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::{TraitRef as HirTraitRef, 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, Generics,
  35     },
  36     AliasEq, AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, DynTy, FnPointer, FnSig,
  37     ImplTraitId, OpaqueTy, PolyFnSig, ProjectionTy, QuantifiedWhereClause, QuantifiedWhereClauses,
  38     ReturnTypeImplTrait, ReturnTypeImplTraits, Substitution, TraitEnvironment, TraitRef, Ty,
  39     TyBuilder, TyKind, TypeWalk, WhereClause,
  40 };
  41
  42 #[derive(Debug)]
  43 pub struct TyLoweringContext<'a> {
  44     pub db: &'a dyn HirDatabase,
  45     pub resolver: &'a Resolver,
  46     in_binders: DebruijnIndex,
  47     /// Note: Conceptually, it's thinkable that we could be in a location where
  48     /// some type params should be represented as placeholders, and others
  49     /// should be converted to variables. I think in practice, this isn't
  50     /// possible currently, so this should be fine for now.
  51     pub type_param_mode: TypeParamLoweringMode,
  52     pub impl_trait_mode: ImplTraitLoweringMode,
  53     impl_trait_counter: std::cell::Cell<u16>,
  54     /// When turning `impl Trait` into opaque types, we have to collect the
  55     /// bounds at the same time to get the IDs correct (without becoming too
  56     /// complicated). I don't like using interior mutability (as for the
  57     /// counter), but I've tried and failed to make the lifetimes work for
  58     /// passing around a `&mut TyLoweringContext`. The core problem is that
  59     /// we're grouping the mutable data (the counter and this field) together
  60     /// with the immutable context (the references to the DB and resolver).
  61     /// Splitting this up would be a possible fix.
  62     opaque_type_data: std::cell::RefCell<Vec<ReturnTypeImplTrait>>,
  63 }
  64
  65 impl<'a> TyLoweringContext<'a> {
  66     pub fn new(db: &'a dyn HirDatabase, resolver: &'a Resolver) -> Self {
  67         let impl_trait_counter = std::cell::Cell::new(0);
  68         let impl_trait_mode = ImplTraitLoweringMode::Disallowed;
  69         let type_param_mode = TypeParamLoweringMode::Placeholder;
  70         let in_binders = DebruijnIndex::INNERMOST;
  71         let opaque_type_data = std::cell::RefCell::new(Vec::new());
  72         Self {
  73             db,
  74             resolver,
  75             in_binders,
  76             impl_trait_mode,
  77             impl_trait_counter,
  78             type_param_mode,
  79             opaque_type_data,
  80         }
  81     }
  82
  83     pub fn with_debruijn<T>(
  84         &self,
  85         debruijn: DebruijnIndex,
  86         f: impl FnOnce(&TyLoweringContext) -> T,
  87     ) -> T {
  88         let opaque_ty_data_vec = self.opaque_type_data.replace(Vec::new());
  89         let new_ctx = Self {
  90             in_binders: debruijn,
  91             impl_trait_counter: std::cell::Cell::new(self.impl_trait_counter.get()),
  92             opaque_type_data: std::cell::RefCell::new(opaque_ty_data_vec),
  93             ..*self
  94         };
  95         let result = f(&new_ctx);
  96         self.impl_trait_counter.set(new_ctx.impl_trait_counter.get());
  97         self.opaque_type_data.replace(new_ctx.opaque_type_data.into_inner());
  98         result
  99     }
 100
 101     pub fn with_shifted_in<T>(
 102         &self,
 103         debruijn: DebruijnIndex,
 104         f: impl FnOnce(&TyLoweringContext) -> T,
 105     ) -> T {
 106         self.with_debruijn(self.in_binders.shifted_in_from(debruijn), f)
 107     }
 108
 109     pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
 110         Self { impl_trait_mode, ..self }
 111     }
 112
 113     pub fn with_type_param_mode(self, type_param_mode: TypeParamLoweringMode) -> Self {
 114         Self { type_param_mode, ..self }
 115     }
 116 }
 117
 118 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 119 pub enum ImplTraitLoweringMode {
 120     /// `impl Trait` gets lowered into an opaque type that doesn't unify with
 121     /// anything except itself. This is used in places where values flow 'out',
 122     /// i.e. for arguments of the function we're currently checking, and return
 123     /// types of functions we're calling.
 124     Opaque,
 125     /// `impl Trait` gets lowered into a type variable. Used for argument
 126     /// position impl Trait when inside the respective function, since it allows
 127     /// us to support that without Chalk.
 128     Param,
 129     /// `impl Trait` gets lowered into a variable that can unify with some
 130     /// type. This is used in places where values flow 'in', i.e. for arguments
 131     /// of functions we're calling, and the return type of the function we're
 132     /// currently checking.
 133     Variable,
 134     /// `impl Trait` is disallowed and will be an error.
