
 529                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 530                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 531                 let cast_ty = self.make_ty(type_ref);
 532                 // FIXME check the cast...
 533                 cast_ty
 534             }
 535             Expr::Ref { expr, rawness, mutability } => {
 536                 let mutability = lower_to_chalk_mutability(*mutability);
 537                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 538                     .only_has_type(&mut self.table)
 539                     .as_ref()
 540                     .and_then(|t| t.as_reference_or_ptr())
 541                 {
 542                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 543                         // FIXME: record type error - expected mut reference but found shared ref,
 544                         // which cannot be coerced
 545                     }
 546                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 547                         // FIXME: record type error - expected reference but found ptr,
 548                         // which cannot be coerced
 549                     }
 550                     Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
 551                 } else {
 552                     Expectation::none()
 553                 };
 554                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 555                 match rawness {
 556                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 557                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 558                 }
 559                 .intern(Interner)
 560             }
 561             Expr::Box { expr } => {
 562                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 563                 if let Some(box_) = self.resolve_boxed_box() {
 564                     TyBuilder::adt(self.db, box_)
 565                         .push(inner_ty)
 566                         .fill_with_defaults(self.db, || self.table.new_type_var())
 567                         .build()
 568                 } else {
 569                     self.err_ty()
 570                 }
 571             }
 572             Expr::UnaryOp { expr, op } => {
 573                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 574                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 575                 match op {
 576                     UnaryOp::Deref => {
 577                         autoderef::deref(&mut self.table, inner_ty).unwrap_or_else(|| self.err_ty())
 578                     }
 579                     UnaryOp::Neg => {
 580                         match inner_ty.kind(Interner) {
 581                             // Fast path for builtins
 582                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
 583                             | TyKind::InferenceVar(
 584                                 _,
 585                                 TyVariableKind::Integer | TyVariableKind::Float,
 586                             ) => inner_ty,
 587                             // Otherwise we resolve via the std::ops::Neg trait
 588                             _ => self
 589                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 590                         }
 591                     }
 592                     UnaryOp::Not => {
 593                         match inner_ty.kind(Interner) {
 594                             // Fast path for builtins
 595                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
 596                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 597                             // Otherwise we resolve via the std::ops::Not trait
 598                             _ => self
 599                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 600                         }
 601                     }
 602                 }
 603             }
 604             Expr::BinaryOp { lhs, rhs, op } => match op {
 605                 Some(BinaryOp::Assignment { op: None }) => {
 606                     let lhs_ty = self.infer_expr(*lhs, &Expectation::none());
 607                     self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
 608                     self.result.standard_types.unit.clone()
 609                 }
 610                 Some(BinaryOp::LogicOp(_)) => {
 611                     let bool_ty = self.result.standard_types.bool_.clone();
 612                     self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
 613                     let lhs_diverges = self.diverges;
 614                     self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
 615                     // Depending on the LHS' value, the RHS can never execute.
