config: warning when the dumped yaml is invalid

Summary: if dumped yaml is unloadable, print warning and save a pkl

Reviewed By: zhanghang1989

Differential Revision: D30975516

fbshipit-source-id: c2eb839c9ffcdee7951d78b01e5c10939debec77

Author: ppwwyyxx

detectron2/config/lazy.py

@@ -255,19 +255,32 @@ def _replace_type_by_name(x):
             # not necessary, but makes yaml looks nicer
             _visit_dict_config(cfg, _replace_type_by_name)
 
+        save_pkl = False
         try:
+            dict = OmegaConf.to_container(cfg, resolve=False)
+            dumped = yaml.dump(dict, default_flow_style=None, allow_unicode=True, width=9999)
             with PathManager.open(filename, "w") as f:
-                dict = OmegaConf.to_container(cfg, resolve=False)
-                dumped = yaml.dump(dict, default_flow_style=None, allow_unicode=True, width=9999)
                 f.write(dumped)
+
+            try:
+                _ = yaml.unsafe_load(dumped)  # test that it is loadable
+            except Exception:
+                logger.warning(
+                    "The config contains objects that cannot serialize to a valid yaml. "
+                    f"{filename} is human-readable but cannot be loaded."
+                )
+                save_pkl = True
         except Exception:
             logger.exception("Unable to serialize the config to yaml. Error:")
+            save_pkl = True
+
+        if save_pkl:
             new_filename = filename + ".pkl"
             try:
                 # retry by pickle
                 with PathManager.open(new_filename, "wb") as f:
                     cloudpickle.dump(cfg, f)
-                logger.warning(f"Config saved using cloudpickle at {new_filename} ...")
+                logger.warning(f"Config is saved using cloudpickle at {new_filename}.")
             except Exception:
                 pass
 

tests/config/test_lazy_config.py

@@ -5,6 +5,7 @@
 from itertools import count
 
 from detectron2.config import LazyConfig, LazyCall as L
+from omegaconf import DictConfig
 
 
 class TestLazyPythonConfig(unittest.TestCase):
@@ -37,6 +38,14 @@ def test_save_load(self):
         # the rest are equal
         self.assertEqual(cfg, cfg2)
 
+    def test_failed_save(self):
+        cfg = DictConfig({"x": lambda: 3}, flags={"allow_objects": True})
+        with tempfile.TemporaryDirectory(prefix="detectron2") as d:
+            fname = os.path.join(d, "test_config.yaml")
+            LazyConfig.save(cfg, fname)
+            self.assertTrue(os.path.exists(fname))
+            self.assertTrue(os.path.exists(fname + ".pkl"))
+
     def test_overrides(self):
         cfg = LazyConfig.load(self.root_filename)
         LazyConfig.apply_overrides(cfg, ["lazyobj.x=123", 'dir1b_dict.a="123"'])