15 files changed, 117 insertions, 131 deletions

diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index 8055a07db..8eb3c577d 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -5,7 +5,7 @@ pub(crate) mod docs;
 
 use std::sync::Arc;
 
-use ra_db::{CrateId, Edition, FileId, SourceRootId};
+use ra_db::{CrateId, Edition, FileId};
 use ra_syntax::ast::{self, NameOwner, TypeAscriptionOwner};
 
 use crate::{
@@ -76,10 +76,8 @@ impl Crate {
         crate_graph.edition(self.crate_id)
     }
 
-    // FIXME: should this be in source_binder?
-    pub fn source_root_crates(db: &impl DefDatabase, source_root: SourceRootId) -> Vec<Crate> {
-        let crate_ids = db.source_root_crates(source_root);
-        crate_ids.iter().map(|&crate_id| Crate { crate_id }).collect()
+    pub fn all(db: &impl DefDatabase) -> Vec<Crate> {
+        db.crate_graph().iter().map(|crate_id| Crate { crate_id }).collect()
     }
 }
 
diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 73d7d6fb6..489a3b19c 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -111,37 +111,37 @@ pub trait DefDatabase: InternDatabase + HirDebugDatabase {
     #[salsa::invoke(CrateDefMap::crate_def_map_query)]
     fn crate_def_map(&self, krate: Crate) -> Arc<CrateDefMap>;
 
-    #[salsa::invoke(crate::impl_block::impls_in_module_with_source_map_query)]
+    #[salsa::invoke(ModuleImplBlocks::impls_in_module_with_source_map_query)]
     fn impls_in_module_with_source_map(
         &self,
         module: Module,
     ) -> (Arc<ModuleImplBlocks>, Arc<ImplSourceMap>);
 
-    #[salsa::invoke(crate::impl_block::impls_in_module)]
+    #[salsa::invoke(ModuleImplBlocks::impls_in_module_query)]
     fn impls_in_module(&self, module: Module) -> Arc<ModuleImplBlocks>;
 
     #[salsa::invoke(crate::generics::GenericParams::generic_params_query)]
     fn generic_params(&self, def: GenericDef) -> Arc<GenericParams>;
 
-    #[salsa::invoke(crate::FnData::fn_data_query)]
+    #[salsa::invoke(FnData::fn_data_query)]
     fn fn_data(&self, func: Function) -> Arc<FnData>;
 
-    #[salsa::invoke(crate::type_alias::type_alias_data_query)]
+    #[salsa::invoke(TypeAliasData::type_alias_data_query)]
     fn type_alias_data(&self, typ: TypeAlias) -> Arc<TypeAliasData>;
 
-    #[salsa::invoke(crate::ConstData::const_data_query)]
+    #[salsa::invoke(ConstData::const_data_query)]
     fn const_data(&self, konst: Const) -> Arc<ConstData>;
 
-    #[salsa::invoke(crate::ConstData::static_data_query)]
+    #[salsa::invoke(ConstData::static_data_query)]
     fn static_data(&self, konst: Static) -> Arc<ConstData>;
 
-    #[salsa::invoke(crate::lang_item::LangItems::module_lang_items_query)]
+    #[salsa::invoke(LangItems::module_lang_items_query)]
     fn module_lang_items(&self, module: Module) -> Option<Arc<LangItems>>;
 
-    #[salsa::invoke(crate::lang_item::LangItems::crate_lang_items_query)]
+    #[salsa::invoke(LangItems::crate_lang_items_query)]
     fn crate_lang_items(&self, krate: Crate) -> Arc<LangItems>;
 
-    #[salsa::invoke(crate::lang_item::LangItems::lang_item_query)]
+    #[salsa::invoke(LangItems::lang_item_query)]
     fn lang_item(&self, start_crate: Crate, item: SmolStr) -> Option<LangItemTarget>;
 
     #[salsa::invoke(crate::code_model::docs::documentation_query)]
diff --git a/crates/ra_hir/src/from_source.rs b/crates/ra_hir/src/from_source.rs
index a012f33f7..f80d8eb5f 100644
--- a/crates/ra_hir/src/from_source.rs
+++ b/crates/ra_hir/src/from_source.rs
@@ -189,14 +189,14 @@ impl Module {
             ModuleSource::SourceFile(_) => None,
         };
 
