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