POC: Validating custom resolver results against type annotation

omegaconf/base.py

@@ -409,7 +409,7 @@ def _resolve_simple_interpolation(
     ) -> Optional["Node"]:
         from omegaconf import OmegaConf
 
-        from .nodes import ValueNode
+        from .nodes import AnyNode, ValueNode
 
         inter_type = ("str:" if inter_type is None else inter_type)[0:-1]
         if inter_type == "str":
@@ -436,6 +436,10 @@ def _resolve_simple_interpolation(
                 root_node = self._get_root()
                 try:
                     value = resolver(root_node, inter_key)
+                    node = self._get_node(key)
+                    if isinstance(node, ValueNode) and not isinstance(node, AnyNode):
+                        value = node.validate_and_convert(value)
+
                     return ValueNode(
                         value=value,
                         parent=self,

tests/test_interpolation.py

@@ -8,6 +8,7 @@
 from _pytest.python_api import RaisesContext
 
 from omegaconf import (
+    SI,
     Container,
     DictConfig,
     IntegerNode,
@@ -18,6 +19,7 @@
 )
 from omegaconf._utils import _ensure_container
 from omegaconf.errors import ConfigKeyError, OmegaConfBaseException
+from tests import User
 
 
 @pytest.mark.parametrize(
@@ -453,3 +455,24 @@ def test_interpolation_after_copy(copy_func: Any, data: Any, key: Any) -> None:
 def test_resolve_interpolation_without_parent() -> None:
     with pytest.raises(OmegaConfBaseException):
         DictConfig(content="${foo}")._dereference_node()
+
+
+def test_custom_resolver_return_validated(restore_resolvers: Any) -> Any:
+    def cast(t: Any, v: Any) -> Any:
+        if t == "str":
+            return str(v)
+        if t == "int":
+            return int(v)
+        assert False
+
+    OmegaConf.register_resolver("cast", cast)
+    cfg = OmegaConf.structured(User(name="Bond", age=SI("${cast:int,7}")))
+    assert cfg.age == 7
+
+    # converted to int per the dataclass age field
+    cfg = OmegaConf.structured(User(name="Bond", age=SI("${cast:str,7}")))
+    assert cfg.age == 7
+
+    cfg = OmegaConf.structured(User(name="Bond", age=SI("${cast:str,seven}")))
+    with pytest.raises(ValidationError):
+        cfg.age

tests/test_matrix.py

@@ -174,7 +174,7 @@ def test_none_construction(self, node_type: Any, values: Any) -> None:
     def test_interpolation(
         self, node_type: Any, values: Any, restore_resolvers: Any
     ) -> None:
-        resolver_output = 9999
+        resolver_output = "9999"
         OmegaConf.register_resolver("func", lambda: resolver_output)
         values = copy.deepcopy(values)
         for value in values: