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_chalk_trait_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         variant_data,
  35     },
  36     AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, FnPointer, FnSig, GenericPredicate,
  37     ImplTraitId, OpaqueTy, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
  38     ReturnTypeImplTraits, Substitution, 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 = inner.iter().map(|tr| self.lower_ty(tr));
 154                 TyKind::Tuple(inner_tys.len(), Substitution::from_iter(&Interner, inner_tys))
 155                     .intern(&Interner)
 156             }
 157             TypeRef::Path(path) => {
 158                 let (ty, res_) = self.lower_path(path);
 159                 res = res_;
 160                 ty
 161             }
 162             TypeRef::RawPtr(inner, mutability) => {
 163                 let inner_ty = self.lower_ty(inner);
 164                 TyKind::Raw(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
 165             }
 166             TypeRef::Array(inner) => {
 167                 let inner_ty = self.lower_ty(inner);
 168                 TyKind::Array(inner_ty).intern(&Interner)
 169             }
 170             TypeRef::Slice(inner) => {
 171                 let inner_ty = self.lower_ty(inner);
 172                 TyKind::Slice(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), inner_ty).intern(&Interner)
 177             }
 178             TypeRef::Placeholder => TyKind::Unknown.intern(&Interner),
 179             TypeRef::Fn(params, is_varargs) => {
 180                 let substs = Substitution(params.iter().map(|tr| self.lower_ty(tr)).collect());
 181                 TyKind::Function(FnPointer {
 182                     num_args: substs.len() - 1,
 183                     sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
 184                     substs,
 185                 })
 186                 .intern(&Interner)
 187             }
 188             TypeRef::DynTrait(bounds) => {
 189                 let self_ty =
 190                     TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 191                 let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 192                     bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
 193                 });
 194                 TyKind::Dyn(predicates).intern(&Interner)
 195             }
 196             TypeRef::ImplTrait(bounds) => {
 197                 match self.impl_trait_mode {
 198                     ImplTraitLoweringMode::Opaque => {
 199                         let idx = self.impl_trait_counter.get();
 200                         self.impl_trait_counter.set(idx + 1);
 201
 202                         assert!(idx as usize == self.opaque_type_data.borrow().len());
 203                         // this dance is to make sure the data is in the right
 204                         // place even if we encounter more opaque types while
 205                         // lowering the bounds
 206                         self.opaque_type_data
 207                             .borrow_mut()
 208                             .push(ReturnTypeImplTrait { bounds: Binders::new(1, Vec::new()) });
 209                         // We don't want to lower the bounds inside the binders
 210                         // we're currently in, because they don't end up inside
 211                         // those binders. E.g. when we have `impl Trait<impl
 212                         // OtherTrait<T>>`, the `impl OtherTrait<T>` can't refer
 213                         // to the self parameter from `impl Trait`, and the
 214                         // bounds aren't actually stored nested within each
 215                         // other, but separately. So if the `T` refers to a type
 216                         // parameter of the outer function, it's just one binder
 217                         // away instead of two.
 218                         let actual_opaque_type_data = self
 219                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
 220                                 ctx.lower_impl_trait(&bounds)
 221                             });
 222                         self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 223
 224                         let func = match self.resolver.generic_def() {
 225                             Some(GenericDefId::FunctionId(f)) => f,
 226                             _ => panic!("opaque impl trait lowering in non-function"),
 227                         };
 228                         let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
 229                         let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 230                         let generics = generics(self.db.upcast(), func.into());
 231                         let parameters = Substitution::bound_vars(&generics, self.in_binders);
 232                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 233                             opaque_ty_id,
 234                             substitution: parameters,
 235                         }))
 236                         .intern(&Interner)
 237                     }
 238                     ImplTraitLoweringMode::Param => {
 239                         let idx = self.impl_trait_counter.get();
 240                         // FIXME we're probably doing something wrong here
 241                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 242                         if let Some(def) = self.resolver.generic_def() {
 243                             let generics = generics(self.db.upcast(), def);
 244                             let param = generics
 245                                 .iter()
 246                                 .filter(|(_, data)| {
 247                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
 248                                 })
 249                                 .nth(idx as usize)
 250                                 .map_or(TyKind::Unknown, |(id, _)| {
 251                                     TyKind::Placeholder(to_placeholder_idx(self.db, id))
 252                                 });
 253                             param.intern(&Interner)
 254                         } else {
 255                             TyKind::Unknown.intern(&Interner)
 256                         }
 257                     }
 258                     ImplTraitLoweringMode::Variable => {
 259                         let idx = self.impl_trait_counter.get();
 260                         // FIXME we're probably doing something wrong here
 261                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 262                         let (parent_params, self_params, list_params, _impl_trait_params) =
 263                             if let Some(def) = self.resolver.generic_def() {
 264                                 let generics = generics(self.db.upcast(), def);
 265                                 generics.provenance_split()
 266                             } else {
 267                                 (0, 0, 0, 0)
 268                             };
 269                         TyKind::BoundVar(BoundVar::new(
 270                             self.in_binders,
 271                             idx as usize + parent_params + self_params + list_params,
 272                         ))
 273                         .intern(&Interner)
 274                     }
 275                     ImplTraitLoweringMode::Disallowed => {
 276                         // FIXME: report error
 277                         TyKind::Unknown.intern(&Interner)
 278                     }
 279                 }
 280             }
 281             TypeRef::Error => TyKind::Unknown.intern(&Interner),
 282         };
 283         (ty, res)
 284     }
 285
 286     /// This is only for `generic_predicates_for_param`, where we can't just
 287     /// lower the self types of the predicates since that could lead to cycles.
