22 files changed, 472 insertions, 226 deletions

diff --git a/crates/hir_def/src/adt.rs b/crates/hir_def/src/adt.rs
index 06f0b9b18..ed36c3109 100644
--- a/crates/hir_def/src/adt.rs
+++ b/crates/hir_def/src/adt.rs
@@ -351,7 +351,7 @@ fn lower_field(
 ) -> FieldData {
     FieldData {
         name: field.name.clone(),
-        type_ref: field.type_ref.clone(),
+        type_ref: item_tree[field.type_ref].clone(),
         visibility: item_tree[override_visibility.unwrap_or(field.visibility)].clone(),
     }
 }
diff --git a/crates/hir_def/src/body.rs b/crates/hir_def/src/body.rs
index b9ecf22fa..9a432f7d1 100644
--- a/crates/hir_def/src/body.rs
+++ b/crates/hir_def/src/body.rs
@@ -33,7 +33,7 @@ use crate::{
     nameres::DefMap,
     path::{ModPath, Path},
     src::HasSource,
-    AsMacroCall, DefWithBodyId, HasModule, Lookup, ModuleId,
+    AsMacroCall, DefWithBodyId, HasModule, LocalModuleId, Lookup, ModuleId,
 };
 
 /// A subset of Expander that only deals with cfg attributes. We only need it to
@@ -46,10 +46,10 @@ pub(crate) struct CfgExpander {
 
 pub(crate) struct Expander {
     cfg_expander: CfgExpander,
-    crate_def_map: Arc<DefMap>,
+    def_map: Arc<DefMap>,
     current_file_id: HirFileId,
     ast_id_map: Arc<AstIdMap>,
-    module: ModuleId,
+    module: LocalModuleId,
     recursion_limit: usize,
 }
 
@@ -91,10 +91,10 @@ impl Expander {
         let ast_id_map = db.ast_id_map(current_file_id);
         Expander {
             cfg_expander,
-            crate_def_map,
+            def_map: crate_def_map,
             current_file_id,
             ast_id_map,
-            module,
+            module: module.local_id,
             recursion_limit: 0,
         }
     }
@@ -102,7 +102,6 @@ impl Expander {
     pub(crate) fn enter_expand<T: ast::AstNode>(
         &mut self,
         db: &dyn DefDatabase,
-        local_scope: Option<&ItemScope>,
         macro_call: ast::MacroCall,
     ) -> ExpandResult<Option<(Mark, T)>> {
         if self.recursion_limit + 1 > EXPANSION_RECURSION_LIMIT {
@@ -112,18 +111,12 @@ impl Expander {
 
         let macro_call = InFile::new(self.current_file_id, &macro_call);
 
-        let resolver = |path: ModPath| -> Option<MacroDefId> {
-            if let Some(local_scope) = local_scope {
-                if let Some(def) = path.as_ident().and_then(|n| local_scope.get_legacy_macro(n)) {
-                    return Some(def);
-                }
-            }
-            self.resolve_path_as_macro(db, &path)
-        };
+        let resolver =
+            |path: ModPath| -> Option<MacroDefId> { self.resolve_path_as_macro(db, &path) };
 
         let mut err = None;
         let call_id =
-            macro_call.as_call_id_with_errors(db, self.crate_def_map.krate(), resolver, &mut |e| {
+            macro_call.as_call_id_with_errors(db, self.def_map.krate(), resolver, &mut |e| {
                 err.get_or_insert(e);
             });
         let call_id = match call_id {
@@ -204,10 +197,7 @@ impl Expander {
     }
 
     fn resolve_path_as_macro(&self, db: &dyn DefDatabase, path: &ModPath) -> Option<MacroDefId> {
-        self.crate_def_map
-            .resolve_path(db, self.module.local_id, path, BuiltinShadowMode::Other)
-            .0
-            .take_macros()
+        self.def_map.resolve_path(db, self.module, path, BuiltinShadowMode::Other).0.take_macros()
     }
 
     fn ast_id<N: AstNode>(&self, item: &N) -> AstId<N> {
diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index 209965fca..28b11cdde 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -1,7 +1,7 @@
 //! Transforms `ast::Expr` into an equivalent `hir_def::expr::Expr`
 //! representation.
 
-use std::{any::type_name, sync::Arc};
+use std::{any::type_name, mem, sync::Arc};
 
 use either::Either;
 use hir_expand::{
@@ -36,8 +36,8 @@ use crate::{
     item_tree::{ItemTree, ItemTreeId, ItemTreeNode},
     path::{GenericArgs, Path},
     type_ref::{Mutability, Rawness, TypeRef},
-    AdtId, ConstLoc, ContainerId, DefWithBodyId, EnumLoc, FunctionLoc, Intern, ModuleDefId,
-    StaticLoc, StructLoc, TraitLoc, TypeAliasLoc, UnionLoc,
+    AdtId, BlockLoc, ConstLoc, ContainerId, DefWithBodyId, EnumLoc, FunctionLoc, Intern,
+    ModuleDefId, StaticLoc, StructLoc, TraitLoc, TypeAliasLoc, UnionLoc,
 };
 
 use super::{diagnostics::BodyDiagnostic, ExprSource, PatSource};
@@ -152,8 +152,8 @@ impl ExprCollector<'_> {
     fn alloc_expr_desugared(&mut self, expr: Expr) -> ExprId {
         self.make_expr(expr, Err(SyntheticSyntax))
     }
-    fn empty_block(&mut self) -> ExprId {
-        self.alloc_expr_desugared(Expr::Block { statements: Vec::new(), tail: None, label: None })
+    fn unit(&mut self) -> ExprId {
+        self.alloc_expr_desugared(Expr::Tuple { exprs: Vec::new() })
     }
     fn missing_expr(&mut self) -> ExprId {
         self.alloc_expr_desugared(Expr::Missing)
@@ -222,7 +222,7 @@ impl ExprCollector<'_> {
                                 MatchArm { pat, expr: then_branch, guard: None },
                                 MatchArm {
                                     pat: placeholder_pat,
-                                    expr: else_branch.unwrap_or_else(|| self.empty_block()),
+                                    expr: else_branch.unwrap_or_else(|| self.unit()),
                                     guard: None,
                                 },
                             ];
@@ -561,7 +561,7 @@ impl ExprCollector<'_> {
         let outer_file = self.expander.current_file_id;
 
         let macro_call = self.expander.to_source(AstPtr::new(&e));
-        let res = self.expander.enter_expand(self.db, Some(&self.body.item_scope), e);
+        let res = self.expander.enter_expand(self.db, e);
 
         match &res.err {
             Some(ExpandError::UnresolvedProcMacro) => {
@@ -697,12 +697,30 @@ impl ExprCollector<'_> {
     }
 
     fn collect_block(&mut self, block: ast::BlockExpr) -> ExprId {
-        let syntax_node_ptr = AstPtr::new(&block.clone().into());
+        let ast_id = self.expander.ast_id(&block);
+        let block_loc =
+            BlockLoc { ast_id, module: self.expander.def_map.module_id(self.expander.module) };
+        let block_id = self.db.intern_block(block_loc);
+        let opt_def_map = self.db.block_def_map(block_id);
+        let has_def_map = opt_def_map.is_some();
+        let def_map = opt_def_map.unwrap_or_else(|| self.expander.def_map.clone());
+        let module = if has_def_map { def_map.root() } else { self.expander.module };
+        let prev_def_map = mem::replace(&mut self.expander.def_map, def_map);
+        let prev_local_module = mem::replace(&mut self.expander.module, module);
+
         self.collect_stmts_items(block.statements());
         let statements =
             block.statements().filter_map(|s| self.collect_stmt(s)).flatten().collect();
         let tail = block.tail_expr().map(|e| self.collect_expr(e));
-        self.alloc_expr(Expr::Block { statements, tail, label: None }, syntax_node_ptr)
+        let syntax_node_ptr = AstPtr::new(&block.clone().into());
+        let expr_id = self.alloc_expr(
+            Expr::Block { id: block_id, statements, tail, label: None },
+            syntax_node_ptr,
+        );
+
+        self.expander.def_map = prev_def_map;
+        self.expander.module = prev_local_module;
+        expr_id
     }
 
