1 files changed, 759 insertions, 0 deletions
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
new file mode 100644
index 000000000..091c60f4f
--- /dev/null
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -0,0 +1,759 @@
+//! Methods for lowering the HIR to types. There are two main cases here:
+//!
+//!  - Lowering a type reference like `&usize` or `Option<foo::bar::Baz>` to a
+//!    type: The entry point for this is `Ty::from_hir`.
+//!  - Building the type for an item: This happens through the `type_for_def` query.
+//!
+//! This usually involves resolving names, collecting generic arguments etc.
+use std::iter;
+use std::sync::Arc;
+use hir_def::{
+    builtin_type::BuiltinType,
+    generics::WherePredicate,
+    path::{GenericArg, Path, PathKind, PathSegment},
+    resolver::{HasResolver, Resolver, TypeNs},
+    type_ref::{TypeBound, TypeRef},
+    AdtId, AstItemDef, ConstId, EnumId, EnumVariantId, FunctionId, GenericDefId, HasModule, ImplId,
+    LocalStructFieldId, Lookup, StaticId, StructId, TraitId, TypeAliasId, UnionId, VariantId,
+};
+use ra_arena::map::ArenaMap;
+use ra_db::CrateId;
+use crate::{
+    db::HirDatabase,
+    primitive::{FloatTy, IntTy},
+    utils::{
+        all_super_traits, associated_type_by_name_including_super_traits, make_mut_slice,
+        variant_data,
+    },
+    FnSig, GenericPredicate, ImplTy, ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment,
+    TraitRef, Ty, TypeCtor, TypeWalk,
+};
+impl Ty {
+    pub fn from_hir(db: &impl HirDatabase, resolver: &Resolver, type_ref: &TypeRef) -> Self {
+        match type_ref {
+            TypeRef::Never => Ty::simple(TypeCtor::Never),
+            TypeRef::Tuple(inner) => {
+                let inner_tys: Arc<[Ty]> =
+                    inner.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect();
+                Ty::apply(
+                    TypeCtor::Tuple { cardinality: inner_tys.len() as u16 },
+                    Substs(inner_tys),
+                )
+            }
+            TypeRef::Path(path) => Ty::from_hir_path(db, resolver, path),
+            TypeRef::RawPtr(inner, mutability) => {
+                let inner_ty = Ty::from_hir(db, resolver, inner);
+                Ty::apply_one(TypeCtor::RawPtr(*mutability), inner_ty)
+            }
+            TypeRef::Array(inner) => {
+                let inner_ty = Ty::from_hir(db, resolver, inner);
+                Ty::apply_one(TypeCtor::Array, inner_ty)
+            }
+            TypeRef::Slice(inner) => {
+                let inner_ty = Ty::from_hir(db, resolver, inner);
+                Ty::apply_one(TypeCtor::Slice, inner_ty)
+            }
+            TypeRef::Reference(inner, mutability) => {
+                let inner_ty = Ty::from_hir(db, resolver, inner);
+                Ty::apply_one(TypeCtor::Ref(*mutability), inner_ty)
+            }
+            TypeRef::Placeholder => Ty::Unknown,
+            TypeRef::Fn(params) => {
+                let sig = Substs(params.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect());
+                Ty::apply(TypeCtor::FnPtr { num_args: sig.len() as u16 - 1 }, sig)
+            }
+            TypeRef::DynTrait(bounds) => {
+                let self_ty = Ty::Bound(0);
+                let predicates = bounds
+                    .iter()
+                    .flat_map(|b| {
+                        GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
+                    })
+                    .collect();
+                Ty::Dyn(predicates)
+            }
+            TypeRef::ImplTrait(bounds) => {
+                let self_ty = Ty::Bound(0);
+                let predicates = bounds
+                    .iter()
+                    .flat_map(|b| {
+                        GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
+                    })
+                    .collect();
+                Ty::Opaque(predicates)
+            }
+            TypeRef::Error => Ty::Unknown,
+        }
+    }
+    /// This is only for `generic_predicates_for_param`, where we can't just
+    /// lower the self types of the predicates since that could lead to cycles.
