lightspeed survey: copy sys.modules before the extension scan

asv/contrib/lightspeed/survey.py

@@ -74,7 +74,7 @@ def _add_extension_deps(
     """
     # Collect packages that have extension modules, deduplicate scan dirs
     seen_dirs: Set[str] = set()
-    for mod in sys.modules.values():
+    for mod in list(sys.modules.values()):
         if mod is None:
             continue
         mod_file = getattr(mod, "__file__", None) or ""

test/test_lightspeed_survey.py

@@ -54,3 +54,18 @@ def time_child_import():
     assert ok, reason
     assert "child.py" in {p.split("/pkg/")[-1] for p in deps}
     assert dict(os.environ) == env_before
+
+
+def test_extension_scan_survives_import_during_scan(tmp_path, monkeypatch):
+    from types import ModuleType
+
+    from asv.contrib.lightspeed.survey import _add_extension_deps
+
+    class Lazy(ModuleType):
+        def __getattr__(self, name):
+            sys.modules.setdefault("lazy_loaded_child", ModuleType("lazy_loaded_child"))
+            raise AttributeError(name)
+
+    monkeypatch.setitem(sys.modules, "lazy_parent", Lazy("lazy_parent"))
+    monkeypatch.delitem(sys.modules, "lazy_loaded_child", raising=False)
+    _add_extension_deps({}, str(tmp_path))