crates/hir_ty/src/infer/expr.rs

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