crates/hir_ty/src/infer/expr.rs

   1 //! Type inference for expressions.
   2
   3 use std::iter::{repeat, repeat_with};
   4 use std::{mem, sync::Arc};
   5
   6 use chalk_ir::{cast::Cast, fold::Shift, Mutability, TyVariableKind};
   7 use hir_def::{
   8     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
   9     path::{GenericArg, GenericArgs},
  10     resolver::resolver_for_expr,
  11     AssocContainerId, FieldId, Lookup,
  12 };
  13 use hir_expand::name::{name, Name};
  14 use stdx::always;
  15 use syntax::ast::RangeOp;
  16
  17 use crate::{
  18     autoderef, consteval,
  19     lower::lower_to_chalk_mutability,
  20     mapping::from_chalk,
  21     method_resolution, op,
  22     primitive::{self, UintTy},
  23     static_lifetime, to_chalk_trait_id,
  24     traits::FnTrait,
  25     utils::{generics, Generics},
  26     AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, InEnvironment, Interner,
  27     ProjectionTyExt, Rawness, Scalar, Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
  28 };
  29
  30 use super::{
  31     find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
  32     InferenceDiagnostic, TypeMismatch,
  33 };
  34
  35 impl<'a> InferenceContext<'a> {
  36     pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
  37         let ty = self.infer_expr_inner(tgt_expr, expected);
  38         if self.resolve_ty_shallow(&ty).is_never() {
  39             // Any expression that produces a value of type `!` must have diverged
  40             self.diverges = Diverges::Always;
  41         }
  42         if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
  43             let could_unify = self.unify(&ty, &expected_ty);
  44             if !could_unify {
  45                 self.result.type_mismatches.insert(
  46                     tgt_expr.into(),
  47                     TypeMismatch { expected: expected_ty, actual: ty.clone() },
  48                 );
  49             }
  50         }
  51         ty
  52     }
  53
  54     /// Infer type of expression with possibly implicit coerce to the expected type.
  55     /// Return the type after possible coercion.
  56     pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
  57         let ty = self.infer_expr_inner(expr, expected);
  58         let ty = if let Some(target) = expected.only_has_type(&mut self.table) {
  59             if !self.coerce(&ty, &target) {
  60                 self.result
  61                     .type_mismatches
  62                     .insert(expr.into(), TypeMismatch { expected: target, actual: ty.clone() });
  63                 // Return actual type when type mismatch.
  64                 // This is needed for diagnostic when return type mismatch.
  65                 ty
  66             } else {
  67                 target
  68             }
  69         } else {
  70             ty
  71         };
  72
  73         ty
  74     }
  75
  76     fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
  77         let krate = self.resolver.krate()?;
  78         let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
  79         let output_assoc_type =
  80             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
  81
  82         let mut arg_tys = vec![];
  83         let arg_ty = TyBuilder::tuple(num_args)
  84             .fill(repeat_with(|| {
  85                 let arg = self.table.new_type_var();
  86                 arg_tys.push(arg.clone());
  87                 arg
  88             }))
  89             .build();
  90
  91         let projection = {
  92             let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
  93             if b.remaining() != 2 {
  94                 return None;
  95             }
  96             b.push(ty.clone()).push(arg_ty).build()
  97         };
  98
  99         let trait_env = self.trait_env.env.clone();
 100         let obligation = InEnvironment {
 101             goal: projection.trait_ref(self.db).cast(&Interner),
 102             environment: trait_env,
 103         };
 104         let canonical = self.canonicalize(obligation.clone());
 105         if self.db.trait_solve(krate, canonical.value.cast(&Interner)).is_some() {
 106             self.push_obligation(obligation.goal);
 107             let return_ty = self.table.normalize_projection_ty(projection);
 108             Some((arg_tys, return_ty))
 109         } else {
 110             None
 111         }
 112     }
 113
 114     pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
 115         match ty.callable_sig(self.db) {
 116             Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
 117             None => self.callable_sig_from_fn_trait(ty, num_args),
 118         }
 119     }
 120
 121     fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
 122         self.db.unwind_if_cancelled();
 123
 124         let body = Arc::clone(&self.body); // avoid borrow checker problem
 125         let ty = match &body[tgt_expr] {
 126             Expr::Missing => self.err_ty(),
 127             Expr::If { condition, then_branch, else_branch } => {
 128                 // if let is desugared to match, so this is always simple if
 129                 self.infer_expr(
 130                     *condition,
 131                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 132                 );
 133
 134                 let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 135                 let mut both_arms_diverge = Diverges::Always;
 136
 137                 let mut result_ty = self.table.new_type_var();
 138                 let then_ty = self.infer_expr_inner(*then_branch, expected);
 139                 both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
 140                 result_ty = self.coerce_merge_branch(Some(*then_branch), &result_ty, &then_ty);
 141                 let else_ty = match else_branch {
 142                     Some(else_branch) => self.infer_expr_inner(*else_branch, expected),
 143                     None => TyBuilder::unit(),
 144                 };
 145                 both_arms_diverge &= self.diverges;
 146                 // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
 147                 result_ty = self.coerce_merge_branch(*else_branch, &result_ty, &else_ty);
 148
 149                 self.diverges = condition_diverges | both_arms_diverge;
 150
 151                 result_ty
 152             }
 153             Expr::Block { statements, tail, label, id: _ } => {
 154                 let old_resolver = mem::replace(
 155                     &mut self.resolver,
