Guard against infinite macro expansions

closes #4463

crates/ra_hir_def/src/nameres/collector.rs

@@ -717,6 +717,11 @@ impl DefCollector<'_> {
         macro_call_id: MacroCallId,
         depth: usize,
     ) {
+        if depth > 100 {
+            mark::hit!(macro_expansion_overflow);
+            log::warn!("macro expansion is too deep");
+            return;
+        }
         let file_id: HirFileId = macro_call_id.as_file();
         let item_tree = self.db.item_tree(file_id);
         let mod_dir = self.mod_dirs[&module_id].clone();

crates/ra_hir_def/src/nameres/tests/macros.rs

@@ -660,3 +660,27 @@ fn expand_multiple_derive() {
     );
     assert_eq!(map.modules[map.root].scope.impls().len(), 2);
 }
+
+#[test]
+fn macro_expansion_overflow() {
+    mark::check!(macro_expansion_overflow);
+    compute_crate_def_map(
+        "
+macro_rules! a {
+    ($e:expr; $($t:tt)*) => {
+        b!($($t)*);
+    };
+    () => {};
+}
+
+macro_rules! b {
+    (static = $e:expr; $($t:tt)*) => {
+        a!($e; $($t)*);
+    };
+    () => {};
+}
+
+b! { static = #[] (); }
+",
+    );
+}