 288     /// So we just check here if the `type_ref` resolves to a generic param, and which.
 289     fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
 290         let path = match type_ref {
 291             TypeRef::Path(path) => path,
 292             _ => return None,
 293         };
 294         if path.type_anchor().is_some() {
 295             return None;
 296         }
 297         if path.segments().len() > 1 {
 298             return None;
 299         }
 300         let resolution =
 301             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 302                 Some((it, None)) => it,
 303                 _ => return None,
 304             };
 305         if let TypeNs::GenericParam(param_id) = resolution {
 306             Some(param_id)
 307         } else {
 308             None
 309         }
 310     }
 311
 312     pub(crate) fn lower_ty_relative_path(
 313         &self,
 314         ty: Ty,
 315         // We need the original resolution to lower `Self::AssocTy` correctly
 316         res: Option<TypeNs>,
 317         remaining_segments: PathSegments<'_>,
 318     ) -> (Ty, Option<TypeNs>) {
 319         if remaining_segments.len() == 1 {
 320             // resolve unselected assoc types
 321             let segment = remaining_segments.first().unwrap();
 322             (self.select_associated_type(res, segment), None)
 323         } else if remaining_segments.len() > 1 {
 324             // FIXME report error (ambiguous associated type)
 325             (TyKind::Unknown.intern(&Interner), None)
 326         } else {
 327             (ty, res)
 328         }
 329     }
 330
 331     pub(crate) fn lower_partly_resolved_path(
 332         &self,
 333         resolution: TypeNs,
 334         resolved_segment: PathSegment<'_>,
 335         remaining_segments: PathSegments<'_>,
 336         infer_args: bool,
 337     ) -> (Ty, Option<TypeNs>) {
 338         let ty = match resolution {
 339             TypeNs::TraitId(trait_) => {
 340                 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
 341                 let self_ty = if remaining_segments.len() == 0 {
 342                     Some(
 343                         TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
 344                             .intern(&Interner),
 345                     )
 346                 } else {
 347                     None
 348                 };
 349                 let trait_ref =
 350                     self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
 351                 let ty = if remaining_segments.len() == 1 {
 352                     let segment = remaining_segments.first().unwrap();
 353                     let found = associated_type_by_name_including_super_traits(
 354                         self.db,
 355                         trait_ref,
 356                         &segment.name,
 357                     );
 358                     match found {
 359                         Some((super_trait_ref, associated_ty)) => {
 360                             // FIXME handle type parameters on the segment
 361                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 362                                 associated_ty_id: to_assoc_type_id(associated_ty),
 363                                 substitution: super_trait_ref.substitution,
 364                             }))
 365                             .intern(&Interner)
 366                         }
 367                         None => {
 368                             // FIXME: report error (associated type not found)
 369                             TyKind::Unknown.intern(&Interner)
 370                         }
 371                     }
 372                 } else if remaining_segments.len() > 1 {
 373                     // FIXME report error (ambiguous associated type)
 374                     TyKind::Unknown.intern(&Interner)
 375                 } else {
 376                     TyKind::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
 377                         .intern(&Interner)
 378                 };
 379                 return (ty, None);
 380             }
 381             TypeNs::GenericParam(param_id) => {
 382                 let generics = generics(
 383                     self.db.upcast(),
 384                     self.resolver.generic_def().expect("generics in scope"),
 385                 );
 386                 match self.type_param_mode {
 387                     TypeParamLoweringMode::Placeholder => {
 388                         TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
 389                     }
 390                     TypeParamLoweringMode::Variable => {
 391                         let idx = generics.param_idx(param_id).expect("matching generics");
 392                         TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
 393                     }
 394                 }
 395                 .intern(&Interner)
 396             }
 397             TypeNs::SelfType(impl_id) => {
 398                 let generics = generics(self.db.upcast(), impl_id.into());
 399                 let substs = match self.type_param_mode {
 400                     TypeParamLoweringMode::Placeholder => {
 401                         Substitution::type_params_for_generics(self.db, &generics)
 402                     }
 403                     TypeParamLoweringMode::Variable => {
 404                         Substitution::bound_vars(&generics, self.in_binders)
 405                     }
 406                 };
 407                 self.db.impl_self_ty(impl_id).subst(&substs)
 408             }
 409             TypeNs::AdtSelfType(adt) => {
 410                 let generics = generics(self.db.upcast(), adt.into());
 411                 let substs = match self.type_param_mode {
 412                     TypeParamLoweringMode::Placeholder => {
 413                         Substitution::type_params_for_generics(self.db, &generics)
 414                     }
 415                     TypeParamLoweringMode::Variable => {