+    /// So we just check here if the `type_ref` resolves to a generic param, and which.
+    fn from_hir_only_param(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        type_ref: &TypeRef,
+    ) -> Option<u32> {
+        let path = match type_ref {
+            TypeRef::Path(path) => path,
+            _ => return None,
+        };
+        if let PathKind::Type(_) = &path.kind {
+            return None;
+        }
+        if path.segments.len() > 1 {
+            return None;
+        }
+        let resolution = match resolver.resolve_path_in_type_ns(db, path) {
+            Some((it, None)) => it,
+            _ => return None,
+        };
+        if let TypeNs::GenericParam(idx) = resolution {
+            Some(idx)
+        } else {
+            None
+        }
+    }
+    pub(crate) fn from_type_relative_path(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        ty: Ty,
+        remaining_segments: &[PathSegment],
+    ) -> Ty {
+        if remaining_segments.len() == 1 {
+            // resolve unselected assoc types
+            let segment = &remaining_segments[0];
+            Ty::select_associated_type(db, resolver, ty, segment)
+        } else if remaining_segments.len() > 1 {
+            // FIXME report error (ambiguous associated type)
+            Ty::Unknown
+        } else {
+            ty
+        }
+    }
+    pub(crate) fn from_partly_resolved_hir_path(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        resolution: TypeNs,
+        resolved_segment: &PathSegment,
+        remaining_segments: &[PathSegment],
+    ) -> Ty {
+        let ty = match resolution {
+            TypeNs::TraitId(trait_) => {
+                let trait_ref =
+                    TraitRef::from_resolved_path(db, resolver, trait_, resolved_segment, None);
+                return if remaining_segments.len() == 1 {
+                    let segment = &remaining_segments[0];
+                    let associated_ty = associated_type_by_name_including_super_traits(
+                        db,
+                        trait_ref.trait_,
+                        &segment.name,
+                    );
+                    match associated_ty {
+                        Some(associated_ty) => {
+                            // FIXME handle type parameters on the segment
+                            Ty::Projection(ProjectionTy {
+                                associated_ty,
+                                parameters: trait_ref.substs,
+                            })
+                        }
+                        None => {
+                            // FIXME: report error (associated type not found)
+                            Ty::Unknown
+                        }
+                    }
+                } else if remaining_segments.len() > 1 {
+                    // FIXME report error (ambiguous associated type)
+                    Ty::Unknown
+                } else {
+                    Ty::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
+                };
+            }
+            TypeNs::GenericParam(idx) => {
+                // FIXME: maybe return name in resolution?
+                let name = resolved_segment.name.clone();
+                Ty::Param { idx, name }
+            }
+            TypeNs::SelfType(impl_id) => db.impl_ty(impl_id).self_type().clone(),
+            TypeNs::AdtSelfType(adt) => db.ty(adt.into()),
+            TypeNs::AdtId(it) => Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into()),
+            TypeNs::BuiltinType(it) => {
+                Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into())
+            }
+            TypeNs::TypeAliasId(it) => {
+                Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into())
+            }
+            // FIXME: report error
+            TypeNs::EnumVariantId(_) => return Ty::Unknown,
+        };
+        Ty::from_type_relative_path(db, resolver, ty, remaining_segments)
+    }
+    pub(crate) fn from_hir_path(db: &impl HirDatabase, resolver: &Resolver, path: &Path) -> Ty {
+        // Resolve the path (in type namespace)
