stubgen: preserve enum value initialisers (#17125)

See python/typing-council#11

mypy/stubgen.py

@@ -453,6 +453,7 @@ def __init__(
         self.analyzed = analyzed
         # Short names of methods defined in the body of the current class
         self.method_names: set[str] = set()
+        self.processing_enum = False
         self.processing_dataclass = False
 
     def visit_mypy_file(self, o: MypyFile) -> None:
@@ -727,6 +728,8 @@ def visit_class_def(self, o: ClassDef) -> None:
         if base_types:
             for base in base_types:
                 self.import_tracker.require_name(base)
+        if self.analyzed and o.info.is_enum:
+            self.processing_enum = True
         if isinstance(o.metaclass, (NameExpr, MemberExpr)):
             meta = o.metaclass.accept(AliasPrinter(self))
             base_types.append("metaclass=" + meta)
@@ -756,6 +759,7 @@ def visit_class_def(self, o: ClassDef) -> None:
             self._state = CLASS
         self.method_names = set()
         self.processing_dataclass = False
+        self.processing_enum = False
         self._current_class = None
 
     def get_base_types(self, cdef: ClassDef) -> list[str]:
@@ -1153,6 +1157,9 @@ def get_init(
                 # Final without type argument is invalid in stubs.
                 final_arg = self.get_str_type_of_node(rvalue)
                 typename += f"[{final_arg}]"
+        elif self.processing_enum:
+            initializer, _ = self.get_str_default_of_node(rvalue)
+            return f"{self._indent}{lvalue} = {initializer}\n"
         elif self.processing_dataclass:
             # attribute without annotation is not a dataclass field, don't add annotation.
             return f"{self._indent}{lvalue} = ...\n"

test-data/unit/stubgen.test

@@ -4342,3 +4342,27 @@ alias = tuple[()]
 def f(x: tuple[()]): ...
 
 class C(tuple[()]): ...
+
+[case testPreserveEnumValue_semanal]
+from enum import Enum
+
+class Foo(Enum):
+    A = 1
+    B = 2
+    C = 3
+
+class Bar(Enum):
+    A = object()
+    B = "a" + "b"
+
+[out]
+from enum import Enum
+
+class Foo(Enum):
+    A = 1
+    B = 2
+    C = 3
+
+class Bar(Enum):
+    A = ...
+    B = ...