diff --git a/crates/ra_analysis/src/descriptors/mod.rs b/crates/ra_analysis/src/descriptors/mod.rs
index f47ac49c5a6..a8489f89c6a 100644
--- a/crates/ra_analysis/src/descriptors/mod.rs
+++ b/crates/ra_analysis/src/descriptors/mod.rs
@@ -20,19 +20,19 @@ use crate::{
 
 salsa::query_group! {
     pub(crate) trait DescriptorDatabase: SyntaxDatabase + IdDatabase {
-        fn module_tree(source_root_id: SourceRootId) -> Cancelable<Arc<ModuleTree>> {
-            type ModuleTreeQuery;
-            use fn module::imp::module_tree;
-        }
-        fn module_scope(source_root_id: SourceRootId, module_id: ModuleId) -> Cancelable<Arc<ModuleScope>> {
-            type ModuleScopeQuery;
-            use fn module::imp::module_scope;
-        }
         fn fn_scopes(fn_id: FnId) -> Arc<FnScopes> {
             type FnScopesQuery;
             use fn function::imp::fn_scopes;
         }
 
+        fn _module_tree(source_root_id: SourceRootId) -> Cancelable<Arc<ModuleTree>> {
+            type ModuleTreeQuery;
+            use fn module::imp::module_tree;
+        }
+        fn _module_scope(source_root_id: SourceRootId, module_id: ModuleId) -> Cancelable<Arc<ModuleScope>> {
+            type ModuleScopeQuery;
+            use fn module::imp::module_scope;
+        }
         fn _fn_syntax(fn_id: FnId) -> FnDefNode {
             type FnSyntaxQuery;
             // Don't retain syntax trees in memory
diff --git a/crates/ra_analysis/src/descriptors/module/imp.rs b/crates/ra_analysis/src/descriptors/module/imp.rs
index ec0885938ea..defe87216c8 100644
--- a/crates/ra_analysis/src/descriptors/module/imp.rs
+++ b/crates/ra_analysis/src/descriptors/module/imp.rs
@@ -86,7 +86,7 @@ pub(crate) fn module_scope(
     source_root_id: SourceRootId,
     module_id: ModuleId,
 ) -> Cancelable<Arc<ModuleScope>> {
-    let tree = db.module_tree(source_root_id)?;
+    let tree = db._module_tree(source_root_id)?;
     let source = module_id.source(&tree).resolve(db);
     let res = match source {
         ModuleSourceNode::SourceFile(it) => ModuleScope::new(it.borrowed().items()),
diff --git a/crates/ra_analysis/src/descriptors/module/mod.rs b/crates/ra_analysis/src/descriptors/module/mod.rs
index a894025eda9..ff7afe16e9c 100644
--- a/crates/ra_analysis/src/descriptors/module/mod.rs
+++ b/crates/ra_analysis/src/descriptors/module/mod.rs
@@ -8,7 +8,7 @@ use ra_editor::find_node_at_offset;
 use ra_syntax::{
     algo::generate,
     ast::{self, AstNode, NameOwner},
-    SmolStr, SyntaxNode, SyntaxNodeRef,
+    SmolStr, SyntaxNode,
 };
 use relative_path::RelativePathBuf;
 
@@ -62,7 +62,7 @@ impl ModuleDescriptor {
         module_source: ModuleSource,
     ) -> Cancelable<Option<ModuleDescriptor>> {
         let source_root_id = db.file_source_root(file_id);
-        let module_tree = db.module_tree(source_root_id)?;
+        let module_tree = db._module_tree(source_root_id)?;
 
         let res = match module_tree.any_module_for_source(module_source) {
             None => None,
@@ -124,7 +124,11 @@ impl ModuleDescriptor {
 
     /// Returns a `ModuleScope`: a set of items, visible in this module.
     pub fn scope(&self, db: &impl DescriptorDatabase) -> Cancelable<Arc<ModuleScope>> {
-        db.module_scope(self.source_root_id, self.module_id)
+        db._module_scope(self.source_root_id, self.module_id)
+    }
+
+    pub fn problems(&self, db: &impl DescriptorDatabase) -> Vec<(SyntaxNode, Problem)> {
+        self.module_id.problems(&self.tree, db)
     }
 }
 
@@ -209,7 +213,7 @@ impl ModuleId {
             .find(|it| it.name == name)?;
         Some(*link.points_to.first()?)
     }
-    pub(crate) fn problems(
+    fn problems(
         self,
         tree: &ModuleTree,
         db: &impl SyntaxDatabase,
diff --git a/crates/ra_analysis/src/imp.rs b/crates/ra_analysis/src/imp.rs
index 1bbf0cb6da9..61296215c8f 100644
--- a/crates/ra_analysis/src/imp.rs
+++ b/crates/ra_analysis/src/imp.rs
@@ -21,7 +21,7 @@ use crate::{
     db::{self, FileSyntaxQuery, SyntaxDatabase},
     descriptors::{
         function::{FnDescriptor, FnId},
-        module::{ModuleDescriptor, ModuleSource, ModuleTree, Problem},
+        module::{ModuleDescriptor, Problem},
         DeclarationDescriptor, DescriptorDatabase,
     },
     input::{FilesDatabase, SourceRoot, SourceRootId, WORKSPACE},
@@ -216,10 +216,6 @@ impl AnalysisImpl {
             .sweep(salsa::SweepStrategy::default().discard_values());
         Ok(query.search(&buf))
     }
-    fn module_tree(&self, file_id: FileId) -> Cancelable<Arc<ModuleTree>> {
-        let source_root = self.db.file_source_root(file_id);
-        self.db.module_tree(source_root)
-    }
     /// This return `Vec`: a module may be inclucded from several places.
     /// We don't handle this case yet though, so the Vec has length at most one.
     pub fn parent_module(&self, position: FilePosition) -> Cancelable<Vec<(FileId, FileSymbol)>> {
@@ -354,7 +350,6 @@ impl AnalysisImpl {
     }
 
     pub fn diagnostics(&self, file_id: FileId) -> Cancelable<Vec<Diagnostic>> {
-        let module_tree = self.module_tree(file_id)?;
         let syntax = self.db.file_syntax(file_id);
 
         let mut res = ra_editor::diagnostics(&syntax)
@@ -365,8 +360,8 @@ impl AnalysisImpl {
                 fix: None,
             })
             .collect::<Vec<_>>();
-        if let Some(m) = module_tree.any_module_for_source(ModuleSource::SourceFile(file_id)) {
-            for (name_node, problem) in m.problems(&module_tree, &*self.db) {
+        if let Some(m) = ModuleDescriptor::guess_from_file_id(&*self.db, file_id)? {
+            for (name_node, problem) in m.problems(&*self.db) {
                 let diag = match problem {
                     Problem::UnresolvedModule { candidate } => {
                         let create_file = FileSystemEdit::CreateFile {