 616                     self.diverges = lhs_diverges;
 617                     bool_ty
 618                 }
 619                 Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
 620                 _ => self.err_ty(),
 621             },
 622             Expr::Range { lhs, rhs, range_type } => {
 623                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 624                 let rhs_expect = lhs_ty
 625                     .as_ref()
 626                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 627                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 628                 match (range_type, lhs_ty, rhs_ty) {
 629                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 630                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 631                         None => self.err_ty(),
 632                     },
 633                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 634                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 635                         None => self.err_ty(),
 636                     },
 637                     (RangeOp::Inclusive, None, Some(ty)) => {
 638                         match self.resolve_range_to_inclusive() {
 639                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 640                             None => self.err_ty(),
 641                         }
 642                     }
 643                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 644                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 645                         None => self.err_ty(),
 646                     },
 647                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 648                         match self.resolve_range_inclusive() {
 649                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 650                             None => self.err_ty(),
 651                         }
 652                     }
 653                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 654                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 655                         None => self.err_ty(),
 656                     },
 657                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 658                 }
 659             }
 660             Expr::Index { base, index } => {
 661                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 662                 let index_ty = self.infer_expr(*index, &Expectation::none());
 663
 664                 if let Some(index_trait) = self.resolve_ops_index() {
 665                     let canonicalized = self.canonicalize(base_ty.clone());
 666                     let receiver_adjustments = method_resolution::resolve_indexing_op(
 667                         self.db,
 668                         self.trait_env.clone(),
 669                         canonicalized.value,
 670                         index_trait,
 671                     );
 672                     let (self_ty, adj) = receiver_adjustments
 673                         .map_or((self.err_ty(), Vec::new()), |adj| {
 674                             adj.apply(&mut self.table, base_ty)
 675                         });
 676                     self.write_expr_adj(*base, adj);
 677                     self.resolve_associated_type_with_params(
 678                         self_ty,
 679                         self.resolve_ops_index_output(),
 680                         &[GenericArgData::Ty(index_ty).intern(Interner)],
 681                     )
 682                 } else {
 683                     self.err_ty()
 684                 }
 685             }
 686             Expr::Tuple { exprs } => {
 687                 let mut tys = match expected
 688                     .only_has_type(&mut self.table)
 689                     .as_ref()
 690                     .map(|t| t.kind(Interner))
 691                 {
 692                     Some(TyKind::Tuple(_, substs)) => substs
 693                         .iter(Interner)
 694                         .map(|a| a.assert_ty_ref(Interner).clone())
 695                         .chain(repeat_with(|| self.table.new_type_var()))
 696                         .take(exprs.len())
 697                         .collect::<Vec<_>>(),
 698                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 699                 };
 700
 701                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 702                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 703                 }
 704
 705                 TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
 706             }
 707             Expr::Array(array) => {
 708                 let elem_ty =
 709                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
 710                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
 711                         _ => self.table.new_type_var(),
 712                     };
 713                 let mut coerce = CoerceMany::new(elem_ty.clone());
 714
 715                 let expected = Expectation::has_type(elem_ty.clone());
 716                 let len = match array {
 717                     Array::ElementList(items) => {
 718                         for &expr in items.iter() {
 719                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
 720                             coerce.coerce(self, Some(expr), &cur_elem_ty);
 721                         }
 722                         consteval::usize_const(Some(items.len() as u64))
 723                     }
 724                     &Array::Repeat { initializer, repeat } => {
 725                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
 726                         self.infer_expr(
 727                             repeat,
 728                             &Expectation::has_type(
 729                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
 730                             ),
 731                         );
 732
 733                         if let Some(g_def) = self.owner.as_generic_def_id() {
 734                             let generics = generics(self.db.upcast(), g_def);
 735                             consteval::eval_to_const(
 736                                 repeat,
 737                                 ParamLoweringMode::Placeholder,
 738                                 self,
 739                                 || generics,
 740                                 DebruijnIndex::INNERMOST,
 741                             )
 742                         } else {
