diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index f159f80af0..113ec2b78e 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -3,6 +3,7 @@
 
 use either::Either;
 use hir_expand::{
+    db::AstDatabase,
     hygiene::Hygiene,
     name::{name, AsName, Name},
     HirFileId, MacroDefId, MacroDefKind,
@@ -41,8 +42,8 @@ pub(crate) struct LowerCtx {
 }
 
 impl LowerCtx {
-    pub fn new(db: &dyn DefDatabase, file_id: HirFileId) -> Self {
-        LowerCtx { hygiene: Hygiene::new(db.upcast(), file_id) }
+    pub fn new(db: &dyn AstDatabase, file_id: HirFileId) -> Self {
+        LowerCtx { hygiene: Hygiene::new(db, file_id) }
     }
     pub fn with_hygiene(hygiene: &Hygiene) -> Self {
         LowerCtx { hygiene: hygiene.clone() }
@@ -119,7 +120,7 @@ impl ExprCollector<'_> {
     }
 
     fn ctx(&self) -> LowerCtx {
-        LowerCtx::new(self.db, self.expander.current_file_id)
+        LowerCtx::new(self.db.upcast(), self.expander.current_file_id)
     }
 
     fn alloc_expr(&mut self, expr: Expr, ptr: AstPtr<ast::Expr>) -> ExprId {
diff --git a/crates/ra_hir_def/src/item_tree.rs b/crates/ra_hir_def/src/item_tree.rs
new file mode 100644
index 0000000000..f4743f0f63
--- /dev/null
+++ b/crates/ra_hir_def/src/item_tree.rs
@@ -0,0 +1,511 @@
+//! A simplified AST that only contains items.
+
+use hir_expand::{
+    ast_id_map::{AstIdMap, FileAstId},
+    hygiene::Hygiene,
+    name::{name, AsName, Name},
+};
+use ra_arena::{Arena, Idx, RawId};
+use ra_syntax::ast;
+
+use crate::{
+    attr::Attrs,
+    generics::GenericParams,
+    path::{path, AssociatedTypeBinding, GenericArgs, ImportAlias, ModPath, Path},
+    type_ref::{Mutability, TypeBound, TypeRef},
+    visibility::RawVisibility,
+};
+use ast::{NameOwner, StructKind, TypeAscriptionOwner};
+use std::{
+    ops::{Index, Range},
+    sync::Arc,
+};
+
+#[derive(Default)]
+pub struct ItemTree {
+    imports: Arena<Import>,
+    functions: Arena<Function>,
+    structs: Arena<Struct>,
+    fields: Arena<Field>,
+    unions: Arena<Union>,
+    enums: Arena<Enum>,
+    variants: Arena<Variant>,
+    consts: Arena<Const>,
+    statics: Arena<Static>,
+    traits: Arena<Trait>,
+    impls: Arena<Impl>,
+    type_aliases: Arena<TypeAlias>,
+    mods: Arena<Mod>,
+    macro_calls: Arena<MacroCall>,
+    exprs: Arena<Expr>,
+}
+
+impl ItemTree {
+    pub fn query(syntax: &ast::SourceFile) -> ItemTree {
+        todo!()
+    }
+}
+
+macro_rules! impl_index {
+    ( $($fld:ident: $t:ty),+ $(,)? ) => {
+        $(
+            impl Index<Idx<$t>> for ItemTree {
+                type Output = $t;
+
+                fn index(&self, index: Idx<$t>) -> &Self::Output {
+                    &self.$fld[index]
+                }
+            }
+        )+
+    };
+}
+
+impl_index!(
+    imports: Import,
+    functions: Function,
+    structs: Struct,
+    fields: Field,
+    unions: Union,
+    enums: Enum,
+    variants: Variant,
+    consts: Const,
+    statics: Static,
+    traits: Trait,
+    impls: Impl,
+    type_aliases: TypeAlias,
+    mods: Mod,
+    macro_calls: MacroCall,
+    exprs: Expr,
+);
+
+pub struct Import {
+    pub path: ModPath,
+    pub alias: Option<ImportAlias>,
+    pub visibility: RawVisibility,
+    pub is_glob: bool,
+    pub is_prelude: bool,
+    pub is_extern_crate: bool,
+    pub is_macro_use: bool,
+}
+
+pub struct Function {
+    pub name: Name,
+    pub attrs: Attrs,
+    pub visibility: RawVisibility,
+    pub generic_params: GenericParams,
+    pub has_self_param: bool,
+    pub params: Vec<TypeRef>,
+    pub ret_type: TypeRef,
+    pub ast: FileAstId<ast::FnDef>,
+}
+
+pub struct Struct {
