176 files changed, 5306 insertions, 2876 deletions

diff --git a/Cargo.lock b/Cargo.lock
index b36bca0ab..e40c12a92 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -37,9 +37,9 @@ dependencies = [
 
 [[package]]
 name = "anyhow"
-version = "1.0.39"
+version = "1.0.40"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "81cddc5f91628367664cc7c69714ff08deee8a3efc54623011c772544d7b2767"
+checksum = "28b2cd92db5cbd74e8e5028f7e27dd7aa3090e89e4f2a197cc7c8dfb69c7063b"
 
 [[package]]
 name = "anymap"
@@ -49,9 +49,9 @@ checksum = "33954243bd79057c2de7338850b85983a44588021f8a5fee574a8888c6de4344"
 
 [[package]]
 name = "arrayvec"
-version = "0.6.0"
+version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "682f88bd1270f264991da8922b89ee1fb520b0da73f97c9f73cda54980123017"
+checksum = "5a2f58b0bb10c380af2b26e57212856b8c9a59e0925b4c20f4a174a49734eaf7"
 
 [[package]]
 name = "atty"
@@ -500,6 +500,7 @@ dependencies = [
  "base_db",
  "cfg",
  "cov-mark",
+ "dashmap",
  "drop_bomb",
  "either",
  "expect-test",
@@ -796,9 +797,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.91"
+version = "0.2.92"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8916b1f6ca17130ec6568feccee27c156ad12037880833a3b842a823236502e7"
+checksum = "56d855069fafbb9b344c0f962150cd2c1187975cb1c22c1522c240d8c4986714"
 
 [[package]]
 name = "libloading"
@@ -821,9 +822,9 @@ dependencies = [
 
 [[package]]
 name = "lock_api"
-version = "0.4.2"
+version = "0.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dd96ffd135b2fd7b973ac026d28085defbe8983df057ced3eb4f2130b0831312"
+checksum = "5a3c91c24eae6777794bb1997ad98bbb87daf92890acab859f7eaa4320333176"
 dependencies = [
  "scopeguard",
 ]
@@ -920,9 +921,9 @@ dependencies = [
 
 [[package]]
 name = "memoffset"
-version = "0.6.1"
+version = "0.6.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "157b4208e3059a8f9e78d559edc658e13df41410cb3ae03979c83130067fdd87"
+checksum = "f83fb6581e8ed1f85fd45c116db8405483899489e38406156c25eb743554361d"
 dependencies = [
  "autocfg",
 ]
@@ -1156,9 +1157,9 @@ checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.24"
+version = "1.0.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+checksum = "a152013215dca273577e18d2bf00fa862b89b24169fb78c4c95aeb07992c9cec"
 dependencies = [
  "unicode-xid",
 ]
@@ -1576,9 +1577,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "1.0.64"
+version = "1.0.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3fd9d1e9976102a03c542daa2eff1b43f9d72306342f3f8b3ed5fb8908195d6f"
+checksum = "3ce15dd3ed8aa2f8eeac4716d6ef5ab58b6b9256db41d7e1a0224c2788e8fd87"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/README.md b/README.md
index 74f944ae4..085c8c0f6 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
     alt="rust-analyzer logo">
 </p>
 
-rust-analyzer is an **experimental** modular compiler frontend for the Rust language.
+rust-analyzer is a modular compiler frontend for the Rust language.
 It is a part of a larger rls-2.0 effort to create excellent IDE support for Rust.
 
 Work on rust-analyzer is sponsored by
diff --git a/crates/base_db/src/lib.rs b/crates/base_db/src/lib.rs
index 5f77a0b1f..980a0ed98 100644
--- a/crates/base_db/src/lib.rs
+++ b/crates/base_db/src/lib.rs
@@ -59,6 +59,8 @@ pub trait CheckCanceled {
         Self: Sized + panic::RefUnwindSafe,
         F: FnOnce(&Self) -> T + panic::UnwindSafe,
     {
+        // Uncomment to debug missing cancellations.
+        // let _span = profile::heartbeat_span();
         panic::catch_unwind(|| f(self)).map_err(|err| match err.downcast::<Canceled>() {
             Ok(canceled) => *canceled,
             Err(payload) => panic::resume_unwind(payload),
@@ -68,6 +70,7 @@ pub trait CheckCanceled {
 
 impl<T: salsa::Database> CheckCanceled for T {
     fn check_canceled(&self) {
+        // profile::heartbeat();
         if self.salsa_runtime().is_current_revision_canceled() {
             Canceled::throw()
         }
diff --git a/crates/cfg/src/tests.rs b/crates/cfg/src/tests.rs
index bd0f9ec48..d8736c893 100644
--- a/crates/cfg/src/tests.rs
+++ b/crates/cfg/src/tests.rs
@@ -8,7 +8,7 @@ fn assert_parse_result(input: &str, expected: CfgExpr) {
     let (tt, _) = {
         let source_file = ast::SourceFile::parse(input).ok().unwrap();
         let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
-        ast_to_token_tree(&tt).unwrap()
+        ast_to_token_tree(&tt)
     };
     let cfg = CfgExpr::parse(&tt);
     assert_eq!(cfg, expected);
@@ -18,7 +18,7 @@ fn check_dnf(input: &str, expect: Expect) {
     let (tt, _) = {
         let source_file = ast::SourceFile::parse(input).ok().unwrap();
         let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
-        ast_to_token_tree(&tt).unwrap()
+        ast_to_token_tree(&tt)
     };
     let cfg = CfgExpr::parse(&tt);
     let actual = format!("#![cfg({})]", DnfExpr::new(cfg));
@@ -29,7 +29,7 @@ fn check_why_inactive(input: &str, opts: &CfgOptions, expect: Expect) {
     let (tt, _) = {
         let source_file = ast::SourceFile::parse(input).ok().unwrap();
         let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
-        ast_to_token_tree(&tt).unwrap()
+        ast_to_token_tree(&tt)
     };
     let cfg = CfgExpr::parse(&tt);
     let dnf = DnfExpr::new(cfg);
@@ -42,7 +42,7 @@ fn check_enable_hints(input: &str, opts: &CfgOptions, expected_hints: &[&str]) {
     let (tt, _) = {
         let source_file = ast::SourceFile::parse(input).ok().unwrap();
         let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
-        ast_to_token_tree(&tt).unwrap()
+        ast_to_token_tree(&tt)
     };
     let cfg = CfgExpr::parse(&tt);
     let dnf = DnfExpr::new(cfg);
diff --git a/crates/hir/Cargo.toml b/crates/hir/Cargo.toml
index 2ef5bcbc9..9e329656f 100644
--- a/crates/hir/Cargo.toml
+++ b/crates/hir/Cargo.toml
@@ -13,7 +13,7 @@ doctest = false
 log = "0.4.8"
 rustc-hash = "1.1.0"
 either = "1.5.3"
-arrayvec = "0.6"
+arrayvec = "0.7"
 itertools = "0.10.0"
 smallvec = "1.4.0"
 
diff --git a/crates/hir/src/db.rs b/crates/hir/src/db.rs
index 1902a8d16..df5758342 100644
--- a/crates/hir/src/db.rs
+++ b/crates/hir/src/db.rs
@@ -1,14 +1,6 @@
 //! FIXME: write short doc here
 
-pub use hir_def::db::{
-    AttrsQuery, BlockDefMapQuery, BodyQuery, BodyWithSourceMapQuery, ConstDataQuery,
-    CrateDefMapQueryQuery, CrateLangItemsQuery, DefDatabase, DefDatabaseStorage, EnumDataQuery,
-    ExprScopesQuery, FileItemTreeQuery, FunctionDataQuery, GenericParamsQuery, ImplDataQuery,
-    ImportMapQuery, InternConstQuery, InternDatabase, InternDatabaseStorage, InternEnumQuery,
-    InternFunctionQuery, InternImplQuery, InternStaticQuery, InternStructQuery, InternTraitQuery,
-    InternTypeAliasQuery, InternUnionQuery, LangItemQuery, StaticDataQuery, StructDataQuery,
-    TraitDataQuery, TypeAliasDataQuery, UnionDataQuery,
-};
+pub use hir_def::db::*;
 pub use hir_expand::db::{
     AstDatabase, AstDatabaseStorage, AstIdMapQuery, HygieneFrameQuery, InternEagerExpansionQuery,
     InternMacroQuery, MacroArgTextQuery, MacroDefQuery, MacroExpandQuery, ParseMacroExpansionQuery,
diff --git a/crates/hir/src/display.rs b/crates/hir/src/display.rs
index 97a78ca25..01a4d205f 100644
--- a/crates/hir/src/display.rs
+++ b/crates/hir/src/display.rs
@@ -9,33 +9,33 @@ use hir_ty::display::{
     write_bounds_like_dyn_trait_with_prefix, write_visibility, HirDisplay, HirDisplayError,
     HirFormatter,
 };
+use hir_ty::Interner;
 use syntax::ast::{self, NameOwner};
 
 use crate::{
     Adt, Const, ConstParam, Enum, Field, Function, GenericParam, HasVisibility, LifetimeParam,
-    Module, Static, Struct, Substitution, Trait, Type, TypeAlias, TypeParam, Union, Variant,
+    Module, Static, Struct, Trait, TyBuilder, Type, TypeAlias, TypeParam, Union, Variant,
 };
 
 impl HirDisplay for Function {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         let data = f.db.function_data(self.id);
         write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
-        let qual = &data.qualifier;
-        if qual.is_default {
+        if data.is_default() {
             write!(f, "default ")?;
         }
-        if qual.is_const {
+        if data.is_const() {
             write!(f, "const ")?;
         }
-        if qual.is_async {
+        if data.is_async() {
             write!(f, "async ")?;
         }
-        if qual.is_unsafe {
+        if data.is_unsafe() {
             write!(f, "unsafe ")?;
         }
-        if let Some(abi) = &qual.abi {
+        if let Some(abi) = &data.abi {
             // FIXME: String escape?
-            write!(f, "extern \"{}\" ", abi)?;
+            write!(f, "extern \"{}\" ", &**abi)?;
         }
         write!(f, "fn {}", data.name)?;
 
@@ -68,7 +68,7 @@ impl HirDisplay for Function {
                 write!(f, ", ")?;
             } else {
                 first = false;
-                if data.has_self_param {
+                if data.has_self_param() {
                     write_self_param(type_ref, f)?;
                     continue;
                 }
@@ -88,10 +88,10 @@ impl HirDisplay for Function {
         // `FunctionData::ret_type` will be `::core::future::Future<Output = ...>` for async fns.
         // Use ugly pattern match to strip the Future trait.
         // Better way?
-        let ret_type = if !qual.is_async {
+        let ret_type = if !data.is_async() {
             &data.ret_type
         } else {
-            match &data.ret_type {
+            match &*data.ret_type {
                 TypeRef::ImplTrait(bounds) => match &bounds[0] {
                     TypeBound::Path(path) => {
                         path.segments().iter().last().unwrap().args_and_bindings.unwrap().bindings
@@ -235,8 +235,9 @@ impl HirDisplay for TypeParam {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         write!(f, "{}", self.name(f.db))?;
         let bounds = f.db.generic_predicates_for_param(self.id);
-        let substs = Substitution::type_params(f.db, self.id.parent);
-        let predicates = bounds.iter().cloned().map(|b| b.subst(&substs)).collect::<Vec<_>>();
+        let substs = TyBuilder::type_params_subst(f.db, self.id.parent);
+        let predicates =
+            bounds.iter().cloned().map(|b| b.substitute(&Interner, &substs)).collect::<Vec<_>>();
         if !(predicates.is_empty() || f.omit_verbose_types()) {
             write_bounds_like_dyn_trait_with_prefix(":", &predicates, f)?;
         }
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 4ee08ef21..003821981 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -44,6 +44,7 @@ use hir_def::{
     per_ns::PerNs,
     resolver::{HasResolver, Resolver},
     src::HasSource as _,
+    type_ref::TraitRef,
     AdtId, AssocContainerId, AssocItemId, AssocItemLoc, AttrDefId, ConstId, ConstParamId,
     DefWithBodyId, EnumId, FunctionId, GenericDefId, HasModule, ImplId, LifetimeParamId,
     LocalEnumVariantId, LocalFieldId, Lookup, ModuleId, StaticId, StructId, TraitId, TypeAliasId,
@@ -54,11 +55,11 @@ use hir_ty::{
     autoderef, could_unify,
     method_resolution::{self, TyFingerprint},
     primitive::UintTy,
-    to_assoc_type_id,
-    traits::{FnTrait, Solution, SolutionVariables},
+    traits::FnTrait,
     AliasEq, AliasTy, BoundVar, CallableDefId, CallableSig, Canonical, CanonicalVarKinds, Cast,
-    DebruijnIndex, InEnvironment, Interner, ProjectionTy, QuantifiedWhereClause, Scalar,
-    Substitution, TraitEnvironment, Ty, TyDefId, TyKind, TyVariableKind, WhereClause,
+    DebruijnIndex, InEnvironment, Interner, QuantifiedWhereClause, Scalar, Solution,
+    SolutionVariables, Substitution, TraitEnvironment, Ty, TyBuilder, TyDefId, TyKind,
+    TyVariableKind, WhereClause,
 };
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
@@ -514,8 +515,8 @@ impl Field {
             VariantDef::Union(it) => it.id.into(),
             VariantDef::Variant(it) => it.parent.id.into(),
         };
-        let substs = Substitution::type_params(db, generic_def_id);
-        let ty = db.field_types(var_id)[self.id].clone().subst(&substs);
+        let substs = TyBuilder::type_params_subst(db, generic_def_id);
+        let ty = db.field_types(var_id)[self.id].clone().substitute(&Interner, &substs);
         Type::new(db, self.parent.module(db).id.krate(), var_id, ty)
     }
 