 416                         Substitution::bound_vars(&generics, self.in_binders)
 417                     }
 418                 };
 419                 self.db.ty(adt.into()).subst(&substs)
 420             }
 421
 422             TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
 423             TypeNs::BuiltinType(it) => {
 424                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 425             }
 426             TypeNs::TypeAliasId(it) => {
 427                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 428             }
 429             // FIXME: report error
 430             TypeNs::EnumVariantId(_) => return (TyKind::Unknown.intern(&Interner), None),
 431         };
 432         self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
 433     }
 434
 435     pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
 436         // Resolve the path (in type namespace)
 437         if let Some(type_ref) = path.type_anchor() {
 438             let (ty, res) = self.lower_ty_ext(&type_ref);
 439             return self.lower_ty_relative_path(ty, res, path.segments());
 440         }
 441         let (resolution, remaining_index) =
 442             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 443                 Some(it) => it,
 444                 None => return (TyKind::Unknown.intern(&Interner), None),
 445             };
 446         let (resolved_segment, remaining_segments) = match remaining_index {
 447             None => (
 448                 path.segments().last().expect("resolved path has at least one element"),
 449                 PathSegments::EMPTY,
 450             ),
 451             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
 452         };
 453         self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
 454     }
 455
 456     fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
 457         if let Some(res) = res {
 458             let ty = associated_type_shorthand_candidates(
 459                 self.db,
 460                 res,
 461                 move |name, t, associated_ty| {
 462                     if name == segment.name {
 463                         let substs = match self.type_param_mode {
 464                             TypeParamLoweringMode::Placeholder => {
 465                                 // if we're lowering to placeholders, we have to put
 466                                 // them in now
 467                                 let s = Substitution::type_params(
 468                                     self.db,
 469                                     self.resolver.generic_def().expect(
 470                                         "there should be generics if there's a generic param",
 471                                     ),
 472                                 );
 473                                 t.substitution.clone().subst_bound_vars(&s)
 474                             }
 475                             TypeParamLoweringMode::Variable => t.substitution.clone(),
 476                         };
 477                         // We need to shift in the bound vars, since
 478                         // associated_type_shorthand_candidates does not do that
 479                         let substs = substs.shift_bound_vars(self.in_binders);
 480                         // FIXME handle type parameters on the segment
 481                         return Some(
 482                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 483                                 associated_ty_id: to_assoc_type_id(associated_ty),
 484                                 substitution: substs,
 485                             }))
 486                             .intern(&Interner),
 487                         );
 488                     }
 489
 490                     None
 491                 },
 492             );
 493
 494             ty.unwrap_or(TyKind::Unknown.intern(&Interner))
 495         } else {
 496             TyKind::Unknown.intern(&Interner)
 497         }
 498     }
 499
 500     fn lower_path_inner(
 501         &self,
 502         segment: PathSegment<'_>,
 503         typeable: TyDefId,
 504         infer_args: bool,
 505     ) -> Ty {
 506         let generic_def = match typeable {
 507             TyDefId::BuiltinType(_) => None,
 508             TyDefId::AdtId(it) => Some(it.into()),
 509             TyDefId::TypeAliasId(it) => Some(it.into()),
 510         };
 511         let substs = self.substs_from_path_segment(segment, generic_def, infer_args);
 512         self.db.ty(typeable).subst(&substs)
 513     }
 514
 515     /// Collect generic arguments from a path into a `Substs`. See also
 516     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
 517     pub(super) fn substs_from_path(
 518         &self,
 519         path: &Path,
 520         // Note that we don't call `db.value_type(resolved)` here,
 521         // `ValueTyDefId` is just a convenient way to pass generics and
 522         // special-case enum variants
 523         resolved: ValueTyDefId,
 524         infer_args: bool,
 525     ) -> Substitution {
 526         let last = path.segments().last().expect("path should have at least one segment");
 527         let (segment, generic_def) = match resolved {
 528             ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
 529             ValueTyDefId::StructId(it) => (last, Some(it.into())),
 530             ValueTyDefId::UnionId(it) => (last, Some(it.into())),
 531             ValueTyDefId::ConstId(it) => (last, Some(it.into())),
 532             ValueTyDefId::StaticId(_) => (last, None),
 533             ValueTyDefId::EnumVariantId(var) => {
 534                 // the generic args for an enum variant may be either specified
 535                 // on the segment referring to the enum, or on the segment
 536                 // referring to the variant. So `Option::<T>::None` and
 537                 // `Option::None::<T>` are both allowed (though the former is
 538                 // preferred). See also `def_ids_for_path_segments` in rustc.
