3 files changed, 1001 insertions, 0 deletions

diff --git a/crates/ra_hir/src/module/imp.rs b/crates/ra_hir/src/module/imp.rs
new file mode 100644
index 000000000..76ea129a7
--- /dev/null
+++ b/crates/ra_hir/src/module/imp.rs
@@ -0,0 +1,194 @@
+use std::sync::Arc;
+
+use ra_syntax::{
+    ast::{self, NameOwner},
+    SmolStr,
+};
+use relative_path::RelativePathBuf;
+use rustc_hash::{FxHashMap, FxHashSet};
+use ra_db::{SourceRoot, SourceRootId, FileResolverImp, Cancelable, FileId,};
+
+use crate::{
+    HirDatabase,
+};
+
+use super::{
+    LinkData, LinkId, ModuleData, ModuleId, ModuleSource,
+    ModuleTree, Problem,
+};
+
+#[derive(Clone, Hash, PartialEq, Eq, Debug)]
+pub enum Submodule {
+    Declaration(SmolStr),
+    Definition(SmolStr, ModuleSource),
+}
+
+impl Submodule {
+    fn name(&self) -> &SmolStr {
+        match self {
+            Submodule::Declaration(name) => name,
+            Submodule::Definition(name, _) => name,
+        }
+    }
+}
+
+pub(crate) fn modules<'a>(
+    root: impl ast::ModuleItemOwner<'a>,
+) -> impl Iterator<Item = (SmolStr, ast::Module<'a>)> {
+    root.items()
+        .filter_map(|item| match item {
+            ast::ModuleItem::Module(m) => Some(m),
+            _ => None,
+        })
+        .filter_map(|module| {
+            let name = module.name()?.text();
+            Some((name, module))
+        })
+}
+
+pub(crate) fn module_tree(
+    db: &impl HirDatabase,
+    source_root: SourceRootId,
+) -> Cancelable<Arc<ModuleTree>> {
+    db.check_canceled()?;
+    let res = create_module_tree(db, source_root)?;
+    Ok(Arc::new(res))
+}
+
+fn create_module_tree<'a>(
+    db: &impl HirDatabase,
+    source_root: SourceRootId,
+) -> Cancelable<ModuleTree> {
+    let mut tree = ModuleTree::default();
+
+    let mut roots = FxHashMap::default();
+    let mut visited = FxHashSet::default();
+
+    let source_root = db.source_root(source_root);
+    for &file_id in source_root.files.iter() {
+        let source = ModuleSource::SourceFile(file_id);
+        if visited.contains(&source) {
+            continue; // TODO: use explicit crate_roots here
+        }
+        assert!(!roots.contains_key(&file_id));
+        let module_id = build_subtree(
+            db,
+            &source_root,
+            &mut tree,
+            &mut visited,
+            &mut roots,
+            None,
+            source,
+        )?;
+        roots.insert(file_id, module_id);
+    }
+    Ok(tree)
+}
+
+fn build_subtree(
+    db: &impl HirDatabase,
+    source_root: &SourceRoot,
+    tree: &mut ModuleTree,
+    visited: &mut FxHashSet<ModuleSource>,
+    roots: &mut FxHashMap<FileId, ModuleId>,
+    parent: Option<LinkId>,
+    source: ModuleSource,
+) -> Cancelable<ModuleId> {
+    visited.insert(source);
+    let id = tree.push_mod(ModuleData {
+        source,
+        parent,
+        children: Vec::new(),
+    });
+    for sub in db.submodules(source)?.iter() {
+        let link = tree.push_link(LinkData {
+            name: sub.name().clone(),
+            owner: id,
+            points_to: Vec::new(),
+            problem: None,
+        });
+
+        let (points_to, problem) = match sub {
+            Submodule::Declaration(name) => {
+                let (points_to, problem) =
+                    resolve_submodule(source, &name, &source_root.file_resolver);
+                let points_to = points_to
+                    .into_iter()
+                    .map(|file_id| match roots.remove(&file_id) {
+                        Some(module_id) => {
+                            tree.mods[module_id].parent = Some(link);
+                            Ok(module_id)
+                        }
+                        None => build_subtree(
+                            db,
