draw the rest of the owl

13 files changed, 953 insertions, 409 deletions

diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index ffd5278ec..a379b9f49 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -31,10 +31,7 @@ use hir_ty::{
 };
 use ra_db::{CrateId, CrateName, Edition, FileId};
 use ra_prof::profile;
-use ra_syntax::{
-    ast::{self, AttrsOwner, NameOwner},
-    AstNode,
-};
+use ra_syntax::ast::{self, AttrsOwner, NameOwner};
 use rustc_hash::FxHashSet;
 
 use crate::{
@@ -205,7 +202,8 @@ impl ModuleDef {
 }
 
 pub use hir_def::{
-    attr::Attrs, item_scope::ItemInNs, visibility::Visibility, AssocItemId, AssocItemLoc,
+    attr::Attrs, item_scope::ItemInNs, item_tree::ItemTreeNode, visibility::Visibility,
+    AssocItemId, AssocItemLoc,
 };
 
 impl Module {
@@ -872,7 +870,7 @@ where
     ID: Lookup<Data = AssocItemLoc<AST>>,
     DEF: From<ID>,
     CTOR: FnOnce(DEF) -> AssocItem,
-    AST: AstNode,
+    AST: ItemTreeNode,
 {
     match id.lookup(db.upcast()).container {
         AssocContainerId::TraitId(_) | AssocContainerId::ImplId(_) => Some(ctor(DEF::from(id))),
diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index 4f2350915..9c5272c2d 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -243,7 +243,7 @@ impl Body {
             }
         };
         let expander = Expander::new(db, file_id, module);
-        let (body, source_map) = Body::new(db, def, expander, params, body);
+        let (body, source_map) = Body::new(db, file_id, def, expander, params, body);
         (Arc::new(body), Arc::new(source_map))
     }
 
@@ -253,12 +253,13 @@ impl Body {
 
     fn new(
         db: &dyn DefDatabase,
+        file_id: HirFileId,
         def: DefWithBodyId,
         expander: Expander,
         params: Option<ast::ParamList>,
         body: Option<ast::Expr>,
     ) -> (Body, BodySourceMap) {
-        lower::lower(db, def, expander, params, body)
+        lower::lower(db, file_id, def, expander, params, body)
     }
 }
 
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index f159f80af..e7cf80676 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -5,7 +5,7 @@ use either::Either;
 use hir_expand::{
     hygiene::Hygiene,
     name::{name, AsName, Name},
-    HirFileId, MacroDefId, MacroDefKind,
+    AstId, HirFileId, MacroDefId, MacroDefKind,
 };
 use ra_arena::Arena;
 use ra_syntax::{
@@ -27,6 +27,7 @@ use crate::{
         LogicOp, MatchArm, Ordering, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
     },
     item_scope::BuiltinShadowMode,
+    item_tree::{FileItemTreeId, ItemTree, ItemTreeSource},
     path::{GenericArgs, Path},
     type_ref::{Mutability, Rawness, TypeRef},
     AdtId, ConstLoc, ContainerId, DefWithBodyId, EnumLoc, FunctionLoc, Intern, ModuleDefId,
@@ -35,6 +36,7 @@ use crate::{
 
 use super::{ExprSource, PatSource};
 use ast::AstChildren;
+use std::sync::Arc;
 
 pub(crate) struct LowerCtx {
     hygiene: Hygiene,
@@ -55,11 +57,13 @@ impl LowerCtx {
 
 pub(super) fn lower(
     db: &dyn DefDatabase,
+    file_id: HirFileId,
     def: DefWithBodyId,
     expander: Expander,
     params: Option<ast::ParamList>,
     body: Option<ast::Expr>,
 ) -> (Body, BodySourceMap) {
+    let item_tree = db.item_tree(file_id);
     ExprCollector {
         db,
         def,
@@ -72,6 +76,7 @@ pub(super) fn lower(
             body_expr: dummy_expr_id(),
             item_scope: Default::default(),
         },
+        item_trees: vec![(file_id, item_tree)],
     }
     .collect(params, body)
 }
@@ -82,6 +87,8 @@ struct ExprCollector<'a> {
     expander: Expander,
     body: Body,
     source_map: BodySourceMap,
+
+    item_trees: Vec<(HirFileId, Arc<ItemTree>)>,
 }
 
 impl ExprCollector<'_> {
@@ -533,6 +540,9 @@ impl ExprCollector<'_> {
                             self.source_map
                                 .expansions
                                 .insert(macro_call, self.expander.current_file_id);
+
+                            let item_tree = self.db.item_tree(self.expander.current_file_id);
+                            self.item_trees.push((self.expander.current_file_id, item_tree));
                             let id = self.collect_expr(expansion);
                             self.expander.exit(self.db, mark);
                             id
@@ -547,6 +557,21 @@ impl ExprCollector<'_> {
         }
     }
 
+    fn find_inner_item<S: ItemTreeSource>(&self, id: AstId<ast::ModuleItem>) -> FileItemTreeId<S> {
+        let index =
+            self.item_trees.iter().position(|(file, _)| *file == id.file_id).unwrap_or_else(|| {
+                panic!("couldn't find item tree for file {:?}", id.file_id);
+            });
+        let tree = &self.item_trees[index].1;
+
+        // Root file (non-macro).
+        tree.all_inner_items()
+            .chain(tree.top_level_items().iter().copied())
+            .filter_map(|mod_item| mod_item.downcast::<S>())
+            .find(|tree_id| tree[*tree_id].ast_id().upcast() == id.value)
+            .unwrap()
+    }
+
     fn collect_expr_opt(&mut self, expr: Option<ast::Expr>) -> ExprId {
         if let Some(expr) = expr {
             self.collect_expr(expr)
@@ -578,56 +603,102 @@ impl ExprCollector<'_> {
 
     fn collect_block_items(&mut self, block: &ast::BlockExpr) {
         let container = ContainerId::DefWithBodyId(self.def);
-        for item in block.items() {
-            let (def, name): (ModuleDefId, Option<ast::Name>) = match item {
-                ast::ModuleItem::FnDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (
-                        FunctionLoc { container: container.into(), ast_id }.intern(self.db).into(),
-                        def.name(),
-                    )
-                }
-                ast::ModuleItem::TypeAliasDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (
-                        TypeAliasLoc { container: container.into(), ast_id }.intern(self.db).into(),
-                        def.name(),
-                    )
-                }
-                ast::ModuleItem::ConstDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (
-                        ConstLoc { container: container.into(), ast_id }.intern(self.db).into(),
-                        def.name(),
-                    )
-                }
-                ast::ModuleItem::StaticDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (StaticLoc { container, ast_id }.intern(self.db).into(), def.name())
-                }
-                ast::ModuleItem::StructDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (StructLoc { container, ast_id }.intern(self.db).into(), def.name())
-                }
-                ast::ModuleItem::EnumDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (EnumLoc { container, ast_id }.intern(self.db).into(), def.name())
-                }
-                ast::ModuleItem::UnionDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (UnionLoc { container, ast_id }.intern(self.db).into(), def.name())
-                }
-                ast::ModuleItem::TraitDef(def) => {
-                    let ast_id = self.expander.ast_id(&def);
-                    (TraitLoc { container, ast_id }.intern(self.db).into(), def.name())
-                }
-                ast::ModuleItem::ExternBlock(_) => continue, // FIXME: collect from extern blocks
-                ast::ModuleItem::ImplDef(_)
-                | ast::ModuleItem::UseItem(_)
-                | ast::ModuleItem::ExternCrateItem(_)
-                | ast::ModuleItem::Module(_)
-                | ast::ModuleItem::MacroCall(_) => continue,
-            };
+
+        let items = block
+            .items()
+            .filter_map(|item| {
+                let (def, name): (ModuleDefId, Option<ast::Name>) = match item {
+                    ast::ModuleItem::FnDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            FunctionLoc { container: container.into(), id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::TypeAliasDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            TypeAliasLoc { container: container.into(), id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::ConstDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            ConstLoc { container: container.into(), id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::StaticDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            StaticLoc { container, id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::StructDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            StructLoc { container, id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::EnumDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            EnumLoc { container, id: ast_id.with_value(id) }.intern(self.db).into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::UnionDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            UnionLoc { container, id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::TraitDef(def) => {
+                        let ast_id = self.expander.ast_id(&def);
+                        let id = self.find_inner_item(ast_id.map(|id| id.upcast()));
+                        (
+                            TraitLoc { container, id: ast_id.with_value(id) }
+                                .intern(self.db)
+                                .into(),
+                            def.name(),
+                        )
+                    }
+                    ast::ModuleItem::ExternBlock(_) => return None, // FIXME: collect from extern blocks
+                    ast::ModuleItem::ImplDef(_)
+                    | ast::ModuleItem::UseItem(_)
+                    | ast::ModuleItem::ExternCrateItem(_)
+                    | ast::ModuleItem::Module(_)
+                    | ast::ModuleItem::MacroCall(_) => return None,
+                };
+
+                Some((def, name))
+            })
+            .collect::<Vec<_>>();
+
+        for (def, name) in items {
             self.body.item_scope.define_def(def);
             if let Some(name) = name {
                 let vis = crate::visibility::Visibility::Public; // FIXME determine correctly
diff --git a/crates/ra_hir_def/src/data.rs b/crates/ra_hir_def/src/data.rs
index 53599e74a..697fde3d2 100644
--- a/crates/ra_hir_def/src/data.rs
+++ b/crates/ra_hir_def/src/data.rs
@@ -5,24 +5,23 @@ use std::sync::Arc;
 use hir_expand::{
     hygiene::Hygiene,
     name::{name, AsName, Name},
-    AstId, InFile,
+    InFile,
 };
 use ra_prof::profile;
-use ra_syntax::ast::{
-    self, AssocItem, AstNode, ModuleItemOwner, NameOwner, TypeAscriptionOwner, TypeBoundsOwner,
-    VisibilityOwner,
-};
+use ra_syntax::ast::{self, NameOwner, TypeAscriptionOwner, TypeBoundsOwner, VisibilityOwner};
 