 539                 let len = path.segments().len();
 540                 let penultimate = if len >= 2 { path.segments().get(len - 2) } else { None };
 541                 let segment = match penultimate {
 542                     Some(segment) if segment.args_and_bindings.is_some() => segment,
 543                     _ => last,
 544                 };
 545                 (segment, Some(var.parent.into()))
 546             }
 547         };
 548         self.substs_from_path_segment(segment, generic_def, infer_args)
 549     }
 550
 551     fn substs_from_path_segment(
 552         &self,
 553         segment: PathSegment<'_>,
 554         def_generic: Option<GenericDefId>,
 555         infer_args: bool,
 556     ) -> Substitution {
 557         let mut substs = Vec::new();
 558         let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
 559
 560         let (parent_params, self_params, type_params, impl_trait_params) =
 561             def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
 562         let total_len = parent_params + self_params + type_params + impl_trait_params;
 563
 564         substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(parent_params));
 565
 566         let mut had_explicit_type_args = false;
 567
 568         if let Some(generic_args) = &segment.args_and_bindings {
 569             if !generic_args.has_self_type {
 570                 substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(self_params));
 571             }
 572             let expected_num =
 573                 if generic_args.has_self_type { self_params + type_params } else { type_params };
 574             let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
 575             // if args are provided, it should be all of them, but we can't rely on that
 576             for arg in generic_args
 577                 .args
 578                 .iter()
 579                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 580                 .skip(skip)
 581                 .take(expected_num)
 582             {
 583                 match arg {
 584                     GenericArg::Type(type_ref) => {
 585                         had_explicit_type_args = true;
 586                         let ty = self.lower_ty(type_ref);
 587                         substs.push(ty);
 588                     }
 589                     GenericArg::Lifetime(_) => {}
 590                 }
 591             }
 592         }
 593
 594         // handle defaults. In expression or pattern path segments without
 595         // explicitly specified type arguments, missing type arguments are inferred
 596         // (i.e. defaults aren't used).
 597         if !infer_args || had_explicit_type_args {
 598             if let Some(def_generic) = def_generic {
 599                 let defaults = self.db.generic_defaults(def_generic);
 600                 assert_eq!(total_len, defaults.len());
 601
 602                 for default_ty in defaults.iter().skip(substs.len()) {
 603                     // each default can depend on the previous parameters
 604                     let substs_so_far = Substitution(substs.clone().into());
 605                     substs.push(default_ty.clone().subst(&substs_so_far));
 606                 }
 607             }
 608         }
 609
 610         // add placeholders for args that were not provided
 611         // FIXME: emit diagnostics in contexts where this is not allowed
 612         for _ in substs.len()..total_len {
 613             substs.push(TyKind::Unknown.intern(&Interner));
 614         }
 615         assert_eq!(substs.len(), total_len);
 616
 617         Substitution(substs.into())
 618     }
 619
 620     fn lower_trait_ref_from_path(
 621         &self,
 622         path: &Path,
 623         explicit_self_ty: Option<Ty>,
 624     ) -> Option<TraitRef> {
 625         let resolved =
 626             match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
 627                 TypeNs::TraitId(tr) => tr,
 628                 _ => return None,
 629             };
 630         let segment = path.segments().last().expect("path should have at least one segment");
 631         Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
 632     }
 633
 634     pub(crate) fn lower_trait_ref_from_resolved_path(
 635         &self,
 636         resolved: TraitId,
 637         segment: PathSegment<'_>,
 638         explicit_self_ty: Option<Ty>,
 639     ) -> TraitRef {
 640         let mut substs = self.trait_ref_substs_from_path(segment, resolved);
 641         if let Some(self_ty) = explicit_self_ty {
 642             substs.0[0] = self_ty;
 643         }
 644         TraitRef { trait_id: to_chalk_trait_id(resolved), substitution: substs }
 645     }
 646
 647     fn lower_trait_ref(
 648         &self,
 649         type_ref: &TypeRef,
 650         explicit_self_ty: Option<Ty>,
 651     ) -> Option<TraitRef> {
 652         let path = match type_ref {
 653             TypeRef::Path(path) => path,
 654             _ => return None,
 655         };
 656         self.lower_trait_ref_from_path(path, explicit_self_ty)
 657     }
 658
 659     fn trait_ref_substs_from_path(
 660         &self,
 661         segment: PathSegment<'_>,
 662         resolved: TraitId,
 663     ) -> Substitution {
 664         self.substs_from_path_segment(segment, Some(resolved.into()), false)
 665     }
 666
 667     pub(crate) fn lower_where_predicate(
 668         &'a self,
 669         where_predicate: &'a WherePredicate,
 670     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 671         match where_predicate {
 672             WherePredicate::ForLifetime { target, bound, .. }
 673             | WherePredicate::TypeBound { target, bound } => {
 674                 let self_ty = match target {
 675                     WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
 676                     WherePredicateTypeTarget::TypeParam(param_id) => {
 677                         let generic_def = self.resolver.generic_def().expect("generics in scope");
 678                         let generics = generics(self.db.upcast(), generic_def);
 679                         let param_id =
 680                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
 681                         let placeholder = to_placeholder_idx(self.db, param_id);
 682                         match self.type_param_mode {
 683                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
 684                             TypeParamLoweringMode::Variable => {
 685                                 let idx = generics.param_idx(param_id).expect("matching generics");
 686                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
 687                             }
 688                         }
 689                         .intern(&Interner)
