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::{
  12         ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, MatchGuard, Ordering, Statement,
  13         UnaryOp,
  14     },
  15     path::{GenericArg, GenericArgs},
  16     resolver::resolver_for_expr,
  17     FieldId, FunctionId, ItemContainerId, Lookup,
  18 };
  19 use hir_expand::name::{name, Name};
  20 use stdx::always;
  21 use syntax::ast::RangeOp;
  22
  23 use crate::{
  24     autoderef::{self, Autoderef},
  25     consteval,
  26     infer::coerce::CoerceMany,
  27     lower::lower_to_chalk_mutability,
  28     mapping::from_chalk,
  29     method_resolution,
  30     primitive::{self, UintTy},
  31     static_lifetime, to_chalk_trait_id,
  32     traits::FnTrait,
  33     utils::{generics, Generics},
  34     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
  35     ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  36 };
  37
  38 use super::{
  39     find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
  40     InferenceDiagnostic, TypeMismatch,
  41 };
  42
  43 impl<'a> InferenceContext<'a> {
  44     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  45         let ty = self.infer_expr_inner(tgt_expr, expected);
  46         if self.resolve_ty_shallow(&ty).is_never() {
  47             // Any expression that produces a value of type `!` must have diverged
  48             self.diverges = Diverges::Always;
  49         }
  50         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  51             let could_unify = self.unify(&ty, &expected_ty);
  52             if !could_unify {
  53                 self.result.type_mismatches.insert(
  54                     tgt_expr.into(),
  55                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  56                 );
  57             }
  58         }
  59         ty
  60     }
  61
  62     /// Infer type of expression with possibly implicit coerce to the expected type.
  63     /// Return the type after possible coercion.
  64     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  65         let ty = self.infer_expr_inner(expr, expected);
  66         if let Some(target) = expected.only_has_type(&mut self.table) {
  67             match self.coerce(Some(expr), &ty, &target) {
  68                 Ok(res) => res.value,
  69                 Err(_) => {
  70                     self.result
  71                         .type_mismatches
  72                         .insert(expr.into(), TypeMismatch { expected: target, actual: ty.clone() });
  73                     // Return actual type when type mismatch.
  74                     // This is needed for diagnostic when return type mismatch.
  75                     ty
  76                 }
  77             }
  78         } else {
  79             ty
  80         }
  81     }
  82
  83     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
  84         let krate = self.resolver.krate()?;
  85         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
  86         let output_assoc_type =
  87             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
  88
  89         let mut arg_tys = vec![];
  90         let arg_ty = TyBuilder::tuple(num_args)
  91             .fill(repeat_with(|| {
  92                 let arg = self.table.new_type_var();
  93                 arg_tys.push(arg.clone());
  94                 arg
  95             }))
  96             .build();
  97
  98         let projection = {
  99             let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
 100             if b.remaining() != 2 {
 101                 return None;
 102             }
 103             b.push(ty.clone()).push(arg_ty).build()
 104         };
 105
 106         let trait_env = self.trait_env.env.clone();
 107         let obligation = InEnvironment {
 108             goal: projection.trait_ref(self.db).cast(Interner),
 109             environment: trait_env,
 110         };
 111         let canonical = self.canonicalize(obligation.clone());
 112         if self.db.trait_solve(krate, canonical.value.cast(Interner)).is_some() {
 113             self.push_obligation(obligation.goal);
 114             let return_ty = self.table.normalize_projection_ty(projection);
 115             Some((arg_tys, return_ty))
 116         } else {
 117             None
 118         }
 119     }
 120
 121     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 122         match ty.callable_sig(self.db) {
 123             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 124             None => self.callable_sig_from_fn_trait(ty, num_args),
 125         }
 126     }
 127
 128     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 129         self.db.unwind_if_cancelled();
 130
 131         let body = Arc::clone(&self.body); // avoid borrow checker problem
 132         let ty = match &body[tgt_expr] {
 133             Expr::Missing => self.err_ty(),
 134             &Expr::If { condition, then_branch, else_branch } => {
 135                 // if let is desugared to match, so this is always simple if
 136                 self.infer_expr(
 137                     condition,
 138                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 139                 );
 140
 141                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 142                 let mut both_arms_diverge = Diverges::Always;
 143
 144                 let result_ty = self.table.new_type_var();
 145                 let then_ty = self.infer_expr_inner(then_branch, expected);
 146                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 147                 let mut coerce = CoerceMany::new(result_ty);
 148                 coerce.coerce(self, Some(then_branch), &then_ty);
 149                 let else_ty = match else_branch {
 150                     Some(else_branch) => self.infer_expr_inner(else_branch, expected),
 151                     None => TyBuilder::unit(),
 152                 };
 153                 both_arms_diverge &= self.diverges;
 154                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 155                 coerce.coerce(self, else_branch, &else_ty);
 156
 157                 self.diverges = condition_diverges | both_arms_diverge;
 158
 159                 coerce.complete()
 160             }
 161             Expr::Block { statements, tail, label, id: _ } => {
 162                 let old_resolver = mem::replace(
 163                     &mut self.resolver,
 164                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 165                 );
 166                 let ty = match label {
 167                     Some(_) => {
 168                         let break_ty = self.table.new_type_var();
 169                         self.breakables.push(BreakableContext {
 170                             may_break: false,
 171                             coerce: CoerceMany::new(break_ty.clone()),
 172                             label: label.map(|label| self.body[label].name.clone()),
 173                         });
 174                         let ty = self.infer_block(
 175                             tgt_expr,
 176                             statements,
 177                             *tail,
 178                             &Expectation::has_type(break_ty),
 179                         );
 180                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 181                         if ctxt.may_break {
 182                             ctxt.coerce.complete()
 183                         } else {
 184                             ty
 185                         }
 186                     }
 187                     None => self.infer_block(tgt_expr, statements, *tail, expected),
 188                 };
 189                 self.resolver = old_resolver;
 190                 ty
 191             }
 192             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 193             Expr::TryBlock { body } => {
 194                 let _inner = self.infer_expr(*body, expected);
 195                 // FIXME should be std::result::Result<{inner}, _>
 196                 self.err_ty()
 197             }
 198             Expr::Async { body } => {
 199                 // Use the first type parameter as the output type of future.