@@ -701,7 +702,7 @@ impl_from!(Struct, Union, Enum for Adt);
 impl Adt {
     pub fn has_non_default_type_params(self, db: &dyn HirDatabase) -> bool {
         let subst = db.generic_defaults(self.into());
-        subst.iter().any(|ty| ty.value.is_unknown())
+        subst.iter().any(|ty| ty.skip_binders().is_unknown())
     }
 
     /// Turns this ADT into a type. Any type parameters of the ADT will be
@@ -831,7 +832,7 @@ impl Function {
     }
 
     pub fn self_param(self, db: &dyn HirDatabase) -> Option<SelfParam> {
-        if !db.function_data(self.id).has_self_param {
+        if !db.function_data(self.id).has_self_param() {
             return None;
         }
         Some(SelfParam { func: self.id })
@@ -863,7 +864,7 @@ impl Function {
     }
 
     pub fn is_unsafe(self, db: &dyn HirDatabase) -> bool {
-        db.function_data(self.id).qualifier.is_unsafe
+        db.function_data(self.id).is_unsafe()
     }
 
     pub fn diagnostics(self, db: &dyn HirDatabase, sink: &mut DiagnosticSink) {
@@ -877,7 +878,7 @@ impl Function {
     ///
     /// This is false in the case of required (not provided) trait methods.
     pub fn has_body(self, db: &dyn HirDatabase) -> bool {
-        db.function_data(self.id).has_body
+        db.function_data(self.id).has_body()
     }
 
     /// A textual representation of the HIR of this function for debugging purposes.
@@ -956,7 +957,7 @@ impl SelfParam {
         func_data
             .params
             .first()
-            .map(|param| match *param {
+            .map(|param| match &**param {
                 TypeRef::Reference(.., mutability) => match mutability {
                     hir_def::type_ref::Mutability::Shared => Access::Shared,
                     hir_def::type_ref::Mutability::Mut => Access::Exclusive,
@@ -1010,7 +1011,7 @@ impl Const {
     }
 
     pub fn type_ref(self, db: &dyn HirDatabase) -> TypeRef {
-        db.const_data(self.id).type_ref.clone()
+        db.const_data(self.id).type_ref.as_ref().clone()
     }
 }
 
@@ -1088,7 +1089,7 @@ pub struct TypeAlias {
 impl TypeAlias {
     pub fn has_non_default_type_params(self, db: &dyn HirDatabase) -> bool {
         let subst = db.generic_defaults(self.id.into());
-        subst.iter().any(|ty| ty.value.is_unknown())
+        subst.iter().any(|ty| ty.skip_binders().is_unknown())
     }
 
     pub fn module(self, db: &dyn HirDatabase) -> Module {
@@ -1100,7 +1101,7 @@ impl TypeAlias {
     }
 
     pub fn type_ref(self, db: &dyn HirDatabase) -> Option<TypeRef> {
-        db.type_alias_data(self.id).type_ref.clone()
+        db.type_alias_data(self.id).type_ref.as_deref().cloned()
     }
 
     pub fn ty(self, db: &dyn HirDatabase) -> Type {
@@ -1128,7 +1129,7 @@ pub struct BuiltinType {
 impl BuiltinType {
     pub fn ty(self, db: &dyn HirDatabase, module: Module) -> Type {
         let resolver = module.id.resolver(db.upcast());
-        Type::new_with_resolver(db, &resolver, Ty::builtin(self.inner))
+        Type::new_with_resolver(db, &resolver, TyBuilder::builtin(self.inner))
             .expect("crate not present in resolver")
     }
 
@@ -1501,8 +1502,8 @@ impl TypeParam {
         let resolver = self.id.parent.resolver(db.upcast());
         let krate = self.id.parent.module(db.upcast()).krate();
         let ty = params.get(local_idx)?.clone();
-        let subst = Substitution::type_params(db, self.id.parent);
-        let ty = ty.subst(&subst.prefix(local_idx));
+        let subst = TyBuilder::type_params_subst(db, self.id.parent);
+        let ty = ty.substitute(&Interner, &subst.prefix(local_idx));
         Some(Type::new_with_resolver_inner(db, krate, &resolver, ty))
     }
 }
@@ -1573,9 +1574,9 @@ impl Impl {
         };
 
         let filter = |impl_def: &Impl| {
-            let target_ty = impl_def.target_ty(db);
-            let rref = target_ty.remove_ref();
-            ty.equals_ctor(rref.as_ref().map_or(&target_ty.ty, |it| &it.ty))
+            let self_ty = impl_def.self_ty(db);
+            let rref = self_ty.remove_ref();
+            ty.equals_ctor(rref.as_ref().map_or(&self_ty.ty, |it| &it.ty))
         };
 
         let mut all = Vec::new();
@@ -1613,16 +1614,16 @@ impl Impl {
 
     // FIXME: the return type is wrong. This should be a hir version of
     // `TraitRef` (ie, resolved `TypeRef`).
-    pub fn target_trait(self, db: &dyn HirDatabase) -> Option<TypeRef> {
-        db.impl_data(self.id).target_trait.clone()
+    pub fn trait_(self, db: &dyn HirDatabase) -> Option<TraitRef> {
+        db.impl_data(self.id).target_trait.as_deref().cloned()
     }
 
-    pub fn target_ty(self, db: &dyn HirDatabase) -> Type {
+    pub fn self_ty(self, db: &dyn HirDatabase) -> Type {
         let impl_data = db.impl_data(self.id);
         let resolver = self.id.resolver(db.upcast());
         let krate = self.id.lookup(db.upcast()).container.krate();
         let ctx = hir_ty::TyLoweringContext::new(db, &resolver);
-        let ty = ctx.lower_ty(&impl_data.target_type);
+        let ty = ctx.lower_ty(&impl_data.self_ty);
         Type::new_with_resolver_inner(db, krate, &resolver, ty)
     }
 
@@ -1702,30 +1703,29 @@ impl Type {
     fn from_def(
         db: &dyn HirDatabase,
         krate: CrateId,
-        def: impl HasResolver + Into<TyDefId> + Into<GenericDefId>,
+        def: impl HasResolver + Into<TyDefId>,
     ) -> Type {
-        let substs = Substitution::build_for_def(db, def).fill_with_unknown().build();
-        let ty = db.ty(def.into()).subst(&substs);
+        let ty = TyBuilder::def_ty(db, def.into()).fill_with_unknown().build();
         Type::new(db, krate, def, ty)
     }
 
     pub fn is_unit(&self) -> bool {
-        matches!(self.ty.interned(&Interner), TyKind::Tuple(0, ..))
+        matches!(self.ty.kind(&Interner), TyKind::Tuple(0, ..))
     }
     pub fn is_bool(&self) -> bool {
-        matches!(self.ty.interned(&Interner), TyKind::Scalar(Scalar::Bool))
+        matches!(self.ty.kind(&Interner), TyKind::Scalar(Scalar::Bool))
     }
 
     pub fn is_mutable_reference(&self) -> bool {
-        matches!(self.ty.interned(&Interner), TyKind::Ref(hir_ty::Mutability::Mut, ..))
+        matches!(self.ty.kind(&Interner), TyKind::Ref(hir_ty::Mutability::Mut, ..))
     }
 
     pub fn is_usize(&self) -> bool {
-        matches!(self.ty.interned(&Interner), TyKind::Scalar(Scalar::Uint(UintTy::Usize)))
+        matches!(self.ty.kind(&Interner), TyKind::Scalar(Scalar::Uint(UintTy::Usize)))
     }
 
     pub fn remove_ref(&self) -> Option<Type> {
-        match &self.ty.interned(&Interner) {
+        match &self.ty.kind(&Interner) {
             TyKind::Ref(.., ty) => Some(self.derived(ty.clone())),
             _ => None,
         }
@@ -1784,13 +1784,10 @@ impl Type {
     }
 
     pub fn impls_trait(&self, db: &dyn HirDatabase, trait_: Trait, args: &[Type]) -> bool {
-        let trait_ref = hir_ty::TraitRef {
-            trait_id: hir_ty::to_chalk_trait_id(trait_.id),
-            substitution: Substitution::build_for_def(db, trait_.id)
-                .push(self.ty.clone())
-                .fill(args.iter().map(|t| t.ty.clone()))
-                .build(),
-        };
+        let trait_ref = TyBuilder::trait_ref(db, trait_.id)
+            .push(self.ty.clone())
+            .fill(args.iter().map(|t| t.ty.clone()))
+            .build();
 
         let goal = Canonical {
             value: hir_ty::InEnvironment::new(self.env.env.clone(), trait_ref.cast(&Interner)),
@@ -1803,11 +1800,10 @@ impl Type {
     pub fn normalize_trait_assoc_type(
         &self,
         db: &dyn HirDatabase,
-        trait_: Trait,
         args: &[Type],
         alias: TypeAlias,
     ) -> Option<Type> {
-        let subst = Substitution::build_for_def(db, trait_.id)
+        let projection = TyBuilder::assoc_type_projection(db, alias.id)
             .push(self.ty.clone())
             .fill(args.iter().map(|t| t.ty.clone()))
             .build();
@@ -1815,10 +1811,7 @@ impl Type {
             InEnvironment::new(
                 self.env.env.clone(),
                 AliasEq {
-                    alias: AliasTy::Projection(ProjectionTy {
-                        associated_ty_id: to_assoc_type_id(alias.id),
-                        substitution: subst,
-                    }),
+                    alias: AliasTy::Projection(projection),
                     ty: TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
                         .intern(&Interner),
                 }
@@ -1828,9 +1821,11 @@ impl Type {
         );
 
         match db.trait_solve(self.krate, goal)? {
-            Solution::Unique(SolutionVariables(subst)) => {
-                subst.value.first().map(|ty| self.derived(ty.clone()))
-            }
+            Solution::Unique(SolutionVariables(subst)) => subst
+                .value
+                .interned()
+                .first()
+                .map(|ty| self.derived(ty.assert_ty_ref(&Interner).clone())),
             Solution::Ambig(_) => None,
         }
     }
@@ -1852,15 +1847,15 @@ impl Type {
     }
 
     pub fn is_closure(&self) -> bool {
-        matches!(&self.ty.interned(&Interner), TyKind::Closure { .. })
+        matches!(&self.ty.kind(&Interner), TyKind::Closure { .. })
     }
 
     pub fn is_fn(&self) -> bool {
-        matches!(&self.ty.interned(&Interner), TyKind::FnDef(..) | TyKind::Function { .. })
+        matches!(&self.ty.kind(&Interner), TyKind::FnDef(..) | TyKind::Function { .. })
     }
 
     pub fn is_packed(&self, db: &dyn HirDatabase) -> bool {
-        let adt_id = match self.ty.interned(&Interner) {
+        let adt_id = match self.ty.kind(&Interner) {
             &TyKind::Adt(hir_ty::AdtId(adt_id), ..) => adt_id,
             _ => return false,
         };
@@ -1873,22 +1868,24 @@ impl Type {
     }
 
     pub fn is_raw_ptr(&self) -> bool {
-        matches!(&self.ty.interned(&Interner), TyKind::Raw(..))
+        matches!(&self.ty.kind(&Interner), TyKind::Raw(..))
     }
 
     pub fn contains_unknown(&self) -> bool {
         return go(&self.ty);
 
         fn go(ty: &Ty) -> bool {
-            match ty.interned(&Interner) {
-                TyKind::Unknown => true,
+            match ty.kind(&Interner) {
+                TyKind::Error => true,
 