 743                             consteval::usize_const(None)
 744                         }
 745                     }
 746                 };
 747
 748                 TyKind::Array(coerce.complete(), len).intern(Interner)
 749             }
 750             Expr::Literal(lit) => match lit {
 751                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
 752                 Literal::String(..) => {
 753                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
 754                         .intern(Interner)
 755                 }
 756                 Literal::ByteString(bs) => {
 757                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 758
 759                     let len = consteval::usize_const(Some(bs.len() as u64));
 760
 761                     let array_type = TyKind::Array(byte_type, len).intern(Interner);
 762                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
 763                 }
 764                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
 765                 Literal::Int(_v, ty) => match ty {
 766                     Some(int_ty) => {
 767                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 768                             .intern(Interner)
 769                     }
 770                     None => self.table.new_integer_var(),
 771                 },
 772                 Literal::Uint(_v, ty) => match ty {
 773                     Some(int_ty) => {
 774                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 775                             .intern(Interner)
 776                     }
 777                     None => self.table.new_integer_var(),
 778                 },
 779                 Literal::Float(_v, ty) => match ty {
 780                     Some(float_ty) => {
 781                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 782                             .intern(Interner)
 783                     }
 784                     None => self.table.new_float_var(),
 785                 },
 786             },
 787             Expr::MacroStmts { tail } => self.infer_expr_inner(*tail, expected),
 788         };
 789         // use a new type variable if we got unknown here
 790         let ty = self.insert_type_vars_shallow(ty);
 791         self.write_expr_ty(tgt_expr, ty.clone());
 792         ty
 793     }
 794
 795     fn infer_overloadable_binop(
 796         &mut self,
 797         lhs: ExprId,
 798         op: BinaryOp,
 799         rhs: ExprId,
 800         tgt_expr: ExprId,
 801     ) -> Ty {
 802         let lhs_expectation = Expectation::none();
 803         let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
 804         let rhs_ty = self.table.new_type_var();
 805
 806         let func = self.resolve_binop_method(op);
 807         let func = match func {
 808             Some(func) => func,
 809             None => {
 810                 let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
 811                 let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
 812                 return self
 813                     .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
 814                     .unwrap_or_else(|| self.err_ty());
 815             }
 816         };
 817
 818         let subst = TyBuilder::subst_for_def(self.db, func)
 819             .push(lhs_ty.clone())
 820             .push(rhs_ty.clone())
 821             .build();
 822         self.write_method_resolution(tgt_expr, func, subst.clone());
 823
 824         let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
 825         self.register_obligations_for_call(&method_ty);
 826
 827         self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
 828
 829         let ret_ty = match method_ty.callable_sig(self.db) {
 830             Some(sig) => sig.ret().clone(),
 831             None => self.err_ty(),
 832         };
 833
 834         let ret_ty = self.normalize_associated_types_in(ret_ty);
 835
 836         // FIXME: record autoref adjustments
 837
 838         // use knowledge of built-in binary ops, which can sometimes help inference
 839         if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
 840             self.unify(&builtin_rhs, &rhs_ty);
 841         }
 842         if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
 843             self.unify(&builtin_ret, &ret_ty);
 844         }
 845
 846         ret_ty
 847     }
 848
 849     fn infer_block(
 850         &mut self,
 851         expr: ExprId,
 852         statements: &[Statement],
 853         tail: Option<ExprId>,
 854         expected: &Expectation,
 855     ) -> Ty {
 856         for stmt in statements {
 857             match stmt {
 858                 Statement::Let { pat, type_ref, initializer, else_branch } => {
 859                     let decl_ty = type_ref
 860                         .as_ref()
 861                         .map(|tr| self.make_ty(tr))
 862                         .unwrap_or_else(|| self.err_ty());
 863
 864                     // Always use the declared type when specified
 865                     let mut ty = decl_ty.clone();
 866
 867                     if let Some(expr) = initializer {
 868                         let actual_ty =
 869                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 870                         if decl_ty.is_unknown() {
 871                             ty = actual_ty;
 872                         }
 873                     }
 874
 875                     if let Some(expr) = else_branch {
 876                         self.infer_expr_coerce(
 877                             *expr,
 878                             &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
 879                         );
 880                     }
 881
 882                     self.infer_pat(*pat, &ty, BindingMode::default());
 883                 }
 884                 Statement::Expr { expr, .. } => {
 885                     self.infer_expr(*expr, &Expectation::none());
 886                 }
 887             }
 888         }
 889
 890         if let Some(expr) = tail {
 891             self.infer_expr_coerce(expr, expected)
 892         } else {
 893             // Citing rustc: if there is no explicit tail expression,
 894             // that is typically equivalent to a tail expression
 895             // of `()` -- except if the block diverges. In that
 896             // case, there is no value supplied from the tail
 897             // expression (assuming there are no other breaks,
 898             // this implies that the type of the block will be
 899             // `!`).
