crates/hir_ty/src/lower.rs

   1 //! Methods for lowering the HIR to types. There are two main cases here:
   2 //!
   3 //!  - Lowering a type reference like `&usize` or `Option<foo::bar::Baz>` to a
   4 //!    type: The entry point for this is `Ty::from_hir`.
   5 //!  - Building the type for an item: This happens through the `type_for_def` query.
   6 //!
   7 //! This usually involves resolving names, collecting generic arguments etc.
   8 use std::{iter, sync::Arc};
   9
  10 use base_db::CrateId;
  11 use chalk_ir::{cast::Cast, Mutability, Safety};
  12 use hir_def::{
  13     adt::StructKind,
  14     builtin_type::BuiltinType,
  15     generics::{TypeParamProvenance, WherePredicate, WherePredicateTypeTarget},
  16     path::{GenericArg, Path, PathSegment, PathSegments},
  17     resolver::{HasResolver, Resolver, TypeNs},
  18     type_ref::{TypeBound, TypeRef},
  19     AdtId, AssocContainerId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
  20     GenericDefId, HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId,
  21     TypeAliasId, TypeParamId, UnionId, VariantId,
  22 };
  23 use hir_expand::name::Name;
  24 use la_arena::ArenaMap;
  25 use smallvec::SmallVec;
  26 use stdx::impl_from;
  27
  28 use crate::{
  29     db::HirDatabase,
  30     to_assoc_type_id, to_placeholder_idx,
  31     traits::chalk::{Interner, ToChalk},
  32     utils::{
  33         all_super_trait_refs, associated_type_by_name_including_super_traits, generics,
  34         make_mut_slice, variant_data,
  35     },
  36     AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, FnPointer, FnSig, GenericPredicate,
  37     ImplTraitId, OpaqueTy, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
  38     ReturnTypeImplTraits, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeWalk,
  39 };
  40
  41 #[derive(Debug)]
  42 pub struct TyLoweringContext<'a> {
  43     pub db: &'a dyn HirDatabase,
  44     pub resolver: &'a Resolver,
  45     in_binders: DebruijnIndex,
  46     /// Note: Conceptually, it's thinkable that we could be in a location where
  47     /// some type params should be represented as placeholders, and others
  48     /// should be converted to variables. I think in practice, this isn't
  49     /// possible currently, so this should be fine for now.
  50     pub type_param_mode: TypeParamLoweringMode,
  51     pub impl_trait_mode: ImplTraitLoweringMode,
  52     impl_trait_counter: std::cell::Cell<u16>,
  53     /// When turning `impl Trait` into opaque types, we have to collect the
  54     /// bounds at the same time to get the IDs correct (without becoming too
  55     /// complicated). I don't like using interior mutability (as for the
  56     /// counter), but I've tried and failed to make the lifetimes work for
  57     /// passing around a `&mut TyLoweringContext`. The core problem is that
  58     /// we're grouping the mutable data (the counter and this field) together
  59     /// with the immutable context (the references to the DB and resolver).
  60     /// Splitting this up would be a possible fix.
  61     opaque_type_data: std::cell::RefCell<Vec<ReturnTypeImplTrait>>,
  62 }
  63
  64 impl<'a> TyLoweringContext<'a> {
  65     pub fn new(db: &'a dyn HirDatabase, resolver: &'a Resolver) -> Self {
  66         let impl_trait_counter = std::cell::Cell::new(0);
  67         let impl_trait_mode = ImplTraitLoweringMode::Disallowed;
  68         let type_param_mode = TypeParamLoweringMode::Placeholder;
  69         let in_binders = DebruijnIndex::INNERMOST;
  70         let opaque_type_data = std::cell::RefCell::new(Vec::new());
  71         Self {
  72             db,
  73             resolver,
  74             in_binders,
  75             impl_trait_mode,
  76             impl_trait_counter,
  77             type_param_mode,
  78             opaque_type_data,
  79         }
  80     }
  81
  82     pub fn with_debruijn<T>(
  83         &self,
  84         debruijn: DebruijnIndex,
  85         f: impl FnOnce(&TyLoweringContext) -> T,
  86     ) -> T {
  87         let opaque_ty_data_vec = self.opaque_type_data.replace(Vec::new());
  88         let new_ctx = Self {
  89             in_binders: debruijn,
  90             impl_trait_counter: std::cell::Cell::new(self.impl_trait_counter.get()),
  91             opaque_type_data: std::cell::RefCell::new(opaque_ty_data_vec),
  92             ..*self
  93         };
  94         let result = f(&new_ctx);
  95         self.impl_trait_counter.set(new_ctx.impl_trait_counter.get());
  96         self.opaque_type_data.replace(new_ctx.opaque_type_data.into_inner());
  97         result
  98     }
  99
 100     pub fn with_shifted_in<T>(
 101         &self,
 102         debruijn: DebruijnIndex,
 103         f: impl FnOnce(&TyLoweringContext) -> T,
 104     ) -> T {
 105         self.with_debruijn(self.in_binders.shifted_in_from(debruijn), f)
 106     }
 107
 108     pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
 109         Self { impl_trait_mode, ..self }
 110     }
 111
 112     pub fn with_type_param_mode(self, type_param_mode: TypeParamLoweringMode) -> Self {
 113         Self { type_param_mode, ..self }
 114     }
 115 }
 116
 117 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 118 pub enum ImplTraitLoweringMode {
 119     /// `impl Trait` gets lowered into an opaque type that doesn't unify with
 120     /// anything except itself. This is used in places where values flow 'out',
 121     /// i.e. for arguments of the function we're currently checking, and return
 122     /// types of functions we're calling.
 123     Opaque,
 124     /// `impl Trait` gets lowered into a type variable. Used for argument
 125     /// position impl Trait when inside the respective function, since it allows
 126     /// us to support that without Chalk.