+        if let PathKind::Type(type_ref) = &path.kind {
+            let ty = Ty::from_hir(db, resolver, &type_ref);
+            let remaining_segments = &path.segments[..];
+            return Ty::from_type_relative_path(db, resolver, ty, remaining_segments);
+        }
+        let (resolution, remaining_index) = match resolver.resolve_path_in_type_ns(db, path) {
+            Some(it) => it,
+            None => return Ty::Unknown,
+        };
+        let (resolved_segment, remaining_segments) = match remaining_index {
+            None => (
+                path.segments.last().expect("resolved path has at least one element"),
+                &[] as &[PathSegment],
+            ),
+            Some(i) => (&path.segments[i - 1], &path.segments[i..]),
+        };
+        Ty::from_partly_resolved_hir_path(
+            db,
+            resolver,
+            resolution,
+            resolved_segment,
+            remaining_segments,
+        )
+    }
+    fn select_associated_type(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        self_ty: Ty,
+        segment: &PathSegment,
+    ) -> Ty {
+        let param_idx = match self_ty {
+            Ty::Param { idx, .. } => idx,
+            _ => return Ty::Unknown, // Error: Ambiguous associated type
+        };
+        let def = match resolver.generic_def() {
+            Some(def) => def,
+            None => return Ty::Unknown, // this can't actually happen
+        };
+        let predicates = db.generic_predicates_for_param(def.into(), param_idx);
+        let traits_from_env = predicates.iter().filter_map(|pred| match pred {
+            GenericPredicate::Implemented(tr) if tr.self_ty() == &self_ty => Some(tr.trait_),
+            _ => None,
+        });
+        let traits = traits_from_env.flat_map(|t| all_super_traits(db, t));
+        for t in traits {
+            if let Some(associated_ty) = db.trait_data(t).associated_type_by_name(&segment.name) {
+                let substs =
+                    Substs::build_for_def(db, t).push(self_ty.clone()).fill_with_unknown().build();
+                // FIXME handle type parameters on the segment
+                return Ty::Projection(ProjectionTy { associated_ty, parameters: substs });
+            }
+        }
+        Ty::Unknown
+    }
+    fn from_hir_path_inner(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        segment: &PathSegment,
+        typable: TyDefId,
+    ) -> Ty {
+        let generic_def = match typable {
+            TyDefId::BuiltinType(_) => None,
+            TyDefId::AdtId(it) => Some(it.into()),
+            TyDefId::TypeAliasId(it) => Some(it.into()),
+        };
+        let substs = substs_from_path_segment(db, resolver, segment, generic_def, false);
+        db.ty(typable).subst(&substs)
+    }
+    /// Collect generic arguments from a path into a `Substs`. See also
+    /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
+    pub(super) fn substs_from_path(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        path: &Path,
+        // Note that we don't call `db.value_type(resolved)` here,
+        // `ValueTyDefId` is just a convenient way to pass generics and
+        // special-case enum variants
+        resolved: ValueTyDefId,
+    ) -> Substs {
+        let last = path.segments.last().expect("path should have at least one segment");
+        let (segment, generic_def) = match resolved {
+            ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
+            ValueTyDefId::StructId(it) => (last, Some(it.into())),
+            ValueTyDefId::ConstId(it) => (last, Some(it.into())),
+            ValueTyDefId::StaticId(_) => (last, None),
+            ValueTyDefId::EnumVariantId(var) => {
+                // the generic args for an enum variant may be either specified
+                // on the segment referring to the enum, or on the segment
+                // referring to the variant. So `Option::<T>::None` and
+                // `Option::None::<T>` are both allowed (though the former is
+                // preferred). See also `def_ids_for_path_segments` in rustc.