 690                     }
 691                 };
 692                 self.lower_type_bound(bound, self_ty).collect::<Vec<_>>().into_iter()
 693             }
 694             WherePredicate::Lifetime { .. } => vec![].into_iter(),
 695         }
 696     }
 697
 698     pub(crate) fn lower_type_bound(
 699         &'a self,
 700         bound: &'a TypeBound,
 701         self_ty: Ty,
 702     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 703         let mut bindings = None;
 704         let trait_ref = match bound {
 705             TypeBound::Path(path) => {
 706                 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
 707                 Some(
 708                     bindings.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented),
 709                 )
 710             }
 711             TypeBound::Lifetime(_) => None,
 712             TypeBound::Error => Some(GenericPredicate::Error),
 713         };
 714         trait_ref.into_iter().chain(
 715             bindings
 716                 .into_iter()
 717                 .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
 718         )
 719     }
 720
 721     fn assoc_type_bindings_from_type_bound(
 722         &'a self,
 723         bound: &'a TypeBound,
 724         trait_ref: TraitRef,
 725     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 726         let last_segment = match bound {
 727             TypeBound::Path(path) => path.segments().last(),
 728             TypeBound::Error | TypeBound::Lifetime(_) => None,
 729         };
 730         last_segment
 731             .into_iter()
 732             .flat_map(|segment| segment.args_and_bindings.into_iter())
 733             .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
 734             .flat_map(move |binding| {
 735                 let found = associated_type_by_name_including_super_traits(
 736                     self.db,
 737                     trait_ref.clone(),
 738                     &binding.name,
 739                 );
 740                 let (super_trait_ref, associated_ty) = match found {
 741                     None => return SmallVec::<[GenericPredicate; 1]>::new(),
 742                     Some(t) => t,
 743                 };
 744                 let projection_ty = ProjectionTy {
 745                     associated_ty_id: to_assoc_type_id(associated_ty),
 746                     substitution: super_trait_ref.substitution,
 747                 };
 748                 let mut preds = SmallVec::with_capacity(
 749                     binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
 750                 );
 751                 if let Some(type_ref) = &binding.type_ref {
 752                     let ty = self.lower_ty(type_ref);
 753                     let projection_predicate =
 754                         ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
 755                     preds.push(GenericPredicate::Projection(projection_predicate));
 756                 }
 757                 for bound in &binding.bounds {
 758                     preds.extend(self.lower_type_bound(
 759                         bound,
 760                         TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
 761                     ));
 762                 }
 763                 preds
 764             })
 765     }
 766
 767     fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
 768         cov_mark::hit!(lower_rpit);
 769         let self_ty =
 770             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 771         let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 772             bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
 773         });
 774         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
 775     }
 776 }
 777
 778 fn count_impl_traits(type_ref: &TypeRef) -> usize {
 779     let mut count = 0;
 780     type_ref.walk(&mut |type_ref| {
 781         if matches!(type_ref, TypeRef::ImplTrait(_)) {
 782             count += 1;
 783         }
 784     });
 785     count
 786 }
 787
 788 /// Build the signature of a callable item (function, struct or enum variant).
 789 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
 790     match def {
 791         CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
 792         CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
 793         CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
 794     }
 795 }
 796
 797 pub fn associated_type_shorthand_candidates<R>(
 798     db: &dyn HirDatabase,
 799     res: TypeNs,
 800     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 801 ) -> Option<R> {
 802     let traits_from_env: Vec<_> = match res {
 803         TypeNs::SelfType(impl_id) => match db.impl_trait(impl_id) {
 804             None => vec![],
 805             Some(trait_ref) => vec![trait_ref.value],
 806         },
 807         TypeNs::GenericParam(param_id) => {
 808             let predicates = db.generic_predicates_for_param(param_id);
 809             let mut traits_: Vec<_> = predicates
 810                 .iter()
 811                 .filter_map(|pred| match &pred.value {
 812                     GenericPredicate::Implemented(tr) => Some(tr.clone()),
 813                     _ => None,
 814                 })
 815                 .collect();
 816             // Handle `Self::Type` referring to own associated type in trait definitions
 817             if let GenericDefId::TraitId(trait_id) = param_id.parent {
 818                 let generics = generics(db.upcast(), trait_id.into());
 819                 if generics.params.types[param_id.local_id].provenance
 820                     == TypeParamProvenance::TraitSelf
 821                 {
 822                     let trait_ref = TraitRef {
 823                         trait_id: to_chalk_trait_id(trait_id),
 824                         substitution: Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST),
 825                     };
 826                     traits_.push(trait_ref);
 827                 }
 828             }
 829             traits_
 830         }
 831         _ => vec![],
 832     };
 833
 834     for t in traits_from_env.into_iter().flat_map(move |t| all_super_trait_refs(db, t)) {
 835         let data = db.trait_data(t.hir_trait_id());
 836
 837         for (name, assoc_id) in &data.items {
 838             match assoc_id {
 839                 AssocItemId::TypeAliasId(alias) => {
 840                     if let Some(result) = cb(name, &t, *alias) {
 841                         return Some(result);
 842                     }
 843                 }
 844                 AssocItemId::FunctionId(_) | AssocItemId::ConstId(_) => {}
 845             }
 846         }
 847     }
 848
 849     None
 850 }
 851
 852 /// Build the type of all specific fields of a struct or enum variant.