 900             if self.diverges.is_always() {
 901                 // we don't even make an attempt at coercion
 902                 self.table.new_maybe_never_var()
 903             } else {
 904                 if let Some(t) = expected.only_has_type(&mut self.table) {
 905                     let _ = self.coerce(Some(expr), &TyBuilder::unit(), &t);
 906                 }
 907                 TyBuilder::unit()
 908             }
 909         }
 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 = method_resolution::lookup_method(
 927             &canonicalized_receiver.value,
 928             self.db,
 929             self.trait_env.clone(),
 930             &traits_in_scope,
 931             self.resolver.module().into(),
 932             method_name,
 933         );
 934         let (receiver_ty, method_ty, substs) = match resolved {
 935             Some((adjust, func)) => {
 936                 let (ty, adjustments) = adjust.apply(&mut self.table, receiver_ty);
 937                 let generics = generics(self.db.upcast(), func.into());
 938                 let substs = self.substs_for_method_call(generics, generic_args);
 939                 self.write_expr_adj(receiver, adjustments);
 940                 self.write_method_resolution(tgt_expr, func, substs.clone());
 941                 (ty, self.db.value_ty(func.into()), substs)
 942             }
 943             None => (
 944                 receiver_ty,
 945                 Binders::empty(Interner, self.err_ty()),
 946                 Substitution::empty(Interner),
 947             ),
 948         };
 949         let method_ty = method_ty.substitute(Interner, &substs);
 950         self.register_obligations_for_call(&method_ty);
 951         let (formal_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 952             Some(sig) => {
 953                 if !sig.params().is_empty() {
 954                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 955                 } else {
 956                     (self.err_ty(), Vec::new(), sig.ret().clone())
 957                 }
 958             }
 959             None => (self.err_ty(), Vec::new(), self.err_ty()),
 960         };
 961         self.unify(&formal_receiver_ty, &receiver_ty);
 962
 963         let expected_inputs =
 964             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
 965
 966         self.check_call_arguments(args, &expected_inputs, &param_tys, &[]);
 967         self.normalize_associated_types_in(ret_ty)
 968     }
 969
 970     fn expected_inputs_for_expected_output(
 971         &mut self,
 972         expected_output: &Expectation,
 973         output: Ty,
 974         inputs: Vec<Ty>,
 975     ) -> Vec<Ty> {
 976         if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
 977             self.table.fudge_inference(|table| {
 978                 if table.try_unify(&expected_ty, &output).is_ok() {
 979                     table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
 980                         chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
 981                         chalk_ir::VariableKind::Lifetime => {
 982                             var.to_lifetime(Interner).cast(Interner)
 983                         }
 984                         chalk_ir::VariableKind::Const(ty) => {
 985                             var.to_const(Interner, ty).cast(Interner)
 986                         }
 987                     })
 988                 } else {
 989                     Vec::new()
 990                 }
 991             })
 992         } else {
 993             Vec::new()
 994         }
 995     }
 996
 997     fn check_call_arguments(
 998         &mut self,
 999         args: &[ExprId],
1000         expected_inputs: &[Ty],
1001         param_tys: &[Ty],
1002         skip_indices: &[u32],
1003     ) {
1004         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
1005         // We do this in a pretty awful way: first we type-check any arguments
1006         // that are not closures, then we type-check the closures. This is so
1007         // that we have more information about the types of arguments when we
1008         // type-check the functions. This isn't really the right way to do this.
1009         for &check_closures in &[false, true] {
1010             let mut skip_indices = skip_indices.into_iter().copied().fuse().peekable();
1011             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
1012             let expected_iter = expected_inputs
1013                 .iter()
1014                 .cloned()
1015                 .chain(param_iter.clone().skip(expected_inputs.len()));
1016             for (idx, ((&arg, param_ty), expected_ty)) in
1017                 args.iter().zip(param_iter).zip(expected_iter).enumerate()
1018             {
1019                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
1020                 if is_closure != check_closures {
1021                     continue;
1022                 }
1023
1024                 while skip_indices.peek().map_or(false, |i| *i < idx as u32) {
1025                     skip_indices.next();
1026                 }
1027                 if skip_indices.peek().copied() == Some(idx as u32) {
1028                     continue;
1029                 }
1030
1031                 // the difference between param_ty and expected here is that
1032                 // expected is the parameter when the expected *return* type is
1033                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
1034                 // the expected type is already `&[i32]`, whereas param_ty is
1035                 // still an unbound type variable. We don't always want to force
1036                 // the parameter to coerce to the expected type (for example in
1037                 // `coerce_unsize_expected_type_4`).
