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.check_canceled();
 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))
 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                 if let Some(t) = expected.only_has_type(&mut self.table) {
 288                     self.coerce(&closure_ty, &t);
 289                 }
 290
 291                 // Now go through the argument patterns
 292                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 293                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 294                 }
 295
 296                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 297                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 298
 299                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 300
 301                 self.diverges = prev_diverges;
 302                 self.return_ty = prev_ret_ty;
 303
 304                 closure_ty
 305             }
 306             Expr::Call { callee, args } => {
 307                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 308                 let canonicalized = self.canonicalize(callee_ty.clone());
 309                 let mut derefs = autoderef(
 310                     self.db,
 311                     self.resolver.krate(),
 312                     InEnvironment {
 313                         goal: canonicalized.value.clone(),
 314                         environment: self.table.trait_env.env.clone(),
 315                     },
 316                 );
 317                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
 318                     .find_map(|callee_deref_ty| {
 319                         self.callable_sig(
 320                             &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 321                             args.len(),
 322                         )
 323                     })
 324                     .unwrap_or((Vec::new(), self.err_ty()));
 325                 self.register_obligations_for_call(&callee_ty);
 326                 self.check_call_arguments(args, &param_tys);
 327                 self.normalize_associated_types_in(ret_ty)
 328             }
 329             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 330                 .infer_method_call(
 331                     tgt_expr,
 332                     *receiver,
 333                     &args,
 334                     &method_name,
 335                     generic_args.as_deref(),
 336                 ),
 337             Expr::Match { expr, arms } => {
 338                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 339
 340                 let mut result_ty = if arms.is_empty() {
 341                     TyKind::Never.intern(&Interner)
 342                 } else {
 343                     self.table.new_type_var()
 344                 };
 345
 346                 let matchee_diverges = self.diverges;
 347                 let mut all_arms_diverge = Diverges::Always;
 348
 349                 for arm in arms {
 350                     self.diverges = Diverges::Maybe;
 351                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 352                     if let Some(guard_expr) = arm.guard {
 353                         self.infer_expr(
 354                             guard_expr,
 355                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 356                         );
 357                     }
 358
 359                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 360                     all_arms_diverge &= self.diverges;
 361                     result_ty = self.coerce_merge_branch(Some(arm.expr), &result_ty, &arm_ty);
 362                 }
 363
 364                 self.diverges = matchee_diverges | all_arms_diverge;
 365
 366                 result_ty
 367             }
 368             Expr::Path(p) => {
 369                 // FIXME this could be more efficient...
 370                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 371                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
 372             }
 373             Expr::Continue { .. } => TyKind::Never.intern(&Interner),
 374             Expr::Break { expr, label } => {
 375                 let last_ty =
 376                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 377                         ctxt.break_ty.clone()
 378                     } else {
 379                         self.err_ty()
 380                     };
 381
 382                 let val_ty = if let Some(expr) = expr {
 383                     self.infer_expr(*expr, &Expectation::none())
 384                 } else {
 385                     TyBuilder::unit()
 386                 };
 387
 388                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 389                 let merged_type = self.coerce_merge_branch(*expr, &last_ty, &val_ty);
 390
 391                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 392                     ctxt.break_ty = merged_type;
 393                     ctxt.may_break = true;
 394                 } else {
 395                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 396                         expr: tgt_expr,
 397                     });
 398                 }
 399                 TyKind::Never.intern(&Interner)
 400             }
 401             Expr::Return { expr } => {
 402                 if let Some(expr) = expr {
 403                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 404                 } else {
 405                     let unit = TyBuilder::unit();
 406                     self.coerce(&unit, &self.return_ty.clone());
 407                 }
 408                 TyKind::Never.intern(&Interner)
 409             }
 410             Expr::Yield { expr } => {
 411                 // FIXME: track yield type for coercion
 412                 if let Some(expr) = expr {
 413                     self.infer_expr(*expr, &Expectation::none());
 414                 }
 415                 TyKind::Never.intern(&Interner)
 416             }
