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,
  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     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::Unknown.intern(&Interner),
 180             TypeRef::Fn(params, is_varargs) => {
 181                 let substs = Substitution(params.iter().map(|tr| self.lower_ty(tr)).collect());
 182                 TyKind::Function(FnPointer {
 183                     num_args: substs.len() - 1,
 184                     sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
 185                     substs,
 186                 })
 187                 .intern(&Interner)
 188             }
 189             TypeRef::DynTrait(bounds) => {
 190                 let self_ty =
 191                     TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 192                 let bounds = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 193                     QuantifiedWhereClauses::from_iter(
 194                         &Interner,
 195                         bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)),
 196                     )
 197                 });
 198                 let bounds = Binders::new(1, bounds);
 199                 TyKind::Dyn(DynTy { bounds }).intern(&Interner)
 200             }
 201             TypeRef::ImplTrait(bounds) => {
 202                 match self.impl_trait_mode {
 203                     ImplTraitLoweringMode::Opaque => {
 204                         let idx = self.impl_trait_counter.get();
 205                         self.impl_trait_counter.set(idx + 1);
 206
 207                         assert!(idx as usize == self.opaque_type_data.borrow().len());
 208                         // this dance is to make sure the data is in the right
 209                         // place even if we encounter more opaque types while
 210                         // lowering the bounds
 211                         self.opaque_type_data
 212                             .borrow_mut()
 213                             .push(ReturnTypeImplTrait { bounds: Binders::new(1, Vec::new()) });
 214                         // We don't want to lower the bounds inside the binders
 215                         // we're currently in, because they don't end up inside
 216                         // those binders. E.g. when we have `impl Trait<impl
 217                         // OtherTrait<T>>`, the `impl OtherTrait<T>` can't refer
 218                         // to the self parameter from `impl Trait`, and the
 219                         // bounds aren't actually stored nested within each
 220                         // other, but separately. So if the `T` refers to a type
 221                         // parameter of the outer function, it's just one binder
 222                         // away instead of two.
 223                         let actual_opaque_type_data = self
 224                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
 225                                 ctx.lower_impl_trait(&bounds)
 226                             });
 227                         self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 228
 229                         let func = match self.resolver.generic_def() {
 230                             Some(GenericDefId::FunctionId(f)) => f,
 231                             _ => panic!("opaque impl trait lowering in non-function"),
 232                         };
 233                         let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
 234                         let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
 235                         let generics = generics(self.db.upcast(), func.into());
 236                         let parameters = Substitution::bound_vars(&generics, self.in_binders);
 237                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 238                             opaque_ty_id,
 239                             substitution: parameters,
 240                         }))
 241                         .intern(&Interner)
 242                     }
 243                     ImplTraitLoweringMode::Param => {
 244                         let idx = self.impl_trait_counter.get();
 245                         // FIXME we're probably doing something wrong here
 246                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 247                         if let Some(def) = self.resolver.generic_def() {
 248                             let generics = generics(self.db.upcast(), def);
 249                             let param = generics
 250                                 .iter()
 251                                 .filter(|(_, data)| {
 252                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
 253                                 })
 254                                 .nth(idx as usize)
 255                                 .map_or(TyKind::Unknown, |(id, _)| {
 256                                     TyKind::Placeholder(to_placeholder_idx(self.db, id))
 257                                 });
 258                             param.intern(&Interner)
 259                         } else {
 260                             TyKind::Unknown.intern(&Interner)
 261                         }
 262                     }
 263                     ImplTraitLoweringMode::Variable => {
 264                         let idx = self.impl_trait_counter.get();
 265                         // FIXME we're probably doing something wrong here
 266                         self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 267                         let (parent_params, self_params, list_params, _impl_trait_params) =
 268                             if let Some(def) = self.resolver.generic_def() {
 269                                 let generics = generics(self.db.upcast(), def);
 270                                 generics.provenance_split()
 271                             } else {
 272                                 (0, 0, 0, 0)
 273                             };
 274                         TyKind::BoundVar(BoundVar::new(
 275                             self.in_binders,
 276                             idx as usize + parent_params + self_params + list_params,
 277                         ))
 278                         .intern(&Interner)
 279                     }
 280                     ImplTraitLoweringMode::Disallowed => {
 281                         // FIXME: report error
 282                         TyKind::Unknown.intern(&Interner)
 283                     }
 284                 }
 285             }
 286             TypeRef::Error => TyKind::Unknown.intern(&Interner),
 287         };
 288         (ty, res)
 289     }
 290
 291     /// This is only for `generic_predicates_for_param`, where we can't just
 292     /// lower the self types of the predicates since that could lead to cycles.
 293     /// So we just check here if the `type_ref` resolves to a generic param, and which.