     fn collect_stmts_items(&mut self, stmts: ast::AstChildren<ast::Stmt>) {
@@ -794,7 +812,7 @@ impl ExprCollector<'_> {
                 }
                 Either::Right(e) => {
                     let mac = MacroDefId {
-                        krate: self.expander.module.krate,
+                        krate: self.expander.def_map.krate(),
                         ast_id: Some(self.expander.ast_id(&e)),
                         kind: MacroDefKind::Declarative,
                         local_inner: false,
@@ -832,9 +850,9 @@ impl ExprCollector<'_> {
                 if annotation == BindingAnnotation::Unannotated && subpat.is_none() {
                     // This could also be a single-segment path pattern. To
                     // decide that, we need to try resolving the name.
-                    let (resolved, _) = self.expander.crate_def_map.resolve_path(
+                    let (resolved, _) = self.expander.def_map.resolve_path(
                         self.db,
-                        self.expander.module.local_id,
+                        self.expander.module,
                         &name.clone().into(),
                         BuiltinShadowMode::Other,
                     );
diff --git a/crates/hir_def/src/body/tests.rs b/crates/hir_def/src/body/tests.rs
index 2e5d0a01e..a92134ba7 100644
--- a/crates/hir_def/src/body/tests.rs
+++ b/crates/hir_def/src/body/tests.rs
@@ -1,7 +1,10 @@
-use base_db::{fixture::WithFixture, SourceDatabase};
+mod block;
+
+use base_db::{fixture::WithFixture, FilePosition, SourceDatabase};
+use expect_test::Expect;
 use test_utils::mark;
 
-use crate::{test_db::TestDB, ModuleDefId};
+use crate::{test_db::TestDB, BlockId, ModuleDefId};
 
 use super::*;
 
@@ -31,6 +34,114 @@ fn check_diagnostics(ra_fixture: &str) {
     db.check_diagnostics();
 }
 
+fn block_def_map_at(ra_fixture: &str) -> String {
+    let (db, position) = crate::test_db::TestDB::with_position(ra_fixture);
+
+    let krate = db.crate_graph().iter().next().unwrap();
+    let def_map = db.crate_def_map(krate);
+
+    let mut block =
+        block_at_pos(&db, &def_map, position).expect("couldn't find enclosing function or block");
+    loop {
+        let def_map = db.block_def_map(block).unwrap_or_else(|| def_map.clone());
+        let new_block = block_at_pos(&db, &def_map, position);
+        match new_block {
+            Some(new_block) => {
+                assert_ne!(block, new_block);
+                block = new_block;
+            }
+            None => {
+                return def_map.dump(&db);
+            }
+        }
+    }
+}
+
+fn block_at_pos(db: &dyn DefDatabase, def_map: &DefMap, position: FilePosition) -> Option<BlockId> {
+    // Find the smallest (innermost) function containing the cursor.
+    let mut size = None;
+    let mut fn_def = None;
+    for (_, module) in def_map.modules() {
+        let file_id = module.definition_source(db).file_id;
+        if file_id != position.file_id.into() {
+            continue;
+        }
+        let root = db.parse_or_expand(file_id).unwrap();
+        let ast_map = db.ast_id_map(file_id);
+        let item_tree = db.item_tree(file_id);
+        for decl in module.scope.declarations() {
+            if let ModuleDefId::FunctionId(it) = decl {
+                let ast = ast_map.get(item_tree[it.lookup(db).id.value].ast_id).to_node(&root);
+                let range = ast.syntax().text_range();
+
+                if !range.contains(position.offset) {
+                    continue;
+                }
+
+                let new_size = match size {
+                    None => range.len(),
+                    Some(size) => {
+                        if range.len() < size {
+                            range.len()
+                        } else {
+                            size
+                        }
+                    }
+                };
+                if size != Some(new_size) {
+                    size = Some(new_size);
+                    fn_def = Some(it);
+                }
+            }
+        }
+    }
+
+    let (body, source_map) = db.body_with_source_map(fn_def?.into());
+
+    // Now find the smallest encompassing block expression in the function body.
+    let mut size = None;
+    let mut block_id = None;
+    for (expr_id, expr) in body.exprs.iter() {
+        if let Expr::Block { id, .. } = expr {
+            if let Ok(ast) = source_map.expr_syntax(expr_id) {
+                if ast.file_id != position.file_id.into() {
+                    continue;
+                }
+
+                let root = db.parse_or_expand(ast.file_id).unwrap();
+                let ast = ast.value.to_node(&root);
+                let range = ast.syntax().text_range();
+
+                if !range.contains(position.offset) {
+                    continue;
+                }
+
+                let new_size = match size {
+                    None => range.len(),
+                    Some(size) => {
+                        if range.len() < size {
+                            range.len()
+                        } else {
+                            size
+                        }
+                    }
+                };
+                if size != Some(new_size) {
+                    size = Some(new_size);
+                    block_id = Some(*id);
+                }
+            }
+        }
+    }
+
+    Some(block_id.expect("can't find block containing cursor"))
+}
+
+fn check_at(ra_fixture: &str, expect: Expect) {
+    let actual = block_def_map_at(ra_fixture);
+    expect.assert_eq(&actual);
+}
+
 #[test]
 fn your_stack_belongs_to_me() {
     mark::check!(your_stack_belongs_to_me);
diff --git a/crates/hir_def/src/nameres/tests/block.rs b/crates/hir_def/src/body/tests/block.rs
index 6cc659513..062560a70 100644
--- a/crates/hir_def/src/nameres/tests/block.rs
+++ b/crates/hir_def/src/body/tests/block.rs
@@ -1,4 +1,5 @@
 use super::*;
+use expect_test::expect;
 
 #[test]
 fn inner_item_smoke() {
@@ -13,6 +14,7 @@ fn outer() {
         expect![[r#"
             block scope
             inner: v
+
             crate
             inner: t
             outer: v
@@ -37,6 +39,7 @@ fn outer() {
             CrateStruct: t v
             SelfStruct: t v
             Struct: t v
+
             crate
             Struct: t v
             outer: v
@@ -61,6 +64,7 @@ fn outer() {
             block scope
             imported: t v
             name: v
+
             crate
             name: t
             outer: v
@@ -87,9 +91,11 @@ fn outer() {
             inner1: t
             inner2: v
             outer: v
+
             block scope
             inner: v
             inner1: t
+
             crate
             outer: v
         "#]],
@@ -112,6 +118,7 @@ struct Struct {}
         expect![[r#"
             block scope
             Struct: t
+
             crate
             Struct: t
             module: t
@@ -142,6 +149,7 @@ fn f() {
         expect![[r#"
             block scope
             Hit: t
+
             crate
             f: v
         "#]],
@@ -176,11 +184,47 @@ pub mod mark {
         expect![[r#"
             block scope
             Hit: t
+
             block scope
             nested: v
+
             crate
             f: v
             mark: t
         "#]],
     );
 }
+
+#[test]
+fn macro_resolve_legacy() {
+    check_at(
+        r#"
+//- /lib.rs
+mod module;
+
+//- /module.rs
+macro_rules! m {
+    () => {
+        struct Def {}
+    };
+}
+
+fn f() {
+    {
+        m!();
+        $0
+    }
+}
+        "#,
+        expect![[r#"
+            block scope
+            Def: t
+
+            crate
+            module: t
+
+            crate::module
+            f: v
+        "#]],
+    )
+}
diff --git a/crates/hir_def/src/data.rs b/crates/hir_def/src/data.rs
index e7b7724f7..42fcca386 100644
--- a/crates/hir_def/src/data.rs
+++ b/crates/hir_def/src/data.rs
@@ -41,8 +41,8 @@ impl FunctionData {
 