 use crate::{
     attr::Attrs,
+    body::Expander,
     body::LowerCtx,
     db::DefDatabase,
+    item_tree::{AssocItem, ItemTreeId, ModItem},
     path::{path, AssociatedTypeBinding, GenericArgs, Path},
     src::HasSource,
     type_ref::{Mutability, TypeBound, TypeRef},
     visibility::RawVisibility,
-    AssocContainerId, AssocItemId, ConstId, ConstLoc, Expander, FunctionId, FunctionLoc, HasModule,
-    ImplId, Intern, Lookup, StaticId, TraitId, TypeAliasId, TypeAliasLoc,
+    AssocContainerId, AssocItemId, ConstId, ConstLoc, FunctionId, FunctionLoc, HasModule, ImplId,
+    Intern, Lookup, ModuleId, StaticId, TraitId, TypeAliasId, TypeAliasLoc,
 };
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -155,30 +154,24 @@ pub struct TraitData {
 impl TraitData {
     pub(crate) fn trait_data_query(db: &dyn DefDatabase, tr: TraitId) -> Arc<TraitData> {
         let tr_loc = tr.lookup(db);
-        let src = tr_loc.source(db);
-        let name = src.value.name().map_or_else(Name::missing, |n| n.as_name());
-        let auto = src.value.auto_token().is_some();
+        let item_tree = db.item_tree(tr_loc.id.file_id);
+        let tr_def = &item_tree[tr_loc.id.value];
+        let name = tr_def.name.clone();
+        let auto = tr_def.auto;
         let module_id = tr_loc.container.module(db);
-
         let container = AssocContainerId::TraitId(tr);
-        let mut items = Vec::new();
-
-        if let Some(item_list) = src.value.item_list() {
-            let mut expander = Expander::new(db, tr_loc.ast_id.file_id, module_id);
-            items.extend(collect_items(
-                db,
-                &mut expander,
-                item_list.assoc_items(),
-                src.file_id,
-                container,
-            ));
-            items.extend(collect_items_in_macros(
-                db,
-                &mut expander,
-                &src.with_value(item_list),
-                container,
-            ));
-        }
+        let mut expander = Expander::new(db, tr_loc.id.file_id, module_id);
+
+        let items = collect_items(
+            db,
+            module_id,
+            &mut expander,
+            tr_def.items.iter().copied(),
+            tr_loc.id.file_id,
+            container,
+            100,
+        );
+
         Arc::new(TraitData { name, items, auto })
     }
 
@@ -209,33 +202,28 @@ impl ImplData {
     pub(crate) fn impl_data_query(db: &dyn DefDatabase, id: ImplId) -> Arc<ImplData> {
         let _p = profile("impl_data_query");
         let impl_loc = id.lookup(db);
-        let src = impl_loc.source(db);
-        let lower_ctx = LowerCtx::new(db, src.file_id);
 
-        let target_trait = src.value.target_trait().map(|it| TypeRef::from_ast(&lower_ctx, it));
-        let target_type = TypeRef::from_ast_opt(&lower_ctx, src.value.target_type());
-        let is_negative = src.value.excl_token().is_some();
+        let item_tree = db.item_tree(impl_loc.id.file_id);
+        let impl_def = &item_tree[impl_loc.id.value];
+        let target_trait = impl_def.target_trait.clone();
+        let target_type = impl_def.target_type.clone();
+        let is_negative = impl_def.is_negative;
         let module_id = impl_loc.container.module(db);
         let container = AssocContainerId::ImplId(id);
+        let mut expander = Expander::new(db, impl_loc.id.file_id, module_id);
 
-        let mut items: Vec<AssocItemId> = Vec::new();
-
-        if let Some(item_list) = src.value.item_list() {
-            let mut expander = Expander::new(db, impl_loc.ast_id.file_id, module_id);
-            items.extend(
-                collect_items(db, &mut expander, item_list.assoc_items(), src.file_id, container)
-                    .into_iter()
-                    .map(|(_, item)| item),
-            );
-            items.extend(
-                collect_items_in_macros(db, &mut expander, &src.with_value(item_list), container)
-                    .into_iter()
-                    .map(|(_, item)| item),
-            );
-        }
+        let items = collect_items(
+            db,
+            module_id,
+            &mut expander,
+            impl_def.items.iter().copied(),
+            impl_loc.id.file_id,
+            container,
+            100,
+        );
+        let items = items.into_iter().map(|(_, item)| item).collect();
 
-        let res = ImplData { target_trait, target_type, items, is_negative };
-        Arc::new(res)
+        Arc::new(ImplData { target_trait, target_type, items, is_negative })
     }
 }
 
@@ -295,28 +283,12 @@ impl StaticData {
     }
 }
 
-fn collect_items_in_macros(
-    db: &dyn DefDatabase,
-    expander: &mut Expander,
-    impl_def: &InFile<ast::ItemList>,
-    container: AssocContainerId,
-) -> Vec<(Name, AssocItemId)> {
-    let mut res = Vec::new();
-
-    // We set a limit to protect against infinite recursion
-    let limit = 100;
-
-    for m in impl_def.value.syntax().children().filter_map(ast::MacroCall::cast) {
-        res.extend(collect_items_in_macro(db, expander, m, container, limit))
-    }
-
-    res
-}
-
-fn collect_items_in_macro(
+fn collect_items(
     db: &dyn DefDatabase,
+    module: ModuleId,
     expander: &mut Expander,
-    m: ast::MacroCall,
+    assoc_items: impl Iterator<Item = AssocItem>,
+    file_id: crate::HirFileId,
     container: AssocContainerId,
     limit: usize,
 ) -> Vec<(Name, AssocItemId)> {
@@ -324,62 +296,62 @@ fn collect_items_in_macro(
         return Vec::new();
     }
 
-    if let Some((mark, items)) = expander.enter_expand(db, None, m) {
-        let items: InFile<ast::MacroItems> = expander.to_source(items);
-        let mut res = collect_items(
-            db,
-            expander,
-            items.value.items().filter_map(|it| AssocItem::cast(it.syntax().clone())),
-            items.file_id,
-            container,
-        );
-
-        // Recursive collect macros
-        // Note that ast::ModuleItem do not include ast::MacroCall
-        // We cannot use ModuleItemOwner::items here
-        for it in items.value.syntax().children().filter_map(ast::MacroCall::cast) {
-            res.extend(collect_items_in_macro(db, expander, it, container, limit - 1))
-        }
-        expander.exit(db, mark);
-        res
-    } else {
-        Vec::new()
-    }
-}
+    let item_tree = db.item_tree(file_id);
+    let cfg_options = db.crate_graph()[module.krate].cfg_options.clone();
 
-fn collect_items(
-    db: &dyn DefDatabase,
-    expander: &mut Expander,
-    assoc_items: impl Iterator<Item = AssocItem>,
-    file_id: crate::HirFileId,
-    container: AssocContainerId,
-) -> Vec<(Name, AssocItemId)> {
-    let items = db.ast_id_map(file_id);
-
-    assoc_items
-        .filter_map(|item_node| match item_node {
-            ast::AssocItem::FnDef(it) => {
-                let name = it.name().map_or_else(Name::missing, |it| it.as_name());
-                if !expander.is_cfg_enabled(&it) {
-                    return None;
+    let mut items = Vec::new();
+    for item in assoc_items {
+        match item {
+            AssocItem::Function(id) => {
+                let item = &item_tree[id];
+                if !item.attrs.is_cfg_enabled(&cfg_options) {
+                    continue;
                 }
-                let def = FunctionLoc { container, ast_id: AstId::new(file_id, items.ast_id(&it)) }
-                    .intern(db);
-                Some((name, def.into()))
+                let def = FunctionLoc { container, id: ItemTreeId::new(file_id, id) }.intern(db);
+                items.push((item.name.clone(), def.into()));
             }
-            ast::AssocItem::ConstDef(it) => {
-                let name = it.name().map_or_else(Name::missing, |it| it.as_name());
-                let def = ConstLoc { container, ast_id: AstId::new(file_id, items.ast_id(&it)) }
-                    .intern(db);
-                Some((name, def.into()))
+            // FIXME: cfg?
+            AssocItem::Const(id) => {
+                let item = &item_tree[id];
+                let name = if let Some(name) = item.name.clone() {
+                    name
+                } else {
+                    continue;
+                };
+                let def = ConstLoc { container, id: ItemTreeId::new(file_id, id) }.intern(db);
+                items.push((name, def.into()));
             }
-            ast::AssocItem::TypeAliasDef(it) => {
-                let name = it.name().map_or_else(Name::missing, |it| it.as_name());
-                let def =
-                    TypeAliasLoc { container, ast_id: AstId::new(file_id, items.ast_id(&it)) }
-                        .intern(db);
-                Some((name, def.into()))
+            AssocItem::TypeAlias(id) => {
+                let item = &item_tree[id];
+                let def = TypeAliasLoc { container, id: ItemTreeId::new(file_id, id) }.intern(db);
+                items.push((item.name.clone(), def.into()));
             }
-        })
-        .collect()
+            AssocItem::MacroCall(call) => {
+                let call = &item_tree[call];
+                let ast_id_map = db.ast_id_map(file_id);
+                let root = db.parse_or_expand(file_id).unwrap();
+                let call = ast_id_map.get(call.ast_id).to_node(&root);
+
+                if let Some((mark, mac)) = expander.enter_expand(db, None, call) {
+                    let src: InFile<ast::MacroItems> = expander.to_source(mac);
+                    let item_tree = db.item_tree(src.file_id);
+                    let iter =
+                        item_tree.top_level_items().iter().filter_map(ModItem::as_assoc_item);
+                    items.extend(collect_items(
+                        db,
+                        module,
+                        expander,
+                        iter,
+                        src.file_id,
+                        container,
+                        limit - 1,
+                    ));
+
+                    expander.exit(db, mark);
+                }
+            }
+        }
+    }
+
+    items
 }
diff --git a/crates/ra_hir_def/src/item_tree.rs b/crates/ra_hir_def/src/item_tree.rs
index aca2503a0..9a5dd701e 100644
--- a/crates/ra_hir_def/src/item_tree.rs
+++ b/crates/ra_hir_def/src/item_tree.rs
@@ -1,6 +1,8 @@
 //! A simplified AST that only contains items.
 
 mod lower;
+#[cfg(test)]
+mod tests;
 
 use std::{
     fmt::{self, Debug},
@@ -31,16 +33,20 @@ use crate::{
     type_ref::{Mutability, TypeBound, TypeRef},
     visibility::RawVisibility,
 };
+use smallvec::SmallVec;
 
 /// The item tree of a source file.
-#[derive(Debug, Default, Eq, PartialEq)]
+#[derive(Debug, Eq, PartialEq)]
 pub struct ItemTree {
+    file_id: HirFileId,
     top_level: Vec<ModItem>,
     top_attrs: Attrs,
     attrs: FxHashMap<ModItem, Attrs>,
     empty_attrs: Attrs,
+    inner_items: FxHashMap<FileAstId<ast::ModuleItem>, SmallVec<[ModItem; 1]>>,
 
     imports: Arena<Import>,
+    extern_crates: Arena<ExternCrate>,
     functions: Arena<Function>,
     structs: Arena<Struct>,
     fields: Arena<Field>,
@@ -63,7 +69,7 @@ impl ItemTree {
         let syntax = if let Some(node) = db.parse_or_expand(file_id) {
             node
         } else {
-            return Default::default();
+            return Arc::new(Self::empty(file_id));
         };
 
         let hygiene = Hygiene::new(db.upcast(), file_id);
@@ -80,20 +86,41 @@ impl ItemTree {
                     file_storage = file;
                     &file_storage
                 },
-                _ => return Default::default(),
+                _ => return Arc::new(Self::empty(file_id)),
             }
         };
 