 294     fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
 295         let path = match type_ref {
 296             TypeRef::Path(path) => path,
 297             _ => return None,
 298         };
 299         if path.type_anchor().is_some() {
 300             return None;
 301         }
 302         if path.segments().len() > 1 {
 303             return None;
 304         }
 305         let resolution =
 306             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 307                 Some((it, None)) => it,
 308                 _ => return None,
 309             };
 310         if let TypeNs::GenericParam(param_id) = resolution {
 311             Some(param_id)
 312         } else {
 313             None
 314         }
 315     }
 316
 317     pub(crate) fn lower_ty_relative_path(
 318         &self,
 319         ty: Ty,
 320         // We need the original resolution to lower `Self::AssocTy` correctly
 321         res: Option<TypeNs>,
 322         remaining_segments: PathSegments<'_>,
 323     ) -> (Ty, Option<TypeNs>) {
 324         if remaining_segments.len() == 1 {
 325             // resolve unselected assoc types
 326             let segment = remaining_segments.first().unwrap();
 327             (self.select_associated_type(res, segment), None)
 328         } else if remaining_segments.len() > 1 {
 329             // FIXME report error (ambiguous associated type)
 330             (TyKind::Unknown.intern(&Interner), None)
 331         } else {
 332             (ty, res)
 333         }
 334     }
 335
 336     pub(crate) fn lower_partly_resolved_path(
 337         &self,
 338         resolution: TypeNs,
 339         resolved_segment: PathSegment<'_>,
 340         remaining_segments: PathSegments<'_>,
 341         infer_args: bool,
 342     ) -> (Ty, Option<TypeNs>) {
 343         let ty = match resolution {
 344             TypeNs::TraitId(trait_) => {
 345                 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
 346                 let self_ty = if remaining_segments.len() == 0 {
 347                     Some(
 348                         TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
 349                             .intern(&Interner),
 350                     )
 351                 } else {
 352                     None
 353                 };
 354                 let trait_ref =
 355                     self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
 356                 let ty = if remaining_segments.len() == 1 {
 357                     let segment = remaining_segments.first().unwrap();
 358                     let found = associated_type_by_name_including_super_traits(
 359                         self.db,
 360                         trait_ref,
 361                         &segment.name,
 362                     );
 363                     match found {
 364                         Some((super_trait_ref, associated_ty)) => {
 365                             // FIXME handle type parameters on the segment
 366                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 367                                 associated_ty_id: to_assoc_type_id(associated_ty),
 368                                 substitution: super_trait_ref.substitution,
 369                             }))
 370                             .intern(&Interner)
 371                         }
 372                         None => {
 373                             // FIXME: report error (associated type not found)
 374                             TyKind::Unknown.intern(&Interner)
 375                         }
 376                     }
 377                 } else if remaining_segments.len() > 1 {
 378                     // FIXME report error (ambiguous associated type)
 379                     TyKind::Unknown.intern(&Interner)
 380                 } else {
 381                     let dyn_ty = DynTy {
 382                         bounds: Binders::new(
 383                             1,
 384                             QuantifiedWhereClauses::from_iter(
 385                                 &Interner,
 386                                 Some(Binders::wrap_empty(WhereClause::Implemented(trait_ref))),
 387                             ),
 388                         ),
 389                     };
 390                     TyKind::Dyn(dyn_ty).intern(&Interner)
 391                 };
 392                 return (ty, None);
 393             }
 394             TypeNs::GenericParam(param_id) => {
 395                 let generics = generics(
 396                     self.db.upcast(),
 397                     self.resolver.generic_def().expect("generics in scope"),
 398                 );
 399                 match self.type_param_mode {
 400                     TypeParamLoweringMode::Placeholder => {
 401                         TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
 402                     }
 403                     TypeParamLoweringMode::Variable => {
 404                         let idx = generics.param_idx(param_id).expect("matching generics");
 405                         TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
 406                     }
 407                 }
 408                 .intern(&Interner)
 409             }
 410             TypeNs::SelfType(impl_id) => {
 411                 let generics = generics(self.db.upcast(), impl_id.into());
 412                 let substs = match self.type_param_mode {
 413                     TypeParamLoweringMode::Placeholder => {
 414                         Substitution::type_params_for_generics(self.db, &generics)
 415                     }
 416                     TypeParamLoweringMode::Variable => {
 417                         Substitution::bound_vars(&generics, self.in_binders)
 418                     }
 419                 };
 420                 self.db.impl_self_ty(impl_id).subst(&substs)
 421             }
 422             TypeNs::AdtSelfType(adt) => {
 423                 let generics = generics(self.db.upcast(), adt.into());
 424                 let substs = match self.type_param_mode {
 425                     TypeParamLoweringMode::Placeholder => {
 426                         Substitution::type_params_for_generics(self.db, &generics)
