3 files changed, 31 insertions, 68 deletions

diff --git a/crates/ra_analysis/src/completion/mod.rs b/crates/ra_analysis/src/completion/mod.rs
index 2e082705e..5e3ee79dd 100644
--- a/crates/ra_analysis/src/completion/mod.rs
+++ b/crates/ra_analysis/src/completion/mod.rs
@@ -2,7 +2,6 @@ mod reference_completion;
 
 use ra_editor::find_node_at_offset;
 use ra_syntax::{
-    algo::find_leaf_at_offset,
     algo::visit::{visitor_ctx, VisitorCtx},
     ast,
     AstNode, AtomEdit,
@@ -12,8 +11,9 @@ use rustc_hash::{FxHashMap};
 
 use crate::{
     db::{self, SyntaxDatabase},
-    descriptors::{DescriptorDatabase, module::ModuleSource},
-    input::{FilesDatabase},
+    descriptors::{
+        module::{ModuleDescriptor}
+    },
     Cancelable, FilePosition
 };
 
@@ -38,14 +38,7 @@ pub(crate) fn completions(
         original_file.reparse(&edit)
     };
 
-    let leaf = match find_leaf_at_offset(original_file.syntax(), position.offset).left_biased() {
-        None => return Ok(None),
-        Some(it) => it,
-    };
-    let source_root_id = db.file_source_root(position.file_id);
-    let module_tree = db.module_tree(source_root_id)?;
-    let module_source = ModuleSource::for_node(position.file_id, leaf);
-    let module_id = match module_tree.any_module_for_source(module_source) {
+    let module = match ModuleDescriptor::guess_from_position(db, position)? {
         None => return Ok(None),
         Some(it) => it,
     };
@@ -55,15 +48,7 @@ pub(crate) fn completions(
     // First, let's try to complete a reference to some declaration.
     if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(file.syntax(), position.offset) {
         has_completions = true;
-        reference_completion::completions(
-            &mut res,
-            db,
-            source_root_id,
-            &module_tree,
-            module_id,
-            &file,
-            name_ref,
-        )?;
+        reference_completion::completions(&mut res, db, &module, &file, name_ref)?;
         // special case, `trait T { fn foo(i_am_a_name_ref) {} }`
         if is_node::<ast::Param>(name_ref.syntax()) {
             param_completions(name_ref.syntax(), &mut res);
diff --git a/crates/ra_analysis/src/completion/reference_completion.rs b/crates/ra_analysis/src/completion/reference_completion.rs
index 6c5fd0be6..c94d9af75 100644
--- a/crates/ra_analysis/src/completion/reference_completion.rs
+++ b/crates/ra_analysis/src/completion/reference_completion.rs
@@ -9,20 +9,16 @@ use ra_syntax::{
 
 use crate::{
     db::RootDatabase,
-    input::{SourceRootId},
     completion::CompletionItem,
-    descriptors::module::{ModuleId, ModuleTree},
+    descriptors::module::{ModuleDescriptor},
     descriptors::function::FnScopes,
-    descriptors::DescriptorDatabase,
     Cancelable
 };
 
 pub(super) fn completions(
     acc: &mut Vec<CompletionItem>,
     db: &RootDatabase,
-    source_root_id: SourceRootId,
-    module_tree: &ModuleTree,
-    module_id: ModuleId,
+    module: &ModuleDescriptor,
     file: &SourceFileNode,
     name_ref: ast::NameRef,
 ) -> Cancelable<()> {
@@ -40,7 +36,7 @@ pub(super) fn completions(
                 complete_expr_snippets(acc);
             }
 
-            let module_scope = db.module_scope(source_root_id, module_id)?;
+            let module_scope = module.scope(db)?;
             acc.extend(
                 module_scope
                     .entries()
@@ -56,9 +52,7 @@ pub(super) fn completions(
                     }),
             );
         }
-        NameRefKind::CratePath(path) => {
-            complete_path(acc, db, source_root_id, module_tree, module_id, path)?
-        }
+        NameRefKind::CratePath(path) => complete_path(acc, db, module, path)?,
         NameRefKind::BareIdentInMod => {
             let name_range = name_ref.syntax().range();
             let top_node = name_ref
@@ -171,16 +165,14 @@ fn complete_fn(name_ref: ast::NameRef, scopes: &FnScopes, acc: &mut Vec<Completi
 fn complete_path(
     acc: &mut Vec<CompletionItem>,
     db: &RootDatabase,
-    source_root_id: SourceRootId,
-    module_tree: &ModuleTree,
-    module_id: ModuleId,
+    module: &ModuleDescriptor,
     crate_path: Vec<ast::NameRef>,
 ) -> Cancelable<()> {
-    let target_module_id = match find_target_module(module_tree, module_id, crate_path) {
+    let target_module = match find_target_module(module, crate_path) {
         None => return Ok(()),
         Some(it) => it,
     };
-    let module_scope = db.module_scope(source_root_id, target_module_id)?;
+    let module_scope = target_module.scope(db)?;
     let completions = module_scope.entries().iter().map(|entry| CompletionItem {
         label: entry.name().to_string(),
         lookup: None,
@@ -191,14 +183,13 @@ fn complete_path(
 }
 