 200                 // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 201                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 202                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 203                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 204                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
 205                     .intern(Interner)
 206             }
 207             Expr::Loop { body, label } => {
 208                 self.breakables.push(BreakableContext {
 209                     may_break: false,
 210                     coerce: CoerceMany::new(self.table.new_type_var()),
 211                     label: label.map(|label| self.body[label].name.clone()),
 212                 });
 213                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 214
 215                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 216
 217                 if ctxt.may_break {
 218                     self.diverges = Diverges::Maybe;
 219                     ctxt.coerce.complete()
 220                 } else {
 221                     TyKind::Never.intern(Interner)
 222                 }
 223             }
 224             Expr::While { condition, body, label } => {
 225                 self.breakables.push(BreakableContext {
 226                     may_break: false,
 227                     coerce: CoerceMany::new(self.err_ty()),
 228                     label: label.map(|label| self.body[label].name.clone()),
 229                 });
 230                 // while let is desugared to a match loop, so this is always simple while
 231                 self.infer_expr(
 232                     *condition,
 233                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
 234                 );
 235                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 236                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 237                 // the body may not run, so it diverging doesn't mean we diverge
 238                 self.diverges = Diverges::Maybe;
 239                 TyBuilder::unit()
 240             }
 241             Expr::For { iterable, body, pat, label } => {
 242                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 243
 244                 self.breakables.push(BreakableContext {
 245                     may_break: false,
 246                     coerce: CoerceMany::new(self.err_ty()),
 247                     label: label.map(|label| self.body[label].name.clone()),
 248                 });
 249                 let pat_ty =
 250                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 251
 252                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 253
 254                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 255                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 256                 // the body may not run, so it diverging doesn't mean we diverge
 257                 self.diverges = Diverges::Maybe;
 258                 TyBuilder::unit()
 259             }
 260             Expr::Lambda { body, args, ret_type, arg_types } => {
 261                 assert_eq!(args.len(), arg_types.len());
 262
 263                 let mut sig_tys = Vec::new();
 264
 265                 // collect explicitly written argument types
 266                 for arg_type in arg_types.iter() {
 267                     let arg_ty = match arg_type {
 268                         Some(type_ref) => self.make_ty(type_ref),
 269                         None => 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                     let ty = &canonicalized.decanonicalize_ty(&mut self.table, callee_deref_ty);
 331                     self.callable_sig(ty, args.len())
 332                 });
 333                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = match res {
 334                     Some(res) => {
 335                         self.write_expr_adj(*callee, self.auto_deref_adjust_steps(&derefs));
 336                         res
 337                     }
 338                     None => (Vec::new(), self.err_ty()),
 339                 };
 340                 self.register_obligations_for_call(&callee_ty);
 341
 342                 let expected_inputs = self.expected_inputs_for_expected_output(
 343                     expected,
 344                     ret_ty.clone(),
 345                     param_tys.clone(),
 346                 );
 347
 348                 self.check_call_arguments(args, &expected_inputs, &param_tys);
 349                 self.normalize_associated_types_in(ret_ty)
 350             }
 351             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 352                 .infer_method_call(
 353                     tgt_expr,
 354                     *receiver,
 355                     args,
 356                     method_name,
 357                     generic_args.as_deref(),
 358                     expected,
 359                 ),
 360             Expr::Match { expr, arms } => {
 361                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 362
 363                 let expected = expected.adjust_for_branches(&mut self.table);
 364
 365                 let result_ty = if arms.is_empty() {
 366                     TyKind::Never.intern(Interner)
 367                 } else {
 368                     match &expected {
 369                         Expectation::HasType(ty) => ty.clone(),
 370                         _ => self.table.new_type_var(),
 371                     }
 372                 };
 373                 let mut coerce = CoerceMany::new(result_ty);
 374
 375                 let matchee_diverges = self.diverges;
 376                 let mut all_arms_diverge = Diverges::Always;
 377
 378                 for arm in arms.iter() {
 379                     self.diverges = Diverges::Maybe;
 380                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 381                     match arm.guard {
 382                         Some(MatchGuard::If { expr: guard_expr }) => {
 383                             self.infer_expr(
 384                                 guard_expr,
 385                                 &Expectation::has_type(
 386                                     TyKind::Scalar(Scalar::Bool).intern(Interner),
 387                                 ),
 388                             );
 389                         }
 390                         Some(MatchGuard::IfLet { expr, pat }) => {
 391                             let input_ty = self.infer_expr(expr, &Expectation::none());
 392                             let _pat_ty = self.infer_pat(pat, &input_ty, BindingMode::default());
 393                         }
 394                         _ => {}
 395                     }
 396
 397                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 398                     all_arms_diverge &= self.diverges;
 399                     coerce.coerce(self, Some(arm.expr), &arm_ty);
 400                 }
 401
 402                 self.diverges = matchee_diverges | all_arms_diverge;
 403
 404                 coerce.complete()
 405             }
 406             Expr::Path(p) => {
 407                 // FIXME this could be more efficient...