+                let len = path.segments.len();
+                let segment = if len >= 2 && path.segments[len - 2].args_and_bindings.is_some() {
+                    // Option::<T>::None
+                    &path.segments[len - 2]
+                } else {
+                    // Option::None::<T>
+                    last
+                };
+                (segment, Some(var.parent.into()))
+            }
+        };
+        substs_from_path_segment(db, resolver, segment, generic_def, false)
+    }
+}
+pub(super) fn substs_from_path_segment(
+    db: &impl HirDatabase,
+    resolver: &Resolver,
+    segment: &PathSegment,
+    def_generic: Option<GenericDefId>,
+    add_self_param: bool,
+) -> Substs {
+    let mut substs = Vec::new();
+    let def_generics = def_generic.map(|def| db.generic_params(def.into()));
+    let (parent_param_count, param_count) =
+        def_generics.map_or((0, 0), |g| (g.count_parent_params(), g.params.len()));
+    substs.extend(iter::repeat(Ty::Unknown).take(parent_param_count));
+    if add_self_param {
+        // FIXME this add_self_param argument is kind of a hack: Traits have the
+        // Self type as an implicit first type parameter, but it can't be
+        // actually provided in the type arguments
+        // (well, actually sometimes it can, in the form of type-relative paths: `<Foo as Default>::default()`)
+        substs.push(Ty::Unknown);
+    }
+    if let Some(generic_args) = &segment.args_and_bindings {
+        // if args are provided, it should be all of them, but we can't rely on that
+        let self_param_correction = if add_self_param { 1 } else { 0 };
+        let param_count = param_count - self_param_correction;
+        for arg in generic_args.args.iter().take(param_count) {
+            match arg {
+                GenericArg::Type(type_ref) => {
+                    let ty = Ty::from_hir(db, resolver, type_ref);
+                    substs.push(ty);
+                }
+            }
+        }
+    }
+    // add placeholders for args that were not provided
+    let supplied_params = substs.len();
+    for _ in supplied_params..parent_param_count + param_count {
+        substs.push(Ty::Unknown);
+    }
+    assert_eq!(substs.len(), parent_param_count + param_count);
+    // handle defaults
+    if let Some(def_generic) = def_generic {
+        let default_substs = db.generic_defaults(def_generic.into());
+        assert_eq!(substs.len(), default_substs.len());
+        for (i, default_ty) in default_substs.iter().enumerate() {
+            if substs[i] == Ty::Unknown {
+                substs[i] = default_ty.clone();
+            }
+        }
+    }
+    Substs(substs.into())
+}
+impl TraitRef {
+    fn from_path(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        path: &Path,
+        explicit_self_ty: Option<Ty>,
+    ) -> Option<Self> {
+        let resolved = match resolver.resolve_path_in_type_ns_fully(db, &path)? {
+            TypeNs::TraitId(tr) => tr,
+            _ => return None,
+        };
+        let segment = path.segments.last().expect("path should have at least one segment");
+        Some(TraitRef::from_resolved_path(db, resolver, resolved.into(), segment, explicit_self_ty))
+    }
+    pub(crate) fn from_resolved_path(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        resolved: TraitId,
+        segment: &PathSegment,
+        explicit_self_ty: Option<Ty>,
+    ) -> Self {
+        let mut substs = TraitRef::substs_from_path(db, resolver, segment, resolved);
+        if let Some(self_ty) = explicit_self_ty {
+            make_mut_slice(&mut substs.0)[0] = self_ty;
+        }
+        TraitRef { trait_: resolved, substs }
+    }
+    fn from_hir(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        type_ref: &TypeRef,
+        explicit_self_ty: Option<Ty>,
+    ) -> Option<Self> {
+        let path = match type_ref {
+            TypeRef::Path(path) => path,
+            _ => return None,
+        };
+        TraitRef::from_path(db, resolver, path, explicit_self_ty)
+    }
+    fn substs_from_path(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        segment: &PathSegment,
+        resolved: TraitId,
+    ) -> Substs {
+        let has_self_param =
+            segment.args_and_bindings.as_ref().map(|a| a.has_self_type).unwrap_or(false);
+        substs_from_path_segment(db, resolver, segment, Some(resolved.into()), !has_self_param)
+    }
+    pub(crate) fn from_type_bound(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        bound: &TypeBound,
+        self_ty: Ty,
+    ) -> Option<TraitRef> {
+        match bound {
+            TypeBound::Path(path) => TraitRef::from_path(db, resolver, path, Some(self_ty)),