 427                     }
 428                     TypeParamLoweringMode::Variable => {
 429                         Substitution::bound_vars(&generics, self.in_binders)
 430                     }
 431                 };
 432                 self.db.ty(adt.into()).subst(&substs)
 433             }
 434
 435             TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
 436             TypeNs::BuiltinType(it) => {
 437                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 438             }
 439             TypeNs::TypeAliasId(it) => {
 440                 self.lower_path_inner(resolved_segment, it.into(), infer_args)
 441             }
 442             // FIXME: report error
 443             TypeNs::EnumVariantId(_) => return (TyKind::Unknown.intern(&Interner), None),
 444         };
 445         self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
 446     }
 447
 448     pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
 449         // Resolve the path (in type namespace)
 450         if let Some(type_ref) = path.type_anchor() {
 451             let (ty, res) = self.lower_ty_ext(&type_ref);
 452             return self.lower_ty_relative_path(ty, res, path.segments());
 453         }
 454         let (resolution, remaining_index) =
 455             match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
 456                 Some(it) => it,
 457                 None => return (TyKind::Unknown.intern(&Interner), None),
 458             };
 459         let (resolved_segment, remaining_segments) = match remaining_index {
 460             None => (
 461                 path.segments().last().expect("resolved path has at least one element"),
 462                 PathSegments::EMPTY,
 463             ),
 464             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
 465         };
 466         self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
 467     }
 468
 469     fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
 470         if let Some(res) = res {
 471             let ty = associated_type_shorthand_candidates(
 472                 self.db,
 473                 res,
 474                 move |name, t, associated_ty| {
 475                     if name == segment.name {
 476                         let substs = match self.type_param_mode {
 477                             TypeParamLoweringMode::Placeholder => {
 478                                 // if we're lowering to placeholders, we have to put
 479                                 // them in now
 480                                 let s = Substitution::type_params(
 481                                     self.db,
 482                                     self.resolver.generic_def().expect(
 483                                         "there should be generics if there's a generic param",
 484                                     ),
 485                                 );
 486                                 t.substitution.clone().subst_bound_vars(&s)
 487                             }
 488                             TypeParamLoweringMode::Variable => t.substitution.clone(),
 489                         };
 490                         // We need to shift in the bound vars, since
 491                         // associated_type_shorthand_candidates does not do that
 492                         let substs = substs.shift_bound_vars(self.in_binders);
 493                         // FIXME handle type parameters on the segment
 494                         return Some(
 495                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 496                                 associated_ty_id: to_assoc_type_id(associated_ty),
 497                                 substitution: substs,
 498                             }))
 499                             .intern(&Interner),
 500                         );
 501                     }
 502
 503                     None
 504                 },
 505             );
 506
 507             ty.unwrap_or(TyKind::Unknown.intern(&Interner))
 508         } else {
 509             TyKind::Unknown.intern(&Interner)
 510         }
 511     }
 512
 513     fn lower_path_inner(
 514         &self,
 515         segment: PathSegment<'_>,
 516         typeable: TyDefId,
 517         infer_args: bool,
 518     ) -> Ty {
 519         let generic_def = match typeable {
 520             TyDefId::BuiltinType(_) => None,
 521             TyDefId::AdtId(it) => Some(it.into()),
 522             TyDefId::TypeAliasId(it) => Some(it.into()),
 523         };
 524         let substs = self.substs_from_path_segment(segment, generic_def, infer_args, None);
 525         self.db.ty(typeable).subst(&substs)
 526     }
 527
 528     /// Collect generic arguments from a path into a `Substs`. See also
 529     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
 530     pub(super) fn substs_from_path(
 531         &self,
 532         path: &Path,
 533         // Note that we don't call `db.value_type(resolved)` here,
 534         // `ValueTyDefId` is just a convenient way to pass generics and
 535         // special-case enum variants
 536         resolved: ValueTyDefId,
 537         infer_args: bool,
 538     ) -> Substitution {
 539         let last = path.segments().last().expect("path should have at least one segment");
 540         let (segment, generic_def) = match resolved {
 541             ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
 542             ValueTyDefId::StructId(it) => (last, Some(it.into())),
 543             ValueTyDefId::UnionId(it) => (last, Some(it.into())),
 544             ValueTyDefId::ConstId(it) => (last, Some(it.into())),
 545             ValueTyDefId::StaticId(_) => (last, None),
 546             ValueTyDefId::EnumVariantId(var) => {
 547                 // the generic args for an enum variant may be either specified
 548                 // on the segment referring to the enum, or on the segment
 549                 // referring to the variant. So `Option::<T>::None` and
 550                 // `Option::None::<T>` are both allowed (though the former is
 551                 // preferred). See also `def_ids_for_path_segments` in rustc.