+                            source_root,
+                            tree,
+                            visited,
+                            roots,
+                            Some(link),
+                            ModuleSource::SourceFile(file_id),
+                        ),
+                    })
+                    .collect::<Cancelable<Vec<_>>>()?;
+                (points_to, problem)
+            }
+            Submodule::Definition(_name, submodule_source) => {
+                let points_to = build_subtree(
+                    db,
+                    source_root,
+                    tree,
+                    visited,
+                    roots,
+                    Some(link),
+                    *submodule_source,
+                )?;
+                (vec![points_to], None)
+            }
+        };
+
+        tree.links[link].points_to = points_to;
+        tree.links[link].problem = problem;
+    }
+    Ok(id)
+}
+
+fn resolve_submodule(
+    source: ModuleSource,
+    name: &SmolStr,
+    file_resolver: &FileResolverImp,
+) -> (Vec<FileId>, Option<Problem>) {
+    let file_id = match source {
+        ModuleSource::SourceFile(it) => it,
+        ModuleSource::Module(..) => {
+            // TODO
+            return (Vec::new(), None);
+        }
+    };
+    let mod_name = file_resolver.file_stem(file_id);
+    let is_dir_owner = mod_name == "mod" || mod_name == "lib" || mod_name == "main";
+
+    let file_mod = RelativePathBuf::from(format!("../{}.rs", name));
+    let dir_mod = RelativePathBuf::from(format!("../{}/mod.rs", name));
+    let points_to: Vec<FileId>;
+    let problem: Option<Problem>;
+    if is_dir_owner {
+        points_to = [&file_mod, &dir_mod]
+            .iter()
+            .filter_map(|path| file_resolver.resolve(file_id, path))
+            .collect();
+        problem = if points_to.is_empty() {
+            Some(Problem::UnresolvedModule {
+                candidate: file_mod,
+            })
+        } else {
+            None
+        }
+    } else {
+        points_to = Vec::new();
+        problem = Some(Problem::NotDirOwner {
+            move_to: RelativePathBuf::from(format!("../{}/mod.rs", mod_name)),
+            candidate: file_mod,
+        });
+    }
+    (points_to, problem)
+}
diff --git a/crates/ra_hir/src/module/mod.rs b/crates/ra_hir/src/module/mod.rs
new file mode 100644
index 000000000..3ae83d8cb
--- /dev/null
+++ b/crates/ra_hir/src/module/mod.rs
@@ -0,0 +1,373 @@
+pub(super) mod imp;
+pub(super) mod nameres;
+
+use std::sync::Arc;
+
+use ra_editor::find_node_at_offset;
+
+use ra_syntax::{
+    algo::generate,
+    ast::{self, AstNode, NameOwner},
+    SmolStr, SyntaxNode,
+};
+use ra_db::{SourceRootId, FileId, FilePosition, Cancelable};
+use relative_path::RelativePathBuf;
+
+use crate::{
+    DefLoc, DefId, Path, PathKind, HirDatabase, SourceItemId,
+    arena::{Arena, Id},
+};
+
+pub use self::nameres::ModuleScope;
+
+/// `Module` is API entry point to get all the information
+/// about a particular module.
+#[derive(Debug, Clone)]
+pub struct Module {
+    tree: Arc<ModuleTree>,
+    source_root_id: SourceRootId,
+    module_id: ModuleId,
+}
+
+impl Module {
+    /// Lookup `Module` by `FileId`. Note that this is inherently
+    /// lossy transformation: in general, a single source might correspond to
+    /// several modules.
+    pub fn guess_from_file_id(
+        db: &impl HirDatabase,
+        file_id: FileId,
+    ) -> Cancelable<Option<Module>> {
+        Module::guess_from_source(db, file_id, ModuleSource::SourceFile(file_id))
+    }
+
+    /// Lookup `Module` by position in the source code. Note that this
+    /// is inherently lossy transformation: in general, a single source might
+    /// correspond to several modules.