 408                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 409                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
 410             }
 411             Expr::Continue { .. } => TyKind::Never.intern(Interner),
 412             Expr::Break { expr, label } => {
 413                 let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
 414                     Some(ctxt) => {
 415                         // avoiding the borrowck
 416                         mem::replace(
 417                             &mut ctxt.coerce,
 418                             CoerceMany::new(self.result.standard_types.unknown.clone()),
 419                         )
 420                     }
 421                     None => CoerceMany::new(self.result.standard_types.unknown.clone()),
 422                 };
 423
 424                 let val_ty = if let Some(expr) = *expr {
 425                     self.infer_expr(expr, &Expectation::none())
 426                 } else {
 427                     TyBuilder::unit()
 428                 };
 429
 430                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 431                 coerce.coerce(self, *expr, &val_ty);
 432
 433                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 434                     ctxt.coerce = coerce;
 435                     ctxt.may_break = true;
 436                 } else {
 437                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 438                         expr: tgt_expr,
 439                     });
 440                 };
 441
 442                 TyKind::Never.intern(Interner)
 443             }
 444             Expr::Return { expr } => {
 445                 if let Some(expr) = expr {
 446                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 447                 } else {
 448                     let unit = TyBuilder::unit();
 449                     let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
 450                 }
 451                 TyKind::Never.intern(Interner)
 452             }
 453             Expr::Yield { expr } => {
 454                 // FIXME: track yield type for coercion
 455                 if let Some(expr) = expr {
 456                     self.infer_expr(*expr, &Expectation::none());
 457                 }
 458                 TyKind::Never.intern(Interner)
 459             }
 460             Expr::RecordLit { path, fields, spread } => {
 461                 let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
 462                 if let Some(variant) = def_id {
 463                     self.write_variant_resolution(tgt_expr.into(), variant);
 464                 }
 465
 466                 if let Some(t) = expected.only_has_type(&mut self.table) {
 467                     self.unify(&ty, &t);
 468                 }
 469
 470                 let substs = ty
 471                     .as_adt()
 472                     .map(|(_, s)| s.clone())
 473                     .unwrap_or_else(|| Substitution::empty(Interner));
 474                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 475                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 476                 for field in fields.iter() {
 477                     let field_def =
 478                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 479                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 480                             None => {
 481                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 482                                     expr: field.expr,
 483                                 });
 484                                 None
 485                             }
 486                         });
 487                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 488                         field_types[it.local_id].clone().substitute(Interner, &substs)
 489                     });
 490                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 491                 }
 492                 if let Some(expr) = spread {
 493                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 494                 }
 495                 ty
 496             }
 497             Expr::Field { expr, name } => {
 498                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 499                 let canonicalized = self.canonicalize(receiver_ty);
 500
 501                 let mut autoderef = Autoderef::new(
 502                     self.db,
 503                     self.resolver.krate(),
 504                     InEnvironment {
 505                         goal: canonicalized.value.clone(),
 506                         environment: self.trait_env.env.clone(),
 507                     },
 508                 );
 509                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
 510                     let module = self.resolver.module();
 511                     let db = self.db;
 512                     let is_visible = |field_id: &FieldId| {
 513                         module
 514                             .map(|mod_id| {
 515                                 db.field_visibilities(field_id.parent)[field_id.local_id]
 516                                     .is_visible_from(db.upcast(), mod_id)
 517                             })
 518                             .unwrap_or(true)
 519                     };
 520                     match canonicalized
 521                         .decanonicalize_ty(&mut self.table, derefed_ty)
 522                         .kind(Interner)
 523                     {
 524                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
 525                             substs
 526                                 .as_slice(Interner)
 527                                 .get(idx)
 528                                 .map(|a| a.assert_ty_ref(Interner))
 529                                 .cloned()
 530                         }),
 531                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 532                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 533                             let field = FieldId { parent: (*s).into(), local_id };
 534                             if is_visible(&field) {
 535                                 self.write_field_resolution(tgt_expr, field);
 536                                 Some(
 537                                     self.db.field_types((*s).into())[field.local_id]
 538                                         .clone()
 539                                         .substitute(Interner, &parameters),
 540                                 )
 541                             } else {
 542                                 None
 543                             }
 544                         }
 545                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 546                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 547                             let field = FieldId { parent: (*u).into(), local_id };
 548                             if is_visible(&field) {
 549                                 self.write_field_resolution(tgt_expr, field);
 550                                 Some(
 551                                     self.db.field_types((*u).into())[field.local_id]
 552                                         .clone()
 553                                         .substitute(Interner, &parameters),
 554                                 )
 555                             } else {
 556                                 None
 557                             }
 558                         }
 559                         _ => None,
 560                     }
 561                 });
 562                 let ty = match ty {
 563                     Some(ty) => {
 564                         self.write_expr_adj(*expr, self.auto_deref_adjust_steps(&autoderef));
 565                         ty
 566                     }
 567                     None => self.err_ty(),
 568                 };
 569                 let ty = self.insert_type_vars(ty);
 570                 self.normalize_associated_types_in(ty)
 571             }
 572             Expr::Await { expr } => {
 573                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 574                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 575             }
 576             Expr::Try { expr } => {
 577                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 578                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 579             }
 580             Expr::Cast { expr, type_ref } => {
 581                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 582                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 583                 let cast_ty = self.make_ty(type_ref);
 584                 // FIXME check the cast...