 417             Expr::RecordLit { path, fields, spread } => {
 418                 let (ty, def_id) = self.resolve_variant(path.as_deref());
 419                 if let Some(variant) = def_id {
 420                     self.write_variant_resolution(tgt_expr.into(), variant);
 421                 }
 422
 423                 if let Some(t) = expected.only_has_type(&mut self.table) {
 424                     self.unify(&ty, &t);
 425                 }
 426
 427                 let substs = ty
 428                     .as_adt()
 429                     .map(|(_, s)| s.clone())
 430                     .unwrap_or_else(|| Substitution::empty(&Interner));
 431                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 432                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 433                 for field in fields.iter() {
 434                     let field_def =
 435                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 436                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 437                             None => {
 438                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 439                                     expr: field.expr,
 440                                 });
 441                                 None
 442                             }
 443                         });
 444                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 445                         field_types[it.local_id].clone().substitute(&Interner, &substs)
 446                     });
 447                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 448                 }
 449                 if let Some(expr) = spread {
 450                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 451                 }
 452                 ty
 453             }
 454             Expr::Field { expr, name } => {
 455                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 456                 let canonicalized = self.canonicalize(receiver_ty);
 457                 let ty = autoderef::autoderef(
 458                     self.db,
 459                     self.resolver.krate(),
 460                     InEnvironment {
 461                         goal: canonicalized.value.clone(),
 462                         environment: self.trait_env.env.clone(),
 463                     },
 464                 )
 465                 .find_map(|derefed_ty| {
 466                     let def_db = self.db.upcast();
 467                     let module = self.resolver.module();
 468                     let is_visible = |field_id: &FieldId| {
 469                         module
 470                             .map(|mod_id| {
 471                                 self.db.field_visibilities(field_id.parent)[field_id.local_id]
 472                                     .is_visible_from(def_db, mod_id)
 473                             })
 474                             .unwrap_or(true)
 475                     };
 476                     match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
 477                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
 478                             substs
 479                                 .as_slice(&Interner)
 480                                 .get(idx)
 481                                 .map(|a| a.assert_ty_ref(&Interner))
 482                                 .cloned()
 483                         }),
 484                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 485                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 486                             let field = FieldId { parent: (*s).into(), local_id };
 487                             if is_visible(&field) {
 488                                 self.write_field_resolution(tgt_expr, field);
 489                                 Some(
 490                                     self.db.field_types((*s).into())[field.local_id]
 491                                         .clone()
 492                                         .substitute(&Interner, &parameters),
 493                                 )
 494                             } else {
 495                                 None
 496                             }
 497                         }
 498                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 499                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 500                             let field = FieldId { parent: (*u).into(), local_id };
 501                             if is_visible(&field) {
 502                                 self.write_field_resolution(tgt_expr, field);
 503                                 Some(
 504                                     self.db.field_types((*u).into())[field.local_id]
 505                                         .clone()
 506                                         .substitute(&Interner, &parameters),
 507                                 )
 508                             } else {
 509                                 None
 510                             }
 511                         }
 512                         _ => None,
 513                     }
 514                 })
 515                 .unwrap_or(self.err_ty());
 516                 let ty = self.insert_type_vars(ty);
 517                 self.normalize_associated_types_in(ty)
 518             }
 519             Expr::Await { expr } => {
 520                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 521                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 522             }
 523             Expr::Try { expr } => {
 524                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 525                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 526             }
 527             Expr::Cast { expr, type_ref } => {
 528                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 529                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 530                 let cast_ty = self.make_ty(type_ref);
 531                 // FIXME check the cast...