+    pub fn guess_from_position(
+        db: &impl HirDatabase,
+        position: FilePosition,
+    ) -> Cancelable<Option<Module>> {
+        let file = db.source_file(position.file_id);
+        let module_source = match find_node_at_offset::<ast::Module>(file.syntax(), position.offset)
+        {
+            Some(m) if !m.has_semi() => ModuleSource::new_inline(db, position.file_id, m),
+            _ => ModuleSource::SourceFile(position.file_id),
+        };
+        Module::guess_from_source(db, position.file_id, module_source)
+    }
+
+    fn guess_from_source(
+        db: &impl HirDatabase,
+        file_id: FileId,
+        module_source: ModuleSource,
+    ) -> Cancelable<Option<Module>> {
+        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(Module {
+                tree: module_tree,
+                source_root_id,
+                module_id,
+            }),
+        };
+        Ok(res)
+    }
+
+    pub(super) fn new(
+        db: &impl HirDatabase,
+        source_root_id: SourceRootId,
+        module_id: ModuleId,
+    ) -> Cancelable<Module> {
+        let module_tree = db.module_tree(source_root_id)?;
+        let res = Module {
+            tree: module_tree,
+            source_root_id,
+            module_id,
+        };
+        Ok(res)
+    }
+
+    /// Returns `mod foo;` or `mod foo {}` node whihc declared this module.
+    /// Returns `None` for the root module
+    pub fn parent_link_source(&self, db: &impl HirDatabase) -> Option<(FileId, ast::ModuleNode)> {
+        let link = self.module_id.parent_link(&self.tree)?;
+        let file_id = link.owner(&self.tree).source(&self.tree).file_id();
+        let src = link.bind_source(&self.tree, db);
+        Some((file_id, src))
+    }
+
+    pub fn source(&self) -> ModuleSource {
+        self.module_id.source(&self.tree)
+    }
+
+    /// Parent module. Returns `None` if this is a root module.
+    pub fn parent(&self) -> Option<Module> {
+        let parent_id = self.module_id.parent(&self.tree)?;
+        Some(Module {
+            module_id: parent_id,
+            ..self.clone()
+        })
+    }
+
+    /// The root of the tree this module is part of
+    pub fn crate_root(&self) -> Module {
+        let root_id = self.module_id.crate_root(&self.tree);
+        Module {
+            module_id: root_id,
+            ..self.clone()
+        }
+    }
+
+    /// `name` is `None` for the crate's root module
+    pub fn name(&self) -> Option<SmolStr> {
+        let link = self.module_id.parent_link(&self.tree)?;
+        Some(link.name(&self.tree))
+    }
+
+    pub fn def_id(&self, db: &impl HirDatabase) -> DefId {
+        let def_loc = DefLoc::Module {
+            id: self.module_id,
+            source_root: self.source_root_id,
+        };
+        def_loc.id(db)
+    }
+
+    /// Finds a child module with the specified name.
+    pub fn child(&self, name: &str) -> Option<Module> {
+        let child_id = self.module_id.child(&self.tree, name)?;
+        Some(Module {
+            module_id: child_id,
+            ..self.clone()
+        })
+    }
+
+    /// Returns a `ModuleScope`: a set of items, visible in this module.
+    pub fn scope(&self, db: &impl HirDatabase) -> Cancelable<ModuleScope> {
+        let item_map = db.item_map(self.source_root_id)?;
+        let res = item_map.per_module[&self.module_id].clone();
+        Ok(res)
+    }
+
+    pub fn resolve_path(&self, db: &impl HirDatabase, path: Path) -> Cancelable<Option<DefId>> {
+        let mut curr = match path.kind {
+            PathKind::Crate => self.crate_root(),
+            PathKind::Self_ | PathKind::Plain => self.clone(),
+            PathKind::Super => ctry!(self.parent()),
+        }
+        .def_id(db);
+
+        let segments = path.segments;
+        for name in segments.iter() {
+            let module = match curr.loc(db) {
+                DefLoc::Module { id, source_root } => Module::new(db, source_root, id)?,
+                _ => return Ok(None),
+            };
+            let scope = module.scope(db)?;
+            curr = ctry!(ctry!(scope.get(&name)).def_id);
+        }
+        Ok(Some(curr))
+    }
+
+    pub fn problems(&self, db: &impl HirDatabase) -> Vec<(SyntaxNode, Problem)> {
+        self.module_id.problems(&self.tree, db)
+    }
+}
+
+/// Phisically, rust source is organized as a set of files, but logically it is
+/// organized as a tree of modules. Usually, a single file corresponds to a
+/// single module, but it is not nessary the case.