-        let map = db.ast_id_map(file_id);
-        let mut ctx = lower::Ctx {
-            tree: ItemTree::default(),
-            hygiene,
-            file: file_id,
-            source_ast_id_map: map,
-            body_ctx: crate::body::LowerCtx::new(db, file_id),
-        };
-        ctx.tree.top_attrs = top_attrs.unwrap_or_default();
-        Arc::new(ctx.lower(item_owner))
+        let ctx = lower::Ctx::new(db, hygiene, file_id);
+        let mut item_tree = ctx.lower(item_owner);
+        item_tree.top_attrs = top_attrs.unwrap_or_default();
+        Arc::new(item_tree)
+    }
+
+    fn empty(file_id: HirFileId) -> Self {
+        Self {
+            file_id,
+            top_level: Default::default(),
+            top_attrs: Default::default(),
+            attrs: Default::default(),
+            empty_attrs: Default::default(),
+            inner_items: Default::default(),
+            imports: Default::default(),
+            extern_crates: Default::default(),
+            functions: Default::default(),
+            structs: Default::default(),
+            fields: Default::default(),
+            unions: Default::default(),
+            enums: Default::default(),
+            variants: Default::default(),
+            consts: Default::default(),
+            statics: Default::default(),
+            traits: Default::default(),
+            impls: Default::default(),
+            type_aliases: Default::default(),
+            mods: Default::default(),
+            macro_calls: Default::default(),
+            exprs: Default::default(),
+        }
     }
 
     /// Returns an iterator over all items located at the top level of the `HirFileId` this
@@ -110,17 +137,49 @@ impl ItemTree {
     pub fn attrs(&self, of: ModItem) -> &Attrs {
         self.attrs.get(&of).unwrap_or(&self.empty_attrs)
     }
+
+    /// Returns the lowered inner items that `ast` corresponds to.
+    ///
+    /// Most AST items are lowered to a single `ModItem`, but some (eg. `use` items) may be lowered
+    /// to multiple items in the `ItemTree`.
+    pub fn inner_items(&self, ast: FileAstId<ast::ModuleItem>) -> &[ModItem] {
+        &self.inner_items[&ast]
+    }
+
+    pub fn all_inner_items(&self) -> impl Iterator<Item = ModItem> + '_ {
+        self.inner_items.values().flatten().copied()
+    }
+
+    pub fn source<S: ItemTreeSource>(
+        &self,
+        db: &dyn DefDatabase,
+        of: FileItemTreeId<S>,
+    ) -> S::Source {
+        // This unwrap cannot fail, since it has either succeeded above, or resulted in an empty
+        // ItemTree (in which case there is no valid `FileItemTreeId` to call this method with).
+        let root = db
+            .parse_or_expand(self.file_id)
+            .expect("parse_or_expand failed on constructed ItemTree");
+
+        let id = self[of].ast_id();
+        let map = db.ast_id_map(self.file_id);
+        let ptr = map.get(id);
+        ptr.to_node(&root)
+    }
 }
 
 /// Trait implemented by all nodes in the item tree.
 pub trait ItemTreeNode: Clone {
     /// Looks up an instance of `Self` in an item tree.
     fn lookup(tree: &ItemTree, index: Idx<Self>) -> &Self;
+
+    /// Downcasts a `ModItem` to a `FileItemTreeId` specific to this type.
+    fn id_from_mod_item(mod_item: ModItem) -> Option<FileItemTreeId<Self>>;
 }
 
 /// Trait for item tree nodes that allow accessing the original AST node.
 pub trait ItemTreeSource: ItemTreeNode {
-    type Source: AstNode;
+    type Source: AstNode + Into<ast::ModuleItem>;
 
     fn ast_id(&self) -> FileAstId<Self::Source>;
 }
@@ -164,12 +223,22 @@ macro_rules! nodes {
             fn lookup(tree: &ItemTree, index: Idx<Self>) -> &Self {
                 &tree.$fld[index]
             }
+
+
+            fn id_from_mod_item(mod_item: ModItem) -> Option<FileItemTreeId<Self>> {
+                if let ModItem::$node(id) = mod_item {
+                    Some(id)
+                } else {
+                    None
+                }
+            }
         }
     )+ };
 }
 
 nodes!(
     Import in imports,
+    ExternCrate in extern_crates,
     Function in functions,
     Struct in structs,
     Union in unions,
@@ -196,6 +265,8 @@ macro_rules! source {
 }
 
 source! {
+    Import -> ast::UseItem,
+    ExternCrate -> ast::ExternCrateItem,
     Function -> ast::FnDef,
     Struct -> ast::StructDef,
     Union -> ast::UnionDef,
@@ -248,7 +319,7 @@ impl<N: ItemTreeNode> Index<FileItemTreeId<N>> for ItemTree {
     }
 }
 
-/// A desugared `extern crate` or `use` import.
+/// A desugared `use` import.
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Import {
     pub path: ModPath,
@@ -256,8 +327,19 @@ pub struct Import {
     pub visibility: RawVisibility,
     pub is_glob: bool,
     pub is_prelude: bool,
-    pub is_extern_crate: bool,
+    /// AST ID of the `use` or `extern crate` item this import was derived from. Note that many
+    /// `Import`s can map to the same `use` item.
+    pub ast_id: FileAstId<ast::UseItem>,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct ExternCrate {
+    pub path: ModPath,
+    pub alias: Option<ImportAlias>,
+    pub visibility: RawVisibility,
+    /// Whether this is a `#[macro_use] extern crate ...`.
     pub is_macro_use: bool,
+    pub ast_id: FileAstId<ast::ExternCrateItem>,
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
@@ -270,7 +352,6 @@ pub struct Function {
     pub params: Vec<TypeRef>,
     pub ret_type: TypeRef,
     pub ast_id: FileAstId<ast::FnDef>,
-    // FIXME inner items
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
@@ -412,6 +493,7 @@ macro_rules! impl_froms {
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
 pub enum ModItem {
     Import(FileItemTreeId<Import>),
+    ExternCrate(FileItemTreeId<ExternCrate>),
     Function(FileItemTreeId<Function>),
     Struct(FileItemTreeId<Struct>),
     Union(FileItemTreeId<Union>),
@@ -429,6 +511,7 @@ impl ModItem {
     pub fn as_assoc_item(&self) -> Option<AssocItem> {
         match self {
             ModItem::Import(_)
+            | ModItem::ExternCrate(_)
             | ModItem::Struct(_)
             | ModItem::Union(_)
             | ModItem::Enum(_)
@@ -442,10 +525,15 @@ impl ModItem {
             ModItem::Function(func) => Some(AssocItem::Function(*func)),
         }
     }
+
+    pub fn downcast<N: ItemTreeNode>(self) -> Option<FileItemTreeId<N>> {
+        N::id_from_mod_item(self)
+    }
 }
 
 impl_froms!(ModItem {
     Import(FileItemTreeId<Import>),
+    ExternCrate(FileItemTreeId<ExternCrate>),
     Function(FileItemTreeId<Function>),
     Struct(FileItemTreeId<Struct>),
     Union(FileItemTreeId<Union>),
@@ -474,6 +562,17 @@ impl_froms!(AssocItem {
     MacroCall(FileItemTreeId<MacroCall>),
 });
 
+impl From<AssocItem> for ModItem {
+    fn from(item: AssocItem) -> Self {
+        match item {
+            AssocItem::Function(it) => it.into(),
+            AssocItem::TypeAlias(it) => it.into(),
+            AssocItem::Const(it) => it.into(),
+            AssocItem::MacroCall(it) => it.into(),
+        }
+    }
+}
+
 #[derive(Debug, Eq, PartialEq)]
 pub struct Variant {
     pub name: Name,
diff --git a/crates/ra_hir_def/src/item_tree/lower.rs b/crates/ra_hir_def/src/item_tree/lower.rs
index 737a69c30..f2b8a9418 100644
--- a/crates/ra_hir_def/src/item_tree/lower.rs
+++ b/crates/ra_hir_def/src/item_tree/lower.rs
@@ -7,9 +7,12 @@ use crate::{
 };
 use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, HirFileId};
 use ra_arena::map::ArenaMap;
-use ra_syntax::ast::{self, ModuleItemOwner};
+use ra_syntax::{
+    ast::{self, ModuleItemOwner},
+    SyntaxNode,
+};
 use smallvec::SmallVec;
-use std::sync::Arc;
+use std::{mem, sync::Arc};
 
 fn id<N: ItemTreeNode>(index: Idx<N>) -> FileItemTreeId<N> {
     FileItemTreeId { index, _p: PhantomData }
@@ -27,78 +30,81 @@ where
 }
 
 pub(super) struct Ctx {
-    pub tree: ItemTree,
-    pub hygiene: Hygiene,
-    pub file: HirFileId,
-    pub source_ast_id_map: Arc<AstIdMap>,
-    pub body_ctx: crate::body::LowerCtx,
+    tree: ItemTree,
+    hygiene: Hygiene,
+    file: HirFileId,
+    source_ast_id_map: Arc<AstIdMap>,
+    body_ctx: crate::body::LowerCtx,
+    inner_items: Vec<ModItem>,
 }
 
 impl Ctx {
+    pub(super) fn new(db: &dyn DefDatabase, hygiene: Hygiene, file: HirFileId) -> Self {
+        Self {
+            tree: ItemTree::empty(file),
+            hygiene,
+            file,
+            source_ast_id_map: db.ast_id_map(file),
+            body_ctx: crate::body::LowerCtx::new(db, file),
+            inner_items: Vec::new(),
+        }
+    }
+
     pub(super) fn lower(mut self, item_owner: &dyn ModuleItemOwner) -> ItemTree {
         self.tree.top_level = item_owner
             .items()
-            .flat_map(|item| self.lower_mod_item(&item))
+            .flat_map(|item| self.lower_mod_item(&item, false))
             .flat_map(|items| items.0)
             .collect();
         self.tree
     }
 