         Arc::new(FunctionData {
             name: func.name.clone(),
-            params: func.params.to_vec(),
-            ret_type: func.ret_type.clone(),
+            params: func.params.iter().map(|id| item_tree[*id].clone()).collect(),
+            ret_type: item_tree[func.ret_type].clone(),
             attrs: item_tree.attrs(db, krate, ModItem::from(loc.id.value).into()).clone(),
             has_self_param: func.has_self_param,
             has_body: func.has_body,
@@ -75,7 +75,7 @@ impl TypeAliasData {
 
         Arc::new(TypeAliasData {
             name: typ.name.clone(),
-            type_ref: typ.type_ref.clone(),
+            type_ref: typ.type_ref.map(|id| item_tree[id].clone()),
             visibility: item_tree[typ.visibility].clone(),
             is_extern: typ.is_extern,
             bounds: typ.bounds.to_vec(),
@@ -144,8 +144,8 @@ impl ImplData {
 
         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 target_trait = impl_def.target_trait.map(|id| item_tree[id].clone());
+        let target_type = item_tree[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);
@@ -182,7 +182,7 @@ impl ConstData {
 
         Arc::new(ConstData {
             name: konst.name.clone(),
-            type_ref: konst.type_ref.clone(),
+            type_ref: item_tree[konst.type_ref].clone(),
             visibility: item_tree[konst.visibility].clone(),
         })
     }
@@ -205,7 +205,7 @@ impl StaticData {
 
         Arc::new(StaticData {
             name: Some(statik.name.clone()),
-            type_ref: statik.type_ref.clone(),
+            type_ref: item_tree[statik.type_ref].clone(),
             visibility: item_tree[statik.visibility].clone(),
             mutable: statik.mutable,
             is_extern: statik.is_extern,
@@ -262,7 +262,7 @@ fn collect_items(
                 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).value {
+                if let Some((mark, mac)) = expander.enter_expand(db, call).value {
                     let src: InFile<ast::MacroItems> = expander.to_source(mac);
                     let item_tree = db.item_tree(src.file_id);
                     let iter =
diff --git a/crates/hir_def/src/db.rs b/crates/hir_def/src/db.rs
index aef7e1f6c..6c01f1ed0 100644
--- a/crates/hir_def/src/db.rs
+++ b/crates/hir_def/src/db.rs
@@ -58,8 +58,23 @@ pub trait DefDatabase: InternDatabase + AstDatabase + Upcast<dyn AstDatabase> {
     #[salsa::invoke(DefMap::crate_def_map_query)]
     fn crate_def_map_query(&self, krate: CrateId) -> Arc<DefMap>;
 
+    /// Computes the block-level `DefMap`, returning `None` when `block` doesn't contain any inner
+    /// items directly.
+    ///
+    /// For example:
+    ///
+    /// ```
+    /// fn f() { // (0)
+    ///     { // (1)
+    ///         fn inner() {}
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// The `block_def_map` for block 0 would return `None`, while `block_def_map` of block 1 would
+    /// return a `DefMap` containing `inner`.
     #[salsa::invoke(DefMap::block_def_map_query)]
-    fn block_def_map(&self, block: BlockId) -> Arc<DefMap>;
+    fn block_def_map(&self, block: BlockId) -> Option<Arc<DefMap>>;
 
     #[salsa::invoke(StructData::struct_data_query)]
     fn struct_data(&self, id: StructId) -> Arc<StructData>;
diff --git a/crates/hir_def/src/expr.rs b/crates/hir_def/src/expr.rs
index 5be838f4a..4d72eaeaf 100644
--- a/crates/hir_def/src/expr.rs
+++ b/crates/hir_def/src/expr.rs
@@ -20,6 +20,7 @@ use crate::{
     builtin_type::{BuiltinFloat, BuiltinInt},
     path::{GenericArgs, Path},
     type_ref::{Mutability, Rawness, TypeRef},
+    BlockId,
 };
 
 pub type ExprId = Idx<Expr>;
@@ -56,6 +57,7 @@ pub enum Expr {
         else_branch: Option<ExprId>,
     },
     Block {
+        id: BlockId,
         statements: Vec<Statement>,
         tail: Option<ExprId>,
         label: Option<LabelId>,
diff --git a/crates/hir_def/src/find_path.rs b/crates/hir_def/src/find_path.rs
index 94a1d567d..aa2c6e04e 100644
--- a/crates/hir_def/src/find_path.rs
+++ b/crates/hir_def/src/find_path.rs
@@ -36,13 +36,13 @@ const MAX_PATH_LEN: usize = 15;
 
 impl ModPath {
     fn starts_with_std(&self) -> bool {
-        self.segments.first() == Some(&known::std)
+        self.segments().first() == Some(&known::std)
     }
 
     // When std library is present, paths starting with `std::`
     // should be preferred over paths starting with `core::` and `alloc::`
     fn can_start_with_std(&self) -> bool {
-        let first_segment = self.segments.first();
+        let first_segment = self.segments().first();
         first_segment == Some(&known::alloc) || first_segment == Some(&known::core)
     }
 }
@@ -157,7 +157,7 @@ fn find_path_inner(
     if let Some(ModuleDefId::EnumVariantId(variant)) = item.as_module_def_id() {
         if let Some(mut path) = find_path(db, ItemInNs::Types(variant.parent.into()), from) {
             let data = db.enum_data(variant.parent);
-            path.segments.push(data.variants[variant.local_id].name.clone());
+            path.push_segment(data.variants[variant.local_id].name.clone());
             return Some(path);
         }
         // If this doesn't work, it seems we have no way of referring to the
@@ -186,7 +186,7 @@ fn find_path_inner(
                 best_path_len - 1,
                 prefixed,
             ) {
-                path.segments.push(name);
+                path.push_segment(name);
 
                 let new_path = if let Some(best_path) = best_path {
                     select_best_path(best_path, path, prefer_no_std)
@@ -215,7 +215,7 @@ fn find_path_inner(
                     prefixed,
                 )?;
                 mark::hit!(partially_imported);
-                path.segments.push(info.path.segments.last().unwrap().clone());
+                path.push_segment(info.path.segments.last().unwrap().clone());
                 Some(path)
             })
         });
diff --git a/crates/hir_def/src/item_scope.rs b/crates/hir_def/src/item_scope.rs
index 2750e1c91..ee46c3330 100644
--- a/crates/hir_def/src/item_scope.rs
+++ b/crates/hir_def/src/item_scope.rs
@@ -8,6 +8,7 @@ use hir_expand::name::Name;
 use hir_expand::MacroDefKind;
 use once_cell::sync::Lazy;
 use rustc_hash::{FxHashMap, FxHashSet};
+use stdx::format_to;
 use test_utils::mark;
 
