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};
  12 use hir_def::{
  13     adt::StructKind,
  14     builtin_type::BuiltinType,
  15     generics::{TypeParamProvenance, WherePredicate, WherePredicateTypeTarget},
  16     path::{GenericArg, Path, PathSegment, PathSegments},
  17     resolver::{HasResolver, Resolver, TypeNs},
  18     type_ref::{TypeBound, TypeRef},
  19     AdtId, AssocContainerId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
  20     GenericDefId, HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId,
  21     TypeAliasId, TypeParamId, UnionId, VariantId,
  22 };
  23 use hir_expand::name::Name;
  24 use la_arena::ArenaMap;
  25 use smallvec::SmallVec;
  26 use stdx::impl_from;
  27
  28 use crate::{
  29     db::HirDatabase,
  30     to_assoc_type_id,
  31     traits::chalk::{Interner, ToChalk},
  32     utils::{
  33         all_super_trait_refs, associated_type_by_name_including_super_traits, generics,
  34         make_mut_slice, variant_data,
  35     },
  36     AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, FnPointer, FnSig, GenericPredicate,
  37     OpaqueTy, OpaqueTyId, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
  38     ReturnTypeImplTraits, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeWalk,
  39 };
  40
  41 #[derive(Debug)]
  42 pub struct TyLoweringContext<'a> {
  43     pub db: &'a dyn HirDatabase,
  44     pub resolver: &'a Resolver,
  45     in_binders: DebruijnIndex,
  46     /// Note: Conceptually, it's thinkable that we could be in a location where
  47     /// some type params should be represented as placeholders, and others
  48     /// should be converted to variables. I think in practice, this isn't
  49     /// possible currently, so this should be fine for now.
  50     pub type_param_mode: TypeParamLoweringMode,
  51     pub impl_trait_mode: ImplTraitLoweringMode,
  52     impl_trait_counter: std::cell::Cell<u16>,
  53     /// When turning `impl Trait` into opaque types, we have to collect the
  54     /// bounds at the same time to get the IDs correct (without becoming too
  55     /// complicated). I don't like using interior mutability (as for the
  56     /// counter), but I've tried and failed to make the lifetimes work for
  57     /// passing around a `&mut TyLoweringContext`. The core problem is that
  58     /// we're grouping the mutable data (the counter and this field) together
  59     /// with the immutable context (the references to the DB and resolver).
  60     /// Splitting this up would be a possible fix.
  61     opaque_type_data: std::cell::RefCell<Vec<ReturnTypeImplTrait>>,
  62 }
  63
  64 impl<'a> TyLoweringContext<'a> {
  65     pub fn new(db: &'a dyn HirDatabase, resolver: &'a Resolver) -> Self {
  66         let impl_trait_counter = std::cell::Cell::new(0);
  67         let impl_trait_mode = ImplTraitLoweringMode::Disallowed;
  68         let type_param_mode = TypeParamLoweringMode::Placeholder;
  69         let in_binders = DebruijnIndex::INNERMOST;
  70         let opaque_type_data = std::cell::RefCell::new(Vec::new());
  71         Self {
  72             db,
  73             resolver,
  74             in_binders,
  75             impl_trait_mode,
  76             impl_trait_counter,
  77             type_param_mode,
  78             opaque_type_data,
  79         }
  80     }
  81
  82     pub fn with_debruijn<T>(
  83         &self,
  84         debruijn: DebruijnIndex,
  85         f: impl FnOnce(&TyLoweringContext) -> T,
  86     ) -> T {
  87         let opaque_ty_data_vec = self.opaque_type_data.replace(Vec::new());
  88         let new_ctx = Self {
  89             in_binders: debruijn,
  90             impl_trait_counter: std::cell::Cell::new(self.impl_trait_counter.get()),
  91             opaque_type_data: std::cell::RefCell::new(opaque_ty_data_vec),
  92             ..*self
  93         };
  94         let result = f(&new_ctx);
  95         self.impl_trait_counter.set(new_ctx.impl_trait_counter.get());
  96         self.opaque_type_data.replace(new_ctx.opaque_type_data.into_inner());
  97         result
  98     }
  99
 100     pub fn with_shifted_in<T>(
 101         &self,
 102         debruijn: DebruijnIndex,
 103         f: impl FnOnce(&TyLoweringContext) -> T,
 104     ) -> T {
 105         self.with_debruijn(self.in_binders.shifted_in_from(debruijn), f)
 106     }
 107
 108     pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
 109         Self { impl_trait_mode, ..self }
 110     }
 111
 112     pub fn with_type_param_mode(self, type_param_mode: TypeParamLoweringMode) -> Self {
 113         Self { type_param_mode, ..self }
 114     }
 115 }
 116
 117 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 118 pub enum ImplTraitLoweringMode {
 119     /// `impl Trait` gets lowered into an opaque type that doesn't unify with
 120     /// anything except itself. This is used in places where values flow 'out',
 121     /// i.e. for arguments of the function we're currently checking, and return
 122     /// types of functions we're calling.
 123     Opaque,
 124     /// `impl Trait` gets lowered into a type variable. Used for argument
 125     /// position impl Trait when inside the respective function, since it allows
 126     /// us to support that without Chalk.
 127     Param,
 128     /// `impl Trait` gets lowered into a variable that can unify with some
 129     /// type. This is used in places where values flow 'in', i.e. for arguments
 130     /// of functions we're calling, and the return type of the function we're
 131     /// currently checking.
 132     Variable,
 133     /// `impl Trait` is disallowed and will be an error.