+            TypeBound::Error => None,
+        }
+    }
+}
+impl GenericPredicate {
+    pub(crate) fn from_where_predicate<'a>(
+        db: &'a impl HirDatabase,
+        resolver: &'a Resolver,
+        where_predicate: &'a WherePredicate,
+    ) -> impl Iterator<Item = GenericPredicate> + 'a {
+        let self_ty = Ty::from_hir(db, resolver, &where_predicate.type_ref);
+        GenericPredicate::from_type_bound(db, resolver, &where_predicate.bound, self_ty)
+    }
+    pub(crate) fn from_type_bound<'a>(
+        db: &'a impl HirDatabase,
+        resolver: &'a Resolver,
+        bound: &'a TypeBound,
+        self_ty: Ty,
+    ) -> impl Iterator<Item = GenericPredicate> + 'a {
+        let trait_ref = TraitRef::from_type_bound(db, &resolver, bound, self_ty);
+        iter::once(trait_ref.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented))
+            .chain(
+                trait_ref.into_iter().flat_map(move |tr| {
+                    assoc_type_bindings_from_type_bound(db, resolver, bound, tr)
+                }),
+            )
+    }
+}
+fn assoc_type_bindings_from_type_bound<'a>(
+    db: &'a impl HirDatabase,
+    resolver: &'a Resolver,
+    bound: &'a TypeBound,
+    trait_ref: TraitRef,
+) -> impl Iterator<Item = GenericPredicate> + 'a {
+    let last_segment = match bound {
+        TypeBound::Path(path) => path.segments.last(),
+        TypeBound::Error => None,
+    };
+    last_segment
+        .into_iter()
+        .flat_map(|segment| segment.args_and_bindings.iter())
+        .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
+        .map(move |(name, type_ref)| {
+            let associated_ty =
+                associated_type_by_name_including_super_traits(db, trait_ref.trait_, &name);
+            let associated_ty = match associated_ty {
+                None => return GenericPredicate::Error,
+                Some(t) => t,
+            };
+            let projection_ty =
+                ProjectionTy { associated_ty, parameters: trait_ref.substs.clone() };
+            let ty = Ty::from_hir(db, resolver, type_ref);
+            let projection_predicate = ProjectionPredicate { projection_ty, ty };
+            GenericPredicate::Projection(projection_predicate)
+        })
+}
+/// Build the signature of a callable item (function, struct or enum variant).
+pub fn callable_item_sig(db: &impl HirDatabase, def: CallableDef) -> FnSig {
+    match def {
+        CallableDef::FunctionId(f) => fn_sig_for_fn(db, f),
+        CallableDef::StructId(s) => fn_sig_for_struct_constructor(db, s),
+        CallableDef::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
+    }
+}
+/// Build the type of all specific fields of a struct or enum variant.
+pub(crate) fn field_types_query(
+    db: &impl HirDatabase,
+    variant_id: VariantId,
+) -> Arc<ArenaMap<LocalStructFieldId, Ty>> {
+    let var_data = variant_data(db, variant_id);
+    let resolver = match variant_id {
+        VariantId::StructId(it) => it.resolver(db),
+        VariantId::UnionId(it) => it.resolver(db),
+        VariantId::EnumVariantId(it) => it.parent.resolver(db),
+    };
+    let mut res = ArenaMap::default();
+    for (field_id, field_data) in var_data.fields().iter() {
+        res.insert(field_id, Ty::from_hir(db, &resolver, &field_data.type_ref))
+    }
+    Arc::new(res)
+}
+/// This query exists only to be used when resolving short-hand associated types
+/// like `T::Item`.
+///
+/// See the analogous query in rustc and its comment:
+/// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
+/// This is a query mostly to handle cycles somewhat gracefully; e.g. the
+/// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
+/// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
+pub(crate) fn generic_predicates_for_param_query(
+    db: &impl HirDatabase,
+    def: GenericDefId,
+    param_idx: u32,
+) -> Arc<[GenericPredicate]> {
+    let resolver = def.resolver(db);
+    resolver
+        .where_predicates_in_scope()
+        // we have to filter out all other predicates *first*, before attempting to lower them
+        .filter(|pred| Ty::from_hir_only_param(db, &resolver, &pred.type_ref) == Some(param_idx))
+        .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+        .collect()
+}
+impl TraitEnvironment {
+    pub fn lower(db: &impl HirDatabase, resolver: &Resolver) -> Arc<TraitEnvironment> {
+        let predicates = resolver
+            .where_predicates_in_scope()
+            .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+            .collect::<Vec<_>>();
+        Arc::new(TraitEnvironment { predicates })
+    }
+}
+/// Resolve the where clause(s) of an item with generics.