 use crate::{
@@ -292,6 +293,30 @@ impl ItemScope {
             *vis = Visibility::Module(this_module);
         }
     }
+
+    pub(crate) fn dump(&self, buf: &mut String) {
+        let mut entries: Vec<_> = self.resolutions().collect();
+        entries.sort_by_key(|(name, _)| name.clone());
+
+        for (name, def) in entries {
+            format_to!(buf, "{}:", name.map_or("_".to_string(), |name| name.to_string()));
+
+            if def.types.is_some() {
+                buf.push_str(" t");
+            }
+            if def.values.is_some() {
+                buf.push_str(" v");
+            }
+            if def.macros.is_some() {
+                buf.push_str(" m");
+            }
+            if def.is_none() {
+                buf.push_str(" _");
+            }
+
+            buf.push('\n');
+        }
+    }
 }
 
 impl PerNs {
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index 42d9f0947..3233b1957 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -24,7 +24,7 @@ use la_arena::{Arena, Idx, RawIdx};
 use profile::Count;
 use rustc_hash::FxHashMap;
 use smallvec::SmallVec;
-use syntax::{ast, match_ast};
+use syntax::{ast, match_ast, SyntaxKind};
 use test_utils::mark;
 
 use crate::{
@@ -80,6 +80,10 @@ impl ItemTree {
     pub(crate) fn item_tree_query(db: &dyn DefDatabase, file_id: HirFileId) -> Arc<ItemTree> {
         let _p = profile::span("item_tree_query").detail(|| format!("{:?}", file_id));
         let syntax = if let Some(node) = db.parse_or_expand(file_id) {
+            if node.kind() == SyntaxKind::ERROR {
+                // FIXME: not 100% sure why these crop up, but return an empty tree to avoid a panic
+                return Default::default();
+            }
             node
         } else {
             return Default::default();
@@ -142,6 +146,7 @@ impl ItemTree {
                 macro_defs,
                 vis,
                 generics,
+                type_refs,
                 inner_items,
             } = &mut **data;
 
@@ -165,6 +170,8 @@ impl ItemTree {
 
             vis.arena.shrink_to_fit();
             generics.arena.shrink_to_fit();
+            type_refs.arena.shrink_to_fit();
+            type_refs.map.shrink_to_fit();
 
             inner_items.shrink_to_fit();
         }
@@ -233,7 +240,7 @@ impl ItemVisibilities {
     fn alloc(&mut self, vis: RawVisibility) -> RawVisibilityId {
         match &vis {
             RawVisibility::Public => RawVisibilityId::PUB,
-            RawVisibility::Module(path) if path.segments.is_empty() => match &path.kind {
+            RawVisibility::Module(path) if path.segments().is_empty() => match &path.kind {
                 PathKind::Super(0) => RawVisibilityId::PRIV,
                 PathKind::Crate => RawVisibilityId::PUB_CRATE,
                 _ => RawVisibilityId(self.arena.alloc(vis).into_raw().into()),
@@ -244,10 +251,8 @@ impl ItemVisibilities {
 }
 
 static VIS_PUB: RawVisibility = RawVisibility::Public;
-static VIS_PRIV: RawVisibility =
-    RawVisibility::Module(ModPath { kind: PathKind::Super(0), segments: Vec::new() });
-static VIS_PUB_CRATE: RawVisibility =
-    RawVisibility::Module(ModPath { kind: PathKind::Crate, segments: Vec::new() });
+static VIS_PRIV: RawVisibility = RawVisibility::Module(ModPath::from_kind(PathKind::Super(0)));
+static VIS_PUB_CRATE: RawVisibility = RawVisibility::Module(ModPath::from_kind(PathKind::Crate));
 
 #[derive(Default, Debug, Eq, PartialEq)]
 struct GenericParamsStorage {
@@ -275,6 +280,32 @@ static EMPTY_GENERICS: GenericParams = GenericParams {
     where_predicates: Vec::new(),
 };
 
+/// `TypeRef` interner.
+#[derive(Default, Debug, Eq, PartialEq)]
+struct TypeRefStorage {
+    arena: Arena<Arc<TypeRef>>,
+    map: FxHashMap<Arc<TypeRef>, Idx<Arc<TypeRef>>>,
+}
+
+impl TypeRefStorage {
+    // Note: We lie about the `Idx<TypeRef>` to hide the interner details.
+
+    fn intern(&mut self, ty: TypeRef) -> Idx<TypeRef> {
+        if let Some(id) = self.map.get(&ty) {
+            return Idx::from_raw(id.into_raw());
+        }
+
+        let ty = Arc::new(ty);
+        let idx = self.arena.alloc(ty.clone());
+        self.map.insert(ty, idx);
+        Idx::from_raw(idx.into_raw())
+    }
+
+    fn lookup(&self, id: Idx<TypeRef>) -> &TypeRef {
+        &self.arena[Idx::from_raw(id.into_raw())]
+    }
+}
+
 #[derive(Default, Debug, Eq, PartialEq)]
 struct ItemTreeData {
     imports: Arena<Import>,
@@ -297,6 +328,7 @@ struct ItemTreeData {
 
     vis: ItemVisibilities,
     generics: GenericParamsStorage,
+    type_refs: TypeRefStorage,
 
     inner_items: FxHashMap<FileAstId<ast::BlockExpr>, SmallVec<[ModItem; 1]>>,
 }
@@ -485,6 +517,14 @@ impl Index<GenericParamsId> for ItemTree {
     }
 }
 
+impl Index<Idx<TypeRef>> for ItemTree {
+    type Output = TypeRef;
+
+    fn index(&self, id: Idx<TypeRef>) -> &Self::Output {
+        self.data().type_refs.lookup(id)
+    }
+}
+
 impl<N: ItemTreeNode> Index<FileItemTreeId<N>> for ItemTree {
     type Output = N;
     fn index(&self, id: FileItemTreeId<N>) -> &N {
@@ -528,9 +568,9 @@ pub struct Function {
     /// Whether the function is located in an `extern` block (*not* whether it is an
     /// `extern "abi" fn`).
     pub is_extern: bool,
-    pub params: Box<[TypeRef]>,
+    pub params: Box<[Idx<TypeRef>]>,
     pub is_varargs: bool,
-    pub ret_type: TypeRef,
+    pub ret_type: Idx<TypeRef>,
     pub ast_id: FileAstId<ast::Fn>,
 }
 
@@ -577,7 +617,7 @@ pub struct Const {
     /// const _: () = ();
     pub name: Option<Name>,
     pub visibility: RawVisibilityId,
-    pub type_ref: TypeRef,
+    pub type_ref: Idx<TypeRef>,
     pub ast_id: FileAstId<ast::Const>,
 }
 
@@ -588,7 +628,7 @@ pub struct Static {
     pub mutable: bool,
     /// Whether the static is in an `extern` block.
     pub is_extern: bool,
-    pub type_ref: TypeRef,
+    pub type_ref: Idx<TypeRef>,
     pub ast_id: FileAstId<ast::Static>,
 }
 