 532                 cast_ty
 533             }
 534             Expr::Ref { expr, rawness, mutability } => {
 535                 let mutability = lower_to_chalk_mutability(*mutability);
 536                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 537                     .only_has_type(&mut self.table)
 538                     .as_ref()
 539                     .and_then(|t| t.as_reference_or_ptr())
 540                 {
 541                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 542                         // FIXME: record type error - expected mut reference but found shared ref,
 543                         // which cannot be coerced
 544                     }
 545                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 546                         // FIXME: record type error - expected reference but found ptr,
 547                         // which cannot be coerced
 548                     }
 549                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 550                 } else {
 551                     Expectation::none()
 552                 };
 553                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 554                 match rawness {
 555                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 556                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 557                 }
 558                 .intern(&Interner)
 559             }
 560             Expr::Box { expr } => {
 561                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 562                 if let Some(box_) = self.resolve_boxed_box() {
 563                     TyBuilder::adt(self.db, box_)
 564                         .push(inner_ty)
 565                         .fill_with_defaults(self.db, || self.table.new_type_var())
 566                         .build()
 567                 } else {
 568                     self.err_ty()
 569                 }
 570             }
 571             Expr::UnaryOp { expr, op } => {
 572                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 573                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 574                 match op {
 575                     UnaryOp::Deref => match self.resolver.krate() {
 576                         Some(krate) => {
 577                             let canonicalized = self.canonicalize(inner_ty);
 578                             match autoderef::deref(
 579                                 self.db,
 580                                 krate,
 581                                 InEnvironment {
 582                                     goal: &canonicalized.value,
 583                                     environment: self.trait_env.env.clone(),
 584                                 },
 585                             ) {
 586                                 Some(derefed_ty) => {
 587                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 588                                 }
 589                                 None => self.err_ty(),
 590                             }
 591                         }
 592                         None => self.err_ty(),
 593                     },
 594                     UnaryOp::Neg => {
 595                         match inner_ty.kind(&Interner) {
 596                             // Fast path for builtins
 597                             TyKind::Scalar(Scalar::Int(_))
 598                             | TyKind::Scalar(Scalar::Uint(_))
 599                             | TyKind::Scalar(Scalar::Float(_))
 600                             | TyKind::InferenceVar(_, TyVariableKind::Integer)
 601                             | TyKind::InferenceVar(_, TyVariableKind::Float) => inner_ty,
 602                             // Otherwise we resolve via the std::ops::Neg trait
 603                             _ => self
 604                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 605                         }
 606                     }
 607                     UnaryOp::Not => {
 608                         match inner_ty.kind(&Interner) {
 609                             // Fast path for builtins
 610                             TyKind::Scalar(Scalar::Bool)
 611                             | TyKind::Scalar(Scalar::Int(_))
 612                             | TyKind::Scalar(Scalar::Uint(_))
 613                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 614                             // Otherwise we resolve via the std::ops::Not trait
 615                             _ => self
 616                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 617                         }
 618                     }
 619                 }
 620             }
 621             Expr::BinaryOp { lhs, rhs, op } => match op {
 622                 Some(op) => {
 623                     let lhs_expectation = match op {
 624                         BinaryOp::LogicOp(..) => {
 625                             Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
 626                         }
 627                         _ => Expectation::none(),
 628                     };
 629                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 630                     let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
 631                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 632                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 633                     let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
 634
 635                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 636
 637                     if ret.is_unknown() {
 638                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 639
 640                         self.resolve_associated_type_with_params(
 641                             lhs_ty,
 642                             self.resolve_binary_op_output(op),
 643                             &[rhs_ty],
 644                         )
 645                     } else {
 646                         ret
 647                     }
 648                 }
 649                 _ => self.err_ty(),
 650             },
 651             Expr::Range { lhs, rhs, range_type } => {
 652                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 653                 let rhs_expect = lhs_ty
 654                     .as_ref()
 655                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 656                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 657                 match (range_type, lhs_ty, rhs_ty) {
