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