 135     Disallowed,
 136 }
 137
 138 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 139 pub enum TypeParamLoweringMode {
 140     Placeholder,
 141     Variable,
 142 }
 143
 144 impl<'a> TyLoweringContext<'a> {
 145     pub fn lower_ty(&self, type_ref: &TypeRef) -> Ty {
 146         self.lower_ty_ext(type_ref).0
 147     }
 148
 149     pub fn lower_ty_ext(&self, type_ref: &TypeRef) -> (Ty, Option<TypeNs>) {
 150         let mut res = None;
 151         let ty = match type_ref {
 152             TypeRef::Never => TyKind::Never.intern(&Interner),
 153             TypeRef::Tuple(inner) => {
 154                 let inner_tys = inner.iter().map(|tr| self.lower_ty(tr));
 155                 TyKind::Tuple(inner_tys.len(), Substitution::from_iter(&Interner, inner_tys))
 156                     .intern(&Interner)
 157             }
 158             TypeRef::Path(path) => {
 159                 let (ty, res_) = self.lower_path(path);
 160                 res = res_;
 161                 ty
 162             }
 163             TypeRef::RawPtr(inner, mutability) => {
 164                 let inner_ty = self.lower_ty(inner);
 165                 TyKind::Raw(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
 166             }
 167             TypeRef::Array(inner) => {
 168                 let inner_ty = self.lower_ty(inner);
 169                 TyKind::Array(inner_ty).intern(&Interner)
 170             }
 171             TypeRef::Slice(inner) => {
 172                 let inner_ty = self.lower_ty(inner);
 173                 TyKind::Slice(inner_ty).intern(&Interner)
 174             }
 175             TypeRef::Reference(inner, _, mutability) => {
 176                 let inner_ty = self.lower_ty(inner);
 177                 TyKind::Ref(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
 178             }
 179             TypeRef::Placeholder => TyKind::Error.intern(&Interner),
 180             TypeRef::Fn(params, is_varargs) => {
 181                 let substs =
 182                     Substitution::from_iter(&Interner, params.iter().map(|tr| self.lower_ty(tr)));
 183                 TyKind::Function(FnPointer {
 184                     num_args: substs.len(&Interner) - 1,
 185                     sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
 186                     substs,
 187                 })
 188                 .intern(&Interner)
 189             }
 190             TypeRef::DynTrait(bounds) => {
 191                 let self_ty =
 192                     TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 193                 let bounds = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 194                     QuantifiedWhereClauses::from_iter(
 195                         &Interner,
 196                         bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)),
 197                     )
 198                 });
 199                 let bounds = crate::make_only_type_binders(1, bounds);
 200                 TyKind::Dyn(DynTy { bounds }).intern(&Interner)
 201             }
 202             TypeRef::ImplTrait(bounds) => {
 203                 match self.impl_trait_mode {
 204                     ImplTraitLoweringMode::Opaque => {
 205                         let idx = self.impl_trait_counter.get();
 206                         self.impl_trait_counter.set(idx + 1);
 207
 208                         assert!(idx as usize == self.opaque_type_data.borrow().len());
 209                         // this dance is to make sure the data is in the right
 210                         // place even if we encounter more opaque types while
 211                         // lowering the bounds
 212                         self.opaque_type_data.borrow_mut().push(ReturnTypeImplTrait {
 213                             bounds: crate::make_only_type_binders(1, Vec::new()),
 214                         });
 215                         // We don't want to lower the bounds inside the binders
 216                         // we're currently in, because they don't end up inside
 217                         // those binders. E.g. when we have `impl Trait<impl
 218                         // OtherTrait<T>>`, the `impl OtherTrait<T>` can't refer
 219                         // to the self parameter from `impl Trait`, and the
 220                         // bounds aren't actually stored nested within each
 221                         // other, but separately. So if the `T` refers to a type
 222                         // parameter of the outer function, it's just one binder
 223                         // away instead of two.
 224                         let actual_opaque_type_data = self
 225                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
 226                                 ctx.lower_impl_trait(&bounds)
 227                             });
 228                         self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 229
 230                         let func = match self.resolver.generic_def() {
 231                             Some(GenericDefId::FunctionId(f)) => f,
 232                             _ => panic!("opaque impl trait lowering in non-function"),
 233                         };
 234                         let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
 235                         let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 236                         let generics = generics(self.db.upcast(), func.into());
 237                         let parameters = generics.bound_vars_subst(self.in_binders);
 238                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 239                             opaque_ty_id,
 240                             substitution: parameters,
 241                         }))
 242                         .intern(&Interner)
 243                     }
 244                     ImplTraitLoweringMode::Param => {
 245                         let idx = self.impl_trait_counter.get();
 246                         // FIXME we're probably doing something wrong here
 247                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 248                         if let Some(def) = self.resolver.generic_def() {
 249                             let generics = generics(self.db.upcast(), def);
 250                             let param = generics
 251                                 .iter()
 252                                 .filter(|(_, data)| {
 253                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
 254                                 })
 255                                 .nth(idx as usize)
 256                                 .map_or(TyKind::Error, |(id, _)| {
 257                                     TyKind::Placeholder(to_placeholder_idx(self.db, id))
 258                                 });
 259                             param.intern(&Interner)
 260                         } else {
 261                             TyKind::Error.intern(&Interner)
 262                         }
 263                     }
 264                     ImplTraitLoweringMode::Variable => {
 265                         let idx = self.impl_trait_counter.get();
 266                         // FIXME we're probably doing something wrong here
 267                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 268                         let (parent_params, self_params, list_params, _impl_trait_params) =
 269                             if let Some(def) = self.resolver.generic_def() {
 270                                 let generics = generics(self.db.upcast(), def);
 271                                 generics.provenance_split()
 272                             } else {
 273                                 (0, 0, 0, 0)
 274                             };
 275                         TyKind::BoundVar(BoundVar::new(
 276                             self.in_binders,
 277                             idx as usize + parent_params + self_params + list_params,
 278                         ))
 279                         .intern(&Interner)
 280                     }
 281                     ImplTraitLoweringMode::Disallowed => {
 282                         // FIXME: report error
 283                         TyKind::Error.intern(&Interner)
 284                     }
 285                 }
 286             }
 287             TypeRef::Error => TyKind::Error.intern(&Interner),
 288         };
 289         (ty, res)
 290     }
 291
 292     /// This is only for `generic_predicates_for_param`, where we can't just
 293     /// lower the self types of the predicates since that could lead to cycles.
 294     /// So we just check here if the `type_ref` resolves to a generic param, and which.