 552                 let len = path.segments().len();
 553                 let penultimate = if len >= 2 { path.segments().get(len - 2) } else { None };
 554                 let segment = match penultimate {
 555                     Some(segment) if segment.args_and_bindings.is_some() => segment,
 556                     _ => last,
 557                 };
 558                 (segment, Some(var.parent.into()))
 559             }
 560         };
 561         self.substs_from_path_segment(segment, generic_def, infer_args, None)
 562     }
 563
 564     fn substs_from_path_segment(
 565         &self,
 566         segment: PathSegment<'_>,
 567         def_generic: Option<GenericDefId>,
 568         infer_args: bool,
 569         explicit_self_ty: Option<Ty>,
 570     ) -> Substitution {
 571         let mut substs = Vec::new();
 572         let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
 573
 574         let (parent_params, self_params, type_params, impl_trait_params) =
 575             def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
 576         let total_len = parent_params + self_params + type_params + impl_trait_params;
 577
 578         substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(parent_params));
 579
 580         let fill_self_params = || {
 581             substs.extend(
 582                 explicit_self_ty
 583                     .into_iter()
 584                     .chain(iter::repeat(TyKind::Unknown.intern(&Interner)))
 585                     .take(self_params),
 586             )
 587         };
 588         let mut had_explicit_type_args = false;
 589
 590         if let Some(generic_args) = &segment.args_and_bindings {
 591             if !generic_args.has_self_type {
 592                 fill_self_params();
 593             }
 594             let expected_num =
 595                 if generic_args.has_self_type { self_params + type_params } else { type_params };
 596             let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
 597             // if args are provided, it should be all of them, but we can't rely on that
 598             for arg in generic_args
 599                 .args
 600                 .iter()
 601                 .filter(|arg| matches!(arg, GenericArg::Type(_)))
 602                 .skip(skip)
 603                 .take(expected_num)
 604             {
 605                 match arg {
 606                     GenericArg::Type(type_ref) => {
 607                         had_explicit_type_args = true;
 608                         let ty = self.lower_ty(type_ref);
 609                         substs.push(ty);
 610                     }
 611                     GenericArg::Lifetime(_) => {}
 612                 }
 613             }
 614         } else {
 615             fill_self_params();
 616         }
 617
 618         // handle defaults. In expression or pattern path segments without
 619         // explicitly specified type arguments, missing type arguments are inferred
 620         // (i.e. defaults aren't used).
 621         if !infer_args || had_explicit_type_args {
 622             if let Some(def_generic) = def_generic {
 623                 let defaults = self.db.generic_defaults(def_generic);
 624                 assert_eq!(total_len, defaults.len());
 625
 626                 for default_ty in defaults.iter().skip(substs.len()) {
 627                     // each default can depend on the previous parameters
 628                     let substs_so_far = Substitution(substs.clone().into());
 629                     substs.push(default_ty.clone().subst(&substs_so_far));
 630                 }
 631             }
 632         }
 633
 634         // add placeholders for args that were not provided
 635         // FIXME: emit diagnostics in contexts where this is not allowed
 636         for _ in substs.len()..total_len {
 637             substs.push(TyKind::Unknown.intern(&Interner));
 638         }
 639         assert_eq!(substs.len(), total_len);
 640
 641         Substitution(substs.into())
 642     }
 643
 644     fn lower_trait_ref_from_path(
 645         &self,
 646         path: &Path,
 647         explicit_self_ty: Option<Ty>,
 648     ) -> Option<TraitRef> {
 649         let resolved =
 650             match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
 651                 TypeNs::TraitId(tr) => tr,
 652                 _ => return None,
 653             };
 654         let segment = path.segments().last().expect("path should have at least one segment");
 655         Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
 656     }
 657
 658     pub(crate) fn lower_trait_ref_from_resolved_path(
 659         &self,
 660         resolved: TraitId,
 661         segment: PathSegment<'_>,
 662         explicit_self_ty: Option<Ty>,
 663     ) -> TraitRef {
 664         let substs = self.trait_ref_substs_from_path(segment, resolved, explicit_self_ty);
 665         TraitRef { trait_id: to_chalk_trait_id(resolved), substitution: substs }
 666     }
 667
 668     fn lower_trait_ref(
 669         &self,
 670         trait_ref: &HirTraitRef,
 671         explicit_self_ty: Option<Ty>,
 672     ) -> Option<TraitRef> {
 673         self.lower_trait_ref_from_path(&trait_ref.path, explicit_self_ty)
 674     }
 675
 676     fn trait_ref_substs_from_path(
 677         &self,
 678         segment: PathSegment<'_>,
 679         resolved: TraitId,
 680         explicit_self_ty: Option<Ty>,
 681     ) -> Substitution {
 682         self.substs_from_path_segment(segment, Some(resolved.into()), false, explicit_self_ty)
 683     }
 684
 685     pub(crate) fn lower_where_predicate(
 686         &'a self,
 687         where_predicate: &'a WherePredicate,
 688         ignore_bindings: bool,
 689     ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
 690         match where_predicate {
 691             WherePredicate::ForLifetime { target, bound, .. }
 692             | WherePredicate::TypeBound { target, bound } => {
 693                 let self_ty = match target {
 694                     WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
 695                     WherePredicateTypeTarget::TypeParam(param_id) => {
 696                         let generic_def = self.resolver.generic_def().expect("generics in scope");
 697                         let generics = generics(self.db.upcast(), generic_def);
 698                         let param_id =
 699                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