-    fn lower_mod_item(&mut self, item: &ast::ModuleItem) -> Option<ModItems> {
+    fn lower_mod_item(&mut self, item: &ast::ModuleItem, inner: bool) -> Option<ModItems> {
+        assert!(inner || self.inner_items.is_empty());
+
+        // Collect inner items for 1-to-1-lowered items.
+        match item {
+            ast::ModuleItem::StructDef(_)
+            | ast::ModuleItem::UnionDef(_)
+            | ast::ModuleItem::EnumDef(_)
+            | ast::ModuleItem::FnDef(_)
+            | ast::ModuleItem::TypeAliasDef(_)
+            | ast::ModuleItem::ConstDef(_)
+            | ast::ModuleItem::StaticDef(_)
+            | ast::ModuleItem::MacroCall(_) => self.collect_inner_items(item.syntax()),
+
+            // These are handled in their respective `lower_X` method (since we can't just blindly
+            // walk them).
+            ast::ModuleItem::TraitDef(_)
+            | ast::ModuleItem::ImplDef(_)
+            | ast::ModuleItem::ExternBlock(_) => {}
+
+            // These don't have inner items.
+            ast::ModuleItem::Module(_)
+            | ast::ModuleItem::ExternCrateItem(_)
+            | ast::ModuleItem::UseItem(_) => {}
+        };
+
         let attrs = Attrs::new(item, &self.hygiene);
         let items = match item {
-            ast::ModuleItem::StructDef(ast) => {
-                self.lower_struct(ast).map(|data| id(self.tree.structs.alloc(data)).into())
-            }
-            ast::ModuleItem::UnionDef(ast) => {
-                self.lower_union(ast).map(|data| id(self.tree.unions.alloc(data)).into())
-            }
-            ast::ModuleItem::EnumDef(ast) => {
-                self.lower_enum(ast).map(|data| id(self.tree.enums.alloc(data)).into())
-            }
-            ast::ModuleItem::FnDef(ast) => {
-                self.lower_function(ast).map(|data| id(self.tree.functions.alloc(data)).into())
-            }
-            ast::ModuleItem::TypeAliasDef(ast) => {
-                self.lower_type_alias(ast).map(|data| id(self.tree.type_aliases.alloc(data)).into())
-            }
-            ast::ModuleItem::StaticDef(ast) => {
-                self.lower_static(ast).map(|data| id(self.tree.statics.alloc(data)).into())
-            }
-            ast::ModuleItem::ConstDef(ast) => {
-                let data = self.lower_const(ast);
-                Some(id(self.tree.consts.alloc(data)).into())
-            }
-            ast::ModuleItem::Module(ast) => {
-                self.lower_module(ast).map(|data| id(self.tree.mods.alloc(data)).into())
-            }
-            ast::ModuleItem::TraitDef(ast) => {
-                self.lower_trait(ast).map(|data| id(self.tree.traits.alloc(data)).into())
-            }
-            ast::ModuleItem::ImplDef(ast) => {
-                self.lower_impl(ast).map(|data| id(self.tree.impls.alloc(data)).into())
-            }
+            ast::ModuleItem::StructDef(ast) => self.lower_struct(ast).map(Into::into),
+            ast::ModuleItem::UnionDef(ast) => self.lower_union(ast).map(Into::into),
+            ast::ModuleItem::EnumDef(ast) => self.lower_enum(ast).map(Into::into),
+            ast::ModuleItem::FnDef(ast) => self.lower_function(ast).map(Into::into),
+            ast::ModuleItem::TypeAliasDef(ast) => self.lower_type_alias(ast).map(Into::into),
+            ast::ModuleItem::StaticDef(ast) => self.lower_static(ast).map(Into::into),
+            ast::ModuleItem::ConstDef(ast) => Some(self.lower_const(ast).into()),
+            ast::ModuleItem::Module(ast) => self.lower_module(ast).map(Into::into),
+            ast::ModuleItem::TraitDef(ast) => self.lower_trait(ast).map(Into::into),
+            ast::ModuleItem::ImplDef(ast) => self.lower_impl(ast).map(Into::into),
             ast::ModuleItem::UseItem(ast) => Some(ModItems(
-                self.lower_use(ast)
-                    .into_iter()
-                    .map(|data| id(self.tree.imports.alloc(data)).into())
-                    .collect::<SmallVec<_>>(),
+                self.lower_use(ast).into_iter().map(Into::into).collect::<SmallVec<_>>(),
             )),
-            ast::ModuleItem::ExternCrateItem(ast) => {
-                self.lower_extern_crate(ast).map(|data| id(self.tree.imports.alloc(data)).into())
+            ast::ModuleItem::ExternCrateItem(ast) => self.lower_extern_crate(ast).map(Into::into),
+            ast::ModuleItem::MacroCall(ast) => self.lower_macro_call(ast).map(Into::into),
+            ast::ModuleItem::ExternBlock(ast) => {
+                Some(ModItems(self.lower_extern_block(ast).into_iter().collect::<SmallVec<_>>()))
             }
-            ast::ModuleItem::MacroCall(ast) => {
-                self.lower_macro_call(ast).map(|data| id(self.tree.macro_calls.alloc(data)).into())
-            }
-            ast::ModuleItem::ExternBlock(ast) => Some(ModItems(
-                self.lower_extern_block(ast)
-                    .into_iter()
-                    .map(|item| match item {
-                        Either::Left(func) => id(self.tree.functions.alloc(func)).into(),
-                        Either::Right(statik) => id(self.tree.statics.alloc(statik)).into(),
-                    })
-                    .collect::<SmallVec<_>>(),
-            )),
         };
 
         if !attrs.is_empty() {
@@ -110,22 +116,28 @@ impl Ctx {
         items
     }
 
-    fn lower_assoc_item(&mut self, item: &ast::AssocItem) -> Option<AssocItem> {
+    fn collect_inner_items(&mut self, container: &SyntaxNode) {
+        let mut inner_items = mem::replace(&mut self.tree.inner_items, FxHashMap::default());
+        inner_items.extend(
+            container.descendants().skip(1).filter_map(ast::ModuleItem::cast).filter_map(|item| {
+                let ast_id = self.source_ast_id_map.ast_id(&item);
+                Some((ast_id, self.lower_mod_item(&item, true)?.0))
+            }),
+        );
+        self.tree.inner_items = inner_items;
+    }
+
+    fn lower_assoc_item(&mut self, item: &ast::ModuleItem) -> Option<AssocItem> {
         match item {
-            ast::AssocItem::FnDef(ast) => {
-                self.lower_function(ast).map(|data| id(self.tree.functions.alloc(data)).into())
-            }
-            ast::AssocItem::TypeAliasDef(ast) => {
-                self.lower_type_alias(ast).map(|data| id(self.tree.type_aliases.alloc(data)).into())
-            }
-            ast::AssocItem::ConstDef(ast) => {
-                let data = self.lower_const(ast);
-                Some(id(self.tree.consts.alloc(data)).into())
-            }
+            ast::ModuleItem::FnDef(ast) => self.lower_function(ast).map(Into::into),
+            ast::ModuleItem::TypeAliasDef(ast) => self.lower_type_alias(ast).map(Into::into),
+            ast::ModuleItem::ConstDef(ast) => Some(self.lower_const(ast).into()),
+            ast::ModuleItem::MacroCall(ast) => self.lower_macro_call(ast).map(Into::into),
+            _ => None,
         }
     }
 
-    fn lower_struct(&mut self, strukt: &ast::StructDef) -> Option<Struct> {
+    fn lower_struct(&mut self, strukt: &ast::StructDef) -> Option<FileItemTreeId<Struct>> {
         let attrs = self.lower_attrs(strukt);
         let visibility = self.lower_visibility(strukt);
         let name = strukt.name()?.as_name();
@@ -138,7 +150,7 @@ impl Ctx {
             ast::StructKind::Unit => StructDefKind::Unit,
         };
         let res = Struct { name, attrs, visibility, generic_params, fields, ast_id, kind };
-        Some(res)
+        Some(id(self.tree.structs.alloc(res)))
     }
 
     fn lower_fields(&mut self, strukt_kind: &ast::StructKind) -> Fields {
@@ -193,7 +205,7 @@ impl Ctx {
         Some(res)
     }
 
-    fn lower_union(&mut self, union: &ast::UnionDef) -> Option<Union> {
+    fn lower_union(&mut self, union: &ast::UnionDef) -> Option<FileItemTreeId<Union>> {
         let attrs = self.lower_attrs(union);
         let visibility = self.lower_visibility(union);
         let name = union.name()?.as_name();
@@ -206,10 +218,10 @@ impl Ctx {
         };
         let ast_id = self.source_ast_id_map.ast_id(union);
         let res = Union { name, attrs, visibility, generic_params, fields, ast_id };
-        Some(res)
+        Some(id(self.tree.unions.alloc(res)))
     }
 
-    fn lower_enum(&mut self, enum_: &ast::EnumDef) -> Option<Enum> {
+    fn lower_enum(&mut self, enum_: &ast::EnumDef) -> Option<FileItemTreeId<Enum>> {
         let attrs = self.lower_attrs(enum_);
         let visibility = self.lower_visibility(enum_);
         let name = enum_.name()?.as_name();
@@ -220,7 +232,7 @@ impl Ctx {
         };
         let ast_id = self.source_ast_id_map.ast_id(enum_);
         let res = Enum { name, attrs, visibility, generic_params, variants, ast_id };
-        Some(res)
+        Some(id(self.tree.enums.alloc(res)))
     }
 
     fn lower_variants(&mut self, variants: &ast::EnumVariantList) -> Range<Idx<Variant>> {
@@ -241,7 +253,7 @@ impl Ctx {
         Some(res)
     }
 
-    fn lower_function(&mut self, func: &ast::FnDef) -> Option<Function> {
+    fn lower_function(&mut self, func: &ast::FnDef) -> Option<FileItemTreeId<Function>> {
         let attrs = self.lower_attrs(func);
         let visibility = self.lower_visibility(func);
         let name = func.name()?.as_name();
@@ -297,37 +309,42 @@ impl Ctx {
             ast_id,
         };
         res.generic_params = self.lower_generic_params(GenericsOwner::Function(&res), func);
-        Some(res)
+
+        Some(id(self.tree.functions.alloc(res)))
     }
 
-    fn lower_type_alias(&mut self, type_alias: &ast::TypeAliasDef) -> Option<TypeAlias> {
+    fn lower_type_alias(
+        &mut self,
+        type_alias: &ast::TypeAliasDef,
+    ) -> Option<FileItemTreeId<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(GenericsOwner::TypeAlias, type_alias);
         let ast_id = self.source_ast_id_map.ast_id(type_alias);
         let res = TypeAlias { name, visibility, generic_params, type_ref, ast_id };
-        Some(res)
+        Some(id(self.tree.type_aliases.alloc(res)))
     }
 