 127     Param,
 128     /// `impl Trait` gets lowered into a variable that can unify with some
 129     /// type. This is used in places where values flow 'in', i.e. for arguments
 130     /// of functions we're calling, and the return type of the function we're
 131     /// currently checking.
 132     Variable,
 133     /// `impl Trait` is disallowed and will be an error.
 134     Disallowed,
 135 }
 136
 137 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 138 pub enum TypeParamLoweringMode {
 139     Placeholder,
 140     Variable,
 141 }
 142
 143 impl<'a> TyLoweringContext<'a> {
 144     pub fn lower_ty(&self, type_ref: &TypeRef) -> Ty {
 145         self.lower_ty_ext(type_ref).0
 146     }
 147
 148     fn lower_ty_ext(&self, type_ref: &TypeRef) -> (Ty, Option<TypeNs>) {
 149         let mut res = None;
 150         let ty = match type_ref {
 151             TypeRef::Never => TyKind::Never.intern(&Interner),
 152             TypeRef::Tuple(inner) => {
 153                 let inner_tys: Arc<[Ty]> = inner.iter().map(|tr| self.lower_ty(tr)).collect();
 154                 TyKind::Tuple(inner_tys.len(), Substs(inner_tys)).intern(&Interner)
 155             }
 156             TypeRef::Path(path) => {
 157                 let (ty, res_) = self.lower_path(path);
 158                 res = res_;
 159                 ty
 160             }
 161             TypeRef::RawPtr(inner, mutability) => {
 162                 let inner_ty = self.lower_ty(inner);
 163                 TyKind::Raw(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
 164                     .intern(&Interner)
 165             }
 166             TypeRef::Array(inner) => {
 167                 let inner_ty = self.lower_ty(inner);
 168                 TyKind::Array(Substs::single(inner_ty)).intern(&Interner)
 169             }
 170             TypeRef::Slice(inner) => {
 171                 let inner_ty = self.lower_ty(inner);
 172                 TyKind::Slice(Substs::single(inner_ty)).intern(&Interner)
 173             }
 174             TypeRef::Reference(inner, _, mutability) => {
 175                 let inner_ty = self.lower_ty(inner);
 176                 TyKind::Ref(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
 177                     .intern(&Interner)
 178             }
 179             TypeRef::Placeholder => TyKind::Unknown.intern(&Interner),
 180             TypeRef::Fn(params, is_varargs) => {
 181                 let substs = Substs(params.iter().map(|tr| self.lower_ty(tr)).collect());
 182                 TyKind::Function(FnPointer {
 183                     num_args: substs.len() - 1,
 184                     sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
 185                     substs,
 186                 })
 187                 .intern(&Interner)
 188             }
 189             TypeRef::DynTrait(bounds) => {
 190                 let self_ty =
 191                     TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 192                 let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 193                     bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
 194                 });
 195                 TyKind::Dyn(predicates).intern(&Interner)
 196             }
 197             TypeRef::ImplTrait(bounds) => {
 198                 match self.impl_trait_mode {
 199                     ImplTraitLoweringMode::Opaque => {
 200                         let idx = self.impl_trait_counter.get();
 201                         self.impl_trait_counter.set(idx + 1);
 202
 203                         assert!(idx as usize == self.opaque_type_data.borrow().len());
 204                         // this dance is to make sure the data is in the right
 205                         // place even if we encounter more opaque types while
 206                         // lowering the bounds
 207                         self.opaque_type_data
 208                             .borrow_mut()
 209                             .push(ReturnTypeImplTrait { bounds: Binders::new(1, Vec::new()) });
 210                         // We don't want to lower the bounds inside the binders
 211                         // we're currently in, because they don't end up inside
 212                         // those binders. E.g. when we have `impl Trait<impl
 213                         // OtherTrait<T>>`, the `impl OtherTrait<T>` can't refer
 214                         // to the self parameter from `impl Trait`, and the
 215                         // bounds aren't actually stored nested within each
 216                         // other, but separately. So if the `T` refers to a type
 217                         // parameter of the outer function, it's just one binder
 218                         // away instead of two.
 219                         let actual_opaque_type_data = self
 220                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
 221                                 ctx.lower_impl_trait(&bounds)
 222                             });
 223                         self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 224
 225                         let func = match self.resolver.generic_def() {
 226                             Some(GenericDefId::FunctionId(f)) => f,
 227                             _ => panic!("opaque impl trait lowering in non-function"),
 228                         };
 229                         let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
 230                         let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 231                         let generics = generics(self.db.upcast(), func.into());
 232                         let parameters = Substs::bound_vars(&generics, self.in_binders);
 233                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 234                             opaque_ty_id,
 235                             substitution: parameters,
 236                         }))
 237                         .intern(&Interner)
 238                     }
 239                     ImplTraitLoweringMode::Param => {
 240                         let idx = self.impl_trait_counter.get();
 241                         // FIXME we're probably doing something wrong here
 242                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 243                         if let Some(def) = self.resolver.generic_def() {
 244                             let generics = generics(self.db.upcast(), def);
 245                             let param = generics
 246                                 .iter()
 247                                 .filter(|(_, data)| {
 248                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
 249                                 })
 250                                 .nth(idx as usize)
 251                                 .map_or(TyKind::Unknown, |(id, _)| {
 252                                     TyKind::Placeholder(to_placeholder_idx(self.db, id))
 253                                 });
 254                             param.intern(&Interner)
 255                         } else {
 256                             TyKind::Unknown.intern(&Interner)
 257                         }
 258                     }
 259                     ImplTraitLoweringMode::Variable => {
 260                         let idx = self.impl_trait_counter.get();
 261                         // FIXME we're probably doing something wrong here
 262                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 263                         let (parent_params, self_params, list_params, _impl_trait_params) =
 264                             if let Some(def) = self.resolver.generic_def() {
 265                                 let generics = generics(self.db.upcast(), def);
 266                                 generics.provenance_split()
 267                             } else {
 268                                 (0, 0, 0, 0)
 269                             };
 270                         TyKind::BoundVar(BoundVar::new(
 271                             self.in_binders,
 272                             idx as usize + parent_params + self_params + list_params,
 273                         ))
 274                         .intern(&Interner)
 275                     }
 276                     ImplTraitLoweringMode::Disallowed => {
 277                         // FIXME: report error
 278                         TyKind::Unknown.intern(&Interner)
 279                     }
 280                 }
 281             }
 282             TypeRef::Error => TyKind::Unknown.intern(&Interner),
 283         };
 284         (ty, res)
 285     }
 286
 287     /// This is only for `generic_predicates_for_param`, where we can't just
 288     /// lower the self types of the predicates since that could lead to cycles.
