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         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 = inner.iter().map(|tr| self.lower_ty(tr));
 154                 TyKind::Tuple(inner_tys.len(), Substs::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 = Substs(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 = Substs::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.substs,
 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                         Substs::type_params_for_generics(self.db, &generics)
 402                     }
 403                     TypeParamLoweringMode::Variable => {
 404                         Substs::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                         Substs::type_params_for_generics(self.db, &generics)
 414                     }
 415                     TypeParamLoweringMode::Variable => {
 416                         Substs::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 = Substs::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.substs.clone().subst_bound_vars(&s)
 474                             }
 475                             TypeParamLoweringMode::Variable => t.substs.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     ) -> Substs {
 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     ) -> Substs {
 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 = Substs(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         Substs(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_: resolved, 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(&self, segment: PathSegment<'_>, resolved: TraitId) -> Substs {
 660         self.substs_from_path_segment(segment, Some(resolved.into()), false)
 661     }
 662
 663     pub(crate) fn lower_where_predicate(
 664         &'a self,
 665         where_predicate: &'a WherePredicate,
 666     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 667         match where_predicate {
 668             WherePredicate::ForLifetime { target, bound, .. }
 669             | WherePredicate::TypeBound { target, bound } => {
 670                 let self_ty = match target {
 671                     WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
 672                     WherePredicateTypeTarget::TypeParam(param_id) => {
 673                         let generic_def = self.resolver.generic_def().expect("generics in scope");
 674                         let generics = generics(self.db.upcast(), generic_def);
 675                         let param_id =
 676                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
 677                         let placeholder = to_placeholder_idx(self.db, param_id);
 678                         match self.type_param_mode {
 679                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
 680                             TypeParamLoweringMode::Variable => {
 681                                 let idx = generics.param_idx(param_id).expect("matching generics");
 682                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
 683                             }
 684                         }
 685                         .intern(&Interner)
 686                     }
 687                 };
 688                 self.lower_type_bound(bound, self_ty).collect::<Vec<_>>().into_iter()
 689             }
 690             WherePredicate::Lifetime { .. } => vec![].into_iter(),
 691         }
 692     }
 693
 694     pub(crate) fn lower_type_bound(
 695         &'a self,
 696         bound: &'a TypeBound,
 697         self_ty: Ty,
 698     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 699         let mut bindings = None;
 700         let trait_ref = match bound {
 701             TypeBound::Path(path) => {
 702                 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
 703                 Some(
 704                     bindings.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented),
 705                 )
 706             }
 707             TypeBound::Lifetime(_) => None,
 708             TypeBound::Error => Some(GenericPredicate::Error),
 709         };
 710         trait_ref.into_iter().chain(
 711             bindings
 712                 .into_iter()
 713                 .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
 714         )
 715     }
 716
 717     fn assoc_type_bindings_from_type_bound(
 718         &'a self,
 719         bound: &'a TypeBound,
 720         trait_ref: TraitRef,
 721     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 722         let last_segment = match bound {
 723             TypeBound::Path(path) => path.segments().last(),
 724             TypeBound::Error | TypeBound::Lifetime(_) => None,
 725         };
 726         last_segment
 727             .into_iter()
 728             .flat_map(|segment| segment.args_and_bindings.into_iter())
 729             .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
 730             .flat_map(move |binding| {
 731                 let found = associated_type_by_name_including_super_traits(
 732                     self.db,
 733                     trait_ref.clone(),
 734                     &binding.name,
 735                 );
 736                 let (super_trait_ref, associated_ty) = match found {
 737                     None => return SmallVec::<[GenericPredicate; 1]>::new(),
 738                     Some(t) => t,
 739                 };
 740                 let projection_ty = ProjectionTy {
 741                     associated_ty_id: to_assoc_type_id(associated_ty),
 742                     substitution: super_trait_ref.substs,
 743                 };
 744                 let mut preds = SmallVec::with_capacity(
 745                     binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
 746                 );
 747                 if let Some(type_ref) = &binding.type_ref {
 748                     let ty = self.lower_ty(type_ref);
 749                     let projection_predicate =
 750                         ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
 751                     preds.push(GenericPredicate::Projection(projection_predicate));
 752                 }
 753                 for bound in &binding.bounds {
 754                     preds.extend(self.lower_type_bound(
 755                         bound,
 756                         TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
 757                     ));
 758                 }
 759                 preds
 760             })
 761     }
 762
 763     fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
 764         cov_mark::hit!(lower_rpit);
 765         let self_ty =
 766             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 767         let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 768             bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone())).collect()
 769         });
 770         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
 771     }
 772 }
 773
 774 fn count_impl_traits(type_ref: &TypeRef) -> usize {
 775     let mut count = 0;
 776     type_ref.walk(&mut |type_ref| {
 777         if matches!(type_ref, TypeRef::ImplTrait(_)) {
 778             count += 1;
 779         }
 780     });
 781     count
 782 }
 783
 784 /// Build the signature of a callable item (function, struct or enum variant).