 853 pub(crate) fn field_types_query(
 854     db: &dyn HirDatabase,
 855     variant_id: VariantId,
 856 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
 857     let var_data = variant_data(db.upcast(), variant_id);
 858     let (resolver, def): (_, GenericDefId) = match variant_id {
 859         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
 860         VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
 861         VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
 862     };
 863     let generics = generics(db.upcast(), def);
 864     let mut res = ArenaMap::default();
 865     let ctx =
 866         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 867     for (field_id, field_data) in var_data.fields().iter() {
 868         res.insert(field_id, Binders::new(generics.len(), ctx.lower_ty(&field_data.type_ref)))
 869     }
 870     Arc::new(res)
 871 }
 872
 873 /// This query exists only to be used when resolving short-hand associated types
 874 /// like `T::Item`.
 875 ///
 876 /// See the analogous query in rustc and its comment:
 877 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
 878 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
 879 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
 880 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 881 pub(crate) fn generic_predicates_for_param_query(
 882     db: &dyn HirDatabase,
 883     param_id: TypeParamId,
 884 ) -> Arc<[Binders<GenericPredicate>]> {
 885     let resolver = param_id.parent.resolver(db.upcast());
 886     let ctx =
 887         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 888     let generics = generics(db.upcast(), param_id.parent);
 889     resolver
 890         .where_predicates_in_scope()
 891         // we have to filter out all other predicates *first*, before attempting to lower them
 892         .filter(|pred| match pred {
 893             WherePredicate::ForLifetime { target, .. }
 894             | WherePredicate::TypeBound { target, .. } => match target {
 895                 WherePredicateTypeTarget::TypeRef(type_ref) => {
 896                     ctx.lower_ty_only_param(type_ref) == Some(param_id)
 897                 }
 898                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
 899             },
 900             WherePredicate::Lifetime { .. } => false,
 901         })
 902         .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
 903         .collect()
 904 }
 905
 906 pub(crate) fn generic_predicates_for_param_recover(
 907     _db: &dyn HirDatabase,
 908     _cycle: &[String],
 909     _param_id: &TypeParamId,
 910 ) -> Arc<[Binders<GenericPredicate>]> {
 911     Arc::new([])
 912 }
 913
 914 pub(crate) fn trait_environment_query(
 915     db: &dyn HirDatabase,
 916     def: GenericDefId,
 917 ) -> Arc<TraitEnvironment> {
 918     let resolver = def.resolver(db.upcast());
 919     let ctx = TyLoweringContext::new(db, &resolver)
 920         .with_type_param_mode(TypeParamLoweringMode::Placeholder);
 921     let mut traits_in_scope = Vec::new();
 922     let mut clauses = Vec::new();
 923     for pred in resolver.where_predicates_in_scope() {
 924         for pred in ctx.lower_where_predicate(pred) {
 925             if pred.is_error() {
 926                 continue;
 927             }
 928             if let GenericPredicate::Implemented(tr) = &pred {
 929                 traits_in_scope.push((tr.self_type_parameter().clone(), tr.hir_trait_id()));
 930             }
 931             let program_clause: chalk_ir::ProgramClause<Interner> =
 932                 pred.clone().to_chalk(db).cast(&Interner);
 933             clauses.push(program_clause.into_from_env_clause(&Interner));
 934         }
 935     }
 936
 937     let container: Option<AssocContainerId> = match def {
 938         // FIXME: is there a function for this?
 939         GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
 940         GenericDefId::AdtId(_) => None,
 941         GenericDefId::TraitId(_) => None,
 942         GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
 943         GenericDefId::ImplId(_) => None,
 944         GenericDefId::EnumVariantId(_) => None,
 945         GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
 946     };
 947     if let Some(AssocContainerId::TraitId(trait_id)) = container {
 948         // add `Self: Trait<T1, T2, ...>` to the environment in trait
 949         // function default implementations (and hypothetical code
 950         // inside consts or type aliases)
 951         cov_mark::hit!(trait_self_implements_self);
 952         let substs = Substitution::type_params(db, trait_id);
 953         let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
 954         let pred = GenericPredicate::Implemented(trait_ref);
 955         let program_clause: chalk_ir::ProgramClause<Interner> =
 956             pred.clone().to_chalk(db).cast(&Interner);
 957         clauses.push(program_clause.into_from_env_clause(&Interner));
 958     }
 959
 960     let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 961
 962     Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 963 }
 964
 965 /// Resolve the where clause(s) of an item with generics.