 700                         let placeholder = to_placeholder_idx(self.db, param_id);
 701                         match self.type_param_mode {
 702                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
 703                             TypeParamLoweringMode::Variable => {
 704                                 let idx = generics.param_idx(param_id).expect("matching generics");
 705                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
 706                             }
 707                         }
 708                         .intern(&Interner)
 709                     }
 710                 };
 711                 self.lower_type_bound(bound, self_ty, ignore_bindings)
 712                     .collect::<Vec<_>>()
 713                     .into_iter()
 714             }
 715             WherePredicate::Lifetime { .. } => vec![].into_iter(),
 716         }
 717     }
 718
 719     pub(crate) fn lower_type_bound(
 720         &'a self,
 721         bound: &'a TypeBound,
 722         self_ty: Ty,
 723         ignore_bindings: bool,
 724     ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
 725         let mut bindings = None;
 726         let trait_ref = match bound {
 727             TypeBound::Path(path) => {
 728                 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
 729                 bindings.clone().map(WhereClause::Implemented).map(|b| Binders::wrap_empty(b))
 730             }
 731             TypeBound::Lifetime(_) => None,
 732             TypeBound::Error => None,
 733         };
 734         trait_ref.into_iter().chain(
 735             bindings
 736                 .into_iter()
 737                 .filter(move |_| !ignore_bindings)
 738                 .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
 739         )
 740     }
 741
 742     fn assoc_type_bindings_from_type_bound(
 743         &'a self,
 744         bound: &'a TypeBound,
 745         trait_ref: TraitRef,
 746     ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
 747         let last_segment = match bound {
 748             TypeBound::Path(path) => path.segments().last(),
 749             TypeBound::Error | TypeBound::Lifetime(_) => None,
 750         };
 751         last_segment
 752             .into_iter()
 753             .flat_map(|segment| segment.args_and_bindings.into_iter())
 754             .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
 755             .flat_map(move |binding| {
 756                 let found = associated_type_by_name_including_super_traits(
 757                     self.db,
 758                     trait_ref.clone(),
 759                     &binding.name,
 760                 );
 761                 let (super_trait_ref, associated_ty) = match found {
 762                     None => return SmallVec::<[QuantifiedWhereClause; 1]>::new(),
 763                     Some(t) => t,
 764                 };
 765                 let projection_ty = ProjectionTy {
 766                     associated_ty_id: to_assoc_type_id(associated_ty),
 767                     substitution: super_trait_ref.substitution,
 768                 };
 769                 let mut preds = SmallVec::with_capacity(
 770                     binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
 771                 );
 772                 if let Some(type_ref) = &binding.type_ref {
 773                     let ty = self.lower_ty(type_ref);
 774                     let alias_eq =
 775                         AliasEq { alias: AliasTy::Projection(projection_ty.clone()), ty };
 776                     preds.push(Binders::wrap_empty(WhereClause::AliasEq(alias_eq)));
 777                 }
 778                 for bound in &binding.bounds {
 779                     preds.extend(self.lower_type_bound(
 780                         bound,
 781                         TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
 782                         false,
 783                     ));
 784                 }
 785                 preds
 786             })
 787     }
 788
 789     fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
 790         cov_mark::hit!(lower_rpit);
 791         let self_ty =
 792             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 793         let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 794             bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)).collect()
 795         });
 796         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
 797     }
 798 }
 799
 800 fn count_impl_traits(type_ref: &TypeRef) -> usize {
 801     let mut count = 0;
 802     type_ref.walk(&mut |type_ref| {
 803         if matches!(type_ref, TypeRef::ImplTrait(_)) {
 804             count += 1;
 805         }
 806     });
 807     count
 808 }
 809
 810 /// Build the signature of a callable item (function, struct or enum variant).
 811 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
 812     match def {
 813         CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
 814         CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
 815         CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
 816     }
 817 }
 818
 819 pub fn associated_type_shorthand_candidates<R>(
 820     db: &dyn HirDatabase,
 821     res: TypeNs,
 822     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 823 ) -> Option<R> {
 824     let mut search = |t| {
 825         for t in all_super_trait_refs(db, t) {
 826             let data = db.trait_data(t.hir_trait_id());
 827
 828             for (name, assoc_id) in &data.items {
 829                 if let AssocItemId::TypeAliasId(alias) = assoc_id {
 830                     if let Some(result) = cb(name, &t, *alias) {
 831                         return Some(result);
 832                     }
 833                 }
 834             }
 835         }
 836         None
 837     };
 838
 839     match res {
 840         // FIXME: how to correctly handle higher-ranked bounds here?
 841         TypeNs::SelfType(impl_id) => {
 842             search(db.impl_trait(impl_id)?.value.shift_bound_vars_out(DebruijnIndex::ONE))
 843         }
 844         TypeNs::GenericParam(param_id) => {
 845             let predicates = db.generic_predicates_for_param(param_id);
 846             let res = predicates.iter().find_map(|pred| match &pred.value.value {
 847                 // FIXME: how to correctly handle higher-ranked bounds here?