-    fn lower_static(&mut self, static_: &ast::StaticDef) -> Option<Static> {
+    fn lower_static(&mut self, static_: &ast::StaticDef) -> Option<FileItemTreeId<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 ast_id = self.source_ast_id_map.ast_id(static_);
         let res = Static { name, visibility, type_ref, ast_id };
-        Some(res)
+        Some(id(self.tree.statics.alloc(res)))
     }
 
-    fn lower_const(&mut self, konst: &ast::ConstDef) -> Const {
+    fn lower_const(&mut self, konst: &ast::ConstDef) -> FileItemTreeId<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);
         let ast_id = self.source_ast_id_map.ast_id(konst);
-        Const { name, visibility, type_ref, ast_id }
+        let res = Const { name, visibility, type_ref, ast_id };
+        id(self.tree.consts.alloc(res))
     }
 
-    fn lower_module(&mut self, module: &ast::Module) -> Option<Mod> {
+    fn lower_module(&mut self, module: &ast::Module) -> Option<FileItemTreeId<Mod>> {
         let name = module.name()?.as_name();
         let visibility = self.lower_visibility(module);
         let kind = if module.semicolon_token().is_some() {
@@ -338,7 +355,7 @@ impl Ctx {
                     .item_list()
                     .map(|list| {
                         list.items()
-                            .flat_map(|item| self.lower_mod_item(&item))
+                            .flat_map(|item| self.lower_mod_item(&item, false))
                             .flat_map(|items| items.0)
                             .collect()
                     })
@@ -349,90 +366,101 @@ impl Ctx {
             }
         };
         let ast_id = self.source_ast_id_map.ast_id(module);
-        Some(Mod { name, visibility, kind, ast_id })
+        let res = Mod { name, visibility, kind, ast_id };
+        Some(id(self.tree.mods.alloc(res)))
     }
 
-    fn lower_trait(&mut self, trait_def: &ast::TraitDef) -> Option<Trait> {
+    fn lower_trait(&mut self, trait_def: &ast::TraitDef) -> Option<FileItemTreeId<Trait>> {
         let name = trait_def.name()?.as_name();
         let visibility = self.lower_visibility(trait_def);
         let generic_params = self.lower_generic_params(GenericsOwner::Trait(trait_def), trait_def);
         let auto = trait_def.auto_token().is_some();
         let items = trait_def.item_list().map(|list| {
-            // FIXME: Does not handle macros
-            list.assoc_items().flat_map(|item| self.lower_assoc_item(&item)).collect()
+            list.items()
+                .flat_map(|item| {
+                    self.collect_inner_items(item.syntax());
+                    self.lower_assoc_item(&item)
+                })
+                .collect()
         });
         let ast_id = self.source_ast_id_map.ast_id(trait_def);
-        Some(Trait {
+        let res = Trait {
             name,
             visibility,
             generic_params,
             auto,
             items: items.unwrap_or_default(),
             ast_id,
-        })
+        };
+        Some(id(self.tree.traits.alloc(res)))
     }
 
-    fn lower_impl(&mut self, impl_def: &ast::ImplDef) -> Option<Impl> {
+    fn lower_impl(&mut self, impl_def: &ast::ImplDef) -> Option<FileItemTreeId<Impl>> {
         let generic_params = self.lower_generic_params(GenericsOwner::Impl, impl_def);
         let target_trait = impl_def.target_trait().map(|tr| self.lower_type_ref(&tr));
         let target_type = self.lower_type_ref(&impl_def.target_type()?);
         let is_negative = impl_def.excl_token().is_some();
+
+        // We cannot use `assoc_items()` here as that does not include macro calls.
         let items = impl_def
             .item_list()?
-            .assoc_items()
-            .filter_map(|item| self.lower_assoc_item(&item))
+            .items()
+            .filter_map(|item| {
+                self.collect_inner_items(item.syntax());
+                let assoc = self.lower_assoc_item(&item)?;
+                Some(assoc)
+            })
             .collect();
         let ast_id = self.source_ast_id_map.ast_id(impl_def);
-        Some(Impl { generic_params, target_trait, target_type, is_negative, items, ast_id })
+        let res = Impl { generic_params, target_trait, target_type, is_negative, items, ast_id };
+        Some(id(self.tree.impls.alloc(res)))
     }
 
-    fn lower_use(&mut self, use_item: &ast::UseItem) -> Vec<Import> {
+    fn lower_use(&mut self, use_item: &ast::UseItem) -> Vec<FileItemTreeId<Import>> {
         // FIXME: cfg_attr
         let is_prelude = use_item.has_atom_attr("prelude_import");
         let visibility = self.lower_visibility(use_item);
+        let ast_id = self.source_ast_id_map.ast_id(use_item);
 
         // Every use item can expand to many `Import`s.
         let mut imports = Vec::new();
+        let tree = &mut self.tree;
         ModPath::expand_use_item(
             InFile::new(self.file, use_item.clone()),
             &self.hygiene,
             |path, _tree, is_glob, alias| {
-                imports.push(Import {
+                imports.push(id(tree.imports.alloc(Import {
                     path,
                     alias,
                     visibility: visibility.clone(),
                     is_glob,
                     is_prelude,
-                    is_extern_crate: false,
-                    is_macro_use: false,
-                });
+                    ast_id,
+                })));
             },
         );
 
         imports
     }
 
-    fn lower_extern_crate(&mut self, extern_crate: &ast::ExternCrateItem) -> Option<Import> {
+    fn lower_extern_crate(
+        &mut self,
+        extern_crate: &ast::ExternCrateItem,
+    ) -> Option<FileItemTreeId<ExternCrate>> {
         let path = ModPath::from_name_ref(&extern_crate.name_ref()?);
         let alias = extern_crate.alias().map(|a| {
             a.name().map(|it| it.as_name()).map_or(ImportAlias::Underscore, ImportAlias::Alias)
         });
         let visibility = self.lower_visibility(extern_crate);
+        let ast_id = self.source_ast_id_map.ast_id(extern_crate);
         // FIXME: cfg_attr
         let is_macro_use = extern_crate.has_atom_attr("macro_use");
 
-        Some(Import {
-            path,
-            alias,
-            visibility,
-            is_glob: false,
-            is_prelude: false,
-            is_extern_crate: true,
-            is_macro_use,
-        })
+        let res = ExternCrate { path, alias, visibility, is_macro_use, ast_id };
+        Some(id(self.tree.extern_crates.alloc(res)))
     }
 
-    fn lower_macro_call(&mut self, m: &ast::MacroCall) -> Option<MacroCall> {
+    fn lower_macro_call(&mut self, m: &ast::MacroCall) -> Option<FileItemTreeId<MacroCall>> {
         let name = m.name().map(|it| it.as_name());
         let attrs = Attrs::new(m, &self.hygiene);
         let path = ModPath::from_src(m.path()?, &self.hygiene)?;
@@ -455,15 +483,26 @@ impl Ctx {
         };
 
         let is_builtin = attrs.by_key("rustc_builtin_macro").exists();
-        Some(MacroCall { name, path, is_export, is_builtin, is_local_inner, ast_id })
+        let res = MacroCall { name, path, is_export, is_builtin, is_local_inner, ast_id };
+        Some(id(self.tree.macro_calls.alloc(res)))
     }
 