 134     Disallowed,
 135 }
 136
 137 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 138 pub enum TypeParamLoweringMode {
 139     Placeholder,
 140     Variable,
 141 }
 142
 143 impl Ty {
 144     pub fn from_hir(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Self {
 145         Ty::from_hir_ext(ctx, type_ref).0
 146     }
 147     pub fn from_hir_ext(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> (Self, Option<TypeNs>) {
 148         let mut res = None;
 149         let ty = match type_ref {
 150             TypeRef::Never => TyKind::Never.intern(&Interner),
 151             TypeRef::Tuple(inner) => {
 152                 let inner_tys: Arc<[Ty]> = inner.iter().map(|tr| Ty::from_hir(ctx, tr)).collect();
 153                 TyKind::Tuple(inner_tys.len(), Substs(inner_tys)).intern(&Interner)
 154             }
 155             TypeRef::Path(path) => {
 156                 let (ty, res_) = Ty::from_hir_path(ctx, path);
 157                 res = res_;
 158                 ty
 159             }
 160             TypeRef::RawPtr(inner, mutability) => {
 161                 let inner_ty = Ty::from_hir(ctx, inner);
 162                 TyKind::Raw(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
 163                     .intern(&Interner)
 164             }
 165             TypeRef::Array(inner) => {
 166                 let inner_ty = Ty::from_hir(ctx, inner);
 167                 TyKind::Array(Substs::single(inner_ty)).intern(&Interner)
 168             }
 169             TypeRef::Slice(inner) => {
 170                 let inner_ty = Ty::from_hir(ctx, inner);
 171                 TyKind::Slice(Substs::single(inner_ty)).intern(&Interner)
 172             }
 173             TypeRef::Reference(inner, _, mutability) => {
 174                 let inner_ty = Ty::from_hir(ctx, inner);
 175                 TyKind::Ref(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
 176                     .intern(&Interner)
 177             }
 178             TypeRef::Placeholder => TyKind::Unknown.intern(&Interner),
 179             TypeRef::Fn(params, is_varargs) => {
 180                 let substs = Substs(params.iter().map(|tr| Ty::from_hir(ctx, tr)).collect());
 181                 TyKind::Function(FnPointer {
 182                     num_args: substs.len() - 1,
 183                     sig: FnSig { variadic: *is_varargs },
 184                     substs,
 185                 })
 186                 .intern(&Interner)
 187             }
 188             TypeRef::DynTrait(bounds) => {
 189                 let self_ty =
 190                     TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 191                 let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 192                     bounds
 193                         .iter()
 194                         .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
 195                         .collect()
 196                 });
 197                 TyKind::Dyn(predicates).intern(&Interner)
 198             }
 199             TypeRef::ImplTrait(bounds) => {
 200                 match ctx.impl_trait_mode {
 201                     ImplTraitLoweringMode::Opaque => {
 202                         let idx = ctx.impl_trait_counter.get();
 203                         ctx.impl_trait_counter.set(idx + 1);
 204
 205                         assert!(idx as usize == ctx.opaque_type_data.borrow().len());
 206                         // this dance is to make sure the data is in the right
 207                         // place even if we encounter more opaque types while
 208                         // lowering the bounds
 209                         ctx.opaque_type_data
 210                             .borrow_mut()
 211                             .push(ReturnTypeImplTrait { bounds: Binders::new(1, Vec::new()) });
 212                         // We don't want to lower the bounds inside the binders
 213                         // we're currently in, because they don't end up inside
 214                         // those binders. E.g. when we have `impl Trait<impl
 215                         // OtherTrait<T>>`, the `impl OtherTrait<T>` can't refer
 216                         // to the self parameter from `impl Trait`, and the
 217                         // bounds aren't actually stored nested within each
 218                         // other, but separately. So if the `T` refers to a type
 219                         // parameter of the outer function, it's just one binder
 220                         // away instead of two.
 221                         let actual_opaque_type_data = ctx
 222                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
 223                                 ReturnTypeImplTrait::from_hir(ctx, &bounds)
 224                             });
 225                         ctx.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 226
 227                         let func = match ctx.resolver.generic_def() {
 228                             Some(GenericDefId::FunctionId(f)) => f,
 229                             _ => panic!("opaque impl trait lowering in non-function"),
 230                         };
 231                         let impl_trait_id = OpaqueTyId::ReturnTypeImplTrait(func, idx);
 232                         let generics = generics(ctx.db.upcast(), func.into());
 233                         let parameters = Substs::bound_vars(&generics, ctx.in_binders);
 234                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 235                             opaque_ty_id: impl_trait_id,
 236                             parameters,
 237                         }))
 238                         .intern(&Interner)
 239                     }
 240                     ImplTraitLoweringMode::Param => {
 241                         let idx = ctx.impl_trait_counter.get();
 242                         // FIXME we're probably doing something wrong here
 243                         ctx.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 244                         if let Some(def) = ctx.resolver.generic_def() {
 245                             let generics = generics(ctx.db.upcast(), def);
 246                             let param = generics
 247                                 .iter()
 248                                 .filter(|(_, data)| {
 249                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
 250                                 })
 251                                 .nth(idx as usize)
 252                                 .map_or(TyKind::Unknown, |(id, _)| TyKind::Placeholder(id));
 253                             param.intern(&Interner)
 254                         } else {
 255                             TyKind::Unknown.intern(&Interner)
 256                         }
 257                     }
 258                     ImplTraitLoweringMode::Variable => {
 259                         let idx = ctx.impl_trait_counter.get();
 260                         // FIXME we're probably doing something wrong here
 261                         ctx.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
 262                         let (parent_params, self_params, list_params, _impl_trait_params) =
 263                             if let Some(def) = ctx.resolver.generic_def() {
 264                                 let generics = generics(ctx.db.upcast(), def);
 265                                 generics.provenance_split()
 266                             } else {
 267                                 (0, 0, 0, 0)
 268                             };
 269                         TyKind::BoundVar(BoundVar::new(
 270                             ctx.in_binders,
 271                             idx as usize + parent_params + self_params + list_params,
 272                         ))
 273                         .intern(&Interner)
 274                     }
 275                     ImplTraitLoweringMode::Disallowed => {
 276                         // FIXME: report error
 277                         TyKind::Unknown.intern(&Interner)
 278                     }
 279                 }
 280             }
 281             TypeRef::Error => TyKind::Unknown.intern(&Interner),
 282         };
 283         (ty, res)
 284     }
 285
 286     /// This is only for `generic_predicates_for_param`, where we can't just
 287     /// lower the self types of the predicates since that could lead to cycles.