 295     fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
 296         let path = match type_ref {
 297             TypeRef::Path(path) => path,
 298             _ => return None,
 299         };
 300         if path.type_anchor().is_some() {
 301             return None;
 302         }
 303         if path.segments().len() > 1 {
 304             return None;
 305         }
 306         let resolution =
 307             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 308                 Some((it, None)) => it,
 309                 _ => return None,
 310             };
 311         if let TypeNs::GenericParam(param_id) = resolution {
 312             Some(param_id)
 313         } else {
 314             None
 315         }
 316     }
 317
 318     pub(crate) fn lower_ty_relative_path(
 319         &self,
 320         ty: Ty,
 321         // We need the original resolution to lower `Self::AssocTy` correctly
 322         res: Option<TypeNs>,
 323         remaining_segments: PathSegments<'_>,
 324     ) -> (Ty, Option<TypeNs>) {
 325         if remaining_segments.len() == 1 {
 326             // resolve unselected assoc types
 327             let segment = remaining_segments.first().unwrap();
 328             (self.select_associated_type(res, segment), None)
 329         } else if remaining_segments.len() > 1 {
 330             // FIXME report error (ambiguous associated type)
 331             (TyKind::Error.intern(&Interner), None)
 332         } else {
 333             (ty, res)
 334         }
 335     }
 336
 337     pub(crate) fn lower_partly_resolved_path(
 338         &self,
 339         resolution: TypeNs,
 340         resolved_segment: PathSegment<'_>,
 341         remaining_segments: PathSegments<'_>,
 342         infer_args: bool,
 343     ) -> (Ty, Option<TypeNs>) {
 344         let ty = match resolution {
 345             TypeNs::TraitId(trait_) => {
 346                 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
 347                 let self_ty = if remaining_segments.len() == 0 {
 348                     Some(
 349                         TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
 350                             .intern(&Interner),
 351                     )
 352                 } else {
 353                     None
 354                 };
 355                 let trait_ref =
 356                     self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
 357                 let ty = if remaining_segments.len() == 1 {
 358                     let segment = remaining_segments.first().unwrap();
 359                     let found = associated_type_by_name_including_super_traits(
 360                         self.db,
 361                         trait_ref,
 362                         &segment.name,
 363                     );
 364                     match found {
 365                         Some((super_trait_ref, associated_ty)) => {
 366                             // FIXME handle type parameters on the segment
 367                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 368                                 associated_ty_id: to_assoc_type_id(associated_ty),
 369                                 substitution: super_trait_ref.substitution,
 370                             }))
 371                             .intern(&Interner)
 372                         }
 373                         None => {
 374                             // FIXME: report error (associated type not found)
 375                             TyKind::Error.intern(&Interner)
 376                         }
 377                     }
 378                 } else if remaining_segments.len() > 1 {
 379                     // FIXME report error (ambiguous associated type)
 380                     TyKind::Error.intern(&Interner)
 381                 } else {
 382                     let dyn_ty = DynTy {
 383                         bounds: crate::make_only_type_binders(
 384                             1,
 385                             QuantifiedWhereClauses::from_iter(
 386                                 &Interner,
 387                                 Some(Binders::wrap_empty(WhereClause::Implemented(trait_ref))),
 388                             ),
 389                         ),
 390                     };
 391                     TyKind::Dyn(dyn_ty).intern(&Interner)
 392                 };
 393                 return (ty, None);
 394             }
 395             TypeNs::GenericParam(param_id) => {
 396                 let generics = generics(
 397                     self.db.upcast(),
 398                     self.resolver.generic_def().expect("generics in scope"),
 399                 );
 400                 match self.type_param_mode {
 401                     TypeParamLoweringMode::Placeholder => {
 402                         TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
 403                     }
 404                     TypeParamLoweringMode::Variable => {
 405                         let idx = generics.param_idx(param_id).expect("matching generics");
 406                         TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
 407                     }
 408                 }
 409                 .intern(&Interner)
 410             }
 411             TypeNs::SelfType(impl_id) => {
 412                 let generics = generics(self.db.upcast(), impl_id.into());
 413                 let substs = match self.type_param_mode {
 414                     TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
 415                     TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
 416                 };
 417                 self.db.impl_self_ty(impl_id).subst(&substs)
 418             }
 419             TypeNs::AdtSelfType(adt) => {
 420                 let generics = generics(self.db.upcast(), adt.into());
 421                 let substs = match self.type_param_mode {
 422                     TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
 423                     TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
 424                 };
 425                 self.db.ty(adt.into()).subst(&substs)
 426             }
 427
 428             TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
 429             TypeNs::BuiltinType(it) => {
 430                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 431             }
 432             TypeNs::TypeAliasId(it) => {
 433                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 434             }
 435             // FIXME: report error
 436             TypeNs::EnumVariantId(_) => return (TyKind::Error.intern(&Interner), None),
 437         };
 438         self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
 439     }
 440
 441     pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
 442         // Resolve the path (in type namespace)
 443         if let Some(type_ref) = path.type_anchor() {
 444             let (ty, res) = self.lower_ty_ext(&type_ref);
 445             return self.lower_ty_relative_path(ty, res, path.segments());
 446         }
 447         let (resolution, remaining_index) =
 448             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 449                 Some(it) => it,
 450                 None => return (TyKind::Error.intern(&Interner), None),
 451             };
 452         let (resolved_segment, remaining_segments) = match remaining_index {
 453             None => (
 454                 path.segments().last().expect("resolved path has at least one element"),
 455                 PathSegments::EMPTY,