 966 pub(crate) fn generic_predicates_query(
 967     db: &dyn HirDatabase,
 968     def: GenericDefId,
 969 ) -> Arc<[Binders<GenericPredicate>]> {
 970     let resolver = def.resolver(db.upcast());
 971     let ctx =
 972         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 973     let generics = generics(db.upcast(), def);
 974     resolver
 975         .where_predicates_in_scope()
 976         .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
 977         .collect()
 978 }
 979
 980 /// Resolve the default type params from generics
 981 pub(crate) fn generic_defaults_query(
 982     db: &dyn HirDatabase,
 983     def: GenericDefId,
 984 ) -> Arc<[Binders<Ty>]> {
 985     let resolver = def.resolver(db.upcast());
 986     let ctx =
 987         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 988     let generic_params = generics(db.upcast(), def);
 989
 990     let defaults = generic_params
 991         .iter()
 992         .enumerate()
 993         .map(|(idx, (_, p))| {
 994             let mut ty =
 995                 p.default.as_ref().map_or(TyKind::Unknown.intern(&Interner), |t| ctx.lower_ty(t));
 996
 997             // Each default can only refer to previous parameters.
 998             ty.walk_mut_binders(
 999                 &mut |ty, binders| match ty.interned_mut() {
1000                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
1001                         if *index >= idx {
1002                             // type variable default referring to parameter coming
1003                             // after it. This is forbidden (FIXME: report
1004                             // diagnostic)
1005                             *ty = TyKind::Unknown.intern(&Interner);
1006                         }
1007                     }
1008                     _ => {}
1009                 },
1010                 DebruijnIndex::INNERMOST,
1011             );
1012
1013             Binders::new(idx, ty)
1014         })
1015         .collect();
1016
1017     defaults
1018 }
1019
1020 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1021     let data = db.function_data(def);
1022     let resolver = def.resolver(db.upcast());
1023     let ctx_params = TyLoweringContext::new(db, &resolver)
1024         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1025         .with_type_param_mode(TypeParamLoweringMode::Variable);
1026     let params = data.params.iter().map(|tr| (&ctx_params).lower_ty(tr)).collect::<Vec<_>>();
1027     let ctx_ret = TyLoweringContext::new(db, &resolver)
1028         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1029         .with_type_param_mode(TypeParamLoweringMode::Variable);
1030     let ret = (&ctx_ret).lower_ty(&data.ret_type);
1031     let generics = generics(db.upcast(), def.into());
1032     let num_binders = generics.len();
1033     Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
1034 }
1035
1036 /// Build the declared type of a function. This should not need to look at the
1037 /// function body.
1038 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1039     let generics = generics(db.upcast(), def.into());
1040     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1041     Binders::new(
1042         substs.len(),
1043         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1044     )
1045 }
1046
1047 /// Build the declared type of a const.
1048 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1049     let data = db.const_data(def);
1050     let generics = generics(db.upcast(), def.into());
1051     let resolver = def.resolver(db.upcast());
1052     let ctx =
1053         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1054
1055     Binders::new(generics.len(), ctx.lower_ty(&data.type_ref))
1056 }
1057
1058 /// Build the declared type of a static.
1059 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1060     let data = db.static_data(def);
1061     let resolver = def.resolver(db.upcast());
1062     let ctx = TyLoweringContext::new(db, &resolver);
1063
1064     Binders::new(0, ctx.lower_ty(&data.type_ref))
1065 }
1066
1067 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1068     let struct_data = db.struct_data(def);
1069     let fields = struct_data.variant_data.fields();
1070     let resolver = def.resolver(db.upcast());
1071     let ctx =
1072         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1073     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1074     let ret = type_for_adt(db, def.into());
1075     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1076 }
1077
1078 /// Build the type of a tuple struct constructor.
1079 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1080     let struct_data = db.struct_data(def);
1081     if let StructKind::Unit = struct_data.variant_data.kind() {
1082         return type_for_adt(db, def.into());
1083     }
1084     let generics = generics(db.upcast(), def.into());
1085     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1086     Binders::new(
1087         substs.len(),
1088         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1089     )
1090 }
1091
1092 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1093     let enum_data = db.enum_data(def.parent);
1094     let var_data = &enum_data.variants[def.local_id];
1095     let fields = var_data.variant_data.fields();
1096     let resolver = def.parent.resolver(db.upcast());
1097     let ctx =
1098         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1099     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1100     let ret = type_for_adt(db, def.parent.into());
1101     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1102 }
1103
1104 /// Build the type of a tuple enum variant constructor.