+///
+/// Module encapsulate the logic of transitioning from the fuzzy world of files
+/// (which can have multiple parents) to the precise world of modules (which
+/// always have one parent).
+#[derive(Default, Debug, PartialEq, Eq)]
+pub struct ModuleTree {
+    mods: Arena<ModuleData>,
+    links: Arena<LinkData>,
+}
+
+impl ModuleTree {
+    pub(crate) fn modules<'a>(&'a self) -> impl Iterator<Item = ModuleId> + 'a {
+        self.mods.iter().map(|(id, _)| id)
+    }
+
+    fn modules_for_source(&self, source: ModuleSource) -> Vec<ModuleId> {
+        self.mods
+            .iter()
+            .filter(|(_idx, it)| it.source == source)
+            .map(|(idx, _)| idx)
+            .collect()
+    }
+
+    fn any_module_for_source(&self, source: ModuleSource) -> Option<ModuleId> {
+        self.modules_for_source(source).pop()
+    }
+}
+
+/// `ModuleSource` is the syntax tree element that produced this module:
+/// either a file, or an inlinde module.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum ModuleSource {
+    SourceFile(FileId),
+    Module(SourceItemId),
+}
+
+/// An owned syntax node for a module. Unlike `ModuleSource`,
+/// this holds onto the AST for the whole file.
+pub(crate) enum ModuleSourceNode {
+    SourceFile(ast::SourceFileNode),
+    Module(ast::ModuleNode),
+}
+
+pub type ModuleId = Id<ModuleData>;
+type LinkId = Id<LinkData>;
+
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+pub enum Problem {
+    UnresolvedModule {
+        candidate: RelativePathBuf,
+    },
+    NotDirOwner {
+        move_to: RelativePathBuf,
+        candidate: RelativePathBuf,
+    },
+}
+
+impl ModuleId {
+    pub(crate) fn source(self, tree: &ModuleTree) -> ModuleSource {
+        tree.mods[self].source
+    }
+    fn parent_link(self, tree: &ModuleTree) -> Option<LinkId> {
+        tree.mods[self].parent
+    }
+    fn parent(self, tree: &ModuleTree) -> Option<ModuleId> {
+        let link = self.parent_link(tree)?;
+        Some(tree.links[link].owner)
+    }
+    fn crate_root(self, tree: &ModuleTree) -> ModuleId {
+        generate(Some(self), move |it| it.parent(tree))
+            .last()
+            .unwrap()
+    }
+    fn child(self, tree: &ModuleTree, name: &str) -> Option<ModuleId> {
+        let link = tree.mods[self]
+            .children
+            .iter()
+            .map(|&it| &tree.links[it])
+            .find(|it| it.name == name)?;
+        Some(*link.points_to.first()?)