 848                 WhereClause::Implemented(tr) => {
 849                     search(tr.clone().shift_bound_vars_out(DebruijnIndex::ONE))
 850                 }
 851                 _ => None,
 852             });
 853             if let res @ Some(_) = res {
 854                 return res;
 855             }
 856             // Handle `Self::Type` referring to own associated type in trait definitions
 857             if let GenericDefId::TraitId(trait_id) = param_id.parent {
 858                 let generics = generics(db.upcast(), trait_id.into());
 859                 if generics.params.types[param_id.local_id].provenance
 860                     == TypeParamProvenance::TraitSelf
 861                 {
 862                     let trait_ref = TraitRef {
 863                         trait_id: to_chalk_trait_id(trait_id),
 864                         substitution: Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST),
 865                     };
 866                     return search(trait_ref);
 867                 }
 868             }
 869             None
 870         }
 871         _ => None,
 872     }
 873 }
 874
 875 /// Build the type of all specific fields of a struct or enum variant.
 876 pub(crate) fn field_types_query(
 877     db: &dyn HirDatabase,
 878     variant_id: VariantId,
 879 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
 880     let var_data = variant_data(db.upcast(), variant_id);
 881     let (resolver, def): (_, GenericDefId) = match variant_id {
 882         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
 883         VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
 884         VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
 885     };
 886     let generics = generics(db.upcast(), def);
 887     let mut res = ArenaMap::default();
 888     let ctx =
 889         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 890     for (field_id, field_data) in var_data.fields().iter() {
 891         res.insert(field_id, Binders::new(generics.len(), ctx.lower_ty(&field_data.type_ref)))
 892     }
 893     Arc::new(res)
 894 }
 895
 896 /// This query exists only to be used when resolving short-hand associated types
 897 /// like `T::Item`.
 898 ///
 899 /// See the analogous query in rustc and its comment:
 900 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
 901 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
 902 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
 903 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 904 pub(crate) fn generic_predicates_for_param_query(
 905     db: &dyn HirDatabase,
 906     param_id: TypeParamId,
 907 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
 908     let resolver = param_id.parent.resolver(db.upcast());
 909     let ctx =
 910         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 911     let generics = generics(db.upcast(), param_id.parent);
 912     resolver
 913         .where_predicates_in_scope()
 914         // we have to filter out all other predicates *first*, before attempting to lower them
 915         .filter(|pred| match pred {
 916             WherePredicate::ForLifetime { target, .. }
 917             | WherePredicate::TypeBound { target, .. } => match target {
 918                 WherePredicateTypeTarget::TypeRef(type_ref) => {
 919                     ctx.lower_ty_only_param(type_ref) == Some(param_id)
 920                 }
 921                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
 922             },
 923             WherePredicate::Lifetime { .. } => false,
 924         })
 925         .flat_map(|pred| {
 926             ctx.lower_where_predicate(pred, true).map(|p| Binders::new(generics.len(), p))
 927         })
 928         .collect()
 929 }
 930
 931 pub(crate) fn generic_predicates_for_param_recover(
 932     _db: &dyn HirDatabase,
 933     _cycle: &[String],
 934     _param_id: &TypeParamId,
 935 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
 936     Arc::new([])
 937 }
 938
 939 pub(crate) fn trait_environment_query(
 940     db: &dyn HirDatabase,
 941     def: GenericDefId,
 942 ) -> Arc<TraitEnvironment> {
 943     let resolver = def.resolver(db.upcast());
 944     let ctx = TyLoweringContext::new(db, &resolver)
 945         .with_type_param_mode(TypeParamLoweringMode::Placeholder);
 946     let mut traits_in_scope = Vec::new();
 947     let mut clauses = Vec::new();
 948     for pred in resolver.where_predicates_in_scope() {
 949         for pred in ctx.lower_where_predicate(pred, false) {
 950             if let WhereClause::Implemented(tr) = &pred.skip_binders() {
 951                 traits_in_scope.push((tr.self_type_parameter().clone(), tr.hir_trait_id()));
 952             }
 953             let program_clause: chalk_ir::ProgramClause<Interner> =
 954                 pred.clone().to_chalk(db).cast(&Interner);
 955             clauses.push(program_clause.into_from_env_clause(&Interner));
 956         }
 957     }
 958
 959     let container: Option<AssocContainerId> = match def {
 960         // FIXME: is there a function for this?
 961         GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
 962         GenericDefId::AdtId(_) => None,
 963         GenericDefId::TraitId(_) => None,
 964         GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
 965         GenericDefId::ImplId(_) => None,
 966         GenericDefId::EnumVariantId(_) => None,
 967         GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
 968     };
 969     if let Some(AssocContainerId::TraitId(trait_id)) = container {
 970         // add `Self: Trait<T1, T2, ...>` to the environment in trait
 971         // function default implementations (and hypothetical code
 972         // inside consts or type aliases)
 973         cov_mark::hit!(trait_self_implements_self);
 974         let substs = Substitution::type_params(db, trait_id);
 975         let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
 976         let pred = WhereClause::Implemented(trait_ref);
 977         let program_clause: chalk_ir::ProgramClause<Interner> = pred.to_chalk(db).cast(&Interner);
 978         clauses.push(program_clause.into_from_env_clause(&Interner));
 979     }
 980
 981     let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 982
 983     Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 984 }
 985
 986 /// Resolve the where clause(s) of an item with generics.