-        let source_root_id = db.file_source_root(src.file_id.original_file(db));
-        db.source_root_crates(source_root_id).iter().map(|&crate_id| Crate { crate_id }).find_map(
-            |krate| {
+        db.relevant_crates(src.file_id.original_file(db))
+            .iter()
+            .map(|&crate_id| Crate { crate_id })
+            .find_map(|krate| {
                 let def_map = db.crate_def_map(krate);
                 let module_id = def_map.find_module_by_source(src.file_id, decl_id)?;
                 Some(Module { krate, module_id })
-            },
-        )
+            })
     }
 }
 
diff --git a/crates/ra_hir/src/ids.rs b/crates/ra_hir/src/ids.rs
index 85b022744..499dcafea 100644
--- a/crates/ra_hir/src/ids.rs
+++ b/crates/ra_hir/src/ids.rs
@@ -85,11 +85,7 @@ impl HirFileId {
                 // Note:
                 // The final goal we would like to make all parse_macro success,
                 // such that the following log will not call anyway.
-                log::warn!(
-                    "fail on macro_parse: (reason: {}) {}",
-                    err,
-                    macro_call_id.debug_dump(db)
-                );
+                log::warn!("fail on macro_parse: (reason: {})", err,);
             })
             .ok()?;
         match macro_file.macro_file_kind {
@@ -367,35 +363,6 @@ impl AstItemDef<ast::TypeAliasDef> for TypeAliasId {
     }
 }
 
-impl MacroCallId {
-    pub fn debug_dump(self, db: &impl AstDatabase) -> String {
-        let loc = self.loc(db);
-        let node = loc.ast_id.to_node(db);
-        let syntax_str = {
-            let mut res = String::new();
-            node.syntax().text().for_each_chunk(|chunk| {
-                if !res.is_empty() {
-                    res.push(' ')
-                }
-                res.push_str(chunk)
-            });
-            res
-        };
-
-        // dump the file name
-        let file_id: HirFileId = self.loc(db).ast_id.file_id();
-        let original = file_id.original_file(db);
-        let macro_rules = db.macro_def(loc.def);
-
-        format!(
-            "macro call [file: {:?}] : {}\nhas rules: {}",
-            db.file_relative_path(original),
-            syntax_str,
-            macro_rules.is_some()
-        )
-    }
-}
-
 /// This exists just for Chalk, because Chalk just has a single `StructId` where
 /// we have different kinds of ADTs, primitive types and special type
 /// constructors like tuples and function pointers.
diff --git a/crates/ra_hir/src/impl_block.rs b/crates/ra_hir/src/impl_block.rs
index 55dfc393b..33ef87563 100644
--- a/crates/ra_hir/src/impl_block.rs
+++ b/crates/ra_hir/src/impl_block.rs
@@ -176,6 +176,25 @@ pub struct ModuleImplBlocks {
 }
 
 impl ModuleImplBlocks {
+    pub(crate) fn impls_in_module_with_source_map_query(
+        db: &(impl DefDatabase + AstDatabase),
+        module: Module,
+    ) -> (Arc<ModuleImplBlocks>, Arc<ImplSourceMap>) {
+        let mut source_map = ImplSourceMap::default();
+        let crate_graph = db.crate_graph();
+        let cfg_options = crate_graph.cfg_options(module.krate.crate_id());
+
+        let result = ModuleImplBlocks::collect(db, cfg_options, module, &mut source_map);
+        (Arc::new(result), Arc::new(source_map))
+    }
+
+    pub(crate) fn impls_in_module_query(
+        db: &impl DefDatabase,
+        module: Module,
+    ) -> Arc<ModuleImplBlocks> {
+        db.impls_in_module_with_source_map(module).0
+    }
+
     fn collect(
         db: &(impl DefDatabase + AstDatabase),
         cfg_options: &CfgOptions,
@@ -264,19 +283,3 @@ impl ModuleImplBlocks {
         }
     }
 }
-
-pub(crate) fn impls_in_module_with_source_map_query(
-    db: &(impl DefDatabase + AstDatabase),
-    module: Module,
-) -> (Arc<ModuleImplBlocks>, Arc<ImplSourceMap>) {
-    let mut source_map = ImplSourceMap::default();
-    let crate_graph = db.crate_graph();
-    let cfg_options = crate_graph.cfg_options(module.krate.crate_id());
-
-    let result = ModuleImplBlocks::collect(db, cfg_options, module, &mut source_map);
-    (Arc::new(result), Arc::new(source_map))
-}
-
-pub(crate) fn impls_in_module(db: &impl DefDatabase, module: Module) -> Arc<ModuleImplBlocks> {
-    db.impls_in_module_with_source_map(module).0
-}
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 9cbd9a8ae..ca261e8f5 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -51,6 +51,7 @@ mod lang_item;
 mod generics;
 mod resolve;
 pub mod diagnostics;
+mod util;
 