 288     /// So we just check here if the `type_ref` resolves to a generic param, and which.
 289     fn from_hir_only_param(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Option<TypeParamId> {
 290         let path = match type_ref {
 291             TypeRef::Path(path) => path,
 292             _ => return None,
 293         };
 294         if path.type_anchor().is_some() {
 295             return None;
 296         }
 297         if path.segments().len() > 1 {
 298             return None;
 299         }
 300         let resolution =
 301             match ctx.resolver.resolve_path_in_type_ns(ctx.db.upcast(), path.mod_path()) {
 302                 Some((it, None)) => it,
 303                 _ => return None,
 304             };
 305         if let TypeNs::GenericParam(param_id) = resolution {
 306             Some(param_id)
 307         } else {
 308             None
 309         }
 310     }
 311
 312     pub(crate) fn from_type_relative_path(
 313         ctx: &TyLoweringContext<'_>,
 314         ty: Ty,
 315         // We need the original resolution to lower `Self::AssocTy` correctly
 316         res: Option<TypeNs>,
 317         remaining_segments: PathSegments<'_>,
 318     ) -> (Ty, Option<TypeNs>) {
 319         if remaining_segments.len() == 1 {
 320             // resolve unselected assoc types
 321             let segment = remaining_segments.first().unwrap();
 322             (Ty::select_associated_type(ctx, res, segment), None)
 323         } else if remaining_segments.len() > 1 {
 324             // FIXME report error (ambiguous associated type)
 325             (TyKind::Unknown.intern(&Interner), None)
 326         } else {
 327             (ty, res)
 328         }
 329     }
 330
 331     pub(crate) fn from_partly_resolved_hir_path(
 332         ctx: &TyLoweringContext<'_>,
 333         resolution: TypeNs,
 334         resolved_segment: PathSegment<'_>,
 335         remaining_segments: PathSegments<'_>,
 336         infer_args: bool,
 337     ) -> (Ty, Option<TypeNs>) {
 338         let ty = match resolution {
 339             TypeNs::TraitId(trait_) => {
 340                 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
 341                 let self_ty = if remaining_segments.len() == 0 {
 342                     Some(
 343                         TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
 344                             .intern(&Interner),
 345                     )
 346                 } else {
 347                     None
 348                 };
 349                 let trait_ref =
 350                     TraitRef::from_resolved_path(ctx, trait_, resolved_segment, self_ty);
 351                 let ty = if remaining_segments.len() == 1 {
 352                     let segment = remaining_segments.first().unwrap();
 353                     let found = associated_type_by_name_including_super_traits(
 354                         ctx.db,
 355                         trait_ref,
 356                         &segment.name,
 357                     );
 358                     match found {
 359                         Some((super_trait_ref, associated_ty)) => {
 360                             // FIXME handle type parameters on the segment
 361                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 362                                 associated_ty: to_assoc_type_id(associated_ty),
 363                                 parameters: super_trait_ref.substs,
 364                             }))
 365                             .intern(&Interner)
 366                         }
 367                         None => {
 368                             // FIXME: report error (associated type not found)
 369                             TyKind::Unknown.intern(&Interner)
 370                         }
 371                     }
 372                 } else if remaining_segments.len() > 1 {
 373                     // FIXME report error (ambiguous associated type)
 374                     TyKind::Unknown.intern(&Interner)
 375                 } else {
 376                     TyKind::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
 377                         .intern(&Interner)
 378                 };
 379                 return (ty, None);
 380             }
 381             TypeNs::GenericParam(param_id) => {
 382                 let generics = generics(
 383                     ctx.db.upcast(),
 384                     ctx.resolver.generic_def().expect("generics in scope"),
 385                 );
 386                 match ctx.type_param_mode {
 387                     TypeParamLoweringMode::Placeholder => TyKind::Placeholder(param_id),
 388                     TypeParamLoweringMode::Variable => {
 389                         let idx = generics.param_idx(param_id).expect("matching generics");
 390                         TyKind::BoundVar(BoundVar::new(ctx.in_binders, idx))
 391                     }
 392                 }
 393                 .intern(&Interner)
 394             }
 395             TypeNs::SelfType(impl_id) => {
 396                 let generics = generics(ctx.db.upcast(), impl_id.into());
 397                 let substs = match ctx.type_param_mode {
 398                     TypeParamLoweringMode::Placeholder => {
 399                         Substs::type_params_for_generics(&generics)
 400                     }
 401                     TypeParamLoweringMode::Variable => {
 402                         Substs::bound_vars(&generics, ctx.in_binders)
 403                     }
 404                 };
 405                 ctx.db.impl_self_ty(impl_id).subst(&substs)
 406             }
 407             TypeNs::AdtSelfType(adt) => {
 408                 let generics = generics(ctx.db.upcast(), adt.into());
 409                 let substs = match ctx.type_param_mode {
 410                     TypeParamLoweringMode::Placeholder => {
 411                         Substs::type_params_for_generics(&generics)
 412                     }
 413                     TypeParamLoweringMode::Variable => {
 414                         Substs::bound_vars(&generics, ctx.in_binders)
 415                     }
 416                 };
 417                 ctx.db.ty(adt.into()).subst(&substs)
 418             }
 419
 420             TypeNs::AdtId(it) => {
 421                 Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