+    }
+    fn children<'a>(self, tree: &'a ModuleTree) -> impl Iterator<Item = (SmolStr, ModuleId)> + 'a {
+        tree.mods[self].children.iter().filter_map(move |&it| {
+            let link = &tree.links[it];
+            let module = *link.points_to.first()?;
+            Some((link.name.clone(), module))
+        })
+    }
+    fn problems(self, tree: &ModuleTree, db: &impl HirDatabase) -> Vec<(SyntaxNode, Problem)> {
+        tree.mods[self]
+            .children
+            .iter()
+            .filter_map(|&it| {
+                let p = tree.links[it].problem.clone()?;
+                let s = it.bind_source(tree, db);
+                let s = s.borrowed().name().unwrap().syntax().owned();
+                Some((s, p))
+            })
+            .collect()
+    }
+}
+
+impl LinkId {
+    fn owner(self, tree: &ModuleTree) -> ModuleId {
+        tree.links[self].owner
+    }
+    fn name(self, tree: &ModuleTree) -> SmolStr {
+        tree.links[self].name.clone()
+    }
+    fn bind_source<'a>(self, tree: &ModuleTree, db: &impl HirDatabase) -> ast::ModuleNode {
+        let owner = self.owner(tree);
+        match owner.source(tree).resolve(db) {
+            ModuleSourceNode::SourceFile(root) => {
+                let ast = imp::modules(root.borrowed())
+                    .find(|(name, _)| name == &tree.links[self].name)
+                    .unwrap()
+                    .1;
+                ast.owned()
+            }
+            ModuleSourceNode::Module(it) => it,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Hash)]
+pub struct ModuleData {
+    source: ModuleSource,
+    parent: Option<LinkId>,
+    children: Vec<LinkId>,
+}
+
+impl ModuleSource {
+    pub(crate) fn new_inline(
+        db: &impl HirDatabase,
+        file_id: FileId,
+        module: ast::Module,
+    ) -> ModuleSource {
+        assert!(!module.has_semi());
+        let items = db.file_items(file_id);
+        let item_id = items.id_of(module.syntax());
+        let id = SourceItemId { file_id, item_id };
+        ModuleSource::Module(id)
+    }
+
+    pub fn as_file(self) -> Option<FileId> {
+        match self {
+            ModuleSource::SourceFile(f) => Some(f),
+            ModuleSource::Module(..) => None,
+        }
+    }
+
+    pub fn file_id(self) -> FileId {
+        match self {
+            ModuleSource::SourceFile(f) => f,
+            ModuleSource::Module(source_item_id) => source_item_id.file_id,
+        }
+    }
+
+    pub(crate) fn resolve(self, db: &impl HirDatabase) -> ModuleSourceNode {
+        match self {
+            ModuleSource::SourceFile(file_id) => {
+                let syntax = db.source_file(file_id);
+                ModuleSourceNode::SourceFile(syntax.ast().owned())
+            }
+            ModuleSource::Module(item_id) => {
+                let syntax = db.file_item(item_id);
+                let syntax = syntax.borrowed();
+                let module = ast::Module::cast(syntax).unwrap();
+                ModuleSourceNode::Module(module.owned())
+            }
+        }
+    }
+}
+
+#[derive(Hash, Debug, PartialEq, Eq)]
+struct LinkData {
+    owner: ModuleId,
+    name: SmolStr,
+    points_to: Vec<ModuleId>,
+    problem: Option<Problem>,
+}
+
+impl ModuleTree {
+    fn push_mod(&mut self, data: ModuleData) -> ModuleId {
+        self.mods.alloc(data)
+    }
+    fn push_link(&mut self, data: LinkData) -> LinkId {
+        let owner = data.owner;
+        let id = self.links.alloc(data);
+        self.mods[owner].children.push(id);
+        id
+    }
+}
diff --git a/crates/ra_hir/src/module/nameres.rs b/crates/ra_hir/src/module/nameres.rs
new file mode 100644
index 000000000..8529e16b3
--- /dev/null
+++ b/crates/ra_hir/src/module/nameres.rs
@@ -0,0 +1,434 @@
+//! Name resolution algorithm. The end result of the algorithm is `ItemMap`: a
+//! map with maps each module to it's scope: the set of items, visible in the
+//! module. That is, we only resolve imports here, name resolution of item
+//! bodies will be done in a separate step.
+//!
+//! Like Rustc, we use an interative per-crate algorithm: we start with scopes
+//! containing only directly defined items, and then iteratively resolve
+//! imports.
+//!
+//! To make this work nicely in the IDE scenarios, we place `InputModuleItems`
+//! in between raw syntax and name resolution. `InputModuleItems` are computed
+//! using only the module's syntax, and it is all directly defined items plus
+//! imports. The plain is to make `InputModuleItems` independent of local
+//! modifications (that is, typing inside a function shold not change IMIs),
+//! such that the results of name resolution can be preserved unless the module
+//! structure itself is modified.