 289     /// So we just check here if the `type_ref` resolves to a generic param, and which.
 290     fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
 291         let path = match type_ref {
 292             TypeRef::Path(path) => path,
 293             _ => return None,
 294         };
 295         if path.type_anchor().is_some() {
 296             return None;
 297         }
 298         if path.segments().len() > 1 {
 299             return None;
 300         }
 301         let resolution =
 302             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 303                 Some((it, None)) => it,
 304                 _ => return None,
 305             };
 306         if let TypeNs::GenericParam(param_id) = resolution {
 307             Some(param_id)
 308         } else {
 309             None
 310         }
 311     }
 312
 313     pub(crate) fn lower_ty_relative_path(
 314         &self,
 315         ty: Ty,
 316         // We need the original resolution to lower `Self::AssocTy` correctly
 317         res: Option<TypeNs>,
 318         remaining_segments: PathSegments<'_>,
 319     ) -> (Ty, Option<TypeNs>) {
 320         if remaining_segments.len() == 1 {
 321             // resolve unselected assoc types
 322             let segment = remaining_segments.first().unwrap();
 323             (self.select_associated_type(res, segment), None)
 324         } else if remaining_segments.len() > 1 {
 325             // FIXME report error (ambiguous associated type)
 326             (TyKind::Unknown.intern(&Interner), None)
 327         } else {
 328             (ty, res)
 329         }
 330     }
 331
 332     pub(crate) fn lower_partly_resolved_path(
 333         &self,
 334         resolution: TypeNs,
 335         resolved_segment: PathSegment<'_>,
 336         remaining_segments: PathSegments<'_>,
 337         infer_args: bool,
 338     ) -> (Ty, Option<TypeNs>) {
 339         let ty = match resolution {
 340             TypeNs::TraitId(trait_) => {
 341                 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
 342                 let self_ty = if remaining_segments.len() == 0 {
 343                     Some(
 344                         TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
 345                             .intern(&Interner),
 346                     )
 347                 } else {
 348                     None
 349                 };
 350                 let trait_ref =
 351                     self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
 352                 let ty = if remaining_segments.len() == 1 {
 353                     let segment = remaining_segments.first().unwrap();
 354                     let found = associated_type_by_name_including_super_traits(
 355                         self.db,
 356                         trait_ref,
 357                         &segment.name,
 358                     );
 359                     match found {
 360                         Some((super_trait_ref, associated_ty)) => {
 361                             // FIXME handle type parameters on the segment
 362                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 363                                 associated_ty_id: to_assoc_type_id(associated_ty),
 364                                 substitution: super_trait_ref.substs,
 365                             }))
 366                             .intern(&Interner)
 367                         }
 368                         None => {
 369                             // FIXME: report error (associated type not found)
 370                             TyKind::Unknown.intern(&Interner)
 371                         }
 372                     }
 373                 } else if remaining_segments.len() > 1 {
 374                     // FIXME report error (ambiguous associated type)
 375                     TyKind::Unknown.intern(&Interner)
 376                 } else {
 377                     TyKind::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
 378                         .intern(&Interner)
 379                 };
 380                 return (ty, None);
 381             }
 382             TypeNs::GenericParam(param_id) => {
 383                 let generics = generics(
 384                     self.db.upcast(),
 385                     self.resolver.generic_def().expect("generics in scope"),
 386                 );
 387                 match self.type_param_mode {
 388                     TypeParamLoweringMode::Placeholder => {
 389                         TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
 390                     }
 391                     TypeParamLoweringMode::Variable => {
 392                         let idx = generics.param_idx(param_id).expect("matching generics");
 393                         TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
 394                     }
 395                 }
 396                 .intern(&Interner)
 397             }
 398             TypeNs::SelfType(impl_id) => {
 399                 let generics = generics(self.db.upcast(), impl_id.into());
 400                 let substs = match self.type_param_mode {
 401                     TypeParamLoweringMode::Placeholder => {
 402                         Substs::type_params_for_generics(self.db, &generics)
 403                     }
 404                     TypeParamLoweringMode::Variable => {
 405                         Substs::bound_vars(&generics, self.in_binders)
 406                     }
 407                 };
 408                 self.db.impl_self_ty(impl_id).subst(&substs)
 409             }
 410             TypeNs::AdtSelfType(adt) => {
 411                 let generics = generics(self.db.upcast(), adt.into());
 412                 let substs = match self.type_param_mode {
 413                     TypeParamLoweringMode::Placeholder => {
 414                         Substs::type_params_for_generics(self.db, &generics)
 415                     }
 416                     TypeParamLoweringMode::Variable => {
 417                         Substs::bound_vars(&generics, self.in_binders)
 418                     }
 419                 };
 420                 self.db.ty(adt.into()).subst(&substs)
 421             }
 422
 423             TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
 424             TypeNs::BuiltinType(it) => {
 425                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 426             }
 427             TypeNs::TypeAliasId(it) => {
 428                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 429             }
 430             // FIXME: report error
 431             TypeNs::EnumVariantId(_) => return (TyKind::Unknown.intern(&Interner), None),
 432         };
 433         self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
 434     }
 435
 436     pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
 437         // Resolve the path (in type namespace)
 438         if let Some(type_ref) = path.type_anchor() {
 439             let (ty, res) = self.lower_ty_ext(&type_ref);
 440             return self.lower_ty_relative_path(ty, res, path.segments());
 441         }
 442         let (resolution, remaining_index) =
 443             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 444                 Some(it) => it,
 445                 None => return (TyKind::Unknown.intern(&Interner), None),
