allow expanding expressions

Author: matklad

crates/ra_hir/src/expr.rs

@@ -830,14 +830,11 @@ where
 
                 if let Some(def) = self.resolver.resolve_macro_call(path) {
                     let call_id = MacroCallLoc { def, ast_id }.id(self.db);
-                    if let Some(tt) = self.db.macro_expand(call_id).ok() {
-                        if let Some(expr) = mbe::token_tree_to_expr(&tt).ok() {
+                    let file_id = call_id.as_file(MacroFileKind::Expr);
+                    if let Some(node) = self.db.parse_or_expand(file_id) {
+                        if let Some(expr) = ast::Expr::cast(&*node) {
                             log::debug!("macro expansion {}", expr.syntax().debug_dump());
-                            let old_file_id = std::mem::replace(
-                                &mut self.current_file_id,
-                                //BUG
-                                call_id.as_file(MacroFileKind::Items),
-                            );
+                            let old_file_id = std::mem::replace(&mut self.current_file_id, file_id);
                             let id = self.collect_expr(&expr);
                             self.current_file_id = old_file_id;
                             return id;

crates/ra_hir/src/ids.rs

@@ -81,6 +81,9 @@ impl HirFileId {
                     MacroFileKind::Items => {
                         Some(mbe::token_tree_to_ast_item_list(&tt).syntax().to_owned())
                     }
+                    MacroFileKind::Expr => {
+                        mbe::token_tree_to_expr(&tt).ok().map(|it| it.syntax().to_owned())
+                    }
                 }
             }
         }
@@ -102,6 +105,7 @@ struct MacroFile {
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub(crate) enum MacroFileKind {
     Items,
+    Expr,
 }
 
 impl From<FileId> for HirFileId {