6 files changed, 358 insertions, 12 deletions

diff --git a/crates/ra_hir_def/src/db.rs b/crates/ra_hir_def/src/db.rs
index 945a0025e..a23d65371 100644
--- a/crates/ra_hir_def/src/db.rs
+++ b/crates/ra_hir_def/src/db.rs
@@ -14,6 +14,7 @@ use crate::{
     docs::Documentation,
     find_path,
     generics::GenericParams,
+    import_map::ImportMap,
     item_scope::ItemInNs,
     lang_item::{LangItemTarget, LangItems},
     nameres::{raw::RawItems, CrateDefMap},
@@ -122,6 +123,9 @@ pub trait DefDatabase: InternDatabase + AstDatabase + Upcast<dyn AstDatabase> {
 
     #[salsa::invoke(find_path::find_path_inner_query)]
     fn find_path_inner(&self, item: ItemInNs, from: ModuleId, max_len: usize) -> Option<ModPath>;
+
+    #[salsa::invoke(ImportMap::import_map_query)]
+    fn import_map(&self, krate: CrateId) -> Arc<ImportMap>;
 }
 
 fn crate_def_map_wait(db: &impl DefDatabase, krate: CrateId) -> Arc<CrateDefMap> {
diff --git a/crates/ra_hir_def/src/find_path.rs b/crates/ra_hir_def/src/find_path.rs
index 4db798473..088e8dd32 100644
--- a/crates/ra_hir_def/src/find_path.rs
+++ b/crates/ra_hir_def/src/find_path.rs
@@ -36,17 +36,6 @@ impl ModPath {
         let first_segment = self.segments.first();
         first_segment == Some(&known::alloc) || first_segment == Some(&known::core)
     }
-
-    fn len(&self) -> usize {
-        self.segments.len()
-            + match self.kind {
-                PathKind::Plain => 0,
-                PathKind::Super(i) => i as usize,
-                PathKind::Crate => 1,
-                PathKind::Abs => 0,
-                PathKind::DollarCrate(_) => 1,
-            }
-    }
 }
 
