diff --git a/crates/libanalysis/src/imp.rs b/crates/libanalysis/src/imp.rs
index 73a6f43064..c1e144025b 100644
--- a/crates/libanalysis/src/imp.rs
+++ b/crates/libanalysis/src/imp.rs
@@ -17,8 +17,8 @@ use libsyntax2::{
 use {
     FileId, FileResolver, Query, Diagnostic, SourceChange, SourceFileEdit, Position, FileSystemEdit,
     JobToken, CrateGraph, CrateId,
-    module_map::Problem,
-    roots::SourceRoot,
+    module_map::{ModuleMap, Problem},
+    roots::{SourceRoot, ReadonlySourceRoot, WritableSourceRoot},
 };
 
 #[derive(Debug)]
@@ -57,6 +57,10 @@ impl AnalysisHostImpl {
         }
         self.data_mut().crate_graph = graph;
     }
+    pub fn set_libraries(&mut self, libs: impl Iterator<Item=impl Iterator<Item=(FileId, String)>>) {
+        let libs = libs.map(ReadonlySourceRoot::new).collect::<Vec<_>>();
+        self.data_mut().libs = Arc::new(libs);
+    }
     fn data_mut(&mut self) -> &mut WorldData {
         Arc::make_mut(&mut self.data)
     }
@@ -85,19 +89,33 @@ impl Clone for AnalysisImpl {
 }
 
 impl AnalysisImpl {
+    fn root(&self, file_id: FileId) -> &SourceRoot {
+        if self.data.root.contains(file_id) {
+            return &self.data.root;
+        }
+        self.data.libs.iter().find(|it| it.contains(file_id)).unwrap()
+    }
     pub fn file_syntax(&self, file_id: FileId) -> &File {
-        self.data.root.syntax(file_id)
+        self.root(file_id).syntax(file_id)
     }
     pub fn file_line_index(&self, file_id: FileId) -> &LineIndex {
-        self.data.root.lines(file_id)
+        self.root(file_id).lines(file_id)
     }
-    pub fn world_symbols(&self,  query: Query, token: &JobToken) -> Vec<(FileId, FileSymbol)> {
+    pub fn world_symbols(&self, query: Query, token: &JobToken) -> Vec<(FileId, FileSymbol)> {
         self.reindex();
-        query.search(&self.data.root.symbols(), token)
+        let mut buf = Vec::new();
+        if query.libs {
+            self.data.libs.iter()
+                .for_each(|it| it.symbols(&mut buf));
+        } else {
+            self.data.root.symbols(&mut buf);
+        }
+        query.search(&buf, token)
+
     }
-    pub fn parent_module(&self, id: FileId) -> Vec<(FileId, FileSymbol)> {
-        let module_map = self.data.root.module_map();
-        let id = module_map.file2module(id);
+    pub fn parent_module(&self, file_id: FileId) -> Vec<(FileId, FileSymbol)> {
+        let module_map = self.root(file_id).module_map();
+        let id = module_map.file2module(file_id);
         module_map
             .parent_modules(
                 id,
@@ -117,12 +135,12 @@ impl AnalysisImpl {
             .collect()
     }
 
-    pub fn crate_for(&self, id: FileId) -> Vec<CrateId> {
-        let module_map = self.data.root.module_map();
+    pub fn crate_for(&self, file_id: FileId) -> Vec<CrateId> {
+        let module_map = self.root(file_id).module_map();
         let crate_graph = &self.data.crate_graph;
         let mut res = Vec::new();
         let mut work = VecDeque::new();
-        work.push_back(id);
+        work.push_back(file_id);
         let mut visited = HashSet::new();
         while let Some(id) = work.pop_front() {
             if let Some(crate_id) = crate_graph.crate_id_for_crate_root(id) {
@@ -148,11 +166,13 @@ impl AnalysisImpl {
     }
     pub fn approximately_resolve_symbol(
         &self,
-        id: FileId,
+        file_id: FileId,
         offset: TextUnit,
         token: &JobToken,
     ) -> Vec<(FileId, FileSymbol)> {
-        let file = self.file_syntax(id);
+        let root = self.root(file_id);
+        let module_map = root.module_map();
+        let file = root.syntax(file_id);
         let syntax = file.syntax();
         if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(syntax, offset) {
             return self.index_resolve(name_ref, token);
@@ -160,7 +180,7 @@ impl AnalysisImpl {
         if let Some(name) = find_node_at_offset::<ast::Name>(syntax, offset) {
             if let Some(module) = name.syntax().parent().and_then(ast::Module::cast) {
                 if module.has_semi() {
-                    let file_ids = self.resolve_module(id, module);
+                    let file_ids = self.resolve_module(module_map, file_id, module);
 
