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diff --git a/crates/ra_hir/src/nameres/crate_def_map.rs b/crates/ra_hir/src/nameres/crate_def_map.rs
new file mode 100644
index 000000000..ea9b4fb50
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+++ b/crates/ra_hir/src/nameres/crate_def_map.rs
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+/// This module implements new import-resolution/macro expansion algorithm.
+///
+/// The result of this module is `CrateDefMap`: a datastructure which contains:
+///
+///   * a tree of modules for the crate
+///   * for each module, a set of items visible in the module (directly declared
+///     or imported)
+///
+/// Note that `CrateDefMap` contains fully macro expanded code.
+///
+/// Computing `CrateDefMap` can be partitioned into several logically
+/// independent "phases". The phases are mutually recursive though, there's no
+/// stric ordering.
+///
+/// ## Collecting RawItems
+///
+///  This happens in the `raw` module, which parses a single source file into a
+///  set of top-level items. Nested importa are desugared to flat imports in
+///  this phase. Macro calls are represented as a triple of (Path, Option<Name>,
+///  TokenTree).
+///
+/// ## Collecting Modules
+///
+/// This happens in the `collector` module. In this phase, we recursively walk
+/// tree of modules, collect raw items from submodules, populate module scopes
+/// with defined items (so, we assign item ids in this phase) and record the set
+/// of unresovled imports and macros.
+///
+/// While we walk tree of modules, we also record macro_rules defenitions and
+/// expand calls to macro_rules defined macros.
+///
+/// ## Resolving Imports
+///
+/// TBD
+///
+/// ## Resolving Macros
+///
+/// While macro_rules from the same crate use a global mutable namespace, macros
+/// from other crates (including proc-macros) can be used with `foo::bar!`
+/// syntax.
+///
+/// TBD;
+mod raw;
+mod collector;
+
+use rustc_hash::FxHashMap;
+use ra_arena::{Arena};
+
+use crate::{
+    Name,
+    module_tree::ModuleId,
+    nameres::ModuleScope,
+};
+
+#[derive(Default, Debug)]
+struct ModuleData {
+    parent: Option<ModuleId>,
+    children: FxHashMap<Name, ModuleId>,
+    scope: ModuleScope,
+}
+
+/// Contans all top-level defs from a macro-expanded crate
+#[derive(Debug)]
+pub(crate) struct CrateDefMap {
+    root: ModuleId,
+    modules: Arena<ModuleId, ModuleData>,
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use ra_db::SourceDatabase;
+    use insta::assert_snapshot_matches;
+
+    use crate::{Crate, mock::MockDatabase, nameres::Resolution};
+
+    use super::*;
+
+    fn compute_crate_def_map(fixture: &str) -> Arc<CrateDefMap> {
+        let db = MockDatabase::with_files(fixture);
+        let crate_id = db.crate_graph().iter().next().unwrap();
+        let krate = Crate { crate_id };
+        collector::crate_def_map_query(&db, krate)
+    }
+
+    fn render_crate_def_map(map: &CrateDefMap) -> String {
+        let mut buf = String::new();
+        go(&mut buf, map, "\ncrate", map.root);
+        return buf;
+
+        fn go(buf: &mut String, map: &CrateDefMap, path: &str, module: ModuleId) {
+            *buf += path;
+            *buf += "\n";
+            for (name, res) in map.modules[module].scope.items.iter() {
+                *buf += &format!("{}: {}\n", name, dump_resolution(res))
+            }
+            for (name, child) in map.modules[module].children.iter() {
+                let path = path.to_string() + &format!("::{}", name);
+                go(buf, map, &path, *child);
+            }
+        }
+
+        fn dump_resolution(resolution: &Resolution) -> &'static str {
+            match (resolution.def.types.is_some(), resolution.def.values.is_some()) {
+                (true, true) => "t v",
+                (true, false) => "t",
+                (false, true) => "v",
+                (false, false) => "_",
+            }
+        }
+    }
+
+    fn def_map(fixtute: &str) -> String {
+        let dm = compute_crate_def_map(fixtute);
+        render_crate_def_map(&dm)
+    }
+
+    #[test]
+    fn crate_def_map_smoke_test() {
+        let map = def_map(
+            "
+            //- /lib.rs
+            mod foo;
+            struct S;
+
+            //- /foo/mod.rs
+            pub mod bar;
+            fn f() {}
+
+            //- /foo/bar.rs
+            pub struct Baz;
+            enum E { V }
+        ",
+        );
+        assert_snapshot_matches!(
+        map,
+            @r###"
+crate
+S: t v
+
+crate::foo
+f: v
+
+crate::foo::bar
+Baz: t v
+E: t
+"###
+        )
+    }
+
+    #[test]
+    fn macro_rules_are_globally_visible() {
+        let map = def_map(
+            "
+            //- /lib.rs
+            macro_rules! structs {
+                ($($i:ident),*) => {
+                    $(struct $i { field: u32 } )*
+                }
+            }
+            structs!(Foo);
+            mod nested;
+
+            //- /nested.rs
+            structs!(Bar, Baz);
+        ",
+        );
+        assert_snapshot_matches!(map, @r###"
+crate
+Foo: t v
+
+crate::nested
+Bar: t v
+Baz: t v
+"###);
+    }
+
+    #[test]
+    fn macro_rules_can_define_modules() {
+        let map = def_map(
+            "
+            //- /lib.rs
+            macro_rules! m {
+                ($name:ident) => { mod $name;  }
+            }
+            m!(n1);
+
+            //- /n1.rs
+            m!(n2)
+            //- /n1/n2.rs
+            struct X;
+        ",
+        );
+        assert_snapshot_matches!(map, @r###"
+crate
+
+crate::n1
+
+crate::n1::n2
+X: t v
+"###);
+    }
+}