 422             }
 423             TypeNs::BuiltinType(it) => {
 424                 Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
 425             }
 426             TypeNs::TypeAliasId(it) => {
 427                 Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
 428             }
 429             // FIXME: report error
 430             TypeNs::EnumVariantId(_) => return (TyKind::Unknown.intern(&Interner), None),
 431         };
 432         Ty::from_type_relative_path(ctx, ty, Some(resolution), remaining_segments)
 433     }
 434
 435     pub(crate) fn from_hir_path(ctx: &TyLoweringContext<'_>, path: &Path) -> (Ty, Option<TypeNs>) {
 436         // Resolve the path (in type namespace)
 437         if let Some(type_ref) = path.type_anchor() {
 438             let (ty, res) = Ty::from_hir_ext(ctx, &type_ref);
 439             return Ty::from_type_relative_path(ctx, ty, res, path.segments());
 440         }
 441         let (resolution, remaining_index) =
 442             match ctx.resolver.resolve_path_in_type_ns(ctx.db.upcast(), path.mod_path()) {
 443                 Some(it) => it,
 444                 None => return (TyKind::Unknown.intern(&Interner), None),
 445             };
 446         let (resolved_segment, remaining_segments) = match remaining_index {
 447             None => (
 448                 path.segments().last().expect("resolved path has at least one element"),
 449                 PathSegments::EMPTY,
 450             ),
 451             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
 452         };
 453         Ty::from_partly_resolved_hir_path(
 454             ctx,
 455             resolution,
 456             resolved_segment,
 457             remaining_segments,
 458             false,
 459         )
 460     }
 461
 462     fn select_associated_type(
 463         ctx: &TyLoweringContext<'_>,
 464         res: Option<TypeNs>,
 465         segment: PathSegment<'_>,
 466     ) -> Ty {
 467         if let Some(res) = res {
 468             let ty =
 469                 associated_type_shorthand_candidates(ctx.db, res, move |name, t, associated_ty| {
 470                     if name == segment.name {
 471                         let substs = match ctx.type_param_mode {
 472                             TypeParamLoweringMode::Placeholder => {
 473                                 // if we're lowering to placeholders, we have to put
 474                                 // them in now
 475                                 let s = Substs::type_params(
 476                                     ctx.db,
 477                                     ctx.resolver.generic_def().expect(
 478                                         "there should be generics if there's a generic param",
 479                                     ),
 480                                 );
 481                                 t.substs.clone().subst_bound_vars(&s)
 482                             }
 483                             TypeParamLoweringMode::Variable => t.substs.clone(),
 484                         };
 485                         // We need to shift in the bound vars, since
 486                         // associated_type_shorthand_candidates does not do that
 487                         let substs = substs.shift_bound_vars(ctx.in_binders);
 488                         // FIXME handle type parameters on the segment
 489                         return Some(
 490                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
 491                                 associated_ty: to_assoc_type_id(associated_ty),
 492                                 parameters: substs,
 493                             }))
 494                             .intern(&Interner),
 495                         );
 496                     }
 497
 498                     None
 499                 });
 500
 501             ty.unwrap_or(TyKind::Unknown.intern(&Interner))
 502         } else {
 503             TyKind::Unknown.intern(&Interner)
 504         }
 505     }
 506
 507     fn from_hir_path_inner(
 508         ctx: &TyLoweringContext<'_>,
 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 = substs_from_path_segment(ctx, segment, generic_def, infer_args);
 519         ctx.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         ctx: &TyLoweringContext<'_>,
 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     ) -> Substs {
 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         substs_from_path_segment(ctx, segment, generic_def, infer_args)
 556     }
 557 }
 558
 559 fn substs_from_path_segment(
 560     ctx: &TyLoweringContext<'_>,
 561     segment: PathSegment<'_>,
 562     def_generic: Option<GenericDefId>,
 563     infer_args: bool,
 564 ) -> Substs {
 565     let mut substs = Vec::new();
 566     let def_generics = def_generic.map(|def| generics(ctx.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::Unknown.intern(&Interner)).take(parent_params));
 573
 574     let mut had_explicit_type_args = false;
 575
 576     if let Some(generic_args) = &segment.args_and_bindings {
 577         if !generic_args.has_self_type {
 578             substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(self_params));
 579         }
 580         let expected_num =
 581             if generic_args.has_self_type { self_params + type_params } else { type_params };
 582         let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
 583         // if args are provided, it should be all of them, but we can't rely on that
 584         for arg in generic_args
 585             .args
 586             .iter()
 587             .filter(|arg| matches!(arg, GenericArg::Type(_)))
 588             .skip(skip)
 589             .take(expected_num)
 590         {
 591             match arg {
 592                 GenericArg::Type(type_ref) => {
 593                     had_explicit_type_args = true;
 594                     let ty = Ty::from_hir(ctx, type_ref);
 595                     substs.push(ty);
 596                 }
 597                 GenericArg::Lifetime(_) => {}
 598             }
 599         }
 600     }
 601
 602     // handle defaults. In expression or pattern path segments without
 603     // explicitly specified type arguments, missing type arguments are inferred
 604     // (i.e. defaults aren't used).