1038                 let param_ty = self.normalize_associated_types_in(param_ty);
1039                 let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
1040                 // infer with the expected type we have...
1041                 let ty = self.infer_expr_inner(arg, &expected);
1042
1043                 // then coerce to either the expected type or just the formal parameter type
1044                 let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
1045                     // if we are coercing to the expectation, unify with the
1046                     // formal parameter type to connect everything
1047                     self.unify(&ty, &param_ty);
1048                     ty
1049                 } else {
1050                     param_ty
1051                 };
1052                 if !coercion_target.is_unknown() {
1053                     if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
1054                         self.result.type_mismatches.insert(
1055                             arg.into(),
1056                             TypeMismatch { expected: coercion_target, actual: ty.clone() },
1057                         );
1058                     }
1059                 }
1060             }
1061         }
1062     }
1063
1064     fn substs_for_method_call(
1065         &mut self,
1066         def_generics: Generics,
1067         generic_args: Option<&GenericArgs>,
1068     ) -> Substitution {
1069         let (parent_params, self_params, type_params, const_params, impl_trait_params) =
1070             def_generics.provenance_split();
1071         assert_eq!(self_params, 0); // method shouldn't have another Self param
1072         let total_len = parent_params + type_params + const_params + impl_trait_params;
1073         let mut substs = Vec::with_capacity(total_len);
1074         // Parent arguments are unknown
1075         for (id, param) in def_generics.iter_parent() {
1076             match param {
1077                 TypeOrConstParamData::TypeParamData(_) => {
1078                     substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner));
1079                 }
1080                 TypeOrConstParamData::ConstParamData(_) => {
1081                     let ty = self.db.const_param_ty(ConstParamId::from_unchecked(id));
1082                     substs
1083                         .push(GenericArgData::Const(self.table.new_const_var(ty)).intern(Interner));
1084                 }
1085             }
1086         }
1087         // handle provided arguments
1088         if let Some(generic_args) = generic_args {
1089             // if args are provided, it should be all of them, but we can't rely on that
1090             for (arg, kind_id) in generic_args
1091                 .args
1092                 .iter()
1093                 .filter(|arg| !matches!(arg, GenericArg::Lifetime(_)))
1094                 .take(type_params + const_params)
1095                 .zip(def_generics.iter_id().skip(parent_params))
1096             {
1097                 if let Some(g) = generic_arg_to_chalk(
1098                     self.db,
1099                     kind_id,
1100                     arg,
1101                     self,
1102                     |this, type_ref| this.make_ty(type_ref),
1103                     |this, c| {
1104                         const_or_path_to_chalk(
1105                             this.db,
1106                             &this.resolver,
1107                             c,
1108                             ParamLoweringMode::Placeholder,
1109                             || generics(this.db.upcast(), (&this.resolver).generic_def().unwrap()),
1110                             DebruijnIndex::INNERMOST,
1111                         )
1112                     },
1113                 ) {
1114                     substs.push(g);
1115                 }
1116             }
1117         };
1118         for (id, data) in def_generics.iter().skip(substs.len()) {
1119             match data {
1120                 TypeOrConstParamData::TypeParamData(_) => {
1121                     substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner))
1122                 }
1123                 TypeOrConstParamData::ConstParamData(_) => {
1124                     substs.push(
1125                         GenericArgData::Const(self.table.new_const_var(
1126                             self.db.const_param_ty(ConstParamId::from_unchecked(id)),
1127                         ))
1128                         .intern(Interner),
1129                     )
1130                 }
1131             }
1132         }
1133         assert_eq!(substs.len(), total_len);
1134         Substitution::from_iter(Interner, substs)
1135     }
1136
1137     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1138         let callable_ty = self.resolve_ty_shallow(callable_ty);
1139         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(Interner) {
1140             let def: CallableDefId = from_chalk(self.db, *fn_def);
1141             let generic_predicates = self.db.generic_predicates(def.into());
1142             for predicate in generic_predicates.iter() {
1143                 let (predicate, binders) = predicate
1144                     .clone()
1145                     .substitute(Interner, parameters)
1146                     .into_value_and_skipped_binders();
1147                 always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
1148                 self.push_obligation(predicate.cast(Interner));
1149             }
1150             // add obligation for trait implementation, if this is a trait method
1151             match def {
1152                 CallableDefId::FunctionId(f) => {
1153                     if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
1154                         // construct a TraitRef
1155                         let substs = crate::subst_prefix(
1156                             &*parameters,
1157                             generics(self.db.upcast(), trait_.into()).len(),
1158                         );
1159                         self.push_obligation(
1160                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1161                                 .cast(Interner),
1162                         );
1163                     }
1164                 }
1165                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1166             }
1167         }
1168     }
1169
1170     /// Returns the argument indices to skip.