@@ -605,8 +645,8 @@ pub struct Trait {
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Impl {
     pub generic_params: GenericParamsId,
-    pub target_trait: Option<TypeRef>,
-    pub target_type: TypeRef,
+    pub target_trait: Option<Idx<TypeRef>>,
+    pub target_type: Idx<TypeRef>,
     pub is_negative: bool,
     pub items: Box<[AssocItem]>,
     pub ast_id: FileAstId<ast::Impl>,
@@ -619,7 +659,7 @@ pub struct TypeAlias {
     /// Bounds on the type alias itself. Only valid in trait declarations, eg. `type Assoc: Copy;`.
     pub bounds: Box<[TypeBound]>,
     pub generic_params: GenericParamsId,
-    pub type_ref: Option<TypeRef>,
+    pub type_ref: Option<Idx<TypeRef>>,
     pub is_extern: bool,
     pub ast_id: FileAstId<ast::TypeAlias>,
 }
@@ -802,6 +842,6 @@ pub enum Fields {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Field {
     pub name: Name,
-    pub type_ref: TypeRef,
+    pub type_ref: Idx<TypeRef>,
     pub visibility: RawVisibilityId,
 }
diff --git a/crates/hir_def/src/item_tree/lower.rs b/crates/hir_def/src/item_tree/lower.rs
index acc001add..8f2f0b340 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -183,6 +183,7 @@ impl Ctx {
                                 block_stack.push(self.source_ast_id_map.ast_id(&block));
                             },
                             ast::Item(item) => {
+                                // FIXME: This triggers for macro calls in expression position
                                 let mod_items = self.lower_mod_item(&item, true);
                                 let current_block = block_stack.last();
                                 if let (Some(mod_items), Some(block)) = (mod_items, current_block) {
@@ -363,6 +364,7 @@ impl Ctx {
                 params.push(type_ref);
             }
         }
+        let params = params.into_iter().map(|param| self.data().type_refs.intern(param)).collect();
 
         let mut is_varargs = false;
         if let Some(params) = func.param_list() {
@@ -384,6 +386,8 @@ impl Ctx {
             ret_type
         };
 
+        let ret_type = self.data().type_refs.intern(ret_type);
+
         let has_body = func.body().is_some();
 
         let ast_id = self.source_ast_id_map.ast_id(func);
@@ -395,7 +399,7 @@ impl Ctx {
             has_body,
             is_unsafe: func.unsafe_token().is_some(),
             is_extern: false,
-            params: params.into_boxed_slice(),
+            params,
             is_varargs,
             ret_type,
             ast_id,
@@ -656,6 +660,7 @@ impl Ctx {
                 generics.fill(&self.body_ctx, sm, node);
                 // lower `impl Trait` in arguments
                 for param in &*func.params {
+                    let param = self.data().type_refs.lookup(*param);
                     generics.fill_implicit_impl_trait_args(param);
                 }
             }
@@ -708,11 +713,15 @@ impl Ctx {
         self.data().vis.alloc(vis)
     }
 
-    fn lower_type_ref(&self, type_ref: &ast::Type) -> TypeRef {
-        TypeRef::from_ast(&self.body_ctx, type_ref.clone())
+    fn lower_type_ref(&mut self, type_ref: &ast::Type) -> Idx<TypeRef> {
+        let tyref = TypeRef::from_ast(&self.body_ctx, type_ref.clone());
+        self.data().type_refs.intern(tyref)
     }
-    fn lower_type_ref_opt(&self, type_ref: Option<ast::Type>) -> TypeRef {
-        type_ref.map(|ty| self.lower_type_ref(&ty)).unwrap_or(TypeRef::Error)
+    fn lower_type_ref_opt(&mut self, type_ref: Option<ast::Type>) -> Idx<TypeRef> {
+        match type_ref.map(|ty| self.lower_type_ref(&ty)) {
+            Some(it) => it,
+            None => self.data().type_refs.intern(TypeRef::Error),
+        }
     }
 
     /// Forces the visibility `vis` to be used for all items lowered during execution of `f`.
@@ -741,7 +750,8 @@ impl Ctx {
 
 fn desugar_future_path(orig: TypeRef) -> Path {
     let path = path![core::future::Future];
-    let mut generic_args: Vec<_> = std::iter::repeat(None).take(path.segments.len() - 1).collect();
+    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() };
diff --git a/crates/hir_def/src/lib.rs b/crates/hir_def/src/lib.rs
index 42b50b5b7..b50923747 100644
--- a/crates/hir_def/src/lib.rs
+++ b/crates/hir_def/src/lib.rs
@@ -81,7 +81,13 @@ pub struct ModuleId {
 impl ModuleId {
     pub fn def_map(&self, db: &dyn db::DefDatabase) -> Arc<DefMap> {
         match self.block {
-            Some(block) => db.block_def_map(block),
+            Some(block) => {
+                db.block_def_map(block).unwrap_or_else(|| {
+                    // NOTE: This should be unreachable - all `ModuleId`s come from their `DefMap`s,
+                    // so the `DefMap` here must exist.
+                    panic!("no `block_def_map` for `ModuleId` {:?}", self);
+                })
+            }
             None => db.crate_def_map(self.krate),
         }
     }
@@ -239,6 +245,7 @@ pub struct BlockId(salsa::InternId);
 #[derive(Debug, Hash, PartialEq, Eq, Clone)]
 pub struct BlockLoc {
     ast_id: AstId<ast::BlockExpr>,
+    /// The containing module.
     module: ModuleId,
 }
 impl_intern!(BlockId, BlockLoc, intern_block, lookup_intern_block);
@@ -655,7 +662,7 @@ impl AsMacroCall for AstIdWithPath<ast::Item> {
             def.as_lazy_macro(
                 db.upcast(),
                 krate,
-                MacroCallKind::Attr(self.ast_id, self.path.segments.last()?.to_string()),
+                MacroCallKind::Attr(self.ast_id, self.path.segments().last()?.to_string()),
             )
             .into(),
         )
diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 0a15fc470..ad2e9bcac 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -73,7 +73,15 @@ use crate::{
     AstId, BlockId, BlockLoc, LocalModuleId, ModuleDefId, ModuleId,
 };
 
-/// Contains all top-level defs from a macro-expanded crate
+/// Contains the results of (early) name resolution.
+///
+/// A `DefMap` stores the module tree and the definitions that are in scope in every module after
+/// item-level macros have been expanded.
+///
+/// Every crate has a primary `DefMap` whose root is the crate's main file (`main.rs`/`lib.rs`),
+/// computed by the `crate_def_map` query. Additionally, every block expression introduces the
+/// opportunity to write arbitrary item and module hierarchies, and thus gets its own `DefMap` that
+/// is computed by the `block_def_map` query.
 #[derive(Debug, PartialEq, Eq)]
 pub struct DefMap {
     _c: Count<Self>,
@@ -91,11 +99,13 @@ pub struct DefMap {
     diagnostics: Vec<DefDiagnostic>,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+/// For `DefMap`s computed for a block expression, this stores its location in the parent map.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
 struct BlockInfo {
+    /// The `BlockId` this `DefMap` was created from.
     block: BlockId,
-    parent: Arc<DefMap>,
-    parent_module: LocalModuleId,
+    /// The containing module.
+    parent: ModuleId,
 }
 
 impl std::ops::Index<LocalModuleId> for DefMap {
@@ -197,21 +207,25 @@ impl DefMap {
         Arc::new(def_map)
     }
 
-    pub(crate) fn block_def_map_query(db: &dyn DefDatabase, block_id: BlockId) -> Arc<DefMap> {
+    pub(crate) fn block_def_map_query(
+        db: &dyn DefDatabase,
+        block_id: BlockId,
+    ) -> Option<Arc<DefMap>> {
         let block: BlockLoc = db.lookup_intern_block(block_id);
-        let parent = block.module.def_map(db);
 
-        // FIXME: It would be good to just return the parent map when the block has no items, but
-        // we rely on `def_map.block` in a few places, which is `Some` for the inner `DefMap`.
+        let item_tree = db.item_tree(block.ast_id.file_id);
+        if item_tree.inner_items_of_block(block.ast_id.value).is_empty() {
+            return None;
+        }
 