 456             ),
 457             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
 458         };
 459         self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
 460     }
 461
 462     fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
 463         if let Some(res) = res {
 464             let ty = associated_type_shorthand_candidates(
 465                 self.db,
 466                 res,
 467                 move |name, t, associated_ty| {
 468                     if name == segment.name {
 469                         let substs = match self.type_param_mode {
 470                             TypeParamLoweringMode::Placeholder => {
 471                                 // if we're lowering to placeholders, we have to put
 472                                 // them in now
 473                                 let generics = generics(
 474                                     self.db.upcast(),
 475                                     self.resolver.generic_def().expect(
 476                                         "there should be generics if there's a generic param",
 477                                     ),
 478                                 );
 479                                 let s = generics.type_params_subst(self.db);
 480                                 t.substitution.clone().subst_bound_vars(&s)
 481                             }
 482                             TypeParamLoweringMode::Variable => t.substitution.clone(),
 483                         };
 484                         // We need to shift in the bound vars, since
 485                         // associated_type_shorthand_candidates does not do that
 486                         let substs = substs.shift_bound_vars(self.in_binders);
 487                         // FIXME handle type parameters on the segment
 488                         return Some(
 489                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 490                                 associated_ty_id: to_assoc_type_id(associated_ty),
 491                                 substitution: substs,
 492                             }))
 493                             .intern(&Interner),
 494                         );
 495                     }
 496
 497                     None
 498                 },
 499             );
 500
 501             ty.unwrap_or(TyKind::Error.intern(&Interner))
 502         } else {
 503             TyKind::Error.intern(&Interner)
 504         }
 505     }
 506
 507     fn lower_path_inner(
 508         &self,
 509         segment: PathSegment<'_>,
 510         typeable: TyDefId,
 511         infer_args: bool,
 512     ) -> Ty {
 513         let generic_def = match typeable {
 514             TyDefId::BuiltinType(_) => None,
 515             TyDefId::AdtId(it) => Some(it.into()),
 516             TyDefId::TypeAliasId(it) => Some(it.into()),
 517         };
 518         let substs = self.substs_from_path_segment(segment, generic_def, infer_args, None);
 519         self.db.ty(typeable).subst(&substs)
 520     }
 521
 522     /// Collect generic arguments from a path into a `Substs`. See also
 523     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
 524     pub(super) fn substs_from_path(
 525         &self,
 526         path: &Path,
 527         // Note that we don't call `db.value_type(resolved)` here,
 528         // `ValueTyDefId` is just a convenient way to pass generics and
 529         // special-case enum variants
 530         resolved: ValueTyDefId,
 531         infer_args: bool,
 532     ) -> Substitution {
 533         let last = path.segments().last().expect("path should have at least one segment");
 534         let (segment, generic_def) = match resolved {
 535             ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
 536             ValueTyDefId::StructId(it) => (last, Some(it.into())),
 537             ValueTyDefId::UnionId(it) => (last, Some(it.into())),
 538             ValueTyDefId::ConstId(it) => (last, Some(it.into())),
 539             ValueTyDefId::StaticId(_) => (last, None),
 540             ValueTyDefId::EnumVariantId(var) => {
 541                 // the generic args for an enum variant may be either specified
 542                 // on the segment referring to the enum, or on the segment
 543                 // referring to the variant. So `Option::<T>::None` and
 544                 // `Option::None::<T>` are both allowed (though the former is
 545                 // preferred). See also `def_ids_for_path_segments` in rustc.
 546                 let len = path.segments().len();
 547                 let penultimate = if len >= 2 { path.segments().get(len - 2) } else { None };
 548                 let segment = match penultimate {
 549                     Some(segment) if segment.args_and_bindings.is_some() => segment,
 550                     _ => last,
 551                 };
 552                 (segment, Some(var.parent.into()))
 553             }
 554         };
 555         self.substs_from_path_segment(segment, generic_def, infer_args, None)
 556     }
 557
 558     fn substs_from_path_segment(
 559         &self,
 560         segment: PathSegment<'_>,
 561         def_generic: Option<GenericDefId>,
 562         infer_args: bool,
 563         explicit_self_ty: Option<Ty>,
 564     ) -> Substitution {
 565         let mut substs = Vec::new();
 566         let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
 567
 568         let (parent_params, self_params, type_params, impl_trait_params) =
 569             def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
 570         let total_len = parent_params + self_params + type_params + impl_trait_params;
 571
 572         substs.extend(iter::repeat(TyKind::Error.intern(&Interner)).take(parent_params));
 573
 574         let fill_self_params = || {
 575             substs.extend(
 576                 explicit_self_ty
 577                     .into_iter()
 578                     .chain(iter::repeat(TyKind::Error.intern(&Interner)))
 579                     .take(self_params),
 580             )
 581         };
 582         let mut had_explicit_type_args = false;
 583
 584         if let Some(generic_args) = &segment.args_and_bindings {
 585             if !generic_args.has_self_type {
 586                 fill_self_params();
 587             }
 588             let expected_num =
 589                 if generic_args.has_self_type { self_params + type_params } else { type_params };
 590             let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
 591             // if args are provided, it should be all of them, but we can't rely on that
 592             for arg in generic_args
 593                 .args
 594                 .iter()
 595                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 596                 .skip(skip)
 597                 .take(expected_num)
 598             {
 599                 match arg {
 600                     GenericArg::Type(type_ref) => {
 601                         had_explicit_type_args = true;
 602                         let ty = self.lower_ty(type_ref);
 603                         substs.push(ty);
 604                     }
 605                     GenericArg::Lifetime(_) => {}
 606                 }
 607             }
 608         } else {
 609             fill_self_params();
 610         }
 611
 612         // handle defaults. In expression or pattern path segments without
 613         // explicitly specified type arguments, missing type arguments are inferred
 614         // (i.e. defaults aren't used).