 pub(crate) fn find_path_inner_query(
@@ -192,9 +181,17 @@ fn find_importable_locations(
 ) -> Vec<(ModuleId, Name)> {
     let crate_graph = db.crate_graph();
     let mut result = Vec::new();
+
     // We only look in the crate from which we are importing, and the direct
     // dependencies. We cannot refer to names from transitive dependencies
     // directly (only through reexports in direct dependencies).
+
+    // For the crate from which we're importing, we have to check whether any
+    // module visible to `from` exports the item we're looking for.
+    // For dependencies of the crate only `pub` items reachable through `pub`
+    // modules from the crate root are relevant. For that we precompute an
+    // import map that tells us the shortest path to any importable item with a
+    // single lookup.
     for krate in Some(from.krate)
         .into_iter()
         .chain(crate_graph[from.krate].dependencies.iter().map(|dep| dep.crate_id))
diff --git a/crates/ra_hir_def/src/import_map.rs b/crates/ra_hir_def/src/import_map.rs
new file mode 100644
index 000000000..7dae64efa
--- /dev/null
+++ b/crates/ra_hir_def/src/import_map.rs
@@ -0,0 +1,323 @@
+//! A map of all publicly exported items in a crate.
+
+use crate::{
+    db::DefDatabase,
+    item_scope::ItemInNs,
+    path::{ModPath, PathKind},
+    visibility::Visibility,
+    ModuleDefId, ModuleId,
+};
+use ra_db::CrateId;
+use rustc_hash::FxHashMap;
+use std::{collections::hash_map::Entry, sync::Arc};
+
+/// A map from publicly exported items to the path needed to import/name them from a downstream
+/// crate.
+///
+/// Reexports of items are taken into account, ie. if something is exported under multiple
+/// names, the one with the shortest import path will be used.
+///
+/// Note that all paths are relative to the containing crate's root, so the crate name still needs
+/// to be prepended to the `ModPath` before the path is valid.
+#[derive(Debug, Eq, PartialEq)]
+pub struct ImportMap {
+    map: FxHashMap<ItemInNs, ModPath>,
+}
+
+impl ImportMap {
+    pub fn import_map_query(db: &dyn DefDatabase, krate: CrateId) -> Arc<Self> {
+        let _p = ra_prof::profile("import_map_query");
+        let def_map = db.crate_def_map(krate);
+        let mut import_map = FxHashMap::with_capacity_and_hasher(64, Default::default());
+
+        // We look only into modules that are public(ly reexported), starting with the crate root.
+        let empty = ModPath { kind: PathKind::Plain, segments: vec![] };
+        let root = ModuleId { krate, local_id: def_map.root };
+        let mut worklist = vec![(root, empty)];
+        while let Some((module, mod_path)) = worklist.pop() {
+            let ext_def_map;
+            let mod_data = if module.krate == krate {
+                &def_map[module.local_id]
+            } else {
+                // The crate might reexport a module defined in another crate.
+                ext_def_map = db.crate_def_map(module.krate);
+                &ext_def_map[module.local_id]
+            };
+
+            let visible_items = mod_data.scope.entries().filter_map(|(name, per_ns)| {
+                let per_ns = per_ns.filter_visibility(|vis| vis == Visibility::Public);
+                if per_ns.is_none() {
+                    None
+                } else {
+                    Some((name, per_ns))
+                }
+            });
+
+            for (name, per_ns) in visible_items {
+                let mk_path = || {
+                    let mut path = mod_path.clone();
+                    path.segments.push(name.clone());
+                    path
+                };
+
+                for item in per_ns.iter_items() {
+                    let path = mk_path();
+                    match import_map.entry(item) {
+                        Entry::Vacant(entry) => {
+                            entry.insert(path);
+                        }
+                        Entry::Occupied(mut entry) => {
+                            // If the new path is shorter, prefer that one.
+                            if path.len() < entry.get().len() {
+                                *entry.get_mut() = path;
+                            } else {
+                                continue;
+                            }
+                        }
+                    }
+
+                    // If we've just added a path to a module, descend into it.
+                    if let Some(ModuleDefId::ModuleId(mod_id)) = item.as_module_def_id() {
+                        worklist.push((mod_id, mk_path()));
+                    }
+                }
+            }
+        }
+
+        Arc::new(Self { map: import_map })
+    }
+
+    /// Returns the `ModPath` needed to import/mention `item`, relative to this crate's root.
+    pub fn path_of(&self, item: ItemInNs) -> Option<&ModPath> {
+        self.map.get(&item)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test_db::TestDB;
+    use insta::assert_snapshot;
+    use ra_db::fixture::WithFixture;
+    use ra_db::SourceDatabase;
+
+    fn import_map(ra_fixture: &str) -> String {
+        let db = TestDB::with_files(ra_fixture);
+        let crate_graph = db.crate_graph();
+
+        let import_maps: Vec<_> = crate_graph
+            .iter()
+            .filter_map(|krate| {
+                let cdata = &crate_graph[krate];
+                let name = cdata.display_name.as_ref()?;
+
+                let map = db.import_map(krate);
+
+                let mut importable_paths: Vec<_> = map
+                    .map
+                    .iter()
+                    .map(|(item, modpath)| {
+                        let ns = match item {
+                            ItemInNs::Types(_) => "t",
+                            ItemInNs::Values(_) => "v",
+                            ItemInNs::Macros(_) => "m",
+                        };
+                        format!("- {} ({})", modpath, ns)
+                    })
+                    .collect();
+
+                importable_paths.sort();
+                let importable_paths = importable_paths.join("\n");
+
+                Some(format!("{}:\n{}", name, importable_paths))
+            })
+            .collect();
+
+        import_maps.join("\n")
+    }
+
+    #[test]
+    fn smoke() {
+        let map = import_map(
+            r"
+            //- /main.rs crate:main deps:lib
+
+            mod private {
+                pub use lib::Pub;
+                pub struct InPrivateModule;
+            }
+
+            pub mod publ1 {
+                use lib::Pub;
+            }
+
+            pub mod real_pub {
+                pub use lib::Pub;
+            }
+            pub mod real_pu2 { // same path length as above
+                pub use lib::Pub;
+            }
+
+            //- /lib.rs crate:lib
+            pub struct Pub {}
+            pub struct Pub2; // t + v
+            struct Priv;
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        main:
+        - publ1 (t)
+        - real_pu2 (t)
+        - real_pub (t)
+        - real_pub::Pub (t)
+        lib:
+        - Pub (t)
+        - Pub2 (t)
+        - Pub2 (v)
+        "###);
+    }
+
+    #[test]
+    fn prefers_shortest_path() {
+        let map = import_map(
+            r"
+            //- /main.rs crate:main
+
+            pub mod sub {
+                pub mod subsub {
+                    pub struct Def {}
+                }
+
+                pub use super::sub::subsub::Def;
+            }
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        main:
+        - sub (t)
+        - sub::Def (t)
+        - sub::subsub (t)
+        "###);
+    }
+
+    #[test]
+    fn type_reexport_cross_crate() {
+        // Reexports need to be visible from a crate, even if the original crate exports the item
+        // at a shorter path.
+        let map = import_map(
+            r"
+            //- /main.rs crate:main deps:lib
+            pub mod m {
+                pub use lib::S;
+            }
+            //- /lib.rs crate:lib
+            pub struct S;
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        main:
+        - m (t)
+        - m::S (t)
+        - m::S (v)
+        lib:
+        - S (t)
+        - S (v)
+        "###);
+    }
+
+    #[test]
+    fn macro_reexport() {
+        let map = import_map(
+            r"
+            //- /main.rs crate:main deps:lib
+            pub mod m {
+                pub use lib::pub_macro;
+            }
+            //- /lib.rs crate:lib
+            #[macro_export]
+            macro_rules! pub_macro {
+                () => {};
+            }
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        main:
+        - m (t)
+        - m::pub_macro (m)
+        lib:
+        - pub_macro (m)
+        "###);
+    }
+
+    #[test]
+    fn module_reexport() {
+        // Reexporting modules from a dependency adds all contents to the import map.
+        let map = import_map(
+            r"
+            //- /main.rs crate:main deps:lib
+            pub use lib::module as reexported_module;
+            //- /lib.rs crate:lib
+            pub mod module {
+                pub struct S;
+            }
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        main:
+        - reexported_module (t)
+        - reexported_module::S (t)
+        - reexported_module::S (v)
+        lib:
+        - module (t)
+        - module::S (t)
+        - module::S (v)
+        "###);
+    }
+
+    #[test]
+    fn cyclic_module_reexport() {
+        // Reexporting modules from a dependency adds all contents to the import map.
+        let map = import_map(
+            r"
+            //- /lib.rs crate:lib
+            pub mod module {
+                pub struct S;
+                pub use super::sub::*;
+            }
+
+            pub mod sub {
+                pub use super::module;
+            }
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        lib:
+        - module (t)
+        - module::S (t)
+        - module::S (v)
+        - sub (t)
+        "###);
+    }
+
+    #[test]
+    fn private_macro() {
+        let map = import_map(
+            r"
+            //- /lib.rs crate:lib
+            macro_rules! private_macro {
+                () => {};
+            }
+        ",
+        );
+
+        assert_snapshot!(map, @r###"
+        lib:
+        "###);
+    }
+}
diff --git a/crates/ra_hir_def/src/lib.rs b/crates/ra_hir_def/src/lib.rs
index 5325a2760..de490fcc5 100644
--- a/crates/ra_hir_def/src/lib.rs
+++ b/crates/ra_hir_def/src/lib.rs
@@ -43,6 +43,7 @@ pub mod child_by_source;
 