1171     fn check_legacy_const_generics(&mut self, callee: Ty, args: &[ExprId]) -> Vec<u32> {
1172         let (func, subst) = match callee.kind(Interner) {
1173             TyKind::FnDef(fn_id, subst) => {
1174                 let callable = CallableDefId::from_chalk(self.db, *fn_id);
1175                 let func = match callable {
1176                     CallableDefId::FunctionId(f) => f,
1177                     _ => return Vec::new(),
1178                 };
1179                 (func, subst)
1180             }
1181             _ => return Vec::new(),
1182         };
1183
1184         let data = self.db.function_data(func);
1185         if data.legacy_const_generics_indices.is_empty() {
1186             return Vec::new();
1187         }
1188
1189         // only use legacy const generics if the param count matches with them
1190         if data.params.len() + data.legacy_const_generics_indices.len() != args.len() {
1191             return Vec::new();
1192         }
1193
1194         // check legacy const parameters
1195         for (subst_idx, arg_idx) in data.legacy_const_generics_indices.iter().copied().enumerate() {
1196             let arg = match subst.at(Interner, subst_idx).constant(Interner) {
1197                 Some(c) => c,
1198                 None => continue, // not a const parameter?
1199             };
1200             if arg_idx >= args.len() as u32 {
1201                 continue;
1202             }
1203             let _ty = arg.data(Interner).ty.clone();
1204             let expected = Expectation::none(); // FIXME use actual const ty, when that is lowered correctly
1205             self.infer_expr(args[arg_idx as usize], &expected);
1206             // FIXME: evaluate and unify with the const
1207         }
1208         let mut indices = data.legacy_const_generics_indices.clone();
1209         indices.sort();
1210         indices
1211     }
1212
1213     fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
1214         let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
1215         let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
1216         match op {
1217             BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
1218                 Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
1219             }
1220             BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
1221             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
1222                 // all integer combinations are valid here
1223                 if matches!(
1224                     lhs_ty.kind(Interner),
1225                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1226                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1227                 ) && matches!(
1228                     rhs_ty.kind(Interner),
1229                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1230                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1231                 ) {
1232                     Some(lhs_ty)
1233                 } else {
1234                     None
1235                 }
1236             }
1237             BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
1238                 // (int, int) | (uint, uint) | (float, float)
1239                 (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
1240                 | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
1241                 | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
1242                     Some(rhs_ty)
1243                 }
1244                 // ({int}, int) | ({int}, uint)
1245                 (
1246                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1247                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1248                 ) => Some(rhs_ty),
1249                 // (int, {int}) | (uint, {int})
1250                 (
1251                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1252                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1253                 ) => Some(lhs_ty),
1254                 // ({float} | float)
1255                 (
1256                     TyKind::InferenceVar(_, TyVariableKind::Float),
1257                     TyKind::Scalar(Scalar::Float(_)),
1258                 ) => Some(rhs_ty),
1259                 // (float, {float})
1260                 (
1261                     TyKind::Scalar(Scalar::Float(_)),
1262                     TyKind::InferenceVar(_, TyVariableKind::Float),
1263                 ) => Some(lhs_ty),