                     let res = file_ids.into_iter().map(|id| {
                         let name = module.name()
@@ -182,13 +202,16 @@ impl AnalysisImpl {
     }
 
     pub fn diagnostics(&self, file_id: FileId) -> Vec<Diagnostic> {
-        let syntax = self.file_syntax(file_id);
+        let root = self.root(file_id);
+        let module_map = root.module_map();
+        let syntax = root.syntax(file_id);
+
         let mut res = libeditor::diagnostics(&syntax)
             .into_iter()
             .map(|d| Diagnostic { range: d.range, message: d.msg, fix: None })
             .collect::<Vec<_>>();
 
-        self.data.root.module_map().problems(
+        module_map.problems(
             file_id,
             &*self.file_resolver,
             &|file_id| self.file_syntax(file_id),
@@ -257,13 +280,12 @@ impl AnalysisImpl {
         self.world_symbols(query, token)
     }
 
-    fn resolve_module(&self, id: FileId, module: ast::Module) -> Vec<FileId> {
+    fn resolve_module(&self, module_map: &ModuleMap, file_id: FileId, module: ast::Module) -> Vec<FileId> {
         let name = match module.name() {
             Some(name) => name.text(),
             None => return Vec::new(),
         };
-        let module_map = self.data.root.module_map();
-        let id = module_map.file2module(id);
+        let id = module_map.file2module(file_id);
         module_map
             .child_module_by_name(
                 id, name.as_str(),
@@ -285,7 +307,8 @@ impl AnalysisImpl {
 #[derive(Clone, Default, Debug)]
 struct WorldData {
     crate_graph: CrateGraph,
-    root: SourceRoot,
+    root: WritableSourceRoot,
+    libs: Arc<Vec<ReadonlySourceRoot>>,
 }
 
 impl SourceChange {
diff --git a/crates/libanalysis/src/lib.rs b/crates/libanalysis/src/lib.rs
index b044fdae81..9ae87d46cf 100644
--- a/crates/libanalysis/src/lib.rs
+++ b/crates/libanalysis/src/lib.rs
@@ -68,6 +68,9 @@ impl AnalysisHost {
     pub fn set_crate_graph(&mut self, graph: CrateGraph) {
         self.imp.set_crate_graph(graph)
     }
+    pub fn set_libraries(&mut self, libs: impl Iterator<Item=impl Iterator<Item=(FileId, String)>>) {
+        self.imp.set_libraries(libs)
+    }
 }
 
 #[derive(Debug)]
@@ -114,6 +117,7 @@ pub struct Query {
     query: String,
     lowercased: String,
     only_types: bool,
+    libs: bool,
     exact: bool,
     limit: usize,
 }
@@ -125,6 +129,7 @@ impl Query {
             query,
             lowercased,
             only_types: false,
+            libs: false,
             exact: false,
             limit: usize::max_value()
         }
@@ -132,6 +137,9 @@ impl Query {
     pub fn only_types(&mut self) {
         self.only_types = true;
     }
+    pub fn libs(&mut self) {
+        self.libs = true;
+    }
     pub fn exact(&mut self) {
         self.exact = true;
     }
diff --git a/crates/libanalysis/src/module_map.rs b/crates/libanalysis/src/module_map.rs
index 5ceb718178..1b225eceed 100644
--- a/crates/libanalysis/src/module_map.rs
+++ b/crates/libanalysis/src/module_map.rs
@@ -56,6 +56,10 @@ pub enum Problem {
 }
 
 impl ModuleMap {
+    pub fn new() -> ModuleMap {
+        Default::default()
+    }
+
     pub fn update_file(&mut self, file: FileId, change_kind: ChangeKind) {
         self.state.get_mut().changes.push((file, change_kind));
     }
diff --git a/crates/libanalysis/src/roots.rs b/crates/libanalysis/src/roots.rs
index 01de3e1284..a65668c9b8 100644
--- a/crates/libanalysis/src/roots.rs
+++ b/crates/libanalysis/src/roots.rs
@@ -13,16 +13,24 @@ use libsyntax2::File;
 use {
     FileId,
     module_map::{ModuleMap, ChangeKind},
-    symbol_index::FileSymbols,
+    symbol_index::SymbolIndex,
 };
 