 pub mod visibility;
 pub mod find_path;
+pub mod import_map;
 
 #[cfg(test)]
 mod test_db;
diff --git a/crates/ra_hir_def/src/path.rs b/crates/ra_hir_def/src/path.rs
index 4512448e0..bfa921de2 100644
--- a/crates/ra_hir_def/src/path.rs
+++ b/crates/ra_hir_def/src/path.rs
@@ -76,6 +76,19 @@ impl ModPath {
         }
     }
 
+    /// Returns the number of segments in the path (counting special segments like `$crate` and
+    /// `super`).
+    pub fn len(&self) -> usize {
+        self.segments.len()
+            + match self.kind {
+                PathKind::Plain => 0,
+                PathKind::Super(i) => i as usize,
+                PathKind::Crate => 1,
+                PathKind::Abs => 0,
+                PathKind::DollarCrate(_) => 1,
+            }
+    }
+
     pub fn is_ident(&self) -> bool {
         self.kind == PathKind::Plain && self.segments.len() == 1
     }
diff --git a/crates/ra_hir_def/src/per_ns.rs b/crates/ra_hir_def/src/per_ns.rs
index 6e435c8c1..74665c588 100644
--- a/crates/ra_hir_def/src/per_ns.rs
+++ b/crates/ra_hir_def/src/per_ns.rs
@@ -5,7 +5,7 @@
 
 use hir_expand::MacroDefId;
 
-use crate::{visibility::Visibility, ModuleDefId};
+use crate::{item_scope::ItemInNs, visibility::Visibility, ModuleDefId};
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct PerNs {
@@ -84,4 +84,12 @@ impl PerNs {
             macros: self.macros.or(other.macros),
         }
     }
+
+    pub fn iter_items(self) -> impl Iterator<Item = ItemInNs> {
+        self.types
+            .map(|it| ItemInNs::Types(it.0))
+            .into_iter()
+            .chain(self.values.map(|it| ItemInNs::Values(it.0)).into_iter())
+            .chain(self.macros.map(|it| ItemInNs::Macros(it.0)).into_iter())
+    }
 }