-    fn lower_extern_block(&mut self, block: &ast::ExternBlock) -> Vec<Either<Function, Static>> {
+    fn lower_extern_block(&mut self, block: &ast::ExternBlock) -> Vec<ModItem> {
         block.extern_item_list().map_or(Vec::new(), |list| {
             list.extern_items()
-                .filter_map(|item| match item {
-                    ast::ExternItem::FnDef(ast) => self.lower_function(&ast).map(Either::Left),
-                    ast::ExternItem::StaticDef(ast) => self.lower_static(&ast).map(Either::Right),
+                .filter_map(|item| {
+                    self.collect_inner_items(item.syntax());
+                    let id = match item {
+                        ast::ExternItem::FnDef(ast) => {
+                            let func = self.lower_function(&ast)?;
+                            func.into()
+                        }
+                        ast::ExternItem::StaticDef(ast) => {
+                            let statik = self.lower_static(&ast)?;
+                            statik.into()
+                        }
+                    };
+                    Some(id)
                 })
                 .collect()
         })
diff --git a/crates/ra_hir_def/src/item_tree/tests.rs b/crates/ra_hir_def/src/item_tree/tests.rs
new file mode 100644
index 000000000..b60e6cbb0
--- /dev/null
+++ b/crates/ra_hir_def/src/item_tree/tests.rs
@@ -0,0 +1,254 @@
+use super::{ItemTree, ModItem, ModKind};
+use crate::{db::DefDatabase, test_db::TestDB};
+use hir_expand::db::AstDatabase;
+use insta::assert_snapshot;
+use ra_db::fixture::WithFixture;
+use ra_syntax::{ast, AstNode};
+use rustc_hash::FxHashSet;
+use std::sync::Arc;
+use stdx::format_to;
+
+fn test_inner_items(ra_fixture: &str) {
+    let (db, file_id) = TestDB::with_single_file(ra_fixture);
+    let tree = db.item_tree(file_id.into());
+    let root = db.parse_or_expand(file_id.into()).unwrap();
+    let ast_id_map = db.ast_id_map(file_id.into());
+
+    // Traverse the item tree and collect all module/impl/trait-level items as AST nodes.
+    let mut outer_items = FxHashSet::default();
+    let mut worklist = tree.top_level_items().to_vec();
+    while let Some(item) = worklist.pop() {
+        let node: ast::ModuleItem = match item {
+            ModItem::Import(it) => tree.source(&db, it).into(),
+            ModItem::ExternCrate(it) => tree.source(&db, it).into(),
+            ModItem::Function(it) => tree.source(&db, it).into(),
+            ModItem::Struct(it) => tree.source(&db, it).into(),
+            ModItem::Union(it) => tree.source(&db, it).into(),
+            ModItem::Enum(it) => tree.source(&db, it).into(),
+            ModItem::Const(it) => tree.source(&db, it).into(),
+            ModItem::Static(it) => tree.source(&db, it).into(),
+            ModItem::TypeAlias(it) => tree.source(&db, it).into(),
+            ModItem::Mod(it) => {
+                if let ModKind::Inline { items } = &tree[it].kind {
+                    worklist.extend(items);
+                }
+                tree.source(&db, it).into()
+            }
+            ModItem::Trait(it) => {
+                worklist.extend(tree[it].items.iter().map(|item| ModItem::from(*item)));
+                tree.source(&db, it).into()
+            }
+            ModItem::Impl(it) => {
+                worklist.extend(tree[it].items.iter().map(|item| ModItem::from(*item)));
+                tree.source(&db, it).into()
+            }
+            ModItem::MacroCall(_) => continue,
+        };
+
+        outer_items.insert(node);
+    }
+
+    // Now descend the root node and check that all `ast::ModuleItem`s are either recorded above, or
+    // registered as inner items.
+    for item in root.descendants().skip(1).filter_map(ast::ModuleItem::cast) {
+        if outer_items.contains(&item) {
+            continue;
+        }
+
+        let ast_id = ast_id_map.ast_id(&item);
+        assert!(!tree.inner_items(ast_id).is_empty());
+    }
+}
+
+fn item_tree(ra_fixture: &str) -> Arc<ItemTree> {
+    let (db, file_id) = TestDB::with_single_file(ra_fixture);
+    db.item_tree(file_id.into())
+}
+
+fn print_item_tree(ra_fixture: &str) -> String {
+    let tree = item_tree(ra_fixture);
+    let mut out = String::new();
+
+    format_to!(out, "inner attrs: {:?}\n\n", tree.top_level_attrs());
+    format_to!(out, "top-level items:\n");
+    for item in tree.top_level_items() {
+        fmt_mod_item(&mut out, &tree, *item);
+        format_to!(out, "\n");
+    }
+
+    if !tree.inner_items.is_empty() {
+        format_to!(out, "\ninner items:\n");
+        for (ast_id, items) in &tree.inner_items {
+            format_to!(out, "{:?}:\n", ast_id);
+            for inner in items {
+                format_to!(out, "- ");
+                fmt_mod_item(&mut out, &tree, *inner);
+                format_to!(out, "\n");
+            }
+        }
+    }
+
+    out
+}
+
+fn fmt_mod_item(out: &mut String, tree: &ItemTree, item: ModItem) {
+    match item {
+        ModItem::ExternCrate(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Import(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Function(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Struct(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Union(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Enum(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Const(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Static(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Trait(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Impl(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::TypeAlias(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::Mod(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+        ModItem::MacroCall(it) => {
+            format_to!(out, "{:?}", tree[it]);
+        }
+    }
+}
+
+#[test]
+fn smoke() {
+    assert_snapshot!(print_item_tree(r"
+        #![attr]
+
+        use {a, b::*};
+        extern crate krate;
+
+        trait Tr<U> {
+            type AssocTy: Tr<()>;
+            const CONST: u8;
+            fn method(&self);
+            fn dfl_method(&mut self) {}
+        }
+
+        struct Struct0<T = ()>;
+        struct Struct1<T>(u8);
+        struct Struct2<T> {
+            fld: (T, ),
+        }
+
+        enum En {
+            Variant {
+                field: u8,
+            },
+        }
+
+        union Un {
+            fld: u16,
+        }
+    "), @r###"
+inner attrs: Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr"))] }, input: None }]) }
+
+top-level items:
+Import { path: ModPath { kind: Plain, segments: [Name(Text("a"))] }, alias: None, visibility: Module(ModPath { kind: Super(0), segments: [] }), is_glob: false, is_prelude: false, ast_id: FileAstId::<ra_syntax::ast::generated::nodes::UseItem>(0) }
+Import { path: ModPath { kind: Plain, segments: [Name(Text("b"))] }, alias: None, visibility: Module(ModPath { kind: Super(0), segments: [] }), is_glob: true, is_prelude: false, ast_id: FileAstId::<ra_syntax::ast::generated::nodes::UseItem>(0) }
+ExternCrate { path: ModPath { kind: Plain, segments: [Name(Text("krate"))] }, alias: None, visibility: Module(ModPath { kind: Super(0), segments: [] }), is_macro_use: false, ast_id: FileAstId::<ra_syntax::ast::generated::nodes::ExternCrateItem>(1) }
+Trait { name: Name(Text("Tr")), visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 2, data: [TypeParamData { name: Some(Name(Text("Self"))), default: None, provenance: TraitSelf }, TypeParamData { name: Some(Name(Text("U"))), default: None, provenance: TypeParamList }] }, where_predicates: [] }, auto: false, items: [TypeAlias(Idx::<TypeAlias>(0)), Const(Idx::<Const>(0)), Function(Idx::<Function>(0)), Function(Idx::<Function>(1))], ast_id: FileAstId::<ra_syntax::ast::generated::nodes::TraitDef>(2) }
+Struct { name: Name(Text("Struct0")), attrs: Attrs { entries: None }, visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 1, data: [TypeParamData { name: Some(Name(Text("T"))), default: Some(Tuple([])), provenance: TypeParamList }] }, where_predicates: [] }, fields: Unit, ast_id: FileAstId::<ra_syntax::ast::generated::nodes::StructDef>(3), kind: Unit }
+Struct { name: Name(Text("Struct1")), attrs: Attrs { entries: None }, visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 1, data: [TypeParamData { name: Some(Name(Text("T"))), default: None, provenance: TypeParamList }] }, where_predicates: [] }, fields: Tuple(Idx::<Field>(0)..Idx::<Field>(1)), ast_id: FileAstId::<ra_syntax::ast::generated::nodes::StructDef>(4), kind: Tuple }
+Struct { name: Name(Text("Struct2")), attrs: Attrs { entries: None }, visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 1, data: [TypeParamData { name: Some(Name(Text("T"))), default: None, provenance: TypeParamList }] }, where_predicates: [] }, fields: Record(Idx::<Field>(1)..Idx::<Field>(2)), ast_id: FileAstId::<ra_syntax::ast::generated::nodes::StructDef>(5), kind: Record }
+Enum { name: Name(Text("En")), attrs: Attrs { entries: None }, visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 0, data: [] }, where_predicates: [] }, variants: Idx::<Variant>(0)..Idx::<Variant>(1), ast_id: FileAstId::<ra_syntax::ast::generated::nodes::EnumDef>(6) }
+Union { name: Name(Text("Un")), attrs: Attrs { entries: None }, visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 0, data: [] }, where_predicates: [] }, fields: Record(Idx::<Field>(3)..Idx::<Field>(4)), ast_id: FileAstId::<ra_syntax::ast::generated::nodes::UnionDef>(7) }
+    "###);
+}
+
+#[test]
+fn simple_inner_items() {
+    let tree = print_item_tree(
+        r"
+        impl<T:A> D for Response<T> {
+            fn foo() {
+                end();
+                fn end<W: Write>() {
+                    let _x: T = loop {};
+                }
+            }
+        }
+    ",
+    );
+
+    assert_snapshot!(tree, @r###"
+inner attrs: Attrs { entries: None }
+
+top-level items:
+Impl { generic_params: GenericParams { types: Arena { len: 0, data: [] }, where_predicates: [] }, target_trait: Some(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("D"))] }, generic_args: [None] })), target_type: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Response"))] }, generic_args: [Some(GenericArgs { args: [Type(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("T"))] }, generic_args: [None] }))], has_self_type: false, bindings: [] })] }), is_negative: false, items: [Function(Idx::<Function>(1))], ast_id: FileAstId::<ra_syntax::ast::generated::nodes::ImplDef>(0) }
+
+inner items:
+FileAstId::<ra_syntax::ast::generated::nodes::ModuleItem>(2):
+- Function { name: Name(Text("end")), attrs: Attrs { entries: None }, visibility: Module(ModPath { kind: Super(0), segments: [] }), generic_params: GenericParams { types: Arena { len: 1, data: [TypeParamData { name: Some(Name(Text("W"))), default: None, provenance: TypeParamList }] }, where_predicates: [WherePredicate { target: TypeRef(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("W"))] }, generic_args: [None] })), bound: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Write"))] }, generic_args: [None] }) }] }, has_self_param: false, params: [], ret_type: Tuple([]), ast_id: FileAstId::<ra_syntax::ast::generated::nodes::FnDef>(2) }
+    "###);
+}
+
+#[test]
+fn cursed_inner_items() {
+    test_inner_items(
+        r"
+        struct S<T: Trait = [u8; { fn f() {} 0 }]>(T);
+
+        enum En {
+            Var1 {
+                t: [(); { trait Inner {} 0 }],
+            },
+
+            Var2([u16; { enum Inner {} 0 }]),
+        }
+
+        type Ty = [En; { struct Inner; 0 }];
+
+        impl En {
+            fn assoc() {
+                trait InnerTrait {}
+                struct InnerStruct {}
+                impl InnerTrait for InnerStruct {}
+            }
+        }
+    ",
+    );
+}
+
+#[test]
+fn assoc_item_macros() {
+    let tree = print_item_tree(
+        r"
+        impl S {
+            items!();
+        }
+    ",
+    );
+
+    assert_snapshot!(tree, @r###"
+inner attrs: Attrs { entries: None }
+
+top-level items:
+Impl { generic_params: GenericParams { types: Arena { len: 0, data: [] }, where_predicates: [] }, target_trait: None, target_type: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("S"))] }, generic_args: [None] }), is_negative: false, items: [MacroCall(Idx::<MacroCall>(0))], ast_id: FileAstId::<ra_syntax::ast::generated::nodes::ImplDef>(0) }
+    "###);
+}
diff --git a/crates/ra_hir_def/src/lib.rs b/crates/ra_hir_def/src/lib.rs
index b5500f370..564434ccc 100644
--- a/crates/ra_hir_def/src/lib.rs
+++ b/crates/ra_hir_def/src/lib.rs
@@ -50,7 +50,7 @@ pub mod import_map;
 #[cfg(test)]
 mod test_db;
 
-use std::hash::Hash;
+use std::hash::{Hash, Hasher};
 
 use hir_expand::{
     ast_id_map::FileAstId, eager::expand_eager_macro, hygiene::Hygiene, AstId, HirFileId, InFile,
@@ -58,10 +58,13 @@ use hir_expand::{
 };
 use ra_arena::Idx;
 use ra_db::{impl_intern_key, salsa, CrateId};
-use ra_syntax::{ast, AstNode};
+use ra_syntax::ast;
 
-use crate::body::Expander;
 use crate::builtin_type::BuiltinType;
+use item_tree::{
+    Const, Enum, Function, Impl, ItemTreeId, ItemTreeNode, ModItem, Static, Struct, Trait,
+    TypeAlias, Union,
+};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct ModuleId {
@@ -72,16 +75,62 @@ pub struct ModuleId {
 /// An ID of a module, **local** to a specific crate
 pub type LocalModuleId = Idx<nameres::ModuleData>;
 