                 TyKind::Adt(_, substs)
                 | TyKind::AssociatedType(_, substs)
                 | TyKind::Tuple(_, substs)
                 | TyKind::OpaqueType(_, substs)
                 | TyKind::FnDef(_, substs)
-                | TyKind::Closure(_, substs) => substs.iter().any(go),
+                | TyKind::Closure(_, substs) => {
+                    substs.iter(&Interner).filter_map(|a| a.ty(&Interner)).any(go)
+                }
 
                 TyKind::Array(ty) | TyKind::Slice(ty) | TyKind::Raw(_, ty) | TyKind::Ref(_, ty) => {
                     go(ty)
@@ -1903,13 +1900,13 @@ impl Type {
                 | TyKind::Dyn(_)
                 | TyKind::Function(_)
                 | TyKind::Alias(_)
-                | TyKind::ForeignType(_) => false,
+                | TyKind::Foreign(_) => false,
             }
         }
     }
 
     pub fn fields(&self, db: &dyn HirDatabase) -> Vec<(Field, Type)> {
-        let (variant_id, substs) = match self.ty.interned(&Interner) {
+        let (variant_id, substs) = match self.ty.kind(&Interner) {
             &TyKind::Adt(hir_ty::AdtId(AdtId::StructId(s)), ref substs) => (s.into(), substs),
             &TyKind::Adt(hir_ty::AdtId(AdtId::UnionId(u)), ref substs) => (u.into(), substs),
             _ => return Vec::new(),
@@ -1919,15 +1916,18 @@ impl Type {
             .iter()
             .map(|(local_id, ty)| {
                 let def = Field { parent: variant_id.into(), id: local_id };
-                let ty = ty.clone().subst(substs);
+                let ty = ty.clone().substitute(&Interner, substs);
                 (def, self.derived(ty))
             })
             .collect()
     }
 
     pub fn tuple_fields(&self, _db: &dyn HirDatabase) -> Vec<Type> {
-        if let TyKind::Tuple(_, substs) = &self.ty.interned(&Interner) {
-            substs.iter().map(|ty| self.derived(ty.clone())).collect()
+        if let TyKind::Tuple(_, substs) = &self.ty.kind(&Interner) {
+            substs
+                .iter(&Interner)
+                .map(|ty| self.derived(ty.assert_ty_ref(&Interner).clone()))
+                .collect()
         } else {
             Vec::new()
         }
@@ -1972,8 +1972,9 @@ impl Type {
             .strip_references()
             .substs()
             .into_iter()
-            .flat_map(|substs| substs.iter())
-            .map(move |ty| self.derived(ty.clone()))
+            .flat_map(|substs| substs.iter(&Interner))
+            .filter_map(|arg| arg.ty(&Interner).cloned())
+            .map(move |ty| self.derived(ty))
     }
 
     pub fn iterate_method_candidates<T>(
@@ -2079,7 +2080,7 @@ impl Type {
             substs: &Substitution,
             cb: &mut impl FnMut(Type),
         ) {
-            for ty in substs.iter() {
+            for ty in substs.iter(&Interner).filter_map(|a| a.ty(&Interner)) {
                 walk_type(db, &type_.derived(ty.clone()), cb);
             }
         }
@@ -2095,7 +2096,12 @@ impl Type {
                     WhereClause::Implemented(trait_ref) => {
                         cb(type_.clone());
                         // skip the self type. it's likely the type we just got the bounds from
-                        for ty in trait_ref.substitution.iter().skip(1) {
+                        for ty in trait_ref
+                            .substitution
+                            .iter(&Interner)
+                            .skip(1)
+                            .filter_map(|a| a.ty(&Interner))
+                        {
                             walk_type(db, &type_.derived(ty.clone()), cb);
                         }
                     }
@@ -2106,7 +2112,7 @@ impl Type {
 
         fn walk_type(db: &dyn HirDatabase, type_: &Type, cb: &mut impl FnMut(Type)) {
             let ty = type_.ty.strip_references();
-            match ty.interned(&Interner) {
+            match ty.kind(&Interner) {
                 TyKind::Adt(..) => {
                     cb(type_.derived(ty.clone()));
                 }
diff --git a/crates/hir/src/semantics.rs b/crates/hir/src/semantics.rs
index 3ff135f41..7955bf0b5 100644
--- a/crates/hir/src/semantics.rs
+++ b/crates/hir/src/semantics.rs
@@ -76,9 +76,11 @@ impl PathResolution {
     pub fn assoc_type_shorthand_candidates<R>(
         &self,
         db: &dyn HirDatabase,
-        mut cb: impl FnMut(TypeAlias) -> Option<R>,
+        mut cb: impl FnMut(&Name, TypeAlias) -> Option<R>,
     ) -> Option<R> {
-        associated_type_shorthand_candidates(db, self.in_type_ns()?, |_, _, id| cb(id.into()))
+        associated_type_shorthand_candidates(db, self.in_type_ns()?, |name, _, id| {
+            cb(name, id.into())
+        })
     }
 }
 
@@ -492,9 +494,9 @@ impl<'db> SemanticsImpl<'db> {
     fn resolve_method_call_as_callable(&self, call: &ast::MethodCallExpr) -> Option<Callable> {
         // FIXME: this erases Substs
         let func = self.resolve_method_call(call)?;
-        let ty = self.db.value_ty(func.into());
+        let (ty, _) = self.db.value_ty(func.into()).into_value_and_skipped_binders();
         let resolver = self.analyze(call.syntax()).resolver;
-        let ty = Type::new_with_resolver(self.db, &resolver, ty.value)?;
+        let ty = Type::new_with_resolver(self.db, &resolver, ty)?;
         let mut res = ty.as_callable(self.db)?;
         res.is_bound_method = true;
         Some(res)
@@ -768,7 +770,7 @@ to_def_impls![
     (crate::TypeParam, ast::TypeParam, type_param_to_def),
     (crate::LifetimeParam, ast::LifetimeParam, lifetime_param_to_def),
     (crate::ConstParam, ast::ConstParam, const_param_to_def),
-    (crate::MacroDef, ast::MacroRules, macro_rules_to_def),
+    (crate::MacroDef, ast::Macro, macro_to_def),
     (crate::Local, ast::IdentPat, bind_pat_to_def),
     (crate::Local, ast::SelfParam, self_param_to_def),
     (crate::Label, ast::Label, label_to_def),
diff --git a/crates/hir/src/semantics/source_to_def.rs b/crates/hir/src/semantics/source_to_def.rs
index 762809fcd..9a5a2255f 100644
--- a/crates/hir/src/semantics/source_to_def.rs
+++ b/crates/hir/src/semantics/source_to_def.rs
@@ -191,10 +191,7 @@ impl SourceToDefCtx<'_, '_> {
     }
 
     // FIXME: use DynMap as well?
-    pub(super) fn macro_rules_to_def(
-        &mut self,
-        src: InFile<ast::MacroRules>,
-    ) -> Option<MacroDefId> {
+    pub(super) fn macro_to_def(&mut self, src: InFile<ast::Macro>) -> Option<MacroDefId> {
         let file_ast_id = self.db.ast_id_map(src.file_id).ast_id(&src.value);
         let ast_id = AstId::new(src.file_id, file_ast_id.upcast());
         let kind = MacroDefKind::Declarative(ast_id);
diff --git a/crates/hir/src/source_analyzer.rs b/crates/hir/src/source_analyzer.rs
index 37d162b32..4ce1c2080 100644
--- a/crates/hir/src/source_analyzer.rs
+++ b/crates/hir/src/source_analyzer.rs
@@ -20,7 +20,7 @@ use hir_def::{
 use hir_expand::{hygiene::Hygiene, name::AsName, HirFileId, InFile};
 use hir_ty::{
     diagnostics::{record_literal_missing_fields, record_pattern_missing_fields},
-    InferenceResult, Substitution,
+    InferenceResult, Interner, Substitution, TyLoweringContext,
 };
 use syntax::{
     ast::{self, AstNode},
@@ -339,7 +339,7 @@ impl SourceAnalyzer {
             .into_iter()
             .map(|local_id| {
                 let field = FieldId { parent: variant, local_id };
-                let ty = field_types[local_id].clone().subst(substs);
+                let ty = field_types[local_id].clone().substitute(&Interner, substs);
                 (field.into(), Type::new_with_resolver_inner(db, krate, &self.resolver, ty))
             })
             .collect()
@@ -466,7 +466,21 @@ fn resolve_hir_path_(
     prefer_value_ns: bool,
 ) -> Option<PathResolution> {
     let types = || {
-        resolver.resolve_path_in_type_ns_fully(db.upcast(), path.mod_path()).map(|ty| match ty {
+        let (ty, unresolved) = match path.type_anchor() {
+            Some(type_ref) => {
+                let (_, res) = TyLoweringContext::new(db, resolver).lower_ty_ext(type_ref);
+                res.map(|ty_ns| (ty_ns, path.segments().first()))
+            }
+            None => {
+                let (ty, remaining) =
+                    resolver.resolve_path_in_type_ns(db.upcast(), path.mod_path())?;
+                match remaining {
+                    Some(remaining) if remaining > 1 => None,
+                    _ => Some((ty, path.segments().get(1))),
+                }
+            }
+        }?;
+        let res = match ty {
             TypeNs::SelfType(it) => PathResolution::SelfType(it.into()),
             TypeNs::GenericParam(id) => PathResolution::TypeParam(TypeParam { id }),
             TypeNs::AdtSelfType(it) | TypeNs::AdtId(it) => {
@@ -476,7 +490,17 @@ fn resolve_hir_path_(
             TypeNs::TypeAliasId(it) => PathResolution::Def(TypeAlias::from(it).into()),
             TypeNs::BuiltinType(it) => PathResolution::Def(BuiltinType::from(it).into()),
             TypeNs::TraitId(it) => PathResolution::Def(Trait::from(it).into()),
-        })
+        };
+        match unresolved {
+            Some(unresolved) => res
+                .assoc_type_shorthand_candidates(db, |name, alias| {
+                    (name == unresolved.name).then(|| alias)
+                })
+                .map(TypeAlias::from)
+                .map(Into::into)
+                .map(PathResolution::Def),
+            None => Some(res),
+        }
     };
 
     let body_owner = resolver.body_owner();
diff --git a/crates/hir_def/Cargo.toml b/crates/hir_def/Cargo.toml
index 475d337f3..43324d8d9 100644
--- a/crates/hir_def/Cargo.toml
+++ b/crates/hir_def/Cargo.toml
@@ -11,6 +11,7 @@ doctest = false
 
 [dependencies]
 cov-mark = { version = "1.1", features = ["thread-local"] }
+dashmap = { version = "4.0.2", features = ["raw-api"] }
 log = "0.4.8"
 once_cell = "1.3.1"
 rustc-hash = "1.1.0"
diff --git a/crates/hir_def/src/adt.rs b/crates/hir_def/src/adt.rs
index 58e35353b..402fb1d8d 100644
--- a/crates/hir_def/src/adt.rs
+++ b/crates/hir_def/src/adt.rs
@@ -15,6 +15,7 @@ use tt::{Delimiter, DelimiterKind, Leaf, Subtree, TokenTree};
 use crate::{
     body::{CfgExpander, LowerCtx},
     db::DefDatabase,
+    intern::Interned,
     item_tree::{AttrOwner, Field, Fields, ItemTree, ModItem, RawVisibilityId},
     src::HasChildSource,
     src::HasSource,
@@ -58,7 +59,7 @@ pub enum VariantData {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct FieldData {
     pub name: Name,
-    pub type_ref: TypeRef,
+    pub type_ref: Interned<TypeRef>,
     pub visibility: RawVisibility,
 }
 
@@ -292,7 +293,7 @@ fn lower_struct(
                     || Either::Left(fd.clone()),
                     || FieldData {
                         name: Name::new_tuple_field(i),
-                        type_ref: TypeRef::from_ast_opt(&ctx, fd.ty()),
+                        type_ref: Interned::new(TypeRef::from_ast_opt(&ctx, fd.ty())),
                         visibility: RawVisibility::from_ast(db, ast.with_value(fd.visibility())),
                     },
                 );
@@ -309,7 +310,7 @@ fn lower_struct(
                     || Either::Right(fd.clone()),
                     || FieldData {
                         name: fd.name().map(|n| n.as_name()).unwrap_or_else(Name::missing),
-                        type_ref: TypeRef::from_ast_opt(&ctx, fd.ty()),
+                        type_ref: Interned::new(TypeRef::from_ast_opt(&ctx, fd.ty())),
                         visibility: RawVisibility::from_ast(db, ast.with_value(fd.visibility())),
                     },
                 );
@@ -358,7 +359,7 @@ fn lower_field(
 ) -> FieldData {
     FieldData {
         name: field.name.clone(),
-        type_ref: item_tree[field.type_ref].clone(),
+        type_ref: field.type_ref.clone(),
         visibility: item_tree[override_visibility.unwrap_or(field.visibility)].clone(),
     }
 }
diff --git a/crates/hir_def/src/attr.rs b/crates/hir_def/src/attr.rs
index 52a2bce9b..ab77d924a 100644
--- a/crates/hir_def/src/attr.rs
+++ b/crates/hir_def/src/attr.rs
@@ -1,6 +1,10 @@
 //! A higher level attributes based on TokenTree, with also some shortcuts.
 
