3 files changed, 58 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/find_path.rs b/crates/ra_hir_def/src/find_path.rs
new file mode 100644
index 000000000..1ddf5fca6
--- /dev/null
+++ b/crates/ra_hir_def/src/find_path.rs
@@ -0,0 +1,44 @@
+//! An algorithm to find a path to refer to a certain item.
+
+use crate::{ModuleDefId, path::ModPath, ModuleId};
+
+pub fn find_path(item: ModuleDefId, from: ModuleId) -> ModPath {
+    todo!()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ra_db::{fixture::WithFixture, SourceDatabase};
+    use crate::{db::DefDatabase, test_db::TestDB};
+    use ra_syntax::ast::AstNode;
+    use hir_expand::hygiene::Hygiene;
+
+    /// `code` needs to contain a cursor marker; checks that `find_path` for the
+    /// item the `path` refers to returns that same path when called from the
+    /// module the cursor is in.
+    fn check_found_path(code: &str, path: &str) {
+        let (db, pos) = TestDB::with_position(code);
+        let module = db.module_for_file(pos.file_id);
+        let parsed_path_file = ra_syntax::SourceFile::parse(&format!("use {};", path));
+        let ast_path = parsed_path_file.syntax_node().descendants().find_map(ra_syntax::ast::Path::cast).unwrap();
+        let mod_path = ModPath::from_src(ast_path, &Hygiene::new_unhygienic()).unwrap();
+
+        let crate_def_map = db.crate_def_map(module.krate);
+        let resolved = crate_def_map.resolve_path(&db, module.local_id, &mod_path, crate::item_scope::BuiltinShadowMode::Module).0.take_types().unwrap();
+
+        let found_path = find_path(resolved, module);
+
+        assert_eq!(mod_path, found_path);
+    }
+
+    #[test]
+    fn same_module() {
+        let code = r#"
+//- /main.rs
+struct S;
+<|>
+"#;
+        check_found_path(code, "S");
+    }
+}
diff --git a/crates/ra_hir_def/src/lib.rs b/crates/ra_hir_def/src/lib.rs
index 61f044ecf..ebc12e891 100644
--- a/crates/ra_hir_def/src/lib.rs
+++ b/crates/ra_hir_def/src/lib.rs
@@ -37,6 +37,7 @@ pub mod src;
 pub mod child_by_source;
 
 pub mod visibility;
+pub mod find_path;
 
 #[cfg(test)]
 mod test_db;
diff --git a/crates/ra_hir_def/src/test_db.rs b/crates/ra_hir_def/src/test_db.rs
index 54e3a84bd..a403f183f 100644
--- a/crates/ra_hir_def/src/test_db.rs
+++ b/crates/ra_hir_def/src/test_db.rs
@@ -6,6 +6,7 @@ use std::{
 };
 
 use ra_db::{salsa, CrateId, FileId, FileLoader, FileLoaderDelegate, RelativePath};
+use crate::db::DefDatabase;
 
 #[salsa::database(
     ra_db::SourceDatabaseExtStorage,
@@ -54,6 +55,18 @@ impl FileLoader for TestDB {
 }
 
 impl TestDB {
+    pub fn module_for_file(&self, file_id: FileId) -> crate::ModuleId {
+        for &krate in self.relevant_crates(file_id).iter() {
+            let crate_def_map = self.crate_def_map(krate);
+            for (local_id, data) in crate_def_map.modules.iter() {
+                if data.origin.file_id() == Some(file_id) {
+                    return crate::ModuleId { krate, local_id };
+                }
+            }
+        }
+        panic!("Can't find module for file")
+    }
+
     pub fn log(&self, f: impl FnOnce()) -> Vec<salsa::Event<TestDB>> {
         *self.events.lock().unwrap() = Some(Vec::new());
         f();