1264                 // ({int}, {int}) | ({float}, {float})
1265                 (
1266                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1267                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1268                 )
1269                 | (
1270                     TyKind::InferenceVar(_, TyVariableKind::Float),
1271                     TyKind::InferenceVar(_, TyVariableKind::Float),
1272                 ) => Some(rhs_ty),
1273                 _ => None,
1274             },
1275         }
1276     }
1277
1278     fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
1279         Some(match op {
1280             BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
1281             BinaryOp::Assignment { op: None } => lhs_ty,
1282             BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
1283                 .resolve_ty_shallow(&lhs_ty)
1284                 .kind(Interner)
1285             {
1286                 TyKind::Scalar(_) | TyKind::Str => lhs_ty,
1287                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1288                 _ => return None,
1289             },
1290             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
1291             BinaryOp::CmpOp(CmpOp::Ord { .. })
1292             | BinaryOp::Assignment { op: Some(_) }
1293             | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
1294                 TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
1295                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1296                 _ => return None,
1297             },
1298         })
1299     }
1300
1301     fn resolve_binop_method(&self, op: BinaryOp) -> Option<FunctionId> {
1302         let (name, lang_item) = match op {
1303             BinaryOp::LogicOp(_) => return None,
1304             BinaryOp::ArithOp(aop) => match aop {
1305                 ArithOp::Add => (name!(add), name!(add)),
1306                 ArithOp::Mul => (name!(mul), name!(mul)),
1307                 ArithOp::Sub => (name!(sub), name!(sub)),
1308                 ArithOp::Div => (name!(div), name!(div)),
1309                 ArithOp::Rem => (name!(rem), name!(rem)),
1310                 ArithOp::Shl => (name!(shl), name!(shl)),
1311                 ArithOp::Shr => (name!(shr), name!(shr)),
1312                 ArithOp::BitXor => (name!(bitxor), name!(bitxor)),
1313                 ArithOp::BitOr => (name!(bitor), name!(bitor)),
1314                 ArithOp::BitAnd => (name!(bitand), name!(bitand)),
1315             },
1316             BinaryOp::Assignment { op: Some(aop) } => match aop {
1317                 ArithOp::Add => (name!(add_assign), name!(add_assign)),
1318                 ArithOp::Mul => (name!(mul_assign), name!(mul_assign)),
1319                 ArithOp::Sub => (name!(sub_assign), name!(sub_assign)),
1320                 ArithOp::Div => (name!(div_assign), name!(div_assign)),
1321                 ArithOp::Rem => (name!(rem_assign), name!(rem_assign)),
1322                 ArithOp::Shl => (name!(shl_assign), name!(shl_assign)),
1323                 ArithOp::Shr => (name!(shr_assign), name!(shr_assign)),
1324                 ArithOp::BitXor => (name!(bitxor_assign), name!(bitxor_assign)),
1325                 ArithOp::BitOr => (name!(bitor_assign), name!(bitor_assign)),
1326                 ArithOp::BitAnd => (name!(bitand_assign), name!(bitand_assign)),
1327             },
1328             BinaryOp::CmpOp(cop) => match cop {
1329                 CmpOp::Eq { negated: false } => (name!(eq), name!(eq)),
1330                 CmpOp::Eq { negated: true } => (name!(ne), name!(eq)),
1331                 CmpOp::Ord { ordering: Ordering::Less, strict: false } => {
1332                     (name!(le), name!(partial_ord))
1333                 }
1334                 CmpOp::Ord { ordering: Ordering::Less, strict: true } => {
1335                     (name!(lt), name!(partial_ord))
1336                 }
1337                 CmpOp::Ord { ordering: Ordering::Greater, strict: false } => {
1338                     (name!(ge), name!(partial_ord))
1339                 }
1340                 CmpOp::Ord { ordering: Ordering::Greater, strict: true } => {
1341                     (name!(gt), name!(partial_ord))
1342                 }
1343             },
1344             BinaryOp::Assignment { op: None } => return None,
1345         };
1346
1347         let trait_ = self.resolve_lang_item(lang_item)?.as_trait()?;
1348
1349         self.db.trait_data(trait_).method_by_name(&name)
1350     }
1351 }