 446             };
 447         let (resolved_segment, remaining_segments) = match remaining_index {
 448             None => (
 449                 path.segments().last().expect("resolved path has at least one element"),
 450                 PathSegments::EMPTY,
 451             ),
 452             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
 453         };
 454         self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
 455     }
 456
 457     fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
 458         if let Some(res) = res {
 459             let ty = associated_type_shorthand_candidates(
 460                 self.db,
 461                 res,
 462                 move |name, t, associated_ty| {
 463                     if name == segment.name {
 464                         let substs = match self.type_param_mode {
 465                             TypeParamLoweringMode::Placeholder => {
 466                                 // if we're lowering to placeholders, we have to put
 467                                 // them in now
 468                                 let s = Substs::type_params(
 469                                     self.db,
 470                                     self.resolver.generic_def().expect(
 471                                         "there should be generics if there's a generic param",
 472                                     ),
 473                                 );
 474                                 t.substs.clone().subst_bound_vars(&s)
 475                             }
 476                             TypeParamLoweringMode::Variable => t.substs.clone(),
 477                         };
 478                         // We need to shift in the bound vars, since
 479                         // associated_type_shorthand_candidates does not do that
 480                         let substs = substs.shift_bound_vars(self.in_binders);
 481                         // FIXME handle type parameters on the segment
 482                         return Some(
 483                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 484                                 associated_ty_id: to_assoc_type_id(associated_ty),
 485                                 substitution: substs,
 486                             }))
 487                             .intern(&Interner),
 488                         );
 489                     }
 490
 491                     None
 492                 },
 493             );
 494
 495             ty.unwrap_or(TyKind::Unknown.intern(&Interner))
 496         } else {
 497             TyKind::Unknown.intern(&Interner)
 498         }
 499     }
 500
 501     fn lower_path_inner(
 502         &self,
 503         segment: PathSegment<'_>,
 504         typeable: TyDefId,
 505         infer_args: bool,
 506     ) -> Ty {
 507         let generic_def = match typeable {
 508             TyDefId::BuiltinType(_) => None,
 509             TyDefId::AdtId(it) => Some(it.into()),
 510             TyDefId::TypeAliasId(it) => Some(it.into()),
 511         };
 512         let substs = self.substs_from_path_segment(segment, generic_def, infer_args);
 513         self.db.ty(typeable).subst(&substs)
 514     }
 515
 516     /// Collect generic arguments from a path into a `Substs`. See also
 517     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
 518     pub(super) fn substs_from_path(
 519         &self,
 520         path: &Path,
 521         // Note that we don't call `db.value_type(resolved)` here,
 522         // `ValueTyDefId` is just a convenient way to pass generics and
 523         // special-case enum variants
 524         resolved: ValueTyDefId,
 525         infer_args: bool,
 526     ) -> Substs {
 527         let last = path.segments().last().expect("path should have at least one segment");
 528         let (segment, generic_def) = match resolved {
 529             ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
 530             ValueTyDefId::StructId(it) => (last, Some(it.into())),
 531             ValueTyDefId::UnionId(it) => (last, Some(it.into())),
 532             ValueTyDefId::ConstId(it) => (last, Some(it.into())),
 533             ValueTyDefId::StaticId(_) => (last, None),
 534             ValueTyDefId::EnumVariantId(var) => {
 535                 // the generic args for an enum variant may be either specified
 536                 // on the segment referring to the enum, or on the segment
 537                 // referring to the variant. So `Option::<T>::None` and
 538                 // `Option::None::<T>` are both allowed (though the former is
 539                 // preferred). See also `def_ids_for_path_segments` in rustc.
 540                 let len = path.segments().len();
 541                 let penultimate = if len >= 2 { path.segments().get(len - 2) } else { None };
 542                 let segment = match penultimate {
 543                     Some(segment) if segment.args_and_bindings.is_some() => segment,
 544                     _ => last,
 545                 };
 546                 (segment, Some(var.parent.into()))
 547             }
 548         };
 549         self.substs_from_path_segment(segment, generic_def, infer_args)
 550     }
 551
 552     fn substs_from_path_segment(
 553         &self,
 554         segment: PathSegment<'_>,
 555         def_generic: Option<GenericDefId>,
 556         infer_args: bool,
 557     ) -> Substs {
 558         let mut substs = Vec::new();
 559         let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
 560
 561         let (parent_params, self_params, type_params, impl_trait_params) =
 562             def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
 563         let total_len = parent_params + self_params + type_params + impl_trait_params;
 564
 565         substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(parent_params));
 566
 567         let mut had_explicit_type_args = false;
 568
 569         if let Some(generic_args) = &segment.args_and_bindings {
 570             if !generic_args.has_self_type {
 571                 substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(self_params));
 572             }
 573             let expected_num =
 574                 if generic_args.has_self_type { self_params + type_params } else { type_params };
 575             let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
 576             // if args are provided, it should be all of them, but we can't rely on that
 577             for arg in generic_args
 578                 .args
 579                 .iter()
 580                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 581                 .skip(skip)
 582                 .take(expected_num)
 583             {
 584                 match arg {
 585                     GenericArg::Type(type_ref) => {
 586                         had_explicit_type_args = true;
 587                         let ty = self.lower_ty(type_ref);
 588                         substs.push(ty);
 589                     }
 590                     GenericArg::Lifetime(_) => {}
 591                 }
 592             }
 593         }
 594
 595         // handle defaults. In expression or pattern path segments without
 596         // explicitly specified type arguments, missing type arguments are inferred
 597         // (i.e. defaults aren't used).