 156                     resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
 157                 );
 158                 let ty = match label {
 159                     Some(_) => {
 160                         let break_ty = self.table.new_type_var();
 161                         self.breakables.push(BreakableContext {
 162                             may_break: false,
 163                             break_ty: break_ty.clone(),
 164                             label: label.map(|label| self.body[label].name.clone()),
 165                         });
 166                         let ty =
 167                             self.infer_block(statements, *tail, &Expectation::has_type(break_ty));
 168                         let ctxt = self.breakables.pop().expect("breakable stack broken");
 169                         if ctxt.may_break {
 170                             ctxt.break_ty
 171                         } else {
 172                             ty
 173                         }
 174                     }
 175                     None => self.infer_block(statements, *tail, expected),
 176                 };
 177                 self.resolver = old_resolver;
 178                 ty
 179             }
 180             Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
 181             Expr::TryBlock { body } => {
 182                 let _inner = self.infer_expr(*body, expected);
 183                 // FIXME should be std::result::Result<{inner}, _>
 184                 self.err_ty()
 185             }
 186             Expr::Async { body } => {
 187                 // Use the first type parameter as the output type of future.
 188                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
 189                 let inner_ty = self.infer_expr(*body, &Expectation::none());
 190                 let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
 191                 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 192                 TyKind::OpaqueType(opaque_ty_id, Substitution::from1(&Interner, inner_ty))
 193                     .intern(&Interner)
 194             }
 195             Expr::Loop { body, label } => {
 196                 self.breakables.push(BreakableContext {
 197                     may_break: false,
 198                     break_ty: self.table.new_type_var(),
 199                     label: label.map(|label| self.body[label].name.clone()),
 200                 });
 201                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 202
 203                 let ctxt = self.breakables.pop().expect("breakable stack broken");
 204                 if ctxt.may_break {
 205                     self.diverges = Diverges::Maybe;
 206                 }
 207
 208                 if ctxt.may_break {
 209                     ctxt.break_ty
 210                 } else {
 211                     TyKind::Never.intern(&Interner)
 212                 }
 213             }
 214             Expr::While { condition, body, label } => {
 215                 self.breakables.push(BreakableContext {
 216                     may_break: false,
 217                     break_ty: self.err_ty(),
 218                     label: label.map(|label| self.body[label].name.clone()),
 219                 });
 220                 // while let is desugared to a match loop, so this is always simple while
 221                 self.infer_expr(
 222                     *condition,
 223                     &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 224                 );
 225                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 226                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 227                 // the body may not run, so it diverging doesn't mean we diverge
 228                 self.diverges = Diverges::Maybe;
 229                 TyBuilder::unit()
 230             }
 231             Expr::For { iterable, body, pat, label } => {
 232                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 233
 234                 self.breakables.push(BreakableContext {
 235                     may_break: false,
 236                     break_ty: self.err_ty(),
 237                     label: label.map(|label| self.body[label].name.clone()),
 238                 });
 239                 let pat_ty =
 240                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 241
 242                 self.infer_pat(*pat, &pat_ty, BindingMode::default());
 243
 244                 self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
 245                 let _ctxt = self.breakables.pop().expect("breakable stack broken");
 246                 // the body may not run, so it diverging doesn't mean we diverge
 247                 self.diverges = Diverges::Maybe;
 248                 TyBuilder::unit()
 249             }
 250             Expr::Lambda { body, args, ret_type, arg_types } => {
 251                 assert_eq!(args.len(), arg_types.len());
 252
 253                 let mut sig_tys = Vec::new();
 254
 255                 // collect explicitly written argument types
 256                 for arg_type in arg_types.iter() {
 257                     let arg_ty = if let Some(type_ref) = arg_type {
 258                         self.make_ty(type_ref)
 259                     } else {
 260                         self.table.new_type_var()
 261                     };
 262                     sig_tys.push(arg_ty);
 263                 }
 264
 265                 // add return type
 266                 let ret_ty = match ret_type {
 267                     Some(type_ref) => self.make_ty(type_ref),
 268                     None => self.table.new_type_var(),
 269                 };
 270                 sig_tys.push(ret_ty.clone());
 271                 let sig_ty = TyKind::Function(FnPointer {
 272                     num_binders: 0,
 273                     sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
 274                     substitution: FnSubst(
 275                         Substitution::from_iter(&Interner, sig_tys.clone()).shifted_in(&Interner),
 276                     ),
 277                 })
 278                 .intern(&Interner);
 279                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
 280                 let closure_ty =
 281                     TyKind::Closure(closure_id, Substitution::from1(&Interner, sig_ty))
 282                         .intern(&Interner);
 283
 284                 // Eagerly try to relate the closure type with the expected
 285                 // type, otherwise we often won't have enough information to
 286                 // infer the body.