+    pub name: Name,
+    pub attrs: Attrs,
+    pub visibility: RawVisibility,
+    pub generic_params: GenericParams,
+    pub fields: Fields,
+    pub ast: FileAstId<ast::StructDef>,
+}
+
+pub struct Union {
+    pub name: Name,
+    pub attrs: Attrs,
+    pub visibility: RawVisibility,
+    pub generic_params: GenericParams,
+    pub fields: Fields,
+}
+
+pub struct Enum {
+    pub name: Name,
+    pub attrs: Attrs,
+    pub visibility: RawVisibility,
+    pub generic_params: GenericParams,
+    pub variants: Range<Idx<Variant>>,
+}
+
+pub struct Const {
+    /// const _: () = ();
+    pub name: Option<Name>,
+    pub visibility: RawVisibility,
+    pub type_ref: TypeRef,
+}
+
+pub struct Static {
+    pub name: Name,
+    pub visibility: RawVisibility,
+    pub type_ref: TypeRef,
+}
+
+pub struct Trait {
+    pub name: Name,
+    pub visibility: RawVisibility,
+    pub generic_params: GenericParams,
+    pub auto: bool,
+    pub items: Vec<AssocItem>,
+}
+
+pub struct Impl {
+    pub generic_params: GenericParams,
+    pub target_trait: Option<TypeRef>,
+    pub target_type: TypeRef,
+    pub is_negative: bool,
+    pub items: Vec<AssocItem>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TypeAlias {
+    pub name: Name,
+    pub visibility: RawVisibility,
+    pub generic_params: GenericParams,
+    pub type_ref: Option<TypeRef>,
+}
+
+pub struct Mod {
+    pub name: Name,
+    pub visibility: RawVisibility,
+    pub items: Vec<ModItem>,
+}
+
+pub struct MacroCall {
+    pub name: Option<Name>,
+    pub path: ModPath,
+    pub export: bool,
+    pub builtin: bool,
+    pub ast_id: FileAstId<ast::MacroCall>,
+}
+
+// NB: There's no `FileAstId` for `Expr`. The only case where this would be useful is for array
+// lengths, but we don't do much with them yet.
+pub struct Expr;
+
+pub enum ModItem {
+    Import(Idx<Import>),
+    Function(Idx<Function>),
+    Struct(Idx<Struct>),
+    Union(Idx<Union>),
+    Enum(Idx<Enum>),
+    Const(Idx<Const>),
+    Static(Idx<Static>),
+    Trait(Idx<Trait>),
+    Impl(Idx<Impl>),
+    TypeAlias(Idx<TypeAlias>),
+    Mod(Idx<Mod>),
+    MacroCall(Idx<MacroCall>),
+}
+
+pub enum AssocItem {
+    Function(Idx<Function>),
+    TypeAlias(Idx<TypeAlias>),
+    Const(Idx<Const>),
+    MacroCall(Idx<MacroCall>),
+}
+
+pub struct Variant {
+    pub name: Name,
+    pub fields: Fields,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Fields {
+    Record(Range<Idx<Field>>),
+    Tuple(Range<Idx<Field>>),
+    Unit,
+}
+
+/// A single field of an enum variant or struct
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Field {
+    pub name: Name,
+    pub type_ref: TypeRef,
+    pub visibility: RawVisibility,
+}
+
+struct Ctx {
+    tree: ItemTree,
+    hygiene: Hygiene,
+    source_ast_id_map: Arc<AstIdMap>,
+    body_ctx: crate::body::LowerCtx,
+}
+
+impl Ctx {
+    fn lower(&mut self, item_owner: &dyn ast::ModuleItemOwner) {
+        for item in item_owner.items() {
+            self.lower_item(&item)
+        }
+    }
+
+    fn lower_item(&mut self, item: &ast::ModuleItem) {
+        match item {
+            ast::ModuleItem::StructDef(ast) => {
+                if let Some(data) = self.lower_struct(ast) {
+                    let idx = self.tree.structs.alloc(data);
+                }
+            }
+            ast::ModuleItem::UnionDef(ast) => {
+                if let Some(data) = self.lower_union(ast) {
+                    let idx = self.tree.unions.alloc(data);
+                }
+            }
+            ast::ModuleItem::EnumDef(ast) => {
+                if let Some(data) = self.lower_enum(ast) {