-use std::{ops, sync::Arc};
+use std::{
+    convert::{TryFrom, TryInto},
+    ops,
+    sync::Arc,
+};
 
 use base_db::CrateId;
 use cfg::{CfgExpr, CfgOptions};
@@ -12,12 +16,13 @@ use mbe::ast_to_token_tree;
 use smallvec::{smallvec, SmallVec};
 use syntax::{
     ast::{self, AstNode, AttrsOwner},
-    match_ast, AstToken, SmolStr, SyntaxNode,
+    match_ast, AstToken, SmolStr, SyntaxNode, TextRange, TextSize,
 };
 use tt::Subtree;
 
 use crate::{
     db::DefDatabase,
+    intern::Interned,
     item_tree::{ItemTreeId, ItemTreeNode},
     nameres::ModuleSource,
     path::{ModPath, PathKind},
@@ -98,7 +103,7 @@ impl RawAttrs {
                 Either::Right(comment) => comment.doc_comment().map(|doc| Attr {
                     index: i as u32,
                     input: Some(AttrInput::Literal(SmolStr::new(doc))),
-                    path: ModPath::from(hir_expand::name!(doc)),
+                    path: Interned::new(ModPath::from(hir_expand::name!(doc))),
                 }),
             })
             .collect::<Arc<_>>();
@@ -451,6 +456,55 @@ impl AttrsWithOwner {
                 .collect(),
         }
     }
+
+    pub fn docs_with_rangemap(
+        &self,
+        db: &dyn DefDatabase,
+    ) -> Option<(Documentation, DocsRangeMap)> {
+        // FIXME: code duplication in `docs` above
+        let docs = self.by_key("doc").attrs().flat_map(|attr| match attr.input.as_ref()? {
+            AttrInput::Literal(s) => Some((s, attr.index)),
+            AttrInput::TokenTree(_) => None,
+        });
+        let indent = docs
+            .clone()
+            .flat_map(|(s, _)| s.lines())
+            .filter(|line| !line.chars().all(|c| c.is_whitespace()))
+            .map(|line| line.chars().take_while(|c| c.is_whitespace()).count())
+            .min()
+            .unwrap_or(0);
+        let mut buf = String::new();
+        let mut mapping = Vec::new();
+        for (doc, idx) in docs {
+            // str::lines doesn't yield anything for the empty string
+            if !doc.is_empty() {
+                for line in doc.split('\n') {
+                    let line = line.trim_end();
+                    let line_len = line.len();
+                    let (offset, line) = match line.char_indices().nth(indent) {
+                        Some((offset, _)) => (offset, &line[offset..]),
+                        None => (0, line),
+                    };
+                    let buf_offset = buf.len();
+                    buf.push_str(line);
+                    mapping.push((
+                        TextRange::new(buf_offset.try_into().ok()?, buf.len().try_into().ok()?),
+                        idx,
+                        TextRange::new(offset.try_into().ok()?, line_len.try_into().ok()?),
+                    ));
+                    buf.push('\n');
+                }
+            } else {
+                buf.push('\n');
+            }
+        }
+        buf.pop();
+        if buf.is_empty() {
+            None
+        } else {
+            Some((Documentation(buf), DocsRangeMap { mapping, source: self.source_map(db).attrs }))
+        }
+    }
 }
 
 fn inner_attributes(
@@ -507,10 +561,48 @@ impl AttrSourceMap {
     }
 }
 
+/// A struct to map text ranges from [`Documentation`] back to TextRanges in the syntax tree.
+pub struct DocsRangeMap {
+    source: Vec<InFile<Either<ast::Attr, ast::Comment>>>,
+    // (docstring-line-range, attr_index, attr-string-range)
+    // a mapping from the text range of a line of the [`Documentation`] to the attribute index and
+    // the original (untrimmed) syntax doc line
+    mapping: Vec<(TextRange, u32, TextRange)>,
+}
+
+impl DocsRangeMap {
+    pub fn map(&self, range: TextRange) -> Option<InFile<TextRange>> {
+        let found = self.mapping.binary_search_by(|(probe, ..)| probe.ordering(range)).ok()?;
+        let (line_docs_range, idx, original_line_src_range) = self.mapping[found].clone();
+        if !line_docs_range.contains_range(range) {
+            return None;
+        }
+
+        let relative_range = range - line_docs_range.start();
+
+        let &InFile { file_id, value: ref source } = &self.source[idx as usize];
+        match source {
+            Either::Left(_) => None, // FIXME, figure out a nice way to handle doc attributes here
+            // as well as for whats done in syntax highlight doc injection
+            Either::Right(comment) => {
+                let text_range = comment.syntax().text_range();
+                let range = TextRange::at(
+                    text_range.start()
+                        + TextSize::try_from(comment.prefix().len()).ok()?
+                        + original_line_src_range.start()
+                        + relative_range.start(),
+                    text_range.len().min(range.len()),
+                );
+                Some(InFile { file_id, value: range })
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Attr {
     index: u32,
-    pub(crate) path: ModPath,
+    pub(crate) path: Interned<ModPath>,
     pub(crate) input: Option<AttrInput>,
 }
 
@@ -524,7 +616,7 @@ pub enum AttrInput {
 
 impl Attr {
     fn from_src(ast: ast::Attr, hygiene: &Hygiene, index: u32) -> Option<Attr> {
-        let path = ModPath::from_src(ast.path()?, hygiene)?;
+        let path = Interned::new(ModPath::from_src(ast.path()?, hygiene)?);
         let input = if let Some(ast::Expr::Literal(lit)) = ast.expr() {
             let value = match lit.kind() {
                 ast::LiteralKind::String(string) => string.value()?.into(),
@@ -532,7 +624,7 @@ impl Attr {
             };
             Some(AttrInput::Literal(value))
         } else if let Some(tt) = ast.token_tree() {
-            Some(AttrInput::TokenTree(ast_to_token_tree(&tt)?.0))
+            Some(AttrInput::TokenTree(ast_to_token_tree(&tt).0))
         } else {
             None
         };
diff --git a/crates/hir_def/src/body.rs b/crates/hir_def/src/body.rs
index 1080d9c2c..96b959967 100644
--- a/crates/hir_def/src/body.rs
+++ b/crates/hir_def/src/body.rs
@@ -226,7 +226,7 @@ pub struct Body {
     /// The `ExprId` of the actual body expression.
     pub body_expr: ExprId,
     /// Block expressions in this body that may contain inner items.
-    pub block_scopes: Vec<BlockId>,
+    block_scopes: Vec<BlockId>,
     _c: Count<Self>,
 }
 
@@ -302,7 +302,8 @@ impl Body {
             }
         };
         let expander = Expander::new(db, file_id, module);
-        let (body, source_map) = Body::new(db, expander, params, body);
+        let (mut body, source_map) = Body::new(db, expander, params, body);
+        body.shrink_to_fit();
         (Arc::new(body), Arc::new(source_map))
     }
 
@@ -310,6 +311,16 @@ impl Body {
         db.body_with_source_map(def).0
     }
 
+    /// Returns an iterator over all block expressions in this body that define inner items.
+    pub fn blocks<'a>(
+        &'a self,
+        db: &'a dyn DefDatabase,
+    ) -> impl Iterator<Item = (BlockId, Arc<DefMap>)> + '_ {
+        self.block_scopes
+            .iter()
+            .map(move |block| (*block, db.block_def_map(*block).expect("block ID without DefMap")))
+    }
+
     fn new(
         db: &dyn DefDatabase,
         expander: Expander,
@@ -318,6 +329,15 @@ impl Body {
     ) -> (Body, BodySourceMap) {
         lower::lower(db, expander, params, body)
     }
+
+    fn shrink_to_fit(&mut self) {
+        let Self { _c: _, body_expr: _, block_scopes, exprs, labels, params, pats } = self;
+        block_scopes.shrink_to_fit();
+        exprs.shrink_to_fit();
+        labels.shrink_to_fit();
+        params.shrink_to_fit();
+        pats.shrink_to_fit();
+    }
 }
 
 impl Index<ExprId> for Body {
diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index 229e81dd4..63e89a1f4 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -673,12 +673,14 @@ impl ExprCollector<'_> {
         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);
-        self.body.block_scopes.push(block_id);
 
-        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 (module, def_map) = match self.db.block_def_map(block_id) {
+            Some(def_map) => {
+                self.body.block_scopes.push(block_id);
+                (def_map.root(), def_map)
+            }
+            None => (self.expander.module, self.expander.def_map.clone()),
+        };
         let prev_def_map = mem::replace(&mut self.expander.def_map, def_map);
         let prev_local_module = mem::replace(&mut self.expander.module, module);
         let prev_statements = std::mem::take(&mut self.statements_in_scope);
diff --git a/crates/hir_def/src/child_by_source.rs b/crates/hir_def/src/child_by_source.rs
index 2a331dcaf..f40a7f80d 100644
--- a/crates/hir_def/src/child_by_source.rs
+++ b/crates/hir_def/src/child_by_source.rs
@@ -160,7 +160,7 @@ impl ChildBySource for EnumId {
 impl ChildBySource for DefWithBodyId {
     fn child_by_source_to(&self, db: &dyn DefDatabase, res: &mut DynMap) {
         let body = db.body(*self);
-        for def_map in body.block_scopes.iter().filter_map(|block| db.block_def_map(*block)) {
+        for (_, def_map) in body.blocks(db) {
             // All block expressions are merged into the same map, because they logically all add
             // inner items to the containing `DefWithBodyId`.
             def_map[def_map.root()].scope.child_by_source_to(db, res);
diff --git a/crates/hir_def/src/data.rs b/crates/hir_def/src/data.rs
index 0be868ba2..135a6698e 100644
--- a/crates/hir_def/src/data.rs
+++ b/crates/hir_def/src/data.rs
@@ -9,8 +9,9 @@ use crate::{
     attr::Attrs,
     body::Expander,
     db::DefDatabase,
-    item_tree::{AssocItem, FunctionQualifier, ItemTreeId, ModItem, Param},
-    type_ref::{TypeBound, TypeRef},
+    intern::Interned,
+    item_tree::{AssocItem, FnFlags, ItemTreeId, ModItem, Param},
+    type_ref::{TraitRef, TypeBound, TypeRef},
     visibility::RawVisibility,
     AssocContainerId, AssocItemId, ConstId, ConstLoc, FunctionId, FunctionLoc, HasModule, ImplId,
     Intern, Lookup, ModuleId, StaticId, TraitId, TypeAliasId, TypeAliasLoc,
@@ -19,17 +20,12 @@ use crate::{
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct FunctionData {
     pub name: Name,
-    pub params: Vec<TypeRef>,
-    pub ret_type: TypeRef,
+    pub params: Vec<Interned<TypeRef>>,
+    pub ret_type: Interned<TypeRef>,
     pub attrs: Attrs,
-    /// True if the first param is `self`. This is relevant to decide whether this
-    /// can be called as a method.
-    pub has_self_param: bool,
-    pub has_body: bool,
-    pub qualifier: FunctionQualifier,
-    pub is_in_extern_block: bool,
-    pub is_varargs: bool,
     pub visibility: RawVisibility,
+    pub abi: Option<Interned<str>>,
+    flags: FnFlags,
 }
 
 impl FunctionData {
@@ -52,31 +48,67 @@ impl FunctionData {
             .next_back()
             .map_or(false, |param| matches!(item_tree[param], Param::Varargs));
 