 615         if !infer_args || had_explicit_type_args {
 616             if let Some(def_generic) = def_generic {
 617                 let defaults = self.db.generic_defaults(def_generic);
 618                 assert_eq!(total_len, defaults.len());
 619
 620                 for default_ty in defaults.iter().skip(substs.len()) {
 621                     // each default can depend on the previous parameters
 622                     let substs_so_far = Substitution::from_iter(&Interner, substs.clone());
 623                     substs.push(default_ty.clone().subst(&substs_so_far));
 624                 }
 625             }
 626         }
 627
 628         // add placeholders for args that were not provided
 629         // FIXME: emit diagnostics in contexts where this is not allowed
 630         for _ in substs.len()..total_len {
 631             substs.push(TyKind::Error.intern(&Interner));
 632         }
 633         assert_eq!(substs.len(), total_len);
 634
 635         Substitution::from_iter(&Interner, substs)
 636     }
 637
 638     fn lower_trait_ref_from_path(
 639         &self,
 640         path: &Path,
 641         explicit_self_ty: Option<Ty>,
 642     ) -> Option<TraitRef> {
 643         let resolved =
 644             match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
 645                 TypeNs::TraitId(tr) => tr,
 646                 _ => return None,
 647             };
 648         let segment = path.segments().last().expect("path should have at least one segment");
 649         Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
 650     }
 651
 652     pub(crate) fn lower_trait_ref_from_resolved_path(
 653         &self,
 654         resolved: TraitId,
 655         segment: PathSegment<'_>,
 656         explicit_self_ty: Option<Ty>,
 657     ) -> TraitRef {
 658         let substs = self.trait_ref_substs_from_path(segment, resolved, explicit_self_ty);
 659         TraitRef { trait_id: to_chalk_trait_id(resolved), substitution: substs }
 660     }
 661
 662     fn lower_trait_ref(
 663         &self,
 664         trait_ref: &HirTraitRef,
 665         explicit_self_ty: Option<Ty>,
 666     ) -> Option<TraitRef> {
 667         self.lower_trait_ref_from_path(&trait_ref.path, explicit_self_ty)
 668     }
 669
 670     fn trait_ref_substs_from_path(
 671         &self,
 672         segment: PathSegment<'_>,
 673         resolved: TraitId,
 674         explicit_self_ty: Option<Ty>,
 675     ) -> Substitution {
 676         self.substs_from_path_segment(segment, Some(resolved.into()), false, explicit_self_ty)
 677     }
 678
 679     pub(crate) fn lower_where_predicate(
 680         &'a self,
 681         where_predicate: &'a WherePredicate,
 682         ignore_bindings: bool,
 683     ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
 684         match where_predicate {
 685             WherePredicate::ForLifetime { target, bound, .. }
 686             | WherePredicate::TypeBound { target, bound } => {
 687                 let self_ty = match target {
 688                     WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
 689                     WherePredicateTypeTarget::TypeParam(param_id) => {
 690                         let generic_def = self.resolver.generic_def().expect("generics in scope");
 691                         let generics = generics(self.db.upcast(), generic_def);
 692                         let param_id =
 693                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
 694                         let placeholder = to_placeholder_idx(self.db, param_id);
 695                         match self.type_param_mode {
 696                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
 697                             TypeParamLoweringMode::Variable => {
 698                                 let idx = generics.param_idx(param_id).expect("matching generics");
 699                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
 700                             }
 701                         }
 702                         .intern(&Interner)
 703                     }
 704                 };
 705                 self.lower_type_bound(bound, self_ty, ignore_bindings)
 706                     .collect::<Vec<_>>()
 707                     .into_iter()
 708             }
 709             WherePredicate::Lifetime { .. } => vec![].into_iter(),
 710         }
 711     }
 712
 713     pub(crate) fn lower_type_bound(
 714         &'a self,
 715         bound: &'a TypeBound,
 716         self_ty: Ty,
 717         ignore_bindings: bool,
 718     ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
 719         let mut bindings = None;
 720         let trait_ref = match bound {
 721             TypeBound::Path(path) => {
 722                 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
 723                 bindings.clone().map(WhereClause::Implemented).map(|b| Binders::wrap_empty(b))
 724             }
 725             TypeBound::Lifetime(_) => None,
 726             TypeBound::Error => None,
 727         };
 728         trait_ref.into_iter().chain(
 729             bindings
 730                 .into_iter()
 731                 .filter(move |_| !ignore_bindings)
 732                 .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
 733         )
 734     }
 735
 736     fn assoc_type_bindings_from_type_bound(
 737         &'a self,
 738         bound: &'a TypeBound,
 739         trait_ref: TraitRef,
 740     ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
 741         let last_segment = match bound {
 742             TypeBound::Path(path) => path.segments().last(),
 743             TypeBound::Error | TypeBound::Lifetime(_) => None,
 744         };
 745         last_segment
 746             .into_iter()
 747             .flat_map(|segment| segment.args_and_bindings.into_iter())
 748             .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
 749             .flat_map(move |binding| {
 750                 let found = associated_type_by_name_including_super_traits(
 751                     self.db,
 752                     trait_ref.clone(),
 753                     &binding.name,
 754                 );
 755                 let (super_trait_ref, associated_ty) = match found {
 756                     None => return SmallVec::<[QuantifiedWhereClause; 1]>::new(),
 757                     Some(t) => t,
 758                 };
 759                 let projection_ty = ProjectionTy {
 760                     associated_ty_id: to_assoc_type_id(associated_ty),
 761                     substitution: super_trait_ref.substitution,
 762                 };
 763                 let mut preds = SmallVec::with_capacity(
 764                     binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
 765                 );
 766                 if let Some(type_ref) = &binding.type_ref {
 767                     let ty = self.lower_ty(type_ref);
 768                     let alias_eq =
 769                         AliasEq { alias: AliasTy::Projection(projection_ty.clone()), ty };
 770                     preds.push(Binders::wrap_empty(WhereClause::AliasEq(alias_eq)));
 771                 }
 772                 for bound in &binding.bounds {
 773                     preds.extend(self.lower_type_bound(
 774                         bound,
 775                         TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
 776                         false,
 777                     ));
 778                 }
 779                 preds
 780             })
 781     }
 782
 783     fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
 784         cov_mark::hit!(lower_rpit);
 785         let self_ty =
 786             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 787         let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 788             bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)).collect()
 789         });
 790         ReturnTypeImplTrait { bounds: crate::make_only_type_binders(1, predicates) }
 791     }
 792 }
 793
 794 fn count_impl_traits(type_ref: &TypeRef) -> usize {
 795     let mut count = 0;
 796     type_ref.walk(&mut |type_ref| {
 797         if matches!(type_ref, TypeRef::ImplTrait(_)) {
 798             count += 1;
 799         }
 800     });
 801     count
 802 }
 803
 804 /// Build the signature of a callable item (function, struct or enum variant).
