Fixed Merging into a MISSING Structured config

news/269.bugfix

@@ -0,0 +1 @@
+Merging into a MISSING Structured config node expands the node first to ensure the result is legal

news/271.bugfix

@@ -0,0 +1 @@
+Fix merging into a config with a read only node if merge is not mutating that node

omegaconf/basecontainer.py

@@ -12,14 +12,14 @@
     _convert_to_omegaconf_container,
     _get_value,
     _is_interpolation,
+    _resolve_optional,
+    get_ref_type,
     get_value_kind,
     get_yaml_loader,
+    is_dict_annotation,
     is_primitive_container,
     is_primitive_dict,
     is_structured_config,
-    get_ref_type,
-    is_dict_annotation,
-    _resolve_optional,
 )
 from .base import Container, ContainerMetadata, Node
 from .errors import MissingMandatoryValue, ReadonlyConfigError, ValidationError
@@ -232,10 +232,7 @@ def pretty(self, resolve: bool = False, sort_keys: bool = False) -> str:
     @staticmethod
     def _map_merge(dest: "BaseContainer", src: "BaseContainer") -> None:
         """merge src into dest and return a new copy, does not modified input"""
-        from omegaconf import OmegaConf
-
         from .dictconfig import DictConfig
-        from .listconfig import ListConfig
         from .nodes import ValueNode
 
         assert isinstance(dest, DictConfig)
@@ -253,9 +250,6 @@ def _map_merge(dest: "BaseContainer", src: "BaseContainer") -> None:
                 else:
                     dest._set_value(type_)
 
-        elif isinstance(dest, ListConfig) and dest._is_missing():
-            dest._set_value([])
-
         for key, src_value in src.items_ex(resolve=False):
             dest_node = dest._get_node(key, validate_access=False)
             if dest_node is not None:

tests/__init__.py

@@ -104,3 +104,13 @@ class MissingDict:
 class DictEnum:
     color_key: Dict[Color, str] = field(default_factory=lambda: {})
     color_val: Dict[str, Color] = field(default_factory=lambda: {})
+
+
+@dataclass
+class A:
+    a: int = 10
+
+
+@dataclass
+class B:
+    x: A = MISSING

tests/test_merge.py

@@ -1,5 +1,5 @@
 from typing import Any, Tuple
-from dataclasses import dataclass
+
 import pytest
 
 from omegaconf import (
@@ -14,6 +14,7 @@
 from omegaconf._utils import is_structured_config
 
 from . import (
+    B,
     ConcretePlugin,
     ConfWithMissingDict,
     Group,
@@ -25,16 +26,6 @@
 )
 
 
-@dataclass
-class A:
-    a: int = 10
-
-
-@dataclass
-class B:
-    x: A = MISSING
-
-
 @pytest.mark.parametrize(  # type: ignore
     "inputs, expected",
     [
@@ -51,14 +42,26 @@ class B:
         (({"a": 1}, {"a": nodes.IntegerNode(10)}), {"a": nodes.IntegerNode(10)}),
         (({"a": nodes.IntegerNode(10)}, {"a": 1}), {"a": 1}),
         (({"a": nodes.IntegerNode(10)}, {"a": 1}), {"a": nodes.IntegerNode(1)}),
-        pytest.param(({"a": "???"}, {"a": {}}), {"a": {}}, id="merge_into_missing"),
         pytest.param(
-            ({"a": "???"}, {"a": {"b": 10}}), {"a": {"b": 10}}, id="merge_into_missing"
+            ({"a": "???"}, {"a": {}}), {"a": {}}, id="dict_merge_into_missing"
+        ),
+        pytest.param(
+            ({"a": "???"}, {"a": {"b": 10}}),
+            {"a": {"b": 10}},
+            id="dict_merge_into_missing",
         ),
         # lists
         (([1, 2, 3], [4, 5, 6]), [4, 5, 6]),
         (([[1, 2, 3]], [[4, 5, 6]]), [[4, 5, 6]]),
         (([1, 2, {"a": 10}], [4, 5, {"b": 20}]), [4, 5, {"b": 20}]),
+        pytest.param(
+            ({"a": "???"}, {"a": []}), {"a": []}, id="list_merge_into_missing"
+        ),
+        pytest.param(
+            ({"a": "???"}, {"a": [1, 2, 3]}),
+            {"a": [1, 2, 3]},
+            id="list_merge_into_missing",
+        ),
         # Interpolations
         # value interpolation
         pytest.param(
@@ -217,22 +220,6 @@ def test_merge(inputs: Any, expected: Any) -> None:
             OmegaConf.merge(*configs)
 
 
-"""
-from omegaconf import OmegaConf, MISSING
-from dataclasses import dataclass
-
-@dataclass
-class A:
-    a : int = 10
-
-@dataclass
-class B:
-    x : A = MISSING
-
-OmegaConf.merge(B, {"x": {}})
-"""
-
-
 def test_merge_error_retains_type() -> None:
     cfg = OmegaConf.structured(ConcretePlugin)
     with pytest.raises(ValidationError):