+pub(crate) trait SourceRoot {
+    fn contains(&self, file_id: FileId) -> bool;
+    fn module_map(&self) -> &ModuleMap;
+    fn lines(&self, file_id: FileId) -> &LineIndex;
+    fn syntax(&self, file_id: FileId) -> &File;
+    fn symbols<'a>(&'a self, acc: &mut Vec<&'a SymbolIndex>);
+}
+
 #[derive(Clone, Default, Debug)]
-pub(crate) struct SourceRoot {
-    file_map: HashMap<FileId, Arc<(FileData, OnceCell<FileSymbols>)>>,
+pub(crate) struct WritableSourceRoot {
+    file_map: HashMap<FileId, Arc<(FileData, OnceCell<SymbolIndex>)>>,
     module_map: ModuleMap,
 }
 
-impl SourceRoot {
+impl WritableSourceRoot {
     pub fn update(&mut self, file_id: FileId, text: Option<String>) {
         let change_kind = if self.file_map.remove(&file_id).is_some() {
             if text.is_some() {
@@ -40,31 +48,6 @@ impl SourceRoot {
             self.file_map.insert(file_id, Arc::new((file_data, Default::default())));
         }
     }
-    pub fn module_map(&self) -> &ModuleMap {
-        &self.module_map
-    }
-    pub fn lines(&self, file_id: FileId) -> &LineIndex {
-        let data = self.data(file_id);
-        data.lines.get_or_init(|| LineIndex::new(&data.text))
-    }
-    pub fn syntax(&self, file_id: FileId) -> &File {
-        let data = self.data(file_id);
-        let text = &data.text;
-        let syntax = &data.syntax;
-        match panic::catch_unwind(panic::AssertUnwindSafe(|| syntax.get_or_init(|| File::parse(text)))) {
-            Ok(file) => file,
-            Err(err) => {
-                error!("Parser paniced on:\n------\n{}\n------\n", &data.text);
-                panic::resume_unwind(err)
-            }
-        }
-    }
-    pub(crate) fn symbols(&self) -> Vec<&FileSymbols> {
-        self.file_map
-            .iter()
-            .map(|(&file_id, data)| symbols(file_id, data))
-            .collect()
-    }
     pub fn reindex(&self) {
         let now = Instant::now();
         self.file_map
@@ -83,9 +66,31 @@ impl SourceRoot {
     }
 }
 
-fn symbols(file_id: FileId, (data, symbols): &(FileData, OnceCell<FileSymbols>)) -> &FileSymbols {
+impl SourceRoot for WritableSourceRoot {
+    fn contains(&self, file_id: FileId) -> bool {
+        self.file_map.contains_key(&file_id)
+    }
+    fn module_map(&self) -> &ModuleMap {
+        &self.module_map
+    }
+    fn lines(&self, file_id: FileId) -> &LineIndex {
+        self.data(file_id).lines()
+    }
+    fn syntax(&self, file_id: FileId) -> &File {
+        self.data(file_id).syntax()
+    }
+    fn symbols<'a>(&'a self, acc: &mut Vec<&'a SymbolIndex>) {
+        acc.extend(
+            self.file_map
+                .iter()
+                .map(|(&file_id, data)| symbols(file_id, data))
+        )
+    }
+}
+
+fn symbols(file_id: FileId, (data, symbols): &(FileData, OnceCell<SymbolIndex>)) -> &SymbolIndex {
     let syntax = data.syntax_transient();
-    symbols.get_or_init(|| FileSymbols::new(file_id, &syntax))
+    symbols.get_or_init(|| SymbolIndex::for_file(file_id, syntax))
 }
 
 #[derive(Debug)]
@@ -103,19 +108,77 @@ impl FileData {
             lines: OnceCell::new(),
         }
     }
+    fn lines(&self) -> &LineIndex {
+        self.lines.get_or_init(|| LineIndex::new(&self.text))
+    }
+    fn syntax(&self) -> &File {
+        let text = &self.text;
+        let syntax = &self.syntax;
+        match panic::catch_unwind(panic::AssertUnwindSafe(|| syntax.get_or_init(|| File::parse(text)))) {
+            Ok(file) => file,
+            Err(err) => {
+                error!("Parser paniced on:\n------\n{}\n------\n", text);
+                panic::resume_unwind(err)
+            }
+        }
+    }
     fn syntax_transient(&self) -> File {
         self.syntax.get().map(|s| s.clone())
             .unwrap_or_else(|| File::parse(&self.text))
     }
 }
 
-// #[derive(Clone, Default, Debug)]
-// pub(crate) struct ReadonlySourceRoot {
-//     data: Arc<ReadonlySourceRoot>
-// }
+#[derive(Debug)]
+pub(crate) struct ReadonlySourceRoot {
+    symbol_index: SymbolIndex,
+    file_map: HashMap<FileId, FileData>,
+    module_map: ModuleMap,
+}
 