 605     if !infer_args || had_explicit_type_args {
 606         if let Some(def_generic) = def_generic {
 607             let defaults = ctx.db.generic_defaults(def_generic);
 608             assert_eq!(total_len, defaults.len());
 609
 610             for default_ty in defaults.iter().skip(substs.len()) {
 611                 // each default can depend on the previous parameters
 612                 let substs_so_far = Substs(substs.clone().into());
 613                 substs.push(default_ty.clone().subst(&substs_so_far));
 614             }
 615         }
 616     }
 617
 618     // add placeholders for args that were not provided
 619     // FIXME: emit diagnostics in contexts where this is not allowed
 620     for _ in substs.len()..total_len {
 621         substs.push(TyKind::Unknown.intern(&Interner));
 622     }
 623     assert_eq!(substs.len(), total_len);
 624
 625     Substs(substs.into())
 626 }
 627
 628 impl TraitRef {
 629     fn from_path(
 630         ctx: &TyLoweringContext<'_>,
 631         path: &Path,
 632         explicit_self_ty: Option<Ty>,
 633     ) -> Option<Self> {
 634         let resolved =
 635             match ctx.resolver.resolve_path_in_type_ns_fully(ctx.db.upcast(), path.mod_path())? {
 636                 TypeNs::TraitId(tr) => tr,
 637                 _ => return None,
 638             };
 639         let segment = path.segments().last().expect("path should have at least one segment");
 640         Some(TraitRef::from_resolved_path(ctx, resolved, segment, explicit_self_ty))
 641     }
 642
 643     pub(crate) fn from_resolved_path(
 644         ctx: &TyLoweringContext<'_>,
 645         resolved: TraitId,
 646         segment: PathSegment<'_>,
 647         explicit_self_ty: Option<Ty>,
 648     ) -> Self {
 649         let mut substs = TraitRef::substs_from_path(ctx, segment, resolved);
 650         if let Some(self_ty) = explicit_self_ty {
 651             make_mut_slice(&mut substs.0)[0] = self_ty;
 652         }
 653         TraitRef { trait_: resolved, substs }
 654     }
 655
 656     fn from_hir(
 657         ctx: &TyLoweringContext<'_>,
 658         type_ref: &TypeRef,
 659         explicit_self_ty: Option<Ty>,
 660     ) -> Option<Self> {
 661         let path = match type_ref {
 662             TypeRef::Path(path) => path,
 663             _ => return None,
 664         };
 665         TraitRef::from_path(ctx, path, explicit_self_ty)
 666     }
 667
 668     fn substs_from_path(
 669         ctx: &TyLoweringContext<'_>,
 670         segment: PathSegment<'_>,
 671         resolved: TraitId,
 672     ) -> Substs {
 673         substs_from_path_segment(ctx, segment, Some(resolved.into()), false)
 674     }
 675 }
 676
 677 impl GenericPredicate {
 678     pub(crate) fn from_where_predicate<'a>(
 679         ctx: &'a TyLoweringContext<'a>,
 680         where_predicate: &'a WherePredicate,
 681     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 682         match where_predicate {
 683             WherePredicate::ForLifetime { target, bound, .. }
 684             | WherePredicate::TypeBound { target, bound } => {
 685                 let self_ty = match target {
 686                     WherePredicateTypeTarget::TypeRef(type_ref) => Ty::from_hir(ctx, type_ref),
 687                     WherePredicateTypeTarget::TypeParam(param_id) => {
 688                         let generic_def = ctx.resolver.generic_def().expect("generics in scope");
 689                         let generics = generics(ctx.db.upcast(), generic_def);
 690                         let param_id =
 691                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
 692                         match ctx.type_param_mode {
 693                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(param_id),
 694                             TypeParamLoweringMode::Variable => {
 695                                 let idx = generics.param_idx(param_id).expect("matching generics");
 696                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
 697                             }
 698                         }
 699                         .intern(&Interner)
 700                     }
 701                 };
 702                 GenericPredicate::from_type_bound(ctx, bound, self_ty)
 703                     .collect::<Vec<_>>()
 704                     .into_iter()
 705             }
 706             WherePredicate::Lifetime { .. } => vec![].into_iter(),
 707         }
 708     }
 709
 710     pub(crate) fn from_type_bound<'a>(
 711         ctx: &'a TyLoweringContext<'a>,
 712         bound: &'a TypeBound,
 713         self_ty: Ty,
 714     ) -> impl Iterator<Item = GenericPredicate> + 'a {
 715         let mut bindings = None;
 716         let trait_ref = match bound {
 717             TypeBound::Path(path) => {
 718                 bindings = TraitRef::from_path(ctx, path, Some(self_ty));
 719                 Some(
 720                     bindings.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented),
 721                 )
 722             }
 723             TypeBound::Lifetime(_) => None,
 724             TypeBound::Error => Some(GenericPredicate::Error),
 725         };
 726         trait_ref.into_iter().chain(
 727             bindings
 728                 .into_iter()
 729                 .flat_map(move |tr| assoc_type_bindings_from_type_bound(ctx, bound, tr)),
 730         )
 731     }
 732 }
 733
 734 fn assoc_type_bindings_from_type_bound<'a>(
 735     ctx: &'a TyLoweringContext<'a>,
 736     bound: &'a TypeBound,
 737     trait_ref: TraitRef,
 738 ) -> impl Iterator<Item = GenericPredicate> + 'a {
 739     let last_segment = match bound {
 740         TypeBound::Path(path) => path.segments().last(),
 741         TypeBound::Error | TypeBound::Lifetime(_) => None,
 742     };
 743     last_segment
 744         .into_iter()
 745         .flat_map(|segment| segment.args_and_bindings.into_iter())
 746         .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
 747         .flat_map(move |binding| {
 748             let found = associated_type_by_name_including_super_traits(
 749                 ctx.db,
 750                 trait_ref.clone(),
 751                 &binding.name,
 752             );
 753             let (super_trait_ref, associated_ty) = match found {
 754                 None => return SmallVec::<[GenericPredicate; 1]>::new(),
 755                 Some(t) => t,
 756             };
 757             let projection_ty = ProjectionTy {
 758                 associated_ty: to_assoc_type_id(associated_ty),
 759                 parameters: super_trait_ref.substs,
 760             };
 761             let mut preds = SmallVec::with_capacity(
 762                 binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
 763             );
 764             if let Some(type_ref) = &binding.type_ref {
 765                 let ty = Ty::from_hir(ctx, type_ref);
 766                 let projection_predicate =
 767                     ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
 768                 preds.push(GenericPredicate::Projection(projection_predicate));
 769             }
 770             for bound in &binding.bounds {
 771                 preds.extend(GenericPredicate::from_type_bound(
 772                     ctx,
 773                     bound,
 774                     TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
 775                 ));
 776             }
 777             preds
 778         })
 779 }
 780
 781 impl ReturnTypeImplTrait {
 782     fn from_hir(ctx: &TyLoweringContext, bounds: &[TypeBound]) -> Self {
 783         cov_mark::hit!(lower_rpit);
 784         let self_ty =
 785             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
 786         let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
 787             bounds
 788                 .iter()
 789                 .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
 790                 .collect()
 791         });
 792         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
 793     }
 794 }
 795
 796 fn count_impl_traits(type_ref: &TypeRef) -> usize {
 797     let mut count = 0;
 798     type_ref.walk(&mut |type_ref| {
 799         if matches!(type_ref, TypeRef::ImplTrait(_)) {
 800             count += 1;
 801         }
 802     });
 803     count
 804 }
 805
 806 /// Build the signature of a callable item (function, struct or enum variant).