 598         if !infer_args || had_explicit_type_args {
 599             if let Some(def_generic) = def_generic {
 600                 let defaults = self.db.generic_defaults(def_generic);
 601                 assert_eq!(total_len, defaults.len());
 602
 603                 for default_ty in defaults.iter().skip(substs.len()) {
 604                     // each default can depend on the previous parameters
 605                     let substs_so_far = Substs(substs.clone().into());
 606                     substs.push(default_ty.clone().subst(&substs_so_far));
 607                 }
 608             }
 609         }
 610
 611         // add placeholders for args that were not provided
 612         // FIXME: emit diagnostics in contexts where this is not allowed
 613         for _ in substs.len()..total_len {
 614             substs.push(TyKind::Unknown.intern(&Interner));
 615         }
 616         assert_eq!(substs.len(), total_len);
 617
 618         Substs(substs.into())
 619     }
 620
 621     fn lower_trait_ref_from_path(
 622         &self,
 623         path: &Path,
 624         explicit_self_ty: Option<Ty>,
 625     ) -> Option<TraitRef> {
 626         let resolved =
 627             match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
 628                 TypeNs::TraitId(tr) => tr,
 629                 _ => return None,
 630             };
 631         let segment = path.segments().last().expect("path should have at least one segment");
 632         Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
 633     }
 634
 635     pub(crate) fn lower_trait_ref_from_resolved_path(
 636         &self,
 637         resolved: TraitId,
 638         segment: PathSegment<'_>,
 639         explicit_self_ty: Option<Ty>,
 640     ) -> TraitRef {
 641         let mut substs = self.trait_ref_substs_from_path(segment, resolved);
 642         if let Some(self_ty) = explicit_self_ty {
 643             make_mut_slice(&mut substs.0)[0] = self_ty;
 644         }
 645         TraitRef { trait_: resolved, substs }
 646     }
 647
 648     fn lower_trait_ref(
 649         &self,
 650         type_ref: &TypeRef,
 651         explicit_self_ty: Option<Ty>,
 652     ) -> Option<TraitRef> {
 653         let path = match type_ref {
 654             TypeRef::Path(path) => path,
 655             _ => return None,
 656         };
 657         self.lower_trait_ref_from_path(path, explicit_self_ty)
 658     }
 659
 660     fn trait_ref_substs_from_path(&self, segment: PathSegment<'_>, resolved: TraitId) -> Substs {
 661         self.substs_from_path_segment(segment, Some(resolved.into()), false)
 662     }
 663
 664     pub(crate) fn lower_where_predicate(
 665         &'a self,
 666         where_predicate: &'a WherePredicate,
 667     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 668         match where_predicate {
 669             WherePredicate::ForLifetime { target, bound, .. }
 670             | WherePredicate::TypeBound { target, bound } => {
 671                 let self_ty = match target {
 672                     WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
 673                     WherePredicateTypeTarget::TypeParam(param_id) => {
 674                         let generic_def = self.resolver.generic_def().expect("generics in scope");
 675                         let generics = generics(self.db.upcast(), generic_def);
 676                         let param_id =
 677                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
 678                         let placeholder = to_placeholder_idx(self.db, param_id);
 679                         match self.type_param_mode {
 680                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
 681                             TypeParamLoweringMode::Variable => {
 682                                 let idx = generics.param_idx(param_id).expect("matching generics");
 683                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
 684                             }
 685                         }
 686                         .intern(&Interner)
 687                     }
 688                 };
 689                 self.lower_type_bound(bound, self_ty).collect::<Vec<_>>().into_iter()
 690             }
 691             WherePredicate::Lifetime { .. } => vec![].into_iter(),
 692         }
 693     }
 694
 695     pub(crate) fn lower_type_bound(
 696         &'a self,
 697         bound: &'a TypeBound,
 698         self_ty: Ty,
 699     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 700         let mut bindings = None;
 701         let trait_ref = match bound {
 702             TypeBound::Path(path) => {
 703                 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
 704                 Some(
 705                     bindings.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented),
 706                 )
 707             }
 708             TypeBound::Lifetime(_) => None,
 709             TypeBound::Error => Some(GenericPredicate::Error),
 710         };
 711         trait_ref.into_iter().chain(
 712             bindings
 713                 .into_iter()
 714                 .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
 715         )
 716     }
 717
 718     fn assoc_type_bindings_from_type_bound(
 719         &'a self,
 720         bound: &'a TypeBound,
 721         trait_ref: TraitRef,
 722     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 723         let last_segment = match bound {
 724             TypeBound::Path(path) => path.segments().last(),
 725             TypeBound::Error | TypeBound::Lifetime(_) => None,
 726         };
 727         last_segment
 728             .into_iter()
 729             .flat_map(|segment| segment.args_and_bindings.into_iter())
 730             .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
 731             .flat_map(move |binding| {
 732                 let found = associated_type_by_name_including_super_traits(
 733                     self.db,
 734                     trait_ref.clone(),
 735                     &binding.name,
 736                 );
 737                 let (super_trait_ref, associated_ty) = match found {
 738                     None => return SmallVec::<[GenericPredicate; 1]>::new(),
 739                     Some(t) => t,
 740                 };
 741                 let projection_ty = ProjectionTy {
 742                     associated_ty_id: to_assoc_type_id(associated_ty),
 743                     substitution: super_trait_ref.substs,
 744                 };
 745                 let mut preds = SmallVec::with_capacity(
 746                     binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
 747                 );
 748                 if let Some(type_ref) = &binding.type_ref {
 749                     let ty = self.lower_ty(type_ref);
 750                     let projection_predicate =
 751                         ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
 752                     preds.push(GenericPredicate::Projection(projection_predicate));
 753                 }
 754                 for bound in &binding.bounds {
 755                     preds.extend(self.lower_type_bound(
 756                         bound,
 757                         TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
 758                     ));
 759                 }
 760                 preds
 761             })
 762     }
 763
 764     fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
 765         cov_mark::hit!(lower_rpit);
 766         let self_ty =
 767             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 768         let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 769             bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
 770         });
 771         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
 772     }
 773 }
 774
 775 fn count_impl_traits(type_ref: &TypeRef) -> usize {
 776     let mut count = 0;
 777     type_ref.walk(&mut |type_ref| {
 778         if matches!(type_ref, TypeRef::ImplTrait(_)) {
 779             count += 1;
 780         }
 781     });
 782     count
 783 }
 784
 785 /// Build the signature of a callable item (function, struct or enum variant).
