feat: raise UnsupportedExtensionError when loading .yml files

hydra/errors.py

@@ -37,3 +37,6 @@ def __init__(
 
 
 class HydraDeprecationError(HydraException): ...
+
+
+class UnsupportedExtensionException(HydraException): ...

hydra/plugins/config_source.py

@@ -10,7 +10,7 @@
 from hydra._internal.deprecation_warning import deprecation_warning
 from hydra.core.default_element import InputDefault
 from hydra.core.object_type import ObjectType
-from hydra.errors import HydraException
+from hydra.errors import HydraException, UnsupportedExtensionException
 from hydra.plugins.plugin import Plugin
 
 
@@ -116,7 +116,12 @@ def full_path(self) -> str:
     @staticmethod
     def _normalize_file_name(filename: str) -> str:
         supported_extensions = [".yaml"]
-        if not version.base_at_least("1.2"):
+        if version.base_at_least("1.2"):
+            if filename.endswith(".yml"):
+                raise UnsupportedExtensionException(
+                    ".yml files are not supported. Use .yaml extension for Hydra config files."
+                )
+        else:
             supported_extensions.append(".yml")
             if filename.endswith(".yml"):
                 deprecation_warning(

tests/test_config_loader.py

@@ -17,6 +17,7 @@
     ConfigCompositionException,
     HydraException,
     MissingConfigException,
+    UnsupportedExtensionException,
 )
 from hydra.test_utils.test_utils import chdir_hydra_root
 from hydra.types import RunMode
@@ -190,6 +191,12 @@ def test_load_yml_file(self, path: str, hydra_restore_singletons: Any) -> None:
         config_loader = ConfigLoaderImpl(
             config_search_path=create_config_search_path(path)
         )
+        with raises(UnsupportedExtensionException):
+            cfg = config_loader.load_configuration(
+                config_name="config.yml",
+                overrides=[],
+                run_mode=RunMode.RUN,
+            )
         version.setbase("1.1")
         with warns(
             UserWarning,