Predict enum value type for unknown member names.

mypy/plugins/enums.py

@@ -78,6 +78,22 @@ class SomeEnum:
     """
     enum_field_name = _extract_underlying_field_name(ctx.type)
     if enum_field_name is None:
+        # We do not know the enum field name (perhaps it was passed to a function and we only
+        # know that it _is_ a member).  All is not lost however, if we can prove that the all
+        # of the enum members have the same value-type, then it doesn't matter which member
+        # was passed in.  The value-type is still known.
+        if isinstance(ctx.type, Instance):
+            info = ctx.type.type
+            stnodes = (info.get(name) for name in info.names)
+            first_node = next(stnodes, None)
+            if first_node is None:
+                return ctx.default_attr_type
+            first_node_type = first_node.type
+            if all(node is not None and node.type == first_node_type for node in stnodes):
+                underlying_type = get_proper_type(first_node_type)
+                if underlying_type is not None:
+                    return underlying_type
+
         return ctx.default_attr_type
 
     assert isinstance(ctx.type, Instance)

test-data/unit/check-enum.test

@@ -59,6 +59,26 @@ reveal_type(Truth.true.name)    # N: Revealed type is 'Literal['true']?'
 reveal_type(Truth.false.value)  # N: Revealed type is 'builtins.bool'
 [builtins fixtures/bool.pyi]
 
+[case testEnumValueExtended]
+from enum import Enum
+class Truth(Enum):
+    true = True
+    false = False
+
+def infer_truth(truth: Truth) -> None:
+    reveal_type(truth.value) # N: Revealed type is 'builtins.bool'
+[builtins fixtures/bool.pyi]
+
+[case testEnumValueInhomogenous]
+from enum import Enum
+class Truth(Enum):
+    true = 'True'
+    false = 0
+
+def cannot_infer_truth(truth: Truth) -> None:
+    reveal_type(truth.value) # N: Revealed type is 'Any'
+[builtins fixtures/bool.pyi]
+
 [case testEnumUnique]
 import enum
 @enum.unique