 585                 cast_ty
 586             }
 587             Expr::Ref { expr, rawness, mutability } => {
 588                 let mutability = lower_to_chalk_mutability(*mutability);
 589                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 590                     .only_has_type(&mut self.table)
 591                     .as_ref()
 592                     .and_then(|t| t.as_reference_or_ptr())
 593                 {
 594                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 595                         // FIXME: record type error - expected mut reference but found shared ref,
 596                         // which cannot be coerced
 597                     }
 598                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 599                         // FIXME: record type error - expected reference but found ptr,
 600                         // which cannot be coerced
 601                     }
 602                     Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
 603                 } else {
 604                     Expectation::none()
 605                 };
 606                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 607                 match rawness {
 608                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 609                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 610                 }
 611                 .intern(Interner)
 612             }
 613             Expr::Box { expr } => {
 614                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 615                 if let Some(box_) = self.resolve_boxed_box() {
 616                     TyBuilder::adt(self.db, box_)
 617                         .push(inner_ty)
 618                         .fill_with_defaults(self.db, || self.table.new_type_var())
 619                         .build()
 620                 } else {
 621                     self.err_ty()
 622                 }
 623             }
 624             Expr::UnaryOp { expr, op } => {
 625                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 626                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 627                 match op {
 628                     UnaryOp::Deref => match self.resolver.krate() {
 629                         Some(krate) => {
 630                             let canonicalized = self.canonicalize(inner_ty);
 631                             match autoderef::deref(
 632                                 self.db,
 633                                 krate,
 634                                 InEnvironment {
 635                                     goal: &canonicalized.value,
 636                                     environment: self.trait_env.env.clone(),
 637                                 },
 638                             ) {
 639                                 Some(derefed_ty) => {
 640                                     canonicalized.decanonicalize_ty(&mut self.table, derefed_ty)
 641                                 }
 642                                 None => self.err_ty(),
 643                             }
 644                         }
 645                         None => self.err_ty(),
 646                     },
 647                     UnaryOp::Neg => {
 648                         match inner_ty.kind(Interner) {
 649                             // Fast path for builtins
 650                             TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
 651                             | TyKind::InferenceVar(
 652                                 _,
 653                                 TyVariableKind::Integer | TyVariableKind::Float,
 654                             ) => inner_ty,
 655                             // Otherwise we resolve via the std::ops::Neg trait
 656                             _ => self
 657                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 658                         }
 659                     }
 660                     UnaryOp::Not => {
 661                         match inner_ty.kind(Interner) {
 662                             // Fast path for builtins
 663                             TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
 664                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 665                             // Otherwise we resolve via the std::ops::Not trait
 666                             _ => self
 667                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 668                         }
 669                     }
 670                 }
 671             }
 672             Expr::BinaryOp { lhs, rhs, op } => match op {
 673                 Some(BinaryOp::Assignment { op: None }) => {
 674                     let lhs_ty = self.infer_expr(*lhs, &Expectation::none());
 675                     self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
 676                     self.result.standard_types.unit.clone()
 677                 }
 678                 Some(BinaryOp::LogicOp(_)) => {
 679                     let bool_ty = self.result.standard_types.bool_.clone();
 680                     self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
 681                     let lhs_diverges = self.diverges;
 682                     self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
 683                     // Depending on the LHS' value, the RHS can never execute.