 786 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
 787     match def {
 788         CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
 789         CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
 790         CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
 791     }
 792 }
 793
 794 pub fn associated_type_shorthand_candidates<R>(
 795     db: &dyn HirDatabase,
 796     res: TypeNs,
 797     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 798 ) -> Option<R> {
 799     let traits_from_env: Vec<_> = match res {
 800         TypeNs::SelfType(impl_id) => match db.impl_trait(impl_id) {
 801             None => vec![],
 802             Some(trait_ref) => vec![trait_ref.value],
 803         },
 804         TypeNs::GenericParam(param_id) => {
 805             let predicates = db.generic_predicates_for_param(param_id);
 806             let mut traits_: Vec<_> = predicates
 807                 .iter()
 808                 .filter_map(|pred| match &pred.value {
 809                     GenericPredicate::Implemented(tr) => Some(tr.clone()),
 810                     _ => None,
 811                 })
 812                 .collect();
 813             // Handle `Self::Type` referring to own associated type in trait definitions
 814             if let GenericDefId::TraitId(trait_id) = param_id.parent {
 815                 let generics = generics(db.upcast(), trait_id.into());
 816                 if generics.params.types[param_id.local_id].provenance
 817                     == TypeParamProvenance::TraitSelf
 818                 {
 819                     let trait_ref = TraitRef {
 820                         trait_: trait_id,
 821                         substs: Substs::bound_vars(&generics, DebruijnIndex::INNERMOST),
 822                     };
 823                     traits_.push(trait_ref);
 824                 }
 825             }
 826             traits_
 827         }
 828         _ => vec![],
 829     };
 830
 831     for t in traits_from_env.into_iter().flat_map(move |t| all_super_trait_refs(db, t)) {
 832         let data = db.trait_data(t.trait_);
 833
 834         for (name, assoc_id) in &data.items {
 835             match assoc_id {
 836                 AssocItemId::TypeAliasId(alias) => {
 837                     if let Some(result) = cb(name, &t, *alias) {
 838                         return Some(result);
 839                     }
 840                 }
 841                 AssocItemId::FunctionId(_) | AssocItemId::ConstId(_) => {}
 842             }
 843         }
 844     }
 845
 846     None
 847 }
 848
 849 /// Build the type of all specific fields of a struct or enum variant.
 850 pub(crate) fn field_types_query(
 851     db: &dyn HirDatabase,
 852     variant_id: VariantId,
 853 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
 854     let var_data = variant_data(db.upcast(), variant_id);
 855     let (resolver, def): (_, GenericDefId) = match variant_id {
 856         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
 857         VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
 858         VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
 859     };
 860     let generics = generics(db.upcast(), def);
 861     let mut res = ArenaMap::default();
 862     let ctx =
 863         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 864     for (field_id, field_data) in var_data.fields().iter() {
 865         res.insert(field_id, Binders::new(generics.len(), ctx.lower_ty(&field_data.type_ref)))
 866     }
 867     Arc::new(res)
 868 }
 869
 870 /// This query exists only to be used when resolving short-hand associated types
 871 /// like `T::Item`.
 872 ///
 873 /// See the analogous query in rustc and its comment:
 874 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
 875 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
 876 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
 877 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 878 pub(crate) fn generic_predicates_for_param_query(
 879     db: &dyn HirDatabase,
 880     param_id: TypeParamId,
 881 ) -> Arc<[Binders<GenericPredicate>]> {
 882     let resolver = param_id.parent.resolver(db.upcast());
 883     let ctx =
 884         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 885     let generics = generics(db.upcast(), param_id.parent);
 886     resolver
 887         .where_predicates_in_scope()
 888         // we have to filter out all other predicates *first*, before attempting to lower them
 889         .filter(|pred| match pred {
 890             WherePredicate::ForLifetime { target, .. }
 891             | WherePredicate::TypeBound { target, .. } => match target {
 892                 WherePredicateTypeTarget::TypeRef(type_ref) => {
 893                     ctx.lower_ty_only_param(type_ref) == Some(param_id)
 894                 }
 895                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
 896             },
 897             WherePredicate::Lifetime { .. } => false,
 898         })
 899         .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
 900         .collect()
 901 }
 902
 903 pub(crate) fn generic_predicates_for_param_recover(
 904     _db: &dyn HirDatabase,
 905     _cycle: &[String],
 906     _param_id: &TypeParamId,
 907 ) -> Arc<[Binders<GenericPredicate>]> {
 908     Arc::new([])
 909 }
 910
 911 pub(crate) fn trait_environment_query(
 912     db: &dyn HirDatabase,
 913     def: GenericDefId,
 914 ) -> Arc<TraitEnvironment> {
 915     let resolver = def.resolver(db.upcast());
 916     let ctx = TyLoweringContext::new(db, &resolver)
 917         .with_type_param_mode(TypeParamLoweringMode::Placeholder);
 918     let mut traits_in_scope = Vec::new();
 919     let mut clauses = Vec::new();
 920     for pred in resolver.where_predicates_in_scope() {
 921         for pred in ctx.lower_where_predicate(pred) {
 922             if pred.is_error() {
 923                 continue;
 924             }
 925             if let GenericPredicate::Implemented(tr) = &pred {
 926                 traits_in_scope.push((tr.self_ty().clone(), tr.trait_));
 927             }
 928             let program_clause: chalk_ir::ProgramClause<Interner> =
 929                 pred.clone().to_chalk(db).cast(&Interner);
 930             clauses.push(program_clause.into_from_env_clause(&Interner));
 931         }
 932     }
 933
 934     let container: Option<AssocContainerId> = match def {
 935         // FIXME: is there a function for this?