-        let block_info =
-            BlockInfo { block: block_id, parent, parent_module: block.module.local_id };
+        let block_info = BlockInfo { block: block_id, parent: block.module };
 
-        let mut def_map = DefMap::empty(block.module.krate, block_info.parent.edition);
+        let parent_map = block.module.def_map(db);
+        let mut def_map = DefMap::empty(block.module.krate, parent_map.edition);
         def_map.block = Some(block_info);
 
         let def_map = collector::collect_defs(db, def_map, Some(block.ast_id));
-        Arc::new(def_map)
+        Some(Arc::new(def_map))
     }
 
     fn empty(krate: CrateId, edition: Edition) -> DefMap {
@@ -275,9 +289,15 @@ impl DefMap {
         ModuleId { krate: self.krate, local_id, block }
     }
 
-    pub(crate) fn crate_root(&self) -> ModuleId {
-        let (root_map, _) = self.ancestor_maps(self.root).last().unwrap();
-        root_map.module_id(root_map.root)
+    pub(crate) fn crate_root(&self, db: &dyn DefDatabase) -> ModuleId {
+        self.with_ancestor_maps(db, self.root, &mut |def_map, _module| {
+            if def_map.block.is_none() {
+                Some(def_map.module_id(def_map.root))
+            } else {
+                None
+            }
+        })
+        .expect("DefMap chain without root")
     }
 
     pub(crate) fn resolve_path(
@@ -292,25 +312,42 @@ impl DefMap {
         (res.resolved_def, res.segment_index)
     }
 
-    /// Iterates over the containing `DefMap`s, if `self` is a `DefMap` corresponding to a block
-    /// expression.
-    fn ancestor_maps(
+    /// Ascends the `DefMap` hierarchy and calls `f` with every `DefMap` and containing module.
+    ///
+    /// If `f` returns `Some(val)`, iteration is stopped and `Some(val)` is returned. If `f` returns
+    /// `None`, iteration continues.
+    fn with_ancestor_maps<T>(
         &self,
+        db: &dyn DefDatabase,
         local_mod: LocalModuleId,
-    ) -> impl Iterator<Item = (&DefMap, LocalModuleId)> {
-        std::iter::successors(Some((self, local_mod)), |(map, _)| {
-            map.block.as_ref().map(|block| (&*block.parent, block.parent_module))
-        })
+        f: &mut dyn FnMut(&DefMap, LocalModuleId) -> Option<T>,
+    ) -> Option<T> {
+        if let Some(it) = f(self, local_mod) {
+            return Some(it);
+        }
+        let mut block = self.block;
+        while let Some(block_info) = block {
+            let parent = block_info.parent.def_map(db);
+            if let Some(it) = f(&parent, block_info.parent.local_id) {
+                return Some(it);
+            }
+            block = parent.block;
+        }
+
+        None
     }
 
     // FIXME: this can use some more human-readable format (ideally, an IR
     // even), as this should be a great debugging aid.
-    pub fn dump(&self) -> String {
+    pub fn dump(&self, db: &dyn DefDatabase) -> String {
         let mut buf = String::new();
+        let mut arc;
         let mut current_map = self;
         while let Some(block) = &current_map.block {
             go(&mut buf, current_map, "block scope", current_map.root);
-            current_map = &*block.parent;
+            buf.push('\n');
+            arc = block.parent.def_map(db);
+            current_map = &*arc;
         }
         go(&mut buf, current_map, "crate", current_map.root);
         return buf;
@@ -318,27 +355,7 @@ impl DefMap {
         fn go(buf: &mut String, map: &DefMap, path: &str, module: LocalModuleId) {
             format_to!(buf, "{}\n", path);
 
-            let mut entries: Vec<_> = map.modules[module].scope.resolutions().collect();
-            entries.sort_by_key(|(name, _)| name.clone());
-
-            for (name, def) in entries {
-                format_to!(buf, "{}:", name.map_or("_".to_string(), |name| name.to_string()));
-
-                if def.types.is_some() {
-                    buf.push_str(" t");
-                }
-                if def.values.is_some() {
-                    buf.push_str(" v");
-                }
-                if def.macros.is_some() {
-                    buf.push_str(" m");
-                }
-                if def.is_none() {
-                    buf.push_str(" _");
-                }
-
-                buf.push('\n');
-            }
+            map.modules[module].scope.dump(buf);
 
             for (name, child) in map.modules[module].children.iter() {
                 let path = format!("{}::{}", path, name);
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 6e86cc4a7..6bd41bc08 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -655,7 +655,7 @@ impl DefCollector<'_> {
                 }
             }
         } else {
-            match import.path.segments.last() {
+            match import.path.segments().last() {
                 Some(last_segment) => {
                     let name = match &import.alias {
                         Some(ImportAlias::Alias(name)) => Some(name.clone()),
@@ -956,7 +956,7 @@ impl DefCollector<'_> {
                 let item_tree = self.db.item_tree(import.file_id);
                 let import_data = &item_tree[import.value];
 
-                match (import_data.path.segments.first(), &import_data.path.kind) {
+                match (import_data.path.segments().first(), &import_data.path.kind) {
                     (Some(krate), PathKind::Plain) | (Some(krate), PathKind::Abs) => {
                         if diagnosed_extern_crates.contains(krate) {
                             continue;
@@ -1449,10 +1449,11 @@ impl ModCollector<'_, '_> {
         if let Some(macro_call_id) =
             ast_id.as_call_id(self.def_collector.db, self.def_collector.def_map.krate, |path| {
                 path.as_ident().and_then(|name| {
-                    self.def_collector
-                        .def_map
-                        .ancestor_maps(self.module_id)
-                        .find_map(|(map, module)| map[module].scope.get_legacy_macro(&name))
+                    self.def_collector.def_map.with_ancestor_maps(
+                        self.def_collector.db,
+                        self.module_id,
+                        &mut |map, module| map[module].scope.get_legacy_macro(&name),
+                    )
                 })
             })
         {
diff --git a/crates/hir_def/src/nameres/path_resolution.rs b/crates/hir_def/src/nameres/path_resolution.rs
index ecf75c777..f2b59172d 100644
--- a/crates/hir_def/src/nameres/path_resolution.rs
+++ b/crates/hir_def/src/nameres/path_resolution.rs
@@ -110,6 +110,7 @@ impl DefMap {
         let mut result = ResolvePathResult::empty(ReachedFixedPoint::No);
         result.segment_index = Some(usize::max_value());
 