 mod code_model;
 
diff --git a/crates/ra_hir/src/mock.rs b/crates/ra_hir/src/mock.rs
index 827424983..0b278deb3 100644
--- a/crates/ra_hir/src/mock.rs
+++ b/crates/ra_hir/src/mock.rs
@@ -5,10 +5,10 @@ use std::{panic, sync::Arc};
 use parking_lot::Mutex;
 use ra_cfg::CfgOptions;
 use ra_db::{
-    salsa, CrateGraph, CrateId, Edition, FileId, FilePosition, SourceDatabase, SourceRoot,
-    SourceRootId,
+    salsa, CrateGraph, CrateId, Edition, FileId, FileLoader, FileLoaderDelegate, FilePosition,
+    SourceDatabase, SourceDatabaseExt, SourceRoot, SourceRootId,
 };
-use relative_path::RelativePathBuf;
+use relative_path::{RelativePath, RelativePathBuf};
 use rustc_hash::FxHashMap;
 use test_utils::{extract_offset, parse_fixture, CURSOR_MARKER};
 
@@ -17,6 +17,7 @@ use crate::{db, debug::HirDebugHelper, diagnostics::DiagnosticSink};
 pub const WORKSPACE: SourceRootId = SourceRootId(0);
 
 #[salsa::database(
+    ra_db::SourceDatabaseExtStorage,
     ra_db::SourceDatabaseStorage,
     db::InternDatabaseStorage,
     db::AstDatabaseStorage,
@@ -34,6 +35,22 @@ pub struct MockDatabase {
 
 impl panic::RefUnwindSafe for MockDatabase {}
 
+impl FileLoader for MockDatabase {
+    fn file_text(&self, file_id: FileId) -> Arc<String> {
+        FileLoaderDelegate(self).file_text(file_id)
+    }
+    fn resolve_relative_path(
+        &self,
+        anchor: FileId,
+        relative_path: &RelativePath,
+    ) -> Option<FileId> {
+        FileLoaderDelegate(self).resolve_relative_path(anchor, relative_path)
+    }
+    fn relevant_crates(&self, file_id: FileId) -> Arc<Vec<CrateId>> {
+        FileLoaderDelegate(self).relevant_crates(file_id)
+    }
+}
+
 impl HirDebugHelper for MockDatabase {
     fn crate_name(&self, krate: CrateId) -> Option<String> {
         self.crate_names.get(&krate).cloned()
diff --git a/crates/ra_hir/src/nameres/tests/incremental.rs b/crates/ra_hir/src/nameres/tests/incremental.rs
index c41862a0b..af9c39760 100644
--- a/crates/ra_hir/src/nameres/tests/incremental.rs
+++ b/crates/ra_hir/src/nameres/tests/incremental.rs
@@ -2,7 +2,7 @@ use super::*;
 
 use std::sync::Arc;
 
-use ra_db::SourceDatabase;
+use ra_db::{SourceDatabase, SourceDatabaseExt};
 
 fn check_def_map_is_not_recomputed(initial: &str, file_change: &str) {
     let (mut db, pos) = MockDatabase::with_position(initial);
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index d161735e8..cc9746f6d 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -17,8 +17,8 @@ use std::sync::Arc;
 use std::{fmt, iter, mem};
 
 use crate::{
-    db::HirDatabase, expr::ExprId, type_ref::Mutability, Adt, Crate, DefWithBody, GenericParams,
-    HasGenericParams, Name, Trait, TypeAlias,
+    db::HirDatabase, expr::ExprId, type_ref::Mutability, util::make_mut_slice, Adt, Crate,
+    DefWithBody, GenericParams, HasGenericParams, Name, Trait, TypeAlias,
 };
 use display::{HirDisplay, HirFormatter};
 