-// #[derive(Clone, Default, Debug)]
-// pub(crate) struct ReadonlySourceRootInner {
-//     file_map: HashMap<FileId, FileData>,
-//     module_map: ModuleMap,
-// }
+impl ReadonlySourceRoot {
+    pub fn new(files: impl Iterator<Item=(FileId, String)>) -> ReadonlySourceRoot {
+        let mut module_map = ModuleMap::new();
+        let file_map: HashMap<FileId, FileData> = files
+            .map(|(id, text)| {
+                module_map.update_file(id, ChangeKind::Insert);
+                (id, FileData::new(text))
+            })
+            .collect();
+        let symbol_index = SymbolIndex::for_files(
+            file_map.par_iter().map(|(&file_id, file_data)| {
+                (file_id, file_data.syntax_transient())
+            })
+        );
+
+        ReadonlySourceRoot {
+            symbol_index,
+            file_map,
+            module_map,
+        }
+    }
+
+    fn data(&self, file_id: FileId) -> &FileData {
+        match self.file_map.get(&file_id) {
+            Some(data) => data,
+            None => panic!("unknown file: {:?}", file_id),
+        }
+    }
+}
+
+impl SourceRoot for ReadonlySourceRoot {
+    fn contains(&self, file_id: FileId) -> bool {
+        self.file_map.contains_key(&file_id)
+    }
+    fn module_map(&self) -> &ModuleMap {
+        &self.module_map
+    }
+    fn lines(&self, file_id: FileId) -> &LineIndex {
+        self.data(file_id).lines()
+    }
+    fn syntax(&self, file_id: FileId) -> &File {
+        self.data(file_id).syntax()
+    }
+    fn symbols<'a>(&'a self, acc: &mut Vec<&'a SymbolIndex>) {
+        acc.push(&self.symbol_index)
+    }
+}
diff --git a/crates/libanalysis/src/symbol_index.rs b/crates/libanalysis/src/symbol_index.rs
index 54952cb943..8fef326ab8 100644
--- a/crates/libanalysis/src/symbol_index.rs
+++ b/crates/libanalysis/src/symbol_index.rs
@@ -4,39 +4,46 @@ use libsyntax2::{
     SyntaxKind::{self, *},
 };
 use fst::{self, Streamer};
+use rayon::prelude::*;
 use {Query, FileId, JobToken};
 
 #[derive(Debug)]
-pub(crate) struct FileSymbols {
+pub(crate) struct SymbolIndex {
     symbols: Vec<(FileId, FileSymbol)>,
     map: fst::Map,
 }
 
-impl FileSymbols {
-    pub(crate) fn new(file_id: FileId, file: &File) -> FileSymbols {
-        let mut symbols = file_symbols(file)
-            .into_iter()
-            .map(|s| (s.name.as_str().to_lowercase(), s))
+impl SymbolIndex {
+    pub(crate) fn for_files(files: impl ParallelIterator<Item=(FileId, File)>) -> SymbolIndex {
+        let mut symbols = files
+            .flat_map(|(file_id, file)| {
+                file_symbols(&file)
+                    .into_iter()
+                    .map(move |symbol| {
+                        (symbol.name.as_str().to_lowercase(), (file_id, symbol))
+                    })
+                    .collect::<Vec<_>>()
+            })
             .collect::<Vec<_>>();
-
-        symbols.sort_by(|s1, s2| s1.0.cmp(&s2.0));
+        symbols.par_sort_by(|s1, s2| s1.0.cmp(&s2.0));
         symbols.dedup_by(|s1, s2| s1.0 == s2.0);
         let (names, symbols): (Vec<String>, Vec<(FileId, FileSymbol)>) =
-            symbols.into_iter()
-                .map(|(name, symbol)| (name, (file_id, symbol)))
-                .unzip();
-
+            symbols.into_iter().unzip();
         let map = fst::Map::from_iter(
             names.into_iter().zip(0u64..)
         ).unwrap();
-        FileSymbols { symbols, map }
+        SymbolIndex { symbols, map }
+    }
+
+    pub(crate) fn for_file(file_id: FileId, file: File) -> SymbolIndex {
+        SymbolIndex::for_files(::rayon::iter::once((file_id, file)))
     }
 }
 
 impl Query {
     pub(crate) fn search(
         mut self,
-        indices: &[&FileSymbols],
+        indices: &[&SymbolIndex],
         token: &JobToken,
     ) -> Vec<(FileId, FileSymbol)> {