 785 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
 786     match def {
 787         CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
 788         CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
 789         CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
 790     }
 791 }
 792
 793 pub fn associated_type_shorthand_candidates<R>(
 794     db: &dyn HirDatabase,
 795     res: TypeNs,
 796     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 797 ) -> Option<R> {
 798     let traits_from_env: Vec<_> = match res {
 799         TypeNs::SelfType(impl_id) => match db.impl_trait(impl_id) {
 800             None => vec![],
 801             Some(trait_ref) => vec![trait_ref.value],
 802         },
 803         TypeNs::GenericParam(param_id) => {
 804             let predicates = db.generic_predicates_for_param(param_id);
 805             let mut traits_: Vec<_> = predicates
 806                 .iter()
 807                 .filter_map(|pred| match &pred.value {
 808                     GenericPredicate::Implemented(tr) => Some(tr.clone()),
 809                     _ => None,
 810                 })
 811                 .collect();
 812             // Handle `Self::Type` referring to own associated type in trait definitions
 813             if let GenericDefId::TraitId(trait_id) = param_id.parent {
 814                 let generics = generics(db.upcast(), trait_id.into());
 815                 if generics.params.types[param_id.local_id].provenance
 816                     == TypeParamProvenance::TraitSelf
 817                 {
 818                     let trait_ref = TraitRef {
 819                         trait_: trait_id,
 820                         substs: Substs::bound_vars(&generics, DebruijnIndex::INNERMOST),
 821                     };
 822                     traits_.push(trait_ref);
 823                 }
 824             }
 825             traits_
 826         }
 827         _ => vec![],
 828     };
 829
 830     for t in traits_from_env.into_iter().flat_map(move |t| all_super_trait_refs(db, t)) {
 831         let data = db.trait_data(t.trait_);
 832
 833         for (name, assoc_id) in &data.items {
 834             match assoc_id {
 835                 AssocItemId::TypeAliasId(alias) => {
 836                     if let Some(result) = cb(name, &t, *alias) {
 837                         return Some(result);
 838                     }
 839                 }
 840                 AssocItemId::FunctionId(_) | AssocItemId::ConstId(_) => {}
 841             }
 842         }
 843     }
 844
 845     None
 846 }
 847
 848 /// Build the type of all specific fields of a struct or enum variant.
 849 pub(crate) fn field_types_query(
 850     db: &dyn HirDatabase,
 851     variant_id: VariantId,
 852 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
 853     let var_data = variant_data(db.upcast(), variant_id);
 854     let (resolver, def): (_, GenericDefId) = match variant_id {
 855         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
 856         VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
 857         VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
 858     };
 859     let generics = generics(db.upcast(), def);
 860     let mut res = ArenaMap::default();
 861     let ctx =
 862         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 863     for (field_id, field_data) in var_data.fields().iter() {
 864         res.insert(field_id, Binders::new(generics.len(), ctx.lower_ty(&field_data.type_ref)))
 865     }
 866     Arc::new(res)
 867 }
 868
 869 /// This query exists only to be used when resolving short-hand associated types
 870 /// like `T::Item`.