+use std::{
+    sync::Arc,
+};
+
+use rustc_hash::FxHashMap;
+use ra_syntax::{
+    TextRange,
+    SmolStr, SyntaxKind::{self, *},
+    ast::{self, AstNode}
+};
+use ra_db::SourceRootId;
+
+use crate::{
+    Cancelable, FileId,
+    DefId, DefLoc,
+    SourceItemId, SourceFileItemId, SourceFileItems,
+    Path, PathKind,
+    HirDatabase,
+    module::{ModuleId, ModuleTree},
+};
+
+/// Item map is the result of the name resolution. Item map contains, for each
+/// module, the set of visible items.
+#[derive(Default, Debug, PartialEq, Eq)]
+pub struct ItemMap {
+    pub per_module: FxHashMap<ModuleId, ModuleScope>,
+}
+
+#[derive(Debug, Default, PartialEq, Eq, Clone)]
+pub struct ModuleScope {
+    items: FxHashMap<SmolStr, Resolution>,
+}
+
+impl ModuleScope {
+    pub fn entries<'a>(&'a self) -> impl Iterator<Item = (&'a SmolStr, &Resolution)> + 'a {
+        self.items.iter()
+    }
+    pub fn get(&self, name: &SmolStr) -> Option<&Resolution> {
+        self.items.get(name)
+    }
+}
+
+/// A set of items and imports declared inside a module, without relation to
+/// other modules.
+///
+/// This stands in-between raw syntax and name resolution and alow us to avoid
+/// recomputing name res: if `InputModuleItems` are the same, we can avoid
+/// running name resolution.
+#[derive(Debug, Default, PartialEq, Eq)]
+pub struct InputModuleItems {
+    items: Vec<ModuleItem>,
+    imports: Vec<Import>,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+struct ModuleItem {
+    id: SourceFileItemId,
+    name: SmolStr,
+    kind: SyntaxKind,
+    vis: Vis,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+enum Vis {
+    // Priv,
+    Other,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct Import {
+    path: Path,
+    kind: ImportKind,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct NamedImport {
+    pub file_item_id: SourceFileItemId,
+    pub relative_range: TextRange,
+}
+
+impl NamedImport {
+    pub fn range(&self, db: &impl HirDatabase, file_id: FileId) -> TextRange {
+        let source_item_id = SourceItemId {
+            file_id,
+            item_id: self.file_item_id,
+        };
+        let syntax = db.file_item(source_item_id);
+        let offset = syntax.borrowed().range().start();
+        self.relative_range + offset
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum ImportKind {
+    Glob,
+    Named(NamedImport),
+}
+
+/// Resolution is basically `DefId` atm, but it should account for stuff like
+/// multiple namespaces, ambiguity and errors.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Resolution {
+    /// None for unresolved
+    pub def_id: Option<DefId>,
+    /// ident by whitch this is imported into local scope.