 658                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 659                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 660                         None => self.err_ty(),
 661                     },
 662                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 663                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 664                         None => self.err_ty(),
 665                     },
 666                     (RangeOp::Inclusive, None, Some(ty)) => {
 667                         match self.resolve_range_to_inclusive() {
 668                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 669                             None => self.err_ty(),
 670                         }
 671                     }
 672                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 673                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 674                         None => self.err_ty(),
 675                     },
 676                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 677                         match self.resolve_range_inclusive() {
 678                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 679                             None => self.err_ty(),
 680                         }
 681                     }
 682                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 683                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 684                         None => self.err_ty(),
 685                     },
 686                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 687                 }
 688             }
 689             Expr::Index { base, index } => {
 690                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 691                 let index_ty = self.infer_expr(*index, &Expectation::none());
 692
 693                 if let (Some(index_trait), Some(krate)) =
 694                     (self.resolve_ops_index(), self.resolver.krate())
 695                 {
 696                     let canonicalized = self.canonicalize(base_ty);
 697                     let self_ty = method_resolution::resolve_indexing_op(
 698                         self.db,
 699                         &canonicalized.value,
 700                         self.trait_env.clone(),
 701                         krate,
 702                         index_trait,
 703                     );
 704                     let self_ty =
 705                         self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
 706                     self.resolve_associated_type_with_params(
 707                         self_ty,
 708                         self.resolve_ops_index_output(),
 709                         &[index_ty],
 710                     )
 711                 } else {
 712                     self.err_ty()
 713                 }
 714             }
 715             Expr::Tuple { exprs } => {
 716                 let mut tys = match expected
 717                     .only_has_type(&mut self.table)
 718                     .as_ref()
 719                     .map(|t| t.kind(&Interner))
 720                 {
 721                     Some(TyKind::Tuple(_, substs)) => substs
 722                         .iter(&Interner)
 723                         .map(|a| a.assert_ty_ref(&Interner).clone())
 724                         .chain(repeat_with(|| self.table.new_type_var()))
 725                         .take(exprs.len())
 726                         .collect::<Vec<_>>(),
 727                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 728                 };
 729
 730                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 731                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 732                 }
 733
 734                 TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
 735             }
 736             Expr::Array(array) => {
 737                 let elem_ty =
 738                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(&Interner)) {
 739                         Some(TyKind::Array(st, _)) | Some(TyKind::Slice(st)) => st.clone(),
 740                         _ => self.table.new_type_var(),
 741                     };
 742
 743                 let len = match array {
 744                     Array::ElementList(items) => {
 745                         for expr in items.iter() {
 746                             // FIXME: use CoerceMany (coerce_merge_branch)
 747                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
 748                         }
 749                         Some(items.len() as u64)
 750                     }
 751                     Array::Repeat { initializer, repeat } => {
 752                         self.infer_expr_coerce(
 753                             *initializer,
 754                             &Expectation::has_type(elem_ty.clone()),
 755                         );
 756                         self.infer_expr(
 757                             *repeat,
 758                             &Expectation::has_type(
 759                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
 760                             ),
 761                         );
 762
 763                         let repeat_expr = &self.body.exprs[*repeat];
 764                         consteval::eval_usize(repeat_expr)
 765                     }
 766                 };
 767
 768                 TyKind::Array(elem_ty, consteval::usize_const(len)).intern(&Interner)
 769             }
 770             Expr::Literal(lit) => match lit {
 771                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
 772                 Literal::String(..) => {
 773                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(&Interner))
 774                         .intern(&Interner)
 775                 }
 776                 Literal::ByteString(bs) => {
 777                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
 778
 779                     let len = consteval::usize_const(Some(bs.len() as u64));
 780
 781                     let array_type = TyKind::Array(byte_type, len).intern(&Interner);
 782                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
 783                 }
 784                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
 785                 Literal::Int(_v, ty) => match ty {
 786                     Some(int_ty) => {
 787                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 788                             .intern(&Interner)
 789                     }
 790                     None => self.table.new_integer_var(),