 871 ///
 872 /// See the analogous query in rustc and its comment:
 873 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
 874 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
 875 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
 876 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 877 pub(crate) fn generic_predicates_for_param_query(
 878     db: &dyn HirDatabase,
 879     param_id: TypeParamId,
 880 ) -> Arc<[Binders<GenericPredicate>]> {
 881     let resolver = param_id.parent.resolver(db.upcast());
 882     let ctx =
 883         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 884     let generics = generics(db.upcast(), param_id.parent);
 885     resolver
 886         .where_predicates_in_scope()
 887         // we have to filter out all other predicates *first*, before attempting to lower them
 888         .filter(|pred| match pred {
 889             WherePredicate::ForLifetime { target, .. }
 890             | WherePredicate::TypeBound { target, .. } => match target {
 891                 WherePredicateTypeTarget::TypeRef(type_ref) => {
 892                     ctx.lower_ty_only_param(type_ref) == Some(param_id)
 893                 }
 894                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
 895             },
 896             WherePredicate::Lifetime { .. } => false,
 897         })
 898         .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
 899         .collect()
 900 }
 901
 902 pub(crate) fn generic_predicates_for_param_recover(
 903     _db: &dyn HirDatabase,
 904     _cycle: &[String],
 905     _param_id: &TypeParamId,
 906 ) -> Arc<[Binders<GenericPredicate>]> {
 907     Arc::new([])
 908 }
 909
 910 pub(crate) fn trait_environment_query(
 911     db: &dyn HirDatabase,
 912     def: GenericDefId,
 913 ) -> Arc<TraitEnvironment> {
 914     let resolver = def.resolver(db.upcast());
 915     let ctx = TyLoweringContext::new(db, &resolver)
 916         .with_type_param_mode(TypeParamLoweringMode::Placeholder);
 917     let mut traits_in_scope = Vec::new();
 918     let mut clauses = Vec::new();
 919     for pred in resolver.where_predicates_in_scope() {
 920         for pred in ctx.lower_where_predicate(pred) {
 921             if pred.is_error() {
 922                 continue;
 923             }
 924             if let GenericPredicate::Implemented(tr) = &pred {
 925                 traits_in_scope.push((tr.self_ty().clone(), tr.trait_));
 926             }
 927             let program_clause: chalk_ir::ProgramClause<Interner> =
 928                 pred.clone().to_chalk(db).cast(&Interner);
 929             clauses.push(program_clause.into_from_env_clause(&Interner));
 930         }
 931     }
 932
 933     let container: Option<AssocContainerId> = match def {
 934         // FIXME: is there a function for this?
 935         GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
 936         GenericDefId::AdtId(_) => None,
 937         GenericDefId::TraitId(_) => None,
 938         GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
 939         GenericDefId::ImplId(_) => None,
 940         GenericDefId::EnumVariantId(_) => None,
 941         GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
 942     };
 943     if let Some(AssocContainerId::TraitId(trait_id)) = container {
 944         // add `Self: Trait<T1, T2, ...>` to the environment in trait
 945         // function default implementations (and hypothetical code
 946         // inside consts or type aliases)
 947         cov_mark::hit!(trait_self_implements_self);
 948         let substs = Substs::type_params(db, trait_id);
 949         let trait_ref = TraitRef { trait_: trait_id, substs };
 950         let pred = GenericPredicate::Implemented(trait_ref);
 951         let program_clause: chalk_ir::ProgramClause<Interner> =
 952             pred.clone().to_chalk(db).cast(&Interner);
 953         clauses.push(program_clause.into_from_env_clause(&Interner));
 954     }
 955
 956     let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 957
 958     Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 959 }
 960
 961 /// Resolve the where clause(s) of an item with generics.
 962 pub(crate) fn generic_predicates_query(
 963     db: &dyn HirDatabase,
 964     def: GenericDefId,
 965 ) -> Arc<[Binders<GenericPredicate>]> {
 966     let resolver = def.resolver(db.upcast());
 967     let ctx =
 968         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 969     let generics = generics(db.upcast(), def);
 970     resolver
 971         .where_predicates_in_scope()
 972         .flat_map(|pred| ctx.lower_where_predicate(pred).map(|p| Binders::new(generics.len(), p)))
 973         .collect()
 974 }
 975
 976 /// Resolve the default type params from generics
 977 pub(crate) fn generic_defaults_query(
 978     db: &dyn HirDatabase,
 979     def: GenericDefId,
 980 ) -> Arc<[Binders<Ty>]> {
 981     let resolver = def.resolver(db.upcast());
 982     let ctx =
 983         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 984     let generic_params = generics(db.upcast(), def);
 985
 986     let defaults = generic_params
 987         .iter()
 988         .enumerate()
 989         .map(|(idx, (_, p))| {
 990             let mut ty =
 991                 p.default.as_ref().map_or(TyKind::Unknown.intern(&Interner), |t| ctx.lower_ty(t));
 992
 993             // Each default can only refer to previous parameters.