+        let mut flags = func.flags;
+        if is_varargs {
+            flags.bits |= FnFlags::IS_VARARGS;
+        }
+
         Arc::new(FunctionData {
             name: func.name.clone(),
             params: enabled_params
                 .clone()
                 .filter_map(|id| match &item_tree[id] {
-                    Param::Normal(ty) => Some(item_tree[*ty].clone()),
+                    Param::Normal(ty) => Some(ty.clone()),
                     Param::Varargs => None,
                 })
                 .collect(),
-            ret_type: item_tree[func.ret_type].clone(),
+            ret_type: func.ret_type.clone(),
             attrs: item_tree.attrs(db, krate, ModItem::from(loc.id.value).into()),
-            has_self_param: func.has_self_param,
-            has_body: func.has_body,
-            qualifier: func.qualifier.clone(),
-            is_in_extern_block: func.is_in_extern_block,
-            is_varargs,
             visibility: item_tree[func.visibility].clone(),
+            abi: func.abi.clone(),
+            flags,
         })
     }
+
+    pub fn has_body(&self) -> bool {
+        self.flags.bits & FnFlags::HAS_BODY != 0
+    }
+
+    /// True if the first param is `self`. This is relevant to decide whether this
+    /// can be called as a method.
+    pub fn has_self_param(&self) -> bool {
+        self.flags.bits & FnFlags::HAS_SELF_PARAM != 0
+    }
+
+    pub fn is_default(&self) -> bool {
+        self.flags.bits & FnFlags::IS_DEFAULT != 0
+    }
+
+    pub fn is_const(&self) -> bool {
+        self.flags.bits & FnFlags::IS_CONST != 0
+    }
+
+    pub fn is_async(&self) -> bool {
+        self.flags.bits & FnFlags::IS_ASYNC != 0
+    }
+
+    pub fn is_unsafe(&self) -> bool {
+        self.flags.bits & FnFlags::IS_UNSAFE != 0
+    }
+
+    pub fn is_in_extern_block(&self) -> bool {
+        self.flags.bits & FnFlags::IS_IN_EXTERN_BLOCK != 0
+    }
+
+    pub fn is_varargs(&self) -> bool {
+        self.flags.bits & FnFlags::IS_VARARGS != 0
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct TypeAliasData {
     pub name: Name,
-    pub type_ref: Option<TypeRef>,
+    pub type_ref: Option<Interned<TypeRef>>,
     pub visibility: RawVisibility,
     pub is_extern: bool,
     /// Bounds restricting the type alias itself (eg. `type Ty: Bound;` in a trait or impl).
@@ -94,7 +126,7 @@ impl TypeAliasData {
 
         Arc::new(TypeAliasData {
             name: typ.name.clone(),
-            type_ref: typ.type_ref.map(|id| item_tree[id].clone()),
+            type_ref: typ.type_ref.clone(),
             visibility: item_tree[typ.visibility].clone(),
             is_extern: typ.is_extern,
             bounds: typ.bounds.to_vec(),
@@ -156,8 +188,8 @@ impl TraitData {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ImplData {
-    pub target_trait: Option<TypeRef>,
-    pub target_type: TypeRef,
+    pub target_trait: Option<Interned<TraitRef>>,
+    pub self_ty: Interned<TypeRef>,
     pub items: Vec<AssocItemId>,
     pub is_negative: bool,
 }
@@ -169,8 +201,8 @@ impl ImplData {
 
         let item_tree = impl_loc.id.item_tree(db);
         let impl_def = &item_tree[impl_loc.id.value];
-        let target_trait = impl_def.target_trait.map(|id| item_tree[id].clone());
-        let target_type = item_tree[impl_def.target_type].clone();
+        let target_trait = impl_def.target_trait.clone();
+        let self_ty = impl_def.self_ty.clone();
         let is_negative = impl_def.is_negative;
         let module_id = impl_loc.container;
         let container = AssocContainerId::ImplId(id);
@@ -187,7 +219,7 @@ impl ImplData {
         );
         let items = items.into_iter().map(|(_, item)| item).collect();
 
-        Arc::new(ImplData { target_trait, target_type, items, is_negative })
+        Arc::new(ImplData { target_trait, self_ty, items, is_negative })
     }
 }
 
@@ -195,7 +227,7 @@ impl ImplData {
 pub struct ConstData {
     /// const _: () = ();
     pub name: Option<Name>,
-    pub type_ref: TypeRef,
+    pub type_ref: Interned<TypeRef>,
     pub visibility: RawVisibility,
 }
 
@@ -207,7 +239,7 @@ impl ConstData {
 
         Arc::new(ConstData {
             name: konst.name.clone(),
-            type_ref: item_tree[konst.type_ref].clone(),
+            type_ref: konst.type_ref.clone(),
             visibility: item_tree[konst.visibility].clone(),
         })
     }
@@ -216,7 +248,7 @@ impl ConstData {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct StaticData {
     pub name: Option<Name>,
-    pub type_ref: TypeRef,
+    pub type_ref: Interned<TypeRef>,
     pub visibility: RawVisibility,
     pub mutable: bool,
     pub is_extern: bool,
@@ -230,7 +262,7 @@ impl StaticData {
 
         Arc::new(StaticData {
             name: Some(statik.name.clone()),
-            type_ref: item_tree[statik.type_ref].clone(),
+            type_ref: statik.type_ref.clone(),
             visibility: item_tree[statik.visibility].clone(),
             mutable: statik.mutable,
             is_extern: statik.is_extern,
diff --git a/crates/hir_def/src/db.rs b/crates/hir_def/src/db.rs
index 068b2ee38..9b7a213a1 100644
--- a/crates/hir_def/src/db.rs
+++ b/crates/hir_def/src/db.rs
@@ -13,6 +13,7 @@ use crate::{
     data::{ConstData, FunctionData, ImplData, StaticData, TraitData, TypeAliasData},
     generics::GenericParams,
     import_map::ImportMap,
+    intern::Interned,
     item_tree::ItemTree,
     lang_item::{LangItemTarget, LangItems},
     nameres::DefMap,
@@ -113,7 +114,7 @@ pub trait DefDatabase: InternDatabase + AstDatabase + Upcast<dyn AstDatabase> {
     fn expr_scopes(&self, def: DefWithBodyId) -> Arc<ExprScopes>;
 
     #[salsa::invoke(GenericParams::generic_params_query)]
-    fn generic_params(&self, def: GenericDefId) -> Arc<GenericParams>;
+    fn generic_params(&self, def: GenericDefId) -> Interned<GenericParams>;
 
     #[salsa::invoke(Attrs::variants_attrs_query)]
     fn variants_attrs(&self, def: EnumId) -> Arc<ArenaMap<LocalEnumVariantId, Attrs>>;
diff --git a/crates/hir_def/src/generics.rs b/crates/hir_def/src/generics.rs
index 7c6cbff11..de5acced8 100644
--- a/crates/hir_def/src/generics.rs
+++ b/crates/hir_def/src/generics.rs
@@ -2,7 +2,6 @@
 //! structs, impls, traits, etc. This module provides a common HIR for these
 //! generic parameters. See also the `Generics` type and the `generics_of` query
 //! in rustc.
-use std::sync::Arc;
 
 use base_db::FileId;
 use either::Either;
@@ -18,6 +17,7 @@ use crate::{
     child_by_source::ChildBySource,
     db::DefDatabase,
     dyn_map::DynMap,
+    intern::Interned,
     keys,
     src::{HasChildSource, HasSource},
     type_ref::{LifetimeRef, TypeBound, TypeRef},
@@ -26,27 +26,27 @@ use crate::{
 };
 
 /// Data about a generic type parameter (to a function, struct, impl, ...).
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct TypeParamData {
     pub name: Option<Name>,
-    pub default: Option<TypeRef>,
+    pub default: Option<Interned<TypeRef>>,
     pub provenance: TypeParamProvenance,
 }
 
 /// Data about a generic lifetime parameter (to a function, struct, impl, ...).
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct LifetimeParamData {
     pub name: Name,
 }
 
 /// Data about a generic const parameter (to a function, struct, impl, ...).
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub struct ConstParamData {
     pub name: Name,
-    pub ty: TypeRef,
+    pub ty: Interned<TypeRef>,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
 pub enum TypeParamProvenance {
     TypeParamList,
     TraitSelf,
@@ -54,7 +54,7 @@ pub enum TypeParamProvenance {
 }
 
 /// Data about the generic parameters of a function, struct, impl, etc.
-#[derive(Clone, PartialEq, Eq, Debug, Default)]
+#[derive(Clone, PartialEq, Eq, Debug, Default, Hash)]
 pub struct GenericParams {
     pub types: Arena<TypeParamData>,
     pub lifetimes: Arena<LifetimeParamData>,
@@ -66,16 +66,16 @@ pub struct GenericParams {
 /// where clauses like `where T: Foo + Bar` are turned into multiple of these.
 /// It might still result in multiple actual predicates though, because of
 /// associated type bindings like `Iterator<Item = u32>`.
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum WherePredicate {
     TypeBound { target: WherePredicateTypeTarget, bound: TypeBound },
     Lifetime { target: LifetimeRef, bound: LifetimeRef },
     ForLifetime { lifetimes: Box<[Name]>, target: WherePredicateTypeTarget, bound: TypeBound },
 }
 
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum WherePredicateTypeTarget {
-    TypeRef(TypeRef),
+    TypeRef(Interned<TypeRef>),
     /// For desugared where predicates that can directly refer to a type param.
     TypeParam(LocalTypeParamId),
 }
@@ -91,7 +91,7 @@ impl GenericParams {
     pub(crate) fn generic_params_query(
         db: &dyn DefDatabase,
         def: GenericDefId,
-    ) -> Arc<GenericParams> {
+    ) -> Interned<GenericParams> {
         let _p = profile::span("generic_params_query");
 
         let generics = match def {
@@ -99,47 +99,49 @@ impl GenericParams {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
             }
             GenericDefId::AdtId(AdtId::StructId(id)) => {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
             }
             GenericDefId::AdtId(AdtId::EnumId(id)) => {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
             }
             GenericDefId::AdtId(AdtId::UnionId(id)) => {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
             }
             GenericDefId::TraitId(id) => {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
             }
             GenericDefId::TypeAliasId(id) => {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
             }
             GenericDefId::ImplId(id) => {
                 let id = id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                tree[item.generic_params].clone()
+                item.generic_params.clone()
+            }
+            GenericDefId::EnumVariantId(_) | GenericDefId::ConstId(_) => {
+                Interned::new(GenericParams::default())
             }
-            GenericDefId::EnumVariantId(_) | GenericDefId::ConstId(_) => GenericParams::default(),
         };
-        Arc::new(generics)
+        generics
     }
 
     fn new(db: &dyn DefDatabase, def: GenericDefId) -> (GenericParams, InFile<SourceMap>) {
@@ -217,6 +219,7 @@ impl GenericParams {
             GenericDefId::EnumVariantId(_) | GenericDefId::ConstId(_) => FileId(!0).into(),
         };
 
+        generics.shrink_to_fit();
         (generics, InFile::new(file_id, sm))
     }
 