 805 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
 806     match def {
 807         CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
 808         CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
 809         CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
 810     }
 811 }
 812
 813 pub fn associated_type_shorthand_candidates<R>(
 814     db: &dyn HirDatabase,
 815     res: TypeNs,
 816     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 817 ) -> Option<R> {
 818     let mut search = |t| {
 819         for t in all_super_trait_refs(db, t) {
 820             let data = db.trait_data(t.hir_trait_id());
 821
 822             for (name, assoc_id) in &data.items {
 823                 if let AssocItemId::TypeAliasId(alias) = assoc_id {
 824                     if let Some(result) = cb(name, &t, *alias) {
 825                         return Some(result);
 826                     }
 827                 }
 828             }
 829         }
 830         None
 831     };
 832
 833     match res {
 834         // FIXME: how to correctly handle higher-ranked bounds here?
 835         TypeNs::SelfType(impl_id) => search(
 836             db.impl_trait(impl_id)?
 837                 .into_value_and_skipped_binders()
 838                 .0
 839                 .shift_bound_vars_out(DebruijnIndex::ONE),
 840         ),
 841         TypeNs::GenericParam(param_id) => {
 842             let predicates = db.generic_predicates_for_param(param_id);
 843             let res = predicates.iter().find_map(|pred| match pred.skip_binders().skip_binders() {
 844                 // FIXME: how to correctly handle higher-ranked bounds here?
 845                 WhereClause::Implemented(tr) => {
 846                     search(tr.clone().shift_bound_vars_out(DebruijnIndex::ONE))
 847                 }
 848                 _ => None,
 849             });
 850             if let res @ Some(_) = res {
 851                 return res;
 852             }
 853             // Handle `Self::Type` referring to own associated type in trait definitions
 854             if let GenericDefId::TraitId(trait_id) = param_id.parent {
 855                 let generics = generics(db.upcast(), trait_id.into());
 856                 if generics.params.types[param_id.local_id].provenance
 857                     == TypeParamProvenance::TraitSelf
 858                 {
 859                     let trait_ref = TyBuilder::trait_ref(db, trait_id)
 860                         .fill_with_bound_vars(DebruijnIndex::INNERMOST, 0)
 861                         .build();
 862                     return search(trait_ref);
 863                 }
 864             }
 865             None
 866         }
 867         _ => None,
 868     }
 869 }
 870
 871 /// Build the type of all specific fields of a struct or enum variant.
 872 pub(crate) fn field_types_query(
 873     db: &dyn HirDatabase,
 874     variant_id: VariantId,
 875 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
 876     let var_data = variant_data(db.upcast(), variant_id);
 877     let (resolver, def): (_, GenericDefId) = match variant_id {
 878         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
 879         VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
 880         VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
 881     };
 882     let generics = generics(db.upcast(), def);
 883     let mut res = ArenaMap::default();
 884     let ctx =
 885         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 886     for (field_id, field_data) in var_data.fields().iter() {
 887         res.insert(field_id, make_binders(&generics, ctx.lower_ty(&field_data.type_ref)))
 888     }
 889     Arc::new(res)
 890 }
 891
 892 /// This query exists only to be used when resolving short-hand associated types
 893 /// like `T::Item`.
 894 ///
 895 /// See the analogous query in rustc and its comment:
 896 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
 897 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
 898 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
 899 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 900 pub(crate) fn generic_predicates_for_param_query(
 901     db: &dyn HirDatabase,
 902     param_id: TypeParamId,
 903 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
 904     let resolver = param_id.parent.resolver(db.upcast());
 905     let ctx =
 906         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 907     let generics = generics(db.upcast(), param_id.parent);
 908     resolver
 909         .where_predicates_in_scope()
 910         // we have to filter out all other predicates *first*, before attempting to lower them
 911         .filter(|pred| match pred {
 912             WherePredicate::ForLifetime { target, .. }
 913             | WherePredicate::TypeBound { target, .. } => match target {
 914                 WherePredicateTypeTarget::TypeRef(type_ref) => {
 915                     ctx.lower_ty_only_param(type_ref) == Some(param_id)
 916                 }
 917                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
 918             },
 919             WherePredicate::Lifetime { .. } => false,
 920         })
 921         .flat_map(|pred| ctx.lower_where_predicate(pred, true).map(|p| make_binders(&generics, p)))
 922         .collect()
 923 }
 924
 925 pub(crate) fn generic_predicates_for_param_recover(
 926     _db: &dyn HirDatabase,
 927     _cycle: &[String],
 928     _param_id: &TypeParamId,
 929 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
 930     Arc::new([])
 931 }
 932
 933 pub(crate) fn trait_environment_query(
 934     db: &dyn HirDatabase,
 935     def: GenericDefId,
 936 ) -> Arc<TraitEnvironment> {
 937     let resolver = def.resolver(db.upcast());
 938     let ctx = TyLoweringContext::new(db, &resolver)
 939         .with_type_param_mode(TypeParamLoweringMode::Placeholder);
 940     let mut traits_in_scope = Vec::new();
 941     let mut clauses = Vec::new();
 942     for pred in resolver.where_predicates_in_scope() {
 943         for pred in ctx.lower_where_predicate(pred, false) {
 944             if let WhereClause::Implemented(tr) = &pred.skip_binders() {
 945                 traits_in_scope
 946                     .push((tr.self_type_parameter(&Interner).clone(), tr.hir_trait_id()));
 947             }
 948             let program_clause: chalk_ir::ProgramClause<Interner> =
 949                 pred.clone().to_chalk(db).cast(&Interner);
 950             clauses.push(program_clause.into_from_env_clause(&Interner));
 951         }
 952     }
 953
 954     let container: Option<AssocContainerId> = match def {
 955         // FIXME: is there a function for this?