 807 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
 808     match def {
 809         CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
 810         CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
 811         CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
 812     }
 813 }
 814
 815 pub fn associated_type_shorthand_candidates<R>(
 816     db: &dyn HirDatabase,
 817     res: TypeNs,
 818     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 819 ) -> Option<R> {
 820     let traits_from_env: Vec<_> = match res {
 821         TypeNs::SelfType(impl_id) => match db.impl_trait(impl_id) {
 822             None => vec![],
 823             Some(trait_ref) => vec![trait_ref.value],
 824         },
 825         TypeNs::GenericParam(param_id) => {
 826             let predicates = db.generic_predicates_for_param(param_id);
 827             let mut traits_: Vec<_> = predicates
 828                 .iter()
 829                 .filter_map(|pred| match &pred.value {
 830                     GenericPredicate::Implemented(tr) => Some(tr.clone()),
 831                     _ => None,
 832                 })
 833                 .collect();
 834             // Handle `Self::Type` referring to own associated type in trait definitions
 835             if let GenericDefId::TraitId(trait_id) = param_id.parent {
 836                 let generics = generics(db.upcast(), trait_id.into());
 837                 if generics.params.types[param_id.local_id].provenance
 838                     == TypeParamProvenance::TraitSelf
 839                 {
 840                     let trait_ref = TraitRef {
 841                         trait_: trait_id,
 842                         substs: Substs::bound_vars(&generics, DebruijnIndex::INNERMOST),
 843                     };
 844                     traits_.push(trait_ref);
 845                 }
 846             }
 847             traits_
 848         }
 849         _ => vec![],
 850     };
 851
 852     for t in traits_from_env.into_iter().flat_map(move |t| all_super_trait_refs(db, t)) {
 853         let data = db.trait_data(t.trait_);
 854
 855         for (name, assoc_id) in &data.items {
 856             match assoc_id {
 857                 AssocItemId::TypeAliasId(alias) => {
 858                     if let Some(result) = cb(name, &t, *alias) {
 859                         return Some(result);
 860                     }
 861                 }
 862                 AssocItemId::FunctionId(_) | AssocItemId::ConstId(_) => {}
 863             }
 864         }
 865     }
 866
 867     None
 868 }
 869
 870 /// Build the type of all specific fields of a struct or enum variant.
 871 pub(crate) fn field_types_query(
 872     db: &dyn HirDatabase,
 873     variant_id: VariantId,
 874 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
 875     let var_data = variant_data(db.upcast(), variant_id);
 876     let (resolver, def): (_, GenericDefId) = match variant_id {
 877         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
 878         VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
 879         VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
 880     };
 881     let generics = generics(db.upcast(), def);
 882     let mut res = ArenaMap::default();
 883     let ctx =
 884         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 885     for (field_id, field_data) in var_data.fields().iter() {
 886         res.insert(field_id, Binders::new(generics.len(), Ty::from_hir(&ctx, &field_data.type_ref)))
 887     }
 888     Arc::new(res)
 889 }
 890
 891 /// This query exists only to be used when resolving short-hand associated types
 892 /// like `T::Item`.
 893 ///
 894 /// See the analogous query in rustc and its comment:
 895 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
 896 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
 897 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
 898 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 899 pub(crate) fn generic_predicates_for_param_query(
 900     db: &dyn HirDatabase,
 901     param_id: TypeParamId,
 902 ) -> Arc<[Binders<GenericPredicate>]> {
 903     let resolver = param_id.parent.resolver(db.upcast());
 904     let ctx =
 905         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 906     let generics = generics(db.upcast(), param_id.parent);
 907     resolver
 908         .where_predicates_in_scope()
 909         // we have to filter out all other predicates *first*, before attempting to lower them
 910         .filter(|pred| match pred {
 911             WherePredicate::ForLifetime { target, .. }
 912             | WherePredicate::TypeBound { target, .. } => match target {
 913                 WherePredicateTypeTarget::TypeRef(type_ref) => {
 914                     Ty::from_hir_only_param(&ctx, type_ref) == Some(param_id)
 915                 }
 916                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
 917             },
 918             WherePredicate::Lifetime { .. } => false,
 919         })
 920         .flat_map(|pred| {
 921             GenericPredicate::from_where_predicate(&ctx, pred)
 922                 .map(|p| Binders::new(generics.len(), p))
 923         })
 924         .collect()
 925 }
 926
 927 pub(crate) fn generic_predicates_for_param_recover(
 928     _db: &dyn HirDatabase,
 929     _cycle: &[String],
 930     _param_id: &TypeParamId,
 931 ) -> Arc<[Binders<GenericPredicate>]> {
 932     Arc::new([])
 933 }
 934
 935 impl TraitEnvironment {
 936     pub fn lower(db: &dyn HirDatabase, resolver: &Resolver) -> Arc<TraitEnvironment> {
 937         let ctx = TyLoweringContext::new(db, &resolver)
 938             .with_type_param_mode(TypeParamLoweringMode::Placeholder);
 939         let mut traits_in_scope = Vec::new();
 940         let mut clauses = Vec::new();
 941         for pred in resolver.where_predicates_in_scope() {
 942             for pred in GenericPredicate::from_where_predicate(&ctx, pred) {
 943                 if pred.is_error() {
 944                     continue;
 945                 }
 946                 if let GenericPredicate::Implemented(tr) = &pred {
 947                     traits_in_scope.push((tr.self_ty().clone(), tr.trait_));
 948                 }
 949                 let program_clause: chalk_ir::ProgramClause<Interner> =
 950                     pred.clone().to_chalk(db).cast(&Interner);
 951                 clauses.push(program_clause.into_from_env_clause(&Interner));
 952             }
 953         }
 954
 955         if let Some(def) = resolver.generic_def() {
 956             let container: Option<AssocContainerId> = match def {
 957                 // FIXME: is there a function for this?