 994             ty.walk_mut_binders(
 995                 &mut |ty, binders| match ty.interned_mut() {
 996                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
 997                         if *index >= idx {
 998                             // type variable default referring to parameter coming
 999                             // after it. This is forbidden (FIXME: report
1000                             // diagnostic)
1001                             *ty = TyKind::Unknown.intern(&Interner);
1002                         }
1003                     }
1004                     _ => {}
1005                 },
1006                 DebruijnIndex::INNERMOST,
1007             );
1008
1009             Binders::new(idx, ty)
1010         })
1011         .collect();
1012
1013     defaults
1014 }
1015
1016 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1017     let data = db.function_data(def);
1018     let resolver = def.resolver(db.upcast());
1019     let ctx_params = TyLoweringContext::new(db, &resolver)
1020         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1021         .with_type_param_mode(TypeParamLoweringMode::Variable);
1022     let params = data.params.iter().map(|tr| (&ctx_params).lower_ty(tr)).collect::<Vec<_>>();
1023     let ctx_ret = TyLoweringContext::new(db, &resolver)
1024         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1025         .with_type_param_mode(TypeParamLoweringMode::Variable);
1026     let ret = (&ctx_ret).lower_ty(&data.ret_type);
1027     let generics = generics(db.upcast(), def.into());
1028     let num_binders = generics.len();
1029     Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
1030 }
1031
1032 /// Build the declared type of a function. This should not need to look at the
1033 /// function body.
1034 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1035     let generics = generics(db.upcast(), def.into());
1036     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1037     Binders::new(
1038         substs.len(),
1039         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1040     )
1041 }
1042
1043 /// Build the declared type of a const.
1044 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1045     let data = db.const_data(def);
1046     let generics = generics(db.upcast(), def.into());
1047     let resolver = def.resolver(db.upcast());
1048     let ctx =
1049         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1050
1051     Binders::new(generics.len(), ctx.lower_ty(&data.type_ref))
1052 }
1053
1054 /// Build the declared type of a static.
1055 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1056     let data = db.static_data(def);
1057     let resolver = def.resolver(db.upcast());
1058     let ctx = TyLoweringContext::new(db, &resolver);
1059
1060     Binders::new(0, ctx.lower_ty(&data.type_ref))
1061 }
1062
1063 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1064     let struct_data = db.struct_data(def);
1065     let fields = struct_data.variant_data.fields();
1066     let resolver = def.resolver(db.upcast());
1067     let ctx =
1068         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1069     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1070     let ret = type_for_adt(db, def.into());
1071     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1072 }
1073
1074 /// Build the type of a tuple struct constructor.
1075 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1076     let struct_data = db.struct_data(def);
1077     if let StructKind::Unit = struct_data.variant_data.kind() {
1078         return type_for_adt(db, def.into());
1079     }
1080     let generics = generics(db.upcast(), def.into());
1081     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1082     Binders::new(
1083         substs.len(),
1084         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1085     )
1086 }
1087
1088 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1089     let enum_data = db.enum_data(def.parent);
1090     let var_data = &enum_data.variants[def.local_id];
1091     let fields = var_data.variant_data.fields();
1092     let resolver = def.parent.resolver(db.upcast());
1093     let ctx =
1094         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1095     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1096     let ret = type_for_adt(db, def.parent.into());
1097     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1098 }
1099
1100 /// Build the type of a tuple enum variant constructor.