+pub(crate) fn generic_predicates_query(
+    db: &impl HirDatabase,
+    def: GenericDefId,
+) -> Arc<[GenericPredicate]> {
+    let resolver = def.resolver(db);
+    resolver
+        .where_predicates_in_scope()
+        .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+        .collect()
+}
+/// Resolve the default type params from generics
+pub(crate) fn generic_defaults_query(db: &impl HirDatabase, def: GenericDefId) -> Substs {
+    let resolver = def.resolver(db);
+    let generic_params = db.generic_params(def.into());
+    let defaults = generic_params
+        .params_including_parent()
+        .into_iter()
+        .map(|p| p.default.as_ref().map_or(Ty::Unknown, |t| Ty::from_hir(db, &resolver, t)))
+        .collect();
+    Substs(defaults)
+}
+fn fn_sig_for_fn(db: &impl HirDatabase, def: FunctionId) -> FnSig {
+    let data = db.function_data(def);
+    let resolver = def.resolver(db);
+    let params = data.params.iter().map(|tr| Ty::from_hir(db, &resolver, tr)).collect::<Vec<_>>();
+    let ret = Ty::from_hir(db, &resolver, &data.ret_type);
+    FnSig::from_params_and_return(params, ret)
+}
+/// Build the declared type of a function. This should not need to look at the
+/// function body.
+fn type_for_fn(db: &impl HirDatabase, def: FunctionId) -> Ty {
+    let generics = db.generic_params(def.into());
+    let substs = Substs::identity(&generics);
+    Ty::apply(TypeCtor::FnDef(def.into()), substs)
+}
+/// Build the declared type of a const.
+fn type_for_const(db: &impl HirDatabase, def: ConstId) -> Ty {
+    let data = db.const_data(def);
+    let resolver = def.resolver(db);
+    Ty::from_hir(db, &resolver, &data.type_ref)
+}
+/// Build the declared type of a static.
+fn type_for_static(db: &impl HirDatabase, def: StaticId) -> Ty {
+    let data = db.static_data(def);
+    let resolver = def.resolver(db);
+    Ty::from_hir(db, &resolver, &data.type_ref)
+}
+/// Build the declared type of a static.
+fn type_for_builtin(def: BuiltinType) -> Ty {
+    Ty::simple(match def {
+        BuiltinType::Char => TypeCtor::Char,
+        BuiltinType::Bool => TypeCtor::Bool,
+        BuiltinType::Str => TypeCtor::Str,
+        BuiltinType::Int(t) => TypeCtor::Int(IntTy::from(t).into()),
+        BuiltinType::Float(t) => TypeCtor::Float(FloatTy::from(t).into()),
+    })
+}
+fn fn_sig_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> FnSig {
+    let struct_data = db.struct_data(def.into());
+    let fields = struct_data.variant_data.fields();
+    let resolver = def.resolver(db);
+    let params = fields
+        .iter()
+        .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
+        .collect::<Vec<_>>();
+    let ret = type_for_adt(db, def.into());
+    FnSig::from_params_and_return(params, ret)
+}
+/// Build the type of a tuple struct constructor.
+fn type_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> Ty {
+    let struct_data = db.struct_data(def.into());
+    if struct_data.variant_data.is_unit() {
+        return type_for_adt(db, def.into()); // Unit struct
+    }
+    let generics = db.generic_params(def.into());
+    let substs = Substs::identity(&generics);
+    Ty::apply(TypeCtor::FnDef(def.into()), substs)
+}
+fn fn_sig_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId) -> FnSig {
+    let enum_data = db.enum_data(def.parent);
+    let var_data = &enum_data.variants[def.local_id];
+    let fields = var_data.variant_data.fields();
+    let resolver = def.parent.resolver(db);
+    let params = fields
+        .iter()
+        .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
+        .collect::<Vec<_>>();
+    let generics = db.generic_params(def.parent.into());
+    let substs = Substs::identity(&generics);
+    let ret = type_for_adt(db, def.parent.into()).subst(&substs);
+    FnSig::from_params_and_return(params, ret)
+}
+/// Build the type of a tuple enum variant constructor.