 958                 GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
 959                 GenericDefId::AdtId(_) => None,
 960                 GenericDefId::TraitId(_) => None,
 961                 GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
 962                 GenericDefId::ImplId(_) => None,
 963                 GenericDefId::EnumVariantId(_) => None,
 964                 GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
 965             };
 966             if let Some(AssocContainerId::TraitId(trait_id)) = container {
 967                 // add `Self: Trait<T1, T2, ...>` to the environment in trait
 968                 // function default implementations (and hypothetical code
 969                 // inside consts or type aliases)
 970                 cov_mark::hit!(trait_self_implements_self);
 971                 let substs = Substs::type_params(db, trait_id);
 972                 let trait_ref = TraitRef { trait_: trait_id, substs };
 973                 let pred = GenericPredicate::Implemented(trait_ref);
 974                 let program_clause: chalk_ir::ProgramClause<Interner> =
 975                     pred.clone().to_chalk(db).cast(&Interner);
 976                 clauses.push(program_clause.into_from_env_clause(&Interner));
 977             }
 978         }
 979
 980         let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 981
 982         Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 983     }
 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<GenericPredicate>]> {
 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             GenericPredicate::from_where_predicate(&ctx, pred)
 999                 .map(|p| Binders::new(generics.len(), p))
1000         })
1001         .collect()
1002 }
1003
1004 /// Resolve the default type params from generics
1005 pub(crate) fn generic_defaults_query(
1006     db: &dyn HirDatabase,
1007     def: GenericDefId,
1008 ) -> Arc<[Binders<Ty>]> {
1009     let resolver = def.resolver(db.upcast());
1010     let ctx =
1011         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1012     let generic_params = generics(db.upcast(), def);
1013
1014     let defaults = generic_params
1015         .iter()
1016         .enumerate()
1017         .map(|(idx, (_, p))| {
1018             let mut ty = p
1019                 .default
1020                 .as_ref()
1021                 .map_or(TyKind::Unknown.intern(&Interner), |t| Ty::from_hir(&ctx, t));
1022
1023             // Each default can only refer to previous parameters.
1024             ty.walk_mut_binders(
1025                 &mut |ty, binders| match &mut ty.0 {
1026                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
1027                         if *index >= idx {
1028                             // type variable default referring to parameter coming
1029                             // after it. This is forbidden (FIXME: report
1030                             // diagnostic)
1031                             *ty = TyKind::Unknown.intern(&Interner);
1032                         }
1033                     }
1034                     _ => {}
1035                 },
1036                 DebruijnIndex::INNERMOST,
1037             );
1038
1039             Binders::new(idx, ty)
1040         })
1041         .collect();
1042
1043     defaults
1044 }
1045
1046 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1047     let data = db.function_data(def);
1048     let resolver = def.resolver(db.upcast());
1049     let ctx_params = TyLoweringContext::new(db, &resolver)
1050         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1051         .with_type_param_mode(TypeParamLoweringMode::Variable);
1052     let params = data.params.iter().map(|tr| Ty::from_hir(&ctx_params, tr)).collect::<Vec<_>>();
1053     let ctx_ret = TyLoweringContext::new(db, &resolver)
1054         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1055         .with_type_param_mode(TypeParamLoweringMode::Variable);
1056     let ret = Ty::from_hir(&ctx_ret, &data.ret_type);
1057     let generics = generics(db.upcast(), def.into());
1058     let num_binders = generics.len();
1059     Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
1060 }
1061
1062 /// Build the declared type of a function. This should not need to look at the
1063 /// function body.
1064 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1065     let generics = generics(db.upcast(), def.into());
1066     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1067     Binders::new(
1068         substs.len(),
1069         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1070     )
1071 }
1072
1073 /// Build the declared type of a const.
1074 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1075     let data = db.const_data(def);
1076     let generics = generics(db.upcast(), def.into());
1077     let resolver = def.resolver(db.upcast());
1078     let ctx =
1079         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1080
1081     Binders::new(generics.len(), Ty::from_hir(&ctx, &data.type_ref))
1082 }
1083
1084 /// Build the declared type of a static.
1085 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1086     let data = db.static_data(def);
1087     let resolver = def.resolver(db.upcast());
1088     let ctx = TyLoweringContext::new(db, &resolver);
1089
1090     Binders::new(0, Ty::from_hir(&ctx, &data.type_ref))
1091 }
1092
1093 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1094     let struct_data = db.struct_data(def);
1095     let fields = struct_data.variant_data.fields();
1096     let resolver = def.resolver(db.upcast());
1097     let ctx =
1098         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1099     let params =
1100         fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
1101     let ret = type_for_adt(db, def.into());
1102     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1103 }
1104
1105 /// Build the type of a tuple struct constructor.
1106 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1107     let struct_data = db.struct_data(def);
1108     if let StructKind::Unit = struct_data.variant_data.kind() {
1109         return type_for_adt(db, def.into());
1110     }
1111     let generics = generics(db.upcast(), def.into());
1112     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1113     Binders::new(
1114         substs.len(),
1115         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1116     )
1117 }
1118
1119 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1120     let enum_data = db.enum_data(def.parent);
1121     let var_data = &enum_data.variants[def.local_id];
1122     let fields = var_data.variant_data.fields();
1123     let resolver = def.parent.resolver(db.upcast());
1124     let ctx =
1125         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1126     let params =
1127         fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
1128     let ret = type_for_adt(db, def.parent.into());
1129     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
1130 }
1131
1132 /// Build the type of a tuple enum variant constructor.