 791                 },
 792                 Literal::Uint(_v, ty) => match ty {
 793                     Some(int_ty) => {
 794                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 795                             .intern(&Interner)
 796                     }
 797                     None => self.table.new_integer_var(),
 798                 },
 799                 Literal::Float(_v, ty) => match ty {
 800                     Some(float_ty) => {
 801                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 802                             .intern(&Interner)
 803                     }
 804                     None => self.table.new_float_var(),
 805                 },
 806             },
 807             Expr::MacroStmts { tail } => self.infer_expr(*tail, expected),
 808         };
 809         // use a new type variable if we got unknown here
 810         let ty = self.insert_type_vars_shallow(ty);
 811         self.write_expr_ty(tgt_expr, ty.clone());
 812         ty
 813     }
 814
 815     fn infer_block(
 816         &mut self,
 817         statements: &[Statement],
 818         tail: Option<ExprId>,
 819         expected: &Expectation,
 820     ) -> Ty {
 821         for stmt in statements {
 822             match stmt {
 823                 Statement::Let { pat, type_ref, initializer } => {
 824                     let decl_ty =
 825                         type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(self.err_ty());
 826
 827                     // Always use the declared type when specified
 828                     let mut ty = decl_ty.clone();
 829
 830                     if let Some(expr) = initializer {
 831                         let actual_ty =
 832                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 833                         if decl_ty.is_unknown() {
 834                             ty = actual_ty;
 835                         }
 836                     }
 837
 838                     self.infer_pat(*pat, &ty, BindingMode::default());
 839                 }
 840                 Statement::Expr { expr, .. } => {
 841                     self.infer_expr(*expr, &Expectation::none());
 842                 }
 843             }
 844         }
 845
 846         let ty = if let Some(expr) = tail {
 847             self.infer_expr_coerce(expr, expected)
 848         } else {
 849             // Citing rustc: if there is no explicit tail expression,
 850             // that is typically equivalent to a tail expression
 851             // of `()` -- except if the block diverges. In that
 852             // case, there is no value supplied from the tail
 853             // expression (assuming there are no other breaks,
 854             // this implies that the type of the block will be
 855             // `!`).
 856             if self.diverges.is_always() {
 857                 // we don't even make an attempt at coercion
 858                 self.table.new_maybe_never_var()
 859             } else {
 860                 if let Some(t) = expected.only_has_type(&mut self.table) {
 861                     self.coerce(&TyBuilder::unit(), &t);
 862                 }
 863                 TyBuilder::unit()
 864             }
 865         };
 866         ty
 867     }
 868
 869     fn infer_method_call(
 870         &mut self,
 871         tgt_expr: ExprId,
 872         receiver: ExprId,
 873         args: &[ExprId],
 874         method_name: &Name,
 875         generic_args: Option<&GenericArgs>,
 876     ) -> Ty {
 877         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 878         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
 879
 880         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 881
 882         let resolved = self.resolver.krate().and_then(|krate| {
 883             method_resolution::lookup_method(
 884                 &canonicalized_receiver.value,
 885                 self.db,
 886                 self.trait_env.clone(),
 887                 krate,
 888                 &traits_in_scope,
 889                 self.resolver.module(),
 890                 method_name,
 891             )
 892         });
 893         let (derefed_receiver_ty, method_ty, substs) = match resolved {
 894             Some((ty, func)) => {
 895                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 896                 let generics = generics(self.db.upcast(), func.into());
 897                 let substs = self.substs_for_method_call(generics, generic_args, &ty);
 898                 self.write_method_resolution(tgt_expr, func, substs.clone());
 899                 (ty, self.db.value_ty(func.into()), substs)
 900             }
 901             None => (
 902                 receiver_ty,
 903                 Binders::empty(&Interner, self.err_ty()),
 904                 Substitution::empty(&Interner),
 905             ),
 906         };
 907         let method_ty = method_ty.substitute(&Interner, &substs);
 908         self.register_obligations_for_call(&method_ty);
 909         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 910             Some(sig) => {
 911                 if !sig.params().is_empty() {
 912                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 913                 } else {
 914                     (self.err_ty(), Vec::new(), sig.ret().clone())
 915                 }
 916             }
 917             None => (self.err_ty(), Vec::new(), self.err_ty()),
 918         };
 919         // Apply autoref so the below unification works correctly
 920         // FIXME: return correct autorefs from lookup_method
 921         let actual_receiver_ty = match self.resolve_ty_shallow(&expected_receiver_ty).as_reference()
 922         {
 923             Some((_, lifetime, mutability)) => {
 924                 TyKind::Ref(mutability, lifetime, derefed_receiver_ty).intern(&Interner)
 925             }
 926             _ => derefed_receiver_ty,
 927         };
 928         self.unify(&expected_receiver_ty, &actual_receiver_ty);
 929
 930         self.check_call_arguments(args, &param_tys);
 931         self.normalize_associated_types_in(ret_ty)
 932     }
 933
 934     fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
 935         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 936         // We do this in a pretty awful way: first we type-check any arguments
 937         // that are not closures, then we type-check the closures. This is so
 938         // that we have more information about the types of arguments when we
 939         // type-check the functions. This isn't really the right way to do this.