+                    let idx = self.tree.enums.alloc(data);
+                }
+            }
+            ast::ModuleItem::FnDef(ast) => {
+                if let Some(data) = self.lower_function(ast) {
+                    let idx = self.tree.functions.alloc(data);
+                }
+            }
+            ast::ModuleItem::TypeAliasDef(ast) => {
+                if let Some(data) = self.lower_type_alias(ast) {
+                    let idx = self.tree.type_aliases.alloc(data);
+                }
+            }
+            ast::ModuleItem::StaticDef(ast) => {
+                if let Some(data) = self.lower_static(ast) {
+                    let idx = self.tree.statics.alloc(data);
+                }
+            }
+            ast::ModuleItem::ConstDef(ast) => {
+                let data = self.lower_const(ast);
+                let idx = self.tree.consts.alloc(data);
+            }
+            ast::ModuleItem::Module(_) => {}
+            ast::ModuleItem::TraitDef(_) => {}
+            ast::ModuleItem::ImplDef(_) => {}
+            ast::ModuleItem::UseItem(_) => {}
+            ast::ModuleItem::ExternCrateItem(_) => {}
+            ast::ModuleItem::MacroCall(_) => {}
+            ast::ModuleItem::ExternBlock(_) => {}
+        }
+    }
+
+    fn lower_struct(&mut self, strukt: &ast::StructDef) -> Option<Struct> {
+        let attrs = self.lower_attrs(strukt);
+        let visibility = self.lower_visibility(strukt);
+        let name = strukt.name()?.as_name();
+        let generic_params = self.lower_generic_params(strukt);
+        let fields = self.lower_fields(&strukt.kind());
+        let ast = self.source_ast_id_map.ast_id(strukt);
+        let res = Struct { name, attrs, visibility, generic_params, fields, ast };
+        Some(res)
+    }
+
+    fn lower_fields(&mut self, strukt_kind: &ast::StructKind) -> Fields {
+        match strukt_kind {
+            ast::StructKind::Record(it) => {
+                let range = self.lower_record_fields(it);
+                Fields::Record(range)
+            }
+            ast::StructKind::Tuple(it) => {
+                let range = self.lower_tuple_fields(it);
+                Fields::Tuple(range)
+            }
+            ast::StructKind::Unit => Fields::Unit,
+        }
+    }
+
+    fn lower_record_fields(&mut self, fields: &ast::RecordFieldDefList) -> Range<Idx<Field>> {
+        let start = self.next_field_idx();
+        for field in fields.fields() {
+            if let Some(data) = self.lower_record_field(&field) {
+                let idx = self.tree.fields.alloc(data);
+            }
+        }
+        let end = self.next_field_idx();
+        start..end
+    }
+
+    fn lower_record_field(&self, field: &ast::RecordFieldDef) -> Option<Field> {
+        let name = field.name()?.as_name();
+        let visibility = self.lower_visibility(field);
+        let type_ref = self.lower_type_ref(&field.ascribed_type()?);
+        let res = Field { name, type_ref, visibility };
+        Some(res)
+    }
+
+    fn lower_tuple_fields(&mut self, fields: &ast::TupleFieldDefList) -> Range<Idx<Field>> {
+        let start = self.next_field_idx();
+        for (i, field) in fields.fields().enumerate() {
+            if let Some(data) = self.lower_tuple_field(i, &field) {
+                let idx = self.tree.fields.alloc(data);
+            }
+        }
+        let end = self.next_field_idx();
+        start..end
+    }
+
+    fn lower_tuple_field(&self, idx: usize, field: &ast::TupleFieldDef) -> Option<Field> {
+        let name = Name::new_tuple_field(idx);
+        let visibility = self.lower_visibility(field);