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct ItemLoc<N: AstNode> {
+#[derive(Debug)]
+pub struct ItemLoc<N: ItemTreeNode> {
     pub container: ContainerId,
-    pub ast_id: AstId<N>,
+    pub id: ItemTreeId<N>,
+}
+
+impl<N: ItemTreeNode> Clone for ItemLoc<N> {
+    fn clone(&self) -> Self {
+        Self { container: self.container, id: self.id }
+    }
+}
+
+impl<N: ItemTreeNode> Copy for ItemLoc<N> {}
+
+impl<N: ItemTreeNode> PartialEq for ItemLoc<N> {
+    fn eq(&self, other: &Self) -> bool {
+        self.container == other.container && self.id == other.id
+    }
 }
 
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct AssocItemLoc<N: AstNode> {
+impl<N: ItemTreeNode> Eq for ItemLoc<N> {}
+
+impl<N: ItemTreeNode> Hash for ItemLoc<N> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.container.hash(state);
+        self.id.hash(state);
+    }
+}
+
+#[derive(Debug)]
+pub struct AssocItemLoc<N: ItemTreeNode> {
     pub container: AssocContainerId,
-    pub ast_id: AstId<N>,
+    pub id: ItemTreeId<N>,
+}
+
+impl<N: ItemTreeNode> Clone for AssocItemLoc<N> {
+    fn clone(&self) -> Self {
+        Self { container: self.container, id: self.id }
+    }
+}
+
+impl<N: ItemTreeNode> Copy for AssocItemLoc<N> {}
+
+impl<N: ItemTreeNode> PartialEq for AssocItemLoc<N> {
+    fn eq(&self, other: &Self) -> bool {
+        self.container == other.container && self.id == other.id
+    }
+}
+
+impl<N: ItemTreeNode> Eq for AssocItemLoc<N> {}
+
+impl<N: ItemTreeNode> Hash for AssocItemLoc<N> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.container.hash(state);
+        self.id.hash(state);
+    }
 }
 
 macro_rules! impl_intern {
@@ -106,22 +155,22 @@ macro_rules! impl_intern {
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct FunctionId(salsa::InternId);
-type FunctionLoc = AssocItemLoc<ast::FnDef>;
+type FunctionLoc = AssocItemLoc<Function>;
 impl_intern!(FunctionId, FunctionLoc, intern_function, lookup_intern_function);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct StructId(salsa::InternId);
-type StructLoc = ItemLoc<ast::StructDef>;
+type StructLoc = ItemLoc<Struct>;
 impl_intern!(StructId, StructLoc, intern_struct, lookup_intern_struct);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct UnionId(salsa::InternId);
-pub type UnionLoc = ItemLoc<ast::UnionDef>;
+pub type UnionLoc = ItemLoc<Union>;
 impl_intern!(UnionId, UnionLoc, intern_union, lookup_intern_union);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct EnumId(salsa::InternId);
-pub type EnumLoc = ItemLoc<ast::EnumDef>;
+pub type EnumLoc = ItemLoc<Enum>;
 impl_intern!(EnumId, EnumLoc, intern_enum, lookup_intern_enum);
 
 // FIXME: rename to `VariantId`, only enums can ave variants
@@ -143,27 +192,27 @@ pub type LocalFieldId = Idx<adt::FieldData>;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct ConstId(salsa::InternId);
-type ConstLoc = AssocItemLoc<ast::ConstDef>;
+type ConstLoc = AssocItemLoc<Const>;
 impl_intern!(ConstId, ConstLoc, intern_const, lookup_intern_const);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct StaticId(salsa::InternId);
-pub type StaticLoc = ItemLoc<ast::StaticDef>;
+pub type StaticLoc = ItemLoc<Static>;
 impl_intern!(StaticId, StaticLoc, intern_static, lookup_intern_static);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct TraitId(salsa::InternId);
-pub type TraitLoc = ItemLoc<ast::TraitDef>;
+pub type TraitLoc = ItemLoc<Trait>;
 impl_intern!(TraitId, TraitLoc, intern_trait, lookup_intern_trait);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct TypeAliasId(salsa::InternId);
-type TypeAliasLoc = AssocItemLoc<ast::TypeAliasDef>;
+type TypeAliasLoc = AssocItemLoc<TypeAlias>;
 impl_intern!(TypeAliasId, TypeAliasLoc, intern_type_alias, lookup_intern_type_alias);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Ord, PartialOrd)]
 pub struct ImplId(salsa::InternId);
-type ImplLoc = ItemLoc<ast::ImplDef>;
+type ImplLoc = ItemLoc<Impl>;
 impl_intern!(ImplId, ImplLoc, intern_impl, lookup_intern_impl);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -367,7 +416,7 @@ impl HasModule for AssocContainerId {
     }
 }
 
-impl<N: AstNode> HasModule for AssocItemLoc<N> {
+impl<N: ItemTreeNode> HasModule for AssocItemLoc<N> {
     fn module(&self, db: &dyn db::DefDatabase) -> ModuleId {
         self.container.module(db)
     }
@@ -394,6 +443,16 @@ impl HasModule for DefWithBodyId {
     }
 }
 
+impl DefWithBodyId {
+    pub fn as_mod_item(self, db: &dyn db::DefDatabase) -> ModItem {
+        match self {
+            DefWithBodyId::FunctionId(it) => it.lookup(db).id.value.into(),
+            DefWithBodyId::StaticId(it) => it.lookup(db).id.value.into(),
+            DefWithBodyId::ConstId(it) => it.lookup(db).id.value.into(),
+        }
+    }
+}
+
 impl HasModule for GenericDefId {
     fn module(&self, db: &dyn db::DefDatabase) -> ModuleId {
         match self {
diff --git a/crates/ra_hir_def/src/nameres/collector.rs b/crates/ra_hir_def/src/nameres/collector.rs
index c227b6da1..40aff830f 100644
--- a/crates/ra_hir_def/src/nameres/collector.rs
+++ b/crates/ra_hir_def/src/nameres/collector.rs
@@ -20,9 +20,7 @@ use test_utils::mark;
 use crate::{
     attr::Attrs,
     db::DefDatabase,
-    item_tree::{
-        FileItemTreeId, Import, ItemTree, MacroCall, Mod, ModItem, ModKind, StructDefKind,
-    },
+    item_tree::{self, ItemTree, ItemTreeId, MacroCall, Mod, ModItem, ModKind, StructDefKind},
     nameres::{
         diagnostics::DefDiagnostic, mod_resolution::ModDir, path_resolution::ReachedFixedPoint,
         BuiltinShadowMode, CrateDefMap, ModuleData, ModuleOrigin, ResolveMode,
@@ -106,9 +104,47 @@ impl PartialResolvedImport {
 }
 
 #[derive(Clone, Debug, Eq, PartialEq)]
+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,
+}
+
+impl From<item_tree::Import> for Import {
+    fn from(it: item_tree::Import) -> Self {
+        Self {
+            path: it.path,
+            alias: it.alias,
+            visibility: it.visibility,
+            is_glob: it.is_glob,
+            is_prelude: it.is_prelude,
+            is_extern_crate: false,
+            is_macro_use: false,
+        }
+    }
+}
+
+impl From<item_tree::ExternCrate> for Import {
+    fn from(it: item_tree::ExternCrate) -> Self {
+        Self {
+            path: it.path,
+            alias: it.alias,
+            visibility: it.visibility,
+            is_glob: false,
+            is_prelude: false,
+            is_extern_crate: true,
+            is_macro_use: it.is_macro_use,
+        }
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
 struct ImportDirective {
     module_id: LocalModuleId,
-    import_id: FileItemTreeId<Import>,
     import: Import,
     status: PartialResolvedImport,
 }
@@ -297,7 +333,7 @@ impl DefCollector<'_> {
     fn import_macros_from_extern_crate(
         &mut self,
         current_module_id: LocalModuleId,
-        import: &Import,
+        import: &item_tree::ExternCrate,
     ) {
         log::debug!(
             "importing macros from extern crate: {:?} ({:?})",
@@ -703,9 +739,9 @@ impl ModCollector<'_, '_> {
         // any other items.
         for item in items {
             if self.is_cfg_enabled(self.item_tree.attrs(*item)) {
-                if let ModItem::Import(import_id) = item {
-                    let import = self.item_tree[*import_id].clone();
-                    if import.is_extern_crate && import.is_macro_use {
+                if let ModItem::ExternCrate(id) = item {
+                    let import = self.item_tree[*id].clone();
+                    if import.is_macro_use {
                         self.def_collector.import_macros_from_extern_crate(self.module_id, &import);
                     }
                 }
@@ -725,8 +761,14 @@ impl ModCollector<'_, '_> {
                     ModItem::Import(import_id) => {
                         self.def_collector.unresolved_imports.push(ImportDirective {
                             module_id: self.module_id,
-                            import_id,
-                            import: self.item_tree[import_id].clone(),
+                            import: self.item_tree[import_id].clone().into(),
+                            status: PartialResolvedImport::Unresolved,
+                        })
+                    }
+                    ModItem::ExternCrate(import_id) => {
+                        self.def_collector.unresolved_imports.push(ImportDirective {
+                            module_id: self.module_id,
+                            import: self.item_tree[import_id].clone().into(),
                             status: PartialResolvedImport::Unresolved,
                         })
                     }
@@ -737,30 +779,28 @@ impl ModCollector<'_, '_> {
                             local_id: self.module_id,
                         };
                         let container = ContainerId::ModuleId(module);
-                        let ast_id = self.item_tree[imp].ast_id;
-                        let impl_id =
-                            ImplLoc { container, ast_id: AstId::new(self.file_id, ast_id) }
-                                .intern(self.def_collector.db);
+                        let impl_id = ImplLoc { container, id: ItemTreeId::new(self.file_id, imp) }
+                            .intern(self.def_collector.db);
                         self.def_collector.def_map.modules[self.module_id]
                             .scope
                             .define_impl(impl_id)
                     }
-                    ModItem::Function(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Function(id) => {
+                        let func = &self.item_tree[id];
                         def = Some(DefData {
                             id: FunctionLoc {
                                 container: container.into(),
-                                ast_id: AstId::new(self.file_id, it.ast_id),
+                                id: ItemTreeId::new(self.file_id, id),
                             }
                             .intern(self.def_collector.db)
                             .into(),
-                            name: &it.name,
-                            visibility: &it.visibility,
+                            name: &func.name,
+                            visibility: &func.visibility,
                             has_constructor: false,
                         });
                     }
-                    ModItem::Struct(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Struct(id) => {
+                        let it = &self.item_tree[id];
 
                         // FIXME: check attrs to see if this is an attribute macro invocation;
                         // in which case we don't add the invocation, just a single attribute
@@ -768,19 +808,16 @@ impl ModCollector<'_, '_> {
                         self.collect_derives(attrs, it.ast_id.upcast());
 