 287                 if let Some(t) = expected.only_has_type(&mut self.table) {
 288                     self.coerce(&closure_ty, &t);
 289                 }
 290
 291                 // Now go through the argument patterns
 292                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
 293                     self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
 294                 }
 295
 296                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
 297                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 298
 299                 self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
 300
 301                 self.diverges = prev_diverges;
 302                 self.return_ty = prev_ret_ty;
 303
 304                 closure_ty
 305             }
 306             Expr::Call { callee, args } => {
 307                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
 308                 let canonicalized = self.canonicalize(callee_ty.clone());
 309                 let mut derefs = autoderef(
 310                     self.db,
 311                     self.resolver.krate(),
 312                     InEnvironment {
 313                         goal: canonicalized.value.clone(),
 314                         environment: self.table.trait_env.env.clone(),
 315                     },
 316                 );
 317                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
 318                     .find_map(|callee_deref_ty| {
 319                         self.callable_sig(
 320                             &canonicalized.decanonicalize_ty(callee_deref_ty.value),
 321                             args.len(),
 322                         )
 323                     })
 324                     .unwrap_or((Vec::new(), self.err_ty()));
 325                 self.register_obligations_for_call(&callee_ty);
 326                 self.check_call_arguments(args, &param_tys);
 327                 self.normalize_associated_types_in(ret_ty)
 328             }
 329             Expr::MethodCall { receiver, args, method_name, generic_args } => self
 330                 .infer_method_call(tgt_expr, *receiver, args, method_name, generic_args.as_deref()),
 331             Expr::Match { expr, arms } => {
 332                 let input_ty = self.infer_expr(*expr, &Expectation::none());
 333
 334                 let expected = expected.adjust_for_branches(&mut self.table);
 335
 336                 let mut result_ty = if arms.is_empty() {
 337                     TyKind::Never.intern(&Interner)
 338                 } else {
 339                     match &expected {
 340                         Expectation::HasType(ty) => ty.clone(),
 341                         _ => self.table.new_type_var(),
 342                     }
 343                 };
 344
 345                 let matchee_diverges = self.diverges;
 346                 let mut all_arms_diverge = Diverges::Always;
 347
 348                 for arm in arms {
 349                     self.diverges = Diverges::Maybe;
 350                     let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
 351                     if let Some(guard_expr) = arm.guard {
 352                         self.infer_expr(
 353                             guard_expr,
 354                             &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner)),
 355                         );
 356                     }
 357
 358                     let arm_ty = self.infer_expr_inner(arm.expr, &expected);
 359                     all_arms_diverge &= self.diverges;
 360                     result_ty = self.coerce_merge_branch(Some(arm.expr), &result_ty, &arm_ty);
 361                 }
 362
 363                 self.diverges = matchee_diverges | all_arms_diverge;
 364
 365                 result_ty
 366             }
 367             Expr::Path(p) => {
 368                 // FIXME this could be more efficient...