1105 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1106     let enum_data = db.enum_data(def.parent);
1107     let var_data = &enum_data.variants[def.local_id].variant_data;
1108     if let StructKind::Unit = var_data.kind() {
1109         return type_for_adt(db, def.parent.into());
1110     }
1111     let generics = generics(db.upcast(), def.parent.into());
1112     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1113     Binders::new(
1114         substs.len(),
1115         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1116     )
1117 }
1118
1119 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1120     let generics = generics(db.upcast(), adt.into());
1121     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1122     Binders::new(substs.len(), Ty::adt_ty(adt, substs))
1123 }
1124
1125 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1126     let generics = generics(db.upcast(), t.into());
1127     let resolver = t.resolver(db.upcast());
1128     let ctx =
1129         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1130     if db.type_alias_data(t).is_extern {
1131         Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
1132     } else {
1133         let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1134         let type_ref = &db.type_alias_data(t).type_ref;
1135         let inner = ctx.lower_ty(type_ref.as_ref().unwrap_or(&TypeRef::Error));
1136         Binders::new(substs.len(), inner)
1137     }
1138 }
1139
1140 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1141 pub enum CallableDefId {
1142     FunctionId(FunctionId),
1143     StructId(StructId),
1144     EnumVariantId(EnumVariantId),
1145 }
1146 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1147
1148 impl CallableDefId {
1149     pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1150         let db = db.upcast();
1151         match self {
1152             CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1153             CallableDefId::StructId(s) => s.lookup(db).container,
1154             CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1155         }
1156         .krate()
1157     }
1158 }
1159
1160 impl From<CallableDefId> for GenericDefId {
1161     fn from(def: CallableDefId) -> GenericDefId {
1162         match def {
1163             CallableDefId::FunctionId(f) => f.into(),
1164             CallableDefId::StructId(s) => s.into(),
1165             CallableDefId::EnumVariantId(e) => e.into(),
1166         }
1167     }
1168 }
1169
1170 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1171 pub enum TyDefId {
1172     BuiltinType(BuiltinType),
1173     AdtId(AdtId),
1174     TypeAliasId(TypeAliasId),
1175 }
1176 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1177
1178 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1179 pub enum ValueTyDefId {
1180     FunctionId(FunctionId),
1181     StructId(StructId),
1182     UnionId(UnionId),
1183     EnumVariantId(EnumVariantId),
1184     ConstId(ConstId),
1185     StaticId(StaticId),
1186 }
1187 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1188
1189 /// Build the declared type of an item. This depends on the namespace; e.g. for
1190 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1191 /// the constructor function `(usize) -> Foo` which lives in the values
1192 /// namespace.
1193 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1194     match def {
1195         TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
1196         TyDefId::AdtId(it) => type_for_adt(db, it),
1197         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1198     }
1199 }
1200
1201 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1202     let num_binders = match *def {
1203         TyDefId::BuiltinType(_) => 0,
1204         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
1205         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
1206     };
1207     Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
1208 }
1209
1210 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1211     match def {
1212         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1213         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1214         ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1215         ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1216         ValueTyDefId::ConstId(it) => type_for_const(db, it),
1217         ValueTyDefId::StaticId(it) => type_for_static(db, it),
1218     }
1219 }
1220
1221 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1222     let impl_data = db.impl_data(impl_id);
1223     let resolver = impl_id.resolver(db.upcast());
1224     let generics = generics(db.upcast(), impl_id.into());
1225     let ctx =
1226         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1227     Binders::new(generics.len(), ctx.lower_ty(&impl_data.target_type))
1228 }
1229
1230 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1231     let parent_data = db.generic_params(def.parent);
1232     let data = &parent_data.consts[def.local_id];
1233     let resolver = def.parent.resolver(db.upcast());
1234     let ctx = TyLoweringContext::new(db, &resolver);
1235
1236     ctx.lower_ty(&data.ty)
1237 }
1238
1239 pub(crate) fn impl_self_ty_recover(
1240     db: &dyn HirDatabase,
1241     _cycle: &[String],
1242     impl_id: &ImplId,
1243 ) -> Binders<Ty> {
1244     let generics = generics(db.upcast(), (*impl_id).into());
1245     Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
1246 }
1247
1248 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1249     let impl_data = db.impl_data(impl_id);
1250     let resolver = impl_id.resolver(db.upcast());
1251     let ctx =
1252         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1253     let self_ty = db.impl_self_ty(impl_id);
1254     let target_trait = impl_data.target_trait.as_ref()?;
1255     Some(Binders::new(self_ty.num_binders, ctx.lower_trait_ref(target_trait, Some(self_ty.value))?))
1256 }
1257
1258 pub(crate) fn return_type_impl_traits(
1259     db: &dyn HirDatabase,
1260     def: hir_def::FunctionId,
1261 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1262     // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1263     let data = db.function_data(def);
1264     let resolver = def.resolver(db.upcast());
1265     let ctx_ret = TyLoweringContext::new(db, &resolver)
1266         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1267         .with_type_param_mode(TypeParamLoweringMode::Variable);
1268     let _ret = (&ctx_ret).lower_ty(&data.ret_type);
1269     let generics = generics(db.upcast(), def.into());
1270     let num_binders = generics.len();
1271     let return_type_impl_traits =
1272         ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1273     if return_type_impl_traits.impl_traits.is_empty() {
1274         None
1275     } else {
1276         Some(Arc::new(Binders::new(num_binders, return_type_impl_traits)))
1277     }
1278 }
1279
1280 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1281     match m {
1282         hir_def::type_ref::Mutability::Shared => Mutability::Not,
1283         hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1284     }
1285 }