@@ -256,7 +259,8 @@ impl GenericParams {
         for type_param in params.type_params() {
             let name = type_param.name().map_or_else(Name::missing, |it| it.as_name());
             // FIXME: Use `Path::from_src`
-            let default = type_param.default_type().map(|it| TypeRef::from_ast(lower_ctx, it));
+            let default =
+                type_param.default_type().map(|it| Interned::new(TypeRef::from_ast(lower_ctx, it)));
             let param = TypeParamData {
                 name: Some(name.clone()),
                 default,
@@ -280,7 +284,7 @@ impl GenericParams {
         for const_param in params.const_params() {
             let name = const_param.name().map_or_else(Name::missing, |it| it.as_name());
             let ty = const_param.ty().map_or(TypeRef::Error, |it| TypeRef::from_ast(lower_ctx, it));
-            let param = ConstParamData { name, ty };
+            let param = ConstParamData { name, ty: Interned::new(ty) };
             let param_id = self.consts.alloc(param);
             sm.const_params.insert(param_id, const_param.clone());
         }
@@ -334,11 +338,11 @@ impl GenericParams {
             (Either::Left(type_ref), bound) => match hrtb_lifetimes {
                 Some(hrtb_lifetimes) => WherePredicate::ForLifetime {
                     lifetimes: hrtb_lifetimes.clone(),
-                    target: WherePredicateTypeTarget::TypeRef(type_ref),
+                    target: WherePredicateTypeTarget::TypeRef(Interned::new(type_ref)),
                     bound,
                 },
                 None => WherePredicate::TypeBound {
-                    target: WherePredicateTypeTarget::TypeRef(type_ref),
+                    target: WherePredicateTypeTarget::TypeRef(Interned::new(type_ref)),
                     bound,
                 },
             },
@@ -369,6 +373,14 @@ impl GenericParams {
         });
     }
 
+    pub(crate) fn shrink_to_fit(&mut self) {
+        let Self { consts, lifetimes, types, where_predicates } = self;
+        consts.shrink_to_fit();
+        lifetimes.shrink_to_fit();
+        types.shrink_to_fit();
+        where_predicates.shrink_to_fit();
+    }
+
     pub fn find_type_by_name(&self, name: &Name) -> Option<LocalTypeParamId> {
         self.types
             .iter()
diff --git a/crates/hir_def/src/intern.rs b/crates/hir_def/src/intern.rs
new file mode 100644
index 000000000..abc304ef0
--- /dev/null
+++ b/crates/hir_def/src/intern.rs
@@ -0,0 +1,216 @@
+//! Global `Arc`-based object interning infrastructure.
+//!
+//! Eventually this should probably be replaced with salsa-based interning.
+
+use std::{
+    collections::HashMap,
+    fmt::{self, Debug},
+    hash::{BuildHasherDefault, Hash, Hasher},
+    ops::Deref,
+    sync::Arc,
+};
+
+use dashmap::{lock::RwLockWriteGuard, DashMap, SharedValue};
+use once_cell::sync::OnceCell;
+use rustc_hash::FxHasher;
+
+use crate::generics::GenericParams;
+
+type InternMap<T> = DashMap<Arc<T>, (), BuildHasherDefault<FxHasher>>;
+type Guard<T> =
+    RwLockWriteGuard<'static, HashMap<Arc<T>, SharedValue<()>, BuildHasherDefault<FxHasher>>>;
+
+pub struct Interned<T: Internable + ?Sized> {
+    arc: Arc<T>,
+}
+
+impl<T: Internable> Interned<T> {
+    pub fn new(obj: T) -> Self {
+        match Interned::lookup(&obj) {
+            Ok(this) => this,
+            Err(shard) => {
+                let arc = Arc::new(obj);
+                Self::alloc(arc, shard)
+            }
+        }
+    }
+}
+
+impl<T: Internable + ?Sized> Interned<T> {
+    fn lookup(obj: &T) -> Result<Self, Guard<T>> {
+        let storage = T::storage().get();
+        let shard_idx = storage.determine_map(obj);
+        let shard = &storage.shards()[shard_idx];
+        let shard = shard.write();
+
+        // Atomically,
+        // - check if `obj` is already in the map
+        //   - if so, clone its `Arc` and return it
+        //   - if not, box it up, insert it, and return a clone
+        // This needs to be atomic (locking the shard) to avoid races with other thread, which could
+        // insert the same object between us looking it up and inserting it.
+
+        // FIXME: avoid double lookup/hashing by using raw entry API (once stable, or when
+        // hashbrown can be plugged into dashmap)
+        match shard.get_key_value(obj) {
+            Some((arc, _)) => Ok(Self { arc: arc.clone() }),
+            None => Err(shard),
+        }
+    }
+
+    fn alloc(arc: Arc<T>, mut shard: Guard<T>) -> Self {
+        let arc2 = arc.clone();
+
+        shard.insert(arc2, SharedValue::new(()));
+
+        Self { arc }
+    }
+}
+
+impl Interned<str> {
+    pub fn new_str(s: &str) -> Self {
+        match Interned::lookup(s) {
+            Ok(this) => this,
+            Err(shard) => {
+                let arc = Arc::<str>::from(s);
+                Self::alloc(arc, shard)
+            }
+        }
+    }
+}
+
+impl<T: Internable + ?Sized> Drop for Interned<T> {
+    #[inline]
+    fn drop(&mut self) {
+        // When the last `Ref` is dropped, remove the object from the global map.
+        if Arc::strong_count(&self.arc) == 2 {
+            // Only `self` and the global map point to the object.
+
+            self.drop_slow();
+        }
+    }
+}
+
+impl<T: Internable + ?Sized> Interned<T> {
+    #[cold]
+    fn drop_slow(&mut self) {
+        let storage = T::storage().get();
+        let shard_idx = storage.determine_map(&self.arc);
+        let shard = &storage.shards()[shard_idx];
+        let mut shard = shard.write();
+
+        // FIXME: avoid double lookup
+        let (arc, _) = shard.get_key_value(&self.arc).expect("interned value removed prematurely");
+
+        if Arc::strong_count(arc) != 2 {
+            // Another thread has interned another copy
+            return;
+        }
+
+        shard.remove(&self.arc);
+
+        // Shrink the backing storage if the shard is less than 50% occupied.
+        if shard.len() * 2 < shard.capacity() {
+            shard.shrink_to_fit();
+        }
+    }
+}
+
+/// Compares interned `Ref`s using pointer equality.
+impl<T: Internable> PartialEq for Interned<T> {
+    // NOTE: No `?Sized` because `ptr_eq` doesn't work right with trait objects.
+
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        Arc::ptr_eq(&self.arc, &other.arc)
+    }
+}
+
+impl<T: Internable> Eq for Interned<T> {}
+
+impl PartialEq for Interned<str> {
+    fn eq(&self, other: &Self) -> bool {
+        Arc::ptr_eq(&self.arc, &other.arc)
+    }
+}
+
+impl Eq for Interned<str> {}
+
+impl<T: Internable + ?Sized> Hash for Interned<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        // NOTE: Cast disposes vtable pointer / slice/str length.
+        state.write_usize(Arc::as_ptr(&self.arc) as *const () as usize)
+    }
+}
+
+impl<T: Internable + ?Sized> AsRef<T> for Interned<T> {
+    #[inline]
+    fn as_ref(&self) -> &T {
+        &self.arc
+    }
+}
+
+impl<T: Internable + ?Sized> Deref for Interned<T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.arc
+    }
+}
+
+impl<T: Internable + ?Sized> Clone for Interned<T> {
+    fn clone(&self) -> Self {
+        Self { arc: self.arc.clone() }
+    }
+}
+
+impl<T: Debug + Internable + ?Sized> Debug for Interned<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (*self.arc).fmt(f)
+    }
+}
+
+pub struct InternStorage<T: ?Sized> {
+    map: OnceCell<InternMap<T>>,
+}
+
+impl<T: ?Sized> InternStorage<T> {
+    pub const fn new() -> Self {
+        Self { map: OnceCell::new() }
+    }
+}
+
+impl<T: Internable + ?Sized> InternStorage<T> {
+    fn get(&self) -> &InternMap<T> {
+        self.map.get_or_init(DashMap::default)
+    }
+}
+
+pub trait Internable: Hash + Eq + 'static {
+    fn storage() -> &'static InternStorage<Self>;
+}
+
+/// Implements `Internable` for a given list of types, making them usable with `Interned`.
+#[macro_export]
+#[doc(hidden)]
+macro_rules! _impl_internable {
+    ( $($t:path),+ $(,)? ) => { $(
+        impl Internable for $t {
+            fn storage() -> &'static InternStorage<Self> {
+                static STORAGE: InternStorage<$t> = InternStorage::new();
+                &STORAGE
+            }
+        }
+    )+ };
+}
+
+pub use crate::_impl_internable as impl_internable;
+
+impl_internable!(
+    crate::type_ref::TypeRef,
+    crate::type_ref::TraitRef,
+    crate::path::ModPath,
+    GenericParams,
+    str,
+);
diff --git a/crates/hir_def/src/item_scope.rs b/crates/hir_def/src/item_scope.rs
index f3ebe7c72..a8ee5eeac 100644
--- a/crates/hir_def/src/item_scope.rs
+++ b/crates/hir_def/src/item_scope.rs
@@ -285,6 +285,28 @@ impl ItemScope {
             buf.push('\n');
         }
     }
+
+    pub(crate) fn shrink_to_fit(&mut self) {
+        // Exhaustive match to require handling new fields.
+        let Self {
+            types,
+            values,
+            macros,
+            unresolved,
+            defs,
+            impls,
+            unnamed_trait_imports,
+            legacy_macros,
+        } = self;
+        types.shrink_to_fit();
+        values.shrink_to_fit();
+        macros.shrink_to_fit();
+        unresolved.shrink_to_fit();
+        defs.shrink_to_fit();
+        impls.shrink_to_fit();
+        unnamed_trait_imports.shrink_to_fit();
+        legacy_macros.shrink_to_fit();
+    }
 }
 
 impl PerNs {
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index ca0048b16..240662486 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -24,14 +24,15 @@ use la_arena::{Arena, Idx, RawIdx};
 use profile::Count;
 use rustc_hash::FxHashMap;
 use smallvec::SmallVec;
-use syntax::{ast, match_ast, SmolStr, SyntaxKind};
+use syntax::{ast, match_ast, SyntaxKind};
 
 use crate::{
     attr::{Attrs, RawAttrs},
     db::DefDatabase,
     generics::GenericParams,
+    intern::Interned,
     path::{path, AssociatedTypeBinding, GenericArgs, ImportAlias, ModPath, Path, PathKind},
-    type_ref::{Mutability, TypeBound, TypeRef},
+    type_ref::{Mutability, TraitRef, TypeBound, TypeRef},
     visibility::RawVisibility,
 };
 
@@ -57,13 +58,6 @@ impl fmt::Debug for RawVisibilityId {
     }
 }
 
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub struct GenericParamsId(u32);
-
-impl GenericParamsId {
-    pub const EMPTY: Self = GenericParamsId(u32::max_value());
-}
-
 /// The item tree of a source file.
 #[derive(Debug, Default, Eq, PartialEq)]
 pub struct ItemTree {
@@ -145,8 +139,6 @@ impl ItemTree {
                 macro_rules,
                 macro_defs,
                 vis,
-                generics,
-                type_refs,
                 inner_items,
             } = &mut **data;
 
@@ -170,9 +162,6 @@ impl ItemTree {
             macro_defs.shrink_to_fit();
 
             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();
         }
@@ -244,58 +233,6 @@ static VIS_PRIV: RawVisibility = RawVisibility::Module(ModPath::from_kind(PathKi
 static VIS_PUB_CRATE: RawVisibility = RawVisibility::Module(ModPath::from_kind(PathKind::Crate));
 
 #[derive(Default, Debug, Eq, PartialEq)]
-struct GenericParamsStorage {
-    arena: Arena<GenericParams>,
-}
-
-impl GenericParamsStorage {
-    fn alloc(&mut self, params: GenericParams) -> GenericParamsId {
-        if params.types.is_empty()
-            && params.lifetimes.is_empty()
-            && params.consts.is_empty()
-            && params.where_predicates.is_empty()
-        {
-            return GenericParamsId::EMPTY;
-        }
-
-        GenericParamsId(self.arena.alloc(params).into_raw().into())
-    }
-}
-
-static EMPTY_GENERICS: GenericParams = GenericParams {
-    types: Arena::new(),
-    lifetimes: Arena::new(),
-    consts: Arena::new(),
-    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>,
     extern_crates: Arena<ExternCrate>,
@@ -317,8 +254,6 @@ struct ItemTreeData {
     macro_defs: Arena<MacroDef>,
 
     vis: ItemVisibilities,
-    generics: GenericParamsStorage,
-    type_refs: TypeRefStorage,
 
     inner_items: FxHashMap<FileAstId<ast::BlockExpr>, SmallVec<[ModItem; 1]>>,
 }
@@ -537,25 +472,6 @@ impl Index<RawVisibilityId> for ItemTree {
     }
 }
 