 684                     self.diverges = lhs_diverges;
 685                     bool_ty
 686                 }
 687                 Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
 688                 _ => self.err_ty(),
 689             },
 690             Expr::Range { lhs, rhs, range_type } => {
 691                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 692                 let rhs_expect = lhs_ty
 693                     .as_ref()
 694                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 695                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 696                 match (range_type, lhs_ty, rhs_ty) {
 697                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 698                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 699                         None => self.err_ty(),
 700                     },
 701                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 702                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 703                         None => self.err_ty(),
 704                     },
 705                     (RangeOp::Inclusive, None, Some(ty)) => {
 706                         match self.resolve_range_to_inclusive() {
 707                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 708                             None => self.err_ty(),
 709                         }
 710                     }
 711                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 712                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 713                         None => self.err_ty(),
 714                     },
 715                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 716                         match self.resolve_range_inclusive() {
 717                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 718                             None => self.err_ty(),
 719                         }
 720                     }
 721                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 722                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 723                         None => self.err_ty(),
 724                     },
 725                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 726                 }
 727             }
 728             Expr::Index { base, index } => {
 729                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 730                 let index_ty = self.infer_expr(*index, &Expectation::none());
 731
 732                 if let (Some(index_trait), Some(krate)) =
 733                     (self.resolve_ops_index(), self.resolver.krate())
 734                 {
 735                     let canonicalized = self.canonicalize(base_ty);
 736                     let self_ty = method_resolution::resolve_indexing_op(
 737                         self.db,
 738                         &canonicalized.value,
 739                         self.trait_env.clone(),
 740                         krate,
 741                         index_trait,
 742                     );
 743                     let self_ty = self_ty.map_or(self.err_ty(), |t| {
 744                         canonicalized.decanonicalize_ty(&mut self.table, t)
 745                     });
 746                     self.resolve_associated_type_with_params(
 747                         self_ty,
 748                         self.resolve_ops_index_output(),
 749                         &[index_ty],
 750                     )
 751                 } else {
 752                     self.err_ty()
 753                 }
 754             }
 755             Expr::Tuple { exprs } => {
 756                 let mut tys = match expected
 757                     .only_has_type(&mut self.table)
 758                     .as_ref()
 759                     .map(|t| t.kind(Interner))
 760                 {
 761                     Some(TyKind::Tuple(_, substs)) => substs
 762                         .iter(Interner)
 763                         .map(|a| a.assert_ty_ref(Interner).clone())
 764                         .chain(repeat_with(|| self.table.new_type_var()))
 765                         .take(exprs.len())
 766                         .collect::<Vec<_>>(),
 767                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 768                 };
 769
 770                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 771                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 772                 }
 773
 774                 TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
 775             }
 776             Expr::Array(array) => {
 777                 let elem_ty =
 778                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
 779                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
 780                         _ => self.table.new_type_var(),
 781                     };
 782                 let mut coerce = CoerceMany::new(elem_ty.clone());
 783
 784                 let expected = Expectation::has_type(elem_ty.clone());
 785                 let len = match array {
 786                     Array::ElementList(items) => {
 787                         for &expr in items.iter() {
 788                             let cur_elem_ty = self.infer_expr_inner(expr, &expected);
 789                             coerce.coerce(self, Some(expr), &cur_elem_ty);
 790                         }
 791                         Some(items.len() as u64)
 792                     }
 793                     &Array::Repeat { initializer, repeat } => {
 794                         self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
 795                         self.infer_expr(
 796                             repeat,
 797                             &Expectation::has_type(
 798                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
 799                             ),
 800                         );
 801
 802                         consteval::eval_usize(
 803                             repeat,
 804                             consteval::ConstEvalCtx {
 805                                 exprs: &body.exprs,
 806                                 pats: &body.pats,
 807                                 local_data: Default::default(),
 808                                 infer: &mut |x| self.infer_expr(x, &expected),
 809                             },
 810                         )
 811                     }
 812                 };
 813
 814                 TyKind::Array(coerce.complete(), consteval::usize_const(len)).intern(Interner)
 815             }
 816             Expr::Literal(lit) => match lit {
 817                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
 818                 Literal::String(..) => {
 819                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
 820                         .intern(Interner)
 821                 }
 822                 Literal::ByteString(bs) => {
 823                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
 824
 825                     let len = consteval::usize_const(Some(bs.len() as u64));
 826
 827                     let array_type = TyKind::Array(byte_type, len).intern(Interner);
 828                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
 829                 }
 830                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
 831                 Literal::Int(_v, ty) => match ty {
 832                     Some(int_ty) => {
 833                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 834                             .intern(Interner)
 835                     }
 836                     None => self.table.new_integer_var(),
 837                 },
 838                 Literal::Uint(_v, ty) => match ty {
 839                     Some(int_ty) => {
 840                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 841                             .intern(Interner)
 842                     }
 843                     None => self.table.new_integer_var(),
 844                 },
 845                 Literal::Float(_v, ty) => match ty {
 846                     Some(float_ty) => {
 847                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 848                             .intern(Interner)
 849                     }
 850                     None => self.table.new_float_var(),
 851                 },
 852             },
 853             Expr::MacroStmts { tail } => self.infer_expr_inner(*tail, expected),
 854         };
 855         // use a new type variable if we got unknown here
 856         let ty = self.insert_type_vars_shallow(ty);
 857         self.write_expr_ty(tgt_expr, ty.clone());
 858         ty
 859     }
 860
 861     fn infer_overloadable_binop(
 862         &mut self,
 863         lhs: ExprId,