@@ -308,12 +308,9 @@ impl Substs {
     }
 
     pub fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
-        // Without an Arc::make_mut_slice, we can't avoid the clone here:
-        let mut v: Vec<_> = self.0.iter().cloned().collect();
-        for t in &mut v {
+        for t in make_mut_slice(&mut self.0) {
             t.walk_mut(f);
         }
-        self.0 = v.into();
     }
 
     pub fn as_single(&self) -> &Ty {
@@ -330,8 +327,7 @@ impl Substs {
                 .params_including_parent()
                 .into_iter()
                 .map(|p| Ty::Param { idx: p.idx, name: p.name.clone() })
-                .collect::<Vec<_>>()
-                .into(),
+                .collect(),
         )
     }
 
@@ -342,8 +338,7 @@ impl Substs {
                 .params_including_parent()
                 .into_iter()
                 .map(|p| Ty::Bound(p.idx))
-                .collect::<Vec<_>>()
-                .into(),
+                .collect(),
         )
     }
 
@@ -541,12 +536,9 @@ impl TypeWalk for FnSig {
     }
 
     fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
-        // Without an Arc::make_mut_slice, we can't avoid the clone here:
-        let mut v: Vec<_> = self.params_and_return.iter().cloned().collect();
-        for t in &mut v {
+        for t in make_mut_slice(&mut self.params_and_return) {
             t.walk_mut(f);
         }
-        self.params_and_return = v.into();
     }
 }
 
@@ -756,11 +748,9 @@ impl TypeWalk for Ty {
                 p_ty.parameters.walk_mut(f);
             }
             Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
-                let mut v: Vec<_> = predicates.iter().cloned().collect();
-                for p in &mut v {
+                for p in make_mut_slice(predicates) {
                     p.walk_mut(f);
                 }
-                *predicates = v.into();
             }
             Ty::Param { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {}
         }
diff --git a/crates/ra_hir/src/ty/infer/unify.rs b/crates/ra_hir/src/ty/infer/unify.rs
index d161aa6b3..014c7981f 100644
--- a/crates/ra_hir/src/ty/infer/unify.rs
+++ b/crates/ra_hir/src/ty/infer/unify.rs
@@ -6,6 +6,7 @@ use crate::ty::{
     Canonical, InEnvironment, InferTy, ProjectionPredicate, ProjectionTy, Substs, TraitRef, Ty,
     TypeWalk,
 };
+use crate::util::make_mut_slice;
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     pub(super) fn canonicalizer<'b>(&'b mut self) -> Canonicalizer<'a, 'b, D>
@@ -74,10 +75,11 @@ where
         })
     }
 
-    fn do_canonicalize_trait_ref(&mut self, trait_ref: TraitRef) -> TraitRef {
-        let substs =
-            trait_ref.substs.iter().map(|ty| self.do_canonicalize_ty(ty.clone())).collect();
-        TraitRef { trait_: trait_ref.trait_, substs: Substs(substs) }
+    fn do_canonicalize_trait_ref(&mut self, mut trait_ref: TraitRef) -> TraitRef {
+        for ty in make_mut_slice(&mut trait_ref.substs.0) {
+            *ty = self.do_canonicalize_ty(ty.clone());
+        }
+        trait_ref
     }
 
     fn into_canonicalized<T>(self, result: T) -> Canonicalized<T> {
@@ -87,10 +89,11 @@ where
         }
     }
 