 936         GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
 937         GenericDefId::AdtId(_) => None,
 938         GenericDefId::TraitId(_) => None,
 939         GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
 940         GenericDefId::ImplId(_) => None,
 941         GenericDefId::EnumVariantId(_) => None,
 942         GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
 943     };
 944     if let Some(AssocContainerId::TraitId(trait_id)) = container {
 945         // add `Self: Trait<T1, T2, ...>` to the environment in trait
 946         // function default implementations (and hypothetical code
 947         // inside consts or type aliases)
 948         cov_mark::hit!(trait_self_implements_self);
 949         let substs = Substs::type_params(db, trait_id);
 950         let trait_ref = TraitRef { trait_: trait_id, substs };
 951         let pred = GenericPredicate::Implemented(trait_ref);
 952         let program_clause: chalk_ir::ProgramClause<Interner> =
 953             pred.clone().to_chalk(db).cast(&Interner);
 954         clauses.push(program_clause.into_from_env_clause(&Interner));
 955     }
 956
 957     let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 958
 959     Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 960 }
 961
 962 /// Resolve the where clause(s) of an item with generics.
 963 pub(crate) fn generic_predicates_query(
 964     db: &dyn HirDatabase,
 965     def: GenericDefId,
 966 ) -> Arc<[Binders<GenericPredicate>]> {
 967     let resolver = def.resolver(db.upcast());
 968     let ctx =
 969         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 970     let generics = generics(db.upcast(), def);
 971     resolver
 972         .where_predicates_in_scope()
 973         .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
 974         .collect()
 975 }
 976
 977 /// Resolve the default type params from generics
 978 pub(crate) fn generic_defaults_query(
 979     db: &dyn HirDatabase,
 980     def: GenericDefId,
 981 ) -> Arc<[Binders<Ty>]> {
 982     let resolver = def.resolver(db.upcast());
 983     let ctx =
 984         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 985     let generic_params = generics(db.upcast(), def);
 986
 987     let defaults = generic_params
 988         .iter()
 989         .enumerate()
 990         .map(|(idx, (_, p))| {
 991             let mut ty =
 992                 p.default.as_ref().map_or(TyKind::Unknown.intern(&Interner), |t| ctx.lower_ty(t));
 993
 994             // Each default can only refer to previous parameters.
 995             ty.walk_mut_binders(
 996                 &mut |ty, binders| match &mut ty.0 {
 997                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
 998                         if *index >= idx {
 999                             // type variable default referring to parameter coming
1000                             // after it. This is forbidden (FIXME: report
1001                             // diagnostic)
1002                             *ty = TyKind::Unknown.intern(&Interner);
1003                         }
1004                     }
1005                     _ => {}
1006                 },
1007                 DebruijnIndex::INNERMOST,
1008             );
1009
1010             Binders::new(idx, ty)
1011         })
1012         .collect();
1013
1014     defaults
1015 }
1016
1017 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1018     let data = db.function_data(def);
1019     let resolver = def.resolver(db.upcast());
1020     let ctx_params = TyLoweringContext::new(db, &resolver)
1021         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1022         .with_type_param_mode(TypeParamLoweringMode::Variable);
1023     let params = data.params.iter().map(|tr| (&ctx_params).lower_ty(tr)).collect::<Vec<_>>();
1024     let ctx_ret = TyLoweringContext::new(db, &resolver)
1025         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1026         .with_type_param_mode(TypeParamLoweringMode::Variable);
1027     let ret = (&ctx_ret).lower_ty(&data.ret_type);
1028     let generics = generics(db.upcast(), def.into());
1029     let num_binders = generics.len();
1030     Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
1031 }
1032
1033 /// Build the declared type of a function. This should not need to look at the
1034 /// function body.
1035 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1036     let generics = generics(db.upcast(), def.into());
1037     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1038     Binders::new(
1039         substs.len(),
1040         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1041     )
1042 }
1043
1044 /// Build the declared type of a const.
1045 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1046     let data = db.const_data(def);
1047     let generics = generics(db.upcast(), def.into());
1048     let resolver = def.resolver(db.upcast());
1049     let ctx =
1050         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1051
1052     Binders::new(generics.len(), ctx.lower_ty(&data.type_ref))
1053 }
1054
1055 /// Build the declared type of a static.
1056 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1057     let data = db.static_data(def);
1058     let resolver = def.resolver(db.upcast());
1059     let ctx = TyLoweringContext::new(db, &resolver);
1060
1061     Binders::new(0, ctx.lower_ty(&data.type_ref))
1062 }
1063
1064 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1065     let struct_data = db.struct_data(def);
1066     let fields = struct_data.variant_data.fields();
1067     let resolver = def.resolver(db.upcast());
1068     let ctx =
1069         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1070     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1071     let ret = type_for_adt(db, def.into());
1072     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1073 }
1074
1075 /// Build the type of a tuple struct constructor.
1076 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1077     let struct_data = db.struct_data(def);
1078     if let StructKind::Unit = struct_data.variant_data.kind() {
1079         return type_for_adt(db, def.into());
1080     }
1081     let generics = generics(db.upcast(), def.into());
1082     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1083     Binders::new(
1084         substs.len(),
1085         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1086     )
1087 }
1088
1089 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1090     let enum_data = db.enum_data(def.parent);
1091     let var_data = &enum_data.variants[def.local_id];
1092     let fields = var_data.variant_data.fields();
1093     let resolver = def.parent.resolver(db.upcast());
1094     let ctx =
1095         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1096     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1097     let ret = type_for_adt(db, def.parent.into());
1098     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1099 }
1100
1101 /// Build the type of a tuple enum variant constructor.