 864         op: BinaryOp,
 865         rhs: ExprId,
 866         tgt_expr: ExprId,
 867     ) -> Ty {
 868         let lhs_expectation = Expectation::none();
 869         let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
 870         let rhs_ty = self.table.new_type_var();
 871
 872         let func = self.resolve_binop_method(op);
 873         let func = match func {
 874             Some(func) => func,
 875             None => {
 876                 let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
 877                 let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
 878                 return self
 879                     .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
 880                     .unwrap_or_else(|| self.err_ty());
 881             }
 882         };
 883
 884         let subst = TyBuilder::subst_for_def(self.db, func)
 885             .push(lhs_ty.clone())
 886             .push(rhs_ty.clone())
 887             .build();
 888         self.write_method_resolution(tgt_expr, func, subst.clone());
 889
 890         let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
 891         self.register_obligations_for_call(&method_ty);
 892
 893         self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
 894
 895         let ret_ty = match method_ty.callable_sig(self.db) {
 896             Some(sig) => sig.ret().clone(),
 897             None => self.err_ty(),
 898         };
 899
 900         let ret_ty = self.normalize_associated_types_in(ret_ty);
 901
 902         // FIXME: record autoref adjustments
 903
 904         // use knowledge of built-in binary ops, which can sometimes help inference
 905         if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
 906             self.unify(&builtin_rhs, &rhs_ty);
 907         }
 908         if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
 909             self.unify(&builtin_ret, &ret_ty);
 910         }
 911
 912         ret_ty
 913     }
 914
 915     fn infer_block(
 916         &mut self,
 917         expr: ExprId,
 918         statements: &[Statement],
 919         tail: Option<ExprId>,
 920         expected: &Expectation,
 921     ) -> Ty {
 922         for stmt in statements {
 923             match stmt {
 924                 Statement::Let { pat, type_ref, initializer, else_branch } => {
 925                     let decl_ty = type_ref
 926                         .as_ref()
 927                         .map(|tr| self.make_ty(tr))
 928                         .unwrap_or_else(|| self.err_ty());
 929
 930                     // Always use the declared type when specified
 931                     let mut ty = decl_ty.clone();
 932
 933                     if let Some(expr) = initializer {
 934                         let actual_ty =
 935                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 936                         if decl_ty.is_unknown() {
 937                             ty = actual_ty;
 938                         }
 939                     }
 940
 941                     if let Some(expr) = else_branch {
 942                         self.infer_expr_coerce(
 943                             *expr,
 944                             &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
 945                         );
 946                     }
 947
 948                     self.infer_pat(*pat, &ty, BindingMode::default());
 949                 }
 950                 Statement::Expr { expr, .. } => {
 951                     self.infer_expr(*expr, &Expectation::none());
 952                 }
 953             }
 954         }
 955
 956         if let Some(expr) = tail {
 957             self.infer_expr_coerce(expr, expected)
 958         } else {
 959             // Citing rustc: if there is no explicit tail expression,
 960             // that is typically equivalent to a tail expression
 961             // of `()` -- except if the block diverges. In that
 962             // case, there is no value supplied from the tail
 963             // expression (assuming there are no other breaks,
 964             // this implies that the type of the block will be
 965             // `!`).
 966             if self.diverges.is_always() {
 967                 // we don't even make an attempt at coercion
 968                 self.table.new_maybe_never_var()
 969             } else {
 970                 if let Some(t) = expected.only_has_type(&mut self.table) {
 971                     let _ = self.coerce(Some(expr), &TyBuilder::unit(), &t);
 972                 }
 973                 TyBuilder::unit()
 974             }
 975         }
 976     }
 977
 978     fn infer_method_call(
 979         &mut self,
 980         tgt_expr: ExprId,
 981         receiver: ExprId,
 982         args: &[ExprId],
 983         method_name: &Name,
 984         generic_args: Option<&GenericArgs>,
 985         expected: &Expectation,
 986     ) -> Ty {
 987         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 988         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
 989
 990         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 991
 992         let resolved = self.resolver.krate().and_then(|krate| {
 993             method_resolution::lookup_method(
 994                 &canonicalized_receiver.value,
 995                 self.db,
 996                 self.trait_env.clone(),
 997                 krate,
 998                 &traits_in_scope,
 999                 self.resolver.module(),
1000                 method_name,
1001             )
1002         });
1003         let (receiver_ty, method_ty, substs) = match resolved {
1004             Some((ty, func)) => {
1005                 let ty = canonicalized_receiver.decanonicalize_ty(&mut self.table, ty);
1006                 let generics = generics(self.db.upcast(), func.into());
1007                 let substs = self.substs_for_method_call(generics, generic_args, &ty);
1008                 self.write_method_resolution(tgt_expr, func, substs.clone());
1009                 (ty, self.db.value_ty(func.into()), substs)
1010             }
1011             None => (
1012                 receiver_ty,
1013                 Binders::empty(Interner, self.err_ty()),
1014                 Substitution::empty(Interner),
1015             ),
1016         };
1017         let method_ty = method_ty.substitute(Interner, &substs);
1018         self.register_obligations_for_call(&method_ty);
1019         let (formal_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
1020             Some(sig) => {
1021                 if !sig.params().is_empty() {
1022                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
1023                 } else {
1024                     (self.err_ty(), Vec::new(), sig.ret().clone())
1025                 }
1026             }
1027             None => (self.err_ty(), Vec::new(), self.err_ty()),
1028         };
1029         self.unify(&formal_receiver_ty, &receiver_ty);
1030
1031         let expected_inputs =
1032             self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
1033
1034         self.check_call_arguments(args, &expected_inputs, &param_tys);
1035         self.normalize_associated_types_in(ret_ty)
1036     }
1037
1038     fn expected_inputs_for_expected_output(
1039         &mut self,
1040         expected_output: &Expectation,
1041         output: Ty,
1042         inputs: Vec<Ty>,
1043     ) -> Vec<Ty> {
1044         if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
1045             self.table.fudge_inference(|table| {
1046                 if table.try_unify(&expected_ty, &output).is_ok() {
1047                     table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
1048                         chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
1049                         chalk_ir::VariableKind::Lifetime => {
1050                             var.to_lifetime(Interner).cast(Interner)
1051                         }
1052                         chalk_ir::VariableKind::Const(ty) => {
1053                             var.to_const(Interner, ty).cast(Interner)
1054                         }
1055                     })
1056                 } else {
1057                     Vec::new()
1058                 }
1059             })
1060         } else {
1061             Vec::new()
1062         }
1063     }
1064
1065     fn check_call_arguments(&mut self, args: &[ExprId], expected_inputs: &[Ty], param_tys: &[Ty]) {
1066         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
1067         // We do this in a pretty awful way: first we type-check any arguments
1068         // that are not closures, then we type-check the closures. This is so
1069         // that we have more information about the types of arguments when we
1070         // type-check the functions. This isn't really the right way to do this.