+    pub import: Option<NamedImport>,
+}
+
+// #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+// enum Namespace {
+//     Types,
+//     Values,
+// }
+
+// #[derive(Debug)]
+// struct PerNs<T> {
+//     types: Option<T>,
+//     values: Option<T>,
+// }
+
+impl InputModuleItems {
+    pub(crate) fn new<'a>(
+        file_items: &SourceFileItems,
+        items: impl Iterator<Item = ast::ModuleItem<'a>>,
+    ) -> InputModuleItems {
+        let mut res = InputModuleItems::default();
+        for item in items {
+            res.add_item(file_items, item);
+        }
+        res
+    }
+
+    fn add_item(&mut self, file_items: &SourceFileItems, item: ast::ModuleItem) -> Option<()> {
+        match item {
+            ast::ModuleItem::StructDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::EnumDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::FnDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::TraitDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::TypeDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::ImplItem(_) => {
+                // impls don't define items
+            }
+            ast::ModuleItem::UseItem(it) => self.add_use_item(file_items, it),
+            ast::ModuleItem::ExternCrateItem(_) => {
+                // TODO
+            }
+            ast::ModuleItem::ConstDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::StaticDef(it) => self.items.push(ModuleItem::new(file_items, it)?),
+            ast::ModuleItem::Module(it) => self.items.push(ModuleItem::new(file_items, it)?),
+        }
+        Some(())
+    }
+
+    fn add_use_item(&mut self, file_items: &SourceFileItems, item: ast::UseItem) {
+        let file_item_id = file_items.id_of(item.syntax());
+        let start_offset = item.syntax().range().start();
+        Path::expand_use_item(item, |path, range| {
+            let kind = match range {
+                None => ImportKind::Glob,
+                Some(range) => ImportKind::Named(NamedImport {
+                    file_item_id,
+                    relative_range: range - start_offset,
+                }),
+            };
+            self.imports.push(Import { kind, path })
+        })
+    }
+}
+
+impl ModuleItem {
+    fn new<'a>(file_items: &SourceFileItems, item: impl ast::NameOwner<'a>) -> Option<ModuleItem> {
+        let name = item.name()?.text();
+        let kind = item.syntax().kind();
+        let vis = Vis::Other;
+        let id = file_items.id_of(item.syntax());
+        let res = ModuleItem {
+            id,
+            name,
+            kind,
+            vis,
+        };
+        Some(res)
+    }
+}
+
+pub(crate) struct Resolver<'a, DB> {
+    pub(crate) db: &'a DB,
+    pub(crate) input: &'a FxHashMap<ModuleId, Arc<InputModuleItems>>,
+    pub(crate) source_root: SourceRootId,
+    pub(crate) module_tree: Arc<ModuleTree>,
+    pub(crate) result: ItemMap,
+}
+
+impl<'a, DB> Resolver<'a, DB>
+where
+    DB: HirDatabase,
+{
+    pub(crate) fn resolve(mut self) -> Cancelable<ItemMap> {
+        for (&module_id, items) in self.input.iter() {
+            self.populate_module(module_id, items)
+        }
+
+        for &module_id in self.input.keys() {
+            self.db.check_canceled()?;
+            self.resolve_imports(module_id);
+        }
+        Ok(self.result)
+    }
+
+    fn populate_module(&mut self, module_id: ModuleId, input: &InputModuleItems) {
+        let file_id = module_id.source(&self.module_tree).file_id();
+
+        let mut module_items = ModuleScope::default();
+
+        for import in input.imports.iter() {
+            if let Some(name) = import.path.segments.iter().last() {
+                if let ImportKind::Named(import) = import.kind {
+                    module_items.items.insert(
+                        name.clone(),
+                        Resolution {
+                            def_id: None,
+                            import: Some(import),
+                        },
+                    );
+                }
+            }
+        }
+
+        for item in input.items.iter() {
+            if item.kind == MODULE {
+                // handle submodules separatelly
+                continue;
+            }
+            let def_loc = DefLoc::Item {
+                source_item_id: SourceItemId {
+                    file_id,
+                    item_id: item.id,
+                },
+            };
+            let def_id = def_loc.id(self.db);
+            let resolution = Resolution {
+                def_id: Some(def_id),
+                import: None,
+            };
+            module_items.items.insert(item.name.clone(), resolution);
+        }
+
+        for (name, mod_id) in module_id.children(&self.module_tree) {
+            let def_loc = DefLoc::Module {
+                id: mod_id,