-    fn do_canonicalize_projection_ty(&mut self, projection_ty: ProjectionTy) -> ProjectionTy {
-        let params =
-            projection_ty.parameters.iter().map(|ty| self.do_canonicalize_ty(ty.clone())).collect();
-        ProjectionTy { associated_ty: projection_ty.associated_ty, parameters: Substs(params) }
+    fn do_canonicalize_projection_ty(&mut self, mut projection_ty: ProjectionTy) -> ProjectionTy {
+        for ty in make_mut_slice(&mut projection_ty.parameters.0) {
+            *ty = self.do_canonicalize_ty(ty.clone());
+        }
+        projection_ty
     }
 
     fn do_canonicalize_projection_predicate(
diff --git a/crates/ra_hir/src/ty/lower.rs b/crates/ra_hir/src/ty/lower.rs
index a604c02e2..366556134 100644
--- a/crates/ra_hir/src/ty/lower.rs
+++ b/crates/ra_hir/src/ty/lower.rs
@@ -22,6 +22,7 @@ use crate::{
     resolve::{Resolver, TypeNs},
     ty::Adt,
     type_ref::{TypeBound, TypeRef},
+    util::make_mut_slice,
     BuiltinType, Const, Enum, EnumVariant, Function, ModuleDef, Path, Static, Struct, StructField,
     Trait, TypeAlias, Union,
 };
@@ -31,11 +32,11 @@ impl Ty {
         match type_ref {
             TypeRef::Never => Ty::simple(TypeCtor::Never),
             TypeRef::Tuple(inner) => {
-                let inner_tys =
-                    inner.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect::<Vec<_>>();
+                let inner_tys: Arc<[Ty]> =
+                    inner.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect();
                 Ty::apply(
                     TypeCtor::Tuple { cardinality: inner_tys.len() as u16 },
-                    Substs(inner_tys.into()),
+                    Substs(inner_tys),
                 )
             }
             TypeRef::Path(path) => Ty::from_hir_path(db, resolver, path),
@@ -57,9 +58,7 @@ impl Ty {
             }
             TypeRef::Placeholder => Ty::Unknown,
             TypeRef::Fn(params) => {
-                let inner_tys =
-                    params.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect::<Vec<_>>();
-                let sig = Substs(inner_tys.into());
+                let sig = Substs(params.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect());
                 Ty::apply(TypeCtor::FnPtr { num_args: sig.len() as u16 - 1 }, sig)
             }
             TypeRef::DynTrait(bounds) => {
@@ -69,8 +68,8 @@ impl Ty {
                     .flat_map(|b| {
                         GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
                     })
-                    .collect::<Vec<_>>();
-                Ty::Dyn(predicates.into())
+                    .collect();
+                Ty::Dyn(predicates)
             }
             TypeRef::ImplTrait(bounds) => {
                 let self_ty = Ty::Bound(0);
@@ -79,8 +78,8 @@ impl Ty {
                     .flat_map(|b| {
                         GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
                     })
-                    .collect::<Vec<_>>();
-                Ty::Opaque(predicates.into())
+                    .collect();
+                Ty::Opaque(predicates)
             }
             TypeRef::Error => Ty::Unknown,
         }
@@ -392,10 +391,7 @@ impl TraitRef {
     ) -> Self {
         let mut substs = TraitRef::substs_from_path(db, resolver, segment, resolved);
         if let Some(self_ty) = explicit_self_ty {
-            // FIXME this could be nicer
-            let mut substs_vec = substs.0.to_vec();
-            substs_vec[0] = self_ty;
-            substs.0 = substs_vec.into();
+            make_mut_slice(&mut substs.0)[0] = self_ty;
         }
         TraitRef { trait_: resolved, substs }
     }
@@ -558,13 +554,12 @@ pub(crate) fn generic_predicates_for_param_query(
     param_idx: u32,
 ) -> Arc<[GenericPredicate]> {
     let resolver = def.resolver(db);
-    let predicates = resolver
+    resolver
         .where_predicates_in_scope()
         // we have to filter out all other predicates *first*, before attempting to lower them
         .filter(|pred| Ty::from_hir_only_param(db, &resolver, &pred.type_ref) == Some(param_idx))
         .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
-        .collect::<Vec<_>>();
-    predicates.into()
+        .collect()
 }
 
 pub(crate) fn trait_env(
@@ -585,11 +580,10 @@ pub(crate) fn generic_predicates_query(
     def: GenericDef,
 ) -> Arc<[GenericPredicate]> {
     let resolver = def.resolver(db);
-    let predicates = resolver
+    resolver
         .where_predicates_in_scope()
         .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
-        .collect::<Vec<_>>();
-    predicates.into()
+        .collect()
 }
 
