1 files changed, 43 insertions, 0 deletions

diff --git a/crates/hir_def/src/src.rs b/crates/hir_def/src/src.rs
new file mode 100644
index 000000000..7a79b0314
--- /dev/null
+++ b/crates/hir_def/src/src.rs
@@ -0,0 +1,43 @@
+//! Utilities for mapping between hir IDs and the surface syntax.
+
+use arena::map::ArenaMap;
+use hir_expand::InFile;
+
+use crate::{db::DefDatabase, item_tree::ItemTreeNode, AssocItemLoc, ItemLoc};
+
+pub trait HasSource {
+    type Value;
+    fn source(&self, db: &dyn DefDatabase) -> InFile<Self::Value>;
+}
+
+impl<N: ItemTreeNode> HasSource for AssocItemLoc<N> {
+    type Value = N::Source;
+
+    fn source(&self, db: &dyn DefDatabase) -> InFile<N::Source> {
+        let tree = db.item_tree(self.id.file_id);
+        let ast_id_map = db.ast_id_map(self.id.file_id);
+        let root = db.parse_or_expand(self.id.file_id).unwrap();
+        let node = &tree[self.id.value];
+
+        InFile::new(self.id.file_id, ast_id_map.get(node.ast_id()).to_node(&root))
+    }
+}
+
+impl<N: ItemTreeNode> HasSource for ItemLoc<N> {
+    type Value = N::Source;
+
+    fn source(&self, db: &dyn DefDatabase) -> InFile<N::Source> {
+        let tree = db.item_tree(self.id.file_id);
+        let ast_id_map = db.ast_id_map(self.id.file_id);
+        let root = db.parse_or_expand(self.id.file_id).unwrap();
+        let node = &tree[self.id.value];
+
+        InFile::new(self.id.file_id, ast_id_map.get(node.ast_id()).to_node(&root))
+    }
+}
+
+pub trait HasChildSource {
+    type ChildId;
+    type Value;
+    fn child_source(&self, db: &dyn DefDatabase) -> InFile<ArenaMap<Self::ChildId, Self::Value>>;
+}