1071         for &check_closures in &[false, true] {
1072             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
1073             let expected_iter = expected_inputs
1074                 .iter()
1075                 .cloned()
1076                 .chain(param_iter.clone().skip(expected_inputs.len()));
1077             for ((&arg, param_ty), expected_ty) in args.iter().zip(param_iter).zip(expected_iter) {
1078                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
1079                 if is_closure != check_closures {
1080                     continue;
1081                 }
1082
1083                 // the difference between param_ty and expected here is that
1084                 // expected is the parameter when the expected *return* type is
1085                 // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
1086                 // the expected type is already `&[i32]`, whereas param_ty is
1087                 // still an unbound type variable. We don't always want to force
1088                 // the parameter to coerce to the expected type (for example in
1089                 // `coerce_unsize_expected_type_4`).
1090                 let param_ty = self.normalize_associated_types_in(param_ty);
1091                 let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
1092                 // infer with the expected type we have...
1093                 let ty = self.infer_expr_inner(arg, &expected);
1094
1095                 // then coerce to either the expected type or just the formal parameter type
1096                 let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
1097                     // if we are coercing to the expectation, unify with the
1098                     // formal parameter type to connect everything
1099                     self.unify(&ty, &param_ty);
1100                     ty
1101                 } else {
1102                     param_ty
1103                 };
1104                 if !coercion_target.is_unknown() {
1105                     if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
1106                         self.result.type_mismatches.insert(
1107                             arg.into(),
1108                             TypeMismatch { expected: coercion_target, actual: ty.clone() },
1109                         );
1110                     }
1111                 }
1112             }
1113         }
1114     }
1115
1116     fn substs_for_method_call(
1117         &mut self,
1118         def_generics: Generics,
1119         generic_args: Option<&GenericArgs>,
1120         receiver_ty: &Ty,
1121     ) -> Substitution {
1122         let (parent_params, self_params, type_params, impl_trait_params) =
1123             def_generics.provenance_split();
1124         assert_eq!(self_params, 0); // method shouldn't have another Self param
1125         let total_len = parent_params + type_params + impl_trait_params;
1126         let mut substs = Vec::with_capacity(total_len);
1127         // Parent arguments are unknown, except for the receiver type
1128         for (_id, param) in def_generics.iter_parent() {
1129             if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
1130                 substs.push(receiver_ty.clone());
1131             } else {
1132                 substs.push(self.table.new_type_var());
1133             }
1134         }
1135         // handle provided type arguments
1136         if let Some(generic_args) = generic_args {
1137             // if args are provided, it should be all of them, but we can't rely on that
1138             for arg in generic_args
1139                 .args
1140                 .iter()
1141                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
1142                 .take(type_params)
1143             {
1144                 match arg {
1145                     GenericArg::Type(type_ref) => {
1146                         let ty = self.make_ty(type_ref);
1147                         substs.push(ty);
1148                     }
1149                     GenericArg::Lifetime(_) => {}
1150                 }
1151             }
1152         };
1153         let supplied_params = substs.len();
1154         for _ in supplied_params..total_len {
1155             substs.push(self.table.new_type_var());
1156         }
1157         assert_eq!(substs.len(), total_len);
1158         Substitution::from_iter(Interner, substs)
1159     }
1160
1161     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1162         let callable_ty = self.resolve_ty_shallow(callable_ty);
1163         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(Interner) {
1164             let def: CallableDefId = from_chalk(self.db, *fn_def);
1165             let generic_predicates = self.db.generic_predicates(def.into());
1166             for predicate in generic_predicates.iter() {
1167                 let (predicate, binders) = predicate
1168                     .clone()
1169                     .substitute(Interner, parameters)
1170                     .into_value_and_skipped_binders();
1171                 always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
1172                 self.push_obligation(predicate.cast(Interner));
1173             }
1174             // add obligation for trait implementation, if this is a trait method
1175             match def {
1176                 CallableDefId::FunctionId(f) => {
1177                     if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
1178                         // construct a TraitRef
1179                         let substs = crate::subst_prefix(
1180                             &*parameters,
1181                             generics(self.db.upcast(), trait_.into()).len(),
1182                         );
1183                         self.push_obligation(
1184                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1185                                 .cast(Interner),
1186                         );
1187                     }
1188                 }
1189                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1190             }
1191         }
1192     }
1193
1194     fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
1195         let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
1196         let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
1197         match op {
1198             BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
1199                 Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
1200             }
1201             BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
1202             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