 369                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
 370                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(self.err_ty())
 371             }
 372             Expr::Continue { .. } => TyKind::Never.intern(&Interner),
 373             Expr::Break { expr, label } => {
 374                 let last_ty =
 375                     if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 376                         ctxt.break_ty.clone()
 377                     } else {
 378                         self.err_ty()
 379                     };
 380
 381                 let val_ty = if let Some(expr) = expr {
 382                     self.infer_expr(*expr, &Expectation::none())
 383                 } else {
 384                     TyBuilder::unit()
 385                 };
 386
 387                 // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
 388                 let merged_type = self.coerce_merge_branch(*expr, &last_ty, &val_ty);
 389
 390                 if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
 391                     ctxt.break_ty = merged_type;
 392                     ctxt.may_break = true;
 393                 } else {
 394                     self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
 395                         expr: tgt_expr,
 396                     });
 397                 }
 398                 TyKind::Never.intern(&Interner)
 399             }
 400             Expr::Return { expr } => {
 401                 if let Some(expr) = expr {
 402                     self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
 403                 } else {
 404                     let unit = TyBuilder::unit();
 405                     self.coerce(&unit, &self.return_ty.clone());
 406                 }
 407                 TyKind::Never.intern(&Interner)
 408             }
 409             Expr::Yield { expr } => {
 410                 // FIXME: track yield type for coercion
 411                 if let Some(expr) = expr {
 412                     self.infer_expr(*expr, &Expectation::none());
 413                 }
 414                 TyKind::Never.intern(&Interner)
 415             }
 416             Expr::RecordLit { path, fields, spread } => {
 417                 let (ty, def_id) = self.resolve_variant(path.as_deref());
 418                 if let Some(variant) = def_id {
 419                     self.write_variant_resolution(tgt_expr.into(), variant);
 420                 }
 421
 422                 if let Some(t) = expected.only_has_type(&mut self.table) {
 423                     self.unify(&ty, &t);
 424                 }
 425
 426                 let substs = ty
 427                     .as_adt()
 428                     .map(|(_, s)| s.clone())
 429                     .unwrap_or_else(|| Substitution::empty(&Interner));
 430                 let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
 431                 let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
 432                 for field in fields.iter() {
 433                     let field_def =
 434                         variant_data.as_ref().and_then(|it| match it.field(&field.name) {
 435                             Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
 436                             None => {
 437                                 self.push_diagnostic(InferenceDiagnostic::NoSuchField {
 438                                     expr: field.expr,
 439                                 });
 440                                 None
 441                             }
 442                         });
 443                     let field_ty = field_def.map_or(self.err_ty(), |it| {
 444                         field_types[it.local_id].clone().substitute(&Interner, &substs)
 445                     });
 446                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
 447                 }
 448                 if let Some(expr) = spread {
 449                     self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
 450                 }
 451                 ty
 452             }
 453             Expr::Field { expr, name } => {
 454                 let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
 455                 let canonicalized = self.canonicalize(receiver_ty);
 456                 let ty = autoderef::autoderef(
 457                     self.db,
 458                     self.resolver.krate(),
 459                     InEnvironment {
 460                         goal: canonicalized.value.clone(),
 461                         environment: self.trait_env.env.clone(),
 462                     },
 463                 )
 464                 .find_map(|derefed_ty| {
 465                     let def_db = self.db.upcast();
 466                     let module = self.resolver.module();
 467                     let is_visible = |field_id: &FieldId| {
 468                         module
 469                             .map(|mod_id| {
 470                                 self.db.field_visibilities(field_id.parent)[field_id.local_id]
 471                                     .is_visible_from(def_db, mod_id)
 472                             })
 473                             .unwrap_or(true)
 474                     };
 475                     match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
 476                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
 477                             substs
 478                                 .as_slice(&Interner)
 479                                 .get(idx)
 480                                 .map(|a| a.assert_ty_ref(&Interner))
 481                                 .cloned()
 482                         }),
 483                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
 484                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
 485                             let field = FieldId { parent: (*s).into(), local_id };
 486                             if is_visible(&field) {
 487                                 self.write_field_resolution(tgt_expr, field);
 488                                 Some(
 489                                     self.db.field_types((*s).into())[field.local_id]
 490                                         .clone()
 491                                         .substitute(&Interner, &parameters),
 492                                 )
 493                             } else {
 494                                 None
 495                             }
 496                         }
 497                         TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
 498                             let local_id = self.db.union_data(*u).variant_data.field(name)?;
 499                             let field = FieldId { parent: (*u).into(), local_id };
 500                             if is_visible(&field) {
 501                                 self.write_field_resolution(tgt_expr, field);
 502                                 Some(
 503                                     self.db.field_types((*u).into())[field.local_id]
 504                                         .clone()
 505                                         .substitute(&Interner, &parameters),
 506                                 )
 507                             } else {
 508                                 None
 509                             }
 510                         }
 511                         _ => None,
 512                     }
 513                 })
 514                 .unwrap_or(self.err_ty());
 515                 let ty = self.insert_type_vars(ty);
 516                 self.normalize_associated_types_in(ty)
 517             }
 518             Expr::Await { expr } => {
 519                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 520                 self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
 521             }
 522             Expr::Try { expr } => {
 523                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 524                 self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
 525             }
 526             Expr::Cast { expr, type_ref } => {
 527                 // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
 528                 let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 529                 let cast_ty = self.make_ty(type_ref);
 530                 // FIXME check the cast...