+        let type_ref = self.lower_type_ref(&field.type_ref()?);
+        let res = Field { name, type_ref, visibility };
+        Some(res)
+    }
+
+    fn lower_union(&mut self, union: &ast::UnionDef) -> Option<Union> {
+        let attrs = self.lower_attrs(union);
+        let visibility = self.lower_visibility(union);
+        let name = union.name()?.as_name();
+        let generic_params = self.lower_generic_params(union);
+        let fields = match union.record_field_def_list() {
+            Some(record_field_def_list) => {
+                self.lower_fields(&StructKind::Record(record_field_def_list))
+            }
+            None => Fields::Record(self.next_field_idx()..self.next_field_idx()),
+        };
+        let res = Union { name, attrs, visibility, generic_params, fields };
+        Some(res)
+    }
+
+    fn lower_enum(&mut self, enum_: &ast::EnumDef) -> Option<Enum> {
+        let attrs = self.lower_attrs(enum_);
+        let visibility = self.lower_visibility(enum_);
+        let name = enum_.name()?.as_name();
+        let generic_params = self.lower_generic_params(enum_);
+        let variants = match &enum_.variant_list() {
+            Some(variant_list) => self.lower_variants(variant_list),
+            None => self.next_variant_idx()..self.next_variant_idx(),
+        };
+        let res = Enum { name, attrs, visibility, generic_params, variants };
+        Some(res)
+    }
+
+    fn lower_variants(&mut self, variants: &ast::EnumVariantList) -> Range<Idx<Variant>> {
+        let start = self.next_variant_idx();
+        for variant in variants.variants() {
+            if let Some(data) = self.lower_variant(&variant) {
+                let idx = self.tree.variants.alloc(data);
+            }
+        }
+        let end = self.next_variant_idx();
+        start..end
+    }
+
+    fn lower_variant(&mut self, variant: &ast::EnumVariant) -> Option<Variant> {
+        let name = variant.name()?.as_name();
+        let fields = self.lower_fields(&variant.kind());
+        let res = Variant { name, fields };
+        Some(res)
+    }
+
+    fn lower_function(&mut self, func: &ast::FnDef) -> Option<Function> {
+        let attrs = self.lower_attrs(func);
+        let visibility = self.lower_visibility(func);
+        let name = func.name()?.as_name();
+        let generic_params = self.lower_generic_params(func);
+
+        let mut params = Vec::new();
+        let mut has_self_param = false;
+        if let Some(param_list) = func.param_list() {
+            if let Some(self_param) = param_list.self_param() {
+                let self_type = if let Some(type_ref) = self_param.ascribed_type() {
+                    TypeRef::from_ast(&self.body_ctx, type_ref)
+                } else {
+                    let self_type = TypeRef::Path(name![Self].into());
+                    match self_param.kind() {
+                        ast::SelfParamKind::Owned => self_type,
+                        ast::SelfParamKind::Ref => {
+                            TypeRef::Reference(Box::new(self_type), Mutability::Shared)
+                        }
+                        ast::SelfParamKind::MutRef => {
+                            TypeRef::Reference(Box::new(self_type), Mutability::Mut)
+                        }
+                    }
+                };
+                params.push(self_type);
+                has_self_param = true;
+            }
+            for param in param_list.params() {
+                let type_ref = TypeRef::from_ast_opt(&self.body_ctx, param.ascribed_type());
+                params.push(type_ref);
+            }
+        }