+        let mut arc;
         let mut current_map = self;
         loop {
             let new = current_map.resolve_path_fp_with_macro_single(
@@ -131,8 +132,9 @@ impl DefMap {
 
             match &current_map.block {
                 Some(block) => {
-                    current_map = &block.parent;
-                    original_module = block.parent_module;
+                    original_module = block.parent.local_id;
+                    arc = block.parent.def_map(db);
+                    current_map = &*arc;
                 }
                 None => return result,
             }
@@ -147,12 +149,12 @@ impl DefMap {
         path: &ModPath,
         shadow: BuiltinShadowMode,
     ) -> ResolvePathResult {
-        let mut segments = path.segments.iter().enumerate();
+        let mut segments = path.segments().iter().enumerate();
         let mut curr_per_ns: PerNs = match path.kind {
             PathKind::DollarCrate(krate) => {
                 if krate == self.krate {
                     mark::hit!(macro_dollar_crate_self);
-                    PerNs::types(self.crate_root().into(), Visibility::Public)
+                    PerNs::types(self.crate_root(db).into(), Visibility::Public)
                 } else {
                     let def_map = db.crate_def_map(krate);
                     let module = def_map.module_id(def_map.root);
@@ -160,7 +162,7 @@ impl DefMap {
                     PerNs::types(module.into(), Visibility::Public)
                 }
             }
-            PathKind::Crate => PerNs::types(self.crate_root().into(), Visibility::Public),
+            PathKind::Crate => PerNs::types(self.crate_root(db).into(), Visibility::Public),
             // plain import or absolute path in 2015: crate-relative with
             // fallback to extern prelude (with the simplification in
             // rust-lang/rust#57745)
@@ -188,7 +190,7 @@ impl DefMap {
                 // BuiltinShadowMode wasn't Module, then we need to try
                 // resolving it as a builtin.
                 let prefer_module =
-                    if path.segments.len() == 1 { shadow } else { BuiltinShadowMode::Module };
+                    if path.segments().len() == 1 { shadow } else { BuiltinShadowMode::Module };
 
                 log::debug!("resolving {:?} in module", segment);
                 self.resolve_name_in_module(db, original_module, &segment, prefer_module)
@@ -201,15 +203,15 @@ impl DefMap {
                         None => match &self.block {
                             Some(block) => {
                                 // Look up remaining path in parent `DefMap`
-                                let new_path = ModPath {
-                                    kind: PathKind::Super(lvl - i),
-                                    segments: path.segments.clone(),
-                                };
+                                let new_path = ModPath::from_segments(
+                                    PathKind::Super(lvl - i),
+                                    path.segments().to_vec(),
+                                );
                                 log::debug!("`super` path: {} -> {} in parent map", path, new_path);
-                                return block.parent.resolve_path_fp_with_macro(
+                                return block.parent.def_map(db).resolve_path_fp_with_macro(
                                     db,
                                     mode,
-                                    block.parent_module,
+                                    block.parent.local_id,
                                     &new_path,
                                     shadow,
                                 );
@@ -256,10 +258,10 @@ impl DefMap {
             curr_per_ns = match curr {
                 ModuleDefId::ModuleId(module) => {
                     if module.krate != self.krate {
-                        let path = ModPath {
-                            segments: path.segments[i..].to_vec(),
-                            kind: PathKind::Super(0),
-                        };
+                        let path = ModPath::from_segments(
+                            PathKind::Super(0),
+                            path.segments()[i..].iter().cloned(),
+                        );
                         log::debug!("resolving {:?} in other crate", path);
                         let defp_map = module.def_map(db);
                         let (def, s) = defp_map.resolve_path(db, module.local_id, &path, shadow);
diff --git a/crates/hir_def/src/nameres/tests.rs b/crates/hir_def/src/nameres/tests.rs
index b36d0b59b..bd3e2701b 100644
--- a/crates/hir_def/src/nameres/tests.rs
+++ b/crates/hir_def/src/nameres/tests.rs
@@ -4,16 +4,16 @@ mod macros;
 mod mod_resolution;
 mod diagnostics;
 mod primitives;
-mod block;
 
 use std::sync::Arc;
 
-use base_db::{fixture::WithFixture, FilePosition, SourceDatabase};
+use base_db::{fixture::WithFixture, SourceDatabase};
 use expect_test::{expect, Expect};
-use syntax::AstNode;
 use test_utils::mark;
 
-use crate::{db::DefDatabase, nameres::*, test_db::TestDB, Lookup};
+use crate::{db::DefDatabase, test_db::TestDB};
+
+use super::DefMap;
 
 fn compute_crate_def_map(ra_fixture: &str) -> Arc<DefMap> {
     let db = TestDB::with_files(ra_fixture);
@@ -21,71 +21,14 @@ fn compute_crate_def_map(ra_fixture: &str) -> Arc<DefMap> {
     db.crate_def_map(krate)
 }
 
-fn compute_block_def_map(ra_fixture: &str) -> Arc<DefMap> {
-    let (db, position) = TestDB::with_position(ra_fixture);
-
-    // FIXME: perhaps we should make this use body lowering tests instead?
-
-    let module = db.module_for_file(position.file_id);
-    let mut def_map = db.crate_def_map(module.krate);
-    while let Some(new_def_map) = descend_def_map_at_position(&db, position, def_map.clone()) {
-        def_map = new_def_map;
-    }
-
-    // FIXME: select the right module, not the root
-
-    def_map
-}
-
-fn descend_def_map_at_position(
-    db: &dyn DefDatabase,
-    position: FilePosition,
-    def_map: Arc<DefMap>,
-) -> Option<Arc<DefMap>> {
-    for (local_id, module_data) in def_map.modules() {
-        let mod_def = module_data.origin.definition_source(db);
-        let ast_map = db.ast_id_map(mod_def.file_id);
-        let item_tree = db.item_tree(mod_def.file_id);
-        let root = db.parse_or_expand(mod_def.file_id).unwrap();
-        for item in module_data.scope.declarations() {
-            match item {
-                ModuleDefId::FunctionId(it) => {
-                    // Technically blocks can be inside any type (due to arrays and const generics),
-                    // and also in const/static initializers. For tests we only really care about
-                    // functions though.
-
-                    let ast = ast_map.get(item_tree[it.lookup(db).id.value].ast_id).to_node(&root);
-
-                    if ast.syntax().text_range().contains(position.offset) {
-                        // Cursor inside function, descend into its body's DefMap.
-                        // Note that we don't handle block *expressions* inside function bodies.
-                        let ast_map = db.ast_id_map(position.file_id.into());
-                        let ast_id = ast_map.ast_id(&ast.body().unwrap());
-                        let block = BlockLoc {
-                            ast_id: InFile::new(position.file_id.into(), ast_id),
-                            module: def_map.module_id(local_id),
-                        };
-                        let block_id = db.intern_block(block);
-                        return Some(db.block_def_map(block_id));
-                    }
-                }
-                _ => continue,
-            }
-        }
-    }
-
-    None
+fn render_crate_def_map(ra_fixture: &str) -> String {
+    let db = TestDB::with_files(ra_fixture);
+    let krate = db.crate_graph().iter().next().unwrap();
+    db.crate_def_map(krate).dump(&db)
 }
 
 fn check(ra_fixture: &str, expect: Expect) {
-    let def_map = compute_crate_def_map(ra_fixture);
-    let actual = def_map.dump();
-    expect.assert_eq(&actual);
-}
-
-fn check_at(ra_fixture: &str, expect: Expect) {
-    let def_map = compute_block_def_map(ra_fixture);
-    let actual = def_map.dump();
+    let actual = render_crate_def_map(ra_fixture);
     expect.assert_eq(&actual);
 }
 
diff --git a/crates/hir_def/src/path.rs b/crates/hir_def/src/path.rs
index 84ea09b53..0e60dc2b6 100644
--- a/crates/hir_def/src/path.rs
+++ b/crates/hir_def/src/path.rs
@@ -20,7 +20,7 @@ use crate::{
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct ModPath {
     pub kind: PathKind,
-    pub segments: Vec<Name>,
+    segments: Vec<Name>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -53,6 +53,11 @@ impl ModPath {
         ModPath { kind, segments }
     }
 
+    /// Creates a `ModPath` from a `PathKind`, with no extra path segments.
+    pub const fn from_kind(kind: PathKind) -> ModPath {
+        ModPath { kind, segments: Vec::new() }
+    }
+
     /// Calls `cb` with all paths, represented by this use item.
     pub(crate) fn expand_use_item(
         item_src: InFile<ast::Use>,
@@ -64,6 +69,18 @@ impl ModPath {
         }
     }
 