+                source_root: self.source_root,
+            };
+            let def_id = def_loc.id(self.db);
+            let resolution = Resolution {
+                def_id: Some(def_id),
+                import: None,
+            };
+            module_items.items.insert(name, resolution);
+        }
+
+        self.result.per_module.insert(module_id, module_items);
+    }
+
+    fn resolve_imports(&mut self, module_id: ModuleId) {
+        for import in self.input[&module_id].imports.iter() {
+            self.resolve_import(module_id, import);
+        }
+    }
+
+    fn resolve_import(&mut self, module_id: ModuleId, import: &Import) {
+        let ptr = match import.kind {
+            ImportKind::Glob => return,
+            ImportKind::Named(ptr) => ptr,
+        };
+
+        let mut curr = match import.path.kind {
+            // TODO: handle extern crates
+            PathKind::Plain => return,
+            PathKind::Self_ => module_id,
+            PathKind::Super => {
+                match module_id.parent(&self.module_tree) {
+                    Some(it) => it,
+                    // TODO: error
+                    None => return,
+                }
+            }
+            PathKind::Crate => module_id.crate_root(&self.module_tree),
+        };
+
+        for (i, name) in import.path.segments.iter().enumerate() {
+            let is_last = i == import.path.segments.len() - 1;
+
+            let def_id = match self.result.per_module[&curr].items.get(name) {
+                None => return,
+                Some(res) => match res.def_id {
+                    Some(it) => it,
+                    None => return,
+                },
+            };
+
+            if !is_last {
+                curr = match def_id.loc(self.db) {
+                    DefLoc::Module { id, .. } => id,
+                    _ => return,
+                }
+            } else {
+                self.update(module_id, |items| {
+                    let res = Resolution {
+                        def_id: Some(def_id),
+                        import: Some(ptr),
+                    };
+                    items.items.insert(name.clone(), res);
+                })
+            }
+        }
+    }
+
+    fn update(&mut self, module_id: ModuleId, f: impl FnOnce(&mut ModuleScope)) {
+        let module_items = self.result.per_module.get_mut(&module_id).unwrap();
+        f(module_items)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use salsa::Database;
+    use ra_db::FilesDatabase;
+    use ra_syntax::SmolStr;
+
+    use crate::{
+        self as hir,
+        db::HirDatabase,
+        mock::MockDatabase,
+};
+
+    fn item_map(fixture: &str) -> (Arc<hir::ItemMap>, hir::ModuleId) {
+        let (db, pos) = MockDatabase::with_position(fixture);
+        let source_root = db.file_source_root(pos.file_id);
+        let module = hir::Module::guess_from_position(&db, pos).unwrap().unwrap();
+        let module_id = module.module_id;
+        (db.item_map(source_root).unwrap(), module_id)
+    }
+
+    #[test]
+    fn test_item_map() {
+        let (item_map, module_id) = item_map(
+            "
+            //- /lib.rs
+            mod foo;
+
+            use crate::foo::bar::Baz;
+            <|>
+
+            //- /foo/mod.rs
+            pub mod bar;
+
+            //- /foo/bar.rs
+            pub struct Baz;
+        ",
+        );
+        let name = SmolStr::from("Baz");
+        let resolution = &item_map.per_module[&module_id].items[&name];
+        assert!(resolution.def_id.is_some());
+    }
+
+    #[test]
+    fn typing_inside_a_function_should_not_invalidate_item_map() {
+        let (mut db, pos) = MockDatabase::with_position(
+            "
+            //- /lib.rs
+            mod foo;<|>
+
+            use crate::foo::bar::Baz;
+
+            fn foo() -> i32 {
+                1 + 1
+            }
+            //- /foo/mod.rs
+            pub mod bar;
+
+            //- /foo/bar.rs
+            pub struct Baz;
+        ",
+        );
+        let source_root = db.file_source_root(pos.file_id);
+        {
+            let events = db.log_executed(|| {
+                db.item_map(source_root).unwrap();
+            });
+            assert!(format!("{:?}", events).contains("item_map"))
+        }
+
+        let new_text = "
+            mod foo;
+
+            use crate::foo::bar::Baz;
+
+            fn foo() -> i32 { 92 }
+        "
+        .to_string();
+
+        db.query_mut(ra_db::FileTextQuery)
+            .set(pos.file_id, Arc::new(new_text));
+
+        {
+            let events = db.log_executed(|| {
+                db.item_map(source_root).unwrap();
+            });
+            assert!(
+                !format!("{:?}", events).contains("_item_map"),
+                "{:#?}",
+                events
+            )
+        }
+    }
+}