 fn find_target_module(
-    module_tree: &ModuleTree,
-    module_id: ModuleId,
+    module: &ModuleDescriptor,
     mut crate_path: Vec<ast::NameRef>,
-) -> Option<ModuleId> {
+) -> Option<ModuleDescriptor> {
     crate_path.pop();
-    let mut target_module = module_id.root(&module_tree);
+    let mut target_module = module.crate_root();
     for name in crate_path {
-        target_module = target_module.child(module_tree, name.text().as_str())?;
+        target_module = target_module.child(name.text().as_str())?;
     }
     Some(target_module)
 }
diff --git a/crates/ra_analysis/src/descriptors/module/mod.rs b/crates/ra_analysis/src/descriptors/module/mod.rs
index d0560244a..a894025ed 100644
--- a/crates/ra_analysis/src/descriptors/module/mod.rs
+++ b/crates/ra_analysis/src/descriptors/module/mod.rs
@@ -15,6 +15,7 @@ use relative_path::RelativePathBuf;
 use crate::{
     db::SyntaxDatabase, syntax_ptr::SyntaxPtr, FileId, FilePosition, Cancelable,
     descriptors::DescriptorDatabase,
+    input::SourceRootId
 };
 
 pub(crate) use self::scope::ModuleScope;
@@ -24,6 +25,7 @@ pub(crate) use self::scope::ModuleScope;
 #[derive(Debug, Clone)]
 pub(crate) struct ModuleDescriptor {
     tree: Arc<ModuleTree>,
+    source_root_id: SourceRootId,
     module_id: ModuleId,
 }
 
@@ -59,13 +61,14 @@ impl ModuleDescriptor {
         file_id: FileId,
         module_source: ModuleSource,
     ) -> Cancelable<Option<ModuleDescriptor>> {
-        let source_root = db.file_source_root(file_id);
-        let module_tree = db.module_tree(source_root)?;
+        let source_root_id = db.file_source_root(file_id);
+        let module_tree = db.module_tree(source_root_id)?;
 
         let res = match module_tree.any_module_for_source(module_source) {
             None => None,
             Some(module_id) => Some(ModuleDescriptor {
                 tree: module_tree,
+                source_root_id,
                 module_id,
             }),
         };
@@ -92,8 +95,8 @@ impl ModuleDescriptor {
     pub fn parent(&self) -> Option<ModuleDescriptor> {
         let parent_id = self.module_id.parent(&self.tree)?;
         Some(ModuleDescriptor {
-            tree: Arc::clone(&self.tree),
             module_id: parent_id,
+            ..self.clone()
         })
     }
 
@@ -109,13 +112,20 @@ impl ModuleDescriptor {
         let link = self.module_id.parent_link(&self.tree)?;
         Some(link.name(&self.tree))
     }
+
+    /// Finds a child module with the specified name.
     pub fn child(&self, name: &str) -> Option<ModuleDescriptor> {
         let child_id = self.module_id.child(&self.tree, name)?;
         Some(ModuleDescriptor {
-            tree: Arc::clone(&self.tree),
             module_id: child_id,
+            ..self.clone()
         })
     }
+
+    /// 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)
+    }
 }
 
 /// Phisically, rust source is organized as a set of files, but logically it is
@@ -190,20 +200,7 @@ impl ModuleId {
         let link = self.parent_link(tree)?;
         Some(tree.link(link).owner)
     }
-    pub(crate) fn root(self, tree: &ModuleTree) -> ModuleId {
-        let mut curr = self;
-        let mut i = 0;
-        while let Some(next) = curr.parent(tree) {
-            curr = next;
-            i += 1;
-            // simplistic cycle detection
-            if i > 100 {
-                return self;
-            }
-        }
-        curr
-    }
-    pub(crate) fn child(self, tree: &ModuleTree, name: &str) -> Option<ModuleId> {
+    fn child(self, tree: &ModuleTree, name: &str) -> Option<ModuleId> {
         let link = tree
             .module(self)
             .children
@@ -260,16 +257,6 @@ struct ModuleData {
 }
 
 impl ModuleSource {
-    pub(crate) fn for_node(file_id: FileId, node: SyntaxNodeRef) -> ModuleSource {
-        for node in node.ancestors() {
-            if let Some(m) = ast::Module::cast(node) {
-                if !m.has_semi() {
-                    return ModuleSource::new_inline(file_id, m);
-                }
-            }
-        }
-        ModuleSource::SourceFile(file_id)
-    }
     pub(crate) fn new_inline(file_id: FileId, module: ast::Module) -> ModuleSource {
         assert!(!module.has_semi());
         let ptr = SyntaxPtr::new(file_id, module.syntax());