 531                 cast_ty
 532             }
 533             Expr::Ref { expr, rawness, mutability } => {
 534                 let mutability = lower_to_chalk_mutability(*mutability);
 535                 let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
 536                     .only_has_type(&mut self.table)
 537                     .as_ref()
 538                     .and_then(|t| t.as_reference_or_ptr())
 539                 {
 540                     if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
 541                         // FIXME: record type error - expected mut reference but found shared ref,
 542                         // which cannot be coerced
 543                     }
 544                     if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
 545                         // FIXME: record type error - expected reference but found ptr,
 546                         // which cannot be coerced
 547                     }
 548                     Expectation::rvalue_hint(Ty::clone(exp_inner))
 549                 } else {
 550                     Expectation::none()
 551                 };
 552                 let inner_ty = self.infer_expr_inner(*expr, &expectation);
 553                 match rawness {
 554                     Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
 555                     Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
 556                 }
 557                 .intern(&Interner)
 558             }
 559             Expr::Box { expr } => {
 560                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 561                 if let Some(box_) = self.resolve_boxed_box() {
 562                     TyBuilder::adt(self.db, box_)
 563                         .push(inner_ty)
 564                         .fill_with_defaults(self.db, || self.table.new_type_var())
 565                         .build()
 566                 } else {
 567                     self.err_ty()
 568                 }
 569             }
 570             Expr::UnaryOp { expr, op } => {
 571                 let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
 572                 let inner_ty = self.resolve_ty_shallow(&inner_ty);
 573                 match op {
 574                     UnaryOp::Deref => match self.resolver.krate() {
 575                         Some(krate) => {
 576                             let canonicalized = self.canonicalize(inner_ty);
 577                             match autoderef::deref(
 578                                 self.db,
 579                                 krate,
 580                                 InEnvironment {
 581                                     goal: &canonicalized.value,
 582                                     environment: self.trait_env.env.clone(),
 583                                 },
 584                             ) {
 585                                 Some(derefed_ty) => {
 586                                     canonicalized.decanonicalize_ty(derefed_ty.value)
 587                                 }
 588                                 None => self.err_ty(),
 589                             }
 590                         }
 591                         None => self.err_ty(),
 592                     },
 593                     UnaryOp::Neg => {
 594                         match inner_ty.kind(&Interner) {
 595                             // Fast path for builtins
 596                             TyKind::Scalar(Scalar::Int(_))
 597                             | TyKind::Scalar(Scalar::Uint(_))
 598                             | TyKind::Scalar(Scalar::Float(_))
 599                             | TyKind::InferenceVar(_, TyVariableKind::Integer)
 600                             | TyKind::InferenceVar(_, TyVariableKind::Float) => inner_ty,
 601                             // Otherwise we resolve via the std::ops::Neg trait
 602                             _ => self
 603                                 .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
 604                         }
 605                     }
 606                     UnaryOp::Not => {
 607                         match inner_ty.kind(&Interner) {
 608                             // Fast path for builtins
 609                             TyKind::Scalar(Scalar::Bool)
 610                             | TyKind::Scalar(Scalar::Int(_))
 611                             | TyKind::Scalar(Scalar::Uint(_))
 612                             | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
 613                             // Otherwise we resolve via the std::ops::Not trait
 614                             _ => self
 615                                 .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
 616                         }
 617                     }
 618                 }
 619             }
 620             Expr::BinaryOp { lhs, rhs, op } => match op {
 621                 Some(op) => {
 622                     let lhs_expectation = match op {
 623                         BinaryOp::LogicOp(..) => {
 624                             Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(&Interner))
 625                         }
 626                         _ => Expectation::none(),
 627                     };
 628                     let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
 629                     let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
 630                     let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
 631                     let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
 632                     let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
 633
 634                     let ret = op::binary_op_return_ty(*op, lhs_ty.clone(), rhs_ty.clone());
 635
 636                     if ret.is_unknown() {
 637                         cov_mark::hit!(infer_expr_inner_binary_operator_overload);
 638
 639                         self.resolve_associated_type_with_params(
 640                             lhs_ty,
 641                             self.resolve_binary_op_output(op),
 642                             &[rhs_ty],
 643                         )
 644                     } else {
 645                         ret
 646                     }
 647                 }
 648                 _ => self.err_ty(),
 649             },
 650             Expr::Range { lhs, rhs, range_type } => {
 651                 let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
 652                 let rhs_expect = lhs_ty
 653                     .as_ref()
 654                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