1101 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1102     let enum_data = db.enum_data(def.parent);
1103     let var_data = &enum_data.variants[def.local_id].variant_data;
1104     if let StructKind::Unit = var_data.kind() {
1105         return type_for_adt(db, def.parent.into());
1106     }
1107     let generics = generics(db.upcast(), def.parent.into());
1108     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1109     Binders::new(
1110         substs.len(),
1111         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1112     )
1113 }
1114
1115 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1116     let generics = generics(db.upcast(), adt.into());
1117     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1118     Binders::new(substs.len(), Ty::adt_ty(adt, substs))
1119 }
1120
1121 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1122     let generics = generics(db.upcast(), t.into());
1123     let resolver = t.resolver(db.upcast());
1124     let ctx =
1125         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1126     if db.type_alias_data(t).is_extern {
1127         Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
1128     } else {
1129         let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1130         let type_ref = &db.type_alias_data(t).type_ref;
1131         let inner = ctx.lower_ty(type_ref.as_ref().unwrap_or(&TypeRef::Error));
1132         Binders::new(substs.len(), inner)
1133     }
1134 }
1135
1136 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1137 pub enum CallableDefId {
1138     FunctionId(FunctionId),
1139     StructId(StructId),
1140     EnumVariantId(EnumVariantId),
1141 }
1142 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1143
1144 impl CallableDefId {
1145     pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1146         let db = db.upcast();
1147         match self {
1148             CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1149             CallableDefId::StructId(s) => s.lookup(db).container,
1150             CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1151         }
1152         .krate()
1153     }
1154 }
1155
1156 impl From<CallableDefId> for GenericDefId {
1157     fn from(def: CallableDefId) -> GenericDefId {
1158         match def {
1159             CallableDefId::FunctionId(f) => f.into(),
1160             CallableDefId::StructId(s) => s.into(),
1161             CallableDefId::EnumVariantId(e) => e.into(),
1162         }
1163     }
1164 }
1165
1166 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1167 pub enum TyDefId {
1168     BuiltinType(BuiltinType),
1169     AdtId(AdtId),
1170     TypeAliasId(TypeAliasId),
1171 }
1172 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1173
1174 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1175 pub enum ValueTyDefId {
1176     FunctionId(FunctionId),
1177     StructId(StructId),
1178     UnionId(UnionId),
1179     EnumVariantId(EnumVariantId),
1180     ConstId(ConstId),
1181     StaticId(StaticId),
1182 }
1183 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1184
1185 /// Build the declared type of an item. This depends on the namespace; e.g. for
1186 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1187 /// the constructor function `(usize) -> Foo` which lives in the values
1188 /// namespace.
1189 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1190     match def {
1191         TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
1192         TyDefId::AdtId(it) => type_for_adt(db, it),
1193         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1194     }
1195 }
1196
1197 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1198     let num_binders = match *def {
1199         TyDefId::BuiltinType(_) => 0,
1200         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
1201         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
1202     };
1203     Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
1204 }
1205
1206 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1207     match def {
1208         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1209         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1210         ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1211         ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1212         ValueTyDefId::ConstId(it) => type_for_const(db, it),
1213         ValueTyDefId::StaticId(it) => type_for_static(db, it),
1214     }
1215 }
1216
1217 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1218     let impl_data = db.impl_data(impl_id);
1219     let resolver = impl_id.resolver(db.upcast());
1220     let generics = generics(db.upcast(), impl_id.into());
1221     let ctx =
1222         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1223     Binders::new(generics.len(), ctx.lower_ty(&impl_data.target_type))
1224 }
1225
1226 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1227     let parent_data = db.generic_params(def.parent);
1228     let data = &parent_data.consts[def.local_id];
1229     let resolver = def.parent.resolver(db.upcast());
1230     let ctx = TyLoweringContext::new(db, &resolver);
1231
1232     ctx.lower_ty(&data.ty)
1233 }
1234
1235 pub(crate) fn impl_self_ty_recover(
1236     db: &dyn HirDatabase,
1237     _cycle: &[String],
1238     impl_id: &ImplId,
1239 ) -> Binders<Ty> {
1240     let generics = generics(db.upcast(), (*impl_id).into());
1241     Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
1242 }
1243
1244 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1245     let impl_data = db.impl_data(impl_id);
1246     let resolver = impl_id.resolver(db.upcast());
1247     let ctx =
1248         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1249     let self_ty = db.impl_self_ty(impl_id);
1250     let target_trait = impl_data.target_trait.as_ref()?;
1251     Some(Binders::new(self_ty.num_binders, ctx.lower_trait_ref(target_trait, Some(self_ty.value))?))
1252 }
1253
1254 pub(crate) fn return_type_impl_traits(
1255     db: &dyn HirDatabase,
1256     def: hir_def::FunctionId,
1257 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1258     // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1259     let data = db.function_data(def);
1260     let resolver = def.resolver(db.upcast());
1261     let ctx_ret = TyLoweringContext::new(db, &resolver)
1262         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1263         .with_type_param_mode(TypeParamLoweringMode::Variable);
1264     let _ret = (&ctx_ret).lower_ty(&data.ret_type);
1265     let generics = generics(db.upcast(), def.into());
1266     let num_binders = generics.len();
1267     let return_type_impl_traits =
1268         ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1269     if return_type_impl_traits.impl_traits.is_empty() {
1270         None
1271     } else {
1272         Some(Arc::new(Binders::new(num_binders, return_type_impl_traits)))
1273     }
1274 }
1275
1276 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1277     match m {
1278         hir_def::type_ref::Mutability::Shared => Mutability::Not,
1279         hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1280     }
1281 }