1 files changed, 45 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/hir-def/src/lower.rs b/src/tools/rust-analyzer/crates/hir-def/src/lower.rs
new file mode 100644
index 000000000..af623fd0e
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-def/src/lower.rs
@@ -0,0 +1,45 @@
+//! Context for lowering paths.
+use hir_expand::{ast_id_map::AstIdMap, hygiene::Hygiene, AstId, HirFileId, InFile};
+use once_cell::unsync::OnceCell;
+use syntax::ast;
+use triomphe::Arc;
+
+use crate::{db::DefDatabase, path::Path};
+
+pub struct LowerCtx<'a> {
+    pub db: &'a dyn DefDatabase,
+    hygiene: Hygiene,
+    ast_id_map: Option<(HirFileId, OnceCell<Arc<AstIdMap>>)>,
+}
+
+impl<'a> LowerCtx<'a> {
+    pub fn new(db: &'a dyn DefDatabase, hygiene: &Hygiene, file_id: HirFileId) -> Self {
+        LowerCtx { db, hygiene: hygiene.clone(), ast_id_map: Some((file_id, OnceCell::new())) }
+    }
+
+    pub fn with_file_id(db: &'a dyn DefDatabase, file_id: HirFileId) -> Self {
+        LowerCtx {
+            db,
+            hygiene: Hygiene::new(db.upcast(), file_id),
+            ast_id_map: Some((file_id, OnceCell::new())),
+        }
+    }
+
+    pub fn with_hygiene(db: &'a dyn DefDatabase, hygiene: &Hygiene) -> Self {
+        LowerCtx { db, hygiene: hygiene.clone(), ast_id_map: None }
+    }
+
+    pub(crate) fn hygiene(&self) -> &Hygiene {
+        &self.hygiene
+    }
+
+    pub(crate) fn lower_path(&self, ast: ast::Path) -> Option<Path> {
+        Path::from_src(ast, self)
+    }
+
+    pub(crate) fn ast_id<N: syntax::AstNode>(&self, item: &N) -> Option<AstId<N>> {
+        let &(file_id, ref ast_id_map) = self.ast_id_map.as_ref()?;
+        let ast_id_map = ast_id_map.get_or_init(|| self.db.ast_id_map(file_id));
+        Some(InFile::new(file_id, ast_id_map.ast_id(item)))
+    }
+}