 655                 let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
 656                 match (range_type, lhs_ty, rhs_ty) {
 657                     (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
 658                         Some(adt) => TyBuilder::adt(self.db, adt).build(),
 659                         None => self.err_ty(),
 660                     },
 661                     (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
 662                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 663                         None => self.err_ty(),
 664                     },
 665                     (RangeOp::Inclusive, None, Some(ty)) => {
 666                         match self.resolve_range_to_inclusive() {
 667                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 668                             None => self.err_ty(),
 669                         }
 670                     }
 671                     (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
 672                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 673                         None => self.err_ty(),
 674                     },
 675                     (RangeOp::Inclusive, Some(_), Some(ty)) => {
 676                         match self.resolve_range_inclusive() {
 677                             Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 678                             None => self.err_ty(),
 679                         }
 680                     }
 681                     (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
 682                         Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
 683                         None => self.err_ty(),
 684                     },
 685                     (RangeOp::Inclusive, _, None) => self.err_ty(),
 686                 }
 687             }
 688             Expr::Index { base, index } => {
 689                 let base_ty = self.infer_expr_inner(*base, &Expectation::none());
 690                 let index_ty = self.infer_expr(*index, &Expectation::none());
 691
 692                 if let (Some(index_trait), Some(krate)) =
 693                     (self.resolve_ops_index(), self.resolver.krate())
 694                 {
 695                     let canonicalized = self.canonicalize(base_ty);
 696                     let self_ty = method_resolution::resolve_indexing_op(
 697                         self.db,
 698                         &canonicalized.value,
 699                         self.trait_env.clone(),
 700                         krate,
 701                         index_trait,
 702                     );
 703                     let self_ty =
 704                         self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
 705                     self.resolve_associated_type_with_params(
 706                         self_ty,
 707                         self.resolve_ops_index_output(),
 708                         &[index_ty],
 709                     )
 710                 } else {
 711                     self.err_ty()
 712                 }
 713             }
 714             Expr::Tuple { exprs } => {
 715                 let mut tys = match expected
 716                     .only_has_type(&mut self.table)
 717                     .as_ref()
 718                     .map(|t| t.kind(&Interner))
 719                 {
 720                     Some(TyKind::Tuple(_, substs)) => substs
 721                         .iter(&Interner)
 722                         .map(|a| a.assert_ty_ref(&Interner).clone())
 723                         .chain(repeat_with(|| self.table.new_type_var()))
 724                         .take(exprs.len())
 725                         .collect::<Vec<_>>(),
 726                     _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
 727                 };
 728
 729                 for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
 730                     self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
 731                 }
 732
 733                 TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
 734             }
 735             Expr::Array(array) => {
 736                 let elem_ty =
 737                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(&Interner)) {
 738                         Some(TyKind::Array(st, _)) | Some(TyKind::Slice(st)) => st.clone(),
 739                         _ => self.table.new_type_var(),
 740                     };
 741
 742                 let len = match array {
 743                     Array::ElementList(items) => {
 744                         for expr in items.iter() {
 745                             // FIXME: use CoerceMany (coerce_merge_branch)
 746                             self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
 747                         }
 748                         Some(items.len() as u64)
 749                     }
 750                     Array::Repeat { initializer, repeat } => {
 751                         self.infer_expr_coerce(
 752                             *initializer,
 753                             &Expectation::has_type(elem_ty.clone()),
 754                         );
 755                         self.infer_expr(
 756                             *repeat,
 757                             &Expectation::has_type(
 758                                 TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(&Interner),
 759                             ),
 760                         );
 761
 762                         let repeat_expr = &self.body.exprs[*repeat];
 763                         consteval::eval_usize(repeat_expr)
 764                     }
 765                 };
 766
 767                 TyKind::Array(elem_ty, consteval::usize_const(len)).intern(&Interner)
 768             }
 769             Expr::Literal(lit) => match lit {
 770                 Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(&Interner),
 771                 Literal::String(..) => {
 772                     TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(&Interner))
 773                         .intern(&Interner)
 774                 }
 775                 Literal::ByteString(bs) => {
 776                     let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(&Interner);
 777
 778                     let len = consteval::usize_const(Some(bs.len() as u64));
 779
 780                     let array_type = TyKind::Array(byte_type, len).intern(&Interner);
 781                     TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(&Interner)