1133 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1134     let enum_data = db.enum_data(def.parent);
1135     let var_data = &enum_data.variants[def.local_id].variant_data;
1136     if let StructKind::Unit = var_data.kind() {
1137         return type_for_adt(db, def.parent.into());
1138     }
1139     let generics = generics(db.upcast(), def.parent.into());
1140     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1141     Binders::new(
1142         substs.len(),
1143         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1144     )
1145 }
1146
1147 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1148     let generics = generics(db.upcast(), adt.into());
1149     let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1150     Binders::new(substs.len(), Ty::adt_ty(adt, substs))
1151 }
1152
1153 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1154     let generics = generics(db.upcast(), t.into());
1155     let resolver = t.resolver(db.upcast());
1156     let ctx =
1157         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1158     if db.type_alias_data(t).is_extern {
1159         Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
1160     } else {
1161         let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
1162         let type_ref = &db.type_alias_data(t).type_ref;
1163         let inner = Ty::from_hir(&ctx, type_ref.as_ref().unwrap_or(&TypeRef::Error));
1164         Binders::new(substs.len(), inner)
1165     }
1166 }
1167
1168 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1169 pub enum CallableDefId {
1170     FunctionId(FunctionId),
1171     StructId(StructId),
1172     EnumVariantId(EnumVariantId),
1173 }
1174 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1175
1176 impl CallableDefId {
1177     pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1178         let db = db.upcast();
1179         match self {
1180             CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1181             CallableDefId::StructId(s) => s.lookup(db).container,
1182             CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1183         }
1184         .krate()
1185     }
1186 }
1187
1188 impl From<CallableDefId> for GenericDefId {
1189     fn from(def: CallableDefId) -> GenericDefId {
1190         match def {
1191             CallableDefId::FunctionId(f) => f.into(),
1192             CallableDefId::StructId(s) => s.into(),
1193             CallableDefId::EnumVariantId(e) => e.into(),
1194         }
1195     }
1196 }
1197
1198 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1199 pub enum TyDefId {
1200     BuiltinType(BuiltinType),
1201     AdtId(AdtId),
1202     TypeAliasId(TypeAliasId),
1203 }
1204 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1205
1206 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1207 pub enum ValueTyDefId {
1208     FunctionId(FunctionId),
1209     StructId(StructId),
1210     UnionId(UnionId),
1211     EnumVariantId(EnumVariantId),
1212     ConstId(ConstId),
1213     StaticId(StaticId),
1214 }
1215 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1216
1217 /// Build the declared type of an item. This depends on the namespace; e.g. for
1218 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1219 /// the constructor function `(usize) -> Foo` which lives in the values
1220 /// namespace.
1221 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1222     match def {
1223         TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
1224         TyDefId::AdtId(it) => type_for_adt(db, it),
1225         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1226     }
1227 }
1228
1229 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1230     let num_binders = match *def {
1231         TyDefId::BuiltinType(_) => 0,
1232         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
1233         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
1234     };
1235     Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
1236 }
1237
1238 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1239     match def {
1240         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1241         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1242         ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1243         ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1244         ValueTyDefId::ConstId(it) => type_for_const(db, it),
1245         ValueTyDefId::StaticId(it) => type_for_static(db, it),
1246     }
1247 }
1248
1249 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1250     let impl_data = db.impl_data(impl_id);
1251     let resolver = impl_id.resolver(db.upcast());
1252     let generics = generics(db.upcast(), impl_id.into());
1253     let ctx =
1254         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1255     Binders::new(generics.len(), Ty::from_hir(&ctx, &impl_data.target_type))
1256 }
1257
1258 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1259     let parent_data = db.generic_params(def.parent);
1260     let data = &parent_data.consts[def.local_id];
1261     let resolver = def.parent.resolver(db.upcast());
1262     let ctx = TyLoweringContext::new(db, &resolver);
1263
1264     Ty::from_hir(&ctx, &data.ty)
1265 }
1266
1267 pub(crate) fn impl_self_ty_recover(
1268     db: &dyn HirDatabase,
1269     _cycle: &[String],
1270     impl_id: &ImplId,
1271 ) -> Binders<Ty> {
1272     let generics = generics(db.upcast(), (*impl_id).into());
1273     Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
1274 }
1275
1276 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1277     let impl_data = db.impl_data(impl_id);
1278     let resolver = impl_id.resolver(db.upcast());
1279     let ctx =
1280         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1281     let self_ty = db.impl_self_ty(impl_id);
1282     let target_trait = impl_data.target_trait.as_ref()?;
1283     Some(Binders::new(
1284         self_ty.num_binders,
1285         TraitRef::from_hir(&ctx, target_trait, Some(self_ty.value))?,
1286     ))
1287 }
1288
1289 pub(crate) fn return_type_impl_traits(
1290     db: &dyn HirDatabase,
1291     def: hir_def::FunctionId,
1292 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1293     // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1294     let data = db.function_data(def);
1295     let resolver = def.resolver(db.upcast());
1296     let ctx_ret = TyLoweringContext::new(db, &resolver)
1297         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1298         .with_type_param_mode(TypeParamLoweringMode::Variable);
1299     let _ret = Ty::from_hir(&ctx_ret, &data.ret_type);
1300     let generics = generics(db.upcast(), def.into());
1301     let num_binders = generics.len();
1302     let return_type_impl_traits =
1303         ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1304     if return_type_impl_traits.impl_traits.is_empty() {
1305         None
1306     } else {
1307         Some(Arc::new(Binders::new(num_binders, return_type_impl_traits)))
1308     }
1309 }
1310
1311 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1312     match m {
1313         hir_def::type_ref::Mutability::Shared => Mutability::Not,
1314         hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1315     }
1316 }