                         def = Some(DefData {
-                            id: StructLoc {
-                                container,
-                                ast_id: AstId::new(self.file_id, it.ast_id),
-                            }
-                            .intern(self.def_collector.db)
-                            .into(),
+                            id: StructLoc { container, id: ItemTreeId::new(self.file_id, id) }
+                                .intern(self.def_collector.db)
+                                .into(),
                             name: &it.name,
                             visibility: &it.visibility,
                             has_constructor: it.kind != StructDefKind::Record,
                         });
                     }
-                    ModItem::Union(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Union(id) => {
+                        let it = &self.item_tree[id];
 
                         // FIXME: check attrs to see if this is an attribute macro invocation;
                         // in which case we don't add the invocation, just a single attribute
@@ -788,7 +825,7 @@ impl ModCollector<'_, '_> {
                         self.collect_derives(attrs, it.ast_id.upcast());
 
                         def = Some(DefData {
-                            id: UnionLoc { container, ast_id: AstId::new(self.file_id, it.ast_id) }
+                            id: UnionLoc { container, id: ItemTreeId::new(self.file_id, id) }
                                 .intern(self.def_collector.db)
                                 .into(),
                             name: &it.name,
@@ -796,8 +833,8 @@ impl ModCollector<'_, '_> {
                             has_constructor: false,
                         });
                     }
-                    ModItem::Enum(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Enum(id) => {
+                        let it = &self.item_tree[id];
 
                         // FIXME: check attrs to see if this is an attribute macro invocation;
                         // in which case we don't add the invocation, just a single attribute
@@ -805,7 +842,7 @@ impl ModCollector<'_, '_> {
                         self.collect_derives(attrs, it.ast_id.upcast());
 
                         def = Some(DefData {
-                            id: EnumLoc { container, ast_id: AstId::new(self.file_id, it.ast_id) }
+                            id: EnumLoc { container, id: ItemTreeId::new(self.file_id, id) }
                                 .intern(self.def_collector.db)
                                 .into(),
                             name: &it.name,
@@ -813,14 +850,14 @@ impl ModCollector<'_, '_> {
                             has_constructor: false,
                         });
                     }
-                    ModItem::Const(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Const(id) => {
+                        let it = &self.item_tree[id];
 
                         if let Some(name) = &it.name {
                             def = Some(DefData {
                                 id: ConstLoc {
                                     container: container.into(),
-                                    ast_id: AstId::new(self.file_id, it.ast_id),
+                                    id: ItemTreeId::new(self.file_id, id),
                                 }
                                 .intern(self.def_collector.db)
                                 .into(),
@@ -830,26 +867,23 @@ impl ModCollector<'_, '_> {
                             });
                         }
                     }
-                    ModItem::Static(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Static(id) => {
+                        let it = &self.item_tree[id];
 
                         def = Some(DefData {
-                            id: StaticLoc {
-                                container,
-                                ast_id: AstId::new(self.file_id, it.ast_id),
-                            }
-                            .intern(self.def_collector.db)
-                            .into(),
+                            id: StaticLoc { container, id: ItemTreeId::new(self.file_id, id) }
+                                .intern(self.def_collector.db)
+                                .into(),
                             name: &it.name,
                             visibility: &it.visibility,
                             has_constructor: false,
                         });
                     }
-                    ModItem::Trait(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::Trait(id) => {
+                        let it = &self.item_tree[id];
 
                         def = Some(DefData {
-                            id: TraitLoc { container, ast_id: AstId::new(self.file_id, it.ast_id) }
+                            id: TraitLoc { container, id: ItemTreeId::new(self.file_id, id) }
                                 .intern(self.def_collector.db)
                                 .into(),
                             name: &it.name,
@@ -857,13 +891,13 @@ impl ModCollector<'_, '_> {
                             has_constructor: false,
                         });
                     }
-                    ModItem::TypeAlias(it) => {
-                        let it = &self.item_tree[it];
+                    ModItem::TypeAlias(id) => {
+                        let it = &self.item_tree[id];
 
                         def = Some(DefData {
                             id: TypeAliasLoc {
                                 container: container.into(),
-                                ast_id: AstId::new(self.file_id, it.ast_id),
+                                id: ItemTreeId::new(self.file_id, id),
                             }
                             .intern(self.def_collector.db)
                             .into(),
diff --git a/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs b/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs
index d42933eed..e9a5e4cba 100644
--- a/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs
+++ b/crates/ra_hir_def/src/nameres/tests/mod_resolution.rs
@@ -722,10 +722,7 @@ fn unresolved_module_diagnostics() {
                         ),
                     ),
                 ),
-                value: FileAstId {
-                    raw: Idx::<SyntaxNodePtr>(1),
-                    _ty: PhantomData,
-                },
+                value: FileAstId::<ra_syntax::ast::generated::nodes::Module>(1),
             },
             candidate: "bar.rs",
         },
diff --git a/crates/ra_hir_def/src/src.rs b/crates/ra_hir_def/src/src.rs
index 46e90da70..10e21d48e 100644
--- a/crates/ra_hir_def/src/src.rs
+++ b/crates/ra_hir_def/src/src.rs
@@ -2,30 +2,37 @@
 
 use hir_expand::InFile;
 use ra_arena::map::ArenaMap;
-use ra_syntax::AstNode;
 
-use crate::{db::DefDatabase, AssocItemLoc, ItemLoc};
+use crate::{db::DefDatabase, item_tree::ItemTreeSource, AssocItemLoc, ItemLoc};
 
 pub trait HasSource {
     type Value;
     fn source(&self, db: &dyn DefDatabase) -> InFile<Self::Value>;
 }
 
-impl<N: AstNode> HasSource for AssocItemLoc<N> {
-    type Value = N;
+impl<N: ItemTreeSource> HasSource for AssocItemLoc<N> {
+    type Value = N::Source;
 
-    fn source(&self, db: &dyn DefDatabase) -> InFile<N> {
-        let node = self.ast_id.to_node(db.upcast());
-        InFile::new(self.ast_id.file_id, node)
+    fn source(&self, db: &dyn DefDatabase) -> InFile<N::Source> {
+        let tree = db.item_tree(self.id.file_id);
+        let ast_id_map = db.ast_id_map(self.id.file_id);
+        let root = db.parse_or_expand(self.id.file_id).unwrap();
+        let node = &tree[self.id.value];
+
+        InFile::new(self.id.file_id, ast_id_map.get(node.ast_id()).to_node(&root))
     }
 }
 
-impl<N: AstNode> HasSource for ItemLoc<N> {
-    type Value = N;
+impl<N: ItemTreeSource> HasSource for ItemLoc<N> {
+    type Value = N::Source;
+
+    fn source(&self, db: &dyn DefDatabase) -> InFile<N::Source> {
+        let tree = db.item_tree(self.id.file_id);
+        let ast_id_map = db.ast_id_map(self.id.file_id);
+        let root = db.parse_or_expand(self.id.file_id).unwrap();
+        let node = &tree[self.id.value];
 
-    fn source(&self, db: &dyn DefDatabase) -> InFile<N> {
-        let node = self.ast_id.to_node(db.upcast());
-        InFile::new(self.ast_id.file_id, node)
+        InFile::new(self.id.file_id, ast_id_map.get(node.ast_id()).to_node(&root))
     }
 }
 
diff --git a/crates/ra_hir_expand/src/ast_id_map.rs b/crates/ra_hir_expand/src/ast_id_map.rs
index d19569245..f4d31526a 100644
--- a/crates/ra_hir_expand/src/ast_id_map.rs
+++ b/crates/ra_hir_expand/src/ast_id_map.rs
@@ -6,6 +6,8 @@
 //! changes.
 
 use std::{
+    any::type_name,
+    fmt,
     hash::{Hash, Hasher},
     marker::PhantomData,
 };
@@ -14,7 +16,6 @@ use ra_arena::{Arena, Idx};
 use ra_syntax::{ast, AstNode, AstPtr, SyntaxNode, SyntaxNodePtr};
 
 /// `AstId` points to an AST node in a specific file.
-#[derive(Debug)]
 pub struct FileAstId<N: AstNode> {
     raw: ErasedFileAstId,
     _ty: PhantomData<fn() -> N>,
@@ -39,11 +40,17 @@ impl<N: AstNode> Hash for FileAstId<N> {
     }
 }
 
+impl<N: AstNode> fmt::Debug for FileAstId<N> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "FileAstId::<{}>({})", type_name::<N>(), self.raw.into_raw())
+    }
+}
+
 impl<N: AstNode> FileAstId<N> {
     // Can't make this a From implementation because of coherence
     pub fn upcast<M: AstNode>(self) -> FileAstId<M>
     where
-        M: From<N>,
+        N: Into<M>,
     {
         FileAstId { raw: self.raw, _ty: PhantomData }
     }
@@ -89,7 +96,7 @@ impl AstIdMap {
         }
     }
 
-    pub(crate) fn get<N: AstNode>(&self, id: FileAstId<N>) -> AstPtr<N> {
+    pub fn get<N: AstNode>(&self, id: FileAstId<N>) -> AstPtr<N> {
         self.arena[id.raw].clone().cast::<N>().unwrap()
     }
 
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index 1fe05c70c..e82f2c11e 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -67,8 +67,8 @@ fn type_at_pos_displayed(
     panic!("Can't find expression")
 }
 
-fn type_at(content: &str) -> String {
-    let (db, file_pos) = TestDB::with_position(content);
+fn type_at(ra_fixture: &str) -> String {
+    let (db, file_pos) = TestDB::with_position(ra_fixture);
     type_at_pos(&db, file_pos)
 }
 
@@ -164,13 +164,19 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
     visit_module(&db, &crate_def_map, module.local_id, &mut |it| defs.push(it));
     defs.sort_by_key(|def| match def {
         DefWithBodyId::FunctionId(it) => {
-            it.lookup(&db).ast_id.to_node(&db).syntax().text_range().start()
+            let loc = it.lookup(&db);
+            let tree = db.item_tree(loc.id.file_id);
+            tree.source(&db, loc.id.value).syntax().text_range().start()
         }
         DefWithBodyId::ConstId(it) => {
-            it.lookup(&db).ast_id.to_node(&db).syntax().text_range().start()
+            let loc = it.lookup(&db);
+            let tree = db.item_tree(loc.id.file_id);
+            tree.source(&db, loc.id.value).syntax().text_range().start()
         }
         DefWithBodyId::StaticId(it) => {
-            it.lookup(&db).ast_id.to_node(&db).syntax().text_range().start()
+            let loc = it.lookup(&db);
+            let tree = db.item_tree(loc.id.file_id);
+            tree.source(&db, loc.id.value).syntax().text_range().start()
         }
     });
     for def in defs {