 782                 }
 783                 Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(&Interner),
 784                 Literal::Int(_v, ty) => match ty {
 785                     Some(int_ty) => {
 786                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
 787                             .intern(&Interner)
 788                     }
 789                     None => self.table.new_integer_var(),
 790                 },
 791                 Literal::Uint(_v, ty) => match ty {
 792                     Some(int_ty) => {
 793                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
 794                             .intern(&Interner)
 795                     }
 796                     None => self.table.new_integer_var(),
 797                 },
 798                 Literal::Float(_v, ty) => match ty {
 799                     Some(float_ty) => {
 800                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
 801                             .intern(&Interner)
 802                     }
 803                     None => self.table.new_float_var(),
 804                 },
 805             },
 806             Expr::MacroStmts { tail } => self.infer_expr_inner(*tail, expected),
 807         };
 808         // use a new type variable if we got unknown here
 809         let ty = self.insert_type_vars_shallow(ty);
 810         self.write_expr_ty(tgt_expr, ty.clone());
 811         ty
 812     }
 813
 814     fn infer_block(
 815         &mut self,
 816         statements: &[Statement],
 817         tail: Option<ExprId>,
 818         expected: &Expectation,
 819     ) -> Ty {
 820         for stmt in statements {
 821             match stmt {
 822                 Statement::Let { pat, type_ref, initializer } => {
 823                     let decl_ty =
 824                         type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(self.err_ty());
 825
 826                     // Always use the declared type when specified
 827                     let mut ty = decl_ty.clone();
 828
 829                     if let Some(expr) = initializer {
 830                         let actual_ty =
 831                             self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
 832                         if decl_ty.is_unknown() {
 833                             ty = actual_ty;
 834                         }
 835                     }
 836
 837                     self.infer_pat(*pat, &ty, BindingMode::default());
 838                 }
 839                 Statement::Expr { expr, .. } => {
 840                     self.infer_expr(*expr, &Expectation::none());
 841                 }
 842             }
 843         }
 844
 845         let ty = if let Some(expr) = tail {
 846             self.infer_expr_coerce(expr, expected)
 847         } else {
 848             // Citing rustc: if there is no explicit tail expression,
 849             // that is typically equivalent to a tail expression
 850             // of `()` -- except if the block diverges. In that
 851             // case, there is no value supplied from the tail
 852             // expression (assuming there are no other breaks,
 853             // this implies that the type of the block will be
 854             // `!`).
 855             if self.diverges.is_always() {
 856                 // we don't even make an attempt at coercion
 857                 self.table.new_maybe_never_var()
 858             } else {
 859                 if let Some(t) = expected.only_has_type(&mut self.table) {
 860                     self.coerce(&TyBuilder::unit(), &t);
 861                 }
 862                 TyBuilder::unit()
 863             }
 864         };
 865         ty
 866     }
 867
 868     fn infer_method_call(
 869         &mut self,
 870         tgt_expr: ExprId,
 871         receiver: ExprId,
 872         args: &[ExprId],
 873         method_name: &Name,
 874         generic_args: Option<&GenericArgs>,
 875     ) -> Ty {
 876         let receiver_ty = self.infer_expr(receiver, &Expectation::none());
 877         let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
 878
 879         let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
 880
 881         let resolved = self.resolver.krate().and_then(|krate| {
 882             method_resolution::lookup_method(
 883                 &canonicalized_receiver.value,
 884                 self.db,
 885                 self.trait_env.clone(),
 886                 krate,
 887                 &traits_in_scope,
 888                 self.resolver.module(),
 889                 method_name,
 890             )
 891         });
 892         let (receiver_ty, method_ty, substs) = match resolved {
 893             Some((ty, func)) => {
 894                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
 895                 let generics = generics(self.db.upcast(), func.into());
 896                 let substs = self.substs_for_method_call(generics, generic_args, &ty);
 897                 self.write_method_resolution(tgt_expr, func, substs.clone());
 898                 (ty, self.db.value_ty(func.into()), substs)
 899             }
 900             None => (
 901                 receiver_ty,
 902                 Binders::empty(&Interner, self.err_ty()),
 903                 Substitution::empty(&Interner),
 904             ),
 905         };
 906         let method_ty = method_ty.substitute(&Interner, &substs);
 907         self.register_obligations_for_call(&method_ty);
 908         let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
 909             Some(sig) => {
 910                 if !sig.params().is_empty() {
 911                     (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
 912                 } else {
 913                     (self.err_ty(), Vec::new(), sig.ret().clone())
 914                 }
 915             }
 916             None => (self.err_ty(), Vec::new(), self.err_ty()),
 917         };
 918         self.unify(&expected_receiver_ty, &receiver_ty);
 919
 920         self.check_call_arguments(args, &param_tys);
 921         self.normalize_associated_types_in(ret_ty)
 922     }
 923
 924     fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
 925         // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
 926         // We do this in a pretty awful way: first we type-check any arguments
 927         // that are not closures, then we type-check the closures. This is so
 928         // that we have more information about the types of arguments when we
 929         // type-check the functions. This isn't really the right way to do this.