-impl Index<GenericParamsId> for ItemTree {
-    type Output = GenericParams;
-
-    fn index(&self, index: GenericParamsId) -> &Self::Output {
-        match index {
-            GenericParamsId::EMPTY => &EMPTY_GENERICS,
-            _ => &self.data().generics.arena[Idx::from_raw(index.0.into())],
-        }
-    }
-}
-
-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 {
@@ -566,7 +482,7 @@ impl<N: ItemTreeNode> Index<FileItemTreeId<N>> for ItemTree {
 /// A desugared `use` import.
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Import {
-    pub path: ModPath,
+    pub path: Interned<ModPath>,
     pub alias: Option<ImportAlias>,
     pub visibility: RawVisibilityId,
     pub is_glob: bool,
@@ -592,38 +508,42 @@ pub struct ExternCrate {
 pub struct Function {
     pub name: Name,
     pub visibility: RawVisibilityId,
-    pub generic_params: GenericParamsId,
-    pub has_self_param: bool,
-    pub has_body: bool,
-    pub qualifier: FunctionQualifier,
-    /// Whether the function is located in an `extern` block (*not* whether it is an
-    /// `extern "abi" fn`).
-    pub is_in_extern_block: bool,
+    pub generic_params: Interned<GenericParams>,
+    pub abi: Option<Interned<str>>,
     pub params: IdRange<Param>,
-    pub ret_type: Idx<TypeRef>,
+    pub ret_type: Interned<TypeRef>,
     pub ast_id: FileAstId<ast::Fn>,
+    pub(crate) flags: FnFlags,
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub enum Param {
-    Normal(Idx<TypeRef>),
+    Normal(Interned<TypeRef>),
     Varargs,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub struct FunctionQualifier {
-    pub is_default: bool,
-    pub is_const: bool,
-    pub is_async: bool,
-    pub is_unsafe: bool,
-    pub abi: Option<SmolStr>,
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
+pub(crate) struct FnFlags {
+    pub(crate) bits: u8,
+}
+impl FnFlags {
+    pub(crate) const HAS_SELF_PARAM: u8 = 1 << 0;
+    pub(crate) const HAS_BODY: u8 = 1 << 1;
+    pub(crate) const IS_DEFAULT: u8 = 1 << 2;
+    pub(crate) const IS_CONST: u8 = 1 << 3;
+    pub(crate) const IS_ASYNC: u8 = 1 << 4;
+    pub(crate) const IS_UNSAFE: u8 = 1 << 5;
+    /// Whether the function is located in an `extern` block (*not* whether it is an
+    /// `extern "abi" fn`).
+    pub(crate) const IS_IN_EXTERN_BLOCK: u8 = 1 << 6;
+    pub(crate) const IS_VARARGS: u8 = 1 << 7;
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Struct {
     pub name: Name,
     pub visibility: RawVisibilityId,
-    pub generic_params: GenericParamsId,
+    pub generic_params: Interned<GenericParams>,
     pub fields: Fields,
     pub ast_id: FileAstId<ast::Struct>,
     pub kind: StructDefKind,
@@ -643,7 +563,7 @@ pub enum StructDefKind {
 pub struct Union {
     pub name: Name,
     pub visibility: RawVisibilityId,
-    pub generic_params: GenericParamsId,
+    pub generic_params: Interned<GenericParams>,
     pub fields: Fields,
     pub ast_id: FileAstId<ast::Union>,
 }
@@ -652,7 +572,7 @@ pub struct Union {
 pub struct Enum {
     pub name: Name,
     pub visibility: RawVisibilityId,
-    pub generic_params: GenericParamsId,
+    pub generic_params: Interned<GenericParams>,
     pub variants: IdRange<Variant>,
     pub ast_id: FileAstId<ast::Enum>,
 }
@@ -662,7 +582,7 @@ pub struct Const {
     /// const _: () = ();
     pub name: Option<Name>,
     pub visibility: RawVisibilityId,
-    pub type_ref: Idx<TypeRef>,
+    pub type_ref: Interned<TypeRef>,
     pub ast_id: FileAstId<ast::Const>,
 }
 
@@ -673,7 +593,7 @@ pub struct Static {
     pub mutable: bool,
     /// Whether the static is in an `extern` block.
     pub is_extern: bool,
-    pub type_ref: Idx<TypeRef>,
+    pub type_ref: Interned<TypeRef>,
     pub ast_id: FileAstId<ast::Static>,
 }
 
@@ -681,7 +601,7 @@ pub struct Static {
 pub struct Trait {
     pub name: Name,
     pub visibility: RawVisibilityId,
-    pub generic_params: GenericParamsId,
+    pub generic_params: Interned<GenericParams>,
     pub is_auto: bool,
     pub is_unsafe: bool,
     pub bounds: Box<[TypeBound]>,
@@ -691,9 +611,9 @@ pub struct Trait {
 
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Impl {
-    pub generic_params: GenericParamsId,
-    pub target_trait: Option<Idx<TypeRef>>,
-    pub target_type: Idx<TypeRef>,
+    pub generic_params: Interned<GenericParams>,
+    pub target_trait: Option<Interned<TraitRef>>,
+    pub self_ty: Interned<TypeRef>,
     pub is_negative: bool,
     pub items: Box<[AssocItem]>,
     pub ast_id: FileAstId<ast::Impl>,
@@ -705,8 +625,8 @@ pub struct TypeAlias {
     pub visibility: RawVisibilityId,
     /// 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<Idx<TypeRef>>,
+    pub generic_params: Interned<GenericParams>,
+    pub type_ref: Option<Interned<TypeRef>>,
     pub is_extern: bool,
     pub ast_id: FileAstId<ast::TypeAlias>,
 }
@@ -731,7 +651,7 @@ pub enum ModKind {
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct MacroCall {
     /// Path to the called macro.
-    pub path: ModPath,
+    pub path: Interned<ModPath>,
     pub ast_id: FileAstId<ast::MacroCall>,
 }
 
@@ -896,6 +816,6 @@ pub enum Fields {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Field {
     pub name: Name,
-    pub type_ref: Idx<TypeRef>,
+    pub type_ref: Interned<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 3f558edd8..c5629af24 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -11,7 +11,7 @@ use syntax::{
 
 use crate::{
     generics::{GenericParams, TypeParamData, TypeParamProvenance},
-    type_ref::LifetimeRef,
+    type_ref::{LifetimeRef, TraitRef},
 };
 
 use super::*;
@@ -174,6 +174,12 @@ impl Ctx {
         let forced_vis = self.forced_visibility.take();
 
         let mut block_stack = Vec::new();
+
+        // if container itself is block, add it to the stack
+        if let Some(block) = ast::BlockExpr::cast(container.clone()) {
+            block_stack.push(self.source_ast_id_map.ast_id(&block));
+        }
+
         for event in container.preorder().skip(1) {
             match event {
                 WalkEvent::Enter(node) => {
@@ -356,7 +362,7 @@ impl Ctx {
                         }
                     }
                 };
-                let ty = self.data().type_refs.intern(self_type);
+                let ty = Interned::new(self_type);
                 let idx = self.data().params.alloc(Param::Normal(ty));
                 self.add_attrs(idx.into(), RawAttrs::new(&self_param, &self.hygiene));
                 has_self_param = true;
@@ -366,7 +372,7 @@ impl Ctx {
                     Some(_) => self.data().params.alloc(Param::Varargs),
                     None => {
                         let type_ref = TypeRef::from_ast_opt(&self.body_ctx, param.ty());
-                        let ty = self.data().type_refs.intern(type_ref);
+                        let ty = Interned::new(type_ref);
                         self.data().params.alloc(Param::Normal(ty))
                     }
                 };
@@ -389,41 +395,51 @@ impl Ctx {
             ret_type
         };
 
-        let ret_type = self.data().type_refs.intern(ret_type);
-
-        let has_body = func.body().is_some();
+        let abi = func.abi().map(|abi| {
+            // FIXME: Abi::abi() -> Option<SyntaxToken>?
+            match abi.syntax().last_token() {
+                Some(tok) if tok.kind() == SyntaxKind::STRING => {
+                    // FIXME: Better way to unescape?
+                    Interned::new_str(tok.text().trim_matches('"'))
+                }
+                _ => {
+                    // `extern` default to be `extern "C"`.
+                    Interned::new_str("C")
+                }
+            }
+        });
 
         let ast_id = self.source_ast_id_map.ast_id(func);
-        let qualifier = FunctionQualifier {
-            is_default: func.default_token().is_some(),
-            is_const: func.const_token().is_some(),
-            is_async: func.async_token().is_some(),
-            is_unsafe: func.unsafe_token().is_some(),
-            abi: func.abi().map(|abi| {
-                // FIXME: Abi::abi() -> Option<SyntaxToken>?
-                match abi.syntax().last_token() {
-                    Some(tok) if tok.kind() == SyntaxKind::STRING => {
-                        // FIXME: Better way to unescape?
-                        tok.text().trim_matches('"').into()
-                    }
-                    _ => {
-                        // `extern` default to be `extern "C"`.
-                        "C".into()
-                    }
-                }
-            }),
-        };
+
+        let mut flags = FnFlags::default();
+        if func.body().is_some() {
+            flags.bits |= FnFlags::HAS_BODY;
+        }
+        if has_self_param {
+            flags.bits |= FnFlags::HAS_SELF_PARAM;
+        }
+        if func.default_token().is_some() {
+            flags.bits |= FnFlags::IS_DEFAULT;
+        }
+        if func.const_token().is_some() {
+            flags.bits |= FnFlags::IS_CONST;
+        }
+        if func.async_token().is_some() {
+            flags.bits |= FnFlags::IS_ASYNC;
+        }
+        if func.unsafe_token().is_some() {
+            flags.bits |= FnFlags::IS_UNSAFE;
+        }
+
         let mut res = Function {
             name,
             visibility,
-            generic_params: GenericParamsId::EMPTY,
-            has_self_param,
-            has_body,
-            qualifier,
-            is_in_extern_block: false,
+            generic_params: Interned::new(GenericParams::default()),
+            abi,
             params,
-            ret_type,
+            ret_type: Interned::new(ret_type),
             ast_id,
+            flags,
         };
         res.generic_params = self.lower_generic_params(GenericsOwner::Function(&res), func);
 
@@ -536,8 +552,11 @@ impl Ctx {
     fn lower_impl(&mut self, impl_def: &ast::Impl) -> Option<FileItemTreeId<Impl>> {
         let generic_params =
             self.lower_generic_params_and_inner_items(GenericsOwner::Impl, impl_def);
-        let target_trait = impl_def.trait_().map(|tr| self.lower_type_ref(&tr));
-        let target_type = self.lower_type_ref(&impl_def.self_ty()?);
+        // FIXME: If trait lowering fails, due to a non PathType for example, we treat this impl
+        // as if it was an non-trait impl. Ideally we want to create a unique missing ref that only
+        // equals itself.
+        let target_trait = impl_def.trait_().and_then(|tr| self.lower_trait_ref(&tr));
+        let self_ty = self.lower_type_ref(&impl_def.self_ty()?);
         let is_negative = impl_def.excl_token().is_some();
 
         // We cannot use `assoc_items()` here as that does not include macro calls.
@@ -554,7 +573,7 @@ impl Ctx {
             })
             .collect();
         let ast_id = self.source_ast_id_map.ast_id(impl_def);
-        let res = Impl { generic_params, target_trait, target_type, is_negative, items, ast_id };
+        let res = Impl { generic_params, target_trait, self_ty, is_negative, items, ast_id };
         Some(id(self.data().impls.alloc(res)))
     }
 