+    pub fn segments(&self) -> &[Name] {
+        &self.segments
+    }
+
+    pub fn push_segment(&mut self, segment: Name) {
+        self.segments.push(segment);
+    }
+
+    pub fn pop_segment(&mut self) -> Option<Name> {
+        self.segments.pop()
+    }
+
     /// Returns the number of segments in the path (counting special segments like `$crate` and
     /// `super`).
     pub fn len(&self) -> usize {
@@ -78,7 +95,7 @@ impl ModPath {
     }
 
     pub fn is_ident(&self) -> bool {
-        self.kind == PathKind::Plain && self.segments.len() == 1
+        self.as_ident().is_some()
     }
 
     pub fn is_self(&self) -> bool {
@@ -87,10 +104,14 @@ impl ModPath {
 
     /// If this path is a single identifier, like `foo`, return its name.
     pub fn as_ident(&self) -> Option<&Name> {
-        if !self.is_ident() {
+        if self.kind != PathKind::Plain {
             return None;
         }
-        self.segments.first()
+
+        match &*self.segments {
+            [name] => Some(name),
+            _ => None,
+        }
     }
 }
 
@@ -180,10 +201,10 @@ impl Path {
         }
         let res = Path {
             type_anchor: self.type_anchor.clone(),
-            mod_path: ModPath {
-                kind: self.mod_path.kind.clone(),
-                segments: self.mod_path.segments[..self.mod_path.segments.len() - 1].to_vec(),
-            },
+            mod_path: ModPath::from_segments(
+                self.mod_path.kind.clone(),
+                self.mod_path.segments[..self.mod_path.segments.len() - 1].iter().cloned(),
+            ),
             generic_args: self.generic_args[..self.generic_args.len() - 1].to_vec(),
         };
         Some(res)
diff --git a/crates/hir_def/src/path/lower.rs b/crates/hir_def/src/path/lower.rs
index 9518ac109..a469546c1 100644
--- a/crates/hir_def/src/path/lower.rs
+++ b/crates/hir_def/src/path/lower.rs
@@ -129,7 +129,7 @@ pub(super) fn lower_path(mut path: ast::Path, hygiene: &Hygiene) -> Option<Path>
         }
     }
 
-    let mod_path = ModPath { kind, segments };
+    let mod_path = ModPath::from_segments(kind, segments);
     return Some(Path { type_anchor, mod_path, generic_args });
 
     fn qualifier(path: &ast::Path) -> Option<ast::Path> {
diff --git a/crates/hir_def/src/path/lower/lower_use.rs b/crates/hir_def/src/path/lower/lower_use.rs
index ba0d1f0e7..d584b0b70 100644
--- a/crates/hir_def/src/path/lower/lower_use.rs
+++ b/crates/hir_def/src/path/lower/lower_use.rs
@@ -75,9 +75,10 @@ fn convert_path(prefix: Option<ModPath>, path: ast::Path, hygiene: &Hygiene) ->
             match hygiene.name_ref_to_name(name_ref) {
                 Either::Left(name) => {
                     // no type args in use
-                    let mut res = prefix.unwrap_or_else(|| ModPath {
-                        kind: segment.coloncolon_token().map_or(PathKind::Plain, |_| PathKind::Abs),
-                        segments: Vec::with_capacity(1),
+                    let mut res = prefix.unwrap_or_else(|| {
+                        ModPath::from_kind(
+                            segment.coloncolon_token().map_or(PathKind::Plain, |_| PathKind::Abs),
+                        )
                     });
                     res.segments.push(name);
                     res
diff --git a/crates/hir_def/src/resolver.rs b/crates/hir_def/src/resolver.rs
index 9021ea712..f9ad50301 100644
--- a/crates/hir_def/src/resolver.rs
+++ b/crates/hir_def/src/resolver.rs
@@ -164,7 +164,7 @@ impl Resolver {
         db: &dyn DefDatabase,
         path: &ModPath,
     ) -> Option<(TypeNs, Option<usize>)> {
-        let first_name = path.segments.first()?;
+        let first_name = path.segments().first()?;
         let skip_to_mod = path.kind != PathKind::Plain;
         for scope in self.scopes.iter().rev() {
             match scope {
@@ -179,7 +179,7 @@ impl Resolver {
 
                 Scope::GenericParams { params, def } => {
                     if let Some(local_id) = params.find_type_by_name(first_name) {
-                        let idx = if path.segments.len() == 1 { None } else { Some(1) };
+                        let idx = if path.segments().len() == 1 { None } else { Some(1) };
                         return Some((
                             TypeNs::GenericParam(TypeParamId { local_id, parent: *def }),
                             idx,
@@ -188,13 +188,13 @@ impl Resolver {
                 }
                 Scope::ImplDefScope(impl_) => {
                     if first_name == &name![Self] {
-                        let idx = if path.segments.len() == 1 { None } else { Some(1) };
+                        let idx = if path.segments().len() == 1 { None } else { Some(1) };
                         return Some((TypeNs::SelfType(*impl_), idx));
                     }
                 }
                 Scope::AdtScope(adt) => {
                     if first_name == &name![Self] {
-                        let idx = if path.segments.len() == 1 { None } else { Some(1) };
+                        let idx = if path.segments().len() == 1 { None } else { Some(1) };
                         return Some((TypeNs::AdtSelfType(*adt), idx));
                     }
                 }
@@ -270,9 +270,9 @@ impl Resolver {
         db: &dyn DefDatabase,
         path: &ModPath,
     ) -> Option<ResolveValueResult> {
-        let n_segments = path.segments.len();
+        let n_segments = path.segments().len();
         let tmp = name![self];
-        let first_name = if path.is_self() { &tmp } else { path.segments.first()? };
+        let first_name = if path.is_self() { &tmp } else { path.segments().first()? };
         let skip_to_mod = path.kind != PathKind::Plain && !path.is_self();
         for scope in self.scopes.iter().rev() {
             match scope {
diff --git a/crates/hir_def/src/visibility.rs b/crates/hir_def/src/visibility.rs
index e79a91102..38da3132b 100644
--- a/crates/hir_def/src/visibility.rs
+++ b/crates/hir_def/src/visibility.rs
@@ -22,8 +22,7 @@ pub enum RawVisibility {
 
 impl RawVisibility {
     pub(crate) const fn private() -> RawVisibility {
-        let path = ModPath { kind: PathKind::Super(0), segments: Vec::new() };
-        RawVisibility::Module(path)
+        RawVisibility::Module(ModPath::from_kind(PathKind::Super(0)))
     }
 
     pub(crate) fn from_ast(
@@ -59,15 +58,15 @@ impl RawVisibility {
                 RawVisibility::Module(path)
             }
             ast::VisibilityKind::PubCrate => {
-                let path = ModPath { kind: PathKind::Crate, segments: Vec::new() };
+                let path = ModPath::from_kind(PathKind::Crate);
                 RawVisibility::Module(path)
             }
             ast::VisibilityKind::PubSuper => {
-                let path = ModPath { kind: PathKind::Super(1), segments: Vec::new() };
+                let path = ModPath::from_kind(PathKind::Super(1));
                 RawVisibility::Module(path)
             }
             ast::VisibilityKind::PubSelf => {
-                let path = ModPath { kind: PathKind::Plain, segments: Vec::new() };
+                let path = ModPath::from_kind(PathKind::Plain);
                 RawVisibility::Module(path)
             }
             ast::VisibilityKind::Pub => RawVisibility::Public,