 930         for &check_closures in &[false, true] {
 931             let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
 932             for (&arg, param_ty) in args.iter().zip(param_iter) {
 933                 let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
 934                 if is_closure != check_closures {
 935                     continue;
 936                 }
 937
 938                 let param_ty = self.normalize_associated_types_in(param_ty);
 939                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
 940             }
 941         }
 942     }
 943
 944     fn substs_for_method_call(
 945         &mut self,
 946         def_generics: Generics,
 947         generic_args: Option<&GenericArgs>,
 948         receiver_ty: &Ty,
 949     ) -> Substitution {
 950         let (parent_params, self_params, type_params, impl_trait_params) =
 951             def_generics.provenance_split();
 952         assert_eq!(self_params, 0); // method shouldn't have another Self param
 953         let total_len = parent_params + type_params + impl_trait_params;
 954         let mut substs = Vec::with_capacity(total_len);
 955         // Parent arguments are unknown, except for the receiver type
 956         for (_id, param) in def_generics.iter_parent() {
 957             if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
 958                 substs.push(receiver_ty.clone());
 959             } else {
 960                 substs.push(self.table.new_type_var());
 961             }
 962         }
 963         // handle provided type arguments
 964         if let Some(generic_args) = generic_args {
 965             // if args are provided, it should be all of them, but we can't rely on that
 966             for arg in generic_args
 967                 .args
 968                 .iter()
 969                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 970                 .take(type_params)
 971             {
 972                 match arg {
 973                     GenericArg::Type(type_ref) => {
 974                         let ty = self.make_ty(type_ref);
 975                         substs.push(ty);
 976                     }
 977                     GenericArg::Lifetime(_) => {}
 978                 }
 979             }
 980         };
 981         let supplied_params = substs.len();
 982         for _ in supplied_params..total_len {
 983             substs.push(self.table.new_type_var());
 984         }
 985         assert_eq!(substs.len(), total_len);
 986         Substitution::from_iter(&Interner, substs)
 987     }
 988
 989     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
 990         let callable_ty = self.resolve_ty_shallow(callable_ty);
 991         if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(&Interner) {
 992             let def: CallableDefId = from_chalk(self.db, *fn_def);
 993             let generic_predicates = self.db.generic_predicates(def.into());
 994             for predicate in generic_predicates.iter() {
 995                 let (predicate, binders) = predicate
 996                     .clone()
 997                     .substitute(&Interner, parameters)
 998                     .into_value_and_skipped_binders();
 999                 always!(binders.len(&Interner) == 0); // quantified where clauses not yet handled
1000                 self.push_obligation(predicate.cast(&Interner));
1001             }
1002             // add obligation for trait implementation, if this is a trait method
1003             match def {
1004                 CallableDefId::FunctionId(f) => {
1005                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
1006                     {
1007                         // construct a TraitRef
1008                         let substs = crate::subst_prefix(
1009                             &*parameters,
1010                             generics(self.db.upcast(), trait_.into()).len(),
1011                         );
1012                         self.push_obligation(
1013                             TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
1014                                 .cast(&Interner),
1015                         );
1016                     }
1017                 }
1018                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
1019             }
1020         }
1021     }
1022 }