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