Fix false multiple decorator error when combining schema.output and tag (#1574)

Changes SchemaOutput inherits from tag and shares its lifecycle name, so multiplicity check tripped on the existing tag instance.
Count only decorators of the same concrete class as self before raising, independent decorators sharing a lifecycle name now compose.

Author: ArnavBalyan

hamilton/function_modifiers/base.py

@@ -119,12 +119,13 @@ def __call__(self, fn: Callable):
         """
         self.validate(fn)
         lifecycle_name = self.__class__.get_lifecycle_name()
-        if hasattr(fn, self.get_lifecycle_name()):
-            if not self.allows_multiple():
+        if hasattr(fn, lifecycle_name):
+            curr_value = getattr(fn, lifecycle_name)
+            same_class_present = any(d.__class__ is self.__class__ for d in curr_value)
+            if same_class_present and not self.allows_multiple():
                 raise ValueError(
                     f"Got multiple decorators for decorator @{self.__class__}. Only one allowed."
                 )
-            curr_value = getattr(fn, lifecycle_name)
             setattr(fn, lifecycle_name, curr_value + [self])
         else:
             setattr(fn, lifecycle_name, [self])

tests/function_modifiers/test_metadata.py

@@ -231,6 +231,21 @@ def foo() -> pd.DataFrame:
     )
 
 
+def test_schema_output_combined_with_tag_does_not_raise():
+    @function_modifiers.schema.output(("ticker", "str"), ("fee", "float"))
+    @function_modifiers.tag(table_type="reference")
+    def ref_table_1() -> pd.DataFrame:
+        return pd.DataFrame.from_records([{"ticker": "AAPL", "fee": 1.0}])
+
+    nodes = function_modifiers.base.resolve_nodes(ref_table_1, {})
+    node_map = {n.name: n for n in nodes}
+    node_ = node_map["ref_table_1"]
+    assert (
+        node_.tags[function_modifiers.schema.INTERNAL_SCHEMA_OUTPUT_KEY] == "ticker=str,fee=float"
+    )
+    assert node_.tags["table_type"] == "reference"
+
+
 def test_decorate_node_with_schema_output_invalid_type():
     # quick test to decorate node with schemas
     # this tests an internal implementation, so we will likely change