1203                 // all integer combinations are valid here
1204                 if matches!(
1205                     lhs_ty.kind(Interner),
1206                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1207                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1208                 ) && matches!(
1209                     rhs_ty.kind(Interner),
1210                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
1211                         | TyKind::InferenceVar(_, TyVariableKind::Integer)
1212                 ) {
1213                     Some(lhs_ty)
1214                 } else {
1215                     None
1216                 }
1217             }
1218             BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
1219                 // (int, int) | (uint, uint) | (float, float)
1220                 (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
1221                 | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
1222                 | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
1223                     Some(rhs_ty)
1224                 }
1225                 // ({int}, int) | ({int}, uint)
1226                 (
1227                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1228                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1229                 ) => Some(rhs_ty),
1230                 // (int, {int}) | (uint, {int})
1231                 (
1232                     TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
1233                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1234                 ) => Some(lhs_ty),
1235                 // ({float} | float)
1236                 (
1237                     TyKind::InferenceVar(_, TyVariableKind::Float),
1238                     TyKind::Scalar(Scalar::Float(_)),
1239                 ) => Some(rhs_ty),
1240                 // (float, {float})
1241                 (
1242                     TyKind::Scalar(Scalar::Float(_)),
1243                     TyKind::InferenceVar(_, TyVariableKind::Float),
1244                 ) => Some(lhs_ty),
1245                 // ({int}, {int}) | ({float}, {float})
1246                 (
1247                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1248                     TyKind::InferenceVar(_, TyVariableKind::Integer),
1249                 )
1250                 | (
1251                     TyKind::InferenceVar(_, TyVariableKind::Float),
1252                     TyKind::InferenceVar(_, TyVariableKind::Float),
1253                 ) => Some(rhs_ty),
1254                 _ => None,
1255             },
1256         }
1257     }
1258
1259     fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
1260         Some(match op {
1261             BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
1262             BinaryOp::Assignment { op: None } => lhs_ty,
1263             BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
1264                 .resolve_ty_shallow(&lhs_ty)
1265                 .kind(Interner)
1266             {
1267                 TyKind::Scalar(_) | TyKind::Str => lhs_ty,
1268                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1269                 _ => return None,
1270             },
1271             BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
1272             BinaryOp::CmpOp(CmpOp::Ord { .. })
1273             | BinaryOp::Assignment { op: Some(_) }
1274             | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
1275                 TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
1276                 TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
1277                 _ => return None,
1278             },
1279         })
1280     }
1281
1282     fn resolve_binop_method(&self, op: BinaryOp) -> Option<FunctionId> {
1283         let (name, lang_item) = match op {
1284             BinaryOp::LogicOp(_) => return None,
1285             BinaryOp::ArithOp(aop) => match aop {
1286                 ArithOp::Add => (name!(add), name!(add)),
1287                 ArithOp::Mul => (name!(mul), name!(mul)),
1288                 ArithOp::Sub => (name!(sub), name!(sub)),
1289                 ArithOp::Div => (name!(div), name!(div)),
1290                 ArithOp::Rem => (name!(rem), name!(rem)),
1291                 ArithOp::Shl => (name!(shl), name!(shl)),
1292                 ArithOp::Shr => (name!(shr), name!(shr)),
1293                 ArithOp::BitXor => (name!(bitxor), name!(bitxor)),
1294                 ArithOp::BitOr => (name!(bitor), name!(bitor)),
1295                 ArithOp::BitAnd => (name!(bitand), name!(bitand)),
1296             },
1297             BinaryOp::Assignment { op: Some(aop) } => match aop {
1298                 ArithOp::Add => (name!(add_assign), name!(add_assign)),
1299                 ArithOp::Mul => (name!(mul_assign), name!(mul_assign)),
1300                 ArithOp::Sub => (name!(sub_assign), name!(sub_assign)),
1301                 ArithOp::Div => (name!(div_assign), name!(div_assign)),
1302                 ArithOp::Rem => (name!(rem_assign), name!(rem_assign)),
1303                 ArithOp::Shl => (name!(shl_assign), name!(shl_assign)),
1304                 ArithOp::Shr => (name!(shr_assign), name!(shr_assign)),
1305                 ArithOp::BitXor => (name!(bitxor_assign), name!(bitxor_assign)),
1306                 ArithOp::BitOr => (name!(bitor_assign), name!(bitor_assign)),
1307                 ArithOp::BitAnd => (name!(bitand_assign), name!(bitand_assign)),
1308             },
1309             BinaryOp::CmpOp(cop) => match cop {
1310                 CmpOp::Eq { negated: false } => (name!(eq), name!(eq)),
1311                 CmpOp::Eq { negated: true } => (name!(ne), name!(eq)),
1312                 CmpOp::Ord { ordering: Ordering::Less, strict: false } => {
1313                     (name!(le), name!(partial_ord))
1314                 }
1315                 CmpOp::Ord { ordering: Ordering::Less, strict: true } => {
1316                     (name!(lt), name!(partial_ord))
1317                 }
1318                 CmpOp::Ord { ordering: Ordering::Greater, strict: false } => {
1319                     (name!(ge), name!(partial_ord))
1320                 }
1321                 CmpOp::Ord { ordering: Ordering::Greater, strict: true } => {
1322                     (name!(gt), name!(partial_ord))
1323                 }
1324             },
1325             BinaryOp::Assignment { op: None } => return None,
1326         };
1327
1328         let trait_ = self.resolve_lang_item(lang_item)?.as_trait()?;
1329
1330         self.db.trait_data(trait_).method_by_name(&name)
1331     }
1332 }