 940         for &check_closures in &[false, true] {
 941             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
 942             for (&arg, param_ty) in args.iter().zip(param_iter) {
 943                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
 944                 if is_closure != check_closures {
 945                     continue;
 946                 }
 947
 948                 let param_ty = self.normalize_associated_types_in(param_ty);
 949                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
 950             }
 951         }
 952     }
 953
 954     fn substs_for_method_call(
 955         &mut self,
 956         def_generics: Generics,
 957         generic_args: Option<&GenericArgs>,
 958         receiver_ty: &Ty,
 959     ) -> Substitution {
 960         let (parent_params, self_params, type_params, impl_trait_params) =
 961             def_generics.provenance_split();
 962         assert_eq!(self_params, 0); // method shouldn't have another Self param
 963         let total_len = parent_params + type_params + impl_trait_params;
 964         let mut substs = Vec::with_capacity(total_len);
 965         // Parent arguments are unknown, except for the receiver type
 966         for (_id, param) in def_generics.iter_parent() {
 967             if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
 968                 substs.push(receiver_ty.clone());
 969             } else {
 970                 substs.push(self.table.new_type_var());
 971             }
 972         }
 973         // handle provided type arguments
 974         if let Some(generic_args) = generic_args {
 975             // if args are provided, it should be all of them, but we can't rely on that
 976             for arg in generic_args
 977                 .args
 978                 .iter()
 979                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 980                 .take(type_params)
 981             {
 982                 match arg {
 983                     GenericArg::Type(type_ref) => {
 984                         let ty = self.make_ty(type_ref);
 985                         substs.push(ty);
 986                     }
 987                     GenericArg::Lifetime(_) => {}
 988                 }
 989             }
 990         };
 991         let supplied_params = substs.len();
 992         for _ in supplied_params..total_len {
 993             substs.push(self.table.new_type_var());
 994         }
 995         assert_eq!(substs.len(), total_len);
 996         Substitution::from_iter(&Interner, substs)
 997     }
 998
 999     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
1000         let callable_ty = self.resolve_ty_shallow(&callable_ty);
1001         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(&Interner) {
1002             let def: CallableDefId = from_chalk(self.db, *fn_def);
1003             let generic_predicates = self.db.generic_predicates(def.into());
1004             for predicate in generic_predicates.iter() {
1005                 let (predicate, binders) = predicate
1006                     .clone()
1007                     .substitute(&Interner, parameters)
1008                     .into_value_and_skipped_binders();
1009                 always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
1010                 self.push_obligation(predicate.cast(&Interner));
1011             }
1012             // add obligation for trait implementation, if this is a trait method
1013             match def {
1014                 CallableDefId::FunctionId(f) => {
1015                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
1016                     {
1017                         // construct a TraitRef
1018                         let substs = crate::subst_prefix(
1019                             &*parameters,
1020                             generics(self.db.upcast(), trait_.into()).len(),
1021                         );
1022                         self.push_obligation(
1023                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1024                                 .cast(&Interner),
1025                         );
1026                     }
1027                 }
1028                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1029             }
1030         }
1031     }
1032 }