 987 pub(crate) fn generic_predicates_query(
 988     db: &dyn HirDatabase,
 989     def: GenericDefId,
 990 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
 991     let resolver = def.resolver(db.upcast());
 992     let ctx =
 993         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 994     let generics = generics(db.upcast(), def);
 995     resolver
 996         .where_predicates_in_scope()
 997         .flat_map(|pred| {
 998             ctx.lower_where_predicate(pred, false).map(|p| Binders::new(generics.len(), p))
 999         })
1000         .collect()
1001 }
1002
1003 /// Resolve the default type params from generics
1004 pub(crate) fn generic_defaults_query(
1005     db: &dyn HirDatabase,
1006     def: GenericDefId,
1007 ) -> Arc<[Binders<Ty>]> {
1008     let resolver = def.resolver(db.upcast());
1009     let ctx =
1010         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1011     let generic_params = generics(db.upcast(), def);
1012
1013     let defaults = generic_params
1014         .iter()
1015         .enumerate()
1016         .map(|(idx, (_, p))| {
1017             let mut ty =
1018                 p.default.as_ref().map_or(TyKind::Unknown.intern(&Interner), |t| ctx.lower_ty(t));
1019
1020             // Each default can only refer to previous parameters.
1021             ty.walk_mut_binders(
1022                 &mut |ty, binders| match ty.interned_mut() {
1023                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
1024                         if *index >= idx {
1025                             // type variable default referring to parameter coming
1026                             // after it. This is forbidden (FIXME: report
1027                             // diagnostic)
1028                             *ty = TyKind::Unknown.intern(&Interner);
1029                         }
1030                     }
1031                     _ => {}
1032                 },
1033                 DebruijnIndex::INNERMOST,
1034             );
1035
1036             Binders::new(idx, ty)
1037         })
1038         .collect();
1039
1040     defaults
1041 }
1042
1043 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1044     let data = db.function_data(def);
1045     let resolver = def.resolver(db.upcast());
1046     let ctx_params = TyLoweringContext::new(db, &resolver)
1047         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1048         .with_type_param_mode(TypeParamLoweringMode::Variable);
1049     let params = data.params.iter().map(|tr| (&ctx_params).lower_ty(tr)).collect::<Vec<_>>();
1050     let ctx_ret = TyLoweringContext::new(db, &resolver)
1051         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1052         .with_type_param_mode(TypeParamLoweringMode::Variable);
1053     let ret = (&ctx_ret).lower_ty(&data.ret_type);
1054     let generics = generics(db.upcast(), def.into());
1055     let num_binders = generics.len();
1056     Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
1057 }
1058
1059 /// Build the declared type of a function. This should not need to look at the
1060 /// function body.
1061 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1062     let generics = generics(db.upcast(), def.into());
1063     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1064     Binders::new(
1065         substs.len(),
1066         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1067     )
1068 }
1069
1070 /// Build the declared type of a const.
1071 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1072     let data = db.const_data(def);
1073     let generics = generics(db.upcast(), def.into());
1074     let resolver = def.resolver(db.upcast());
1075     let ctx =
1076         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1077
1078     Binders::new(generics.len(), ctx.lower_ty(&data.type_ref))
1079 }
1080
1081 /// Build the declared type of a static.
1082 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1083     let data = db.static_data(def);
1084     let resolver = def.resolver(db.upcast());
1085     let ctx = TyLoweringContext::new(db, &resolver);
1086
1087     Binders::new(0, ctx.lower_ty(&data.type_ref))
1088 }
1089
1090 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1091     let struct_data = db.struct_data(def);
1092     let fields = struct_data.variant_data.fields();
1093     let resolver = def.resolver(db.upcast());
1094     let ctx =
1095         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1096     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1097     let ret = type_for_adt(db, def.into());
1098     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1099 }
1100
1101 /// Build the type of a tuple struct constructor.
1102 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1103     let struct_data = db.struct_data(def);
1104     if let StructKind::Unit = struct_data.variant_data.kind() {
1105         return type_for_adt(db, def.into());
1106     }
1107     let generics = generics(db.upcast(), def.into());
1108     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1109     Binders::new(
1110         substs.len(),
1111         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1112     )
1113 }
1114
1115 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1116     let enum_data = db.enum_data(def.parent);
1117     let var_data = &enum_data.variants[def.local_id];
1118     let fields = var_data.variant_data.fields();
1119     let resolver = def.parent.resolver(db.upcast());
1120     let ctx =
1121         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1122     let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1123     let ret = type_for_adt(db, def.parent.into());
1124     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1125 }
1126
1127 /// Build the type of a tuple enum variant constructor.