+        let ret_type = match func.ret_type().and_then(|rt| rt.type_ref()) {
+            Some(type_ref) => TypeRef::from_ast(&self.body_ctx, type_ref),
+            _ => TypeRef::unit(),
+        };
+
+        let ret_type = if func.async_token().is_some() {
+            let future_impl = desugar_future_path(ret_type);
+            let ty_bound = TypeBound::Path(future_impl);
+            TypeRef::ImplTrait(vec![ty_bound])
+        } else {
+            ret_type
+        };
+
+        let ast = self.source_ast_id_map.ast_id(func);
+        let res = Function {
+            name,
+            attrs,
+            visibility,
+            generic_params,
+            has_self_param,
+            params,
+            ret_type,
+            ast,
+        };
+        Some(res)
+    }
+
+    fn lower_type_alias(&mut self, type_alias: &ast::TypeAliasDef) -> Option<TypeAlias> {
+        let name = type_alias.name()?.as_name();
+        let type_ref = type_alias.type_ref().map(|it| self.lower_type_ref(&it));
+        let visibility = self.lower_visibility(type_alias);
+        let generic_params = self.lower_generic_params(type_alias);
+        let res = TypeAlias { name, visibility, generic_params, type_ref };
+        Some(res)
+    }
+
+    fn lower_static(&mut self, static_: &ast::StaticDef) -> Option<Static> {
+        let name = static_.name()?.as_name();
+        let type_ref = self.lower_type_ref_opt(static_.ascribed_type());
+        let visibility = self.lower_visibility(static_);
+        let res = Static { name, visibility, type_ref };
+        Some(res)
+    }
+
+    fn lower_const(&mut self, konst: &ast::ConstDef) -> Const {
+        let name = konst.name().map(|it| it.as_name());
+        let type_ref = self.lower_type_ref_opt(konst.ascribed_type());
+        let visibility = self.lower_visibility(konst);
+        Const { name, visibility, type_ref }
+    }
+
+    fn lower_generic_params(&mut self, item: &impl ast::TypeParamsOwner) -> GenericParams {
+        None.unwrap()
+    }
+
+    fn lower_attrs(&self, item: &impl ast::AttrsOwner) -> Attrs {
+        Attrs::new(item, &self.hygiene)
+    }
+    fn lower_visibility(&self, item: &impl ast::VisibilityOwner) -> RawVisibility {
+        RawVisibility::from_ast_with_hygiene(item.visibility(), &self.hygiene)
+    }
+    fn lower_type_ref(&self, type_ref: &ast::TypeRef) -> TypeRef {
+        TypeRef::from_ast(&self.body_ctx, type_ref.clone())
+    }
+    fn lower_type_ref_opt(&self, type_ref: Option<ast::TypeRef>) -> TypeRef {
+        TypeRef::from_ast_opt(&self.body_ctx, type_ref)
+    }
+
+    fn next_field_idx(&self) -> Idx<Field> {
+        Idx::from_raw(RawId::from(self.tree.fields.len() as u32))
+    }
+    fn next_variant_idx(&self) -> Idx<Variant> {
+        Idx::from_raw(RawId::from(self.tree.variants.len() as u32))
+    }
+}
+
+fn desugar_future_path(orig: TypeRef) -> Path {
+    let path = path![std::future::Future];
+    let mut generic_args: Vec<_> = std::iter::repeat(None).take(path.segments.len() - 1).collect();
+    let mut last = GenericArgs::empty();
+    let binding =
+        AssociatedTypeBinding { name: name![Output], type_ref: Some(orig), bounds: Vec::new() };
+    last.bindings.push(binding);
+    generic_args.push(Some(Arc::new(last)));
+
+    Path::from_known_path(path, generic_args)
+}
diff --git a/crates/ra_hir_def/src/lib.rs b/crates/ra_hir_def/src/lib.rs
index af2a717c9d..b5500f3707 100644
--- a/crates/ra_hir_def/src/lib.rs
+++ b/crates/ra_hir_def/src/lib.rs
@@ -25,6 +25,8 @@ pub mod item_scope;
 pub mod dyn_map;
 pub mod keys;
 
+pub mod item_tree;
+
 pub mod adt;
 pub mod data;
 pub mod generics;