 956         GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
 957         GenericDefId::AdtId(_) => None,
 958         GenericDefId::TraitId(_) => None,
 959         GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
 960         GenericDefId::ImplId(_) => None,
 961         GenericDefId::EnumVariantId(_) => None,
 962         GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
 963     };
 964     if let Some(AssocContainerId::TraitId(trait_id)) = container {
 965         // add `Self: Trait<T1, T2, ...>` to the environment in trait
 966         // function default implementations (and hypothetical code
 967         // inside consts or type aliases)
 968         cov_mark::hit!(trait_self_implements_self);
 969         let substs = TyBuilder::type_params_subst(db, trait_id);
 970         let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
 971         let pred = WhereClause::Implemented(trait_ref);
 972         let program_clause: chalk_ir::ProgramClause<Interner> = pred.to_chalk(db).cast(&Interner);
 973         clauses.push(program_clause.into_from_env_clause(&Interner));
 974     }
 975
 976     let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 977
 978     Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 979 }
 980
 981 /// Resolve the where clause(s) of an item with generics.
 982 pub(crate) fn generic_predicates_query(
 983     db: &dyn HirDatabase,
 984     def: GenericDefId,
 985 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
 986     let resolver = def.resolver(db.upcast());
 987     let ctx =
 988         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 989     let generics = generics(db.upcast(), def);
 990     resolver
 991         .where_predicates_in_scope()
 992         .flat_map(|pred| ctx.lower_where_predicate(pred, false).map(|p| make_binders(&generics, p)))
 993         .collect()
 994 }
 995
 996 /// Resolve the default type params from generics
 997 pub(crate) fn generic_defaults_query(
 998     db: &dyn HirDatabase,
 999     def: GenericDefId,
1000 ) -> Arc<[Binders<Ty>]> {
1001     let resolver = def.resolver(db.upcast());
1002     let ctx =
1003         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1004     let generic_params = generics(db.upcast(), def);
1005
1006     let defaults = generic_params
1007         .iter()
1008         .enumerate()
1009         .map(|(idx, (_, p))| {
1010             let mut ty =
1011                 p.default.as_ref().map_or(TyKind::Error.intern(&Interner), |t| ctx.lower_ty(t));
1012
1013             // Each default can only refer to previous parameters.
1014             ty.walk_mut_binders(
1015                 &mut |ty, binders| match ty.interned_mut() {
1016                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
1017                         if *index >= idx {
1018                             // type variable default referring to parameter coming
1019                             // after it. This is forbidden (FIXME: report
1020                             // diagnostic)
1021                             *ty = TyKind::Error.intern(&Interner);
1022                         }
1023                     }
1024                     _ => {}
1025                 },
1026                 DebruijnIndex::INNERMOST,
1027             );
1028
1029             crate::make_only_type_binders(idx, ty)
1030         })
1031         .collect();
1032
1033     defaults
1034 }
1035
1036 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1037     let data = db.function_data(def);
1038     let resolver = def.resolver(db.upcast());
1039     let ctx_params = TyLoweringContext::new(db, &resolver)
1040         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1041         .with_type_param_mode(TypeParamLoweringMode::Variable);
1042     let params = data.params.iter().map(|tr| ctx_params.lower_ty(tr)).collect::<Vec<_>>();
1043     let ctx_ret = TyLoweringContext::new(db, &resolver)
1044         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1045         .with_type_param_mode(TypeParamLoweringMode::Variable);
1046     let ret = ctx_ret.lower_ty(&data.ret_type);
1047     let generics = generics(db.upcast(), def.into());
1048     make_binders(&generics, CallableSig::from_params_and_return(params, ret, data.is_varargs()))
1049 }
1050
1051 /// Build the declared type of a function. This should not need to look at the
1052 /// function body.
1053 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1054     let generics = generics(db.upcast(), def.into());
1055     let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
1056     make_binders(
1057         &generics,
1058         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1059     )
1060 }
1061
1062 /// Build the declared type of a const.
1063 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1064     let data = db.const_data(def);
1065     let generics = generics(db.upcast(), def.into());
1066     let resolver = def.resolver(db.upcast());
1067     let ctx =
1068         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1069
1070     make_binders(&generics, ctx.lower_ty(&data.type_ref))
1071 }
1072
1073 /// Build the declared type of a static.
1074 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1075     let data = db.static_data(def);
1076     let resolver = def.resolver(db.upcast());
1077     let ctx = TyLoweringContext::new(db, &resolver);
1078
1079     Binders::empty(&Interner, ctx.lower_ty(&data.type_ref))
1080 }
1081
1082 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1083     let struct_data = db.struct_data(def);
1084     let fields = struct_data.variant_data.fields();
1085     let resolver = def.resolver(db.upcast());
1086     let ctx =
1087         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1088     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1089     let (ret, binders) = type_for_adt(db, def.into()).into_value_and_skipped_binders();
1090     Binders::new(binders, CallableSig::from_params_and_return(params, ret, false))
1091 }
1092
1093 /// Build the type of a tuple struct constructor.
1094 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1095     let struct_data = db.struct_data(def);
1096     if let StructKind::Unit = struct_data.variant_data.kind() {
1097         return type_for_adt(db, def.into());
1098     }
1099     let generics = generics(db.upcast(), def.into());
1100     let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
1101     make_binders(
1102         &generics,
1103         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1104     )
1105 }
1106
1107 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1108     let enum_data = db.enum_data(def.parent);
1109     let var_data = &enum_data.variants[def.local_id];
1110     let fields = var_data.variant_data.fields();
1111     let resolver = def.parent.resolver(db.upcast());
1112     let ctx =
1113         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1114     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1115     let (ret, binders) = type_for_adt(db, def.parent.into()).into_value_and_skipped_binders();
1116     Binders::new(binders, CallableSig::from_params_and_return(params, ret, false))
1117 }
1118
1119 /// Build the type of a tuple enum variant constructor.