1128 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1129     let enum_data = db.enum_data(def.parent);
1130     let var_data = &enum_data.variants[def.local_id].variant_data;
1131     if let StructKind::Unit = var_data.kind() {
1132         return type_for_adt(db, def.parent.into());
1133     }
1134     let generics = generics(db.upcast(), def.parent.into());
1135     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1136     Binders::new(
1137         substs.len(),
1138         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1139     )
1140 }
1141
1142 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1143     let generics = generics(db.upcast(), adt.into());
1144     let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
1145     Binders::new(substs.len(), Ty::adt_ty(adt, substs))
1146 }
1147
1148 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1149     let generics = generics(db.upcast(), t.into());
1150     let resolver = t.resolver(db.upcast());
1151     let ctx =
1152         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1153     if db.type_alias_data(t).is_extern {
1154         Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
1155     } else {
1156         let type_ref = &db.type_alias_data(t).type_ref;
1157         let inner = ctx.lower_ty(type_ref.as_ref().unwrap_or(&TypeRef::Error));
1158         Binders::new(generics.len(), inner)
1159     }
1160 }
1161
1162 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1163 pub enum CallableDefId {
1164     FunctionId(FunctionId),
1165     StructId(StructId),
1166     EnumVariantId(EnumVariantId),
1167 }
1168 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1169
1170 impl CallableDefId {
1171     pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1172         let db = db.upcast();
1173         match self {
1174             CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1175             CallableDefId::StructId(s) => s.lookup(db).container,
1176             CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1177         }
1178         .krate()
1179     }
1180 }
1181
1182 impl From<CallableDefId> for GenericDefId {
1183     fn from(def: CallableDefId) -> GenericDefId {
1184         match def {
1185             CallableDefId::FunctionId(f) => f.into(),
1186             CallableDefId::StructId(s) => s.into(),
1187             CallableDefId::EnumVariantId(e) => e.into(),
1188         }
1189     }
1190 }
1191
1192 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1193 pub enum TyDefId {
1194     BuiltinType(BuiltinType),
1195     AdtId(AdtId),
1196     TypeAliasId(TypeAliasId),
1197 }
1198 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1199
1200 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1201 pub enum ValueTyDefId {
1202     FunctionId(FunctionId),
1203     StructId(StructId),
1204     UnionId(UnionId),
1205     EnumVariantId(EnumVariantId),
1206     ConstId(ConstId),
1207     StaticId(StaticId),
1208 }
1209 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1210
1211 /// Build the declared type of an item. This depends on the namespace; e.g. for
1212 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1213 /// the constructor function `(usize) -> Foo` which lives in the values
1214 /// namespace.
1215 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1216     match def {
1217         TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
1218         TyDefId::AdtId(it) => type_for_adt(db, it),
1219         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1220     }
1221 }
1222
1223 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1224     let num_binders = match *def {
1225         TyDefId::BuiltinType(_) => 0,
1226         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
1227         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
1228     };
1229     Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
1230 }
1231
1232 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1233     match def {
1234         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1235         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1236         ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1237         ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1238         ValueTyDefId::ConstId(it) => type_for_const(db, it),
1239         ValueTyDefId::StaticId(it) => type_for_static(db, it),
1240     }
1241 }
1242
1243 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1244     let impl_data = db.impl_data(impl_id);
1245     let resolver = impl_id.resolver(db.upcast());
1246     let generics = generics(db.upcast(), impl_id.into());
1247     let ctx =
1248         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1249     Binders::new(generics.len(), ctx.lower_ty(&impl_data.self_ty))
1250 }
1251
1252 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1253     let parent_data = db.generic_params(def.parent);
1254     let data = &parent_data.consts[def.local_id];
1255     let resolver = def.parent.resolver(db.upcast());
1256     let ctx = TyLoweringContext::new(db, &resolver);
1257
1258     ctx.lower_ty(&data.ty)
1259 }
1260
1261 pub(crate) fn impl_self_ty_recover(
1262     db: &dyn HirDatabase,
1263     _cycle: &[String],
1264     impl_id: &ImplId,
1265 ) -> Binders<Ty> {
1266     let generics = generics(db.upcast(), (*impl_id).into());
1267     Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
1268 }
1269
1270 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1271     let impl_data = db.impl_data(impl_id);
1272     let resolver = impl_id.resolver(db.upcast());
1273     let ctx =
1274         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1275     let self_ty = db.impl_self_ty(impl_id);
1276     let target_trait = impl_data.target_trait.as_ref()?;
1277     Some(Binders::new(self_ty.num_binders, ctx.lower_trait_ref(target_trait, Some(self_ty.value))?))
1278 }
1279
1280 pub(crate) fn return_type_impl_traits(
1281     db: &dyn HirDatabase,
1282     def: hir_def::FunctionId,
1283 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1284     // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1285     let data = db.function_data(def);
1286     let resolver = def.resolver(db.upcast());
1287     let ctx_ret = TyLoweringContext::new(db, &resolver)
1288         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1289         .with_type_param_mode(TypeParamLoweringMode::Variable);
1290     let _ret = (&ctx_ret).lower_ty(&data.ret_type);
1291     let generics = generics(db.upcast(), def.into());
1292     let num_binders = generics.len();
1293     let return_type_impl_traits =
1294         ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1295     if return_type_impl_traits.impl_traits.is_empty() {
1296         None
1297     } else {
1298         Some(Arc::new(Binders::new(num_binders, return_type_impl_traits)))
1299     }
1300 }
1301
1302 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1303     match m {
1304         hir_def::type_ref::Mutability::Shared => Mutability::Not,
1305         hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1306     }
1307 }