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