1120 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1121     let enum_data = db.enum_data(def.parent);
1122     let var_data = &enum_data.variants[def.local_id].variant_data;
1123     if let StructKind::Unit = var_data.kind() {
1124         return type_for_adt(db, def.parent.into());
1125     }
1126     let generics = generics(db.upcast(), def.parent.into());
1127     let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
1128     make_binders(
1129         &generics,
1130         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1131     )
1132 }
1133
1134 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1135     let generics = generics(db.upcast(), adt.into());
1136     let b = TyBuilder::adt(db, adt);
1137     let ty = b.fill_with_bound_vars(DebruijnIndex::INNERMOST, 0).build();
1138     make_binders(&generics, ty)
1139 }
1140
1141 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1142     let generics = generics(db.upcast(), t.into());
1143     let resolver = t.resolver(db.upcast());
1144     let ctx =
1145         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1146     if db.type_alias_data(t).is_extern {
1147         Binders::empty(&Interner, TyKind::Foreign(crate::to_foreign_def_id(t)).intern(&Interner))
1148     } else {
1149         let type_ref = &db.type_alias_data(t).type_ref;
1150         let inner = ctx.lower_ty(type_ref.as_deref().unwrap_or(&TypeRef::Error));
1151         make_binders(&generics, inner)
1152     }
1153 }
1154
1155 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1156 pub enum CallableDefId {
1157     FunctionId(FunctionId),
1158     StructId(StructId),
1159     EnumVariantId(EnumVariantId),
1160 }
1161 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1162
1163 impl CallableDefId {
1164     pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1165         let db = db.upcast();
1166         match self {
1167             CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1168             CallableDefId::StructId(s) => s.lookup(db).container,
1169             CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1170         }
1171         .krate()
1172     }
1173 }
1174
1175 impl From<CallableDefId> for GenericDefId {
1176     fn from(def: CallableDefId) -> GenericDefId {
1177         match def {
1178             CallableDefId::FunctionId(f) => f.into(),
1179             CallableDefId::StructId(s) => s.into(),
1180             CallableDefId::EnumVariantId(e) => e.into(),
1181         }
1182     }
1183 }
1184
1185 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1186 pub enum TyDefId {
1187     BuiltinType(BuiltinType),
1188     AdtId(AdtId),
1189     TypeAliasId(TypeAliasId),
1190 }
1191 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1192
1193 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1194 pub enum ValueTyDefId {
1195     FunctionId(FunctionId),
1196     StructId(StructId),
1197     UnionId(UnionId),
1198     EnumVariantId(EnumVariantId),
1199     ConstId(ConstId),
1200     StaticId(StaticId),
1201 }
1202 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1203
1204 /// Build the declared type of an item. This depends on the namespace; e.g. for
1205 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1206 /// the constructor function `(usize) -> Foo` which lives in the values
1207 /// namespace.
1208 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1209     match def {
1210         TyDefId::BuiltinType(it) => Binders::empty(&Interner, TyBuilder::builtin(it)),
1211         TyDefId::AdtId(it) => type_for_adt(db, it),
1212         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1213     }
1214 }
1215
1216 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1217     let generics = match *def {
1218         TyDefId::BuiltinType(_) => {
1219             return Binders::empty(&Interner, TyKind::Error.intern(&Interner))
1220         }
1221         TyDefId::AdtId(it) => generics(db.upcast(), it.into()),
1222         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()),
1223     };
1224     make_binders(&generics, TyKind::Error.intern(&Interner))
1225 }
1226
1227 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1228     match def {
1229         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1230         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1231         ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1232         ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1233         ValueTyDefId::ConstId(it) => type_for_const(db, it),
1234         ValueTyDefId::StaticId(it) => type_for_static(db, it),
1235     }
1236 }
1237
1238 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1239     let impl_data = db.impl_data(impl_id);
1240     let resolver = impl_id.resolver(db.upcast());
1241     let generics = generics(db.upcast(), impl_id.into());
1242     let ctx =
1243         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1244     make_binders(&generics, ctx.lower_ty(&impl_data.self_ty))
1245 }
1246
1247 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1248     let parent_data = db.generic_params(def.parent);
1249     let data = &parent_data.consts[def.local_id];
1250     let resolver = def.parent.resolver(db.upcast());
1251     let ctx = TyLoweringContext::new(db, &resolver);
1252
1253     ctx.lower_ty(&data.ty)
1254 }
1255
1256 pub(crate) fn impl_self_ty_recover(
1257     db: &dyn HirDatabase,
1258     _cycle: &[String],
1259     impl_id: &ImplId,
1260 ) -> Binders<Ty> {
1261     let generics = generics(db.upcast(), (*impl_id).into());
1262     make_binders(&generics, TyKind::Error.intern(&Interner))
1263 }
1264
1265 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1266     let impl_data = db.impl_data(impl_id);
1267     let resolver = impl_id.resolver(db.upcast());
1268     let ctx =
1269         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1270     let (self_ty, binders) = db.impl_self_ty(impl_id).into_value_and_skipped_binders();
1271     let target_trait = impl_data.target_trait.as_ref()?;
1272     Some(Binders::new(binders, ctx.lower_trait_ref(target_trait, Some(self_ty))?))
1273 }
1274
1275 pub(crate) fn return_type_impl_traits(
1276     db: &dyn HirDatabase,
1277     def: hir_def::FunctionId,
1278 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1279     // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1280     let data = db.function_data(def);
1281     let resolver = def.resolver(db.upcast());
1282     let ctx_ret = TyLoweringContext::new(db, &resolver)
1283         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1284         .with_type_param_mode(TypeParamLoweringMode::Variable);
1285     let _ret = (&ctx_ret).lower_ty(&data.ret_type);
1286     let generics = generics(db.upcast(), def.into());
1287     let return_type_impl_traits =
1288         ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1289     if return_type_impl_traits.impl_traits.is_empty() {
1290         None
1291     } else {
1292         Some(Arc::new(make_binders(&generics, return_type_impl_traits)))
1293     }
1294 }
1295
1296 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1297     match m {
1298         hir_def::type_ref::Mutability::Shared => Mutability::Not,
1299         hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1300     }
1301 }
1302
1303 fn make_binders<T>(generics: &Generics, value: T) -> Binders<T> {
1304     crate::make_only_type_binders(generics.len(), value)
1305 }