@@ -570,7 +589,7 @@ impl Ctx {
             &self.hygiene,
             |path, _use_tree, is_glob, alias| {
                 imports.push(id(tree.imports.alloc(Import {
-                    path,
+                    path: Interned::new(path),
                     alias,
                     visibility,
                     is_glob,
@@ -599,7 +618,7 @@ impl Ctx {
     }
 
     fn lower_macro_call(&mut self, m: &ast::MacroCall) -> Option<FileItemTreeId<MacroCall>> {
-        let path = ModPath::from_src(m.path()?, &self.hygiene)?;
+        let path = Interned::new(ModPath::from_src(m.path()?, &self.hygiene)?);
         let ast_id = self.source_ast_id_map.ast_id(m);
         let res = MacroCall { path, ast_id };
         Some(id(self.data().macro_calls.alloc(res)))
@@ -633,8 +652,10 @@ impl Ctx {
                         ast::ExternItem::Fn(ast) => {
                             let func_id = self.lower_function(&ast)?;
                             let func = &mut self.data().functions[func_id.index];
-                            func.qualifier.is_unsafe = is_intrinsic_fn_unsafe(&func.name);
-                            func.is_in_extern_block = true;
+                            if is_intrinsic_fn_unsafe(&func.name) {
+                                func.flags.bits |= FnFlags::IS_UNSAFE;
+                            }
+                            func.flags.bits |= FnFlags::IS_IN_EXTERN_BLOCK;
                             func_id.into()
                         }
                         ast::ExternItem::Static(ast) => {
@@ -661,7 +682,7 @@ impl Ctx {
         &mut self,
         owner: GenericsOwner<'_>,
         node: &impl ast::GenericParamsOwner,
-    ) -> GenericParamsId {
+    ) -> Interned<GenericParams> {
         // Generics are part of item headers and may contain inner items we need to collect.
         if let Some(params) = node.generic_param_list() {
             self.collect_inner_items(params.syntax());
@@ -677,7 +698,7 @@ impl Ctx {
         &mut self,
         owner: GenericsOwner<'_>,
         node: &impl ast::GenericParamsOwner,
-    ) -> GenericParamsId {
+    ) -> Interned<GenericParams> {
         let mut sm = &mut Default::default();
         let mut generics = GenericParams::default();
         match owner {
@@ -685,8 +706,7 @@ impl Ctx {
                 generics.fill(&self.body_ctx, sm, node);
                 // lower `impl Trait` in arguments
                 for id in func.params.clone() {
-                    if let Param::Normal(ty) = self.data().params[id] {
-                        let ty = self.data().type_refs.lookup(ty);
+                    if let Param::Normal(ty) = &self.data().params[id] {
                         generics.fill_implicit_impl_trait_args(ty);
                     }
                 }
@@ -719,7 +739,8 @@ impl Ctx {
             }
         }
 
-        self.data().generics.alloc(generics)
+        generics.shrink_to_fit();
+        Interned::new(generics)
     }
 
     fn lower_type_bounds(&mut self, node: &impl ast::TypeBoundsOwner) -> Vec<TypeBound> {
@@ -740,14 +761,20 @@ impl Ctx {
         self.data().vis.alloc(vis)
     }
 
-    fn lower_type_ref(&mut self, type_ref: &ast::Type) -> Idx<TypeRef> {
+    fn lower_trait_ref(&mut self, trait_ref: &ast::Type) -> Option<Interned<TraitRef>> {
+        let trait_ref = TraitRef::from_ast(&self.body_ctx, trait_ref.clone())?;
+        Some(Interned::new(trait_ref))
+    }
+
+    fn lower_type_ref(&mut self, type_ref: &ast::Type) -> Interned<TypeRef> {
         let tyref = TypeRef::from_ast(&self.body_ctx, type_ref.clone());
-        self.data().type_refs.intern(tyref)
+        Interned::new(tyref)
     }
-    fn lower_type_ref_opt(&mut self, type_ref: Option<ast::Type>) -> Idx<TypeRef> {
+
+    fn lower_type_ref_opt(&mut self, type_ref: Option<ast::Type>) -> Interned<TypeRef> {
         match type_ref.map(|ty| self.lower_type_ref(&ty)) {
             Some(it) => it,
-            None => self.data().type_refs.intern(TypeRef::Error),
+            None => Interned::new(TypeRef::Error),
         }
     }
 
diff --git a/crates/hir_def/src/lib.rs b/crates/hir_def/src/lib.rs
index c9e07de86..be9a5e1a0 100644
--- a/crates/hir_def/src/lib.rs
+++ b/crates/hir_def/src/lib.rs
@@ -27,6 +27,7 @@ pub mod dyn_map;
 pub mod keys;
 
 pub mod item_tree;
+pub mod intern;
 
 pub mod adt;
 pub mod data;
diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 9e8e4e9ec..7dd68219f 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -409,6 +409,31 @@ impl DefMap {
             }
         }
     }
+
+    fn shrink_to_fit(&mut self) {
+        // Exhaustive match to require handling new fields.
+        let Self {
+            _c: _,
+            exported_proc_macros,
+            extern_prelude,
+            diagnostics,
+            modules,
+            block: _,
+            edition: _,
+            krate: _,
+            prelude: _,
+            root: _,
+        } = self;
+
+        extern_prelude.shrink_to_fit();
+        exported_proc_macros.shrink_to_fit();
+        diagnostics.shrink_to_fit();
+        modules.shrink_to_fit();
+        for (_, module) in modules.iter_mut() {
+            module.children.shrink_to_fit();
+            module.scope.shrink_to_fit();
+        }
+    }
 }
 
 impl ModuleData {
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index f4e2bda86..f42f92702 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -23,10 +23,11 @@ use crate::{
     attr::Attrs,
     db::DefDatabase,
     derive_macro_as_call_id,
+    intern::Interned,
     item_scope::{ImportType, PerNsGlobImports},
     item_tree::{
-        self, FileItemTreeId, ItemTree, ItemTreeId, MacroCall, MacroRules, Mod, ModItem, ModKind,
-        StructDefKind,
+        self, FileItemTreeId, ItemTree, ItemTreeId, MacroCall, MacroDef, MacroRules, Mod, ModItem,
+        ModKind, StructDefKind,
     },
     macro_call_as_call_id,
     nameres::{
@@ -54,20 +55,22 @@ pub(super) fn collect_defs(
 ) -> DefMap {
     let crate_graph = db.crate_graph();
 
-    // populate external prelude
-    for dep in &crate_graph[def_map.krate].dependencies {
-        log::debug!("crate dep {:?} -> {:?}", dep.name, dep.crate_id);
-        let dep_def_map = db.crate_def_map(dep.crate_id);
-        def_map
-            .extern_prelude
-            .insert(dep.as_name(), dep_def_map.module_id(dep_def_map.root).into());
-
-        // look for the prelude
-        // If the dependency defines a prelude, we overwrite an already defined
-        // prelude. This is necessary to import the "std" prelude if a crate
-        // depends on both "core" and "std".
-        if dep_def_map.prelude.is_some() {
-            def_map.prelude = dep_def_map.prelude;
+    if block.is_none() {
+        // populate external prelude
+        for dep in &crate_graph[def_map.krate].dependencies {
+            log::debug!("crate dep {:?} -> {:?}", dep.name, dep.crate_id);
+            let dep_def_map = db.crate_def_map(dep.crate_id);
+            def_map
+                .extern_prelude
+                .insert(dep.as_name(), dep_def_map.module_id(dep_def_map.root).into());
+
+            // look for the prelude
+            // If the dependency defines a prelude, we overwrite an already defined
+            // prelude. This is necessary to import the "std" prelude if a crate
+            // depends on both "core" and "std".
+            if dep_def_map.prelude.is_some() {
+                def_map.prelude = dep_def_map.prelude;
+            }
         }
     }
 
@@ -106,7 +109,9 @@ pub(super) fn collect_defs(
         }
     }
     collector.collect();
-    collector.finish()
+    let mut def_map = collector.finish();
+    def_map.shrink_to_fit();
+    def_map
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -137,7 +142,7 @@ enum ImportSource {
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 struct Import {
-    path: ModPath,
+    path: Interned<ModPath>,
     alias: Option<ImportAlias>,
     visibility: RawVisibility,
     is_glob: bool,
@@ -179,7 +184,10 @@ impl Import {
         let attrs = &tree.attrs(db, krate, ModItem::from(id.value).into());
         let visibility = &tree[it.visibility];
         Self {
-            path: ModPath::from_segments(PathKind::Plain, iter::once(it.name.clone())),
+            path: Interned::new(ModPath::from_segments(
+                PathKind::Plain,
+                iter::once(it.name.clone()),
+            )),
             alias: it.alias.clone(),
             visibility: visibility.clone(),
             is_glob: false,
@@ -395,7 +403,7 @@ impl DefCollector<'_> {
     /// macro_rules! foo { () => {} }
     /// use foo as bar;
     /// ```
-    fn define_macro(
+    fn define_macro_rules(
         &mut self,
         module_id: LocalModuleId,
         name: Name,
@@ -430,6 +438,21 @@ impl DefCollector<'_> {
         self.def_map.modules[module_id].scope.define_legacy_macro(name, mac);
     }
 
+    /// Define a macro 2.0 macro
+    ///
+    /// The scoped of macro 2.0 macro is equal to normal function
+    fn define_macro_def(
+        &mut self,
+        module_id: LocalModuleId,
+        name: Name,
+        macro_: MacroDefId,
+        vis: &RawVisibility,
+    ) {
+        let vis =
+            self.def_map.resolve_visibility(self.db, module_id, vis).unwrap_or(Visibility::Public);
+        self.update(module_id, &[(Some(name), PerNs::macros(macro_, vis))], vis, ImportType::Named);
+    }
+
     /// Define a proc macro
     ///
     /// A proc macro is similar to normal macro scope, but it would not visible in legacy textual scoped.
@@ -1061,40 +1084,7 @@ impl ModCollector<'_, '_> {
                 }
                 ModItem::MacroCall(mac) => self.collect_macro_call(&self.item_tree[mac]),
                 ModItem::MacroRules(id) => self.collect_macro_rules(id),
-                ModItem::MacroDef(id) => {
-                    let mac = &self.item_tree[id];
-                    let ast_id = InFile::new(self.file_id, mac.ast_id.upcast());
-
-                    // "Macro 2.0" is not currently supported by rust-analyzer, but libcore uses it
-                    // to define builtin macros, so we support at least that part.
-                    let attrs = self.item_tree.attrs(
-                        self.def_collector.db,
-                        krate,
-                        ModItem::from(id).into(),
-                    );
-                    if attrs.by_key("rustc_builtin_macro").exists() {
-                        let krate = self.def_collector.def_map.krate;
-                        let macro_id = find_builtin_macro(&mac.name, krate, ast_id)
-                            .or_else(|| find_builtin_derive(&mac.name, krate, ast_id));
-                        if let Some(macro_id) = macro_id {
-                            let vis = self
-                                .def_collector
-                                .def_map
-                                .resolve_visibility(
-                                    self.def_collector.db,
-                                    self.module_id,
-                                    &self.item_tree[mac.visibility],
-                                )
-                                .unwrap_or(Visibility::Public);
-                            self.def_collector.update(
-                                self.module_id,
-                                &[(Some(mac.name.clone()), PerNs::macros(macro_id, vis))],
-                                vis,
-                                ImportType::Named,
-                            );
-                        }
-                    }
-                }
+                ModItem::MacroDef(id) => self.collect_macro_def(id),
                 ModItem::Impl(imp) => {
                     let module = self.def_collector.def_map.module_id(self.module_id);
                     let impl_id =
@@ -1412,9 +1402,19 @@ impl ModCollector<'_, '_> {
 
         // Case 1: builtin macros
         if attrs.by_key("rustc_builtin_macro").exists() {
+            // `#[rustc_builtin_macro = "builtin_name"]` overrides the `macro_rules!` name.
+            let name;
+            let name = match attrs.by_key("rustc_builtin_macro").string_value() {
+                Some(it) => {
+                    // FIXME: a hacky way to create a Name from string.
+                    name = tt::Ident { text: it.clone(), id: tt::TokenId::unspecified() }.as_name();
+                    &name
+                }
+                None => &mac.name,
+            };
             let krate = self.def_collector.def_map.krate;
-            if let Some(macro_id) = find_builtin_macro(&mac.name, krate, ast_id) {
-                self.def_collector.define_macro(
+            if let Some(macro_id) = find_builtin_macro(name, krate, ast_id) {
+                self.def_collector.define_macro_rules(
                     self.module_id,
                     mac.name.clone(),
                     macro_id,
@@ -1430,11 +1430,53 @@ impl ModCollector<'_, '_> {
             kind: MacroDefKind::Declarative(ast_id),
             local_inner: is_local_inner,
         };
-        self.def_collector.define_macro(self.module_id, mac.name.clone(), macro_id, is_export);
+        self.def_collector.define_macro_rules(
+            self.module_id,
+            mac.name.clone(),
+            macro_id,
+            is_export,
+        );
+    }
+
+    fn collect_macro_def(&mut self, id: FileItemTreeId<MacroDef>) {