 /// Resolve the default type params from generics
@@ -603,9 +597,9 @@ pub(crate) fn generic_defaults_query(db: &impl HirDatabase, def: GenericDef) ->
         .map(|p| {
             p.default.as_ref().map_or(Ty::Unknown, |path| Ty::from_hir_path(db, &resolver, path))
         })
-        .collect::<Vec<_>>();
+        .collect();
 
-    Substs(defaults.into())
+    Substs(defaults)
 }
 
 fn fn_sig_for_fn(db: &impl HirDatabase, def: Function) -> FnSig {
diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index b0f67ae50..0cb5c3798 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -89,7 +89,7 @@ pub(crate) fn impls_for_trait_query(
     }
     let crate_impl_blocks = db.impls_in_crate(krate);
     impls.extend(crate_impl_blocks.lookup_impl_blocks_for_trait(trait_));
-    impls.into_iter().collect::<Vec<_>>().into()
+    impls.into_iter().collect()
 }
 
 /// A set of clauses that we assume to be true. E.g. if we are inside this function:
diff --git a/crates/ra_hir/src/ty/traits/chalk.rs b/crates/ra_hir/src/ty/traits/chalk.rs
index 9168de709..00aaf65d9 100644
--- a/crates/ra_hir/src/ty/traits/chalk.rs
+++ b/crates/ra_hir/src/ty/traits/chalk.rs
@@ -126,8 +126,7 @@ impl ToChalk for Substs {
                 chalk_ir::Parameter(chalk_ir::ParameterKind::Ty(ty)) => from_chalk(db, ty),
                 chalk_ir::Parameter(chalk_ir::ParameterKind::Lifetime(_)) => unimplemented!(),
             })
-            .collect::<Vec<_>>()
-            .into();
+            .collect();
         Substs(tys)
     }
 }
diff --git a/crates/ra_hir/src/type_alias.rs b/crates/ra_hir/src/type_alias.rs
index 3b38c4740..674a46102 100644
--- a/crates/ra_hir/src/type_alias.rs
+++ b/crates/ra_hir/src/type_alias.rs
@@ -17,12 +17,14 @@ pub struct TypeAliasData {
     pub(crate) type_ref: Option<TypeRef>,
 }
 
-pub(crate) fn type_alias_data_query(
-    db: &(impl DefDatabase + AstDatabase),
-    typ: TypeAlias,
-) -> Arc<TypeAliasData> {
-    let node = typ.source(db).ast;
-    let name = node.name().map_or_else(Name::missing, |n| n.as_name());
-    let type_ref = node.type_ref().map(TypeRef::from_ast);
-    Arc::new(TypeAliasData { name, type_ref })
+impl TypeAliasData {
+    pub(crate) fn type_alias_data_query(
+        db: &(impl DefDatabase + AstDatabase),
+        typ: TypeAlias,
+    ) -> Arc<TypeAliasData> {
+        let node = typ.source(db).ast;
+        let name = node.name().map_or_else(Name::missing, |n| n.as_name());
+        let type_ref = node.type_ref().map(TypeRef::from_ast);
+        Arc::new(TypeAliasData { name, type_ref })
+    }
 }
diff --git a/crates/ra_hir/src/util.rs b/crates/ra_hir/src/util.rs
new file mode 100644
index 000000000..0095ee45d
--- /dev/null
+++ b/crates/ra_hir/src/util.rs
@@ -0,0 +1,12 @@
+//! Internal utility functions.
+
+use std::sync::Arc;
+
+/// Helper for mutating `Arc<[T]>` (i.e. `Arc::make_mut` for Arc slices).
+/// The underlying values are cloned if there are other strong references.
+pub(crate) fn make_mut_slice<T: Clone>(a: &mut Arc<[T]>) -> &mut [T] {
+    if Arc::get_mut(a).is_none() {
+        *a = a.iter().cloned().collect();
+    }
+    Arc::get_mut(a).unwrap()
+}