+fn type_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId) -> Ty {
+    let enum_data = db.enum_data(def.parent);
+    let var_data = &enum_data.variants[def.local_id].variant_data;
+    if var_data.is_unit() {
+        return type_for_adt(db, def.parent.into()); // Unit variant
+    }
+    let generics = db.generic_params(def.parent.into());
+    let substs = Substs::identity(&generics);
+    Ty::apply(TypeCtor::FnDef(EnumVariantId::from(def).into()), substs)
+}
+fn type_for_adt(db: &impl HirDatabase, adt: AdtId) -> Ty {
+    let generics = db.generic_params(adt.into());
+    Ty::apply(TypeCtor::Adt(adt), Substs::identity(&generics))
+}
+fn type_for_type_alias(db: &impl HirDatabase, t: TypeAliasId) -> Ty {
+    let generics = db.generic_params(t.into());
+    let resolver = t.resolver(db);
+    let type_ref = &db.type_alias_data(t).type_ref;
+    let substs = Substs::identity(&generics);
+    let inner = Ty::from_hir(db, &resolver, type_ref.as_ref().unwrap_or(&TypeRef::Error));
+    inner.subst(&substs)
+}
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum CallableDef {
+    FunctionId(FunctionId),
+    StructId(StructId),
+    EnumVariantId(EnumVariantId),
+}
+impl_froms!(CallableDef: FunctionId, StructId, EnumVariantId);
+impl CallableDef {
+    pub fn krate(self, db: &impl HirDatabase) -> CrateId {
+        match self {
+            CallableDef::FunctionId(f) => f.lookup(db).module(db).krate,
+            CallableDef::StructId(s) => s.module(db).krate,
+            CallableDef::EnumVariantId(e) => e.parent.module(db).krate,
+        }
+    }
+}
+impl From<CallableDef> for GenericDefId {
+    fn from(def: CallableDef) -> GenericDefId {
+        match def {
+            CallableDef::FunctionId(f) => f.into(),
+            CallableDef::StructId(s) => s.into(),
+            CallableDef::EnumVariantId(e) => e.into(),
+        }
+    }
+}
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum TyDefId {
+    BuiltinType(BuiltinType),
+    AdtId(AdtId),
+    TypeAliasId(TypeAliasId),
+}
+impl_froms!(TyDefId: BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId);
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum ValueTyDefId {
+    FunctionId(FunctionId),
+    StructId(StructId),
+    EnumVariantId(EnumVariantId),
+    ConstId(ConstId),
+    StaticId(StaticId),
+}
+impl_froms!(ValueTyDefId: FunctionId, StructId, EnumVariantId, ConstId, StaticId);
+/// Build the declared type of an item. This depends on the namespace; e.g. for
+/// `struct Foo(usize)`, we have two types: The type of the struct itself, and
+/// the constructor function `(usize) -> Foo` which lives in the values
+/// namespace.
+pub(crate) fn ty_query(db: &impl HirDatabase, def: TyDefId) -> Ty {
+    match def {
+        TyDefId::BuiltinType(it) => type_for_builtin(it),
+        TyDefId::AdtId(it) => type_for_adt(db, it),
+        TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
+    }
+}
+pub(crate) fn value_ty_query(db: &impl HirDatabase, def: ValueTyDefId) -> Ty {
+    match def {
+        ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
+        ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
+        ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
+        ValueTyDefId::ConstId(it) => type_for_const(db, it),
+        ValueTyDefId::StaticId(it) => type_for_static(db, it),
+    }
+}
+pub(crate) fn impl_ty_query(db: &impl HirDatabase, impl_id: ImplId) -> ImplTy {
+    let impl_data = db.impl_data(impl_id);
+    let resolver = impl_id.resolver(db);
+    let self_ty = Ty::from_hir(db, &resolver, &impl_data.target_type);
+    match impl_data.target_trait.as_ref() {
+        Some(trait_ref) => {
+            match TraitRef::from_hir(db, &resolver, trait_ref, Some(self_ty.clone())) {
+                Some(it) => ImplTy::TraitRef(it),
+                None => ImplTy::Inherent(self_ty),
+            }
+        }
+        None => ImplTy::Inherent(self_ty),
+    }
+}