1102 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1103     let enum_data = db.enum_data(def.parent);
1104     let var_data = &enum_data.variants[def.local_id].variant_data;
1105     if let StructKind::Unit = var_data.kind() {
1106         return type_for_adt(db, def.parent.into());
1107     }
1108     let generics = generics(db.upcast(), def.parent.into());
1109     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1110     Binders::new(
1111         substs.len(),
1112         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1113     )
1114 }
1115
1116 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1117     let generics = generics(db.upcast(), adt.into());
1118     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1119     Binders::new(substs.len(), Ty::adt_ty(adt, substs))
1120 }
1121
1122 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1123     let generics = generics(db.upcast(), t.into());
1124     let resolver = t.resolver(db.upcast());
1125     let ctx =
1126         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1127     if db.type_alias_data(t).is_extern {
1128         Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
1129     } else {
1130         let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1131         let type_ref = &db.type_alias_data(t).type_ref;
1132         let inner = ctx.lower_ty(type_ref.as_ref().unwrap_or(&TypeRef::Error));
1133         Binders::new(substs.len(), inner)
1134     }
1135 }
1136
1137 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1138 pub enum CallableDefId {
1139     FunctionId(FunctionId),
1140     StructId(StructId),
1141     EnumVariantId(EnumVariantId),
1142 }
1143 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1144
1145 impl CallableDefId {
1146     pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1147         let db = db.upcast();
1148         match self {
1149             CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1150             CallableDefId::StructId(s) => s.lookup(db).container,
1151             CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1152         }
1153         .krate()
1154     }
1155 }
1156
1157 impl From<CallableDefId> for GenericDefId {
1158     fn from(def: CallableDefId) -> GenericDefId {
1159         match def {
1160             CallableDefId::FunctionId(f) => f.into(),
1161             CallableDefId::StructId(s) => s.into(),
1162             CallableDefId::EnumVariantId(e) => e.into(),
1163         }
1164     }
1165 }
1166
1167 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1168 pub enum TyDefId {
1169     BuiltinType(BuiltinType),
1170     AdtId(AdtId),
1171     TypeAliasId(TypeAliasId),
1172 }
1173 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1174
1175 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1176 pub enum ValueTyDefId {
1177     FunctionId(FunctionId),
1178     StructId(StructId),
1179     UnionId(UnionId),
1180     EnumVariantId(EnumVariantId),
1181     ConstId(ConstId),
1182     StaticId(StaticId),
1183 }
1184 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1185
1186 /// Build the declared type of an item. This depends on the namespace; e.g. for
1187 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1188 /// the constructor function `(usize) -> Foo` which lives in the values
1189 /// namespace.
1190 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1191     match def {
1192         TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
1193         TyDefId::AdtId(it) => type_for_adt(db, it),
1194         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1195     }
1196 }
1197
1198 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1199     let num_binders = match *def {
1200         TyDefId::BuiltinType(_) => 0,
1201         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
1202         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
1203     };
1204     Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
1205 }
1206
1207 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1208     match def {
1209         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1210         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1211         ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1212         ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1213         ValueTyDefId::ConstId(it) => type_for_const(db, it),
1214         ValueTyDefId::StaticId(it) => type_for_static(db, it),
1215     }
1216 }
1217
1218 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1219     let impl_data = db.impl_data(impl_id);
1220     let resolver = impl_id.resolver(db.upcast());
1221     let generics = generics(db.upcast(), impl_id.into());
1222     let ctx =
1223         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1224     Binders::new(generics.len(), ctx.lower_ty(&impl_data.target_type))
1225 }
1226
1227 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1228     let parent_data = db.generic_params(def.parent);
1229     let data = &parent_data.consts[def.local_id];
1230     let resolver = def.parent.resolver(db.upcast());
1231     let ctx = TyLoweringContext::new(db, &resolver);
1232
1233     ctx.lower_ty(&data.ty)
1234 }
1235
1236 pub(crate) fn impl_self_ty_recover(
1237     db: &dyn HirDatabase,
1238     _cycle: &[String],
1239     impl_id: &ImplId,
1240 ) -> Binders<Ty> {
1241     let generics = generics(db.upcast(), (*impl_id).into());
1242     Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
1243 }
1244
1245 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1246     let impl_data = db.impl_data(impl_id);
1247     let resolver = impl_id.resolver(db.upcast());
1248     let ctx =
1249         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1250     let self_ty = db.impl_self_ty(impl_id);
1251     let target_trait = impl_data.target_trait.as_ref()?;
1252     Some(Binders::new(self_ty.num_binders, ctx.lower_trait_ref(target_trait, Some(self_ty.value))?))
1253 }
1254
1255 pub(crate) fn return_type_impl_traits(
1256     db: &dyn HirDatabase,
1257     def: hir_def::FunctionId,
1258 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1259     // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1260     let data = db.function_data(def);
1261     let resolver = def.resolver(db.upcast());
1262     let ctx_ret = TyLoweringContext::new(db, &resolver)
1263         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1264         .with_type_param_mode(TypeParamLoweringMode::Variable);
1265     let _ret = (&ctx_ret).lower_ty(&data.ret_type);
1266     let generics = generics(db.upcast(), def.into());
1267     let num_binders = generics.len();
1268     let return_type_impl_traits =
1269         ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1270     if return_type_impl_traits.impl_traits.is_empty() {
1271         None
1272     } else {
1273         Some(Arc::new(Binders::new(num_binders, return_type_impl_traits)))
1274     }
1275 }
1276
1277 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1278     match m {
1279         hir_def::type_ref::Mutability::Shared => Mutability::Not,
1280         hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1281     }
1282 }